METHOD OF MAKING MEMBRANE ELECTRODE ASSEMBLIES
A method of making a membrane electrode assembly is provided. The method includes providing a non-porous polymeric substrate which has sufficient structural integrity and elastic deformation such that no significant deformations occur during processing to facilitate reuse. The substrate is optionally formed into a loop for continuous processing. A slurry is formed which includes an ionically conductive material, an electrically conductive material, a catalyst, and a high boiling point solvent. The slurry is applied onto the non-porous polymeric substrate, for example, in a pattern of discrete regions. The slurry is dried to form decals. The decals are bonded to a membrane and then the substrate is peeled from the decal in a substantially undamaged condition so that it may be reused.
1 . A method of fabricating an assembly comprising an electrode in a continuous process comprising:
moving a continuous strip of a non-porous polymeric substrate along a feed path;
forming a slurry comprising an ionically conductive material, an electrically conductive material, a catalyst, and a casting solvent at a first station along said feed path;
advancing said continuous strip of said non-porous polymeric substrate to said first station;
applying said slurry at said first station to one or more discrete regions on a surface of said continuous strip of said non-porous polymeric substrate;
drying said slurry to form a film at each of said discrete regions;
advancing said continuous strip to position a membrane adjacent a respective one of said films at said discrete regions;
bonding said film to said membrane to form an electrode;
removing said electrode from said continuous strip;
advancing said continuous strip to a cleaning station to clean said discrete regions of said surface from which said electrode was removed; and
advancing said cleaned continuous strip of said substrate to said first station.
2 . The method according to claim 1 , wherein two continuous non-porous polymeric substrates move along two independent feed paths, and said advancing, applying, and drying occur simultaneously along said discrete regions of both of said continuous non-porous polymeric substrates forming a first and a second film, respectively, wherein said advancing of said discrete regions of both of said substrates positions said membrane between said first and second films, and wherein said bonding forms electrodes along two sides of said membrane.
2 . The method according to claim 1 , wherein said non-porous polymeric substrate comprises a polymer selected from the group consisting of: ethylene tetrafluoroethylene, polytetrafluoroethylene, polyimide, and polyphenylsulfone.
4 . The method according to claim 1 , wherein said slurry comprises water.
5 . The method according to claim 1 , wherein said casting solvent comprises an organic solvent.
6 . The method according to claim 1 , wherein said casting solvent has a boiling point greater than about 100° C.
7 . The method according to claim 1 , wherein said casting solvent is selected from the group consisting of: n-butanol, 2-pentanol, 2-octanol, butyl acetate, water, and mixtures thereof.
8 . The method according to claim 1 , wherein said bonding is accomplished by hot pressing at least one said film to said membrane and occurs at a temperature at or above the glass transition temperature of said ionomer, but below the glass transition temperature of said non-porous polymeric substrate.
9 . The method according to claim 1 , wherein said applying includes a coating process selected from the group consisting of: a printing and a spraying process.
10 . The method according to claim 1 , wherein said electrically conductive material comprises carbon and said catalyst comprises a metal.
11 . The method according to claim 1 , wherein said ionically conductive material is a perfluorosulfonate ionomer.
12 . The method according to claim 1 , wherein said cleaning is conducted with a solvent comprising an organic solvent.
13 . The method according to claim 1 , wherein said cleaning is conducted with a solvent selected from the group consisting of: propanol, isopropanol, ethanol, methanol, water, and mixtures thereof.