WO2005097311A1 - Chemical reactors and methods for making same - Google Patents

Abstract

Chemical reactors such as fuel cells, electrolysis cells or the like may be made up of frames which combine a process layer with a perimeter barrier. The perimeter barrier defines a low aspect ratio cavity on the process layer. The low aspect ratio cavity may be filled with porous diffusion media or other materials. The frames may be incorporated into intermediate assemblies that can be combined to form reactors. Intermediate assemblies may be bonded together to form the reactors. In an assembled reactor, the cavities have high aspect ratios.

Description

CHEMICAL REACTORS AND METHODS FOR MAKING SAME

Cross Reference to Related Applications

[0001] This application claims priority from the following previously-filed United States patent applications: 10/818,610 entitled COMPACT CHEMICAL REACTOR WITH REACTOR FRAME filed 6 April 2004; 10/818,611 entitled COMPACT FUEL CELL LAYER filed 6 April 2004; 10/818,612 entitled METHOD FOR FORMING COMPACT CHEMICAL REACTORS WITH REACTOR FRAMES filed 6 April 2004; 10/818,780 entitled COMPACT CHEMICAL REACTOR filed 6 April 2004; 10/818,826 entitled METHOD FOR MAKING COMPACT CHEMICAL REACTORS filed 6 April 2004; and, 10/818,843 entitled FUEL CELL LAYER WITH REACTOR FRAME filed 6 April 2004. For purposes of the United States of America, this application is a contϊnuation-in-part of each of the above-noted previously-filed applications which are hereby incorporated herein by reference.

Technical Field

[0002] The^' invention relates to chemical reactors. The invention has particular application to electrochemical reactors such as fuel cells and electrolysis cells. Certain aspects of the invention may be applied to other types of chemical reactors, heat exchangers, or the like. The invention also relates to methods for making chemical reactors.

Background

[0003] Some electrochemical cells are made up of a stack of layers. Fuel cells are an example of a type of electrochemical reactor that is often provided in the form of a stack, With the exception of high temperature fuel cells, such as molten carbonate cells, most proton exchange membrane, direct methanol, solid oxide or alkaline fuel cells have a layered planar structure in which the layers are first formed as distinct components and then assembled into a functional fuel cell stack by placing the layers in contact with each other. Prior designs for such layered electrochemical cells suffer from various problems. [0004] Many fuel cell stacks are designed to provide relatively large amounts of electrical power. While it would be desirable to provide smaller, less expensive and more portable fuel cells, one problem is that the designs of many existing fuel cells cannot readily be scaled down to smaller sizes.

[0005] Maintaining consistent contact between different layers in larger fuel cell stacks can present problems. If the overall area of each layer is very large then very large clamping forces must be applied to provide contact pressures sufficient to hold the different layers of the fuel cell stack together in the manner required for proper operation of tire fuel cell stack, This pressure can be required both to make seals between layers of the stack and to maintain electrical contact between the different layers of the stack. Further, it is difficult to make the pressure uniform. Applying enough force to ensure that the pressure between layers is sufficient in all regions of a cell stack can result in excessive pressures being applied in some regions.

[0006] In a typical bipolar fuel cell stack, all electrical current produced by the fuel cell stack must pass through each layer in the stack. The layers must contact one another well enough to keep electrical resistance of the fuel cell stack to satisfactorily low levels. Both sealing and maintaining electrical conductivity require the assembled stack to be clamped together with significant force in order to activate perimeter seals and reduce internal contact resistance.

[0007] Fuel cell stacks having large-area layers also present challenges in preventing active areas of the fuel cell stack from overheating and removing water from inner recesses of the fuel ceils.

[0008] In existing fuel cell stacks it is necessary to provide ways for both f el and oxidant to flow in planes parallel to the layers of the fuel cell. Typically, at least four and up to six distinct layers have been required to form each unit fuel cell in a fuel cell stack. Typically these layers include: a first flow field layer; a first gas diffusion layer; a first catalyst layer; a first electrolyte layer; a second catalyst layer; a second gas diffusion layer; a second flow field layer; and a separator. These portions of the fuel cell stack are usually manufactured as separate components. The bipolar plates, which typically serve as oxidant and fuel flow fields, and the separator are often constructed from graphite, which is difficult to machine, adding significant cost to the fuel cell stack. A membrane electrode assembly (MEA) typically incorporates the electrolyte and catalyst layers. The MEA is usually constructed by coating a solid polymer electrolyte with catalyst on either side and then pressing gas diffusion electrodes onto the electrolyte. The fuel cell assembly requires multiple individual bipolar plates and membrane electrode assemblies to be connected together in a serial manner, Usually discrete seals must be attached between adjacent bipolar plates and ME As and the whole stack of sealed bipolar and MEA layers must be held together under considerable compressive force. Care must be taken not to clamp the layers so tightly together that gas diffusion within the layers is prevented. However, the layers must be clamped tightly enough together to prevent gas from leaking out between layers of the assembled fuel cell stack.

[0009] The task of assembling a fuel cell stack made up of many layers presents problems. Laying out layers of material and compressing them together using the brute force approach typically used to make conventional fuel cell stacks is inefficient and expensive. In manufacturing layered fuel cell stacks, it is difficult to accurately align the layers. Inaccurate alignment has a detrimental effect on the performance and durability of the fuel cell stacks.

[0010] Further, fuel cells and other layered electrochemical cells according to many current designs suffer from long term performance degradation through the action of thermal and mechanical cycles in the operation of the fuel cells.

[0011] WO 03067693 entitled APPARATUS OF HIGH POWER DENSITY FUEL CELL LAYER WITH MICRO STRUCTURED COMPONENTS discloses a fuel cell having an integrated design in which the fimctions of gas diffusion layers, catalyst layers, and electrolyte layers are integrated into a single substrate. Such fuel cells have desirable characteristics but can be undesirably expensive to manufacture. [0012] GB 2,339,058 discloses a fuel cell having an undulating electrolyte layer. A conventional layered membrane electrode assembly (MEA) is constructed in an undulating fashion. The MEA is placed between bipolar plates. This design increases the active area that can be packed into a given volume. However, this design still relies on the expensive and complicated layered structure with explicit seals and requires compressive force to maintain internal electrical contact and sealing.

10013] JP 50903/1996 presents a solid polymer fuel cell having generally planar separators with alternating protruding parts serving to damp a power generation element into a non-planar but piecewise linear shape.

[0014]Thin layer fuel cells are described in US patent application Nos. 10/348,867; 10/349,127; 10/349,128; 10/349,133; 10/349,136; 10/349,338 and 10/349,459.

[0015] Despite all of the research that has been done in the field of electrochemical reactors, there remains a general need for practical electrochemical reactors that avoid, at least in part, some of the problems of existing chemical reactors or provide alternatives to existing chemical reactors. For example, it can be seen from the above that existing fuel cell designs present various problems. Despite the wide range of available designs for fuel cells there remains a need for fuel cells having high volumetric power density that can be scaled up or down over a wide range of power capacities and physical sizes, particularly to small or even micro sizes. There is a particular need for such fuel cells that can be manufactured cost effectively. There is also a need for fuel cells and other chemical reactors that have active areas that are large in comparison to their volumes. There is also a need for cost effective methods for making fuel cells and other compact chemical reactors.

Summary of the Invention

[0016] This invention has a number of aspects. One aspect of the.invention provides a chemical reactor comprising a first process layer and a perimeter barrier on the first process layer. The perimeter barrier and first process layer define a cavity. A second process layer is disposed adjacent to the perimeter barrier with the cavity between the first and second process layers. An aspect ratio of: a dimension of the cavity along the process layers to a distance between the first and second process layers is greater than 1 :1. A typical chemical reactor according to the invention has multiple first and second process layers. In some embodiments The first process layer and perimeter barrier are attached to one another to provide a frame.

[0017] Another aspect of the invention provides a chemical reactor comprising at least a first unit reactor and a second unit reactor disposed adjacent one another to form a first side and a second Side of the reactor; a first reactant plenum communicating with the first side; and a second reactant plenum communicating with the second side. One of the first and second plenums may optionally be open to the environment. Each of the unit reactors comprises: a first process layer; a second process layer; a first cavity formed between the first and second process layers; a second cavity formed between the second process layer and the first process layer of adjacent unit reactors; a first perimeter barrier disposed on the second process layer to define a perimeter of the second cavity; and a second perimeter barrier disposed on the first process layer to define a perimeter of the first cavity. The first cavity is in communication with.the first side and the second cavity is in communication with the second side. At least one of the process layers facilitates a transport process between the reactant plenums.

[0018] The invention also provides methods for making chemical reactors. One aspect of the invention provides a method comprising providing a first process layer and a perimeter barrier on the first process layer, the perimeter barrier and first process layer defining a cavity having an opening, the opening having a perimeter defined by the perimeter barrier, the cavity having an aspect ratio of: a height of the perimeter barrier in a direction substantially perpendicular to the first process layer to a dimension of the cavity in a direction along a surface of the first process layer of less than 1:1; and, j oining the perimeter barrier to a second process layer, the second process layer closing the opening of the cavity. Materials such as porous diffusion media, catalysts or the like may be introduced into the cavity prior to joining the perimeter barrier to a second process layer. In some embodiments, there is a gap in the perimeter barrier and the method comprises placing the cavity in fluid communication with a reactant plenum by way of the gap. [0019] A further aspect of the invention provides a method for making a chemical reactor. The method comprises: a) forming at least two low aspect ratio process layers; b) forming at least one low aspect ratio perimeter barrier; c) creating an intermediate assembly comprising a low aspect ratio cavity by joining the low aspect ratio perimeter barrier to at least one side of one of the low aspect ratio process layers; d) repeating steps (a) to (c) to create a plurality of intermediate assemblies comprising low aspect ratio cavities; e) creating a high aspect ratio cavity by joining one of the low aspect ratio process layers to the intermediate assembly, and f) repeating steps (d) and (e) to create a plurality of joined intermediate assemblies to create a chemical reactor with high aspect ratio cavities; g) joining the chemical reactor to two reactant plenums to facilitate a transport process between the reactant plenums by way of the process layers

[0020] Another aspect of the invention provides a method for making a chemical reactor having high aspect ratio cavities, the method comprising: forming at least one intermediate assembly, comprising one of: i. at least one frame comprising: a process layer, a perimeter barrier and at least one low aspect ratio cavity; or ii. at least one frame comprising: a process layer, two perimeter barriers, and at least two low aspect ratio cavities disposed on either side of the process layer; or iii. at least one layer comprising a perimeter barrier formed on one side of a process layer with at least one low aspect ratio cavity; or iv. combinations of (i) and (iii) joined together; joining at least two intermediate assemblies to together to create a chemical reactor having at least one high aspect ratio cavity; and joining the chemical reactor to two reactant plenums to facilitate a transport process between the reactant plenums by way of the process layers.

[0021] Further aspects of the invention and features of embodiments of the invention are described below. Brief Description of the Drawings

[0022] The appended drawings illustrate non-limiting embodiments of the invention:

[0023] Figure 1 is a cut-away isometric view of a chemical reactor according to an embodiment of the invention.

[0024] Figure 1A is an expanded cross-sectional view of the chemical reactor of Figure 1.

[0025] Figure IB is an expanded cross-section through a chemical reactor like that of Figure

1 configured as a bipolar fuel cell.

[0026] Figure 2 is an isometric view of a chemical τeactor according to an embodiment of the invention having a flat construction.

[0027] Figure 3 is a conceptual view showing a chemical reactor having a thin curvilinear construction,

[0028] Figure 4 is a view of a chemical reactor having unit reactors arranged to form a cylindrical surface wherein the unit cells are arranged parallel to a central axis of the reactor.

[0029] Figures 4A and 4B are cut away isometric views of frames that may be used in the chemical reactor of Figure 4.

[0030] Figure 5 is a view of another chemical reactor having unit reactors arranged to form a cylindrical surface wherein the unit cells are arranged parallel to a central axis of the reactor, [0031] Figure 6 is a view of a chemical reactor having unit reactors arranged to form a surface wherein some of the unit reactors are disposed at arbitrary angles to other ones of the unit reactors. [0032] Figure 7 is a fragmentary isometric view of an individual unit reactor. [0033] Figure 8 is an exploded isometric view of a unit reactor having one frame. [0034] Figure 9 is an exploded isometric view of a unit reactor having two frames. [0035] Figure 10 is an exploded isometric view of a unit reactor having a frame that defines two cavities. [0036] Figure 11 is a schematic cross-section through two unit reactors of an electrochemical cell stack having an embedded plenum. [0037] Figure 12 is a schematic cross-section through two unit reactors of an electrochemical cell stack having two embedded plenums. [0038] Figure 13 is an exploded perspective view of an undulating unit reactor. [0039] Figure 13 A shows a frame for a chemical reactor having undulating process layers.

[0040] Figure 14 shows a reactor held together with mechanical fasteners.

[0041] Figure 15 is cross-section through a fuel cell showing two unit fuel cells connected in a bipolar manner.

[0042] Figure 1 is a cross-sectional schematic view of a uni-polar fuel cell showing two unit fuel cells connected in an edge collected manner.

[0043] Figure 17 is a schematic depiction of a fuel cell according to the invention supplying electrical power to an electrical appliance.

[0044] Figures 18 A to 18F are views of a reactor according to an example embodiment of the invention in which; Figure 18 A is an isometric view of the reactor; figure 1 SB is a partially cut-away view thereof; Figure 1 SC is a cross-section thereof; Figure 18E) is an isometric view of a frame thereof; Figure 18E is a cut-away view of a frame thereof; and Figure 18F is an exploded view thereof.

[0045] Figure 19 is a flowchart showing a method for making a chemical reactor.

[0046] Figure 19A shows a frame having a low aspect ratio cavity.

[0047] Figures 20A through 20E are schematic views illustrating intermediate stages in making a reactor according to a method according to an embodiment of the invention.

[0048] Figure 21 illustrates a number of intermediate assemblies being combined to form a reactor.

[0049] Figure 22 illustrates a frame that provides support structures.

Description

[0050] Throughout the following description specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the present invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[0051] This invention provides chemical reactors that have a plurality of unit cells. The unit cells comprise frames that are attached to other frames or to process layers to provide a thin layer reactor comprising a contiguous arrangement of unit cells. A frame is a structure that combines a process layer and a perimeter seal. The perimeter seal and the process layer together define a shallow cavity. Some embodiments of the invention provide fuel cells. Other embodiments of the invention provide electrolysis cells or other types of chemical or electrochemical reactor.

[0052] Figures 1 and 1 A show a chemical reactor 10 according to one embodiment of the invention. Chemical reactor 10 may be a fuel cell, an electrolysis cell, or the like, for example. Chemical reactor 10 is made up of a plurality of frames 12 and layers 14^, Each frame 12 comprises a base portion 16 which provides a first process layer, and a perimeter barrier 18 on at least one side of the base portion 16. Layers 14 provide second process layers. The process layers provided by base portions 16 of frames 12 may be of the same type as or may be different in type from the process layers provided by layers 14. In the illustrated embodiment, Frames 12 each have a perimeter barrier 18 on both sides of base portion 16 except for end frames 12 A and 12B which each have a base portion 1 with a perimeter barrier 18 only on one side.

[0053] Cavities 20 having openings 22 on a first face 24 of chemical reactor 10 are defined by frames 12 and layers 14. The perimeter of each cavity 20 is closed by the perimeter barrier 18 of one of frames 12 except in the vicinity of its opening 22. Cavities 26 having openings 28 on a second face 29 of chemical reactor 10 are also defined by frames 12 and layers 14. The perimeter of each cavity 26 is closed by the perimeter barrier IS of one of frames 12 except in the vicinity of its opening 28. Openings 22 and 28 are provided by gaps in perimeter barriers 18.

[0054] Frames 12, as illustrated, are generally flat. Edges of frames 12 and layers 14 make up faces 24 and 29 of chemical reactor 10.

[0055] Perimeter barriers 18 and base portions 16 may be integrally formed of the same material or may comprise separate parts that are attached to one another in a preliminary manufacturing step. The possibility that perimeter barriers 18 are separate parts from base portions 16 is indicated by dotted lines 35 in Figure 1 A. In the illustrated embodiment, perimeter barriers 18 are generally U-shaped,

[0056] Cavities 26 are interleaved between cavities 20. Except for the cavity 20A at the end of chemical reactor 10, each cavity 20 lies between two cavities 26. A layer 14 lies between each cavity 20 and one adjacent cavity 26. The base portion 16 of a frame 12 lies between the cavity 20 and the other adjacent cavity 26. Chemical reactor 10 can be adapted to perform a particular function, for example to operate as a fuel cell, by selecting appropriate materials for base portion 16 and for layers 14 and by adding other features such as appropriate catalysts and diffusion layers as described in more detail below.

[0057] A plenum indicated schematically by 32 permits a first reactant to be introduced into cavities 20. A second plenum indicated schematically by 34 permits a first reactant to be introduced into cavities 26. One of plenums 32 or 34 can be omitted where chemical reactor 10 accepts ambient air as one reactant. Perimeter barriers 18 prevent reactant from plenum 32 from migrating into plenum 34 or vice versa, Where chemical reactor 10 is a fuel cell having a fuel in one plenum 32, 34 and an oxidant in the other plenum 34, 32 then perimeter barriers 18 prevent the uncontrolled mixing of fuel and oxidant. Reactants can enter cavities 20 and 26 from plenums 32 and 34 respectively, as indicated by arrows 36 and 37. .

[0058] Perimeter barriers 18 are made of a material and have a form that blocks migration of reactant from the chamber 20 or 26 defined by the perimeter barrier 18. Materials for the perimeter barriers can include, without limitation: • metals, such as stainless steel; silicone, such as RTV™ available from Dow Corning of Midland, Michigan; rubber, such as those available from the Apple Rubber Company of Lancaster, New York; polyamides, such as nylon (for example, a nylon 6 or a nylon 6, 6) available from E.L Du Pont De Nemours and Company of Wilmington, Delaware; • polyimides, such as Kapton™ available from EJ. Du Pont de Nemours and Company of Wilmington, Delaware; synthetic rubbers, such as BUNA available from Dow Synthetic Rubber of Edegem, Belgium; ' « suitable epoxies, for example those available from EPO Tech of Billerica, Massachusetts; polytetrafluoroethylene, available as Teflon™;

_* polyvinyldifluoride, available as ynai™ from Arkema Inc, of Philadelphia, Pennsylvania; and,

• composites, laminates, alloys, blends and or other combinations of these materials. Usable forms for the perimeter barriers include micro-structures or three-dimensional structures that create a tortuous path for the reactant as well as simple seals that block the migration of reactant.

[0059] As shown in Figure 1 A, cavities 20 each have a height HI and a depth DL It is not mandatory that Hi and Dl are the same for all cavities 20. Cavities 26 each have a height H2 and a depth D2. It is not mandatory that H2 and D2 are the same for all cavities 26. It is not mandatory that HI and H2 be equal or that Dl and D2 be equal. It is also not mandatory that HI and Dl are constant within a particular cavity 20.

[0060] Cavities 20 and 26 each have a high aspect ratio (i.e. ratio of D1.H1 or D2:H2). The aspect ratio of at least one of cavities 20 and 26 is preferably at least 1 :1 and may be at least 2 V.: 1. The aspect ratio is more preferably between 1 : 1 and 100 : 1 and is most preferably in the range of about 2VzΛ- to 15:1. Providing high aspect ratio cavities permits the active areas of layers 14 and body portions 16 of frames 12 to be large relative to the area of faces 24 and 29. In particular, the sum of the active areas of layers 14 can readily be made to exceed the area of face 24 or 29. Since the cavity heights HI and H2 re determined by the height of the corresponding perimeter barrier 18, the distance from the first or second face (24 or 29) t the opposite side of a cavity (20 or 26) that opens onto that face is much larger than the height of perimeter barrier 18.

[0061] The aspect ratios of the cavities should be chosen with regard to the properties of the reactant and any porous media which may be in the cavities. For example, in a fuel cell, if the transport of fuel and oxidant from the plenums to a gas diffusion electrode formed in the cavities is primarily by diffusion, the aspect ratio should not be so high that the rate at which reactants can diffuse into the cavities is insufficient to sustain reactions throughout the electrode.

[0062] It can be seen that chemical reactor 10 has a configuration that provides at least two faces. Chemical reactor 10 may have a prismatic form. In the illustrated embodiment, the core of chemical reactor 10 is in the form of a slab or block having at least two planar faces. First cavities 20 communicate with one of the faces (face 24) while second cavities 26 communicate with a different one of the faces (face 29), In the illustrated embodiment, faces 24 and 29 are parallel to one another and opposed to one another. This is not mandatory. In alternative embodiments, some of which are described below, first cavities 20 could be interconnected by an internal plenum and/or second cavities 26 could be interconnected by an internal plenum. When an internal plenum is provided, the cavities in communication with the internal plenum do not necessarily open onto a face of the chemical reactor. In such cases, perimeter barriers 18 can extend completely around the periphery of the cavity.

[0063] Chemical reactor 10 can be scaled up to larger sizes, for example, by making frames 12 longer (i.e. extending frames 12 in the direction parallel to openings 22) and/or by using a larger number of frames. Chemical reactor 10 can be made very small because it does not require mechanical fasteners to hold it together, especially in small sizes.

[0064] Chemical reactor 10 of Figure 1 has a number of advantageous features including:

• providing relatively large surface areas over which reactions can occur;

^• chemical reactor 10 can be scaled to larger or small sizes, including very small sizes;

• chemical reactor 10 can be made in a manner that does not require an external clamping system to hold it together;

^« as described below, chemical reactor 10 can be made to have a wide range of overall form factors; ^• chemical reactor 10 has fewer parts than some other layered chemical reactors and can therefore be simpler to assemble and align as well as more cost effective to manufacture; chemical reactor 10 may be made in a manner that does not require clamping to hold it together; the use of frames 12 simplifies the overall design and increases the precision with which the components of chemical reactor 10 can be aligned with one another; and, a chemical reactor 10 can be designed to use composite frames such that the final assembly of chemical reactor 10 does not require bonding of dissimilar materials to one another.

[0065] Chemical reactor 10 can be adapted to perform a particular function, for example to operate as a fuel cell, by selecting appropriate materials for base portion 16 and for layers 14 and by adding other features such as appropriate catalysts and diffusion layers as described in more detail below and by providing suitable reactants in cavities 20 and 26. Chemical reactor 10 is made up of a series of unit cells 30. The chemical reactor illustrated in Figure 1 has six unit cells 30.

[0066] Figure IB shows a fuel cell 10A that has a basic construction like that of chemical reactor 10. In fuel cell 10 A one of layers 14 and base portions 16 of frames 12 conducts electrons and the other conducts ions (e.g. protons). Layers 14 and base portions 16 each form substantially a gas barrier that prevents the flow of fuel or oxidant. In the illustrated embodiment, base portions 16 are electron conductors while layers 14 are ion conductors.

[0067] In the illustrated embodiment, frames 12, including perimeter barriers 18 are integrally formed of a suitable metal, such as stainless steel. Base portions 16 could also comprise an alternative electrical conductor such as a filled metal composite, a filled micro-structure of polymer, filled epoxy composite, graphite composite, or combinations thereof or a thin film of metal, such as copper, stainless steel, aluminum or tin, or a silver filled epoxy such as model number TF12202 from Tech Film of Peabody, Massachusetts, [0068] Layers 14 act as gas barriers but conduct ions (e.g. protons). Layers 14 may comprise, for example, suitable proton exchange membranes (PEMs), electrolyte filled micro-porous structures, liquid electrolytes trapped in a matrix, such as a mesh, and combinations thereof. Nafion™ available from E.I. Du Pont De Nemours and Company of Wilmington, Delaware is an example of a PEM that may be used for layers 14.

[0069] A suitable catalyst 38 is provided on or adjacent to the surface of layer 14 that faces cavity 20. A suitable catalyst 39 is provided on or adjacent to the surface of layer 14 that faces cavity 26. Catalysts 38 and 39 may be coated onto layer 14. The catalyst layer may be composed of a noble metal catalyst, a transition metal catalyst, alloys thereof and combinations thereof, for example. The catalyst layer may constitute a carbon supported catalyst or a thin film, catalyst formed by spraying, sputtering, electroplating, printing, pulsed laser deposition, or combinations thereof. Alternatively, the catalyst layer can be cracked.

[0070] Cavities 20 and 26 are each filled, at least partially, with a porous electrically- conducting material 40. Porous electrically-conducting material 40 and frames 12 provide a path for electron conduction between catalyst 38 of one unit cell and catalyst 39 of an adjoining unit cell as indicated by arrow 42. The porous material in cavities 20 may be the same or different from the porous material in cavities 26.

[0071] Cavities 20 or 26 may each hold two or more layers of different porous materials. This permits the characteristics of the porous materials to vary, particularly across the height of each cavity. For example: * The porosity of the porous material may be graded so that surface area is increased in portions of the porous material that will be nearest an electrolyte layer. The hydrophobicity of the porous material may be graded to alter water retention characteristics of the porous material. The catalyst and/or ionomer content of the porous material may be graded.

[0072] Porous electrically-conducting material 40 may comprise a graphite-impregnated paper, an electrically-conductive and gas-permeable matrix of particles, a sintered powder, a poly er bound carbon composite, a micro_rstructured carbon monolith, a porous conductive media, a porous metal foam, conductive micro-structure, combinations thereof, or the like. Material 40 may comprise, for example, a porous media, a catalyst, an electrical conductor, a binder, or combinations of two or more thereof. .

[0073] Where the chemical reactor is a PEM type fuel cell, a fuel, such as hydrogen, is supplied to plenum 34 while an oxidant, such as oxygen or air is supplied to plenum 32. The fuel diffuses through porous material 40 to catalyst 39 wherein it participates in an anode-side electrochemical reaction to liberate ions, which pass through layer 14 and electrons which flow to the next unit cell as indicated by arrow 42. The oxidant diffuses through porous material to catalyst 38 where it participates in a cathode-side electrochemical reaction. The basic electrochemistry of fuel cells is well understood to those skilled in the art and is therefore not discussed further herein.

[0074] As noted above, a chemical reactor according to the invention can be made to have any of a wide range of form factors. Figure 2 is an isometric view of a chemical reactor 50 in which unit cells 30 are disposed in a thin generally flat slab 52. Overall, reactor 50 has a thin flat construction. Chemical reactor 50 may have an overall construction as described above, for example. Chemical reactor 50 comprises at least 10 unit reactors (cells) 30. Each unit reactor, as depicted, has two process layers.

[0075] Chemical reactor 50 may be compact. An example chemical reactor 50 may have an overall dimension which is between 1 centimetre and 10 centimetres in length, between 5 millimetres and 80 millimetres in width, and about ^lA millimetre to 4 millimetres in thickness. Chemical reactor 50 preferably has an overall dimension that is between about 1 centimetre and about 100 centimetres in length, between about 1 millimetre and about 50 centimetres in width, and a thickness of between about 100 nanometres and about 4 or 5 millimetres. In other embodiments the thickness may be 4 or 5 centimetres or more.

[0076] A chemical reactor according to the invention comprises a plurality of unit cells. The reactor may comprise any practical number of unit cells. Such a chemical reactor can have from 2 unit cells to a very large number, such as 50,000 or more unit cells. Fuel cells according to certain embodiments of the invention have between 2 unit fuel cells and 300 or 500 unit fuel cells. Fuel cells according to some preferred embodiments have between 2 unit fuel cells and 100 unit fuel cells. Figure 2 shows an example chemical reactor having 15 unit cells 30 which may be electrically connected together.

[0077] Unit reactors of chemical reactor 50 are disposed adjacent to one another and form a first face 24 and a second face 29 of slab 52. First face 24 communicates -with first reactant plenum 32 and the second face 29 communicates with second reactant plenum 34. Where chemical reactor 50 is a fuel cell, first reactant plenum 32 may constitute an oxidant plenum while second reactant plenum 34 constitutes a fuel plenum, or vice versa.

[0078] First reactant plenum 32 is optionally enclosed by a structure 54. Structure 54 can either be a closed container or open to ambient atmosphere. Figure 2 depicts an embodiment wherein structure 54 is open to the ambient atmosphere. When the first reactant plenum is open to the atmosphere, enclosing structure 54 is optional. Structure 54, when open to the atmosphere, adds structural support to slab 52. Where chemical reactor 50 is a fuel cell, structure 54 may contain an oxidant such as oxygen, air, or a means for generating oxygen such as hydrogen peroxide. Where reactant plenum 32 is open to the ambient atmosphere, structure 54 may be replaced by any suitable structural support for slab 52 that does not block openings 22.

[0079] Second reactant plenum 34 is enclosed by a device 56 which may be similar to structure 54. Device 56 may be a closed container or may be open to ambient atmosphere. When device 56 is open to the atmosphere, it adds structural support to slab 52. In the embodiment shown in Figure 2, device 56 is a closed container with a solid back wall 58. Where chemical reactor 50 is a fuel cell, device 56 may contain a fuel such as hydrogen, hydrogen from reformate, liquid phase hydrocarbons, gas phase hydrocarbons, methanol, ethaπol, formic acid, ammonia, sodium borohydride or other chemical hydrides, combinations of these, or other suitable fuels. Liquid phase materials which can serve as reactants include methanol, ethanol, butanol, and formic acid. Gas phase hydrocarbons include propane, butane, methane, and combinations of these.

[0080] First and/or second plenums 32 and 34 may be defined, in part, by walls that provide some other function. For example, a circuit board, instrument case or the like may form part of the walls that enclose one or both of plenums 32 and 34.

[0081] Figure 3 depicts a group of unit cells 30 formed as a thin curvilinear structure 60.

[0082] Figure 4 shows a chemical reactor 70, which may be a fuel cell, having an overall cylindrical configuration. By way of example, chemical reactor 70 may have an overall diameter in the range of 1 centimetre to 5 centimetres, and a height in the range of 5 millimetres and 80 millimetres- Unit cells 30 of reactor 70 may have thicknesses in the range of Vβ millimetres to 5 millimetres, for example. Reactor 70 may be made up by making a stack of ring-like frames 72 as shown in Figure 4 A alternating with annular layers 14. Frame 72 has a central aperture 73. In the alternative, reactor 70 may be made up by making a stack of ring-like frames 74 having perimeter barriers IS on their outer peripheries alternating with ring-like frames 76 having perimeter barriers 18 on their inner peripheries. In this embodiment, each unit reactor is made up by a layer 14, the frames 72 on either side of the layer 14 and the cavities between the frames 72 and the layer 14.

[0083] Figure 4B shows frames 74 and 76 that may be used in place of a frame 72 in an alternative embodiment of the invention.

[0084] Chemical reactor 70 has the feature that the structure made up of unit cells 30 forms (or at least partly encloses) plenum 34. The unit fuel cells can conform to the shape of the plenum 34. Plenum 34 can be formed by the unit fuel cells themselves. For example, where chemical reactor 70 is a fuel cell, plenum 34 may contain a fuel. It is not necessary that plenum 34 occupy the entire volume inside chemical reactor 70. [0085] A chemical reactor similar to reactor 70 can be made in other cross-sectional shapes. The reactor may have a cross-section following a rectangle, a square, a triangle, an octagon, a pentagon, other prismatic shapes, or irregular shapes. This may be done by assembling the chemical reactor from frames having the desired shape. Unit cells may be arranged to provide a prismatic shape, a box-like shape or an irregular three dimensional shape.

[0086] In the embodiment depicted in Figure 4, unit cells 30 are disposed roughly parallel to one another. Unit cells 30 are disposed in planes that are perpendicular to a central axis 77 of chemical reactor 70.

[0087] Figure 5 depicts a chemical reactor 80 having unit cells 30 that are disposed roughly parallel to one another and parallel to central axis 77. In this embodiment, each of unit cells 30 may be trapezoidal in cross-section so that the layer of unit cells naturally curves around into a cylindrical configuration.

[0088] Figure 6 shows a chemical reactor 90 wherein unit reactors 30 are disposed on a irregular three dimensional surface 92. Unit reactors 30 are arranged in groups. Within each slab, unit reactors 30 are roughly parallel to one another. In the illustrated embodiment, each group of unit cells forms a contiguous slab. The unit reactors of each group are at an arbitrary angle to central axis 77 of the chemical reactor 90. Unit cells 30 of different groups of unit cells 30 are at arbitrary angles relative to one another. Reactor 90 optionally sits within a container 94 which provides an outer plenum 95. An inner plenum 96 lies within surface 92.

[0089] Figures 2 through 6 illustrate some of the wide variety of chemical reactor arrangements that can be made with unit cells made from frames according to the invention. A layer of unit cells 30 can have a variable thickness. Variable thickness unit cells can be used to provide a chemical reactor having a desired form factor, A unit cell or layer of unit cells may be narrower at one end and wider at another end. Different unit cells may have thicknesses that are different from the thicknesses of adjacent unit cells. By making frames for different unit cells in different shapes or by making frames which are tapered or otherwise shaped it is possible to provide a chemical reactor that can fit into an available space. For example, a fuel cell may be made to fit into an available space within a device to be powered by the fuel cell by providing frames of shapes that cause the fuel cell, when assembled, to have a shape complementary to the space into which it is desired to fit the fuel cell.

[0090] Figures 7 to 10 illustrate some of the ways that perimeter barriers can be attached to or formed on process layers to provide frames that can be assembled to make a chemical reactor. Figure 7 is a cutaway isometric view of an individual unit reactor 100. Unit reactor 100 may be a unit electrolysis cell, a unit fuel cell or a unit reactor of another type. Unit reactor 100 comprises a first process layer 102 and a second process layer 104. Process layers 102 and 104 are shown in this embodiment as thin sheets. In preferred embodiments, each process layer has a thickness between about 1 nanometre and about 2 centimetres. Not all process layers need have the same thickness- One or more of the process layers can have a thickness different from another process layer. The process layers are not necessarily thin sheets, A process layer can be a layer of a single material or may comprise two or more thin layers that are placed in contact with each other.

[0091] The process layers may be made from any of a variety of materials as are suitable for the application to which unit reactor 100 will be put. For example, the material of one or both of process layers 102 and 104 could be: • an electrolyte, a filled metal composite such as a stainless steel filled with carbon, of the type available from Angstrom Power Incorporated of Vancouver, Canada; a filled micro-structure of polymer such as Primea™ membrane available from W.L. . Gore & Associates, Inc. of Newark, Delaware; • a filled epoxy composite, such as those available from Tech Film of Peabody, Massachusetts; a graphite composite such as Grafoil™ available from UCAR Graph-Tech Inc. of Lakewood, Ohio; • an ion exchange membrane; ■ a filtration membrane; • ^' a separation membrane;

• a micro-structured diffusion mixer;

• a heater;

• a catalyst;

• an electrical conductor; a layer of material that has been rendered porous by a suitable process, the pores may be filled with another material having desired properties;

• a thermal conductor; or

• ' combinations of these.

Nafion™ available from E J. Du Pont De Nemours and Company of Wilmington, Delaware is an example of a workable ion exchange membrane,

[0092] Unit reactor 100 has a first cavity 106 and a second cavity 108. First cavity 106 is formed between first and second process layers (102 and 104). Second cavity.10S is formed when two unit reactors 100 are arranged adjacent one another. Second cavity 108 is formed between second process layer 104 of one unit reactor 100 and first process layer 102 of an adjacent unit reactor. Each unit reactor 100 includes a first perimeter barrier 110 and a second perimeter barrier 111. First perimeter barrier 110 is located on first process layer 102 and defines second cavity 108. first perimeter barrier 110 can optionally completely enclose second cavity 108 if a suitable passage is provided for introducing a reactant into second cavity 108.

[0093] Likewise, second perimeter barrier 111 can be located on second process layer 104 where it defines first cavity 106. Second perimeter barrier 111 can optionally completely enclose first cavity 106 if a suitable passage is provided for introducing a reactant into first cavity 106.

[0094] First and second cavities 106 and 108 provide paths for reactants to move from reactant plenums to the process layers. First cavity 106 communicates with a first face 24 (Figure 2) of a reactor structure and second cavity 108 communicates with a second face 29 of the reactor structure- [0095] In operation reactants move from reactant plenums into the corresponding cavities of the unit reactors to come into contact with the process layers. In some embodiments, the only transport mechanism for the movement of reactants into the cavities is by diffusion. In alternative embodiments, diffusion can be aided by other transport mechanisms such as convection and forced flow. Pumps and/or blowers (not shown) may be provided to move reactants into cavities 106 and 108. Cavities 106 and 108 can be filled with material or structured to aid in the distribution of reactants to the process layers, A micro-structure may be embedded within at least one of the cavities to enhance the flow of reactant into the cavity and/or to enhance the flow of reaction by-products out of the cavity.

[0096] First process layer 102 may perform a different process from second process layer 104. For example, the first process layer can be an electrolyte and the second process layer can comprise an electrical conductor.

[0097] Where unit reactor 100 is a unit fuel cell, at least one process layer must be an ionically conductive process layer in order to facilitate the transport of ions between the first and second cavities. Optionally, at least one process layer may be made electronically conductive to transport electrons between unit fuel cells. The electronically conducting process layer may be made from an electronically conducting material or alternatively, made conductive by filling a porous region with a nonporous conductive material. The ionically conductive process layer may be made from an ionic conductor, such as Nafion™. Alternatively, the frame material can be made from an electrically-insulating material such as polyethylene with a porous region that has been filed with Nafion™ to render the porous region ionically conductive. Either or both of the electronically conductive and ionically conductive process layers may be incorporated into frames.

[0098] A unit fuel cell comprises a front face and a back face. The first cavity is in communication with an oxidant plenum and the second cavity is in communication with a fuel plenum. The fuel and oxidant are able to be transported to be in contact with the process layers. The process layers have anodes and cathodes which may be provided by filling the cavities with electrochemically active materials. Electricity is produced by the fuel cell reaction. The electricity is transported out of the fuel cell through conductive paths in the layer structure. Water and heat are produced as by-products of the reaction. The water is transported out of the cavities back into the reactant plenum. Heat dissipates through the physical structure.

[0099] Each unit reactor can be made of one or more frames. Example frames are shown in Figures 8 to 10. A frame can function as both a perimeter barrier and as a process layer. A frame may be made of a single material which has desirable properties as a process layer and as a perimeter barrier. A frame may be integrally formed.

[0100] Figure 8 is an exploded isometric view of a unit reactor 120 comprising one frame 122. Frame 122 serves as a process layer 124 and also provides a perimeter barrier 125 which defines a formed first cavity 126. Unit reactor 120 may be configured as a fuel cell, an electrolysis cell, or as some other type of reactor. A-plurality of such unit reactors may be assembled to form a reactor- Unit reactor 120 includes a process layer 127 and a perimeter barrier 128 that may be assembled to frame 122 to provide a second cavity 129 adjoining frame 122.

[0101] Figure 9 is an exploded isometric view of a unit reactor 130 constructed from two frames 132 and 134. Each frame 132 and 134 provides both a process layer 133 and a perimeter barrier 135. The perimeter barriers define formed cavities 136 and 137. The two process layers can have different functions in this embodiment, for example the process layer of frame 132 can be electrically-conductive and the process layer of frame 134 can be electrically-insulating. Unit reactor 130 may be configured as a fuel cell, an electrolysis cell or as some other type of reactor. A reactor may comprise a plurality of unit reactors 130 assembled together.

[0102] When unit reactor 130 is used as a fuel cell, at least one of frames 132 and 134 is preferably made ionically conductive. This may be done by forming the frame from an ion conducting material or rendering a portion of an otherwise non-ion-conducting frame ionically conductive. It is convenient to make one of frames 132, 134 electronically conducting and the other ionically conducting. The electronically conducting frame may be made from an electronically conducting material or alternatively may be made conductive by filling a porous region with a nonporous conductive material. The ionically conductive frame may be made from an ionic conductor, such as Nafion™ from E.I. Du Pont De Nemours and Company. If an electrolyte such as Nafion™ is used to ake the frame, then the perimeter barrier of the frame may also be made of the electrolyte. Alternatively, the frame can be made from electrically- insulating material such as polyethylene with a porous region that has been filled with an electrolyte such as Nafion™ to render the region ionically conductive- The frames can be made of identical materials or the each frame may be made of different materials).

[0103] Figure 10 is an isometric view of a unit reactor 140 having a frame 142 that provides a process layer 144, a first cavity 146, and a second cavity 148. Each of cavities 146, 148 is surrounded by a corresponding integral perimeter barrier 147 and 149. Frame 142 can be joined to a second process layer 150 to provide unit reactor 140. Unit reactor 140 may be configured as a fuel cell, an electrolysis cell or as some other type of reactor.

[0104] First cavity 146 opens onto first and second surfaces 151 and 152 of frame 142. The opening onto surface 151 is shallow. From the perspective of this opening, cavity 146 has a low aspect ratio. The opening onto surface 152 has a small height (which is determined by the height of perimeter barrier 147). This height is significantly less than the depth of the cavity as measured from surface 152. From the perspective of this opening, cavity 146 has a high aspect ratio.

[0105] Similarly, second cavity 148 opens onto third and fourth surfaces 153 and 154 of frame 142. The opening onto surface 153 is shallow. From the perspective of this opening, cavity 148 has a low aspect ratio. The opening onto surface 154 has a small height (which is determined by the height of perimeter barrier 149). This height is significantly less than the depth of the cavity as measured from surface 154. From the perspective of this opening, cavity 148 has a high aspect ratio. [0106] When unit reactor 140 is configured as a fuel cell, each unit cell comprises one or more ion-conducting process layers. These process layers may comprise a suitable electrolyte. One or more of the cavities includes a first catalyst forming at least one anode. One or more other cavities include a second catalyst forming at least one cathode. The anode and the cathode are disposed on either side of the electrolyte. Frame 142 serves as a separator between unit fuel cells as well as forming the two perimeter barriers 147 and 149. A plurality of unit reactors 140 may be assembled together to form a reactor.

[0107] Frames may be made by stamping, embossing, ablating, machining, melding, casting, water jet cutting, or otherwise gouging, or chemically etching a substrate material. Frames can also be mad© by attaching multiple pieces together by way of suitable adhesives, welding, diffusion bonding, or other processes. Typical materials from which frames may be made are stainless steel, Nafion™, a composite, a metal filled composite, electrolyte filled composites, or combinations of these. Portions of frames may be selectively made porous to one or more reactants or reaction by products.

[0108] Frames are advantageously one-piece structures to reduce the number of parts. It is simpler to align one-piece frames when assembling a reactor that it would be to align separate seals and process layers. This, in turn, can reduce costs and shorten times required for manufacturing chemical reactors. Further, providing chemical reactors made with one-piece frames can also make it unnecessary to bond dissimilar materials to one another, Thus a chemical reactor built with such frames can have better integrity and fewer maintenance issues than reactors made with constructions that require more parts.

[0109] The cavities shown in any of Figures 8 through 10, or in any of the other reactors described herein, may be filled or partially filled with one or more materials to aid in the transport of reactants into the cavity or reaction by-products out of the cavity. Materials may also be provided in the cavities to assist in the reaction or other function of the reactor. In typical embodiments of the invention gas diffusion materials are provided in some or all of the cavities. The gas diffusion materials may comprise electrodes. The gas diffusion electrodes may comprise one or more porous layers and one or more catalyst layers. The catalyst layers are preferably located adjacent to the process layers where they form anodes or cathodes, depending on the reactant presented to the interface. Some or all of the cavities can be at least partially filled by a catalyst or a material incorporating a catalyst to promote the function of the reactor. A porous media, such as those available from Angstrom Power Incorporated of North Vancouver, Canada, may be used as a gas diffusion medium. In some fuel cell embodiments, the cavities are substantially completely filled with the porous media. In some cases a fuel cell or other reactor that requires a porous medium to be present in the cavities will function acceptably with the cavities, or some of them, containing a reduced amount of the porous material. For example, in some cavities the porous media may occupy as little as 5% of the cavity volume and still provide the necessary function.

[0110] Figures 11 and 12 illustrate chemical reactors which have plenums formed at least in part within frames of the chemical reactors. Figure 11 is a cross-sectional view of a chemical reactor 160, which may be a fuel cell. Two unit reactors 162 and 164 of chemical reactor 160 are shown. Each unit reactor is constituted in part by a frame 165. A process layer 166 is located between each pair of adjacent frames 165. Figure 11 shows a portion of a reactant plenum 168 which is embedded in three frames 165A, 165B and 165C. Passageways 169 which connect plenum 168 to cavities 170 are formed in frames 165. Cavities 170 alternate with cavities 172. Cavities 172 communicate with a plenum or with the environment by way of openings 174. Each process layer 166 lies between a cavity 170 and a cavity 172, Providing a common plenum (e.g. plenum 168) on one side of chemical reactor 160 advantageously enables one reactant to be fed into chemical reactor 160 in a controlled manner while the other reactant plenum may be left open to the environment. Where chemical reactor 160 is a fuel cell, the common plenum 168 is preferably the fuel plenum.

[0111] In cases where it is desired to provide forced flow of a reactant through a chamber, two reactant plenums may be connected by suitable passageways to the same cavity. A reactant may then be circulated from one plenum, through the cavity to the other plenum. [0112] Where chemical reactor 160 is a fuel cell, the common plenum 168 is preferably the fuel plenum. In a fuel cell, process layer 166 may be ion conducting and process layers 167 provided by frames 165 may be electrically-conductive.

[0113] Figure 12 shows a portion of a chemical reactor 180 which includes two unit reactors 182A and 182B (collectively unit reactors 182). Reactor 180 could be a fuel cell, for example, Each unit reactor 182 has two reactor frames. Reactor 182A includes frames 184A and 185A. Reactor 184B includes frames 184B and 1S5B. First and second reactant plenums 190 and 192 are provided in frames 182. Passages 194 connect first reactant plenum 190 to cavities 198 while passages 195 connect second reactant plenum 192 to cavities 199.

[0114] Figure 12 also illustrates that perimeter barriers 200 and 201 provided on frames 184 and 185 of the unit reactors have dimensions of height and width. Perimeter barriers 200 and 201 have heights H3 and H4 respectively. The height dimension is preferably in the range of about 100 nanometres to about 10 millimetres. The height dimensions H3 and H4 respectively determine the height of cavities 198 and 199. Perimeter barriers 200 and 201 have widths Wl and W2 respectively, The width dimensions preferably range from about 10 nanometres to about 5 millimetres. In some embodiments, perimeter barriers 200 and 201 can vary in width, having less width on one portion of the perimeter barrier and greater width on another portion of the perimeter barrier. Providing perimeter barriers having small widths can enhance sealing between the frame and an adjacent structure. Very narrow perimeter barriers may incise the adjacent structure,

[0115] Process layers in reactors according to the invention are not necessarily flat or nearly so. Figure 13 is an exploded isometric view of a unit reactor 220, which may be a fuel cell, for example, in which the process layers are undulating. Undulating process layers are non-planar. Undulating process layers may, for example, be sinusoidal in shape, or follow arcs, or be irregular in some other manner. Some process layers can be undulating while other process layers are planar. Providing undulating process layers increases the active surface area of the process layers and thereby increases the capacity of the chemical reactor. [0116] Unit reactor 220 has process layers 222 and 224. First and second undulating cavities 226 and 228 are formed adjacent to process layers 222 and 224. Cavities 226 and 228 are bounded by undulating first and second perimeter barriers 230 and 232.

[0117] Preferably each of perimeter barriers 230 and 232 is affixed to or formed integrally with one of process layers 222 and 224 to provide a frame. Figure 13A shows a frame 236 having an undulating process layer 222 and an undulating perimeter barrier 230. Perimeter barriers 230 and 232 may both be affixed to or formed integrally with the same one of process layers 222 and 224 or may each be affixed to or formed integrally with a different one of process layers 222 and 224.

[0118] Figure 14 is an elevation view of a chemical reactor 240 that is held together by a mechanical Fastener 242. Each unit reactor in chemical reactor 240 can be formed from two or more frames. Reactor 240 includes a process layer 244 between frames 246. Some examples of mechanical devices usable to connect unit reactors to make a chemical reactor include snap- fit connections, mechanical clips 242 (as depicted in Figure 14), tie rods, adhesive bonds, tape, external compression bands, keys, and combinations of these mechanical devices. In some embodiments of the invention, reactor frames are held together by providing one or more protrusions on a reactor frame that are received in a corresponding indentation on an adjacent reactor frame, The protrusions and indentations may be formed from the frame material, and may be attached to the frames. The frame on each unit reactor may be formed to correspond with another unit reactor,

[0119] Figure 15 is a cross-sectional schematic view of a bipolar fuel cell layer 250 made with frames 252- Layer 250 includes two unit fuel cells (254A and 254B, collectively 254) connected in a bipolar manner. Each unit fuel cell 254 comprises one process layer 256 that is ionically conductive and one process layer 257 that is electronically conductive.

[0120] In a bipolar configuration, as shown in Figure 15, a porous conductive layer 260 electrically connects a catalyst layer 262 (individually labelled 262A, 262B, 262C and 262D) to the electronically conductive process layer 257. Catalyst layers 262 each connect directly to an adjacent ionically conductive process layer 256. Porous layer 260 may be uniform throughout or, optionally, may be made of two or more layers of different porous materials. In the illustrated embodiment, each porous layer 260 is made up of two different layers 260 A and 260B of porous materials. Porous layers 260 enable current to flow between electrodes of adjacent unit fuel cells. A fuel 263 is introduced from one side of fuel cell 250 and an oxidant 264 is introduced from the other side of fuel cell 250.

[0121] Figure 16 is a cross-sectional schematic view showing a fuel cell 270 made with frames 272, Fuel cell 270 includes two unit fuel cells 272A and 272B that are connected in an edge-collected manner. Process layers 275 are ionically conducting. Catalyst layers 276A and 276B adjoin process layers 275 to form two identical polarity electrodes 278A and 278B. Electric current flowing into or out of identical polarity electrodes 278A and 278B passes through at least one porous conductive layer 280. The flow of current through porous conductive layers 280 provides an edge-collected uni-polar fuel cell layer.

[0122] Figure 17 depicts an embodiment wherein a fuel cell 285 is used to provide electrical power to an electrical appliance 286. Fuel cell 285 comprises a number of unit fuel cells 288 that each comprise one or more process layers 289 of electrolyte. Frames provide cavities 290 and 291 on either side of process layers 289. One or more of cavities 290 contain a first catalyst 292 forming a cathode 293, Cavities 291 contain a second catalyst 293 forming an anode 294. Anode 294 and cathode 293 are disposed on opposite sides of electrolyte process layers 289. One or more of the reactant plenums contains an oxidant 295 and the other of the reactant plenums contains a fuel 296. Anode 294 and cathode 293 connect to the electrical appliance and provide power.

[0123] Examples of electrical appliances that can be powered by a fuel cell according to the invention include airplane electronics, car electronics, laser pointers, cellular telephones, wireless telephones, projectors, televisions, compact disc players, DVD players, radios, flashlights, digital cameras, digital imaging equipment, digital image viewing equipment, and the like. [0124] Figures ISA through 18F show components of a chemical reactor 300, which may be a fuel cell according to a particular embodiment of the invention. Reactor 300 comprises a plurality of frames 302 interleaved with process layers 304, In a preferred embodiment, frames 302 are electrically-conductive frames made, for example, from stainless steel and process layers 304 are electrolyte membranes- Process layers 304 may have layers of catalyst (not shown) deposited in active areas on either side of the process layers.

[0125] As shown best in Figures ISA and 18F, frames 302 and process layers 304 have apertures in them. The apertures provide plenums 305A and 305B that extend through reactor 300. Outer parts 308 of each frame provide physical support for a central slab 310 in which the active areas of reactor 300 are located. Outer areas 308 can also sink heat generated by the operation of reactor 300.

[0126] Reactor 300 demonstrates that frames may include alignment features that can be used to achieve proper alignment of frames with one another during assembly of a reactor. In the illustrated embodiment, the alignment features include holes 312A and 312B. Holes 312A and 312B may be used to align frames 302 and process layers 304 while building a reactor 300. Fasteners passing through holes 312A and 312B may optionally be used to mount chemical reactor 300 and/or to compress process layers 304 and frames 302 together. Other alignment features such as notches, indentations, projections or the like could be provided on frames to facilitate alignment of the frames during assembly of a reactor.

[0127] As seen best in Figures 18C and 18E, each frame provides a cavity 315A that communicates with plenum 305A and a cavity 315B that communicates with plenum 305B. Cavities 315A and 315B are on opposing sides of the frame 302. Cavities 315A and 315B are located in a part 316 of frame 302 that extends between plenums 305A and 305B. Cavities 315 A and 315B are filled with a porous, electrically-conductive material that permits reactants to reach catalyst-containing areas within the cavity. The porous, electrically-conductive material provides paths for electron conduction between the frames and the catalyst-containing areas. A fuel may be introduced into one of plenums 305A and 305B while an oxidant is introduced into the other one of plenums 305 A and 305B. [0128] It is possible to provide frames that define multiple central slabs 310 each located between a fuel plenum and an oxidant plenum. Each slab 310 may contain a number of unit fuel cells connected in series with one another. The fuel cells of different slabs 310 may be electrically connected in parallel with the fuel cells of other slabs 310 by way of the electrically-conducting frames.

[0129] The invention has application reactor types other than fuel cells. For example, a chemical reactor according to the invention may be configured to provide an electrolysis cell by forming anodes and cathodes on either side of some of the process layers and at least partially filling the cavities with electrochemically active materials. The reactant plenums may be filled with water which is transported into the electrolyzer to come into contact with the anodes and cathodes at the process layers. The electrolysis reaction uses electrical energy to decompose water into hydrogen and oxygen. The hydrogen and oxygen are formed at the electrodes and transported back into the reactant plenums by convection, diffusion, pressure gradients or other transport processes.

[0130] A reactor according to the invention may be configured to transport a reactant or one or more attributes of a reactant across process layers within the reactor. Attributes that may be passed through a process layer (either a process layer of a frame or a separate process layer) include: ionic charge (for example, ionic charge may pass through an electrolyte process layer in a fuel cell); heat (when used as a heat exchanger); • moisture content (when used as a humidifier); • pressure (when used with a gas permeable membrane to allow gas to diffuse out of a liquid); • concentration (when used to transport material from a substance in which the material has a first concentration to another substance in which the material has a different concentration); • electrical charge; and • other similar physical characteristics.

[0131] Examples of reactants that may be processed in a reactor according to the invention include: fuels; water; oxidants; beverages, such as wine, juices, and liquids containing particuϊates; liquid phase hydrocarbons, such as methanol, ethanol, butanol, and formic acid; gas phase hydrocarbons, such as propane, butane, methane, and combinations of these; foodstuffs, such as whey of cheese products, chocolate-based liquids, and other foodstuffs which are initially liquid and then solidify; by-products of a reaction that occurs in the reactor; and, combinations of these materials.

[0132] A reactor may be configured to operate as a heat exchanger by providing thermally- conductive process layers, Usable thermal conductors can be metal sheets or foils or thermally- conductive epoxy adhesive films such as those also available from Tech Film. Such a reactor may transfer large amounts of heat from a first reactant plenum to a second reactant plenum. For example, heat could be transferred from hot water at an elevated temperature such as about 90 degrees Celsius on one side and cold water having a temperature, for example, of about 20 degrees Celsius on the other side.

[0133] By providing a process layer configured as a micro-structured diffusion mixer, liquid can be transported from one cavity to another by diffusion without use of a separation membrane. Micro-structured diffusion mixers are available from Micronics of Seattle, Washington. Micro-structured diffusion mixers have small channels. Liquid can be pushed through the channels. Blood testing is one application for micro-structured diffusion mixers. Such mixers can be used to introduce a test liquid into blood without permitting blood to contaminate the test liquid. [0134] In some embodiments of the invention a heater is provided on one or more process layers. A type of heater suitable for use in a reactor according to the invention is a thin film resistive heater, such as those available from Omega of Stamford, Connecticut.

[0135] Reactors according to some embodiments of the invention include catalysts. Examples of catalysts that are contemplated as useable in such reactors include: • inorganic carbon catalysts, such as Novacarb™ from Mast Carbon of the United Kingdom.

[0136] The embodiments described herein have various combinations of features. These embodiments are intended as examples only. Features of different embodiments described herein may be combined to provide additional embodiments of the invention. For example, in general, the structures described in any of the embodiments described above could support any of the different types of catalyst, process layer, diffusion material described above. The particular combination of features used in the construction of a particular reactor will depend on the use to which the reactor will be put.

[0137] In addition to reactors, this invention provides methods for making reactors. It can be difficult to fill a high aspect-ratio cavity with a material such as a porous diffusion medium. This is especially the case when the cavity has a very small height (i.e. a small dimension HI or H2 as shown in Figure lA). Methods according to some embodiments of the invention involve filling cavities defined by frames when the frames have not yet been assembled to form a reactor. The cavities are filled through their large open sides. It is therefore relatively sfraightforward to fill the cavities with a porous diffusion medium, a catalyst, and/or any other material which is desirably present in the cavities. When the frames are assembled to form a reactor the large open sides of the cavities are closed by another frame or a process layer.

[0138] Figure 1 is a flowchart showing a method 400 for making a chemical reactor with frames and with high aspect ratio cavities. Method 400 begins by providing a frame in block 402. The frame includes a process layer and a perimeter barrier. The perimeter barrier and frame define a cavity. Figure 1 A shows a simple frame 410 having a process layer 412 and a peri eter barrier 414 that define a cavity 415. The depth H of cavity 415 is determined by the height H of perimeter barrier 414. Cavity 415 is a low aspect ratio cavity. That is, H is significantly less than the minimum dimension of the large open side of cavity 415. In the illustrated embodiment, H is significantly smaller than either of dimensions D and W. The preferred low aspect ratio is a ratio of D to H greater than one (W is typically significantly greater than D and so the ratio W to H is also greater than one in preferred embodiments).

[0139] A frame may be provided by forming the frame from a single material or by assembling a franϊe from two or more parts. For example, a frame may be made by: attaching a perimeter barrier to a process layer, the perimeter barrier may be previously formed from a suitable barrier material; • shaping a material that has properties suitable for use both as a perimeter barrier and a process layer into a form that includes both a process layer and a perimeter barrier; forming a perimeter barrier on a process layer; or • providing a part that includes a perimeter barrier and has an opening where it is desired to provide a process layer and either forming a process layer in the opening or affixing a pre-formed process layer to span the opening.

[0140] Shaping a material for use as a frame may include forming the material by ablating, etching, stamping, printing, milling, die cutting, molding, casting, water jetting, injection molding, or depositing of the material on a substrate, The material can be formed in any shape desired for the frame including a rectangle, a square, a cylinder, a triangle, an octagon, a pentagon, irregular shapes, or other prismatic shapes. In some embodiments, the shape includes one or more central apertures that will define one or more plenums in the assembled reactor.

[0141] Frames can be made out of electrolyte by molding or stamping a block of electrolyte into the desired shape. Frames can be made out of anon-conductive material made to have an electrolyte function by being made proton conducting in a specific region. Frames made of metal can provide separation of portions of a cell. Frames made of non-conductive material and then formed to have conductive paths can provide separator functions from each other. [0142] In some cases, creating a frame includes depositing a suitable precursor material on a substrate. The types of precursor materials usable with the method include: electrolytes; ion exchange membranes (which may be proton exchange membranes); filtration membranes; separation membranes; micro-structured diffusion mixers; heaters; catalysts, electrical conductors; thermal conductors; micro-structures of polymers; filled micro-structures of a polymer; filled epoxy composites; filled graphite composites; filled metal composites; plastics; or Other similar materials.

[0143] The substrate on which the precursor materials are deposited can be a release layer, such as a polyamide, like nylon, nylon 6 or nylon 6, 6, a polyethylene, or polytetrafluoroethylene. The substrate can be another frame, another unit reactor, a portion of a unit reactor, such as a frame or other portion of a unit reactor that includes a filled or partially filled low aspect ratio cavity, or a fuel cell.

[0144] Figures 20A and 20B schematically illustrate the creation of a frame 410 by adding a perimeter barrier 414 to a process layer 412, The step of joining the perimeter barrier to the process layer may be performed by welding, adhering, clamping, screwing, or otherwise engaging the perimeter barrier to the process layer. [0145] A material, for example a porous medium, is optionally introduced into cavity 415 in block 403. Optionally, several layers of material may be sequentially introduced into cavity 415 in block 403. Figures 20C and 20D show the introduction of two layers 419A and 419B of material into cavity 415 of frame 410. The materials of layers 419A and 419B may have different properties. For example, layer 419A may contain a catalyst while layer 419B has no catalyst or less catalyst. One material or two or or more different materials may be spatially distributed over the surface of process layer 412 within cavity 415 in different ways. For example, one material may be deposited around the perimeter of a process layer while a different material is deposited on a central area of the process layer. It is relatively straightforward to introduce layers 419A and 419B into cavity 415 using any of a wide range of available processes because the layers can be introduced through large open side 420 of cavity 415. In respect of opening 420, cavity 415 is a low aspect ratio cavity.

[0146] In embodiments which include introducing a material into a cavity, the material may be provided as a pre-formed quantity of material to be inserted into the cavity or the material may be formed in the cavity. Multiple layers of material may be placed into the cavity or formed in the cavity. Material may be introduced into the cavity by any suitable deposition process including processes such as: spraying;

• casting; syringe injecting;

• compression molding;

• silk screening; • spreading; printing; inkjetting; and the like.

[0147] Where the reactor will be a fuel cell or other reactor in which the presence of a catalyst is required or desired then the catalyst may be introduced in block 403 if the catalyst is not already present in the frame. [0148] At block 406 the frame is assembled to an adjacent part that closes the open side 420 of the frame to provide a high aspect ratio cavity. Figure 20E shows the introduction of a process layer 422 to close open side 420 of frame 410. Block 406 may involve assembling frame 410 into a reactor. Block 406 may, in the alternative, comprise assembling frame 410 to an adjacent part to make an intermediate assembly. A number of intermediate assemblies can then be assembled to one another, possibly together with other parts, to make the reactor.

[0149] Block 406 may comprise assembling frame 410 to a process layer 422 or other adjacent part using a suitable adhesive.

[0150] After process layer 422 is in place, cavity 415 is accessible through opening 425- The small dimension, H, of opening 425 is much smaller than either dimension D or W of opening 420. In respect of opening 425, cavity 415 is a high aspect ratio cavity. That is, the ratio H to D is less than one.

[0151] Blocks 402, 406 and, when present, 403 are repeated until the reactor includes a desired number of layers-

[0152] At block 408 a reactant plenum is placed in fluid communication with the cavity. Optionally the frame is assembled into an intermediate assembly that may include more than one frame or one or more process layers in addition to the frame before assembling the frame into a reactor, The intermediate assembly may include more than one frame or one or more process layers in addition to the frame. The frame may be assembled to the adjacent part either as part of assembling the intermediate assembly or when the intermediate assembly is assembled into the reactor. Between 2 and 100,000 intermediate assemblies are joined to form the compact chemical reactor.

[0153] Where an intermediate assembly is formed, the intermediate assembly may comprise, for example: at least one frame comprising: (i) a process layer, a perimeter barrier and at least one low aspect ratio cavity; (ii) at least one frame comprising: a process layer, two perimeter barriers, and at least two low aspect ratio cavities disposed on a second process layer; (iii) at least one layer comprising a perimeter barrier formed on one side of a process layer with at least one low aspect ratio cavity; or combinations of (i) and (iii) joined together.

[0154] In a preferred embodiment, assembling the reactor comprises connecting together at least four intermediate assemblies each of which constitutes Vi of a unit reactor 30 (see Figure 1). In a preferred embodiment, the compact chemical reactor comprises two or more unit reactors (which may be fuel cells, for example). A plurality of the components illustrated in any of Figures 8 to 10 could be combined to form an intermediate assembly, for example.

[0155] Figure 21 shows an example in which intermediate assemblies 440A, 440B and 440C (collectively 440) are each made up of frames 442 and 444 and a process layer 443 sandwiched between the frames. When frames 442 and 444 are made of the same material, frames 442 and 444 of different intermediate assemblies may be bonded together with a suitable adhesive 445 to link the intermediate assemblies together. For example, where frames 442 and 444 are both made of metal then frame 442 of intermediate assembly 440C may be bonded to frame 444 of intermediate assembly 440B using a suitable electrically-conductive adhesive. Additional mechanical support members may be added to improve the robustness of the resulting reactor.

[0156] Intermediate assemblies 440 may be made up by filling frame 442 with suitable material(s) 447, filling frame 444 with suitable materials 448, and bonding filled frames 442 and 444 on either side of process layer 443 so that openings 449 and 450 open onto different faces of intermediate assembly 440.

10157] Since intermediate assemblies 440 are functionally independent of one another it is not mandatory that frames 442 and 444 of adjacent intermediate assemblies be maintained in tight intimate contact with one another- All that is required is that an electrical connection is made and that an acceptable seal is made to prevent reactants from leaking between frames 442 and 444. [0158] Assembling the intermediate assemblies, where used, and assembling the reactor may comprise using alignment features of the frames to align frames and/or intermediate assemblies with one another.

[0159] Block 408 comprises joining the reactor to one or more reactant plenums. In a preferred embodiment, the reactor is joined to two reactant plenums to facilitate a transport process between the reactant plenums and the process layers. Where the reactor is a fuel cell, one of the reactant plenums may comprise a fuel plenum connected or connectible to a source of a fuel while the other is an oxidant plenum that is open to the ambient atmosphere or is connected or connectible to a source of an oxidant.

[0160] In the case of a compact chemical reactor used as a fuel cell, two types of frames can be used in making the fuel cell, an electronically conducting frame and an ionically conducting frame, The electronically conducting frame may be made from an electronically conducting material or, alternatively, made conductive by filling a porous region with a nonporous conductive material. The ionically conductive frame may be made from an ionic conductor, such as Nafion™. If Nafion™ is used, then the perimeter barrier may also be formed from Nafion™, Alternatively, the frame material can be made from electrically-insulating material such as polyethylene with a porous region that has been filled with electrolyte such as Nafion™ to render the region ionically conductive. The frames can be made of identical materials or each frame can be of a different material.

[0161] The frames are typically one-piece structures to advantageously reduce the number of parts. The one-piece construction makes aligning the unit reactors of the compact chemical reactors simpler, which, in turn, makes the process cheaper and quicker than construction using layered materials.

[0162] By using a one-piece formed construction of frames, there is no need for the extra step of bonding dissimilar materials together such as bonding perimeter barrier material to process layer material. Thus a compact chemical reactor built using frames can have better integrity and fewer maintenance issues than multipart constructions. [0163] Another aspect of the invention provides a method comprising:

• providing, by forming or otherwise, at least two process layers; forming a perimeter barrier on at least one side of at least one of the process layers to provide an intermediate assembly having at least one Jow aspect ratio cavity;

• repeating these two steps to create additional intermediate assemblies each having at least one low aspect ratio cavity;

• joining intermediate assemblies together to create a chemical reactor that includes high aspect ratio cavities; and, providing at least one reactant plenum communicating with at least one of the high aspect ratio cavities.

[0164] It can be appreciated that methods according to the invention can be embodied in ways that provide various advantages including:

• The methods may be used to make chemical reactors that have increased reactant surface areas as compared to chemical reactors having more conventional configurations. The methods permit the manufacture o chemical reactors that are scaled to micro-dimensions, so that very small compact chemical reactors can be created. The use of frames simplifies the method of assembly by reducing the number of components needed in construction.

• The use of frames to build compact chemical reactors improves the precision in alignment between process layers and perimeter barriers.

• The formation of low aspect ratio cavities in the intermediate assemblies greatly simplifies the task of inserting active materials into the cavities.

[0165] Where a component (e.g. a process layer, catalyst, reactant, fastener, assembly, device, circuit, etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a "means") should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

[0166] As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the scope thereof- Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A chemical reactor comprising: a first process layer; a perimeter barrier on the first process layer, the perimeter barrier and first process layer defining a cavity; a second process layer disposed adjacent to the perimeter barrier with the cavity between the first and second process layers; wherein an aspect ratio of: a dimension of the cavity along the process layers to a distance between the first and second process layers is greater than 1 : 1.

2. A chemical reactor according ϊo claim 1 wherein the first process layer and perimeter barrier are attached to one another to provide a frame.

3. A chemical reactor according to claim 2 wherein the frame constitutes a first frame of a plurality of frames each comprising a first process layer and a perimeter barrier on the first process layer, and the reactor comprises a corresponding plurality of cavities defined by perimeter barriers of the frames,

4. A chemical reactor according to claim 3 wherein the plurality of cavities comprises a plurality of first cavities interleaved with a plurality of second cavities.

5. A chemical reactor according to claim 4 wherein the first cavities are in fluid communication with each other and the second cavities are in fluid communication with each other.

6. A chemical reactor according to claim 4 wherein the first cavities open out to a first face of the reactor.

7. A chemical reactor according to claim 6 wherein the second cavities open out to a second face of the reactor different from the first face of the reactor.

8. A chemical reactor according to claim 7 wherein the first face is opposed to the second face.

9. A chemical reactor according to claim 8 wherein the first and second faces are substantially planar and parallel to one another.

10. A chemical reactor according to any one of claims 7 to 9 wherein the distance between the first and second process layers is small in comparison to a dimension of the first and second faces. ->

11. A chemical reactor according to any one of claims 7 to 10 comprising at least one plenum interconnected to a supply of a reactant, wherein the plenum is in fluid communication with one of the first and second faces of the reactor.

12. A chemical reactor according to any of claims 7 to 11 comprising: a. a first plenum in fluid communication with the first face of the reactor, wherein the first plenum is interconnected to a supply of a first reactant; and b. a second plenum in fluid communication with the second face of the reactor, wherein the second plenum is interconnected to a supply of a second reactant.

13. A chemical reactor according to claim 12, wherein each perimeter barrier comprises a material that prevents reactants from the first and second plenums from intermixing.

14. A chemical reactor according to any one of claims 1 to 13 wherein at least one perimeter barrier is integral with an adjoining process layer,

15. A chemical reactor according to any one of claims 1 to 13 wherein the first process layer and perimeter barrier are separate parts that are attached to one another.

1 . A chemical reactor according to any one of claims 1 to 15, wherein the aspect ratio is at least 2^l/₂:l

17. A chemical reactor according to any one of claims 1 to 15 wherein the aspect ratio is between 5:1 and 100:1.

18. A chemical reactor according to any one of claims 1 to 15 wherein the aspect ratio is between 2 V_:l and 15:1.

1 . A chemical reactor according to any one of claims 2 to 18 wherein: the cavity opens onto first and second surfaces of the frame, an opening of the cavity on the first surface of the frame extends generally parallel to the first process layer of the frame and an opening of the cavity onto the second surface of the frame is disposed adjacent to an edge of the first process layer; and, the second process layer is adjacent to the second surface of the frame.

20. A chemical reactor according to claim 19 wherein the frame has a thin flat configuration and the first surface of the frame constitutes a face of the frame and the second surface of the frame constitutes an edge of the frame.

21. A chemical reactor according to claim 2 wherein the perimeter barrier constitutes a first perimeter barrier defining a first cavity on a first side of the first process layer and the frame comprises a second perimeter barrier on a second side of the first process layer opposed to the first side, the second perimeter barrier defining a second cavity on the frame.

22. A chemical reactor according to claim 21 wherein: the first cavity opens onto first and second surfaces of the frame, an opening of the first cavity on the first surface of the frame extends generally parallel to the first process layer of the frame and an opening of the cavity onto the second surface of the frame is disposed adjacent to an edge of the first process layer; the second cavity opens onto third and fourth surfaces of the frame, an opening of the second cavity on the third surface of the frame extends generally parallel to the first process layer and an opening of the second cavity onto the fourth surface of the frame is disposed adjacent to an edge of the first process layer; and, the first and third surfaces of the frame are opposed to one another and the second and fourth surfaces of the frame are opposed to one another.

23. A chemical reactor according to claim 21 or 22 wherein: the frame comprises one of a plurality of frames; the second process layer comprises one of a plurality of second process layers; and, the second process layers are interleaved with the plurality of frames such that each of the plurality of second process layers has a first cavity of one frame on one side and a second cavity of an adjacent frame on its other side.

24. A chemical reactor according to claim 23 wherein openings of the first cavity of one frame on one side of the second process layer and the second cavity of the adjacent frame on the other side of the second process layer are oriented in different directions.

25. A chemical reactor according to claim 2 wherein the frame constitutes one of a plurality of first frames and the reactor comprises a plurality of second frames interleaved between the first frames, each of the second frames having a second process layer of a type different from the first process layer and a perimeter barrier disposed on the second process layer.

26. A chemical reactor according to claim 25 wherein the cavity in each of the first frames has an opening or openings extending adjacent an edge of the first process layer, the cavity in each of the second frames has an opening or openings extending adjacent an edge of the second process layer and the openings of the cavities of the first and second frames are oriented in different directions.

27. A chemical reactor according to claim 25 wherein the different directions are opposing directions.

28. A chemical reactor according to any one of claims 25 to 27 wherein the process layers of the first frames are electronically conductive and the process layers of the second frames are ionically conductive.

29. A chemical reactor according to any one of claims 1 to 28 wherein one or more of the cavities of the reactor are at least partially filled with a porous medium.

30. A chemical reactor according to claim 29 wherein the porous medium comprises a plurality of layers of porous material in each of the one or more cavities, the plurality of layers having properties different from one another.

31. A chemical reactor according to claim 30 wherein the plurality of layers of porous material extend generally parallel to a process layer bounding the cavity within which the layers are situated,

32. A chemical reactor according to claim 2 wherein the frame constitutes a first frame and the chemical reactor comprises a second frame comprising a third process layer and a perimeter barrier on the third process layer, the perimeter barrier defining a cavity on the second frame; wherein the second process layer is disposed between the cavities on the first and second frames.

33. A chemical reactor according to claim 32 wherein the cavity in the first frame has an opening or openings extending adjacent an edge of the first process layer, the cavity in the second frame has an opening or openings extending adjacent an edge of the third process layer and the openings of the cavities of the first and second frames are oriented in different directions.

34. A chemical reactor according to claim 32 or 33 comprising a plurality of interconnected intermediate assemblies, each of the intermediate assemblies comprising a first frame, a second process layer and a second frame wherein the second process layer of each intermediate assembly is disposed between the cavities on the first and second frames.

35. A chemical reactor according to claim 34 wherein the first and second frames arc made of a metal.

36. A chemical reactor according to any one of claims 32 to 35 comprising a gas diffusion electrode material in the cavities of the first and second frames.

37. A chemical reactor according to any one of claims 32 to 36 wherein the first process layer is electronically conductive.

38. A chemical reactor according to any one of claims 32 to 37 wherein the second process layer is ionically conductive.

39. A chemical reactor according to any one of claims 1 to 38 comprising a first catalyst located on or adjacent to a first surface of the second process layer in the first cavity.

40. A chemical reactor according to clai 39 comprising a second catalyst located on or adjacent to a second surface of the second process layer in the second cavity.

41. A chemical reactor according to any one of claims 1 to 40 comprising a plurality of interconnected unit reactors each comprising at least one process layer and at least one perimeter barrier disposed ot the process layer to define a cavity.

42. A chemical reactor according to claim 41 wherein the plurality of interconnected unit reactors are disposed on and conform to a non-planar surface.

43. A chemical reactor according to any one of claims 1 to 42, wherein the reactor is a fuel cell.

44. A chemical reactor according to any one of claims 1 to 42, wherein the reactor is an electrolyzer.

45. A chemical reactor comprising: at least a first unit reactor and a second unit reactor disposed adjacent one another to form a first side and a second side of the reactor; a first reactant plenum communicating with the first side; a second reactant plenum communicating with the second side; wherein each of the unit reactors comprises: a first process layer; a second process layer; a first cavity formed between the first and second process layers; a second cavity formed between the second process layer and the first process layer of adjacent unit reactors; a first perimeter barrier disposed on the second process layer to define a perimeter of the second cavity; and a second perimeter barrier disposed on the first process layer to define a perimeter of the first cavity; wherein the first cavity is in communication with the first side and the second cavity is in communication with the second side; and wherein at least one of the process layers facilitates a transport process between the reactant plenums.

46. A reactor according to claim 45, wherein: at least one of the unit reactors comprises at least one frame formed from one of the process layers and at least one of the perimeter barriers, and at least one of the cavities is defined by the at least one frame,

47. A reactor according to claim 45, wherein: at least one of the unit reactors comprises a frame formed from one of the process layers and two of the perimeter barriers; and, the frame defines two of the cavities.

48. A reactor according to claim 45, wherein: at least one of the xmit reactors comprises two frames, each of the two frames formed from one of the process layers, and at least one of the perimeter barriers, and the frame defines at least one of the cavities.

49. A reactor according to claim 45, wherein each unit reactor has a frame integrally formed from at least one process layer between at least one perimeter barrier and a second perimeter barrier, and wherein a second process layer is disposed on the frame.

50. A reactor according to any of claims 45 to 49, wherein the frame from one of the unit reactors connects to a frame of the other unit reactor with a mechanical device. 1. A reactor according to any of claims 45 to 50, wherein the frames are held together by a protrusion and corresponding indentation formed from the frames that provide a snap 'fit connection, a mechanical clip, a tie rod, an adhesive bond, tape, external compression bands, a key, or combinations therein.

52. A reactor according to claim 46, comprising a second process layer, a second perimeter barrier disposed on the second process layer, and a second cavity formed in the at least one reactor frame; and wherein the at least one cavity is in communication with one of the sides of the reactor and the second cavity is in communication with the other side of the reactor.

53. A reactor according to claim 52, wherein the at least one process layer is held in place by a mechanical device coupling the frame from the first xmit reactor to a second frame in the second unit reactor.

54. A reactor according to any of claims 46 to 53, wherein at least a portion of one of the reactant plenums is embedded in at least one of the frames,

55. A reactor according to any of claims 45 to 54, wherein the unit reactors are disposed parallel to one another orthogonal around a central axis of the reactor.

56. A reactor according to any of claims 45 to 55, wherein the unit reactors are disposed parallel to each other parallel to a central axis of the reactor.

57. A reactor according to any of claims 45 to 55, wherein the unit reactors are formed into groups of parallel unit reactors and each group is disposed at an arbitrary angle to adjacent groups.

58. A reactor according to any of claims 45 to 57, wherein adjacent unit reactors connect adj cent first perimeter barriers and first process layers.

59. A reactor according to any of claims 45 to 58, wherein the reactor comprises more than two unit reactors.

60. A reactor according to any of claims 45 to 59, wherein the reactor has a three dimensional shape selected from the group consisting of a cylindric, prismatic, boxlike, or irregular shape.

61. A reactor according to any of claims 45 to 60 wherein an overall thickness between the first side and the second side of the reactor is a variable thickness.

62. A reactor according to claim of any of claims 45 to 61 wherein an overall length of the reactor is between 1 millimetre and 100 centimetres and an overall width of the reactor is between 1 millimetres and 50 centimetres and an overall thickness between the first side and the second side of the reactor is between 100 nanometres and 5 centimetres.

63. A reactor according to any of claims 45 to 62 wherein at least one of the first and second unit reactors are arranged to form the second reactant plenum.

64. A reactor according to any of claims 45 to 63 , wherein at least one of the first and second unit reactors surrounds the second reactant plenum and conforms to the shape of the second reactant plenum.

65. A reactor according to any of claims 45 to 64 wherein the first reactant plenum is enclosed by a structure.

66. A reactor according to claim 65 wherein the structure is open to ambient atmosphere.

67. A reactor according to claim 65 wherein the structure is a closed container.

68. A reactor according to any of claims 45 to 67, wherein the second reactant plenum is enclosed by a device.

69. A reactor according to claim 68 wherein the device is open to ambient atmosphere.

70. A reactor according to claim 68 wherein the device is a closed container.

71. A reactor according to any of claims 45 to 70 wherein one of the process layers performs a function different from the function of the other process layer.

72. A reactor according to any of claims 45 to 71 , wherein at least one process layer comprises an ion conducting material.

73. A reactor according to claim 72, wherein at least one process layer comprises an electrolyte, an ion exchange membrane, a proton exchange membrane, an electrolyte filled micro porous structure, a liquid electrolyte trapped in a matrix, an electrolysis membrane, a filtration membrane, a separation membrane, a micro-structured diffusion mixer, a heater, a catalyst, electrical conductors, thermal conductors, or combinations thereof.

74. A reactor according to any of claims 45 to 73 wherein at least one process layer comprises an electrically conductive material.

75. A reactor according to any of claims 45 to 74 wherein adjacent process layers are alternatively ionic conducting process layers and electrically conducting process layers.

76. A reactor according to any of claims 45 to 75 wherein at least one of the process layers comprises at least one thin sheet.

77. A reactor according to any of claims 45 to 76, wherein at least one of the process layers comprises two or more thin process layers that are in contact with one another.

78. A reactor according to any of claims 45 to 77 wherein at least one process layer has a thickness different from a thickness of another process layer.

79. A reactor according to any of claims 45 to 78, wherein at least one cavity is at least partially filled with a catalyst.

80. A reactor according to any of claims 45 to 79 wherein at least one cavity is at least partially filled with a material to aid in the transport of a reactant or an attribute of a reactant or byproducts of a reaction of the reactant at the process layers.

81. A reactor according to any of claims 45 to 80 wherein at least one cavity is at least partially filled with a gas diffusion electrode structure comprising at least one catalyst layer and at least one porous conductive layer.

82. A reactor according to claim 81 configures as a bipolar connected reactor wherein the catalyst layer adjoins an ionically-conducting process layer to provide an anode or a cathode, and wherein the porous conductive layer electrically connects the catalyst layer to an electronically conducting process layer enabling cuιτent to flow between gas diffusion electrode structures.

83. A reactor according to claim 81 or 82 wherein the porous conductive layer comprises at least two layers, each layer of a different porous material.

84. A reactor according to claim 81 wherein the gas diffusion electrode comprises first and second catalyst layers; wherein the first catalyst layer adjoins the first process layer and the second catalyst layer adjoins the second process layer to provide an edge-collected uni-polar fuel cell layer.

85. A reactor according to any of claims 45 to 84, wherein at least one cavity has an aspect ratio greater than 1:1.

86. A reactor according to any of claims 45 to 85, wherem at least one cavity has an aspect ratio between 2.5:1 and 15:1.

87. A reactor according to any of claims 45 to 85 wherein at least two cavities have aspect ratios different from one another.

88. A reactor according to any of claims 45 to 85, wherein the first perimeter barrier completely surrounds the second cavity.

89. A reactor according to any of claims 45 to 88 wherein the second perimeter barrier completely surrounds the first cavity.

90. A reactor according to any of the claims 45 to 89 wherein the first and second perimeter barriers each comprise a height ranging from 100 nanometres.

91. A reactor according to any of claims 45 to 90, wherein at least one of the perimeter barriers has a width wherein the width is narrower on one portion of the perimeter barrier than it is in another portion of the perimeter barrier.

92. A reactor according to any of claims 45 to 91 , wherein at least one first process layer is undulating, at least one second process layer is undulating, at least one first cavity is undulating, at least one second cavity is undulating, at least one first perimeter barrier is undulating and at least one second perimeter barrier is undulating.

93. A reactor according to any of claims 45 to 92, wherein the reactor is a fuel cell.

94. A reactor according to any of claims 45 to 92 wherein the reactor is an electrolysis reactor.

95. An electrical appliance, comprising, as a source of power, a fuel cell according to claim 93.

96. An electrical appliance according to claim 95 wherein the electrical appliance is selected from the group consisting of airplane electronics, car electronics, laser pointers, cellular telephones, wireless telephones, projectors, televisions, compact disc players, DVD players, radios, flashlights, digital cameras, digital imaging equipment, and digital image viewing equipment.

97. A method for making a chemical reactor, the method comprising: providing a first process layer and a perimeter barrier on the first process layer, the perimeter barrier and first process layer defining a cavity having an opening, the opening having a perimeter defined by the perimeter barrier, the cavity having an aspect ratio of: a height of the perimeter barrier in a direction substantially perpendicular to the first process layer to a dimension of the cavity in a direction along a surface of the first process layer of less than 1:1; and, joining the perimeter barrier to a second process layer, the second process layer closing the opening of the cavity.

98. A method according to claim 97 wherein there is a gap in the perimeter barrier and the method comprises placing the cavity in fluid communication with a reactant plenum by way of the gap.

99. A method according to claim 97 or 98 comprising depositing a material into the cavity prior to joining the perimeter barrier to the second process layer.

100. A method according to claim 99 wherein depositing a material into the cavity comprises depositing a plurality of layers of material into the cavity.

101. A method according to claim 100 wherein the plurality of layers include at least one catalyst-containing layer.

102. A method according to any one of claims 97 to 101 wherein providing a first process layer and a perimeter barrier on the first process layer comprises providing a frame having the perimeter barrier attached to the first process layer.

103. A method according to any one of claims 97 to 102 comprising: assembling a plurality of intermediate assemblies, each of the intermediate assemblies comprising at least a first and second process layer, and a perimeter barrier defining a cavity defined between the first and second process layers; and, assembling the intermediate assemblies together.

104. A method according to claim 103 wherein assembling the intermediate assemblies together comprises attaching the intermediate assemblies to one another with an adhesive.

105. A method according to any on<s of claims 97 to 104 comprising repeating providing a first process layer and a perimeter barrier on the first process layer, the perimeter barrier and first process layer defining a cavity having an opening, the opening having a perimeter defined by the perimeter barrier, the cavity having an aspect ratio of: a height of the perimeter barrier in a direction substantially perpendicular to the first process layer to a dimension of the cavity in a direction along a surface of the first process layer of less than 1:1; and, joining the perimeter barrier to a second process layer, the second process layer closing the opening of the cavity to provide a reactor comprising a plurality of interconnected unit reactors.

1 6. A method for making a chemical reactor, comprising: a) forming at least two low aspect ratio process layers; b) forming at least one low aspect ratio perimeter barrier, c) creating an intermediate assembly comprising a low aspect ratio cavity by joining the low aspect ratio perimeter barrier to at least one side of one of the low aspect ratio process layers; d) repeating steps (a) to (c) to create a plurality of intermediate assemblies comprising low aspect ratio cavities; e) creating a high aspect ratio cavity by joining one of the low aspect ratio process layers to the intermediate assembly; and f) repeating steps (d) and (e) to create a plurality of joined intermediate assemblies to create a chemical reactor with high aspect ratio cavities; g) joining the chemical reactor to two reactant plenums to facilitate a transport process between the reactant plenums by way of the process layers.

107. A method according to claim 106, wherein forming the perimeter barrier comprises depositing the barrier material on a portion of at least one of the process layers and forming the barrier material into a shape.

108. A method according to claim 106, wherein forming the perimeter barrier comprises making a structural form that prevents reactant from one plenum from moving into the other plenum.

109. A method according to claim 108, wherein the structural form is a micro-structure or a three-dimensional structure with a tortuous path.

110. A method according to any of claims 106 to 109, wherein forming the process layers comprises depositing a precursor material on a substrate and forming the precursor material into a shape.

111. A method according to claim 110 comprising forming the precursor material into a shape selected from the group consisting of: a rectangle, a square, a triangle, an annular ring, an arc, an irregular shape, and other prismatic shapes.

112. A method according to any of claims 106 to 111 comprising at least partially filling at least one of the low aspect ratio cavities with at least one material.

113. A method according to claim 112 wherein the material comprises a catalyst, a porous material, an electrical conductor, a hydrophobic polymeric binder, or combinations thereof-

114. A method according to one of claims 112 and 113, wherein at least partially filling the low aspect ratio cavity comprises forming a micro-structure in the low aspect ratio cavity,

115. A method according to any one of claims 110 to 111 wherein the substrate comprises a release layer.

116. A method according to any of claims 110 to 111 , wherein the substrate comprises one of the low aspect ratio process layers.

117. A method according to any of claims 110 to 111, wherein the substrate comprises an at least partially filled low aspect ratio cavity.

118. A method according to any of claims 110 to 111 , wherein the substrate comprises at least a portion of a unit reactor.

119. A method according to any of claims 106 to 118, wherein the high aspect ratio cavities have ratios of depth D to height H which are greater than 1:1.

120. A method according to any one of claims 1 6 to 119, wherein the reactor is an electrolyzer.

121. A method according to any one of claims 106 to 119, wherein the reactor is a fuel cell layer.

122. A method according to claim 121, wherein the two reactant plenums constitute an oxidant plenum carrying oxidant and a fuel plenum carrying a fuel.

123. A method according to claim 121 , comprising at least partially filling at least one of the low aspect ratio cavities with the material to provide two gas diffusion electrodes.

124. A method according to any of claims 106 to 123, wherein creating the plurality of joined intermediate assemblies comprises substantially encircling a volume with the intermediate assemblies.

125. An electrolyzer made by any of claims 106 to 120.

126. A method for making a chemical reactor having high aspect ratio cavities, the method comprising: a) forming at least one intermediate assembly, comprising one of: i. at least one frame comprising: a process l yer, a perimeter barrier and at least one low aspect ratio cavity; or ii. at least one frame comprising: a process layer, two perimeter barriers, and at least two low aspect ratio cavities disposed on either side of the process layer; or iii. at least one layer comprising a perimeter barrier formed on one side of a process layer with at least one low aspect ratio cavity; or iv. combinations of (i) and (iii) oined together; b) joining at least two intermediate assemblies to together to create a chemical reactor having at least one high aspect ratio cavity; and c) joining the chemical reactor to two reactant plenums to facilitate a transport process between the reactant plenums by way of the process layers.

127. A method according to claim 126, wherein forming the intermediate assembly comprises making a structural form that prevents reactant from one reactant plenum from moving into the other reactant plenum.

128. A method according to claim 127, wherein the structural form is a micro-structure or a three dimensional structure with a tortuous path.

129. A method according to any of claims 126 to 128, wherein forming the perimeter barrier comprises forming a barrier from barrier material and then joining the formed barrier material to at least a portion of at least one of the process layers.

130. A method according to any of claims 126 to 129, wherein forming the intermediate assembly further comprises creating process layers each having a shape selected from the group: a rectangle, a square, a triangle, an annular ring, an arc, and an arbitrary pattern.

131. A method according to any of claims 126 to 130, comprising at least partially filling at least a portion of one of the low aspect ratio cavities with a material to facilitate the transport of reactant material or the transport of reactant attributes.

132. A method according to claim 131, wherein the material used to fill the low aspect ratio cavity forms a micro-structure.

133. A method according to any one of claims 126 to 131 wherein high aspect ratio cavity has an aspect ratio greater than 1:1.

134. A method according to any one of claims 126 to 133, wherein forming the intermediate assembly comprises making at least one of the process layers an undulating process layer.

135. A thin flat chemical reactor made by any of claims 126 to 134.

136. A thin curvilinear chemical reactor made by a method according to any of claims 126 to 134.

137. A method according to any of claims 126 to 134, wherein the chemical reactor is a fuel cell layer.

138. A method according to claim 137 comprising filling the low aspect ratio cavities with gas diffusion electrode material to form gas diffusion electrodes.

139. A method according to claim 138 wherein the two reactant plenums constitute a fuel plenum and an oxidant plenu to transport fuel and oxidant, respectively, into the gas diffusion electrodes.

140. A method comprising any new inventive step, act, combination of steps and/or acts or sub-combination of steps and/or acts described herein.

141. Apparatus comprising any new inventive feature, combination of features and/or means, or sub-combination of features and/or means described herein.