Membrane electrode assembly for 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 electrolytic 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), the frame elements (6.1, 6.2) each abut on the transport layers (3, 4) arranged on the same side of the membrane (2) in an abutment region (7, 8), and wherein the frame elements (6.1, 6.2) are designed with different widths such that the abutment regions (7, 8) on both sides of the membrane (2) are arranged offset from one another. According to the invention, a recess (9) is formed on the membrane side in the wider frame part (6.2), said recess lying opposite the abutment region (7) on the other side of the membrane (2). The invention also relates to an electrochemical cell having a membrane electrode assembly (1) according to the invention.

Description

Technical Field

[0001] The present invention relates to a membrane electrode assembly for an electrochemical cell, in particular for a fuel cell or an electrolysis cell. The present invention also relates to an electrochemical cell having a membrane electrode assembly according to the invention. Background Art

[0002] In practice, a plurality of electrochemical cells are connected to form a cell stack, in particular a fuel cell stack or an electrolysis cell stack. Preferred areas of application are therefore fuel cell stacks and / or electrolysis cell stacks. The electrolysis device can in particular be a PEM electrolysis cell stack or AEM electrolysis cell stack for producing hydrogen, or a CO2 electrolysis device.

[0003] Electrochemical cells have a multi-layer or multi-level structure. The intermediate layer forms the diaphragm, which is typically coated on both sides with a catalytically active material to form the anode and cathode. A transport layer rests on the diaphragm on both the anode and cathode sides, through which the corresponding reaction medium is supplied to the diaphragm. The diaphragm is typically surrounded by a frame structure in at least one edge region protruding beyond the transport layer. This frame structure supports the diaphragm and can also serve as a seal. The frame structure, which typically consists of two frame parts, is also called a gasket or subgasket.

[0004] During operation of an electrochemical cell, different pressures prevail on the anode and cathode sides. Typically, a higher pressure prevails on the cathode side than on the anode side. This results in a pressure load on the diaphragm perpendicular to the diaphragm plane. This pressure load causes the diaphragm to be pressed against the transmission layer and the adjacent frame element on the side with less pressure, typically the anode side. Edges of the transmission layer and frame element can thus damage the diaphragm.

[0005] Furthermore, the membrane is also subjected to pressure due to the external bipolar plates, which are clamped together to seal the electrochemical cell from the outside. The clamping force acts in particular on the frame structure, so that the two frame parts of the frame structure press against the membrane located therebetween. Summary of the Invention

[0006] The present invention addresses the object of reducing the pressure load on the membrane in order to increase the robustness and service life of the membrane, thereby extending the service life of an electrochemical cell having the membrane.

[0007] To achieve this object, a membrane-electrode assembly is proposed having the features of claim 1. Advantageous further developments of the invention can be derived from the dependent claims. Furthermore, an electrochemical cell having a membrane-electrode assembly according to the invention is proposed.

[0008] A membrane-electrode assembly proposed for an electrochemical cell, in particular a fuel cell or electrolysis cell, comprises a membrane arranged between two transfer layers and, in at least one edge region, between two frame parts of a frame. The frame parts each abut against a transfer layer arranged on the same side of the membrane in an abutment region. The frame parts are designed to have different widths, so that the abutment regions are arranged offset from one another on both sides of the membrane. According to the invention, a groove is formed on the membrane side in the wider frame part, which groove is opposite the abutment region on the other side of the membrane.

[0009] The grooves in the wider frame have the effect of unloading the diaphragm, specifically in the area of ​​the docking region opposite the grooves. In particular, the diaphragm is relieved of the pressure load caused by the contact force of the external bipolar plates used to generate the sealing force. This is because the grooves in the frame interrupt the flow of force from the bipolar plates toward the diaphragm. This means that the diaphragm is not pressed against the docking region opposite the grooves and the edges that delimit the docking region due to this pressure. Accordingly, the risk of diaphragm damage is reduced, which increases the robustness and service life of the diaphragm. The same applies to electrochemical cells having a membrane electrode assembly according to the present invention.

[0010] The diaphragm is further relieved of stress by offsetting the abutment areas formed on both sides between the corresponding frame parts and the corresponding transport layers. Since, during operation of the electrochemical cell, a higher internal pressure generally prevails on the cathode side than on the anode side, the diaphragm is pressed toward the anode-side abutment area by the internal pressure on the anode side or the pressure resulting therefrom. If the anode-side abutment area is now offset from the area of ​​the internal pressure applied on the cathode side due to the offset, the diaphragm is no longer pressed, or at least not as strongly, against the anode-side abutment area by the internal pressure applied on the cathode side.

[0011] The wider frame part of the frame is therefore preferably arranged on the cathode side, so that the anode-side abutment region on the membrane lies opposite this frame part.

[0012] The groove formed in the wider frame part, preferably arranged on the cathode side, is preferably arranged essentially centrally with respect to the abutment area on the other side of the diaphragm. This measure ensures that the groove is opposite the abutment area on the other side of the diaphragm even in the event of possible manufacturing and / or assembly errors.

[0013] Alternatively or additionally, it is provided that the groove is designed mirror-symmetrically with respect to the abutment region on the other side of the membrane. The mirror-symmetrical design simplifies the design of the groove.

[0014] Preferably, the groove is formed in the sealing surface of the frame member that rests on the diaphragm, so that the groove is adjacent to the sealing surface on both sides. The pressing force of the external bipolar plate is introduced into the diaphragm via the sealing surfaces adjacent on both sides, so that the groove is sealed on both sides.

[0015] Alternatively, a sealing surface resting against the diaphragm adjoins the groove on at least one side. This sealing surface can be a sealing surface of the frame or a sealing surface of a seal formed on or in the frame. In this case, the groove is sealed only on one side, preferably the outer side. The sealing force presses the diaphragm only against the other frame part and not against the transport layer on the other side, preferably the anode side.

[0016] Furthermore, it is proposed that the groove preferably has a width B which is at least as great as the thickness D of the membrane. This measure ensures that the membrane is significantly relieved of stress.

[0017] Furthermore, the groove is preferably arranged at a distance a from the abutment area on the same side of the membrane, which distance is at least as great as the width B of the groove. This ensures a sufficiently large offset between the abutment areas formed on both sides of the membrane, since the offset corresponds to the distance a plus half the width B of the groove.

[0018] Advantageously, the groove is bounded on at least one side by a chamfered or rounded edge. This means that no sharp or acute edges are formed on at least one side, preferably on both sides. This has the advantage that the edges do not press as strongly into the diaphragm under the pressure of the outer bipolar plate, thus further relieving the diaphragm.

[0019] Furthermore, it is proposed that the membrane and / or at least one transport layer be coated with a catalytically active material. The membrane can be coated on one side or on both sides. If one side is uncoated, a transport layer coated with a catalytically active material is preferably placed against at least this side. Preferably, both sides of the membrane are coated with a catalytically active material, so that coating the transport layer with the catalytically active material can be omitted.

[0020] Since electrochemical cells are a preferred field of application for the membrane electrode assembly according to the invention, an electrochemical cell, in particular a fuel cell or an electrolysis cell, comprising the 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, resulting in a prolonged service life for the electrochemical cell.

[0021] The membrane electrode assembly of the electrochemical cell is preferably arranged between two bipolar plates. The bipolar plates are pressed together in at least one edge region, in which the membrane is arranged between two frame parts of the frame, so that the two frame parts rest sealingly against the membrane. Due to the grooves in the wider frame parts, no sealing force acts on the membrane in this region, so that the membrane is unloaded. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Preferred embodiments of the present invention are explained in more detail below with reference to the accompanying drawings, which schematically show a longitudinal section through a membrane electrode assembly according to the present invention with externally arranged bipolar plates. DETAILED DESCRIPTION

[0023] The figure shows a membrane-electrode assembly 1 having 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, in this case the cathode-side frame part 6.2, has a width y that is greater than the width x of the lower frame part 6.1 or the anode-side frame part 6.1. This means that abutment regions 7, 8, which are arranged offset relative to one another in the plane of the membrane 2, are formed between the transport layers 3, 4 and the frame parts 6.1, 6.2. 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 a higher internal pressure generally prevails on the cathode side than on the anode side, the membrane 2 is pressed in the direction of the anode-side abutment region 7. However, due to this offset, the internal pressure on the cathode side is not directly applied to the membrane in the region of the anode-side abutment region 7. The membrane 2 is thus relieved in the region of the anode-side abutment region 7, and in particular is not pressed so strongly against the edge 11 of the frame part 6.1 and the transport layer 3 which delimits the anode-side abutment region 7. Furthermore, since the edge 11 is chamfered for this purpose, damage to the membrane 2 is avoided.

[0024] In the illustrated membrane-electrode assembly 1, a bipolar plate 12 rests on the cathode side. This bipolar plate presses against the upper frame part 6.2 to generate a sealing force between the sealing surface 10 of the frame part 6.2 and the diaphragm 2. A groove 9 is formed in the sealing surface 10, which lies opposite the abutment area 7 on the other side of the diaphragm 2. This further relieves the diaphragm 2, as the groove 9 interrupts the flow of force from the bipolar plate 12 toward the diaphragm 2.

[0025] For this purpose, the groove 9 has a width B that corresponds at least to the thickness D of the membrane 2 and is arranged at a distance a from the abutment region 8 on the same side. The distance a is selected to be at least as large as the width B. Since the groove 9 is arranged centrally relative to the abutment region 7 on the other side of the membrane 2, the sum of half the width B and the distance a results in the offset between the abutment regions 7, 8 formed on both sides of the membrane 2.

Claims

1. A 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) are respectively butted against the transmission layers (3, 4) arranged on the same side of the membrane (2) in a butt joint region (7, 8), and the frame parts (6.1, 6.2) are designed to have different widths so that the butt joint regions (7, 8) on both sides of the membrane (2) are arranged offset to one another. It is characterized in that a groove (9) is formed in the wider frame part (6.2) on the membrane side, which groove is opposite the abutment area (7) on the other side of the membrane (2).

2. The membrane electrode assembly (1) according to claim 1, characterized in that The groove (9) is arranged or configured substantially centrally and / or mirror-symmetrically with respect to the abutment region (7) on the other side of the membrane (2).

3. The membrane electrode assembly (1) according to claim 1 or 2, characterized in that The groove (9) is formed in a sealing surface (10) of the frame part (6.2) that rests on the diaphragm (2), or the groove (9) is adjoined at least on one side by a sealing surface (10) that rests on the diaphragm (2).

4. The membrane electrode assembly (1) according to any one of the preceding claims, It is characterized by: The groove (9) has a width (B) that is at least as great as the thickness (D) of the membrane (2).

5. The membrane electrode assembly (1) according to claim 4, characterized in that The groove (9) is arranged at a distance (a) from the abutment area (8) on the same side of the membrane (2), the distance being at least as great as the width (B) of the groove.

6. The membrane electrode assembly (1) according to any one of the preceding claims, It is characterized by: The groove (9) is delimited at least on one side by a chamfered or rounded edge (11).

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

8. An electrochemical cell, in particular a fuel cell or an electrolysis cell, comprising a membrane electrode assembly (1) according to any one of the preceding claims.

9. The electrochemical cell according to claim 8, It is characterized by: The membrane electrode assembly (1) is arranged between two bipolar plates (12).

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