Process for manufacturing an electrochemical cell, electrochemical cell

Abstract

The invention relates to a process for manufacturing an electrochemical cell (10) comprising: - a membrane electrode assembly or a catalyst-coated membrane (1), abbreviated MEA / CCM (1), forming a cathode (2) on one side and an anode (3) on the other side, - a porous transport layer or gas diffusion layer (4, 5), abbreviated PTL / GDL (4, 5), on each side of the MEA / CCM (1) and - a frame element (6, 7) on each side of the MEA / CCM (1) which encloses the respective PTL / GDL (4, 5). According to the present invention, at least one PTL / GDL (4, 5) is inserted into the respective frame element (6, 7) under a preload during manufacturing. The invention also relates to an electrochemical cell (10) and an electrochemical cell stack.

Description

[0001] The present invention relates to a process for manufacturing an electrochemical cell, e.g., an electrolysis cell or a fuel cell. Furthermore, the present invention relates to an electrochemical cell, in particular an electrolysis cell or a fuel cell. State of the art

[0002] An electrochemical cell, such as an electrolysis cell or a fuel cell, has a layered structure that typically includes: - An electrically insulating and chemically separating, but ion-conducting (composite polymer) membrane with a respective electrode / catalyst layer provided on each side, forming an anode and a cathode. The anode and cathode catalyst layers comprise catalyst particles mixed with a binder and support materials, typically an ionomer. This layered arrangement of membrane and electrodes is often referred to as a membrane electrode assembly (MEA) or a catalyst-coated membrane (CCM), the latter referring to the conventional MEA manufacturing process of coating the membrane with an electrode-catalyst mixture dissolved in a volatile solvent; - A porous transport or gas diffusion layer (PTL / GDL) on each side of the MEA / CCM for transporting an electric current to or from the electrodes, while allowing an electrolyte and / or the electrochemical reactant(s) and product(s) to be delivered to or transported away from a respective electrode of the CCM. In some publications on electrochemical stacks, the MEA is defined as containing the PTL / GDL. In fact, the catalyst may be applied to the PTL / GDL rather than to the membrane, in which case the PTL / GDL thus coated is referred to as a porous transport electrode (PTE). The PTL / GDL may be provided as a metal foam, a (sintered) metal powder, a felt or mesh of metal fibers / hairs, (woven or nonwoven) carbon fibers, and the like.Effective porosity, average pore size, tortuosity, and electrical conductivity are all relevant properties of PTL / GDL. - a seal with a frame element on each side of the MEA / CCM for sealing and supporting the MEA / CCM; - A bipolar metal plate (BPP) shared by adjacent cells, which chemically isolates them to couple an electric current to or from them. The BPP may be corrugated to define a fluid flow field for transporting the electrolyte, reactant, product, and / or cooling medium through the active area of ​​the cell.

[0003] A large number of identical cells are stacked and clamped together to form an electrochemical stack, e.g., an electrolysis cell stack or a fuel cell stack.

[0004] An electrochemical cell stack, particularly an electrolysis cell stack, is typically operated either at a balanced pressure between the anode and cathode or with a higher pressure on one side, generally the cathode side. Due to this high differential pressure, local areas of the MEA / CCM can undergo plastic deformation. Areas particularly at risk are those extending across a gap between the anode-side PTL / GDL and the anode-side frame element, as the MEA / CCM in these areas is forced into the gap. During prolonged operation of the electrolysis cell stack, this can lead to membrane fatigue, cracks and / or fractures within the MEA / CCM, and, in the worst case, to the sudden failure of the cell stack.

[0005] To avoid this, cell configurations have been proposed in which the cathode side PTL / GDL has smaller dimensions than the anode side PTL / GDL, as for example in Fig. 5 is shown.

[0006] Fig. Figure 5 shows an MEA / CCM 1 with a cathode 2 and an anode 3. The MEA / CCM 1 is covered on each side by a PTL / GDL 4, 5 and a frame element 6, 7. The frame element 6, 7 encloses the respective PTL / GDL 6, 7, thus forming a gap 11. On the cathode side, in Fig. 6. On the top side, the PTL / GDL 4 is smaller than the PTL / GDL 5 on the anode side. Fig. 6 the underside. Thus, the gap 11 on the anode side is offset relative to the gap 11 on the cathode side. If, during cell operation, the pressure on the cathode side is higher than on the anode side, the MEA / CCM 1 is pressed mainly against the anode side PTL / GDL 5 but not against the anode side gap 11.

[0007] However, this approach can still fail if gas escapes through the interface between the frame element 6 of the cathode side and the MEA / CCM 1.

[0008] The objective of the present invention is to prevent cell wear caused by plastic deformation of the MEA / CCM during operation with higher pressure on one side of the cell, generally on the cathode side of the cell.

[0009] The objective is achieved by the process for manufacturing an electrochemical cell according to claim 1 and by the electrochemical cell according to claim 6. The dependent claims relate to preferred embodiments of the invention. Disclosure of the invention

[0010] The proposed process is used to manufacture an electrochemical cell that includes: - a membrane electrode assembly or a catalyst-coated membrane, abbreviated MEA / CCM, which forms a cathode on one side and an anode on the other side, - a porous transport layer or gas diffusion layer, abbreviated PTL / GDL, on each side of the MEA / CCM and - a frame element on each side of the MEA / CCM, which encloses the respective PTL / GDL.

[0011] According to the invention, at least one PTL / GDL is inserted into the respective frame element under preload during manufacturing. In other words, the at least one PTL / GDL is preloaded against the corresponding frame element. Consequently, after manufacturing, there is no gap or a minimized gap between the at least one PTL / GDL and the corresponding frame element. Accordingly, the risk of deformation of the MEA / CCM by being forced into a gap is also minimized.

[0012] The product of the proposed process is an electrochemical cell, such as an electrolysis cell or a fuel cell, that is less susceptible to material fatigue, cracking, and / or fractures, and therefore has a longer lifespan. This is particularly true when the pressure during operation is higher on the cathode side than on the anode side, so that a differential pressure forces the MEA / CCM on the anode side against the PTL / GDL. Therefore, it is also proposed that at least the PTL / GDL of the anode side be inserted into the frame element of the anode side under preload during manufacturing.

[0013] A PTL / GDL (Polythermal Transformer / Grid-type Flexible Transformer) is typically made of a material that is either not plastically deformable or only very limitedly so. To nevertheless enable the PTL / GDL to be installed under preload, it is proposed that at least one PTL / GDL be cut and plastically deformed under mechanical stress before manufacturing, so that the PTL / GDL is larger than the cutout in the frame component into which it is inserted during manufacturing. The cuts impart deformable properties to the PTL / GDL, specifically allowing for plastic deformation. This plastic deformation is achieved by stretching the PTL / GDL. This opens the cuts, giving the PTL / GDL spring-like properties. These spring-like properties, in turn, allow for elastic deformation and thus preloading of the PTL / GDL when it is inserted into the corresponding frame element.

[0014] The at least one PTL / GDL is preferably cut perpendicular and / or obliquely to the plane of the PTL / GDL. In any case, the cuts do not extend from one side to the other of the PTL / GDL, as this would otherwise cut the PTL / GDL into several pieces. Compared to perpendicular cuts, oblique cuts have the advantage that, after the PTL / GDL is inserted into the corresponding frame element, two inclined planes lie on top of each other in the area of ​​the cut, so that all forces acting perpendicularly on the PTL / GDL press the two inclined planes together.

[0015] Furthermore, at least one PTL / GDL is preferably cut using a laser or a water jet. Both allow for very precise cuts.

[0016] Furthermore, an electrochemical cell, in particular an electrolysis cell or a fuel cell, is proposed, which includes: - a membrane electrode assembly or a catalyst-coated membrane, abbreviated MEA / CCM, which forms a cathode on one side and an anode on the other side, - a porous transport layer or gas diffusion layer, abbreviated PTL / GDL, on each side of the MEA / CCM and - a frame element on each side of the MEA / CCM, which encloses the respective PTL / GDL.

[0017] According to the invention, at least one PTL / GDL is inserted and preloaded against the corresponding frame element.

[0018] Preloading prevents a gap from forming between the at least one PTL / GDL and the corresponding frame element. If only one PTL / GDL is preloaded against the corresponding frame element, this is preferably the anode-side PTL / GDL, since during operation the pressure on the cathode side is usually higher than on the anode side, so the MEA / CCM is pressed against the anode-side PTL / GDL and the corresponding frame element. If a gap exists between the PTL / GDL and the frame element, the MEA / CCM is forced into the gap. The deformation stresses the MEA / CCM until a crack or fracture occurs. If no such gap exists, the stress on the MEA / CCM decreases and its service life increases.

[0019] According to a preferred embodiment of the invention, the at least one PTL / GDL is provided with at least one cut that extends perpendicular and / or obliquely to the plane of the PTL / GDL. The cut allows plastic deformation of the PTL / GDL prior to manufacturing, thereby giving the PTL / GDL spring properties. These spring properties, in turn, allow elastic deformation of the PTL / GDL, which is necessary for insertion under a preload.

[0020] Advantageously, at least one cut runs at an angle to the plane of the PTL / GDL. In this case, two inclined planes lie on top of each other. All forces acting perpendicular to the PTL / GDL will compress these two planes even further.

[0021] According to a further preferred embodiment of the invention, the at least one PTL / GDL has at least two incisions arranged at an angle to each other, in particular at right angles. The incisions can, for example, be arranged in a cross shape. In this arrangement, the incisions allow the PTL / GDL to be deformed in more than one direction, in particular in a direction parallel to the plane of the PTL / GDL and in a plane perpendicular to this plane. This gives the PTL / GDL spring properties in more than one direction. According to a preferred embodiment, the at least one PTL / GDL thus forms a unidirectional or a bidirectional spring.

[0022] Since the proposed electrochemical cell is preferably used in an electrochemical stack, an electrochemical stack comprising at least one electrochemical cell according to the invention is also proposed. Preferably, a number of identical cells are stacked on top of each other and clamped together.

[0023] Preferred embodiments of the invention are explained in connection with the accompanying figures. The figures show: Fig. 1 a longitudinal section through a first PTL / GDL for an electrochemical cell according to the invention before manufacturing, Fig. 2 a) a longitudinal section through a second PTL / GDL for an electrochemical cell according to the invention before manufacturing and b) after manufacturing, Fig. 3 a) a longitudinal section through a third PTL / GDL for an electrochemical cell according to the invention before manufacturing and b) after manufacturing, Fig. 4 a) a longitudinal section through a fourth PTL / GDL for an electrochemical cell according to the invention before manufacturing and b) after manufacturing, Fig. 5 a longitudinal section through an electrochemical cell according to the state of the art. Detailed description of the figures

[0024] The Fig. Figures 1 to 4 are limited to the representation of a PTL / GDL 4, 5 for an electrochemical cell 10 according to the invention. The cell 10 can, incidentally, be manufactured analogously to the electrochemical cell 10 described in Fig. 5 is shown. Regarding the description of Fig. 5 refers to the introduction of the description.

[0025] Fig. Figure 1 shows a first PTL / GDL 5 for an electrochemical cell 10 according to the invention. The PTL / GDL 5 is arranged on one side of the anode 3. Alternatively, the PTL / GDL (see reference numeral 4 in brackets) could be arranged on the side of the cathode 2. This is applicable to all PTLs / GDLs 5 (4) that are in the Fig. 1 to 4 will be shown.

[0026] The PTL / GDL 5, which is in Fig. As shown in Figure 1, the PTL / GDL 5 has two incisions 8 on opposite sides. This allows plastic deformation under mechanical stress, causing the incisions 8 to open. In this state, the PTL / GDL 5 forms a unidirectional spring that allows elastic deformation. Accordingly, the PTL / GDL 5 can be inserted into a frame element 7 under preload, thus avoiding the formation of a gap 11, as shown in Figure 1. Fig. 5 is shown.

[0027] The PTL / GDL 5, which is in Fig. Figure 2 shows a multitude of incisions 8, 9 arranged parallel and perpendicular to each other. Under a mechanical load, the incisions 8, 9 open (see Figure 2). Fig. 2a)). In this state, the PTL / GDL 5 forms a bidirectional spring, allowing elastic deformation of the PTL / GDL 5 in two directions. When the PTL / GDL 5 is inserted into a frame element 7, it is compressed so that the incisions 8, 9 close again (see Fig. 2b)).

[0028] Another example of a PTL / GDL 5 forming a bidirectional spring is shown in Fig. Figure 3 shows the incisions 8 and 9 arranged in a cross-shaped pattern, which forms a star-shaped opening under mechanical stress.

[0029] The PTL / GDL 5 of the Fig. 4 is cut only once, but at an angle to the plane of the PTL / GDL 5. Under mechanical stress, the angled cut 8 forms a gap (see Fig. 4a)), but after the PTL / GDL 5 is inserted into a frame element 7, the preload of the PTL / GDL 5 closes the gap so that two inclined planes lie on top of each other (see Fig. 4b)). A force resulting from the fact that the pressure on the cathode side 2 is higher than that on the anode side 3 causes a force perpendicular to the plane of cell 10, which presses the MEA / CCM 1 against the PTL / GDL 5 of the anode side. In the area of ​​the inclined cut 8, the force causes the two inclined planes to be compressed even further.

Claims

[1] Process for manufacturing an electrochemical cell (10) comprising: - a membrane electrode assembly or a catalyst-coated membrane (1), abbreviated MEA / CCM (1), forming a cathode (2) on one side and an anode (3) on the other side, - a porous transport layer or gas diffusion layer (4, 5), abbreviated PTL / GDL (4, 5), on each side of the MEA / CCM (1) and - a frame element (6, 7) on each side of the MEA / CCM (1) which encloses the respective PTL / GDL (4, 5), characterized by , that during manufacturing at least one PTL / GDL (4, 5) is inserted into the respective frame element (6, 7) under a preload. [2] Process according to claim 1, characterized by , that during manufacturing at least the PTL / GDL (5) of the anode side is inserted into the frame element (7) of the anode side under a preload. [3] Process according to claim 1 or 2, characterized by, that prior to manufacturing at least one PTL / GDL (4, 5) is cut and plastically deformed under a mechanical load, so that the PTL / GDL (4, 5) is larger than a cutout (8) of the frame part into which the PTL / GDL (4, 5) is inserted during manufacturing. [4] Process according to claim 3, characterized by , that at least one PTL / GDL (4, 5) is cut perpendicular and / or obliquely to the plane of the PTL / GDL (4, 5). [5] Process according to claim 3 or 4, characterized by , that at least one PTL / GDL (4, 5) is cut using a laser or a water jet. [6] Electrochemical cell (10), in particular an electrolysis cell or a fuel cell, comprising: - a membrane electrode assembly or a catalyst-coated membrane (1), abbreviated MEA / CCM (1), forming a cathode (2) on one side and an anode (3) on the other side, - a porous transport layer or gas diffusion layer (4, 5), abbreviated PTL / GDL (4, 5), on each side of the MEA / CCM (1) and - a frame element (6, 7) on each side of the MEA / CCM (1) which encloses the respective PTL / GDL (4, 5), characterized by , that at least one PTL / GDL (4, 5) is inserted and preloaded against the corresponding frame element (6, 7). [7] Electrochemical cell (10) according to claim 6, characterized by , that the at least one PTL / GDL (4, 5) is provided with at least one incision (8) that runs perpendicular and / or oblique to the plane of the PTL / GDL. [8] Electrochemical cell (10) according to claim 6 or 7, characterized by , that the at least one PTL / GDL (4, 5) has at least two incisions (8, 9) which are arranged at an angle to each other, in particular at right angles. [9] Electrochemical cell (10) according to any one of claims 6 to 8, characterized by, that at least one PTL / GDL (4, 5) forms a unidirectional or a bidirectional spring. [10] Electrochemical cell stack comprising at least one electrochemical cell (10) according to any one of claims 6 to 9.

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