Abstract: in φ-lgi relations steady-state were determined for the O₂ evolution on Pt electrode in HClO₄ and H₂SO₄ solutions of concentrations from 0.05-40mol·kg^-1. There are three regions on the φ-lgi curves. The first is the lower overpotential region with ∂φ/∂lgi = 2.303RT/βF(β= 0.5), followed by the second potential jump region, and then the third regionagain with a Tafel slope of approximately to 2.303θRT/βF. The reaction order of O₂ evolu-tion with respect to a_w was found to be 1 in the first and second regions, while in the third region the reaction order of O₂ evolution with respect to a_w·a_ClO4^- or a_w·a_HSO4^-was found to be 1/2. Possible mechanisms for oxygen evolution were proposed. Some of them explain quite satisfactorily the difference in Tafel slope in different region of polarization curves and thevarious order of reaction with respect to different reactants.

Key words: oxygen evolution, platinum anode, kinetics, mechanism