Patent Application
20250030009
The disclosure relates to a layer system for coating a substrate to form an electrode plate, comprising at least one coating (1a) made of metal oxide. The disclosure further relates to an electrode plate comprising a substrate and such a layer system and a method for the production thereof. Furthermore, the disclosure relates to a fuel cell, an electrolyzer or a redox flow cell comprising at least one such electrode plate.
A bipolar plate for a fuel cell or an electrolyzer is already known from DE 100 58 337 A1, in which a conductive and corrosion-resistant protective coating made of a metal oxide is formed on at least one side of a metal sheet. The metal oxide is formed in particular from an oxide of the elements or alloys from the group comprising tin, zinc and indium. Doping that ensures conductivity and consists of at least one element from the group comprising aluminum, chromium, silver, boron, fluorine, antimony, chlorine, bromine, phosphorus, molybdenum, and carbon can be present in the metal oxide. The metal sheets used are those made of aluminum, copper, stainless steel, chrome-plated stainless steel, titanium, titanium alloys and iron-containing compounds, which can have a coating of at least one of the elements tin, zinc, nickel, and chromium.
It is the object of the disclosure to provide an improved layer system for an electrode plate and to provide such a electrode plate. Furthermore, it is the object of the disclosure to provide a method for the production of the electrode plate and to propose a fuel cell, an electrolyzer or a redox flow cell with at least one such electrode plate.
The object is for the layer system for coating a substrate to form an electrode plate, comprising at least one first coating made of metal oxide, wherein the at least one first coating is a homogeneous, polycrystalline doped indium tin oxide layer, and a top layer in the form of a polycrystalline doped indium tin oxide layer made of a network of nanofibers is formed thereon, wherein the indium tin oxide of the at least one first coating and of the top layer is doped with at least one element of the group comprising carbon, nitrogen, boron, fluorine, hydrogen, phosphorus, sulfur, chlorine, bromine, aluminum, silicon, titanium, chromium, cobalt, nickel, copper, zirconium, niobium, molybdenum, silver, antimony, hafnium, tantalum and tungsten.
The layer system is characterized by a high level of long-term stability with simultaneously high electrical conductivity and low cost, since it is extensive or without precious metal. In addition, the layer system ensures excellent corrosion protection for a metallic base material or substrate of an electrode plate, in particular a bipolar plate. An indium tin oxide is also referred to below as ITO (indium tin oxide).
The layer system is preferably formed by a PVD or a CVD process (PVD: physical vapor deposition; CVD: chemical vapor deposition) or a PACVD process (PACVD: plasma-assisted chemical vapor deposition).
Nanofibers are elongated or stem-like structures that have a diameter of up to 200 nm and a length of up to 1000 nm. The nanofibers can be tapered.
For the formation of a top layer made of a network of nanofibers, reference is made here to the publication “3D ITO-nanowire networks as transparent electrode for all terrain substrate”, Qiang Li et al., Scientific Reports (2019) 9:4983. Seeat: https://doi.org/10.1038/s41598-019-41579-2
The applicant could also produce ITO nanofibers for fuel cell, electrolysis and redox flow bipolar plates using non-reactive sputtering technology with a deposition rate of 40 Å/min and from a target made of In2O3:SnO2 with a concentration of 90:10 at %. The temperature and the SnO2 content are the main growth factors in the production of the ITO nanofibers. Growth occurs by atoms that are vaporized from the target and deposited on a substrate. The temperature range for the growth is 150° C. to 500° C. Increasing the temperature increases the mean fiber length and the mean diameter of the fibers, reduces the adjacent distance and increases the number of fibers per unit area. The SnO2 content is preferably a maximum of 30 at %. The development of the mean length and the mean diameter of the nanofibers depends on the deposition time. The ITO nanofibers preferably grow on a thin, dense ITO layer.
The preferred overall layer thickness of the layer system is <1 μm and is in particular in the range from 0.01 to 0.5 μm.
A concentration of the elements of the doping in the indium tin oxide is in particular in the range from <0 to 20 at %.
Particularly preferably, first coatings and top layers here are made of indium tin oxide which have an indium content in the range from 70 to 90 at %. Particularly preferably, indium contents are in the range from 75 to 85 at %, which have a high level of electrical conductivity.
In particular, the following layer systems for coating a metallic substrate, preferably made of steel, in particular austenitic steel or austenitic stainless steel, have proven to be advantageous for forming an electrode plate:
The object is achieved for an electrode plate comprising a metallic substrate and a layer system according to the disclosure with a structure of the electrode plate in the order: substrate, at least one first coating made of metal oxide and a top layer made of nanofibers.
The substrate preferably has a thickness in the range of 0.001 to 5 mm.
In particular, the substrate is formed from an iron alloy, in particular steel, or titanium or a titanium alloy or aluminum or an aluminum alloy or zinc or a zinc alloy or a tin alloy or copper or a copper alloy or nickel or a nickel alloy or silver or a silver alloy or chromium or a chromium alloy or based on graphite.
This is preferably an electrode plate with a metallic substrate or a metallic carrier plate. A carrier plate can be designed in one or more parts. In particular, the electrode plate is designed as a bipolar plate.
According to the disclosure, the method for producing an electrode plate according to the disclosure comprises the following steps: providing the substrate; forming the underlayer on a surface of the metallic substrate; forming the at least one first coating on the substrate, forming the top layer on the at least one first coating, wherein the at least one first coating and the top layer of metal oxide are formed on the substrate using non-reactive sputtering with an amorphous structure; and annealing the at least one first coating and the top layer at one temperature in the range of 220 to 400° C. in such a way that the amorphous structure is converted into a polycrystalline structure.
This is a deposition process that can be carried out cost-effectively on a series scale and can also be used to produce nanofibers.
The object is further achieved for a fuel cell, in particular an oxygen-hydrogen fuel cell, or an electrolyzer, in particular for producing hydrogen and oxygen from water, or a redox flow cell, in particular comprising at least one organic electrolyte, comprising at least one electrode plate according to the disclosure. The fuel cell preferably comprises at least one polymer electrolyte membrane.
In the test, the layer system showed stability up to at least 1.4 V in relation to Ag/AgCl ex situ under harsh fuel cell conditions in a 0.5-mM H2SO4 electrolyte at pH 3+0.1 ppm HF, and is therefore comparable to the precious metal coating. The contact resistance before and after this electrochemical load (see parameters above) is <3 mOhm·cm2 at a contact pressure of 100 N/cm2 and a measuring temperature of 24° C.
The corrosion currents are <10−7 A/cm2 under the relevant fuel cell application potentials up to 1.0 V in relation to Ag/AgCl.
No attack on the layer or substrate was detected optically or microscopically up to at least 1.4 V in relation to Ag/AgCl. A stainless steel substrate with the material number 1.4404 according to DIN was used as the substrate.
In the test, the layer system showed stability up to at least 2.2 V in relation to the NHE (normal hydrogen electrode) ex situ under harsh electrolysis conditions in an H2SO4 electrolyte at pH 4. The contact resistance before and after this electrochemical load (see parameters above) is <3 mOhm·cm2 at a contact pressure of 100 N/cm2 and a measuring temperature of 24° C.
No attack on the layer or substrate was detected optically or microscopically up to at least 2.2 V in relation to the NHE. A stainless steel substrate with the material number 1.4404 according to DIN was used as the substrate.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021128462.7 | Nov 2021 | DE | national |
The present application is the U.S. National Phase of PCT Patent Application Number PCT/DE2022/100729, filed on Sep. 30, 2022, which claims priority to German Patent Application Serial Number 10 2021 128 462.7, filed on Nov. 2, 2021, the entire disclosures of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2022/100729 | 9/30/2022 | WO |
