Cyclic voltammetry study of arsenic in acidic solutions

An electrochemical investigation of arsenic species in acidic solutions, using cyclic voltammetry at a platinum rotating disk electrode, has been carried out. A well defined peak at about 1 V_SCE, with a large overpotential (>0.5 V) is attributed to the oxidation of As(III) to As(V). The reaction is under the mixed control of ionic transport and charge transfer. The corresponding reduction of As(V) is not observed in the potential range of the study (-0.6 to +1.2 V_SCE). As(V) is not electrochemically active in this range and it has no effect on hydrogen evolution. With As(III) in solution, hydrogen evolution on Pt is shifted towards more negative potentials and it takes place simultaneously with arsine production. A small cathodic peak at -0.2 V_SCE and a corresponding anodic peak at +0.3 V_SCE are attributed to the deposition of a thin layer of As by reduction of As(III) and its dissolution.