FUEL CELL DEVICE COMPRISING A MEMBRANE ELECTRODE ASSEMBLY

Abstract

The present invention relates to an electrochemical fuel cell device having stacked cells and a membrane-electrode assembly (20). The membrane-electrode assembly (20) comprises, amongst others, a first gas diffusion layer (21) arranged on one side of a membrane (23) and a second gas diffusion layer (22) arranged on the opposite side of the membrane (23) for distributing fluids across each side of the membrane (23). The first gas diffusion layer (21) is formed to extend across and beyond planar dimensions of the membrane (23) (an active area of the stack) into at least one transition region adjacently arranged to the planar dimensions of the membrane (23) for covering an interfacing surface in the fuel cell stack within the transition region, and the second gas diffusion layer (22) is formed to extend across the planar dimensions of the membrane (23) without extending beyond, or is formed to extend across and beyond the planar dimensions of the membrane (23) into another one of the at least one region adjacently arranged to the planar dimensions of the membrane (23) which is a transition region of the fuel cell stack for accommodating fluid flow to and from the fuel cell for covering an interfacing surface of the fuel cell stack.

Claims

1. An electrochemical fuel cell device (100) having a stack arrangement of stacked cells, comprising bipolar plates (30) stacked between each of the cells for providing electrical conduction between the cells, wherein a cross-section of the stack arrangement is divided into an active region (120) for accommodating an electrochemical reaction of the cells, and at least one transition region (130) arranged adjacent to the active region (120) for accommodating pathways (31) for supplying and returning fluids reacting in the cells; and each cell includes a membrane-electrode assembly (20) comprising: an ion-conducting membrane (23) for conduction of ions between two sides of the membrane (23), catalyst layers or a catalyst coating for electrochemical conversion reactions across each side of the membrane (23), and a first gas diffusion layer (21) arranged on one side of the membrane (23) and a second gas diffusion layer (22) arranged on the opposite side of the membrane (23) for distributing fluids across each side of the membrane (23); and with respect to the cross-section of the stack arrangement of the fuel cell device (100), the first gas diffusion layer (21) is formed to extend across the active region (120) and across or into the at least one transition region (130) for covering an interfacing surface of a bipolar plate (30), and the second gas diffusion layer (22) is formed to extend across the active region (120) without extending beyond the active region (120), or formed to extend across the active region (120) and across or into another one of the at least one transition region (130) for covering an interfacing surface of a bipolar plate (30).

2. The electrochemical fuel cell device (100) according to claim 1, further comprising: a frame member (10) overlapping with the membrane-electrode assembly (20) in a peripheral section for supporting the membrane-electrode assembly (20), and extending outside the peripheral section for fixing the frame member (10) between interfacing surfaces of two bipolar plates (30); wherein a respective gas diffusion layer section in a respective transition region (130) covers interfacing surfaces between the frame member (10) and one of the two bipolar plates (30).

3. The electrochemical fuel cell device (100) according to claim 1, wherein the first gas diffusion layer (21) and the second gas diffusion layer (22) of the membrane-electrode assembly (20) have different planar dimensions.

4. The electrochemical fuel cell device (100) according to claim 1, wherein, the first gas diffusion layer (21) and the second gas diffusion layer (22) of the membrane-electrode assembly (20) have basically the same planar dimensions, wherein the first gas diffusion layer (21) and the second gas diffusion layer (22) of the membrane-electrode assembly (20) are arranged in shifted positions with respect to the planar dimensions of the membrane (23).

5. The electrochemical fuel cell device (100) according to claim 3, wherein the stack arrangement comprises at least two transition regions (130) diametrically arranged on opposite sides with respect to the active region (120); and the first gas diffusion layer (21) extends across the at least two transition regions (130), and the second gas diffusion layer (22) has smaller planar dimensions and extends into none of the at least two transition regions (130).

6. The electrochemical fuel cell device (100) according to claim 4, wherein the stack arrangement comprises at least two transition regions (130) diametrically arranged on opposite sides with respect to the active region (120); and the first gas diffusion layer (21) extends across one of the at least two transition regions (130), and the second gas diffusion layer (22) is shifted in position so as to extend across another of the at least two transition regions (130).

7. The electrochemical fuel cell device (100) according to claim 6, wherein a respective gas diffusion layer section formed to extend across or into a respective transition region (130) has a modified structure, including impregnation or inclusion of a further material, including an elastic material for sealing and/or compensating of tolerances.

8. The electrochemical fuel cell device (100) according to claim 6, wherein a respective gas diffusion layer section formed to extend across or into a respective transition region (130) is built by another material than a respective gas diffusion layer section extending within the active region (120) only, for distributing fluids.

9. The electrochemical fuel cell device (100) according to claim 6, wherein a respective gas diffusion layer section formed to extend across or into a respective transition region (130) has another thickness of the same material, particularly is thinner than a respective gas diffusion layer section extending within the active region (120) only, for distributing fluids.

10. The electrochemical fuel cell device (100) according to claim 6, wherein the first gas diffusion layer (21) has another material and/or thickness than the second gas diffusion layer (22).

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0027] Further objectives, advantages, features and applications of the present invention arise from the following description of the exemplary embodiments with reference to the drawings. In the drawing:

[0028] FIG. 1A shows a schematic view on an upper side of a membrane-electrode assembly supported in a frame member according to a first embodiment of the present invention;

[0029] FIG. 1B shows a schematic view on a lower side of the membrane-electrode assembly according to the embodiment of first the present invention;

[0030] FIG. 2A shows a schematic view on an upper side of the membrane-electrode assembly supported the frame member according to a second embodiment of the present invention;

[0031] FIG. 2B shows a schematic view on a lower side of the membrane-electrode assembly according to the second embodiment of the present invention;

[0032] FIG. 3 shows a cross-section of a stacked cell in a stack arrangement of a fuel cell device according to an embodiment of the present invention; and

[0033] FIG. 4 shows corresponding cross-sections of a stacked cell in prior art designs of a fuel cell stack arrangement.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

[0034] FIGS. 1A and 1B show an upper side and a lower side of a cell comprising a membrane-electrode assembly 20 framed by a frame member 10, wherein the shape and the perspective on the frame member 10 also represent an overall cross-section of a stack arrangement which is perpendicular to a stacking direction in a fuel cell device 100. Certain regions marked by dashed lines define for the whole stack arrangement a centrally arranged active region 120 and two transition regions 130 diametrically arranged on opposite sides of the active region 120. The active region accommodates the cells, or more particularly is occupied by a membrane-electrode assembly (MEA) including all electrochemically active elements of the cells. The transition regions 130 accommodate fluid pathways having a flat shaped flow cross-section for fitting into or between the stacked elements, particularly bipolar plates 30. Furthermore the transition regions 130 constitute a fluid interface enclosing internal pathways forming a fluid communication between the cells and outer arranged ports 110 being part of an internal manifold or other structures for a supply of air and a hydrogen based fuel gas or for a discharge of exhaust gas and water. One port 110 per side of a cell may also deliver and return a coolant for cooling the cell, however such port is not in fluid communication with the cell 20 via internal pathways enclosed with in one of the transition regions 130.

[0035] The frame member 10 illustrated in FIG. 1A and FIG. 1B, comprise basically the same outer contours shared with bipolar plates 30 and is mostly formed flat with planar interface surfaces to be stacked properly when facing each other with two facing bipolar plates, as to be seen in FIG. 3. The frame member 10 serves for mechanical supporting and mounting the electrochemically active membrane-electrode assembly 20 in the stack arrangement.

[0036] Within the transition regions 130 of the stack arrangement marked by dashed lines on the bipolar plate in FIG. 3, the bipolar plates 30 provide dedicated plate features 32 and fluid pathways 31 recessed therebetween in a surface of the bipolar plates 30. The plate features 32 and fluid pathways 31 have distinctive shapes for promoting, in a flat flow cross-section, a flow distribution of a fluid to be supplied or discharged throughout a transverse dimension of the membrane-electrode assembly 20 while achieving a preferable even pressure distribution across said flat flow cross-section. Such distinctive shapes for promoting a diffusion of fluid pressure might represent an array of round pillars form arranged in equal distances. However, alternative embodiments might provide another suitable design of plate features 32 for effecting the desired flow dynamics including, for example, plate features 32 in the form of channel walls for a splitting-up channel arrangement or the like.

[0037] FIG. 3 shows a focussed part of a cross-section of one stacked cell in the stack arrangement of the fuel cell device 100. This cross-section is parallel to a stacking direction of the stack arrangement and reveals the sandwich structure of the membrane-electrode assembly 20. The membrane-electrode assembly 20 includes an ion-conductive membrane 23 or proton-exchange membrane (PEM) having a catalytic surface coating on each side. The membrane 23 is embedded between a first gas diffusion layer 21, also shown from an upper side plan view in FIG. 1A, and a second gas diffusion layer 22, also shown from a lower side plan view in FIG. 1B. The two gas diffusion layers 21, 22 serve for receiving and distributing or dissipating and leading away a gas or fluid in communication between a transition region 130 and the surface areas of the membrane 23.

[0038] FIGS. 1A and 1B show a first embodiment of the invention. It becomes apparent in a comparison of FIGS. 1A and 1B that the upper arranged first gas diffusion layer 21 has a larger planar dimension than the lower arranged second gas diffusion layer 22. The first gas diffusion layer 21 covers the active area 120 or the membrane-electrode assembly 20 and reaches out across the transition region 130 to cover an interfacing between the frame member 10 and the upper bipolar plate 30. On the other side, the second gas diffusion layer 22 covers the active area 120 only. This arrangement corresponds to an axis symmetrical configuration as focussed by FIG. 3 on both sides of the stack arrangement in the fuel cell device 100.

[0039] The illustrated cross-section of FIG. 3 also shows the before mentioned surfaces and recesses in the profile of the plate features 32 and fluid pathways 31 of an embodiment of the bipolar plates 30 within the transition region 130. The frame member 10 is fixed to the stack arrangement of the fuel cell device 100 by being clamped between the two adjacently facing bipolar plates 30, also and particularly within the transition region 130 of the stack arrangement. Areas of extensive partial contact pressure and sharp edges exhibited by the plate features 32 in the profile of the bipolar plates 30 directly cushioned on the upper side of the frame member 10 by means of the first diffusion layer 21 and are at least indirectly dampened to a substantially reduced impact on the lower side of the frame member 10.

[0040] Furthermore, flow cross-sections of the fluid pathways 31 recessed in the lower bipolar plate 30 remain unobstructed to a full depth of profile and providing a maximum flow capacity with respect to the thickness dimension of the bipolar plates 30 in the respective design of stack arrangement. With the first gas diffusion layer reaching into the transition region 130 on the upper side only, a small portion of the height of the flow cross-sections of the fluid pathways 31 recessed in the upper bipolar plate 30 (a much smaller portion of height than depicted in the drawings for illustrative reasons) is subjected to intrusion of pillowing material of the gas diffusion layer. Without any elaborated modifications hereto, a slightly reduced flow capacity with respect to the plate thickness is to be expected due to material of the first gas diffusion layer intruding within a potential full depth of profile. The latter issue of a reduced flow capacity might however be already addressed at the stage of plate designing by taking such intrusion of pillowing material into account.

[0041] FIGS. 2A and 2B show a second embodiment of the invention. It becomes apparent in a comparison of FIGS. 2A and 2B that the upper arranged first gas diffusion layer 21 and the lower arranged second gas diffusion layer 22 have the same planar dimensions, but are positioned differently with respect to the cell. The first gas diffusion layer 21 covers the active area 120 or the membrane-electrode assembly 20 and reaches out across the transition region 130 illustrated on the left-hand side to cover an interfacing between the frame member 10 and the upper bipolar plate 30. The second gas diffusion layer 22 covers the active area 120 or the membrane-electrode assembly 20 and reaches out across the transition region 130 illustrated on the right-hand side to cover an interfacing between the frame member 10 and the upper bipolar plate 30. This arrangement corresponds to point symmetrical configuration as focussed by FIG. 3 with respect to both sides of the stack arrangement in the fuel cell device 100.

[0042] FIG. 4 shows a prior art design where the gas diffusion layers on both sides of the membrane are extended to reach into the transition region. However, in this way, flow cross-sections of all pathways in all bipolar plates are reduced by intrusion of gas diffusion layer material with respect to the potential full depth of plate feature profile on both sides of the plate (please note: realistic depth of intrusion is smaller than depicted in the drawings for illustrative reasons).

[0043] Furthermore, FIG. 4 also shows a prior art design where the profile features for diffusion of a fluid are arranged in direct contact on both sides of a MEA frame. Due to a hardness of materials commonly used for the bipolar plates and sharp edges of such profiles, this structure is prone to problems like impingement leaks and excessive wear on interface surfaces, as mentioned in the introductory part of the present disclosure.

TABLE-US-00001 List of Reference Characters 10 frame member 20 membrane-electrode assembly (20) 21 first gas diffusion layer 22 second gas diffusion layer 23 membrane 30 bipolar plate 31 fluid pathway 32 plate feature 100 fuel cell device 110 fluid port 120 active region 130 transition region