Non-stoichiometric molybdenum sulfide clusters and their reactions with the hydrogen molecule

Abstract

Structures of non-stoichiometric Mo_xS_y clusters (x = 2–4; y = 2–10) were studied by density functional calculations with global optimization. Besides 1T phase like structures, a novel regular grid structure in which Mo atoms are well separated by S atoms was found, which might be used as a building-block to construct a new type of two-dimensional molybdenum sulfide monolayer. The hydrogen molecule prefers to be adsorbed onto Mo atoms rather than S atoms, and Mo atoms with less S coordination have a higher ability to adsorb H₂. In addition, the reaction pathways for H₂ dissociation were studied on two clusters with the highest H₂ adsorption energy (Mo₂S₄ and Mo₃S₃). The vacant bridge site of Mo–Mo in S-deficient clusters, which corresponds to the sulfur vacancy in the bulk phase MoS₂, is favored by H atom adsorption and plays an important role in the H atom transfer on Mo_xS_y clusters. Our results provide a new aspect to understand the reason why S defect in MoS₂ and MoS₂ with an Mo-edge could enhance the catalytic performance in the hydrogen evolution reaction.