Patent Application
20240421326
The disclosure relates to a coating system for coating a metal substrate to form an electrode plate, comprising at least one top coat made of metal oxide. The disclosure further relates to an electrode plate comprising a metal substrate and to such a coating system and to 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. A dopant which 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 an object of the disclosure to provide an improved coating system for an electrode plate and to provide such an electrode plate. Furthermore, it is an 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 solved by the coating system for coating a metal substrate to form an electrode plate, comprising at least one top coat made of metal oxide, at least one intermediate coat carrying the top coat and a base coat carrying the intermediate coat(s),
The coating system is characterized by high long-term stability with simultaneously high electrical conductivity and low costs, since it dispenses with noble metal. In addition, the coating system ensures excellent corrosion protection for a metallic base material or substrate of an electrode plate, in particular a bipolar plate. Indium tin oxide is also referred to below by the abbreviation ITO.
The coating system is preferably formed using 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 elongate 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 coat from 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. See below: https://doi.org/10.1038/s41598-019-41579-2
The applicant was also able to 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 through atoms that are vaporized from the target and deposited on a substrate. The temperature range for growth is 150° C. to 500° C. Increasing the temperature increases the mean fiber length and the mean diameter of the fibers, reduces the neighbor distance and increases the number of fibers per unit area. The SnO2 content is preferably a maximum of 30 at %. Development of the mean length and the mean diameter of the nanofibers depends on deposition time. The ITO nanofibers preferably grow on a thin, dense ITO layer.
Such nanofiber production is also possible on the basis of doped tin oxide.
The first dopant preferably corresponds to the third dopant and the second dopant preferably corresponds to the fourth dopant.
A concentration of the elements of the first and/or third dopant in the indium tin oxide is in particular in the range of >0 to 20 at %, preferably in the range of 0.5 to 20 at %.
A concentration of the elements of the second and/or the fourth dopant in the tin oxide is in particular in the range of >0 to 20 at %, preferably in the range of 0.5 to 20 at %.
Top coats made of indium tin oxide which have an indium content in the range of 70 to 90 at % are particularly preferred here. Indium contents in the range of 75 to 85 at % are particularly preferred which have a high level of electrical conductivity.
The base coat is used in particular as an adhesion promoter between a metal substrate and the at least one intermediate coat. Furthermore, the base coat forms conductive oxides and thus provides galvanic corrosion protection for the metal substrate of a bipolar plate. The base coat preferably has a coat thickness in the range of 1 nm to 300 nm.
In particular, the intermediate coat is also used as an adhesion promoter between the base coat and the top coat. Furthermore, depending on the selection, the at least one intermediate coat can form conductive oxides and thus provide galvanic corrosion protection for the base coat and the metal substrate of an electrode plate. The at least one intermediate coat also provides a barrier for hydrogen, preventing it from penetrating toward the metal substrate and damaging it. A coat thickness of an individual intermediate coat is preferably selected in the range of 0.1 to 3.0 μm. However, there can be two or more intermediate coats.
The top coat protects the base coat and the intermediate coat(s) mechanically and from corrosive attack. The top coat in particular has a coat thickness in the range of 0.01 to 15 μm, in particular in the range of 0.1 to 3 μm.
The coating system according to the disclosure, comprising the base coat, at least one intermediate coat and the top coat, preferably has a total thickness in the range of 0.1 to 20 μm.
In particular, the following coating systems for coating a metal substrate, preferably made of steel, in particular austenitic steel or austenitic stainless steel, have proven to be advantageous for forming an electrode plate:
Top coat: Indium tin oxide nanofibers with 90 vol % indium content Coat thickness: 100 nm
The object is achieved for an electrode plate comprising a metal substrate and a coating system according to the disclosure with an electrode plate structure in the following order:
The electrode plate preferably comprises a metal substrate or a metal carrier plate, preferably made of steel, in particular made of austenitic steel or stainless steel. Alternatively, the substrate may be formed of 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.
A carrier plate can be designed to be single-or multi-part. 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:
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 coating system exhibited 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 noble metal coating. The contact resistance before and after this electrochemical loading (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 coating 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 coating system exhibited 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 loading (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 coating 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.
Opening
| Number | Date | Country | Kind |
|---|---|---|---|
| 102021128468.6 | Nov 2021 | DE | national |
This application is the U.S. National Phase of PCT Appln. No. PCT/DE2022/100476, filed Jun. 30, 2022, which claims the benefit of German Patent Appln. No. 102021128468.6, filed Nov. 2, 2021, the entire disclosures of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2022/100476 | 6/30/2022 | WO |
