DE29803325U1 - Fuel cell and fuel cell arrangement - Google Patents

Description

Dipl.-Ing. A. Wasmeier Dipl.-Ing. H. Graf

Admitted to the European Patent Office · Professional Representatives before the European Patent Office

Patent Attorneys PO Box 10 08 26 93008 Regensburg

German Patent Office
Zweibrückenstr. 12

80297 Munich

D-93008 REGENSBURG P.O. BOX 10 08 26

D-93055 REGENSBURG GREFLINGERSTRASSE 7

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H/g 18.144a

Date
Date

24 February 1998 gr-ra

Applicant:

H2-Interpower GmbH Mühlenstrasse 4 91126 Schwabach

Title:

Fuel cell and fuel cell arrangement

Accounts: Bayerische Vereinsbank (bank code 750 200 73) 5 839 Postgiroamt München (bank code 700 100 80) 893 69-801 Place of jurisdiction Regensburg A18144.DOC 09.02.9810:46

Fuel cell and fuel cell arrangement

The innovation relates to a fuel cell according to the generic term of claim 1 and to a fuel cell arrangement.

Fuel cells for generating electrical current through chemical reaction or cold combustion from a reactant and an oxidant are known per se.

The aim of the innovation is to demonstrate a fuel cell that is suitable for the low-power range and can be manufactured inexpensively and operated safely. To solve this problem, a fuel cell is designed in accordance with claim 1. A fuel cell unit is designed in accordance with claim 8.

The fuel cell according to the innovation can be used in the low-power range and is particularly suitable for schools, leisure activities and for demonstrating environmentally friendly fuel cells or hydrogen technology. Further developments of the invention are the subject of the subclaims.

The innovation is explained in more detail below using the figures and examples of implementation. They show:

Fig. 1 shows a perspective exploded view of an embodiment of the

innovative fuel cell;
Fig. 2 and 3 in simplified representation and in plan view several, each connected to a common fuel source (hydrogen source)

fuel cells;
Fig. 4 shows several fuel cells connected electrically in series via a fuel cell arrangement;

Fig. 5 - 8 in individual representation several elements of the fuel cell of Figure 1 in individual representation;

Fig. 9 is a section along the line I-1 of Fig. 7;

Fig. 10 shows a hydrogen adapter for use with the fuel cell of Figure 1; Fig. 11 shows a simplified representation and a side view of a hydrogen tank for use with the fuel cell of Figure 1.

The fuel cell, generally designated 1 in the figures, is essentially constructed in a stack-like manner and comprises, among other things, two outer plates 2 and 3, each made of plastic, of which plate 2 forms the fuel or hydrogen side and plate 3 forms the oxygen side. As Figure 1 shows, the following elements are arranged between the two plates 2 and 3, in the order shown below, starting from plate 2:

• A plate-shaped hydrogen electrode 4 made of an electrically conductive material;

• a plate-shaped hydrogen diffuser layer 5 (diffusion layer), which in the illustrated embodiment consists of a rectangular cut out of an electrically conductive grid or mesh material;

• a plate-shaped PE membrane 6, which acts as a solid electrolyte (polymer electrolyte membrane or proton exchange membrane) and is provided or coated with a catalyst on both sides;

• Oxygen diffuser layer 7 (diffusion layer), which is designed in the same way as the diffuser layer 5;

• Oxygen electrode 8, which is designed in the same way as the electrode 4.

The electrode 8 is then followed by the plate 2. Platinum, for example, is used as a catalyst. The electrodes 4 and 8 consist of a corrosion-resistant metal, for example of rust-proof chrome-nickel steel, whereby at least the electrodes 4 and 8 can be provided with a precious metal coating on their surface sides, namely to improve the electrical conductivity and to reduce the contact resistance between the respective electrode 4 or 5 and the

associated diffuser layer 5 or 7. By reducing the contact resistance, the internal electrical resistance of the fuel cell 1 is significantly reduced.

The electrodes 4 and 8 are made as flat electrode elements 9 by punching or etching from a thin sheet or foil and each have a large number of gas passage openings in their active area, which are made, for example, by punching and/or etching and/or drilling and/or piercing. At two diagonally opposite corners, the rectangular electrode elements are each made in one piece with a tab 10, with the tabs 10 on each electrode 4 and 8 or electrode element 9 projecting beyond one of two opposite narrow sides 9'. The electrode elements 9 are designed identically on both surface sides, so that the same electrode elements 9 can be used for the electrodes 4 and 8, with the electrode element 9 forming the electrode 8 simply being mounted rotated by 180° around an axis M relative to the electrode element forming the electrode 4. The axis M is the central axis, which lies in the plane of the electrode element 9 parallel to the two sides 9'. A hole 11 is provided in each of the tabs 10.

When the fuel cell 10 is mounted, a total of four current sockets 12, which also serve as hollow rivets, are led through the holes 11 of the tabs 10 of the electrodes 4 and 8, which also extend into corresponding holes 12 and 13 in the plate 2 and 3, respectively. In accordance with the arrangement of the tabs 10 and the holes 11 there, the holes 12 and 13 on each plate 2 and 3 are provided in such a way that these holes form the corner points of a rectangle. When functional elements 4-8 are arranged between the two outer plates 2 and 3 and clamped between these plates and lie tightly against one another and against the plates 2 and 3, the plates 2 and 3 are connected to one another to form the fuel cell 1 by the current sockets 14 used as hollow rivets. For this purpose, the ends of the power sockets 14 extend through the holes 12 and 13 to the outside of the plates 2 and 3 facing away from the functional elements 4-8 and are widened there like hollow rivets.

In order to obtain the lowest possible resistance contact between the current sockets 14, which are also made of a corrosion-resistant metal, for example chrome-nickel steel, and the electrodes 4 or 8 or the tabs 10 there, the holes 11 are designed as grommet-like holes, as shown in simplified form in Figure 9, so that after a current socket 14 is passed through or pressed through a hole 11, the relevant tab 10 is pressed resiliently against the current socket 14 with the edge of the hole 11. It is also possible to provide the current socket 14 with a precious metal coating on the entire outer surface.

As Figure 1 shows, the outer plates 2 and 3 have dimensions that are larger than the dimensions of the functional elements 4 arranged between these plates. In particular, the dimensions of the outer plates 2 and 3 are also larger than the clear dimensions of the electrodes 4 and 8 including the tabs 10, so that when the functional elements 4 - 8 are mounted and clamped between the plates 2 and 3, a gap remains on the circumference of the fuel cell between the plates 2 and 3, which is then filled with a suitable plastic material. After hardening, the plastic material forms a frame 15 between the outer plates 2 and 3 that seals the interior of the fuel cells gas-tight to the outside and also additionally fixes the functional elements 2 - 8, as is indicated in Figures 2 and 3.

To supply the hydrogen, a continuous bore 16 with an internal thread is provided on the plate 2, in the area between the bores 12 there. In the embodiment shown, the center axis of the bore 16 lies on the connecting line of the axes of two bores 12, namely on a connecting line running perpendicular to the sides 9' of the electrodes 4 and 8. A hydrogen connection 17 made of metal with a seal can be screwed into the bore 16, so that the hydrogen introduced into the fuel cell 1 via the hydrogen connection 17 and emerging on the inside of the plate 2 is at least partially deposited on the inner surface of the plate 2 between this and the

adjacent electrode 4, then passes through the openings of the electrode 4 and is again distributed over the entire surface in the hydrogen diffuser layer 5.

A further hole 18 with an internal thread is provided in the plate 2, and in the embodiment shown, in relation to the rectangular arrangement of the holes 12, it is approximately diagonally opposite the hole 16. A closure plug 19 made of a suitable material, e.g. metal, is screwed into the hole 18. By removing this closure plug, the hydrogen area of the fuel cell can be vented, for example when it is first put into operation, i.e. when it is first put into operation, with the closure plug 19 removed, hydrogen is initially supplied via the hydrogen connection 17 and the closure plug 19 is then closed as soon as the entire hydrogen area has been sufficiently vented.

The plate 3 is provided with several continuous slot-shaped openings 20, which are provided parallel and spaced from one another and whose longitudinal extension, when the fuel cell is fully assembled, is parallel to the sides 9' of the electrodes 4 and 8. The slots 20, which form the air inlet openings of the fuel cell 1 on its oxygen side, are provided in the area between the holes 13. A web 21 remains between two adjacent slots 20. The slots are made, for example, by milling with a multiple tool. The webs 21 formed between the slots 20 ensure the required contact pressure on the inside of the plate 3 facing the electrode 8 and thus the required electrical surface contact between the functional elements 4-8, which are arranged between the plates 2 and 3. The slots 20 are designed in terms of cross-section and shape such that a sufficient convective supply of air and oxygen is ensured for the operation of the fuel cell 1.

In the embodiment shown, the two plates 2 and 3 are made of a transparent plastic, namely acrylic, for example. A transparent plastic, such as liquid acrylic, is also used for the frame 15. After assembling the fuel cell and filling the gap between

•Φ ···· ·· &phgr;&phgr;

ϕ V · · ϕ ϕ ϕ -

φφφφφ ··· ·φ φφφφφ *φ ··

the two plates 2 and 3, i.e. after the production of the frame 15, the fuel cell is freed from any protruding material residues on its outer surface and optionally polished so that the functional elements 4 - 8 are housed in a crystal-clear plastic body formed by the plates 2 and 3 and the frame 15 and the functional elements and the function of the fuel cell 1 (including the formation of water on the oxygen side) are optimally visible from the outside.

The ends of the power sockets 14, which are accessible on the outside of the plate 2, form the electrical connections there, namely the two power sockets 14, which are connected to the tabs 10 of the electrode 4, two connections 22 for the negative pole of the fuel cell and the power sockets 14, which are connected to the tabs 10 of the electrode 8, two connections 23 for the positive pole of the fuel cell 1.

Just like the oxygen supply or air supply, the hydrogen is also supplied to the fuel cell 1 practically without pressure. The hydrogen is supplied by a supply container 24 which is designed as a thick-walled stainless steel vessel filled with a metal hydride filler (metal hydride alloy) which can absorb about 500 times its volume of hydrogen almost without pressure and release it again when required. The container 24 is provided with a connection 25 with a special hydrogen adapter 26, the latter essentially consisting of a tube 27 which can be tightly inserted into the hydrogen connection 17 and in which a cylinder 28 made of rubber or another elastic material and a screw 29 provided with an Allen hexagon and engaging in an internal thread of the tube 27 are arranged. The screw 29 is located in the area of the open side of the tube 27, with which the adapter 26 can be inserted into the hydrogen connection 17, whereby the hexagon socket at this open end is accessible with a suitable tool. The rubber cylinder 28, which is located further inside the tube when viewed from the open end of the tube 27 , rests with one end against the screw 29 and with the other end against a stop in the tube 27. The cylinder 28 can now be pressed together with the screw in such a way that its diameter increases or decreases according to the compression, whereby a gap between the

The gap remaining between the cylinder 28 and the inner surface of the tube 27 can be continuously changed in width and the screw 29 can be used to open and close the valve formed by the screw 29 and the cylinder 28, as well as to adjust the opening cross-section of this valve. The thread play between the screw 29 and the tube 27 is used as a further hydrogen channel. This simultaneously limits the maximum hydrogen flow rate, which represents an important safety aspect (inherent safety).

The fuel cell works in the known manner, in which electrical current is generated by "cold combustion" of a fuel or reactant, in this case hydrogen, with an oxidant, in this case oxygen from the air. The necessary hydrogen enters the fuel cell from the supply tank 24 via the hydrogen connection 17. The hydrogen in molecular form flows through the electrode 4 and the diffuser 5 and is then converted into atomic hydrogen by the catalyst at the catalyst/electrolyte phase boundary (membrane 6), whereby the following anode reaction takes place at the hydrogen electrode 4 and the diffuser 5 or in the area of the catalyst at the phase boundary of the solid electrolyte 6:

_H2 -»2H

2H->2H+ +2e\

Each hydrogen atom gives off an electron e" and then migrates as hydrogen!on (H + ) through the solid electrolyte 6 to the electrode 8. On the other side of the electrolyte 6, i.e. on the air or oxygen side formed by the electrode 8 and the diffuser 7, oxygen from the ambient air is offered at the catalyst/solid electrolyte 6 phase boundary. The offered oxygen O ₂ then combines briefly with the absorption of two electrons e" to form H ₂ O ₂ , which becomes pure water under the catalytic effect and with the further absorption of two �EEgr; ions and two electrons. The reaction on the oxygen side (cathode) or on the

i··

the electrode 8 and the diffuser layer 7 can thus be simplified as follows:

4H ⁺ + O ₂ + 2e"->2H ₂ O.

Free electrons are therefore available at electrode 4 during this reaction, while there is a shortage of electrons at electrode 8, so that when both electrodes or connections 22 and 23 are connected via an external consumer, a current flow is created that is maintained as long as sufficient hydrogen and oxygen are available. The theoretical open circuit voltage is 1.229 volts. In practice, open circuit voltages of between 0.9 and 0.94 volts are achieved with the fuel cell described. With dimensions of the fuel cell of approximately 68x68x21 mm and an active area of 12 cm ^2, a maximum current of 2-5 amperes can be achieved when breathing with air.

In order to achieve higher voltages, as shown in Figure 4, several fuel cells 1 are electrically connected to form a fuel cell arrangement 30, whereby the arrangement of the connections 22 and 23 makes it possible to have this series connection with very short bridges 31, and in particular it is also possible to have this series connection in several layers with short bridges 31. The supply of the fuel cells 1 of the fuel arrangement 30 is shown in Figures 2 and . In the configuration of Figure 2, the fuel cells 1 are also connected in series with regard to their supply of hydrogen, i.e. only the last fuel cell 1 in this series connection has the sealing plug 19 on its plate 2, while in every other preceding fuel cell 1 in this series connection the sealing plug 19 is removed and the bore 18 of such a fuel cell is connected via a hose connection 32 to the bore 16 of the subsequent fuel cell 1 in the series connection. Only the first fuel cell in the series connection has the hydrogen connection 17 for connecting to the supply tank 24 or in the adapter 26. In Figure 13, the fuel cells for the hydrogen supply are connected in parallel, i.e. each fuel cell is connected to its

Hydrogen connection 17 is connected to a supply line 33 connected to the supply tank 24.

The innovation has been described above using exemplary embodiments. It goes without saying that numerous changes and modifications are possible without thereby departing from the inventive concept underlying the innovation.

A18I44.DOC

List of reference symbols

1 fuel cell

2.3 H ₂ /O ₂ plate

4 H ₂ electrode

5 Hj diffuser layer

6 Solid electrolyte

7 O ₂ - Diffuser layer

8 O ₂ electrode

9 Electrode element 9' Page

10 Tab 11,12,13 Hole

14 Power socket

15 plastic frames

16 Hole

17 Hydrogen connection

18 Hole (venting)

19 Plugs

20 Slot

21 Bridge 22,23 Connection

24 hydrogen supply tanks

25 Connection

26 Adapter

27 Pipe section

28 rubber cylinders

29 Screw

30 Fuel cell arrangement

31 electric bridge

32 H ₂ line (parallel connection)

33 H ₂ -Connection cable (series connection)

Claims (9)

Protection claims 1. Fuel cell with at least two electrodes (4, 8) arranged in a cell housing (2, 3, 15), with a solid electrolyte (6) between these electrodes (4, 8), with at least one hydrogen connection (16, 17) on at least one first electrode (4) and with an oxygen supply (20) on at least one second electrode (8), characterized in that the housing of the fuel cell has two outer housing plates (2, 3), of which a first plate (2) is provided with the at least one hydrogen connection (17) and a second plate (3) with at least one opening (20) for the entry of ambient air for a pressure-free oxygen supply to the second electrode from the ambient air, and that the two electrodes (4, 8) and the solid electrolyte are arranged as plate-shaped elements between the two outer housing plates (2, 3). 2. Fuel cell according to claim 1, characterized in that a plate-shaped diffuser (5, 7) made of an electrically conductive material, preferably a grid-like or mesh-like material, is arranged between each electrode (4, 8) and the solid electrolyte (6). 3. Fuel cell according to one of the preceding claims, characterized in that the plate-shaped solid electrolyte consists of a PE membrane. 4. Fuel cell according to one of the preceding claims, characterized in that the housing plates (2, 3) are connected to one another by current conductors, preferably by waveguides or current sockets (14), and specifically by bracing the functional elements arranged between them. 5. Fuel cell according to one of the preceding claims, characterized in that the housing is made of a clear, transparent material or plastic, preferably acrylic glass. 6. Fuel cell according to one of the preceding claims, characterized in that the electrodes (4, 8) and/or diffusers (5, 7) and/or current conductors (14) are provided with a precious metal coating on the surface. 7. Fuel cell according to one of the preceding claims, characterized by a supply container (24) with a metal hydride filling for the pressureless or almost pressureless storage and release of hydrogen and with an adapter (26) provided with a shut-off and/or metering valve (28, 29) for
Connection to at least one fuel cell (1). 8. Fuel cell arrangement consisting of several electrically connected
connected, preferably series-connected fuel cells (1) according to one of the preceding claims. 9. Fuel cell arrangement according to claim 8, characterized in that the
The fuel cells are supplied with hydrogen in series and/or parallel.