Hydrogen evolution reaction on metallic rhenium in acid media with or without methanol

Abstract

The cathodic behavior of metallic rhenium in acid media in the presence of absence of methanol was studied in this report. Voltammetry, polarization curve and the impedance spectra were analyzed to determine the behavior of the hydrogen evolution reaction (HER) on polycrystalline rhenium. Only one single charge transfer resistance was observed, and then Randles equivalent circuit fulfills the impedance characteristics of the HER on metallic rhenium. Exchange density current in acid media, with or without methanol, is in the order of magnitude of ∼10−6 Acm−2, and Tafel slope is 63 ± 4.66 mV decade−1. The HER on rhenium proceeds via the Volmer–Heyrovsky reaction mechanism in all solutions. The electrodes were polarized at −0.1 V, and subsequently ex-situ XPS experiments were performed after removal of the electrodes from the electrolyte, with or without methanol. Ex-situ XPS spectra indicate that the atomic surfaces consist of Re0 and suggest a minor formation of Re1+. In addition, XPS spectra suggest that the Volmer–Heyrovsky reaction mechanism generate adsorbed water (H2Oads). These molecules dissociate and generate adsorption of hydroxyl groups (HOads). It is proposed that the HER electroactivity on rhenium is directly strengthened by the interaction between hydrogen ad-atom (Hads) and protonated species, which are different in solutions with or without methanol. The H-bonds formed in sulfuric acid−methanol−water probably required higher energy to surpass the energy barrier in the Heyrovsky reaction. The HOads species can effectively prevent the Hydrogen Oxidation Reaction, the Hydrogen under-potential deposition and methanol adsorption.