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The hydrogen evolution reaction on the low index planes of single-crystal Au electrodes has been studied in HClO4 solutions with the aim of ascertaining the extent of the sensitivity of the reaction rate to the surface crystallographic structure. The use of the hanging meniscus rotating disk technique allowed to carry out all measurements under rotation, thus avoiding blocking effects produced by hydrogen bubbles and accumulation of dissolved hydrogen in the interfacial region during potential excursions into relatively high overpotentials. In contrast with previously published results showing only slight variations in activity with Au crystal face, a pronounced structural sensitivity is reported for the first time. The catalytic activity presents the following sequence Au(111) > Au(100) > Au(110).

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a b s t r a c tThe particle size effect for ethanol oxidation on carbon supported platinum catalysts in the Pt particle size range from 2.2 to 3.6 nm was investigated both in half-cell and in a single direct ethanol fuel cells (DECF). The specific activity for ethanol oxidation presented a maximum at a Pt particle size of 2.5 nm, ascribed to the best compromise between structural effects and/or oxophilicity effects of the Pt surface. In DEFCs, the particle size effect at the anode side was less significant than that observed in half-cell measurements, likely due to concomitant effects of ethanol oxidation products on the oxygen reduction at the cathode side.