Hydrogen Evolution Mechanism on Pt Surface in NonAcidic Media: A DFT Study

Abstract

Noble metal Pt is a very classic hydrogen evolution catalyst and its activity can be markedly affected by the pH of electrolyte solution. In acidic media, the hydrogen evolution reaction (HER) on Pt follows the Tafel-step-limited Volmer-Tafel mechanism. However, the detailed hydrogen evolution mechanism of Pt in nonacidic media and the key factors influenced its activity are still unclear. Herein, the nonacidic hydrogen evolution mechanisms of Pt were systematically investigated by the density functional theory (DFT) method. The calculations indicate that Pt catalyzes nonacidic HER by the H₂O dissociation-limited Volmer-Tafel mechanism and OH originated from H₂O dissociation can observably reduce the HER rate of adjacent Pt atom. The adsorbed H and OH on top site generate an increased barrier for H₂O dissociation on adjacent Pt atom and the effect of OH is more remarkable. More importantly, the adsorbed OH causes that adjacent Pt atom loses its activity for catalyzing the Tafel reaction. The low activity of Pt in alkaline solution may be from the strong function of adsorbed OH⁻ in retarding H₂O dissociation reaction.