Can hydrogen anion be a possible intermediate of the hydrogen electrode reaction?

Abstract

• New mechanism for the hydrogen evolution reaction (HER) proposed. • Hydride anion formation investigated as possible reaction intermediate. • Potential range of stability of hydride anion depends on work function of electrode. • Potential range of stability of hydride anion depends on dielectric constant of solvent. • Rate determining term approach used to predict Tafel slope of HER. We discuss the possibility of a new mechanism for the hydrogen evolution reaction (HER) involving hydrogen anion as the reaction intermediate. A simple thermodynamic analysis reveals that this mechanism is unfavourable at most relevant catalysts in aqueous solution in the usual potential range encountered for the HER. Its likelihood, however, increases when the dielectric permittivity of the electrolyte solution decreases, the work function of the catalyst decreases, and when the electrode potential decreases. We suggest that carbon-based catalysts with low dielectric constant solvents, such as n -Hexane, are plausible systems to observe hydrogen anion as the intermediate for hydrogen reactions. In the cases where the proposed HER mechanism is permissible, values of Tafel slope are calculated using a simple kinetic analysis based on the rate-determining term concept.