Method for the production of membrane electrode assemblies for fuel cells
The present invention relates to a method for the production of a membrane electrode assembly comprising a polymer electrolyte membrane with two opposing membrane surfaces and a cathode and an anode electrode each comprising a catalyst layer and a gas distribution layer. Each catalyst layer is interposed between a membrane surface and the corresponding gas distribution layer. The catalyst layer of the cathode and/or the catalyst layer of the anode comprise at least two sub-layers. According to the present invention at least one of the sub-layers of the cathode electrode and/or the anode electrode is applied directly to the surface of the membrane while the remaining sub-layers are applied to the corresponding gas distribution layers. Finally the assembly of the coated membrane and the coated gas distribution layers is produced.
1. A method for manufacturing a membrane electrode assembly comprising a polymer electrolyte membrane, with two opposing membrane surfaces, and a cathode electrode and an anode electrode, each electrode comprising a catalyst layer and a gas distribution layer, and each catalyst layer is interposed between one membrane surface and the gas distribution layer corresponding to the catalyst layer's electrode, and wherein the catalyst layer of the cathode electrode or the catalyst layer of the anode electrode or both comprises at least two sub-layers, the method comprising applying at least one of the sub-layers directly to the membrane surface and the remaining sub-layers to the gas distribution layer corresponding to the sub-layer's electrode before assembly of the membrane electrode assembly, wherein the sub-layer or sub-layers applied directly to the membrane are manufactured from one or more catalyst inks containing mainly organic solvents and the sub-layers applied to the gas distribution layers are manufactured from one or more catalyst inks containing mainly water.
2. The method according to claim 1 , wherein the assembly of the membrane electrode assembly is carried out by combining the membrane coated with catalyst layers with the two gas distribution layers coated with catalyst layers at pressures lower than about 5 bar and at temperatures lower than about 100° C.
3. The method according to claim 1 , wherein the catalyst inks containing mainly water comprise a total water content of about 50 to about 90 wt.-% and the catalyst inks containing mainly organic solvents comprise a content of organic solvents of about 50 to about 90 wt.-%.
4. The method according to claim 3 wherein the application of the sub-layers onto the membrane and the gas distribution layers is accomplished by coating methods selected from the group consisting of screen printing, offset printing, transfer printing, stencil printing, doctor blading or spraying.
5. The method according to claim 4 , wherein the application of the sub-layers onto the membrane and the gas distribution layers comprises drying of the sub-layers at temperatures in the range of about 50 to about 150° C.
6. A membrane electrode assembly for membrane fuel cells, having a cathode electrode with an associated catalyst layer and an anode electrode with an associated catalyst layer, wherein one or both of the catalyst layers each comprises at least two catalyst-containing sub-layers of different hydrophobicities.
7. A membrane electrode assembly for membrane fuel cells manufactured according to the method according to claim 1 .
8. A polymer electrolyte fuel cell or a direct methanol fuel cell comprising the membrane electrode assembly produced according to the method in claim 1 .