Gold electrocatalyst, methods for preparing it, electrodes prepared

Abstract

The disclosed electrocatalyst material is useful in electrodes, especially in cathodes for the reduction of oxygen or peroxide to water or hydroxide. The electrocatalyst typically comprises 0.1 to 20 weight-%, based on the weight of the material, of a supported particulate elemental gold wherein the particles are apparently crystalline in nature, apparently with exposed (100) faces, but smaller in size than 5 nanometers (<50.ANG.). These tiny monocrystals of gold are supported on carbon back or particulate conductive ceramic-like compounds having a B.E.T. surface area of at least 50 m.sup.2 /g. The supported gold monocrystals appear to be selective for the reductions described above, and performance in air- or O.sub.2 -cathodes is outstanding, e.g. >0.7 volt vs. RHE at 200 mA/cm.sup.2, generally indicating a substantial proportion of four-electron change reactions when oxygen is being reduced. The electrodes (which are also useful as anodes in acid electrolytes) are made by impregnating the support material with a reducible gold compound dissolved in a polar solvent, gently evaporating the solvent, and chemically reducing the gold compound in situ at a moderate temperature with a flowing reducing gas (e.g. H.sub.2), then applying the resulting supported gold to a porous backing material. Typical gold content levels at the electrode surface are <2 mg/cm.sup.2. Cathodes of this invention are useful in various types of air or oxygen-depolarized cells, alkaline fuel cells, metal/air c