Voltammograms of the single-crystal electrodes of palladium in aqueous sulfuric acid electrolyte: Pd(S)-[n(111)×(111)] and Pd(S)-[n(100)×(111)]

A series of Pd(S)-[n(111)×(111)] and Pd(S)-[n(100)×(111)] electrodes give voltammograms in 0.5 M H2SO4, which depend remarkably on the surface structure. Pd surfaces with more than three atomic rows of terrace show redox peaks due to the desorption and adsorption of HSO4−/SO42− between 0.25 and 0.33 V (RHE). In the oxide film formation region, Pd(S)-[n(111)×(111)] electrodes give two anodic peaks at 0.95 and 1.1 V (RHE): the charge of the former peak increases with the increase of the step atom density, whereas that of the latter depends linearly on the terrace atom density. Pd(S)-[n(100)×(111)] electrodes provide an anodic peak at 0.93 V (RHE). The charge correlates with the terrace width. These electrodes give no peak for which the charge depends on the step density.