The dissolution of Pt(100), Pt(110), and Pt(111) single crystal surfaces under potential cycling conditions in 0.5 M H2SO4 solution was investigated by electrochemical measurements, ICP-MS analyses, and EC-STM observations. Pt(111) surface had higher corrosion resistance than Pt(100) and Pt(110) during potential cycles in 0.5 M H2SO4 solution, and hardly dissolved in the potential range below 1.2 V. EC-STM observations revealed the step structures became straight in the Pt(100) surface and the roughness in Pt(111) terraces gradually increases by the potential cycling in the range of 0.5 – 1.4 V. The formation of Pt islands with a higher surface energy by the potential cycling brought the increase of Pt dissolution rate in the Pt(111) surface with the number of cycle.

Microelectrochemical polarization measurements of polycrystalline Pt were performed to clarify the effect of the crystal orientation and grain boundary on the surface oxidation of Pt. Cyclic voltammograms (CV) for Pt(100)-like and Pt(110)-like grains on polycrystalline Pt after mechanical polishing showed no anodic peak below 1.35 V, which is similar to that for well-annealed Pt(111) single crystal. The anodic current of Pt(110)-like grain was significantly larger than Pt(100)-like. A small but concrete current increase appeared around 1.051.3 V in the CV of the surface including grain boundaries. This suggests the grain boundary may be the preferential site for the dissolution.

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