Mechanism of hydrogen generation on stable Mo-edge of 2H-MoS2 in water from density functional theory

Abstract

In this paper, the stable structure of Mo-edge of 2H-MoS2 in water and the H2 evolution mechanism at Mo-edge in 2H-Mo7S17 cluster were investigated by the B3LYP method of the density functional theory. The calculations suggested that the stable structure of the Mo-edge in gas and water was different. The Mo-edge with the upright S bonded by one Mo atom was more stable in water while the S atom of Mo-edge was bonded by two Mo atoms to generate a stable Mo-edge in gas. The adsorption energy of H on S was higher than that on Mo at Mo-edge; as a result, the hydrogen evolution reactions on S and Mo were limited by the Heyrovsky and Volmer step, respectively. In hydrogen evolution reaction, the Volmer reaction occurs on S to produce Mo7S17HS, leading to the aggregation of electron on Mo and thus decreasing the barriers for H2 evolution reaction on Mo. Subsequently, the Mo in Mo7S17HS severing as active sites efficiently catalyzed hydrogen evolution reaction through the Volmer–Heyrovsky mechanism, in which the Volmer reaction was identified as the rate-determining step with a potential barrier of 17.9 kcal/mol, being close to the experimental value of 19.9 kcal/mol.