A process for manufacturing a bipolar plate for an electrochemical cell and an electrochemical cell

Abstract

The invention relates to a process for manufacturing a bipolar plate (1), comprising the steps - Providing a metal foil (2), - Applying particles (3) of a conductive material on a surface (4) of the metal foil (2), - Pressing the particles (3) into the surface (4) of the metal foil (2) by using rollers (5), - Stamping the metal foil (2). The invention further relates to an electrochemical cell comprising a bipolar plate (1).

Description

[0001] Description

[0002] A process for manufacturing a bipolar plate for an electrochemical cell and an electrochemical cell

[0003] The present invention relates to a process for manufacturing a bipolar plate for an electrochemical cell, in particular an electrolysis cell or a fuel cell.

[0004] Furthermore, the present invention relates to an electrochemical cell, in particular an electrolysis cell or a fuel cell, comprising a bipolar plate manufactured by a process according to the present invention.

[0005] Background

[0006] An electrochemical cell, such like an electrolysis cell or a fuel cell, has a layered construction, typically comprising:

[0007] An electrically insulating and chemically separating, but ion conducting (composite polymer) membrane with a respective electrode / catalyst layer provided on either side thereof, forming an anode and a cathode The anode and cathode catalyst layers comprise catalyst particles mixed with binder and support materials, typically an ionomer. This layered assembly of the membrane and the electrodes is often referred to as membrane electrode assembly (ME A) or catalyst coated membrane (CCM), the latter referring to the conventional MEA production process of coating the membrane with the electrode catalyst mixture dissolved in a volatile solvent.

[0008] A porous transport or gas diffusion layer (PTL / GDL) on either side of the MEA / CCM for carrying electric current to or away from the electrodes, while allowing electrolyte and / or the electrochemical reactant(s) and product(s) to be supplied to or carried away from a respective electrode of the CCM. In some publications on electrochemical stacks, the MEA is defined to include the PTL / GDL. In fact, the catalyst can be applied to the PTL / GDL, instead of the membrane, in which case the thus coated PTL / GDL is typically referred to as a porous transport electrode (PTE). The PTL / GDL can be provided as a metal foam, (sintered) metal powder, metal fibers / whiskers felt or mesh, (woven or nonwoven) carbon fibers and the like. Effective porosity, average pore size, tortuosity, as well as electric conductance are all relevant characteristics of the PTL / GDL.

[0009] A metal bipolar plate (BPP) shared between and mutually (chemically) separating adjacent cells for coupling electric current out of or, respectively, into these cells. The BBP can be corrugated such that it defines a fluid flow field for the transport of the electrolyte, the reactant, the product and / or a cooling medium across the active area of the cell.

[0010] Most bipolar plates are provided with a conductive layer, for example a platinum layer, for enhancing the conductivity of the bipolar plate. Thus, generally, the process of manufacturing a bipolar plate comprises a coating process which is often done in a vacuum. Thereby, the coating process increases manufacturing costs and is less suitable for the mass production of bipolar plates.

[0011] The object of the present invention is to simplify the manufacturing of bipolar plates and to reduce manufacturing costs.

[0012] The object is solved by the process according to claim 1 . The dependent claims contain preferable embodiments of the invention. The object is further solved by the electrochemical cell according to claim 9.

[0013] Disclosure of the invention

[0014] The proposed process for manufacturing a bipolar plate comprises the steps:

[0015] Providing a metal foil,

[0016] Applying particles of a conductive material on a surface of the metal foil, Pressing the particles into the surface of the metal foil by using rollers, Stamping the metal foil. The application of the particles on the surface of the metal foil according to the proposed process does not afford a vacuum. Therefore, the process is less timeconsuming and less cost-intensive. Furthermore, it is suitable for mass production.

[0017] In addition, during application of the particles no thermal impact is exercised. This reduces the risk of thermal deformation, in particular thermal distortion. Thus, the process is very robust. By using a plurality of rollers for pressing the particles into the surface of the metal foil, at least one roller can be placed on either side of the metal foil, such that the metal foil is evenly strained.

[0018] Preferably, a metal foil is provided that is made of titanium or a titanium alloy. Titanium has a high strength-to-weight ratio. Thus, weight is reduced without reducing the strength of the bipolar plate. The surface of titanium metal and its alloys oxidize immediately upon exposure to air to form a thin non-porous passivation layer that protects the bulk metal from further oxidation or corrosion. When pressing the particles into the surface of the metal foil, the particles penetrate this passivation layer thereby, advantageously, reducing the interfacial contact resistance.

[0019] Further preferably, particles of noble metal, in particular platinum or gold, metal oxides and / or other materials with a good conductivity are applied to the metal foil.

[0020] According to an preferred embodiment of the invention the metal foil is stamped for defining functional surface areas. The functional surface areas are elevated areas serving as contact areas when mounting the bipolar plate to another layer of an electrochemical cell, for example a gas diffusion layer (PTL / GDL).

[0021] Preferably, the metal foil is stamped after the application of the particles of a conductive material. Thus, the metal foil is still even when fed to the rollers in order to bond the particles to the metal foil. Preferably, the application of particles of a conductive material is restricted to certain surface areas, in particular to the functional surface areas. Accordingly, less particles are needed so that the consumption of precious metals decreases.

[0022] Further preferably, the application of the particles of a conductive material is restricted to 5 to 10% of the entire surface area of the metal foil. With other words, only 5 to 10% of the metal foil is covered by a conductive material. However, between the individual particles conductive bridges are formed leading to the enhanced conductivity of the bipolar plate.

[0023] According to another preferred embodiment of the invention, the metal foil is provided with positioning holes. The positioning holes facilitate the application of the particles in the surface areas that later, after stamping, form the functional surface areas. The positioning holes can be arranged in particular along one longitudinal edge or along two opposite longitudinal edges of the metal foil.

[0024] Preferably, the metal foil is a strip that is coiled and cut to size after the application of the particles and / or after stamping. In this case, the laterally arranged positioning holes can then also be used to transport the metal foil forward.

[0025] According to another preferred embodiment of the invention, the metal foil is oxidized after the application of the particles of a conductive material, preferably after stamping of the metal foil. The oxidation layer prevents hydrogen embrittlement when the manufactured bipolar plate is used in an electrochemical cell, in particular in an electrolysis cell or a fuel cell.

[0026] Furthermore, since the preferred field of application is an electrochemical cell, an electrochemical cell, in particular an electrolysis cell or a fuel cell, is further suggested. The cell comprises a bipolar plate manufactured by a process according to the invention. The fact that the process makes it possible to manufacture a bipolar plate at low cost also means that the costs of manufacturing the electrochemical cell can be reduced. Preferred embodiments of the invention are explained in conjunction with the enclosed figures. The figures show:

[0027] Figure 1 a sectional view through a plant for the manufacturing of bipolar plates according to the present invention,

[0028] Figure 2 a cross section through a bipolar plate manufactured by a process according to the present invention,

[0029] Figure 3 a top view of another bipolar plate manufactured by a process according to the present invention and

[0030] Figure 4 a cross section through an electrochemical cell in the area of a bipolar plate manufactured by a process according to the present invention.

[0031] Detailed description of the figures

[0032] Figure 1 shows a process for manufacturing a bipolar plate 1 according to the present invention. The base material is a metal foil 2 that is taken from a coil 6. The process is therefore particularly suitable for the mass production of bipolar plates 1 .

[0033] As shown in figure 1 , particles 3 of a conductive material are applied to a surface 4 of an unwound section of the metal foil 2. After this, the metal foil 2 is passed between two rollers 5, by means of which the particles 3 are pressed into the surface 4 of the metal foil 2. Thereby, the particles 3 are bonded to the metal foil 2.

[0034] As shown in figure 2, when pressed into the surface 4 of the metal foil 2, the particles 3 penetrate an oxide layer 9 of the metal foil 2, thereby reducing the interfacial contact resistance. Furthermore, the particles 3 form conductive bridges across the oxide layer 9.

[0035] In figure 3, the metal foil 2 is provided with positioning holes 8 arranged along the longitudinal edges of the metal foil 2. The positioning holes 8 ensure the correct alignment of the metal foil 2 during stamping, which is a process step that follows the application of the particles 3. By stamping the metal foil 2 functional surface areas 7 are defined which form the later contact surfaces of the bipolar plate 1. Preferably, the application of the particles 3 is restricted to the functional surface areas 7. Since the process step of stamping is carried out after the application of the particles 3, the metal foil 2 must be precisely aligned in both steps so that the particles come to rest on the surfaces areas that later form the functional surface areas 7. This is done with the help of the positioning holes 8. Figure 4 shows a bipolar plate 1 manufactured by a process according to the present invention mounted to another layer of an electrochemical cell, for example a gas diffusion layer 10. The functional surface areas 7 form contact surfaces which are in contact with the gas diffusion layer 10. To enhance the conductivity of the bipolar plate 1 in the area of the contact surface, the functional surface areas 7 are coated with particles 3 of a conductive material, for example particles 3 of platinum or gold.

Claims

Claims1 . A process for manufacturing a bipolar plate (1), comprising the steps Providing a metal foil (2),Applying particles (3) of a conductive material on a surface (4) of the metal foil (2), Pressing the particles (3) into the surface (4) of the metal foil (2) by using rollers (5), Stamping the metal foil (2).

2. The process according to claim 1 , characterized in that a metal foil (2) is provided that is made of titanium or a titanium alloy.

3. The process according to claim 1 or 2, characterized in that particles (3) of noble metal, in particular platinum or gold, metal oxides and / or other materials with a good conductivity are applied to the metal foil (2).

4. The process according to any of the preceding claims, characterized in that the metal foil (2) is stamped for defining functional surface areas (7), preferably after the application of the particles (3) of a conductive material.

5. The process according to any of the preceding claims, characterized in that the application of particles (3) of a conductive material is restricted to certain surface areas, in particular to the functional surface areas (7).

6. The process according to any preceding claims, characterized in that the application of the particles (3) of a conductive material is restricted to 5 to 10% of the entire surface area of the metal foil (2).

7. The process according to any preceding claims, characterized in that the metal foil (2) is provided with positioning holes (8), preferably before the application of the particles (3) of a conductive material.

8. The process according to any of the preceding claims, characterized in that the metal foil (2) is oxidized after the application of the particles (3) of a conductive material, preferably after stamping of the metal foil (2).

9. An electrochemical cell, in particular an electrolysis cell or a fuel cell, comprising a bipolar plate (1) manufactured by a process according to any of the preceding claims.

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