Membrane / electrode assembly for an electrochemical cell, and electrochemical cell

Abstract

The invention relates to a membrane / electrode assembly (1) for an electrochemical cell, in particular for a fuel cell or an electrolysis cell, having a membrane (2), which is arranged between two transporting layers (3, 4) and, in at least a peripheral region (5), between two frame parts (6.1, 6.2) of a frame (6), wherein the frame parts (6.1, 6.2) butt respectively in a butting region (7, 8) against the transporting layer (3, 4) arranged on the same side of the membrane (2) and wherein the frame parts (6.1, 6.2) are formed with different widths, and therefore the butting regions (7, 8) on the two sides of the membrane (2) are offset in relation to one another. According to the invention, in the wider frame part (6.2) a clearance (9) is formed on the membrane side, the clearance lying opposite the butting region (7) on the other side of the membrane (2). The invention also relates to an electrochemical cell with a membrane / electrode assembly (1) according to the invention.

Description

[0001] Description

[0002] Title:

[0003] Membrane electrode assembly for an electrochemical cell and electrochemical cell

[0004] The invention relates to a membrane-electrode assembly for an electrochemical cell, in particular for a fuel cell or an electrolysis cell. Furthermore, the invention relates to an electrochemical cell with a membrane-electrode assembly according to the invention.

[0005] In practice, a plurality of electrochemical cells are combined to form a cell stack, in particular a fuel cell stack or an electrolysis cell stack. The preferred application areas are therefore fuel cell stacks and / or electrolysis cell stacks. The electrolyzer can, in particular, be a PEM or AEM electrolysis cell stack for producing hydrogen or a CO2 electrolyzer.

[0006] State of the art

[0007] Electrochemical cells have a multi-layered structure. The central layer forms a membrane, which is usually coated on both sides with a catalytically active material to form an anode and a cathode. A transport layer, through which the respective reaction medium is fed to the membrane, is attached to both the anode and cathode sides of the membrane. Typically, the membrane is enclosed in at least one edge region extending beyond the transport layers by a frame structure. This frame structure supports the membrane and can also function as a seal. The frame structure, which usually consists of two frame sections, is also called a gasket or subgasket.

[0008] During operation of an electrochemical cell, different pressures prevail on the anode and cathode sides. Typically, the pressure on the cathode side is higher than on the anode side. This leads to compressive loading of the membrane perpendicular to the membrane plane, causing the membrane on the side with the lower pressure, usually the anode side, to be pressed against the transport layer and the adjacent frame part. The edges of the transport layer and the frame part can thus cause damage to the membrane.

[0009] In addition, the membrane is subjected to compressive stress by the external bipolar plates, which are clamped together to seal the electrochemical cell from the outside. This tension acts particularly on the frame structure, forcing the two frame sections against the intermediate membrane.

[0010] The present invention aims to reduce the pressure load on the membrane in order to increase its robustness and service life. As a result, the service life of the electrochemical cell containing the membrane is to be increased.

[0011] To achieve this objective, the membrane electrode assembly having the features of claim 1 is proposed. Advantageous further developments of the invention are set forth in the subclaims. Furthermore, an electrochemical cell having a membrane electrode assembly according to the invention is proposed.

[0012] Disclosure of the invention

[0013] The membrane-electrode assembly proposed for an electrochemical cell, in particular for a fuel cell or an electrolysis cell, has a membrane that is arranged between two transport layers and in at least one edge region between two frame parts of a frame. The frame parts each abut the transport layer arranged on the same side of the membrane in a butt region. The frame parts are designed with different widths so that the butt regions on both sides of the membrane are offset from one another. According to the invention, a recess is formed in the wider frame part on the membrane side, which recess is opposite the butt region on the other side of the membrane. The recess in the wider frame part has the effect of relieving the membrane of stress in the region of the butt region opposite the recess.In particular, it is relieved of a compressive force resulting from the contact pressure of an external bipolar plate to generate a sealing force. This is because the recess in the frame interrupts the flow of force from the bipolar plate toward the membrane. This means that the membrane is not pressed against the joint area opposite the recess and the edges bordering the joint area by the compressive force. Accordingly, the risk of damage to the membrane is reduced, thus increasing the robustness and service life of the membrane. The same applies to an electrochemical cell with a membrane-electrode arrangement according to the invention.

[0014] Further relief of the membrane is achieved by offsetting the joint areas formed on both sides between the respective frame part and the respective transport layer. Since the internal pressure on the cathode side is generally higher than on the anode side during operation of an electrochemical cell, the membrane is pressed toward the anode side joint area by the internal pressure on the cathode side or the resulting compressive force. If the anode side joint area is now moved out of the area of ​​the internal pressure on the cathode side by the offset, the membrane is no longer pressed against the anode side joint area by the internal pressure on the cathode side, or at least the pressure is reduced.

[0015] The wider frame part of the frame is therefore preferably arranged on the cathode side, so that the anode-side joint area on the membrane is opposite it.

[0016] The recess formed in the wider frame part, preferably located on the cathode side, is preferably positioned substantially centrally with respect to the joint area on the other side of the membrane. This measure ensures that the recess is positioned opposite the joint area on the other side of the membrane, even in the event of any manufacturing and / or assembly tolerances.

[0017] Alternatively or additionally, it is proposed that the recess be designed with mirror symmetry relative to the joint area on the other side of the membrane. This mirror symmetry facilitates the formation of the recess.

[0018] Preferably, the recess is formed in a sealing surface of the frame part adjacent to the membrane, so that a sealing surface borders the recess on both sides. The contact pressure of an external bipolar plate is then introduced into the membrane via the sealing surfaces adjacent to both sides, so that the recess is sealed on both sides.

[0019] Alternatively, it is proposed that a sealing surface adjacent to the membrane be adjacent to the recess on at least one side. This sealing surface can be a sealing surface of the frame part or a sealing surface of a seal formed on or in the frame part. In this case, the recess is sealed on only one side, preferably on the outer side. The sealing force then presses the membrane only against the other frame part and not against the transport layer of the other side, preferably the anode side.

[0020] Furthermore, the recess preferably has a width B that is at least as large as a thickness D of the membrane. This measure ensures a noticeable relief of the membrane's load.

[0021] Furthermore, the recess is preferably arranged at a distance a from the joint area on the same side of the membrane that is at least as large as the width B of the recess. This ensures a sufficiently large offset between the joint areas formed on both sides of the membrane. This is because the offset corresponds to the distance a including half the width B of the recess.

[0022] Advantageously, the recess is delimited at least on one side by a chamfered or rounded edge. This means that at least on one side, preferably on both sides, no sharp or acute-angled edge is formed. This has the advantage that the edge presses less strongly into the membrane under the contact pressure of an external bipolar plate, thus further relieving the membrane. Furthermore, it is proposed that the membrane and / or at least one of the transport layers be coated with a catalytically active material. The membrane can be coated on one or both sides. If one side is uncoated, a transport layer coated with a catalytically active material preferably rests at least on this side. Preferably, both sides of the membrane are coated with a catalytically active material, so that coating the transport layers with a catalytically active material can be omitted.

[0023] Since the preferred application of a membrane-electrode assembly according to the invention is an electrochemical cell, an electrochemical cell, in particular a fuel cell or an electrolysis cell, with a membrane-electrode assembly according to the invention is also proposed. The increased robustness of the membrane-electrode assembly according to the invention has a positive effect on the robustness of the electrochemical cell, so that it also has a longer service life.

[0024] Preferably, the membrane-electrode assembly of the electrochemical cell is arranged between two bipolar plates. The bipolar plates are pressed together in at least one edge region where the membrane is arranged between the two frame parts of the frame, so that the two frame parts form a sealing contact with the membrane. Due to the recess in the wider frame part, no sealing force acts on the membrane in this area, thus relieving its load.

[0025] A preferred embodiment of the invention is explained in more detail below with reference to the accompanying drawing. This shows a schematic longitudinal section through a membrane electrode assembly according to the invention with an external bipolar plate.

[0026] Detailed description of the drawing

[0027] The figure shows a membrane electrode assembly 1 with a membrane 2, which is arranged between two transport layers 3, 4 and in an edge region 5 between two frame parts 6.1, 6.2 of a frame 6. The upper frame part 6.2, which in this case is the cathode-side frame part 6.2, has a width y that is greater than a width x of the lower frame part 6.1 or the anode-side frame part 6.1. This means that abutment regions 7, 8 are formed between the transport layers 3, 4 and the frame parts 6.1, 6.2, which abutment regions are arranged offset from one another in the plane of the membrane 2. The upper frame part 6.2 thus covers the abutment region 7 between the lower frame part 6.1 and the lower transport layer 3. Since the internal pressure on the cathode side is generally higher than on the anode side, the membrane 2 is pressed towards the anode-side impact area 7.Due to the offset, however, the internal pressure on the cathode side is not directly applied to the membrane in the area of ​​the anode-side joint area 7. The membrane 2 is therefore relieved of stress in the area of ​​the anode-side joint area 7, in particular, it is pressed less strongly against edges 11 of the frame part 6.1 and the transport layer 3, which delimit the anode-side joint area 7. Since the edges 11 are also chamfered in this case, damage to the membrane 2 is avoided.

[0028] A bipolar plate 12 is located on the cathode side of the illustrated membrane-electrode assembly 1. This plate presses against the upper frame part 6.2 to generate a sealing force between a sealing surface 10 of the frame part 6.2 and the membrane 2. A recess 9 is formed in the sealing surface 10, which is opposite the joint area 7 on the other side of the membrane 2. This further relieves the load on the membrane 2, since the recess 9 interrupts the flow of force from the bipolar plate 12 toward the membrane 2.

[0029] For this purpose, the recess 9 has a width B that corresponds at least to a thickness D of the membrane 2 and is arranged at a distance a from the joint area 8 on the same side. The distance a is selected to be at least as large as the width B. Since the recess 9 is arranged centrally with respect to the joint area 7 on the other side of the membrane 2, half of the width B and the distance a together result in the offset between the joint areas 7, 8 formed on both sides of the membrane 2.

Claims

Claims 1. Membrane electrode assembly (1) for an electrochemical cell, in particular for a fuel cell or an electrolysis cell, comprising a membrane (2) which is arranged between two transport layers (3, 4) and in at least one edge region (5) between two frame parts (6.1, 6.2) of a frame (6), wherein the frame parts (6.1, 6.2) each abut the transport layer (3, 4) arranged on the same side of the membrane (2) in a butt region (7, 8), and wherein the frame parts (6.1, 6.2) are designed to have different widths, so that the butt regions (7, 8) on both sides of the membrane (2) are arranged offset from one another, characterized in that a recess (9) is formed in the wider frame part (6.2) on the membrane side, which recess is opposite the butt region (7) on the other side of the membrane (2).

2. Membrane electrode arrangement (1) according to claim 1, characterized in that the recess (9) is arranged or formed substantially centrally and / or mirror-symmetrically with respect to the joint region (7) on the other side of the membrane (2).

3. Membrane electrode arrangement (1) according to claim 1 or 2, characterized in that the recess (9) is formed in a sealing surface (10) of the frame part (6.2) which rests on the membrane (2) or a sealing surface (10) which rests on the membrane (2) adjoins the recess (9) at least on one side.

4. Membrane electrode assembly (1) according to one of the preceding claims, characterized in that the recess (9) has a width (B) which is at least as large as a thickness (D) of the membrane (2).

5. Membrane electrode assembly (1) according to claim 4, characterized in that the recess (9) is arranged at a distance (a) from the joint region (8) on the same side of the membrane (2) which is at least as large as the width (B) of the recess.

6. Membrane electrode assembly (1) according to one of the preceding claims, characterized in that the recess (9) is delimited at least on one side by a chamfered or rounded edge (11).

7. Membrane electrode assembly (1) according to one of the preceding claims, characterized in that the membrane (2), preferably on both sides, and / or at least one of the transport layers (3, 4) is or are coated with a catalytically active material.

8. Electrochemical cell, in particular fuel cell or electrolysis cell, with a membrane electrode arrangement (1) according to one of the preceding claims.

9. Electrochemical cell according to claim 8, characterized in that the membrane electrode assembly (1) is arranged between two bipolar plates (12).

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