Electrochemical cell and use

Abstract

The invention relates to an electrochemical cell (10) in the form of a fuel cell, an electrolyser or a redox-flow cell, comprising two reaction chambers (4, 5) separated from one another by a polymer membrane (6), and comprising at least one transport layer (1, 1 ') which is arranged in at least one of the reaction chambers (4, 5) with an electrically conductive, open-pore coating (3) facing the polymer membrane (6), the transport layer (1, 1 ') comprising a metal carrier structure (2) having the coating (3) applied to at least portions of the carrier structure (2), and the coating (3) being formed of a mixture of substoichiometric titanium oxide and chromium oxide, which mixture contains at most 0.5 wt.% elements from the group comprising Nb, Zr, Y, AI, Sn, Zn, Ni, Ta, Mo, Ag, Cu, Au, Pt, V, Ru, W, Si, Fe, Ca, Mg, Na, H, N, and C. The invention also relates to a use of at least one transport layer (1, 1 ') in an electrochemical cell (10) of this kind.

Description

[0001] Electrochemical cell and use

[0002] The invention relates to an electrochemical cell in the form of a fuel cell, an electrolyzer or a redox flow cell and to a use of a transport layer in such an electrochemical cell.

[0003] Transport layers exhibit electrical conductivity and are known per se. They are also referred to as gas diffusion bodies, gas diffusion layers, current collectors, transport layers, and the like, and serve to conduct and / or distribute fluids within a reaction chamber of an electrochemical cell. Materials used include metal foams, metal meshes, metal knits, metal felts, metal thread scrims, sintered metals with open porosity, expanded metals, and the like. These materials can be attached to one side of a gas-tight metal plate and can additionally be coated at least in certain regions to establish a specific open porosity with suitable pore diameters of the coating. The coating is used in contact with a polymer membrane separating the reaction chambers in an electrochemical cell.

[0004] For example, DE 10 2018 132 399 A1 already describes a gas diffusion body comprising at least one base layer with through-openings, which is formed either from electrically conductive expanded metal, fabric, or mesh, or from an electrically conductive metal plate provided with openings. Furthermore, an additional layer is present, which is applied as a powdered material using a thermal spraying process. The powdered material consists primarily of particles of electrically conductive material, in particular titanium, and can contain additives in the form of platinum particles, gold particles, iridium particles, or combinations thereof. The gas diffusion body is used in electrochemical cells, in particular electrolyzers or fuel cells.

[0005] DE 10 2020 203 398 A1 describes a process for additively manufacturing a metal support for a fuel cell. The metal support is constructed by applying a metal layer to a base structure. A metal grid and / or a metal mesh can serve as the base structure. The porosity of the metal layer can be gradually adjusted, but gas-tight regions can also be created.

[0006] DE 10 2015 111 918 A1 discloses a method for producing a current collector for an electrode of an electrochemical cell, in particular an electrolyzer. A substrate is provided, and at least one microporous layer consisting of or containing titanium is applied to the substrate by plasma spraying in a vacuum. The titanium powder used for this purpose can be sprayed with at least one other metal powder made of a base metal, in particular aluminum, iron, or zinc. A titanium expanded metal mesh or sintered titanium powder is described as the substrate. A corrosion protection layer, in particular made of precious metal or a porous electrocatalyst, such as SnO2:Sb, Ti4O2, SnO2:M with M = Sb, In, Nb, or TiO2:M with M = W, Nb, Mo, can be applied to the at least one microporous layer.

[0007] US Patent No. 4,931,213 A describes an electrically conductive ceramic material made of substoichiometric titanium oxide, which is used in electrochemical applications. Titanium dioxide is combined with graphite and reduced to substoichiometric titanium oxide.

[0008] US 2022 / 0 033 288 A1 discloses an electrochemical device for purifying a fluid, such as waste water or sludge, comprising an electrochemical filter membrane and an open-porous metallic support having a coating containing TiOx with x= 1.5 to 1.9.

[0009] It is an object of the invention to provide an electrochemical cell which is improved with regard to electrochemical stability and electrical conductivity of a transport layer used in the electrochemical cell.

[0010] The object is achieved by an electrochemical cell in the form of a fuel cell, an electrolyzer or a redox flow cell, comprising two reaction spaces separated from one another by a polymer membrane, and having at least one transport layer which is arranged in at least one of the reaction spaces with an electrically conductive, open-porous coating facing the polymer membrane, wherein the transport layer is formed comprising a metallic support structure with the coating applied at least in regions to the support structure, wherein the coating is formed from a mixture of substoichiometric titanium oxide and chromium oxide which has a maximum of 0.5 wt. % of elements from the group comprising Nb, Zr, Y, Al, Sn, Zn, Ni, Ta, Mo, Ag, Cu, Au, Pt, V, Ru, W, Si, Fe, Ca, Mg, Na, H, N, C.

[0011] The electrochemical cell has a significantly improved long-term cell performance due to the high electrochemical stability and electrical conductivity of the transport layer used.

[0012] The interfacial resistance of the coating is preferably below 25 mOhmcm 2 , where a TPV measurement (TVP = "through plane voltage") is standardized to gold and at a pressure of 100 N / cm 2 and a current density of 2 A / cm 2 Preferably, the electrical conductivity should be at least 3*10 3 S / m for the coating.

[0013] The substoichiometric titanium oxide preferably has the formula TiO2-x where 0 < x < 1, in particular where 0.01 < x < 0.2. A particularly high electrical conductivity can be achieved in this case.

[0014] The substoichiometric titanium oxide is preferably present in the coating in a ratio of 95:5 to 5:95 wt.% to the chromium oxide. In particular, the substoichiometric titanium oxide is present in the coating at 75 to 85 wt.%. The chromium oxide is preferably stoichiometric.

[0015] The coating is preferably applied to the support structure by thermal spraying. This allows open porosities in the coating to be specifically adjusted and modified. The open-porous coating is preferably formed on the support structure by thermal spraying a titanium powder and / or titanium oxide powder and a chromium powder and / or chromium oxide powder, optionally with prior mixing of these powders.

[0016] In the region of a free surface of the coating, an open porosity is preferably set with an average pore diameter in the single-digit micrometer range, in particular in the range from 5 to 15 pm, while on the side of the coating facing the support structure, an open porosity is preferably set with an average pore diameter in the single-digit millimeter range, in particular in the range from 0.5 to 1.5 mm. Starting from the support structure, the pore diameter in the coating is successively reduced towards the free surface.

[0017] Particularly preferably, an open porosity in the range of 25 to 35 vol.% is formed on the side of the open-porous coating facing the support structure and an open porosity in the range of 78 to 82 vol.% is formed in the region of the free surface of the open-porous coating.

[0018] For thermal spraying, powders with grain sizes in the range of 1 to 100 pm, especially in the range of 25 ± 5 pm, are preferred. Powders that already have the required substoichiometric composition of titanium oxide and a stoichiometric composition of chromium oxide are particularly used.

[0019] Preferably, the provided powders or the mixed powders are sprayed onto the support structure using atmospheric plasma spraying. However, other thermal spraying processes are also applicable. The process utilizes the fact that thermal spraying can be used to produce open, porous layers or components. Furthermore, the ability of this deposition technology to generatively produce geometric structures from the micrometer to millimeter range is utilized. In this way, three-dimensional flow channels can be formed by spraying an open-porous coating of varying thickness locally. These flow channels are suitable for guiding the fluid flows within the electrochemical cell. There are virtually no limits to the geometric shape of the flow channels. This enables fluid transport in both the lateral and normal directions to a polymer membrane.

[0020] The metallic support structure is preferably plate-shaped and comprises at least one open-porous layer, for example made of a sintered metal part, metal foam, metal mesh, metal knit, metal fleece, metal thread scrim, and the like, onto which the coating is sprayed on at least one side. The support structure can further comprise at least one gas-impermeable metal plate arranged on the side of the open-porous layer facing away from the coating. The support structure has a thickness in the range of 0.1 mm to 5 mm, in particular 0.5 mm. Both a metal plate and an open-porous layer can have three-dimensional structures for forming macroscopically recognizable flow channels or flow guide structures. These three-dimensional structures can be formed by embossing, molding, and the like.

[0021] The open-porous coating is preferably applied to the support structure, in particular to the open-porous layer, in a layer thickness ranging from 0.5 mm to 5 mm. Three-dimensional structures can also be formed in-situ during thermal spraying on a free surface of the coating facing away from the support structure.

[0022] The use of at least one transport layer, comprising a metallic support structure with an electrically conductive, open-porous coating applied at least in regions to the support structure, wherein the coating is formed from a mixture of substoichiometric titanium oxide and chromium oxide, which has a maximum of 0.5 wt. % of elements from the group comprising Nb, Zr, Y, Al, Sn, Zn, Ni, Ta, Mo, Ag, Cu, Au, Pt, V, Ru, W, Si, Fe, Ca, Mg, Na, H, N, C, in an electrochemical cell in the form of a fuel cell, an electrolyzer or a redox flow cell, comprising two reaction spaces separated from one another by a polymer membrane, wherein the at least one transport layer is arranged in at least one of the reaction spaces with the coating facing the polymer membrane, has proven successful.

[0023] Figures 1 to 3 illustrate transport layers for use in an electrochemical cell and their application in an electrochemical cell. They show:

[0024] Figure 1 shows a first transport layer for use in an electrochemical cell in a schematic three-dimensional view,

[0025] Figure 2 shows a second transport layer for use in an electrochemical cell in a schematic three-dimensional view, and

[0026] Figure 3 shows a section through an electrochemical cell of an electrolyzer.

[0027] Figure 1 shows a first transport layer 1 for use in an electrochemical cell 10 (see Figure 3) in a schematic three-dimensional view. The first transport layer 1 comprises a metallic support structure 2 formed from an open-pore metal sintered part 2c made of titanium in plate form. An electrically conductive, open-pore coating 3 is applied to one side of the support structure 2 by atmospheric plasma spraying using a thermal spraying device 20, which is shown only schematically here. The coating 3 is formed from a mixture of substoichiometric titanium oxide and chromium oxide, which further contains a maximum of 0.5 wt. % of elements from the group comprising Nb, Zr, Y, Al, Sn, Zn, Ni, Ta, Mo, Ag, Cu, Au, Pt, V, Ru, W, Si, Fe, Ca, Mg, Na, H, N, and C.

[0028] Figure 2 shows a second transport layer 1' for use in an electrochemical cell 10 (see Figure 3) in a schematic three-dimensional view. The second transport layer 1' comprises a metallic support structure 2 in plate form, which comprises a gas-tight metal plate 2a made of steel, which is connected on one side to an open-porous metal mesh 2b made of steel. An electrically conductive, open-porous coating 3 is applied to the free side of the open-porous metal mesh 2b by atmospheric plasma spraying using a thermal spraying device 20, which is shown only schematically here. The coating 3 is formed from a mixture of substoichiometric titanium oxide and chromium oxide, which further comprises a maximum of 0.5 wt.% of elements from the group comprising Nb, Zr, Y, Al, Sn, Zn, Ni, Ta, Mo, Ag, Cu, Au, Pt, V, Ru, W, Si, Fe, Ca, Mg, Na, H, N, C.

[0029] Figure 3 shows a section through an electrochemical cell 10 in the form of an electrolyzer. The electrochemical cell 10 comprises two reaction chambers 4, 5 separated from one another by a polymer membrane 6, in this case a polymer electrolyte membrane. On both sides of the polymer membrane 6, a transport layer 1' is arranged for each reaction chamber 4, 5, with a free surface 3a (cf. Figures 1 and 2) of the coating 3 facing the polymer membrane 6. An electrically conductive catalyst layer (not shown separately) comprising a catalyst material is arranged on both sides of the polymer electrolyte membrane. The metal plates 2a here each have flow channels 7 on their sides facing the metal mesh 2b in order to improve the supply of reaction medium (water) and the removal of reaction products (water, hydrogen, oxygen).Such flow channels 7 are only optionally present and can alternatively or additionally also be formed in-situ on the free surface 3a of the coating 3 during thermal spraying.

[0030] List of reference symbols, transport position

[0031] Support structure a metal plate b metal mesh c metal sintered part open-porous coating a free surface , 5 reaction chamber

[0032] Polymer membrane

[0033] Flow channels 0 electrochemical cell 0 thermal spraying device

Claims

Patent claims 1. An electrochemical cell (10) in the form of a fuel cell, an electrolyzer or a redox flow cell, comprising two reaction chambers (4, 5) separated from one another by a polymer membrane (6), and having at least one transport layer (1, 1') which is arranged in at least one of the reaction chambers (4, 5) with an electrically conductive, open-porous coating (3) facing the polymer membrane (6), wherein the transport layer (1, 1') comprises a metallic support structure (2) with the coating (3) applied at least in regions to the support structure (2), wherein the coating (3) is formed from a mixture of substoichiometric titanium oxide and chromium oxide, which contains a maximum of 0.5 wt. % of elements from the group comprising Nb, Zr, Y, Al, Sn, Zn, Ni, Ta, Mo, Ag, Cu, Au, Pt, V, Ru, W, Si, Fe, Ca, Mg, Na, H, N, C.

2. Electrochemical cell (10) according to claim 1, wherein the substoichiometric titanium oxide has the formula TiO2-x with 0 < x < 1.

3. Electrochemical cell (10) according to claim 2, wherein the substoichiometric titanium oxide has the formula TiO2-x with 0.01 < x < 0.

2.

4. Electrochemical cell (10) according to one of claims 1 to 3, wherein the coating (3) is formed by thermal spraying on the support structure (2).

5. Electrochemical cell (10) according to one of claims 1 to 4, wherein the substoichiometric titanium oxide to the chromium oxide is present in a ratio of 95:5 to 5:95 wt.% in the coating (3).

6. Electrochemical cell (10) according to claim 5, wherein the substoichiometric titanium oxide is present in the coating (3) at 75 to 85 wt.%.

7. Electrochemical cell (10) according to one of claims 1 to 6, wherein the open-pore coating (3) on the support structure (2) is formed by thermal spraying of a titanium powder and / or titanium oxide powder and further a chromium powder and / or chromium oxide powder, optionally with prior mixing of these powders.

8. Use of at least one transport layer (1, 1') comprising a metallic support structure (2) with an electrically conductive, open-porous coating (3) applied at least in regions to the support structure (2), wherein the coating (3) is formed from a mixture of substoichiometric titanium oxide and chromium oxide, which has a maximum of 0.5 wt. % of elements from the group comprising Nb, Zr, Y, Al, Sn, Zn, Ni, Ta, Mo, Ag, Cu, Au, Pt, V, Ru, W, Si, Fe, Ca, Mg, Na, H, N, C, in an electrochemical cell (10) in the form of a fuel cell, an electrolyzer or a redox flow cell, comprising two reaction spaces (4, 5) separated from one another by a polymer membrane (6), wherein the at least one transport layer (1, 1') in at least one of the reaction spaces (4, 5) is provided with the coating (3) is arranged facing the polymer membrane (6).

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