Fuel cell stack

A fuel cell stack includes: a cell stack structure formed by stacking a plurality of cells; a pair of current collectors; a pair of end members; and a fastener band wrapped around a cell stack formed by stacking the cell stack structure, the pair of current collectors, and the pair of end members. Each of the pair of end members includes a plurality of plate members. The plate members have a same arched shape in which a height from a surface to contacting a corresponding one of the pair of current collectors gradually increases toward a center portion from both ends, and are disposed in parallel while being apart from each other in a width direction of the fastener band. Adjacent plate members are coupled to each other through a bendable coupling member at part of facing surfaces.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of foreign priority to Japanese Patent Application No. 2013-222107, filed on Oct. 25, 2013, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a fuel cell stack, and more particularly relates to a fuel cell stack in which a cell stack is fastened using a fastener band.

BACKGROUND ART

Fuel cells feature high energy efficiency and very low CO2emissions, and thus have been under vigorous technological development in recent years. Polymer electrolyte fuel cells (PEFCs) are the fuel cells using a polymer as an electrolyte. Due to their capability to operate under relatively low temperatures, the PEFCs are expected to be more progressively used.

FIG. 17is a diagram showing a configuration of a typical conventional PEFC100. As shown inFIG. 17, the PEFC100is formed by disposing a pair of current collectors102and a pair of insulating end plates103, in this order, on the outer sides of a stack structure formed by stacking a plurality of cells101, and fastening the resultant cell stack. The current collectors102each include a terminal102athrough which current is outputted.

Each cell101is formed by sandwiching a membrane electrode assembly (MEA)104by an anode side conductive separator105and a cathode side conductive separator106.

In the MEA104, a polymer electrolyte membrane107is sandwiched by an anode electrode108and a cathode electrode109. The anode electrode108includes an anode side catalyst layer108aand an anode side gas diffusion layer108b. The cathode electrode109includes a cathode side catalyst layer109aand a cathode side gas diffusion layer109b.

The anode side conductive separator105and the cathode side conductive separator106have grooves formed in a circumference of a center portion to be in contact with the MEA104. The grooves are used to supply fuel gas to the anode electrode108and oxidant gas to the cathode electrode109.

Generally, the stack structure of the cells101is fastened by a fastener band.FIG. 18is a diagram showing a conventional cell module200disclosed in Japanese Patent No. 4656585 (patent document 1).

As shown inFIG. 18, in the cell module200, end plates203are disposed on the outer sides of a stack structure in which unit cells201and barriers202are alternately arranged. The stack structure and the end plates203are fastened by a band204.

Unfortunately, application of the fastening structure of the cell module200described in patent document 1 to the PEFC100shown inFIG. 17still leaves room for improvement that higher performance is difficult to achieve.

Specifically, as one possible method for improving the performance of the PEFC100shown inFIG. 17, unevenness of the pressure applied to the MEA104from the anode side conductive separator105and the cathode side conductive separator106may be reduced. Thus, a uniform contact resistance is achieved, which in turn reduces unevenness in power generation distribution.

The method requires high strength and flatness of the end plates103. Unfortunately, when the cell101is large, the end plate103with a large area is required, which is difficult to have large strength and high flatness.

When the end plate103is made by aluminum die-casting, high flatness cannot be achieved without secondary processing of machining a surface of parts obtained by the aluminum die-casting. Thus, the method requires high part manufacturing cost.

When the end plate103is made of a resin material, the high flatness is difficult to achieve after the end plate103warps.

SUMMARY OF THE DISCLOSURE

The present disclosure has been made to solve the conventional problems described above, and an object of the present disclosure is to provide a fuel cell stack capable of reducing unevenness of pressure applied to a MEA to effectively reduce unevenness of power generation distribution.

A fuel cell stack according to the present disclosure includes: a cell stack structure formed by stacking a plurality of cells each including a membrane electrode assembly and a pair of separators sandwiching the membrane electrode assembly; a pair of current collectors disposed on outer sides of the pair of separators; a pair of end members disposed on outer sides of the pair of current collectors; and a fastener band wrapped around a cell stack formed by stacking the cell stack structure, the pair of current collectors, and the pair of end members. The pair of end members each include a plurality of plate members. The plate members have a same arched shape with a height from a surface to be in contact with corresponding one of the pair of current collectors gradually increasing toward a center portion from both ends, and are disposed in parallel with each other while being apart from each other in a width direction of the fastener band. Adjacent plate members of the plurality of plate members are coupled to each other through a bendable coupling member, at part of facing surfaces of the adjacent plate members.

In a fuel cell stack according to the present disclosure, unevenness of pressure applied to a MEA can be reduced, and thus unevenness of power generation distribution can be effectively reduced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. Throughout the drawings, the same or corresponding components and members are designated by the same reference numerals and repetitive description thereof will be omitted.

In the embodiments described below, the present disclosure is applied to a polymer electrolyte fuel cell (PEFC) but is widely applicable to other kinds of fuel cells such as, but not limited to, solid oxide fuel cell (SOFC) or phosphoric acid fuel cell (PAFC).

FIG. 1is a perspective view of a fuel cell stack1according to Embodiment 1 of the present disclosure, in an assembled state. As shown inFIG. 1, the fuel cell stack1includes cells2, current collectors3, end members4, and a fastener band5. A cell stack6is formed by joining together a stack structure formed by stacking a plurality of the cells2, a pair of the current collectors3, and a pair of the end members4.

FIG. 1includes three dimensional orthogonal coordinate axes respectively indicating a Z axis direction in which the cells2are stacked, a Y axis direction as the longitudinal direction of the cell stack6, and an X axis direction orthogonal to the Z- and Y-axis directions.

The cell2is also known as a single cell module, and is formed by sandwiching a MEA by a pair of separators. The pair of conductive current collectors3are disposed on outer sides of the plurality of stacked cells2. The pair of insulating end members4are disposed on outer sides of the pair of the current collectors3.

The fastener band5is wrapped around the cell stack6in such a manner as to sandwich the pair of end members4. The stack structure of the cells2, the current collectors3, and the end members4are fastened by the fastener band5.

FIG. 2is an exploded perspective view of the fuel cell stack1according to Embodiment 1 of the present disclosure. As shown inFIG. 2, the end members4each include plate members4aand a coupling member4b.FIG. 3is an enlarged view of the end member4shown inFIG. 2.FIG. 4is a cross-sectional view of the end member4shown inFIG. 3, taken along a plane orthogonal to the Y axis direction.

As shown inFIGS. 2 to 4, the plate members4ahave the same arched shape, with a height h from a surface4c, to be in contact with the current collector3, gradually increasing toward a center portion from both ends. In other words, the two-dimensional shape of the surface orthogonal to the Y axis direction is the same among the plate members4a.

The plate members4aare arranged in parallel with each other, while being apart from each other in the Y axis direction. The adjacent plate members4aare coupled to each other, through the thin and bendable coupling member4b, at part of the facing surfaces of the plate members4a.

The plate members4aand the coupling member4bshown inFIG. 3are integrally molded. For example, the plate members4aand the coupling member4bare made of a polyphenylene sulfide (PPS) resin material (for example, PPS resin Z2140 manufactured by DIC Corporation).

It is to be noted that the PPS resin, which is a thermoplastic resin, is not the only choice, and the plate members4aand the coupling member4bmay be made of a resin material other than the thermoplastic resin. Furthermore, the plate members4aand the coupling member4bmay be made of a thermoplastic resin material other than the PPS resin.

Furthermore, the plate members4aand the coupling member4bmay be made of a thermosetting resin material, or may be made by die casting a material such as aluminum. When the aluminum is used as the material, an insulating member needs to be provided to ensure insulation between the plate members4aand the current collector3.

As shown inFIG. 2, the fastener band5includes a first band section5ahaving coupling sections5b, a second band section5chaving coupling sections5d, and pins5eand5f. The coupling sections5band5dhave through holes for inserting the pins5eand5f. The first and the second band sections5aand5care joined together by inserting the pins5eand5fin the through holes.

The first and the second band sections5aand5chave the same width as the cell2and the current collector3, and cover all the plate members4a. The coupling sections5band5dare not positioned on surfaces of the plate members4a, but are positioned on side surfaces of the plurality of stacked cells2or the current collectors3.

The coupling sections5band5dare formed as follows. Specifically, the end portions of the first and the second band sections5aand5care bent to form a U shape, welded on, and then cut out in such a manner that the end portions mesh with each other.

After the cell stack6is formed by stacking the plurality of cells2, the pair of current collectors3, and the pair of end members4, the first and the second band sections5aand5care disposed on the outer sides of the pair of end members4. Then, the pins5eand5fare inserted in the through holes of the coupling sections5band5d, and thus the plurality of cells2, the pair of current collectors3, and the pair of end members4are fastened.

The fastener band5may be made of a metal material, known as a steel special use stainless (SUS) material and a steel plate cold commercial (SPCC), that is almost unable to be expanded but is able to be bent.

For example, the fastener band5having high flatness in the Y axis direction can be relatively easily formed by bending a flat plate of SUS304 t0.8, which is the SUS material, along the surfaces of the cell stack6. The fastener band5thus formed has high bending strength.

The configuration described above provides an advantage that unevenness of pressure applied to the MEA can be reduced with the rigidity and the flatness lower than that of the end plate103in the conventional configuration illustrated inFIG. 17.

The advantage can be provided because the adjacent plate members4aare coupled to each other through the thin and bendable coupling member4b. Here, the end member4needs to be flat only in an area to be in contact with the current collector3, and thus needs not to be highly flat in the entire area, as is the case with the end plate103shown inFIG. 17.

As described above, the fastener band5has the high bending strength, and thus, the fastener band5fastening the cell stack6prevents the end members4from warping in the Z axis direction. Thus, low strength of the end member4will not lead to a critical problem.

With the cell stack6being fastened by the fastener band5that is highly flat in the Y axis direction, even when the integrally molded end member4warps in the Z axis direction for example, the warpage can be corrected by the bending of the coupling members4b. Thus, the unevenness of the pressure applied to the MEA can be reduced.

Furthermore, when the number of plate members4ais increased and the width of the plate members4ais reduced, practically only the flatness of the contact surfaces4cof the plate members4ain the X axis direction needs to be maintained at a high level. Thus, the end member4can be formed very easily.

As described above, with the configuration of the present embodiment, the end member4can be formed very easily and the uniform contact resistance between the separator and the MEA can be achieved. As a result, uniform power generation distribution can be achieved, and thus the performance of the fuel cell stack1can be effectively improved.

When a manifold for supplying fuel gas, oxidant gas, or cooling water protrudes from the current collector3in the Z axis direction, the fastener band5may be provided with a through hole through which the manifold passes.

FIG. 5is an exploded perspective view of the fuel cell stack1including the fastener band5provided with through holes8. In the example shown inFIG. 5, protruding sections7of the manifold extend in the Z axis direction from the current collector3. The through holes8, through which the protruding sections7are inserted, are formed in the first and the second band sections5aand5cof the fastener band5.

When the cell stack6is fastened by the fastener band5, the protruding sections7pass through the space between the adjacent plate members4aof the end member4, and then are inserted through the through holes8. Thus, the fuel cell stack1including the manifold can be easily manufactured, while ensuring the effect of achieving uniform power generation distribution.

The configuration of the fastener band is not limited to the one shown inFIG. 2.FIG. 6is an exploded perspective view of the fuel cell stack1including a fastener band9of an alternative configuration.

The fastener band9inFIG. 6includes a first band section9ahaving coupling sections9b, a second band section9chaving coupling sections9d, coupling plates9fincluding coupling sections9e, and pins9g,9h,9i, and9j.

The coupling sections9b,9d, and9einclude through holes for inserting the pins9g,9h,9i, and9j. The first band section9a, the second band section9c, and the coupling plates9fare joined together by inserting the pins9g,9h,9i, and9jin the through holes.

The coupling plates9fare not disposed on the surface of the plate member4abut are positioned on side surfaces of the plurality of stacked cells2or the current collectors3.

With this configuration also, the fuel cell stack1that can reduce the unevenness of the pressure applied to the MEA and thus can achieve the uniform power generation distribution can be easily manufactured, as in the case shown inFIG. 2.

In Embodiment 1 described above, the adjacent plate members4aof the end member4are coupled together at one coupling point as described by referring toFIG. 3. Alternatively, the number of coupling points may be two or more. In Embodiment 2, the case where the number of coupling points is two or more is described.

FIG. 7is a diagram showing an example of an end member10in Embodiment 2.FIG. 8is a cross-sectional view of the end member10shown inFIG. 7, taken along a plane orthogonal to the Y axis direction.

As in Embodiment 1, the end member10is formed by integrally molding the PPS resin. The material of the end member10is not limited to the PPS resin, and other resin materials, or materials such as aluminum may be used. When the aluminum is used as the conductive material, an insulating member needs to be provided to ensure insulation between the plate members10aand the current collector3.

As shown inFIGS. 7 and 8, the end member10includes plate members10aand two coupling members10b.

The plate members10ahave the same arched shape, with the height h from a contact surface10c, to be in contact with the current collector3, gradually increasing toward a center portion from both ends. In other words, the two-dimensional shape of the surface orthogonal to the Y axis direction is the same among the plate members10a.

The plate members10aare arranged in parallel with each other, while being apart from each other in the Y axis direction. The adjacent plate members10aare coupled to each other, through the two thin and bendable coupling members10b, at part of the facing surfaces of the plate members10a.

The strength of the end member10, in the configuration described above, is higher than that in the case shown inFIG. 3. Thus, the end member10is less susceptible to damage while the cell stack6is being assembled or in other occasions. As in Embodiment 1, the unevenness of the pressure applied to the MEA can be reduced with the two coupling members10bbending when the fastener band5is attached.

In Embodiments 1 and 2, the end members4and10are each formed by integrally molding a material such as PPS resin. Alternatively, the end members4and10may be formed through a different method. In Embodiment 3, a case where a method other than the integral molding is employed to form an end member is described.

FIG. 9is a diagram showing an example of a method for forming an end member11according to Embodiment 3. As shown inFIG. 9, the end member11includes plate members11aand a coupling member11b. The plate member11ahas the same shape as the plate members4aand10arespectively described in Embodiments 1 and 2.

In the end member11shown inFIG. 9, the plate members11aand the coupling member11bare separately prepared. The plate members11aeach have a through hole for inserting the coupling member11b. The end member11is formed by inserting the coupling member11bthrough the through holes of the plate members11aso that the plate members11aare integrated.

The plate members11aand the coupling member11bmay be made of the same material (the PPS resin described in Embodiment 1, for example), or may be made of different materials.

Using the same material can achieve lower manufacturing cost, and using the different materials enables the plate members11aand the coupling member11bto have the bendability separately adjusted.

The coupling member11bcan be fixed to the plate members11aby various generally employed methods. For example, the coupling member11bmay be fixed to the plate members11awith an adhesive or a screw. The coupling member11band the plate members11amay be fixed with a mechanism element. The coupling member11bmay be press fit to the plate members11a.

FIG. 9illustrates a case where the plate members11aare fixed with the single coupling member11b. Alternatively, the plate members11amay be fixed with two or more coupling members11bas in Embodiment 2.

The configurations described above where the end member11is formed by a method other than the integral molding can also achieve the same effect as in Embodiments 1 and 2. Specifically, the unevenness of the pressure applied to the MEA can be reduced by the coupling member11bbending when the fastener band5is attached.

In Embodiments 1 to 3, the plate members4a,10a, and11aof the respective end members4,10, and11each have a uniform width. Alternatively, the width of the contact surface to be in contact with the fastener band5can be partially increased. In Embodiment 4, the case where the width of the contact surface to be in contact with the fastener band5is partially increased will be described.

FIG. 10is a diagram showing an example of a surface of an end member12in Embodiment 4.FIG. 11is a diagram showing an example of a back surface of the end member12in Embodiment 4.

As shown inFIGS. 10 and 11, the end member12includes plate members12aand a coupling member12b.

As in Embodiments 1 and 2, the plate members12aand the coupling member12bare formed by integrally molding the PPS resin. Alternatively, the plate members12aand the coupling member12bmay be separately prepared as in Embodiment 3.

The material of the end member12is not limited to the PPS resin, and other resin materials, or materials such as aluminum may be used. When the aluminum is used as the conductive material, an insulating member needs to be provided to ensure insulation between the plate members12aand the current collector3.

The plate members12ahave the same arched shape, with the height h from a contact surface12c, to be in contact with the current collector3, gradually increasing toward a center portion from both ends. In other words, the two-dimensional shape of the surface orthogonal to the Y axis direction is the same among the plate members12a.

The plate members12aare arranged in parallel with each other, while being apart from each other in the Y axis direction. The adjacent plate members12aare coupled to each other, through the thin and bendable coupling member12b, at part of the facing surfaces of the plate members12a.

As shown inFIG. 11, each of the plate members12ahas a wide section12dwhere a width w1 of a contact surface to be in contact with the fastener band5is larger than a width w2 of a plate section supporting the contact surface. With the wide section12d, the stress on the surface to be in contact with the fastener band5can be largely reduced.

The configuration described above where the each of the plate members12ahas the wide section12dcan also achieve the same effect as in Embodiments 1 to 3. Specifically, the unevenness of the pressure applied to the MEA can be reduced by the coupling member12bbending when the fastener band5is attached.

In the example shown inFIGS. 10 and 11, the plate members12aeach have the wide section12dprovided entirely over the area to be in contact with the fastener band5. Alternatively, the wide section12dmay be provided at a partial area of each plate member12a.

FIG. 12is a diagram showing an example of a surface of an end member13partially provided with wide sections13d.FIG. 13is a diagram showing an example of a back surface of the end member13partially provided with the wide sections13d.FIG. 14is a cross-sectional view of the end member13shown inFIGS. 12 and 13, taken along a plane orthogonal to the Y axis direction.

As shown inFIGS. 12 to 14, the end member13includes plate members13aand a coupling member13b.

The plate members13ahave the same arched shape, with the height h from a contact surface13c, to be in contact with the current collector3, gradually increasing toward a center portion from both ends. In other words, the two-dimensional shape of the surface orthogonal to the Y axis direction is the same among the plate members13a.

The plate members13aare arranged in parallel with each other, while being apart from each other in the Y axis direction. The adjacent plate members13aare coupled to each other, through the thin and bendable coupling member13b, at part of the facing surfaces of the plate members13a.

As shown inFIG. 13, each of the plate members13ahas wide sections13dwhere a width w1 of a contact surface to be in contact with the fastener band5is partially larger than a width w2 of a plate section supporting the contact surface. With the wide sections13d, the stress on the surface to be in contact with the fastener band5can be largely reduced.

Also with the configurations described above where the each of the plate members13ais partially provided with the wide sections13d, the unevenness of the pressure applied to the MEA can be reduced by the coupling member13bbending when the fastener band5is attached.

In Embodiment 4 described above, the coupling member13bthat couples the adjacent plate members13ais provided separately from the wide section13d. Alternatively, plate members may be provided with wide sections that couple between the adjacent plate members and reduce the stress on the fastener band5.

FIG. 15is a diagram showing an example of a surface of an end member14including wide sections14bhaving a coupling function and a stress reducing function.FIG. 16is a diagram showing an example of a back surface of the end member14including the wide sections14bhaving the coupling function and the stress reducing function.

As shown inFIGS. 15 and 16, in the end member14, wide sections14bare formed on the plate members14aand couple between the adjacent plate members14a.

The plate members14ahave the same arched shape, with the height h from a contact surface14c, to be in contact with the current collector3, gradually increasing toward a center portion from both ends. In other words, the two-dimensional shape of the surface orthogonal to the Y axis direction is the same among the plate members14a.

The plate members14aare arranged in parallel with each other, while being apart from each other in the Y axis direction. The adjacent plate members14aare coupled to each other, through the thin and bendable wide sections14b, at part of the facing surfaces of the plate members14a.

As shown inFIG. 16, a width w1 of the wide section14bis larger than a width w2 of the plate section supporting the wide section14b. With the wide section14b, the stress on the surface to be in contact with the fastener band5can be largely reduced.

The unevenness of the pressure applied to the MEA can be reduced with the wide sections14bbending when the fastener band5is attached.

InFIGS. 15 and 16, the wide section14bis provided on each of both ends of the plate members14a. Alternatively, the wide section14bmay be provided at a single portion or three or more portions.

Each of the configurations described in the embodiments of the present disclosure may be combined with the configuration described in another embodiment as appropriate. For example, in the configuration shown inFIG. 10, the number of coupling member12bmay be two or more as described in Embodiment 2.

In the configuration shown inFIG. 10, the end member12can be formed in the manner described in Embodiment 3. Specifically, the coupling member12band the plate members12ahaving the through holes may be separately prepared, and the coupling member12bmay be inserted in the through holes.

In the configuration shown inFIG. 10, the wide sections12dof the adjacent plate members12amay be partially or entirely coupled to each other as described in Embodiment 5, and thus the coupling member12bcan be omitted.

A fuel cell stack according to the present disclosure can achieve uniform contact resistance between MEA and a separator to achieve uniform power generation distribution, and thus can be suitably used in a technical field of a fuel cell.