Electrocatalytic behaviour of MoPt3 intermetallic phase for hydrogen evolution in acid solution

Abstract

Metallurgicaly prepared MoPt3 intermetallic compound has been investigated as electrocatalyst for the cathodic evolution of hydrogen (HER) in 0.5 mol dm-3 HClO4 solution at 298 K. The HER on activated and non-activated electrode has been studied by means of classical steady-state voltammetry and ac impedance spectroscopy measurements. Within the potential range of E = 0,00 - (-0.08) V (RHE), the mechanism of the HER on activated MoPt3 electrode, can be realised as a consecutive combination of the electrosorption of Hads species (Volmer step), followed dominantly by the chemical recombination of Hads species to form H2 (Tafel step), while the contribution of the parallel electrodesorption step (Heyrovski step) is negligible. For potentials E < - 0.080 V (RHE), at practically full coverage of Hads on the electrode surface (θH → 1), the mechanism is a consecutive combination of the Volmer step, followed by Heyrovski step. At the non-activated MoPt3 electrode HER is described by the same mechanism, but full coverage on the electrode was reached when 14% of the available sites on the electrode surface were occupied by Hads. The Tafel step controls the rate of the HER up to E = - 0.080 V (RHE), and a curvilinear shape of the curve is a result of the influence Hads coverage (θ H) on the rate of the Tafel step.