Hydrodynamic voltammetry and hydrodynamically modulated voltammetry at a disk electrode, and shielding experiments at a ring-disk electrode, were applied in a study of the electrochemical response of As (III). The adsorption of As(III) occurs at Pt electrodes with partial charge transfer. The adsorption isotherm was determined and a maximum coverage is established for CbAS(m~ > 6 X 10 ~M. The oxidation of As(III) is electrocatalyzed dramatically by formation of PtOH on the electrode, but is slow for a surface covered by a well developed layer of PtO. The rate-determining step (rds) for As(III) oxidation at the PtO-covered electrode does not involve charge transfer in the region E = 0.9 -1.2V vs. SCE. The log of the rate constant for the rds measured at 1.1V decreases linearly with the increasing charge equivalent to the surface oxide. The oxidation of As(III) at an oxide-covered electrode is catalyzed by evolution of O2(g). The electrocatalysis is concluded to be the result of -OH generated at the electrode surface.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 129.108.9.184 Downloaded on 2014-08-18 to IP

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