An immitance study of the mechanism of hydrogen reactions on a tungsten carbide electrode: Part I. Experiment and analysis in terms of a linear model

Abstract

The ac admittance spectra of a smooth tungsten carbide (WC) electrode in a stirred H 2-saturated 0.5 M H 2SO 4 solution were measured at hydrogen overpotentials from −0.15 to +0.25 V in the frequency range from 0.1 to 900 Hz, at a temperature of 80°C. An extended analysis of immitance spectra in diagrams of various coordinates led to an interpretation of the system under study at any potential in terms of a linear model which took into account the constant phase element behaviour of the electrode double layer and the presence of two parallel, activation-controlled faradaic processes: the hydrogen ionization/evolution process and an additional electrochemical adsorption reaction passivating the electrode surface for the hydrogen process. Computerized fitting of a rational equivalent circuit to the immitance spectra for all the potentials gave the dependences of the equivalent circuit elements on the potential. The fits proved that the mechanism of the faradaic processes taking place on the electrode is probably the same in the entire range of potentials.