Membrane-electrode assembly for a direct methanol fuel cell

DETAILED DESCRIPTION The present invention is an MEA and a method of fabricating an MEA which can be used in a direct methanol PEM fuel cell.
The MEA includes a partially reduced metal oxide anode porous electrode structure which can operate directly on a liquid or vapor methanol/water feed without the addition of a liquid electrolyte, a proton-exchange membrane electrolyte, and an efficient cathode gas-diffusion electrode.
In this invention, a proton-exchange membrane is used as the sole electrolyte, and an intimate partially reduced metal oxide porous electrode-PEM contact is maintained throughout the structure.
In the partially reduced metal oxide anode porous electrode-PEM structure, a film of ionomer is formed from the face of the electrode in contact with the PEM extending back into the porous electrode toward the current collector.
The catalyst particles that make intimate electronic contact with each other and with the current collector are coated with a thin solid ionomer film.
There is a continuous ionomer proton-conducting ionic linkage throughout the porous electrode-solid ionomer composite structure that extends into the PEM, thus there is a continuous mechanism for rapid proton transport from the current collector to the PEM.
The partially reduced catalyst particles, (Pt--Ru)O.
sub.
x, used in the anode electrode structure are prepared in a very-high-surface-area (70 m.
sup.
2 /g or greater) form.
The particulate material is then coated with ionomer and fabricated into a porous electrode forming a high-surface-area interface with the solid ionomer-coated film and bonded to the solid PEM.
It has been found that 1) ionomer coating the very-high-surface-area partially reduced catalyst particles, (Pt--Ru)O.
sub.
x, 2) forming a porous electrode from the coated particles, 3) integrally bonding the porous electrode to one side of a PEM, 4) integrally bonding a methanol-tolerant Teflon-bonded Pt black cathode structure to the opposite side of the PEM to form a complete MEA, and 5) placing the MEA in conventional fuel cell hardware, a device is obtained which, when liquid methanol/water is flowed across the solid ionomer-coated porous electrode, and pure O