GB2286482A - A plurality of fuel cells stacked in modular configuration and fuel cell stack arrays - Google Patents

Abstract

A fuel cell stack comprises a plurality of fuel cells stacked in modular configuration. A plurality of fuel cells is created on a single piece of electrolyte eg. by screen printing electrodes to form a layer. A plurality of layers may be arranged such that cathodes and anodes of respective layers face each other with a space therebetween to permit supply of fuel maintained by spacers 7. A fuel stack array comprises such a stack connected to an adjacent further cell stack and electrically insulated from each other (Figures 4A, 4B), fuel being fed and exhausted from one side of a stack, and a further fuel fed and exhausted from the other side, each of the fuels and exhausts being separated by dividers. The feed gases can be fed centrally and shared between cell stacks. Multiple stack arrangements can be built up in any direction (Figs. 5 - 8) and the stack arrays supported within a water-cooled housing (Fig. 9). Failed modules can be removed and replaced. Any number of modules can be added to meet power and voltage requirements. <IMAGE>

Description

"A fuel cell stack and method of stacking fuel cells" This invention relates to a fuel cell stack and the use of the fuel cells assembled into a stack and housing, for the production of electrical power using a variety of fuel gases and oxidants.

Three main techniques for stack design are as follows: 1) Tubular (as manufactured by Westinghouse); Advantages are ease of sealing; Disadvantages are relatively low power density, necessity of support tube, high cost.

2) Monolithic (as manufactured by Argonne National Laboratory); Advantages are high power density, 'one-piece' manufacture, and moderate costs; Disadvantages are sealing difficulties, manufacturing without component fracture, restrictions in manufacturing flexibility.

3) Planar (as manufactured by Ceramate; Siemens etc); Advantages are high power density, easier control of manufacturing stages, and moderate costs; Disadvantages are stack configuration complexity and sealing.

In accordance with first aspect of the present invention there is provided a fuel cell stack for the production of electrical power comprising a plurality of fuel cells stacked in modular configuration.

Preferably the fuel cell stack has planar configuration.

Preferably an individual fuel cell comprises an electrolyte having an anode created on one side and a cathode created on the other side.

Preferably a plurality of fuel cells may be created on one piece of electrolyte, with an electrical break between said fuel cells, to form a layer of fuel cells.

Preferably the fuel cells in a layer are connectable in series by connection of the cathode of one cell to the anode of the next cell, to give a voltage output across the extremities of said layer which is the product of the number of cells and the voltage across a single cell.

Preferably the anodes and cathodes of the fuel cells are screen printed on the electrolyte to allow numerous cells to be created on a single piece of electrolyte, giving high voltage output.

Preferably the fuel cell stack wherein a plurality of layers are arranged such that cathodes face each other and anodes face each other to form electrode pairs, and such that there is space between adjacent anodes and adjacent cathodes to permit the supply of fuel to and from these electrodes.

Preferably the space is maintained by provision of spacers between the cell layers.

Preferably the spacers allow electrical connection of the electrode pairs so that each layer is effectively in parallel with every other layer.

Preferably the spacers act as contact for connecting a power lead to the stack as a means for taking power from the stack.

Preferably wherein the spacers act as a sealant to retain the fuel and exclude foreign matter.

Preferably wherein the spacers provide means to support the structure.

Preferably the fuel cell stack is adjacently connectable to at least one further fuel cell stack to form a fuel cell stack array and said fuel cell stacks being electrically insulated from each other where they join.

According to a further aspect of the present invention, there is provided a fuel cell stack array comprising at least two adjacently connectable fuel cell stacks electrically insulated from each other wherein a fuel is fed to, and its exhaust products are removed from, one side of a stack; and a further fuel is fed to, and its exhaust products are removed from, the opposite side of said stack, each of said fuels and its exhaust products being separated by dividers.

Preferably the said fuels are provided centrally and shared among up to four fuel stacks which comprise said array, and wherein a common manifold is provided for the exhaust products of each fuel.

Preferably the spacers provided to separate fuels and their exhaust products may be used to form the side electrical connections of adjacent cells.

Preferably the fuel cell stack array may be combined with a plurality of like arrays in any dimension to form a modular unit.

According to a further aspect of the present invention, there is provided a fuel cell module comprising a plurality of fuel cell stack arrays which can be supported within a housing, said module being connectable to any number of like modules to form an assembly, each module being individually replaceable.

Preferably the fuels are introduced between fuel cell stack arrays and exhaust products ducted above and below fuel cell stack arrays.

According to a further aspect of the present invention, there is provided a method of stacking fuel cells wherein assemblies comprising a plurality of arrays of fuel cell stacks modularly arranged are reversibly conjoined by means of extension pieces.

Preferably the extension pieces are provided, said extension piece having means for passage of fuel and electricity between the cell stacks which they conjoin.

Preferably wherein each module and extension piece may be individually removed and replaced.

Also according to the invention a fuel cell comprises a planar solid electrolyte; on one side of the electrolyte a planar anode; on the other side of the electrolyte a planar cathode; and means for providing fluid fuels to the faces of anode and the cathode remote from the electrolyte.

Preferably the cathode and the anode are formed of porous material, and the fuels are gaseous fuels.

Optionally, the cathode and the anode are formed on the planar solid electrolyte by a screen printing process.

Optionally there may be provided a plurality of fuel cells formed on a single planar solid electrolyte, comprising a plurality of planar anodes spaced from each other, and an equal number of spaced planar cathodes. Such a plurality of fuel cells will be referred to herein as a multiple fuel cell.

Further, according to the invention a stack of multiple fuel cells may also be provided by arranging a plurality of multiple fuel cells according to the invention with alternately the anodes and the cathodes in face-to-face spaced arrangement. In such a stack, the spaces between the adjacent anodes and cathodes allow the supply of fuel to these electrodes.

Preferably the spaces are provided by placing at the outer ends of each fuel cell stack and in contact with the outer electrodes of each multiple fuel cell electrically conducting spacers which comprise means (a) to allow the electrical connection of all the anodes and of all the cathodes in each stack, and/or (b) to allow the connection of a power lead by which electrical power can be drawn from the stack, and/or (c) to provide a gaseous fuel sealant, and/or (d) to provide means for mechanically holding the stack together.

Yet further, a plurality of stacks of multiple fuel cells may be provided, the stacks being placed side-byside and electrically insulated for each other. In such an arrangement, the inlet ports for the gaseous fuels to one end of the stacks adjacent the electrically insulating means, and the outlet ports for the spent fuels and waste products may be provided to the other ends of the stacks adjacent the electrically insulating means. That is, each gas inlet or outlet is shared between two stacks. In this arrangement, the electrical spacers, conveniently made of metal sponge, are arranged to channel the fuel gas and the exhaust gases, and may additionally be used to electrically connect one stack to the side-by-side stack.

In a further arrangement according to the invention, a modular array of several layers each comprising a plurality of stacks in side-by-side arrangements may be provided.

In such a modular array, each gas inlet and each gas outlet may be connected to four adjacent fuel cell stacks, except for stacks at the outer edges of the array. Between each layer of stacks, gas inlets and gas outlets will be arranged alternately.

In a variation of a modular array, the stacks are arranged in a side-by-side spaced array to form vertical channels between the stacks so that fuel gases and waste gases pass through the vertical channels to gas inlets or gas outlets above and below the modular array.

Embodiments of the present invention are described with reference to the figures in which: Fig 1 is a fuel cell as combined in a fuel cell stack in accordance with the present invention; Fig 2 is an illustration of five cells as shown in Fig 1 linked in series on a common electrolyte substrate; Fig 3 is an illustration of four sets of cells as shown in Fig 1, linked in series/parallel arrangement; Fig 4a is a front elevation of two fuel cells stacked in accordance with the present invention, electrically separate and showing hydrogen entrance and exit ports; Fig 4b is a plan view of two fuel cell stacks in accordance with the present invention showing divides separating gas inlets and outlets; Fig 5 is a plan view of a modular stack arrangement in accordance with the present invention, made up of four fuel cell arrays; Fig 6 is a three dimensional view of part of the arrangement of Fig 5 showing gas feed and exhaust detail; Fig 7 is a plan view of modular stack arrangement in accordance with the present invention; Fig 8 is a three dimensional view of part of the arrangement of Fig 7; Fig 9 is a cross section of the arrangement of Fig 8; Fig 10 shows a fuel cell stack assembly, housed in accordance with the present invention, being lowered into a female casting.

Although for simplicity, the solid oxide fuel cell operation is described, the principles and much of the practice, are applicable to all fuel cell types. Again for simplicity, oxygen and hydrogen have been considered as reactants, although methane, methanol, coal gas and natural gas and of the fuels together with oxidants such as air (20% oxygen) are equally applicable.

Refering to the drawings.

Figure 1 shows the basics of a single fuel cell 1.

Open circuit voltage is typically 1 volt. All the cell components are solid, and comprise a central oxygenion-carrying electrolyte 2 (typically stabilised zirconia), with on one of its sides an anode 3 (generally a porous nickel cermet), and on its other side a cathode 4 (typically a porous lanthanum manganite). Oxygen 5 gas is presented to the cathode 4, becomes ionised by taking up electrons, and diffuses through the electrolyte lattice to the anode. Here it reacts with hydrogen 6 gas in contact with the anode 3, to form water, and give up its electrons, which then travel round the external electrical circuit, producing work on their way back to the cathode 4.

Figure 2 shows the construction of a 5-cell unit. This comprises an electrolyte 2 with the anode 3 screen printed (or otherwise created) on one side, and the corresponding cathode 4 screen printed (or otherwise created) on the other. To give 5 cells, 5 such prints or strips are made on the one piece of electrolyte 2, with an electrical break between each strip. When these strips are connected in series by joining the cathode 4 of one cell to the anode 3 of the next, the voltage between the two extreme ends of any one layer will be 5 times the voltage of a single cell. Although only five cells are shown in the Figure 2, screen printing allows numerous cells to be created on one piece of electrolyte to give a high voltage output.

Figure 3 is an extension of Figure 2, and shows four layers of cells (numbered 1 to 4) arranged with cathodes 4 facing each other, and anodes 3 facing each other, with a gap between these electrode pairs to admit and channel the respective gas. The spacer 7 between the electrodes acts as both spacer 7 to form a gap for the gas, and electrical conductor to join top and bottom of the electrode pairs together and to act as a stud contact to take off a power lead. It also acts as a sealant to retain or exclude gases, and 'adhesive' to hold the structure together.

Each of the four layers of the assembly generates 5 volts, but each layer is effectively connected in parallel with every other layer such that four times the current delivered by one, will be delivered at the same five volt (open-circuit) level.

Figure 4a is a further development of Figure 3, but for simplicity, now shown without the electrical connections. Two cell stacks 6 are shown next to each other, but electrically insulated from one other where they join (the vertical dotted line). Further insulating gas sealants 7 have been added, which cause the hydrogen 6 to be channelled in through gas inlet port 10 and exhaust hydrogen and water vapour 8 to be removed from gas outlet port 11, from the front side of the stack, while at the opposite side of the stack, the oxygen 5 is similarly channelled in through gas inlet port 12, and exhaust oxygen 9 removed from gas outlet port 13. Ceramic dividers 14 separate feed gas from exhaust gas.

The plan view of this arrangement is shown in Figure 4b and shows the feed gases fed centrally, and shared between the two cell stacks with the exhaust gases appearing at the LHS and RHS of the divides. By confining the hydrogen feed, and the hydrogen + water vapour exhaust gases to a central section of their own, electrical links made of materials such as nickel sponge can be used to form the side electrical connections of one cell to the next (cf Figure 3).

As shown in Figure 5, the elements of Figure 4 can be combined to form a multiple stack arrangement, extending to virtually any physical size and power rating by building in the x, y, and z directions. A plan view is shown. The feed gases can now be made common to four individual cell stacks, instead of two apart from those at perimeter positions, simplifying the manifolding. These are indicated 1 to 4 on sketch.

All exhaust gases enter their respective common manifold between the individual gas feed manifolds.

Figure 6 shows this type of arrangement in three dimensions. The feed gases would normally be preheated by passing down metal or ceramic tubes within the exhaust gas ducting, and then introduced into the manifold system from below.

Figure 7 shows yet another arrangement, allowing the feed gases to be introduced into simplified ducting between the stack arrays. the exhaust gases exit from the individual cells into channels within the arrays, these passing up (the hydrogen waste gases) and down (the oxygen waste gas) into the respective ducting above and below the arrays.

Figure 8 again shows part of the arrangement of Figure 7, but in three dimensions. The respective feed gas is introduced between each 'tower-block' array, with the waste gases appearing at top and bottom respectively of the channel in the 'tower-blocks'.

Figure 9 is based on Figure 8, but now shows the means of supporting the cell stack arrays within a water cooled housing 15, and the technique of separating gas feeds and exhausts. Electrical connections, and gas pipework, into and out of the housing are, for simplicity, not illustrated. The housing is made from only two types of castings, one 'male' 16, and one 'female' 17, probably of nodular cast iron, to give dimensional stability, and to allow for welding. The supports for the cell arrays, could be of alumina or other suitable ceramic, which completely surrounds the stacks, and is sealed to them with ceramic adhesive/cement. Where these supports enter the outriders of the water cooled castings, sealing with silicone rubber or other elastomer 18 should become possible, as the temperature should not be above 150 celsius. This will give some compliance to accommodate thermal expansion differences between the cooled housing, and the stack support components. Insulation baord 19 is provided.

The modularity approach allows arrays to be built within a module housing, tested, and simply joined to the next module via the other casting, ostensibly and 'extension piece', but containing electrical and gas 'feed-troughs'. All module sections are self-aligning, assembled with silicone elastomer 18, and then bolted together (not shown). Where one module fails in service, it can simply be removed, and replaced with a working module. Any number of modules may be added together to meet power and voltage requirements.

Figure 10 shows three dimensional detail of one of the castings (the 'female' 17 one), with the ceramic support plate 20, containing a cell stack array 21 being lowered into it.

The present invention is preferably of the planar variety, and further has the advantage over other designs that: 1) This design is expected to have the lowest manufacturing costs, operating costs, and maintenance costs of all presently known designs.

2) Power density (watts per square centimetre of active cell surface) is expected to be high (.1 amp/sq cm) contributing to high gas-to-electricity conversion efficiency.

3) The stack construction is modular, allowing power unit designs spanning from watts to megawatts as required, by simply unbolting part of the existing stack, and bolting in the extra modules and extension pieces as required. This ensures highly efficient combined heat and power sources for use in domestic dwellings, hospitals, ships, power stations etc.

4) A unique approach of back-to-back cell design with integral gas routing, simplifies fuel and oxidant management, enhances gas reaction rates, and reduces weight and material usage.

5) The manufacturing stages and gas sealing, are straightforward, and are based on well established technology. Most layering and interconnecting operations should be possible by the (inexpensive) screen printing route.

6) All internal electrical connections can be in the fuel gas manifold, allowing the use of metallic connectors at the typical 1000C working temperature.

7) The stack has high built-in manufacturability, maintainability, and serviceability.

Claims (23)

1. A fuel cell stack for the production of electrical power comprising a plurality of fuel cells stacked in modular configuration.

2. A fuel cell stack as claimed in Claim 1 wherein the configuration is planar.

3. A fuel cell stack as claimed in Claim 1 or Claim 2 wherein an individual fuel cell comprises an electrolyte having an anode created on one side and a cathode created on the other side.

4. A fuel cell stack as claimed in Claim 3 wherein a plurality of fuel cells may be created on one piece of electrolyte, with an electrical break between said fuel cells, to form a layer of fuel cells.

5. A fuel cell stack as claimed in Claim 4, wherein the fuel cells in a layer are connectable in series by connection of the cathode of one cell to the anode of the next cell, to give a voltage output across the extremities of said layer which is the product of the number of cells and the voltage across a single cell.

6. A fuel cell stack as claimed in Claims 3, 4 or 5 wherein the anodes and cathodes of the fuel cells are screen printed on the electrolyte to allow numerous cells to be created on a single piece of electrolyte, giving high voltage output.

7. A fuel cell stack as claimed in Claim 4 wherein a plurality of layers are arranged such that cathodes face each other and anodes face each other to form electrode pairs, and such that there is space between adjacent anodes and adjacent cathodes to permit the supply of fuel to and from these electrodes.

8. A fuel cell stack as claimed in Claim 7 wherein the space is maintained by provision of spacers between the cell layers.

9. A fuel cell stack as claimed in Claim 8 wherein the spacers allow electrical connection of the electrode pairs so that each layer is effectively in parallel with every other layer.

10. A fuel cell stack as claimed in Claim 8 or 9 wherein the spacers act as contact for connecting a power lead to the stack as a means for taking power from the stack.

11. A fuel cell stack as claimed in Claim 8, 9 or 10 wherein the spacers act as a sealant to retain the fuel and exclude foreign matter.

12. A full cell stack as claimed in Claim 8, 9, 10 or 11 wherein the spacers provide means to support the structure.

13. A fuel cell stack as claimed in Claim 7, 8, 9, 10 or 11 which is adjacently connectable to at least one further fuel cell stack to form a fuel cell stack array; said fuel cell stacks being electrically insulated from each other where they join.

14. A fuel cell stack array comprising at least two adjacently connectable fuel cell stacks electrically insulated from each other wherein a fuel is fed to, and its exhaust products are removed from, one side of a stack; and a further fuel is fed to, and its exhaust products are removed from, the opposite side of said stack, each of said fuels and its exhaust products being separated by dividers.

15. A fuel cell stack array as claimed in Claim 14 wherein said fuels are provided centrally and shared among up to four fuel stacks which comprise said array, and wherein a common manifold is provided for the exhaust products of each fuel.

16. A fuel cell stack array as claimed in Claim 14 or 15 wherein spacers provided to separate fuels and their exhaust products may be used to form the side electrical connections of adjacent cells.

17. A fuel cell stack array as claimed in Claims 14-16 which may be combined with a plurality of like arrays in any dimension to form a modular unit.

18. A fuel cell module comprising a plurality of fuel cell stack arrays which can be supported within a housing, said module being connectable to any number of like modules to form an assembly, each module being individually replaceable.

19. A fuel cell module as claimed in Claim 18 wherein fuels are introduced between fuel cell stack arrays and exhaust products ducted above and below fuel cell stack arrays.

20. A method of stacking fuel cells wherein assemblies comprising a plurality of arrays of fuel cell stacks modularly arranged are reversibly conjoined by means of extension pieces.

21. A method of stacking fuel cells as claimed in Claim 20 wherein extension pieces are provided, said extension piece having means for passage of fuel and electricity between the cell stacks which they conjoin.

22. A method of stacking fuel cells as claimed in Claim 20 or 21 wherein each module and extension piece may be individually removed and replaced.

23. A fuel cell stack and method of stacking fuel cells substantially as hereinbefore described with reference to the accompanying drawings.