Method for producing a green paper for producing a gas diffusion layer for a fuel cell
A method is provided for producing a green paper for producing a gas diffusion layer (GDL) for a fuel cell. A use is described of an accordingly produced gas diffusion layer (GDL) in a fuel cell. A first paper web is loaded with metal powder and/or metal fibers, and a microporous layer (MPL) is in the form of at least one coating is applied onto the paper web. The paper web is then subjected to a binder removal process, a sintering process, a coating process, atomic layer deposition (ALD) using thermal ALD methods, and optionally additional process steps in order to obtain the final GDL. After the sintering process, all of the organic components of the green paper are pyrolyzed and thus no longer contained in the GDL, and the GDL consists virtually exclusively of a metal framework.
1 . A process for producing a green paper for production of a gas diffusion layer (GDL) for a fuel cell,
wherein a first paper web is produced, with added metal powder and/or metal fibers, and a microporous layer (MPL) in the form of at least one coating is applied to the first paper web,
wherein a watermark is made in the first paper web such that the watermark defines one or more flow field channels.
2 . The process according to claim 1 , wherein the at least one coating is applied to the paper web by a paper coating method, a screenprinting method or plasma coating.
3 . The process according to claim 2 , wherein the at least one coating is applied to the paper web prior to sintering of the green paper and includes a powder having a grain size of 0.4 μm to 5 μm, with the powder present in an organic binder matrix in paper coating methods or screenprinting methods.
4 . The process according to claim 2 , wherein the coating is applied to the paper web after the green paper has been sintered.
5 . The process according to claim 1 , wherein the coating takes the form of multiple plies, where the different plies have different grain sizes and/or different layer thicknesses and/or are applied partially and/or in a structured manner on the side of the green paper facing a catalyst layer (CL) or a bipolar plate (BPP) in the fuel cell.
6 . The process according to claim 1 , wherein the application of the coating is preceded by formation of at least one further paper web, which is combined with and bonded to the first paper web in a still-moist state.
7 . The process according to claim 6 , wherein the first paper web and/or each further paper web is produced in a cylinder paper machine and/or in a short former in which the paper stock is jetted onto a cylindrical screen.
8 . The process according to claim 6 , wherein the application of the coating is preceded by formation of a second paper web, wherein the first paper web has a higher density than the second paper web, where the first paper web has a density of 3 g/cm 3 to 10 g/cm 3 and the second paper web a density of 1 g/cm 3 to 5 g/cm 3 .
9 . The process according to claim 8 , wherein the first paper web is formed by a finer paper fiber slurry than the second paper web.
10 . The process according to claim 6 , wherein the application of the coating is preceded by formation of a second paper web, wherein the first paper web in the gas diffusion layer (GDL) produced from the green paper forms a diffusion layer for a membrane (CL) coated with catalytic metal, including platinum, and the second paper web forms a distribution layer with a flow field in the gas diffusion layer (GDL) produced from the green paper.
11 . The process according to claim 1 , wherein the watermark is a true watermark where the thickness of the paper varies, but the density of the paper does not vary, and/or in that the watermark is an artificial watermark where the thickness of the paper is reduced, but the density of the paper is simultaneously increased.
12 . The process according to claim 1 , wherein the application of the coating is preceded by formation of a second paper web, which is combined with and bonded to the first paper web in a still moist state, wherein the first paper web and a second paper web each have a watermark comprising watermark structures, where the watermark structures of the first paper web and of the second paper web are not identical, but have exact mirror symmetry in the plane and in the direction of material thickness.
13 . The process according to claim 1 , wherein the green paper has a gram weight of 100 g/m 2 to 1200 g/m 2 .
14 . The process according to claim 1 , wherein the metal powders and/or metal fibers comprise titanium, copper, zinc, and/or rust-free stainless steels.
15 . A gas diffusion layer (GDL) that has been produced from a green paper according to claim 1 , wherein the gas diffusion layer is configured for use in a proton exchange membrane fuel cell (PEMFC), in a proton exchange membrane electrolyzer cell (PEMEC), in electrolyzer cells or any other power-to-X technology that requires correspondingly porous conductive material for gas/power/reactant distribution.
16 . A process for producing a green paper for production of a gas diffusion layer (GDL) for a fuel cell,
wherein a paper web is produced, with added metal powder and/or metal fibers, and a microporous layer (MPL) in the form of at least one coating is applied to the paper web,
wherein a watermark is made in the paper web such that the watermark defines one or more flow field channels, and
wherein the paper web comprises of paper made from cellulose fibers.
17 . The process according to claim 16 , wherein the paper web further comprises cotton fibers.
18 . The process according to claim 16 , wherein the metal powders and/or metal fibers comprise titanium, copper, zinc, and/or rust-free stainless steels.