Process for producing a membrane electrode assembly and the membrane electrode assembly produced thereby
The invention comprises a process for making a membrane electrode assembly comprising a polymer electrolyte membrane having two opposite faces, on each face of which is applied a catalyst layer and a gas distribution layer. The two gas distribution layers in the membrane electrode assembly are formed by hydrophobized carbon substrates which, using appropriate inks containing at least one catalyst, dissolved ionomer and solvent, are each coated with a catalyst layer and are then laid on opposite faces of the polymer electrolyte membrane with the catalyst layers still in the moist state. Afterwards, a firm bond between electrolyte membrane, catalyst layers and carbon substrates is produced by treating the membrane electrode assembly at elevated temperature under pressure.
1. A method of making a membrane electrode assembly, comprising:
(a) applying a gas distribution layer to each opposite face of a polymer electrolyte membrane having two opposite faces, wherein the gas distribution layer on each opposite face is formed by hydrophobized carbon substrates, and wherein the hydrophobized carbon substrates have one or more inks with at least one catalyst, a dissolved ionomer and solvent, so as to form a catalyst layer, on each opposite face of the polymer electrolyte membrane; and,
(b) treating the membrane electrode assembly at elevated temperature under pressure while the catalyst layers are moist, so as to establish a firm bond between the electrolyte membrane, the catalyst layers, and the hydrophobized carbon substrates, thereby making a membrane electrode assembly.
2. A method according to claim 1 , wherein hydrophilic inks are employed to produce the catalyst layers.
3. A method according to claim 2 , wherein the inks contain water as the main solvent.
4. A method according to claim 1 , wherein prior to making the electrode assembly the polymer electrolyte membrane is pre-swollen in the solvent employed for the catalyst layers.
5. A method according to claim 1 , wherein polytetrafluoroethylene is loaded onto the carbon substrate, and wherein the polytetrafluoroethylene loading on the carbon substrate is between about 1% and about 30% by weight, with respect to the total weight of the hydrophobized carbon substrate.
6. A method according to claim 1 , wherein in step (b), the membrane electrode assembly is treated for about one to about ten minutes with a temperature between about 70 ° C. and about 100 ° C. and a pressure between about 1 and about 5 bar, and then treated for about one to about ten minutes at a temperature between about 120 ° C. and about 145 ° C. and a pressure between about 10 and about 120 bar.
7. A membrane electrode assembly for polymer electrolyte membrane fuel cells, comprising:
a polymer electrolyte membrane with two opposite faces, wherein one face forms an anode side of a fuel cell, and the second face forms a cathode side of a fuel cell;
a catalyst layer disposed on the cathode and the anode side; and,
a gas distribution layer on each side of the anode and cathode sides, wherein the gas distribution layers comprise a hydrophobized carbon substrate, the gas distribution layers are in direct contact with the catalyst layers in the membrane electrode assembly, and the membrane electrode assembly is made while the catalyst layers are moist.
8. A membrane electrode assembly according to claim 7 , wherein the hydrophobized carbon substrate is selected from the group consisting of a carbon fiber fabric, a carbon fiber non-woven, a graphite felt, and carbon fiber paper.
9. A membrane electrode assembly for fuel cells, made by the process of claim 1 .