Membrane catalyst layer for fuel cells

• US 5,211,984 A
• Filed: 12/20/1991
• Issued: 05/18/1993
• Est. Priority Date: 02/19/1991
• Status: Expired due to Term

• Current Assignee: Los Alamos National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Wilson, Mahlon S.
• Primary Examiner(s): KALAFUT, STEPHEN J
• Application Number:
  US07/811,220
• Time in Patent Office: 515 Days
• Field of Search: 427/115, 429/33, 429/42
• US Class Current: 427/115
• CPC Class Codes: H01M 2300/0082 Organic polymers
• CPC Class Codes: H01M 4/926 on carbon or graphite
• CPC Class Codes: H01M 8/1004 characterised by membrane-electrode assemblies [MEA] H01M8/12 takes precedence
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

A gas reaction fuel cell incorporates a thin catalyst layer between a solid polymer electrolyte (SPE) membrane and a porous electrode backing. The catalyst layer is preferably less than about 10 μm in thickness with a carbon supported platinum catalyst loading less than about 0.35 mgPt/cm². The film is formed as an ink that is spread and cured on a film release blank. The cured film is then transferred to the SPE membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and catalyst distribution. Alternatively, the catalyst layer is formed by applying a Na⁺ form of a perfluorosulfonate ionomer directly to the membrane, drying the film at a high temperature, and then converting the film back to the protonated form of the ionomer. The layer has adequate gas permeability so that cell performance is not affected and has a density and particle distribution effective to optimize proton access to the catalyst and electronic continuity for electron flow from the half-cell reaction occurring at the catalyst.

Claims

1. A method for fabricating a SPE membrane assembly for use in a gas reaction fuel cell, comprising the steps of:

furnishing a SPE membrane in Na⁺ form;

furnishing a perfluorosulfonate ionomer in a Na⁺ form or thermoplastic form;

uniformly dispersing a supported Pt catalyst and a solvent in said Na⁺ or said thermoplastic form of said ionomer to form an ink;

forming a film of said ink containing a predetermined amount of said catalyst on a surface of said SPE membrane in said Na⁺ form;

heating said film of said ink to a temperature effective to dry said ink; and

converting said film of said ink and said SPE membrane to a protonated form of perfluorosulfonate.

2. A method according to claim 1, wherein the step of furnishing said perfluorosulfonate ionomer in a Na⁺ form includes the step of adding NaOH to a protonated form of said perfluorosulfonate ionomer.

3. A method according to claim 1, further including the step of maintaining said membrane in a planar condition on a vacuum table while forming said film of said ink on said membrane.

4. A method according to claim 1, wherein the step of furnishing said perfluorosulfonate ionomer in a thermoplastic form includes the step of ion-exchange of a hydrophobic cation with said perfluorosulfonate.

5. A method according to claim 4, wherein said hydrophobic cation is tetra-butyl ammonium.