OXYGEN REDUCTION ON RU-OXIDE PYROCHLORES BONDED TO A PROTON-EXCHANGE MEMBRANE

Oxygen reduction at a gas-fed, porous, ruthenium-pyrochlore electrode attached to a Dow Developmental Fuel Cell Membrane was measured in solutions of various pH. Electrode assemblies containing high surface area Pb2Ru(2-x)Pb(x)O7-y or Bi2Ru(2-x)Bi(x)O7-y with different amounts of Teflon content with/without the incorporation of Dow gel in the active part of the electrode with/without a CO2-treated Vulcan XC-72 carbon substrate were tested. The oxide pyrochlores were found to be chemically stable and to show their lowest overpotential if separated from a 2.5 M H2SO4 proton reservoir by the membrane. Interesting oxygen reduction activity at room temperature was obtained with the Pb2Ru1.74Pb0.26O7-y electrode bonded with 22% by weight Teflon and incorporating 5% by weight Dow gel. The performance of the oxides against B-site Pb concentration and the measurement of the surface charge on the particles indicate that, in this configuration, the active sites for the oxygen reduction reaction are OH- species at the O-site positions of the A2B2O6O'1-y pyrochlores, especially the bridging oxygen with one Ru and one Pb near neighbour, i.e. Pb-O(b)-Ru. Evidence that oxide particles precipitated on CO2-treated carbon transfer electrons to the substrate is also presented.