JP5665631B2 - Fuel cell - Google Patents

Description

  The present invention relates to fuel cell technology.

  Generally, a fuel cell is arranged in order on a membrane electrode assembly (MEA) having an electrolyte membrane and anode and cathode electrodes arranged on both sides of the electrolyte membrane, and on both sides of the membrane electrode assembly. A pore layer (also referred to as a current collecting layer, a microporous layer (MPL) or the like), a gas diffusion layer, and a separator are provided. In the above fuel cell, the fuel gas is provided to the anode electrode, and the oxidant gas is provided to the cathode electrode to perform an electrochemical reaction.

  In recent years, a fuel cell structure that eliminates the gas diffusion layer disposed on either the anode electrode or the cathode electrode or reduces the film thickness in order to meet the demands for miniaturization, cost reduction, and high performance of fuel cells. Has been proposed (see, for example, Patent Documents 1 to 4). However, if the gas diffusion layer on either the anode side or the cathode side is abolished, flooding caused by poor drainage of water in the fuel cell and poor water retention in the fuel cell The resulting dry up (drying) occurs. For example, if the gas diffusion layer on the anode electrode side is abolished or the thickness thereof is reduced, the water generated on the cathode electrode side from the cathode electrode side through the electrolyte membrane is caused by the electrochemical reaction that occurs in the fuel cell. The movement to the side decreases and flooding occurs on the cathode side. In addition, for example, if the gas diffusion layer on the cathode electrode side is eliminated or the thickness thereof is reduced, water generated on the cathode electrode side is likely to be discharged outside the fuel cell without remaining on the cathode electrode side. Dry up occurs on the side. Thus, when flooding or dry-up occurs in the fuel cell, it becomes difficult to stably maintain the power generation performance of the fuel cell.

JP 2006-12546 A JP 2010-182383 A JP 2009-64615 A JP 2008-53064 A

  Therefore, an object of the present invention is to provide a fuel cell that can suppress flooding and dry-up that occur in the fuel cell.

The fuel cell of the present invention comprises a membrane electrode assembly comprising an electrolyte membrane and anode and cathode electrodes disposed on both sides of the electrolyte membrane, a pore layer disposed on both sides of the membrane electrode assembly, A gas diffusion layer disposed outside the pore layer on the anode electrode side, and the gas diffusion layer is not disposed outside the pore layer on the cathode electrode side, and at least of the porous channel layer and the separator In any one of the fuel cells, the pore layer on the anode electrode side and the cathode electrode side has hydrophilicity.

  In the fuel cell, it is preferable that a porous flow path layer is disposed outside the pore layer on the cathode electrode side and outside the gas diffusion layer.

  In the fuel cell, the gas diffusion layer preferably has water repellency.

Further, in the fuel cell, a region from 1/10 to 9/10 of the entire pore layer on the anode electrode side has water repellency from the upstream side to the downstream side in the fuel gas supply. Is preferred.

The fuel cell of the present invention includes a membrane electrode assembly including an electrolyte membrane and an anode electrode and a cathode electrode arranged on both sides of the electrolyte membrane, and a pore layer arranged on both sides of the membrane electrode assembly. And a gas diffusion layer is not disposed outside the pore layer on the anode electrode side and the cathode electrode side, and at least one of a porous channel layer and a separator is disposed on the fuel cell. The pore layer on the anode electrode side has water repellency, and the pore layer on the cathode electrode side has hydrophilicity.

  In the fuel cell, it is preferable that a porous flow path layer is disposed outside the pore layer on the anode electrode side and the cathode electrode side.

Further, in the fuel cell, from the upstream side in the fuel gas supply toward the downstream side, with respect to the total pore layer of the anode electrode side, not less than 1/10 to 9/10 or less regions have a water repellent , a region other than the region of the pore layer of the anode electrode side is preferable to have a hydrophilic property.

  According to the present invention, drying of the electrolyte membrane can be suppressed and stable power generation performance of the fuel cell can be maintained.

It is a schematic cross section which shows an example of a structure of the fuel cell which concerns on this embodiment. It is a schematic cross section which shows another example of a structure of the fuel cell which concerns on this embodiment. It is a schematic cross section which shows another example of a structure of the fuel cell which concerns on this embodiment. It is a schematic cross section which shows another example of a structure of the fuel cell which concerns on this embodiment. It is a schematic cross section which shows another example of a structure of the fuel cell which concerns on this embodiment. It is a schematic cross section which shows another example of a structure of the fuel cell which concerns on this embodiment. 4 is a schematic cross-sectional view showing an example of a configuration of a fuel cell of Reference Example 1. FIG. 6 is a schematic cross-sectional view showing an example of a configuration of a fuel cell of Reference Example 2. FIG.

  Embodiments of the present invention will be described below.

  FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the fuel cell according to the present embodiment. As shown in FIG. 1, the fuel cell 1 includes a membrane electrode assembly 16 including an electrolyte membrane 10 and an anode electrode 12 and a cathode electrode 14 provided on both sides of the electrolyte membrane 10, and outside the anode electrode 12 and the cathode electrode 14. The pore layers 18 and 20 provided, the gas diffusion layer 22 provided outside the pore layer 18 on the anode electrode 12 side, the outside of the gas diffusion layer 22 installed on the anode electrode 12 side, and the pores on the cathode electrode 14 side Separators 24 and 26 provided outside the layer 20 are provided.

  In the separators 24 and 26 shown in FIG. 1, gas flow path grooves 28 and 30 having a linear shape or a meandering shape are formed. The gas flow path grooves 28 and 30 serve as flow paths for the reaction gas supplied to the electrodes. Although not shown, fuel gas inlets and outlets, oxidant gas inlets and outlets are formed on the outer peripheries of the separators 24 and 26, and the gas passage groove 28 of the separator 24 on the anode electrode 12 side is a fuel gas inlet. The gas passage groove 30 of the separator 26 on the cathode electrode 14 side is in communication with the oxidant gas inlet and outlet.

  The structure of the separator is not limited to this, and a flat type separator in which the gas flow channel grooves 28 and 30 are not formed may be used. The configuration of a fuel cell using a flat type separator will be described below.

  FIG. 2 is a schematic cross-sectional view showing another example of the configuration of the fuel cell according to the present embodiment. In the fuel cell 2 shown in FIG. 2, the same reference numerals are given to the same configurations as those of the fuel cell 1 shown in FIG. As shown in FIG. 2, the fuel cell 2 includes an electrolyte membrane 10, a membrane electrode assembly 16 including an anode electrode 12 and a cathode electrode 14 provided on both sides of the electrolyte membrane 10, and outside the anode electrode 12 and the cathode electrode 14. The pore layers 18 and 20 provided, the gas diffusion layer 22 provided outside the pore layer 18 on the anode electrode 12 side, the outside of the gas diffusion layer 22 installed on the anode electrode 12 side, and the pores on the cathode electrode 14 side The porous body flow path layers 32 and 34 provided in the outer side of the layer 20, and the separators 36 and 38 provided in the outer side of the porous body flow path layers 32 and 34 are provided.

  The porous body flow path layers 32 and 34 are composed of a conductive porous body, and the reaction gas (fuel gas, oxidant gas) supplied to the porous body flow path layers 32 and 34 is applied to the entire surface of the electrode. It functions as a gas flow path to be supplied. The reaction gas supplied to the porous channel layers 32 and 34 mainly flows in the direction of the laminated surface of the members.

  The separators 36 and 38 shown in FIG. 2 are made of a flat conductive material (that is, the gas passage grooves 28 and 30 are not formed). Although not shown, fuel gas inlets and outlets, oxidant gas inlets and outlets are formed on the outer peripheries of the separators 36 and 38, and the fuel gas inlets and outlets are the porous channel layer 32 on the anode electrode 12 side. The oxidant gas inlet and outlet are in communication with the porous channel layer 34 on the cathode electrode 14 side.

  The pore layers 18 and 20 used in the present embodiment are made of a material having gas permeability and conductivity, and are also referred to as a current collecting layer, a microporous layer (MPL), or the like. The pore layer 18 provided on the anode electrode 12 side has a function of exchanging electrons with the anode electrode 12, and the pore layer 20 provided on the cathode electrode 14 side exchanges electrons with the cathode electrode 14. It has a function to perform. Moreover, the pore layers 18 and 20 used in this embodiment have hydrophilicity (hydrophilic action). Here, having hydrophilicity means that the contact angle of water measured with a contact angle measuring device using a droplet method is 70 degrees or less. The hydrophilization treatment of the pore layers 18 and 20 will be described later.

  The gas diffusion layer 22 disposed on the anode electrode 12 side of the present embodiment is a conductive porous substrate made of a material having gas diffusibility and conductivity, and has a function of diffusing gas to the electrode. The fuel gas supplied to the gas diffusion layer 22 mainly diffuses toward the electrode.

  The electrolyte membrane 10 constituting the membrane electrode assembly 16 of the present embodiment is made of a material having proton conductivity and electrical insulation. The anode electrode 12 constituting the membrane electrode assembly 16 includes a catalyst that promotes oxidation of fuel, and the fuel causes an oxidation reaction on the catalyst to generate protons and electrons. Further, the cathode electrode 14 constituting the membrane electrode assembly 16 includes a catalyst that promotes the reduction of the oxidant, and the oxidant takes in protons and electrons on the catalyst to cause a reduction reaction.

  Next, the operation of the fuel cell will be described using the fuel cell 2 of FIG.

  First, a fuel gas such as hydrogen gas is supplied from the fuel gas inlet of the separator 36 on the anode electrode 12 side to the porous body flow path layer 32. The fuel gas reaches the gas diffusion layer 22 while flowing through the porous flow path layer 32, passes through the gas diffusion layer 22 and the pore layer 18 on the anode electrode 12 side, and reaches the anode electrode 12. Hydrogen in the fuel gas that has reached the anode electrode 12 is separated into protons and electrons. The protons conduct through the electrolyte membrane 10 and reach the cathode electrode 14. The electrons are collected by the pore layer 18 on the anode electrode 12 side, transmitted to the gas diffusion layer 22 and the separator 36, and pass through an external circuit (not shown) to be separated on the cathode 38 side separator 38 and the porous channel layer. 34, and reaches the cathode electrode 14 through the pore layer 20.

  On the other hand, an oxidant gas such as air is supplied to the porous flow path layer 34 from the oxidant gas inlet of the separator 38 on the cathode electrode 14 side. The oxidant gas passes through the pore layer 20 on the cathode electrode 14 side and reaches the cathode electrode 14 while flowing through the porous channel layer 34. In the cathode 14, oxygen, protons, and electrons in the oxidant gas react to generate water and generate electric power. Through the above operation, the fuel cell 2 generates power.

  The produced water generated at the cathode electrode 14 along with the power generation is discharged from the oxidant gas outlet of the separator 38 through the pore layer 20 and the porous body flow path layer 34 together with the oxidant exhaust gas. The generated water generated at the cathode electrode 14 along with the power generation passes through the electrolyte membrane 10 and moves to the anode electrode 12 side, and along with the fuel exhaust gas, the pore layer 18, the gas diffusion layer 22, the porous body flow path. It passes through the layer 32 and is mainly discharged from the fuel gas outlet of the separator 36.

  Here, normally, when the gas diffusion layer is not installed on the cathode side of the fuel cell (the gas diffusion layer is installed on the anode side), the oxidant gas flowing through the pore layer on the cathode side The gas flow rate is faster than when a gas diffusion layer is installed. If it does so, the product water produced | generated by a cathode pole with an electric power generation will be carried away more than necessary from a cathode pole by the oxidizing agent gas (oxidant waste gas) of a high flow velocity. In particular, when the pore layer on the cathode electrode side is water-repellent, the ability to retain water is reduced, so water is taken away from the cathode electrode. As a result, the cathode electrode side is dried (dry-up), so that the ionic conductivity of the electrolyte membrane is lowered and the power generation performance of the fuel cell is lowered.

  Therefore, in the present embodiment, the above-described hydrophilic pore layer 18 is disposed on the anode electrode 12 side and the hydrophilic pore layer 20 is disposed on the cathode electrode 14 side, whereby the pore layers 18 and 20 are disposed in the pore layers 18 and 20. A lot of moisture can be retained. Therefore, even if the gas diffusion layer 22 is not installed on the cathode electrode 14 side of the fuel cell 2, the generated water generated at the cathode electrode 14 during power generation is caused by the oxidant gas (oxidant exhaust gas) having a high flow rate. Unnecessary removal from the cathode electrode 14 can be suppressed. Further, since the gas diffusion layer on the cathode electrode 14 side is eliminated, the fuel cell can be reduced in size, cost, and performance.

  In general, in the power generation process of a fuel cell, the electrolyte membrane swells and the volume increases. When the gas diffusion layer is discarded from the fuel cell, the volume increase caused by the swelling of the electrolyte membrane cannot be absorbed by the elastic deformation of the gas diffusion layer, and a compressive force is applied to the membrane electrode assembly. May be damaged. However, in this embodiment, by using a flat type separator, and by arranging a pore layer on both outer sides of the membrane power assembly, the compressive force applied to the membrane electrode assembly is suppressed, and the membrane electrode junction It is possible to prevent body damage.

  Next, details of each member of the fuel cells 1 and 2 will be described.

  The pore layers 18 and 20 of the present embodiment are obtained, for example, by applying a solution obtained by mixing a conductive material and a dispersion solvent such as methanol or ethanol to the porous channel layer, the diffusion layer, or the catalyst layer. It is formed. Application methods include spraying, screen printing, applicator, and ink jet. Examples of the conductive material constituting the pore layers 18 and 20 include carbon materials, noble metals such as Au, Pt, and Pd, Ti, Ta, W, Nb, Ni, Al, Cr, Ag, Cu, Zn, and Su. And metals such as Si, nitrides thereof, carbides, carbonitrides thereof, and alloys such as stainless steel, Cu—Cr, Ni—Cr, and Ti—Pt. More preferably, it contains at least one element selected from the group consisting of Pt, Ti, Au, Ag, Cu, Ni, and W. By including such an element, the specific resistance of the pore layers 18 and 20 is reduced, so that the voltage drop due to the resistance of the pore layers 18 and 20 can be reduced, and higher power generation characteristics can be obtained. In the case of using a metal having poor corrosion resistance in an acidic atmosphere such as Cu, Ag, Zn, etc., noble metals and metal materials having corrosion resistance such as Au, Pt, Pd, conductive polymers, conductive nitriding A material, a conductive carbide, a conductive carbonitride, a conductive oxide or the like can be used as the surface coating. Thereby, the lifetime of the fuel cell can be extended.

  As a method for hydrophilizing the pore layers 18 and 20, for example, plasma treatment, ozone treatment, flame treatment, laser treatment, electron beam treatment, ion implantation method, ion beam treatment, ion irradiation treatment, A solvent treatment or the like immersed in an alkaline aqueous solution can be employed. As a preferred hydrophilic treatment method, laser irradiation treatment is desirable in terms of work efficiency and the like.

  Examples of the gas diffusion layer 22 used in the present embodiment include those mainly composed of a conductive inorganic substance. Examples of the conductive inorganic substance include a fired body from polyacrylonitrile and a fired body from pitch. , Carbon materials such as graphite and expanded graphite, nanocarbon materials thereof, stainless steel, molybdenum, titanium, and the like. Further, the form of the conductive inorganic substance of the gas diffusion layer 22 is not particularly limited as long as it is a porous base material capable of diffusing gas. For example, it is used in the form of fibers or particles. From the viewpoint of properties, it is an inorganic conductive fiber, and carbon fiber is particularly preferable. As the gas diffusion layer 22 using an inorganic conductive fiber, a woven fabric or a nonwoven fabric can be used, and examples thereof include carbon paper and carbon cloth. The woven fabric is not particularly limited, such as plain weave, crest weave, and bound weave, and examples of the nonwoven fabric include those made by a papermaking method and a water jet punch method.

  The gas diffusion layer 22 installed on the anode electrode 12 side in the present embodiment preferably has water repellency. Thereby, since it is suppressed that water flows from the pore layer 18 to the gas diffusion layer 22 side, much water can be held in the pore layer 18 on the anode electrode 12 side. Examples of the method for water repellency treatment of the gas diffusion layer 22 include a method of applying a water repellent to the gas diffusion layer 22. The water repellent is polytetrafluoroethylene (hereinafter referred to as “PTFE”), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluorovinyl ether copolymer (PFA), A fluororesin such as polyvinylidene fluoride (PVdF) can be used.

  The separators 24 and 26 (and the separators 36 and 38) are not particularly limited as long as they are gas-impermeable and conductive materials. For example, titanium alloys and stainless steel are representative. Metal, carbon, conductive resin, etc. are mentioned.

  The porous body flow path layers 32 and 34 used in the present embodiment are made of, for example, a foam sintered metal such as stainless steel, titanium, or a titanium alloy, or a porous body having a large number of pores inside a metal mesh or the like. It is formed. The porous body flow path layers 32 and 34 are preferably made of a porous body having a relatively high porosity in order to suppress the pressure loss of the reaction gas. The porous flow path layers 32 and 34 are preferably hydrophilic in that water that has moved to the porous flow path layers 32 and 34 can be quickly discharged from the gas outlets of the separators 36 and 38. .

  The electrolyte membrane 10 constituting the membrane electrode assembly 16 is not particularly limited as long as it is a material having proton conductivity and electrical insulation. For example, fluorine ion exchange having a sulfonic acid group or a carbonyl group is possible. The film is formed from a non-fluorine polymer such as a substituted phenylene oxide, a sulfonated polyaryletherketone, a sulfonated polyarylethersulfone, or a sulfonated phenylene sulfide.

  The anode electrode 12 and the cathode electrode 14 are prepared by mixing, for example, a conductive carrier (particulate carbon carrier or the like) carrying a catalyst, an electrolyte, and a dispersion solvent (organic solvent) to form a catalyst solution (catalyst). Ink) is applied to a substrate such as the electrolyte membrane 10 or the like. Here, the electrolyte forming the catalyst solution is a proton conductive polymer, an ion exchange resin having a skeleton of an organic fluorine-containing polymer, such as a perfluorocarbon sulfonic acid resin, a sulfonated polyether ketone, a sulfonated polyether. Examples thereof include sulfonated plastic electrolytes such as sulfone, sulfonated polyetherethersulfone, sulfonated polysulfone, sulfonated polysulfide, and sulfonated polyphenylene. Examples of commercially available materials include Nafion (registered trademark) (Nafion, manufactured by DuPont) and Flemion (registered trademark) (Flemion, manufactured by Asahi Glass Co., Ltd.). In addition, examples of the dispersion solvent include solvents such as alcohols such as methanol and ethanol.

  Examples of the conductive carrier on which the catalyst is supported include carbon materials such as carbon black, carbon nanotubes, and carbon nanofibers, and carbon compounds typified by silicon carbide. Examples of the catalyst (metal catalyst) include platinum, platinum alloy, palladium, rhodium, gold, silver, osmium, iridium and the like, and platinum or platinum alloy is preferably used.

  FIG. 3 is a schematic cross-sectional view showing another example of the configuration of the fuel cell according to the present embodiment. In the fuel cell 3 shown in FIG. 3, the same components as those in the fuel cell 2 shown in FIG.

  In the fuel cell 3 shown in FIG. 3, the pore layer 18 installed on the anode electrode 12 side is a region (upstream side) of 1/10 to 9/10 upstream of the fuel gas supply in the entire pore layer 18. The region 18a) has water repellency. Here, in the fuel cell 3 shown in FIG. 3, the upstream side in the fuel gas supply of the pore layer 18 on the anode electrode 12 side faces the downstream side in the oxidant gas supply of the pore layer 20 on the cathode electrode 14 side. It has a fuel cell structure. That is, as shown in FIG. 3, for example, fuel gas is introduced from the top of the figure and fuel exhaust gas is discharged from the bottom of the figure, whereas oxidant gas is introduced from the bottom of the figure, and from the top of the figure. It is a gas flow from which oxidant exhaust gas is discharged.

  Thus, by making the upstream region 18a in the fuel gas supply out of the entire pore layer 18 on the anode electrode 12 side, the upstream side in the fuel gas supply of the pore layer 18 on the anode electrode 12 side is made water-repellent. The region 18a is easily dried. Then, the difference in water concentration with the downstream region in the oxidant gas supply of the pore layer 20 on the cathode electrode 14 side facing the upstream region 18a becomes large, so the downstream cathode in the oxidant gas supply The movement of water from the electrode 14 side to the upstream anode electrode 12 side in the fuel gas supply is promoted, and a large amount of water is easily discharged from the downstream cathode electrode 14 in the oxidant gas supply. Further, in the entire pore layer 18 on the anode electrode 12 side, the downstream region in the fuel gas supply and the pore layer 20 on the cathode electrode 14 side are hydrophilic, and therefore the cathode electrode facing the downstream region. The difference in water concentration from the upstream region in the oxidant gas supply of the 14th pore layer 20 is reduced. Therefore, the movement of water from the upstream cathode electrode 14 side in the oxidant gas supply to the downstream anode electrode 12 side in the fuel gas supply is suppressed, and water accumulates in the upstream cathode electrode 14 in the oxidant gas supply. It becomes easy. Then, by setting the moisture state in the fuel cell to such a state, it becomes possible to improve the high-temperature operation performance of the fuel cell 3 as described below.

  In the high-temperature operation of the fuel cell, water tends to stay at the downstream cathode electrode in the oxidant gas supply due to the increase in gas flow rate and generated water, and the upstream cathode electrode in the oxidant gas supply tends to dry. However, as described above, in the present embodiment, a large amount of water is discharged from the cathode electrode 14 on the downstream side in the oxidant gas supply, and therefore the cathode on the downstream side in the oxidant gas supply even during high temperature operation of the fuel cell 3. It can suppress that much water retains in the pole 14. Further, since the movement of water on the upstream cathode electrode 14 side in the oxidant gas supply is suppressed, drying of the upstream cathode electrode 14 in the oxidant gas supply is suppressed even during high temperature operation of the fuel cell 3. Can do. As a result, the fuel cell 3 can be stably generated even during high temperature operation.

  FIG. 4 is a schematic cross-sectional view showing another example of the configuration of the fuel cell according to the present embodiment. As shown in FIG. 4, the fuel cell 100 includes a membrane electrode assembly 116 including an electrolyte membrane 110 and an anode electrode 112 and a cathode electrode 114 provided on both sides of the electrolyte membrane 110, and outside the anode electrode 112 and the cathode electrode 114. Provided are pore layers 118 and 120 provided, and separators 124 and 126 provided outside the pore layers 118 and 120. And the fuel cell 100 of this embodiment is not provided with the gas diffusion layer which has the function to diffuse gas to an electrode.

  The separators 124 and 126 shown in FIG. 4 are formed with gas flow path grooves 128 and 130 having a linear shape or a meandering shape. The gas flow path grooves 128 and 130 serve as flow paths for the reaction gas supplied to the electrodes. Although not shown, fuel gas inlets and outlets, oxidant gas inlets and outlets are formed on the outer peripheries of the separators 124 and 126, and the gas flow path grooves 128 of the separator 124 on the anode electrode 112 side are fuel gas inlets. The gas flow path groove 130 of the separator 126 on the cathode electrode 114 side communicates with the oxidant gas inlet and outlet.

  The structure of the separator is not limited to this, and a flat type separator in which the gas flow channel grooves 128 and 130 are not formed may be used. The configuration of a fuel cell using a flat type separator will be described below.

  FIG. 5 is a schematic cross-sectional view showing another example of the configuration of the fuel cell according to the present embodiment. As shown in FIG. 5, the fuel cell 102 has a membrane electrode assembly 116 including an electrolyte membrane 110 and an anode electrode 112 and a cathode electrode 114 provided on both sides of the electrolyte membrane 110, and outside the anode electrode 112 and the cathode electrode 114. Porous layers 118 and 120 provided, porous channel layers 132 and 134 provided outside the pore layers 118 and 120, and separators 136 and 138 provided outside the porous channel layers 132 and 134, respectively. Yes.

  The porous body flow path layers 132 and 134 are made of a conductive porous body, and the reaction gas (fuel gas, oxidant gas) supplied to the porous flow path layers 132 and 134 is applied to the entire surface of the electrode. It functions as a gas flow path to be supplied. The reaction gas supplied to the porous flow path layers 132 and 134 mainly flows in the direction of the laminated surface of the members.

  The separators 136 and 138 shown in FIG. 5 are made of a flat conductive material (that is, the gas flow path grooves 128 and 130 are not formed). Although not shown, fuel gas inlets and outlets, oxidant gas inlets and outlets are formed on the outer peripheries of the separators 136 and 138, and the fuel gas inlets and outlets are the porous channel layer 132 on the anode electrode 112 side. The oxidant gas inlet and outlet are in communication with the porous channel layer 134 on the cathode electrode 114 side.

  The pore layers 118 and 120 used in the present embodiment are made of a material having gas permeability and conductivity, and are also called a current collecting layer, a microporous layer (MPL), or the like. The pore layer 118 provided on the anode electrode 112 side has a function of exchanging electrons with the anode electrode 112, and the pore layer 120 provided on the cathode electrode 114 side exchanges electrons with the cathode electrode 114. It has a function to perform. Further, the pore layer 118 provided on the anode electrode 112 side used in the present embodiment has water repellency (water repellency), and the pore layer 120 provided on the cathode electrode 114 side is hydrophilic ( It has a hydrophilic action. Here, having hydrophilicity means that the contact angle of water measured with a contact angle measuring device using a droplet method is 70 degrees or less. Also, having water repellency means that the contact angle of water measured with a contact angle measuring device using a droplet method is more than 70 degrees. The water repellent treatment and hydrophilic treatment of the pore layers 118 and 120 will be described later.

  The electrolyte membrane 110 constituting the membrane electrode assembly 116 of the present embodiment is made of a material having proton conductivity and electrical insulation. The anode 112 constituting the membrane electrode assembly 116 includes a catalyst that promotes oxidation of fuel (for example, hydrogen gas), and the fuel causes an oxidation reaction on the catalyst to generate protons and electrons. Further, the cathode electrode 114 constituting the membrane electrode assembly 116 includes a catalyst that promotes reduction of an oxidant (for example, air), and the oxidant takes in protons and electrons on the catalyst to cause a reduction reaction.

  Next, the operation of the fuel cell will be described using the fuel cell 102 of FIG.

  First, a fuel gas such as hydrogen gas is supplied to the porous flow path layer 132 from the fuel gas inlet of the separator 136 on the anode electrode 112 side. The fuel gas passes through the pore layer 118 on the anode electrode 112 side and reaches the anode electrode 112 while flowing through the porous body flow path layer 132. The hydrogen in the fuel gas that has reached the anode 112 is separated into protons and electrons. Protons are conducted through the electrolyte membrane 110 and reach the cathode electrode 114. The electrons are collected by the pore layer 118 on the anode electrode 112 side, transmitted to the porous body flow path layer 132 and the separator 136, and passed through an external circuit (not shown) to be separated from the separator 138 on the cathode electrode 114 side and the porous body flow. The cathode layer 114 is reached via the path layer 134 and the pore layer 120.

  On the other hand, an oxidant gas such as air is supplied to the porous channel layer 134 from the oxidant gas inlet of the separator 138 on the cathode electrode 114 side. The oxidant gas passes through the pore layer 120 on the cathode electrode 114 side and reaches the cathode electrode 114 while flowing through the porous channel layer 134. At the cathode electrode 114, oxygen, protons, and electrons in the oxidant gas react to generate water and power. With the above operation, the fuel cell 102 generates power.

  The generated water generated at the cathode electrode 114 along with the power generation is discharged from the oxidant gas outlet of the separator 138 through the pore layer 120 and the porous channel layer 134 together with the oxidant exhaust gas. In addition, water generated at the cathode electrode 114 along with power generation passes through the electrolyte membrane 110 and moves to the anode electrode 112 side, passes through the pore layer 118 and the porous body channel layer 132 together with the fuel exhaust gas, It is mainly discharged from the fuel gas outlet of the separator 136.

  Here, normally, when the gas diffusion layer is not installed on the cathode side of the fuel cell (the gas diffusion layer is installed on the anode side), the oxidant gas flowing through the pore layer on the cathode side The gas flow rate is faster than when a gas diffusion layer is installed. If it does so, the product water produced | generated by a cathode pole with an electric power generation will be carried away more than necessary from a cathode pole by the oxidizing agent gas (oxidant waste gas) of a high flow velocity. In particular, when the pore layer on the cathode electrode side is water-repellent, the ability to retain water is reduced, so water is taken away from the cathode electrode. As a result, the cathode electrode side is dried (dry-up), so that the ionic conductivity of the electrolyte membrane is lowered and the power generation performance of the fuel cell is lowered.

  In addition, when the gas diffusion layer is not installed on the anode side of the fuel cell (the gas diffusion layer is installed on the cathode side), the liquid water condensed near the anode side separator is a hydrophilic anode. Since it penetrates into the pore layer on the pole side and the moisture concentration gradient between the anode pole and the cathode pole becomes small, the water produced on the cathode pole side hardly permeates the electrolyte membrane and moves to the anode pole side. Thus, flooding occurs on the cathode side. In particular, if the pore layer on the anode pole side is made hydrophilic, sufficient moisture is retained in the pore layer on the anode pole side, so that the difference in water concentration between the anode pole side and the cathode pole side becomes small. The movement of water from the pole side to the anode side is also reduced. As a result, since a large amount of liquid water stays on the cathode electrode side, flooding is likely to occur. The occurrence of flooding causes a decrease in the voltage of the fuel cell and the like, leading to a decrease in the power generation performance of the fuel cell.

  When the gas diffusion layer is not installed on the anode side and the cathode side of the fuel cell, the cathode side due to the fact that the gas diffusion layer is not installed on the cathode side depending on the temperature of the fuel cell. (Drying up) occurs, or flooding on the cathode electrode side due to the absence of the gas diffusion layer on the anode electrode side occurs.

  Therefore, in the present embodiment, a fuel cell configuration in which the above-described pore layer 118 having water repellency is disposed on the anode electrode 112 side and the pore layer 120 having hydrophilicity is disposed on the cathode electrode 114 side is employed. By adopting the above-described configuration, the pore layer 120 on the cathode electrode 114 side is hydrophilic even in a situation where drying (dry-up) on the cathode electrode 114 side is likely to occur. It is held and drying on the cathode electrode 114 side is suppressed. Even in the situation where flooding on the cathode electrode 114 side is likely to occur, the pore layer 120 on the cathode electrode 114 side is hydrophilic and the pore layer 118 on the anode electrode 112 side is water repellent, so that the concentration of water between the electrodes The difference is large, and water moves from the cathode electrode 114 side to the anode electrode 112 side, and the occurrence of flooding on the cathode electrode 114 side is suppressed. Further, since the gas diffusion layers on the cathode electrode 114 side and the anode electrode 112 side are eliminated, the fuel cell can be reduced in size, cost, and performance.

  In general, in the power generation process of a fuel cell, the electrolyte membrane swells and the volume increases. When the gas diffusion layer is discarded from the fuel cell, the volume increase caused by the swelling of the electrolyte membrane cannot be absorbed by the elastic deformation of the gas diffusion layer, and a compressive force is applied to the membrane electrode assembly. May be damaged. However, in this embodiment, by using a flat type separator, and by arranging a pore layer on both outer sides of the membrane power assembly, the compressive force applied to the membrane electrode assembly is suppressed, and the membrane electrode junction It is possible to prevent body damage.

  Next, details of each member of the fuel cells 100 and 102 will be described.

  The pore layers 118 and 120 of the present embodiment are formed, for example, by applying a solution obtained by mixing a conductive material and a dispersion solvent such as methanol or ethanol to the porous channel layer or the catalyst layer. . Examples of the application method include spraying, screen printing, applicator, and inkjet. Examples of the conductive material constituting the pore layers 118 and 120 include carbon materials, noble metals such as Au, Pt, and Pd, Ti, Ta, W, Nb, Ni, Al, Cr, Ag, Cu, Zn, and Su. And metals such as Si, nitrides thereof, carbides, carbonitrides thereof, and alloys such as stainless steel, Cu—Cr, Ni—Cr, and Ti—Pt. More preferably, it contains at least one element selected from the group consisting of Pt, Ti, Au, Ag, Cu, Ni, and W. By including such an element, the specific resistance of the pore layers 118 and 120 is reduced, so that the voltage drop due to the resistance of the pore layers 118 and 120 can be reduced, and higher power generation characteristics can be obtained. In the case of using a metal having poor corrosion resistance in an acidic atmosphere such as Cu, Ag, Zn, etc., noble metals and metal materials having corrosion resistance such as Au, Pt, Pd, conductive polymers, conductive nitriding A material, a conductive carbide, a conductive carbonitride, a conductive oxide or the like can be used as the surface coating. Thereby, the lifetime of the fuel cell can be extended.

  As a method for hydrophilizing the pore layers 118 and 120, for example, plasma treatment, ozone treatment, flame treatment, laser treatment, electron beam treatment, ion implantation treatment, ion beam treatment, ion irradiation treatment, A solvent treatment or the like immersed in an alkaline aqueous solution can be employed. As a preferred hydrophilic treatment method, laser irradiation treatment is desirable in terms of work efficiency and the like.

  The separators 124 and 126 (and the separators 136 and 138) are not particularly limited as long as they are gas-impermeable and conductive materials. For example, titanium alloys and stainless steel are representative. Metal, carbon, conductive resin, etc. are mentioned.

  The porous body flow path layers 132 and 134 used in the present embodiment are made of, for example, a foam sintered metal such as stainless steel, titanium, or a titanium alloy, or a porous body having a large number of pores inside a metal mesh or the like. It is formed. The porous body flow path layers 132 and 134 are preferably made of a porous body having a relatively high porosity in order to suppress the pressure loss of the reaction gas. The porous flow path layers 132 and 134 are preferably hydrophilic in that water that has moved to the porous flow path layers 132 and 134 can be quickly discharged from the gas outlets of the separators 136 and 138. .

  The electrolyte membrane 110 constituting the membrane electrode assembly 116 is not particularly limited as long as it is a material having proton conductivity and electrical insulation. For example, a fluorine ion exchange having a sulfonic acid group or a carbonyl group is possible. The film is formed from a non-fluorine polymer such as a substituted phenylene oxide, a sulfonated polyaryletherketone, a sulfonated polyarylethersulfone, or a sulfonated phenylene sulfide.

  The anode electrode 112 and the cathode electrode 114 are prepared by mixing a conductive carrier (particulate carbon carrier or the like) carrying a catalyst, an electrolyte, and a dispersion solvent (organic solvent) to form a catalyst solution (catalyst ink). Is applied to a base material such as the electrolyte membrane 110. Here, the electrolyte forming the catalyst solution is a proton conductive polymer, an ion exchange resin having a skeleton of an organic fluorine-containing polymer, such as a perfluorocarbon sulfonic acid resin, a sulfonated polyether ketone, a sulfonated polyether. Examples thereof include sulfonated plastic electrolytes such as sulfone, sulfonated polyetherethersulfone, sulfonated polysulfone, sulfonated polysulfide, and sulfonated polyphenylene. Examples of commercially available materials include Nafion (registered trademark) (Nafion, manufactured by DuPont) and Flemion (registered trademark) (Flemion, manufactured by Asahi Glass Co., Ltd.). In addition, examples of the dispersion solvent include solvents such as alcohols such as methanol and ethanol.

  Examples of the conductive carrier on which the catalyst is supported include carbon materials such as carbon black, carbon nanotubes, and carbon nanofibers, and carbon compounds typified by silicon carbide. Examples of the catalyst (metal catalyst) include platinum, platinum alloy, palladium, rhodium, gold, silver, osmium, iridium, and the like, and it is preferable to use platinum or a platinum alloy.

  FIG. 6 is a schematic cross-sectional view showing another example of the configuration of the fuel cell according to the present embodiment. In the fuel cell 103 shown in FIG. 6, the same components as those of the fuel cell 102 shown in FIG.

  In the fuel cell 103 shown in FIG. 6, the pore layer 118 installed on the anode electrode 112 side is a region (upstream side) of 1/10 to 9/10 upstream of the fuel gas supply in the entire pore layer 118. It is preferable that the region 118a) has water repellency and the region on the downstream side in the fuel gas supply in the entire pore layer 118 has hydrophilicity. Here, in the fuel cell 103 shown in FIG. 6, the upstream side in the fuel gas supply of the pore layer 118 on the anode electrode 112 side faces the downstream side in the oxidant gas supply of the pore layer 120 on the cathode electrode 114 side. It has a fuel cell structure. That is, as shown in FIG. 6, for example, fuel gas is introduced from the top of the figure and fuel exhaust gas is discharged from the bottom of the figure, whereas oxidant gas is introduced from the bottom of the figure and from the top of the figure. It is a gas flow from which oxidant exhaust gas is discharged.

  In this way, by making the downstream region in the fuel gas supply hydrophilic in the entire pore layer 118 on the anode electrode 112 side, the pore layer 120 on the cathode electrode 114 side that faces the downstream region. The difference in water concentration with the upstream region in the oxidant gas supply becomes small. Accordingly, the movement of water from the upstream cathode electrode 114 side in the oxidant gas supply to the downstream anode electrode 112 side in the fuel gas supply is suppressed, and water accumulates in the upstream cathode electrode 114 in the oxidant gas supply. It becomes easy. In addition, since the upstream region 118a in the fuel gas supply in the entire pore layer 118 on the anode electrode 112 side is water-repellent, the oxidation of the pore layer 120 on the cathode electrode 114 side facing the upstream region 118a is performed. The difference in water concentration with the downstream region in the agent gas supply becomes large. Accordingly, the movement of water from the downstream cathode electrode 114 side in the oxidant gas supply to the upstream anode electrode 112 side in the fuel gas supply is promoted, and a large amount of water flows from the downstream cathode electrode 114 in the oxidant gas supply. Is easily discharged. Then, by setting the moisture state in the fuel cell to such a state, it is possible to improve the high temperature operation performance of the fuel cell 103 as described below.

  In the high-temperature operation of the fuel cell, the upstream cathode electrode in the oxidant gas supply is easily dried and the water tends to stay in the downstream cathode electrode in the oxidant gas supply due to an increase in gas flow rate and generated water. However, as described above, in this embodiment, since the movement of the water on the upstream cathode electrode 114 side in the oxidant gas supply is suppressed, the upstream side in the oxidant gas supply even during the high temperature operation of the fuel cell 103 is suppressed. Drying of the cathode electrode 114 can be suppressed. Further, since a large amount of water is discharged from the downstream cathode electrode 114 in the oxidant gas supply, a large amount of water stays in the downstream cathode electrode 114 in the oxidant gas supply even when the fuel cell 103 is operated at a high temperature. This can be suppressed. As a result, the fuel cell 103 can be stably generated even during high temperature operation.

  A configuration of a fuel cell in which no gas diffusion layer is installed on the anode electrode side will be described below as a reference example.

  FIG. 7 is a schematic cross-sectional view showing an example of the configuration of the fuel cell of Reference Example 1. The fuel cell 200 of FIG. 7 includes a membrane electrode assembly 216 including an electrolyte membrane 210 and an anode electrode 212 and a cathode electrode 214 provided on both sides of the electrolyte membrane 210, and pores provided outside the anode electrode 212 and the cathode electrode 214. Layers 218, 220, a gas diffusion layer 222 provided outside the pore layer 220 on the cathode electrode 214 side, a gas diffusion layer 222 on the cathode electrode 214 side, and a porous body provided outside the pore layer 218 on the anode electrode 212 side There are provided flow path layers 232 and 234 and separators 236 and 238 provided outside the porous flow path layers 232 and 234. The pore layer 218 on the anode electrode 212 side is water repellent. The gas diffusion layer 222 is water repellent, and the porous flow path layers 232 and 234 are hydrophilic.

  Normally, when the gas diffusion layer is not installed on the anode side of the fuel cell (the gas diffusion layer is installed on the cathode side), the liquid water condensed near the anode side separator is a hydrophilic anode. Since it penetrates into the pore layer on the pole side and the moisture concentration gradient between the anode pole and the cathode pole becomes small, the water produced on the cathode pole side hardly permeates the electrolyte membrane and moves to the anode pole side. Thus, flooding occurs on the cathode side. The occurrence of flooding causes a decrease in the voltage of the fuel cell and the like, leading to a decrease in the power generation performance of the fuel cell. However, as in the fuel cell 200 of the reference example, by making the pore layer 218 on the anode electrode 212 side water-repellent, the water retainability of the pore layer 218 on the anode electrode 212 side is reduced, and the cathode electrode 214 is reduced. The water concentration difference between the anode and the anode 212 can be increased to promote the movement of water between the electrodes. As a result, water generated on the cathode electrode 214 side easily moves to the anode electrode 212 side through the electrolyte membrane 210, and flooding on the cathode electrode 214 side can be suppressed.

  FIG. 8 is a schematic cross-sectional view showing an example of the configuration of the fuel cell of Reference Example 2. In the fuel cell 202 of FIG. 8, the same reference numerals are given to the same components as those of the fuel cell 200 of FIG. In the fuel cell 202 shown in FIG. 8, the pore layer 218 installed on the anode electrode 212 side is a region (upstream side) of 1/10 to 9/10 upstream of the fuel gas supply in the entire pore layer 218. Region 218a) has water repellency, and makes the region on the downstream side in the fuel gas supply of the entire pore layer 218 hydrophilic. Here, in the fuel cell 202 shown in FIG. 8, the upstream side in the fuel gas supply of the pore layer 218 on the anode electrode 212 side and the downstream side in the oxidant gas supply of the pore layer 220 on the cathode electrode 214 side face each other. It has a fuel cell structure. That is, as shown in FIG. 8, for example, fuel gas is introduced from the top of the figure and fuel exhaust gas is discharged from the bottom of the figure, whereas oxidant gas is introduced from the bottom of the figure, and from the top of the figure. It is a gas flow from which oxidant exhaust gas is discharged.

  By making the downstream region in the fuel gas supply hydrophilic in the entire pore layer 218 on the anode electrode 212 side, as described above, water easily stays on the cathode electrode 214 on the upstream side in the oxidant gas supply. Become. In addition, since the upstream region 218a in the fuel gas supply in the entire pore layer 218 on the anode electrode 212 side is water-repellent, as described above, a large amount from the downstream cathode electrode 214 side in the oxidant gas supply. Water is easily discharged. And it becomes possible to improve the high-temperature driving | running performance of the fuel cell 202 by making the moisture state in a fuel cell into such a state.

  The fuel cell of the present embodiment can be suitably used as, for example, a small power source for mobile devices such as a mobile phone and a portable personal computer, a power source for automobiles, a household power source, etc., but is not limited thereto. .

  1-3, 100, 102, 103, 200, 202 Fuel cell 10, 110, 210 electrolyte membrane, 12, 112, 212 Anode electrode, 14, 114, 214 Cathode electrode, 16, 116, 216 Membrane electrode assembly, 18, 20, 118, 120, 218, 220 pore layer, 18a, 118a, 218a upstream region, 22, 222 gas diffusion layer, 24, 26, 36, 38, 124, 126, 136, 138, 236, 238 Separator, 28, 30, 128, 130 Gas channel groove, 32, 34, 132, 134, 232, 234 porous body channel layer.

Claims (4)

Membrane electrode assembly comprising an electrolyte membrane and anode and cathode electrodes disposed on both sides of the electrolyte membrane, a pore layer disposed on both sides of the membrane electrode assembly, and a pore layer on the anode electrode side A gas diffusion layer disposed on the outside of the cathode electrode, and at least one of the porous channel layer and the separator is disposed outside the pore layer on the cathode electrode side without the gas diffusion layer being disposed. A fuel cell,
The pore layer of the anode electrode side and the cathode side, the fuel cell according to claim Rukoto which have a hydrophilic. From the upstream side in the fuel gas supply toward the downstream side, according to claim 1, wherein for the whole pore layer of the anode electrode side, 1/10 or more to 9/10 following areas are characterized by having a water repellent serial mounting fuel cell. A membrane electrode assembly comprising an electrolyte membrane and anode and cathode electrodes disposed on both sides of the electrolyte membrane; and a pore layer disposed on both sides of the membrane electrode assembly, the anode electrode side and wherein the outside of the cathode side pores layer of a fuel cell at least one is disposed within the porous passage layer and the separator without being disposed gas diffusion layer,
The anode cell side pore layer has water repellency, and the cathode electrode side pore layer has hydrophilicity. From the upstream side to the downstream side in the fuel gas supply, a region of 1/10 or more to 9/10 or less has water repellency with respect to the entire pore layer on the anode electrode side. The fuel cell according to claim 3, wherein a region other than the region in the pore layer has hydrophilicity.

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