Fast faradaic processes observed during the potentiodynamic polarization of polycrystalline palladium in acid electrolyte

Abstract

Two almost reversible electrochemical systems are detected during the potentiodynamic anodization of polycrystalline palladium in 1 M H2SO4 and 1 M HClO₄ by applying the triangular modulated triangular potential sweep technique. The first electrochemical system which appears in the 0.7–0.9 V range (vs. RHE) corresponds to the reaction Pd+H₂O=PdOH+H⁺+e⁻ whose reversible potential is estimated as 0.80±0.02 V and the average half-life time of PdOH species is estimated as 6×10⁻³ s. The second electrochemical system appears when the anodizing potential sweep extends to the oxygen evolution potential region. The appearance of the second electrochemical system is accompanied by a change in colour of the electrode surface, a shift of the current-potential curve of the oxygen evolution reaction and an increase in thickness of the oxide anodic layer. The reversible response is tentatively assigned to the PdO₂/PdO₃ redox couple.