WO2008055343A1

WO2008055343A1 - Fuel cell stack design for reducing effect of excess water

Info

Publication number: WO2008055343A1
Application number: PCT/CA2007/001983
Authority: WO
Inventors: Hao Tang; Dingrong Bai; David ELKAÏM; Jean-Guy Chouinard
Original assignee: Hyteon Inc.
Priority date: 2006-11-06
Filing date: 2007-11-02
Publication date: 2008-05-15

Abstract

There is described a fuel cell stack comprising: a plurality of flow field plates each having at least one dual manifold structure comprising a supply aperture, a distribution aperture and a transitory channel fluidly connecting the supply aperture to the distribution aperture, the supply aperture forming an elongated supply manifold extending through the fuel cell stack and the distribution aperture forming an elongated distribution manifold extending through the fuel cell stack and communicating a fluid to a flow field of each of the flow field plates; and a recessed portion at a bottom of the fuel cell stack after a last fuel cell in the fuel cell stack for collecting an excess amount of water therein.

Description

FUEL CELL STACK DESIGN FOR REDUCING EFFECT OF EXCESS WATER

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority of US Provisional Patent Application filed on November 06, 2006 and bearing serial number 60/856,798.

TECHNICAL FIELD

[0002] The present invention relates to the field of fuel cells, and more particularly, to the design of the stack to improve reactant distribution uniformity and water management amongst a plurality of unitary cells.

BACKGROUND OF THE INVENTION

[0003] Reducing cell voltage variation in a fuel cell stack is one of the major challenges for the fuel cell industry. Uniform cell-to-cell voltage distribution in fuel cell stacks generally leads to improvements of fuel cell performance and durability. In common fuel cell stack designs, the end cells (top/bottom cells) usually have lower performances due to a variety of reasons . Among these reasons, reactant distribution non-uniformity from end cells to middle cells inside the manifolds plays a significant role.

[0004] To improve reactant distribution uniformity in fuel cell stacks, US patent application publication number 2005/0271910 Al assigned to Hyteon Inc. discloses a novel design concept of dual manifolds for fuel cell stacks, which comprises a reactant transport manifold and a reactant distribution manifold. The dual manifold structure effectively minimizes the fluid inlet geometric effect on fuel cell stack flow distribution, and thus results in uniform flow distribution to individual cells at a wide range of operating conditions.

[0005] In this same dual manifold design, the flow passages communicating between the two manifolds and between the manifolds and the individual cells are flush with the surface of the neighboring plate, current collectors or end plates. Due to potential water condensation and accumulation near the bottom flow passages, the reactant flowing to the first cell, or even the second cell and other adjacent cells, is lower, leading to fuel or air starvation. The risk of fuel or air starvation increases during stack startup and shutdown while the stack temperature is lower than that of the incoming reactants

[0006] There is therefore a need to reduce or eliminate liquid water formation and accumulation in the end cells of fuel cell stack designs with dual manifolds.

SUMMARY OF THE INVENTION

[0007] There is described herewith a design for fuel cell stacks that will reduce or eliminate anode/cathode water flooding, and improve stack performance and lifetime.

[0008] To further improve reactant distribution uniformity, the present invention discloses the uses of (1) fabricating a recess portion at the position of the second manifold on the endplate to provide a water reservoir,- (2) adding a drain opening on the endplate in order to drain the condensed water from the second fluid distribution manifold through either external water drainage means (such as a mechanical drain valve) or through the connection to the first manifold; (3) adding at least one blank cell plate between the end cells and the current collectors or between the current collectors and the endplates, at the position of the second manifold, to provide space as a water reservoir. These embodiments can be employed either alone or in combination.

[0009] In accordance with a first broad aspect of the present invention, there is provided a method for reducing an effect of excess water accumulating at a bottom of a fuel cell stack, the method comprising: inputting a fluid in an elongated supply manifold extending through the fuel cell stack, the elongated supply manifold being formed by a fluid supply aperture provided in each one of a plurality of flow field plates of the fuel cell stack; laterally diverting the fluid to an elongated distribution manifold extending through the fuel cell stack and communicating the fluid to a flow field of each of the flow field plates, wherein the flow field plates are each fed in parallel from the elongated distribution manifold; and collecting at the bottom of the fuel cell stack the excess water in a recessed portion provided after a last fuel cell in the fuel cell stack.

[0010] In accordance with a second broad aspect of the present invention, there is provided a fuel cell stack comprising: a plurality of flow field plates each having at least one dual manifold structure comprising a supply aperture, a distribution aperture and a transitory channel fluidly connecting the supply aperture to the distribution aperture, the supply aperture forming an elongated supply manifold extending through the fuel cell stack and the distribution aperture forming an elongated distribution manifold extending through the fuel cell stack and communicating a fluid to a flow field of each of the flow field plates; and a recessed portion at a bottom of the fuel cell stack after a last fuel cell in the fuel cell stack for collecting an excess amount of water therein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:

[0012] Fig. 1 is a front view of a single plate with a dual manifold structure in accordance with the prior art;

[0013] Fig. 2 is a cross-sectional view of a fuel cell stack having plates with a dual manifold structure in accordance with the prior art;

[0014] Fig. 3 is a cross-sectional view of a fuel cell stack with a recess in an endplate in accordance with an embodiment of the present invention;

[0015] Fig. 4 is a cross-sectional view of a fuel cell stack with a an additional blank recessed cell plate added between the collector ^• plate and the end plate, in accordance with an embodiment of the present invention;

[0016] Fig. 5 is a cross-sectional view of a fuel cell stack with an additional blank recessed plate added between the last fuel cell unit and the current collector plate, in accordance with an embodiment of the present invention,-

[0017] Fig. 6 is a cross-sectional view of a fuel cell stack with a recess connected to the supply manifold by a lateral draining channel, in accordance with an embodiment of the present invention; [0018] Fig. 7 is a cross-sectional view of a fuel cell stack with a recess connected to the supply manifold by a draining channel extending diagonally through the current collector plate, the isolation plate and part of the end plate, in accordance with an embodiment of the present invention;

[0019] Fig. 8 is a cross-sectional view of a fuel cell stack with a recess connected to a vertical draining channel extending to the outside of the stack, in accordance with an embodiment of the present invention,-

[0020] Fig. 9 is a cross-sectional view of a fuel cell stack with an external drain attached to the recess illustrated in figure 3, in accordance with an embodiment of the present invention,- and

[0021] Fig. 10 is a cross-sectional view of a fuel cell stack with an internally connected drain attached to the recess illustrated in figure 3, in accordance with an embodiment of the present invention.

[0022] It will be noted that throughout the appended drawings, like features are identified by like reference numerals .

DETAILED DESCRIPTION

[0023] Figure 1 illustrates the prior art, wherein a flow field plate 50 has its manifolds designed according to a dual manifold structure. An aperture 52 is present on plate 50 and on all of the plates of the fuel cell stack, forming thereby a stack-penetrating supply manifold. An aperture 54 is also present on the plate 50 and on all of the plates of the fuel cell stack, thus forming a distribution manifold which penetrates all of the fuel cell units in the stack. Apertures 52 and 54 are fluidly connected by a transitory channel 56. This channel 56 may be a groove or a hole inside said plate 50. A reactant enters the first aperture 52 by which said reactant is supplied to the stack, and then is directed through the transistory channel 56 to the aperture 54 by which said reactant is distributed to the individual flow fields. A plurality of flow channels or grooves are connected to the aperture 54 and extend to the first passage of the flow channels. Figure 1 represents one of many embodiments possible for the dual manifold design. Further description of the dual manifold design can be found in US 2005/0271910, the contents of which are hereby incorporated by reference.

[0024] Figure 2 illustrates a cross-sectional view of a conventional fuel cell stack 100 using the plates 50 according to line AA in figure 1. The stack 100 comprises a top endplate 102 and a bottom endplate 104. Insulation plates 106, 108 and current collector plates 110, 112 are located between the endplates 102 and 104. A plurality of fuel cell units 113 are located between the current collector plates 110 and 112. Each fuel cell unit 113 includes a flow field plate 50 for distribution of a first reactant, a second flow field plate 114 for distribution of a second reactant and an electrolyte membrane and a gasket assembly therebetween. The anode/cathode reactant enters the stack as illustrated by 118, goes through the supply manifold 120 formed by holes 52 and is then directed in transitory channels 56 as illustrated by 124. The anode/cathode reactant then comes to the distribution manifold 126 formed by holes 54 to distribute the reactant to each individual cell 113. A fuel cell stack provided with a dual manifold structure can provide uniform reactant flow to individual fuel cells, allowing a uniform reactant distribution or cell-to-cell voltage variation to be achieved during normal operation conditions. However, during stack startup or shutdown, excess water 130 can condense and accumulate between the bottom cell plate of the stack 100 and the current collector plate 112, leading to low reactant flow to the bottom fuel cell units inside the stack. Excess water 130 can also block the flow of reactant to the bottom fuel cell units. This accumulation of excess water can also occur when the stack temperature is lower than that of the incoming water- saturated reactants or when the stack temperature is lower than the water dew point of the incoming reactants.

[0025] Figure 3 illustrates a cross-sectional view of an embodiment of a stack 150 used to avoid the accumulation of excess water. The endplate 152, the insulation plate 154 and the current collector plate 156 located at the bottom of the stack 150 are recessed along the position of the distribution manifold 158. The recess 160 extends through the entire current collector plate 156, the entire insulation plate 154 and only part of the endplate 152. The recess 160 collects water 162 and permits the cathode/anode reactant to be normally distributed to the fuel cell units located at the bottom of the stack 150, as illustrated by- arrow 166. The recess 160 can be used as a reservoir to reduce or eliminate bottom cell flooding.

[0026] It should be understood that the recess 160 may only extend through part of or the entire current collector plate 156. Alternatively, the recess may only extend through the entire current collector plate 156 and part of or the entire isolation plate 154. [0027] Figure 4 illustrates another embodiment used to avoid the excess water 201 to cause air or fuel starvation in the bottom fuel cell units. The stack 200 comprises an additional blank cell plate 202 which is inserted between the current collector plate 204 and the insulation plate 206. A recess 208 is provided in the current collector plate 204 and in the additional blank cell plate 202, which is blank otherwise, to reduce or eliminate the bottom cell flooding. Thanks to the additional blank cell plate 202, the recess 208 can collect more excess water and the endplate 210 is maintained intact as no recess is provided therein.

[0028] Alternatively, the recess 208 may further extends through part of or the entire insulation plate 206. The recess 208 may also extend through the entire insulation plate 206 and part of the endplate 210. The recess thus obtained presents an increased volume in order to collect more excess water.

[0029] Figure 5 illustrates an embodiment wherein the stack 250 presents a recess 252 that only extends through an additional blank cell plate 254. The additional blank cell plate 254 is located between the current collector plate 256 and the last fuel cell unit 258. The recess is provided only in the additional blank cell plate and the current collector plate and end plate remain intact. The thickness of the additional blank cell plate may vary depending on the amount of excess water to be collected and the depth of the recess, as desired. Alternatively, several additional blank cell plates can used.

[0030] In one embodiment, the recess may be filled with a material which enhances the absorption of water and/or the holding back of water. For example, the recess may be filled with pozzolana or with a super-absorptive gel polymer.

[0031] Figure 6 illustrates an embodiment of a stack 260 wherein a draining channel 262 fluidly connects the recess 264 to the supply manifold 120. The recess 264 extends through an additional plate 266 located between the current collector plate 256 and the last fuel cell unit 258. Excess water 201 passes from the recess 264 to the supply manifold 120 to be drained out of the stack 260 as illustrated by 268. In this embodiment, the draining channel 262 is located in the additional blank plate 266.

[0032] It should be understood that the additional plate 266 can be located beneath the current collector plate 274. Alternatively, the additional plate can be omitted and the recess can extend through only the current collector plate, the current collector plate and the isolation plate, or the current collector plate, the isolation plate and part of the endplate, with a draining channel substantially at the bottom of the recess and connecting the recess to the supply manifold.

[0033] Figure 7 illustrates an embodiment of a stack 270 wherein the recess 271 is fluidly connected to the supply manifold 120 by a draining channel 272 extending through more than one plate diagonally. The recess 271 extends through an additional plate 273 located between the current collector plate 274 and the last fuel cell unit 258. The draining channel 272 extends through the current collector plate 274, the isolation plate 275 and part of the endplate 276. It should be understood the draining channel 272 could only be located in the current collector plate 274 or only in the current collector plate 274 and the isolation plate 275. [0034] It should be understood that the additional plate 266 can be located beneath the current collector plate 274 with a draining channel extending through only the isolation plate or the isolation plate and part of the endplate. Alternatively, the additional plate can be omitted and the recess can extend through only the current collector plate, the current collector plate and the isolation plate, or the current collector plate, the isolation plate and part of the endplate, with a draining channel located beneath the recess and connecting the recess to the supply manifold.

[0035] Figure 8 illustrates an embodiment of a stack 280 wherein the excess water 201 is drained out of the stack 280 by a draining channel 281. The recess 282 extends through an additional blank plate 283 and the draining channel 281 penetrates the current collector plate 284, the isolation plate 285 and the endplate 286. Alternatively, the additional plate 283 may be located beneath the current collector plate 284.

[0036] It should be understood that the additional plate can be omitted and the recess can extend through only the current collector plate, the current collector plate and the isolation plate, or the current collector plate, the isolation plate and part of the endplate, with a draining channel penetrating all plates located beneath the recess.

[0037] Figure 9 illustrates an embodiment of a stack 300 wherein the recess 302 extends through the current collector plate 304, the insulation plate 306 and the endplate 308 and is connected to a water drain 310. The drain 310 permits the removal of the excess water at the bottom of the stack 300. The drain may be physically outside the stack, as shown in figure 9, or it can be internal to the stack as illustrated in Fig. 10.

[0038] Fig. 10 illustrates an embodiment of a stack 350 wherein the drain 352 is connected to the channel 354 which brings the anode/cathode reactant into the supply manifold 120 in order to drain the excess water 201 by the channel 354. The recess 358 extends through the current collector plate 360, the insulation plate 362 and the endplate 364 and is connected to the drain 352. A channel 366 fluidly connects the drain 352 to the channel 354. The excess water 201 is drained by the pipe 354 as illustrated by 370.

[0039] In one embodiment, the width of the recess 160 is substantially equal to the width of the distribution manifold 158 which distributes the anode/cathode reactant to the fuel cell units. Alternatively, the width of the recess 160 may be larger or smaller than that of the distribution manifold 158.

[0040] In one embodiment the length of the recess 160 extends along the entire width of the stack. Alternatively, the recess 160 may extend through only part of the stack width.

[0041] In another embodiment, the stack may include several separated recesses, each being connected or not to a drain. A combination of recesses connected to a drain and of recesses unconnected to a drain may also be possible. Alternatively, a pipe may connect the different recesses to a single drain.

[0042] It should be noted that the fuel cell stack may exclude the insulation plates, or have an insulation layer integrated in the current collector plate or the endplate. The insulating plates may also be replaced by any electric and/or thermal insulating material of any appropriate shape .

[0043] The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.

Claims

I/WE CLAIM :

1. A method for reducing an effect of excess water accumulating at a bottom of a fuel cell stack, the method comprising : inputting a fluid in an elongated supply manifold extending through said fuel cell stack, said elongated supply manifold being formed by a fluid supply aperture provided in each one of a plurality of flow field plates of said fuel cell stack; laterally diverting said fluid to an elongated distribution manifold extending through said fuel cell stack and communicating said fluid to a flow field of each of said flow field plates, wherein said flow field plates are each fed in parallel from said elongated distribution manifold; and collecting at said bottom of said fuel cell stack said excess water in a recessed portion provided after a last fuel cell in said fuel cell stack.

2. A method as claimed in claim 1, wherein said collecting at said bottom of said fuel cell stack comprises collecting said excess water in said recessed portion in a current collector plate.

3. A method as claimed in claim 2, wherein said collecting comprises collecting in said recessed portion in an endplate beneath said current collector plate.

4. A method as claimed in claim 3, wherein said collecting comprises draining said excess water from said recessed portion which extends through said endplate.

5. A method as claimed in claim 1, wherein said collecting comprises collecting said excess water in said recessed portion extending through an additional blank cell plate located after said last fuel cell in said fuel cell stack.

6. A method as claimed in claim 5, wherein said collecting comprises collecting said excess water in said recessed portion extending through a collector plate and said additional blank cell plate located between said collector plate and an endplate .

7. A method as claimed in claim 5, wherein said collecting comprises collecting said excess water in said recessed portion extending through an additional blank cell plate located between a collector plate and said last fuel cell.

8. A method as claimed in claim 1, wherein said collecting comprises draining said excess water via a draining channel fluidly connecting said recessed portion to said elongated supply manifold.

9. A method as claimed in claim 1, wherein said collecting comprises draining said excess water via a draining channel communicating externally with said stack.

10. A fuel cell stack comprising: a plurality of flow field plates each having at least one dual manifold structure comprising a supply aperture, a distribution aperture and a transitory channel fluidly connecting said supply aperture to said distribution aperture, said supply aperture forming an elongated supply manifold extending through said fuel cell stack and said distribution aperture forming an elongated distribution manifold extending through said fuel cell stack and communicating a fluid to a flow field of each of said flow field plates; and a recessed portion at a bottom of said fuel cell stack after a last fuel cell in said fuel cell stack for collecting an excess amount of water therein.

11. A fuel cell stack as claimed in claim 10, wherein said recessed portion is in a current collector plate after said bottom cell and before an endplate.

12. A fuel cell stack as claimed in claim 11, wherein said recessed portion further extends through said endplate .

13. A fuel cell stack as claimed in claim 10, wherein said recessed portion is fluidly connected to said elongated supply manifold to drain said excess water out of said stack.

14. A fuel cell stack as claimed in claim 10, further comprising a draining channel extending from said recessed portion and communicating externally with said stack.

15. A fuel cell stack as claimed in claim 10, further comprising an additional blank cell plate after said last fuel cell in said fuel cell stack, and wherein said recessed portion extends through said additional blank cell plate .

16. A fuel cell stack as claimed in claim 15, wherein said additional blank cell plate is between a collector plate and said endplate, and said collector plate also comprises a recessed portion.

17. A fuel cell stack as claimed in claim 15, wherein said additional blank cell plate is between a collector plate and said last fuel cell.

18. A fuel cell stack as claimed in claim 12, wherein a drain external to the fuel cell stack is attached to said recessed portion after said endplate.