Fourier transform electrochemical impedance spectroscopic studies on platinum electrodes in an acidic medium

The platinum electrode/electrolyte interface has been characterized in 0.50 M H2SO4 by staircase cyclic voltammetry–Fourier transform electrochemical impedance spectroscopy combined experiments in a wide potential range. From analysis of a large body of data, we propose a single equivalent circuit for the description of the interface, which accommodates impedance responses from capacitance dispersions, hydrogen underpotential deposition (H-UPD), and Faradaic reactions in 0.50 M H2SO4 within the potential range of 0.05–1.5 V. Analysis of the impedance data revealed that the equivalent circuits reported in the literature in specific potential regions represent specific forms of the circuit proposed here. The capacitance dispersions are rather small in H-UPD and oxide-covered capacitive regions due to large double-layer capacitances in relation to pseudo-capacitances. Electrochemical oxidation of platinum and its oxide reduction are shown to proceed via two step one-electron-transfer reactions and their respective kinetic parameters are reported.