Catalytic activity for hydrogen evolution reaction in square phase Janus MoSSe monolayer: A first-principles study

Abstract

Based on density-functional theory, the catalytic property for hydrogen evolution reaction (HER) of square phase Janus MoSSe monolayer is systematically investigated. Similar to 2H-phase transition metal dichalcogenides, the basal plane of pristine 1S- MX 2 and 1S- MXY ( M : Mo; X/Y : S/Se) are catalytically inert. By introducing vacancy defects, the catalytic performance of the basal plane can be activated. The calculated Gibbs free energy differences (Δ G H ) of non-Janus 1S-MoS 2 and 1S-MoSe 2 with point vacancies reduce to 35 and −105 meV, respectively. Due to the atomic asymmetry of Janus structure, Δ G H of 1S-MoSSe monolayer are −53 and −28 meV for S- and Se-vacancy defect, respectively. Qualitatively, the catalytic activity of 1S-MoSSe and 1S-MoS 2 with S vacancy are comparable while 1S-MoSSe is much better than 1S-MoSe 2 with Se vacancy. Additionally, Δ G H of 1S-MoSSe with Se-vacancy keeps within ±50 meV under a −2%–2% biaxial strain, demonstrating high robustness of catalytic activity against strain. The results indicate the potential of square phase Janus MoSSe monolayer as an option for monolayer HER catalyst. • Basal planes of pristine square phase non-Janus and Janus TMD monolayers are catalytically inert. • Introduction of vacancy defects can activate the basal plane of 1S-MoSSe monolayer. • Δ G H of 1S-MoSSe_VSe and 1S-MoSSe_VS are −0.028 eV and −0.053 eV by DFT calculations, respectively. • Introduction of tensile (compressive) biaxial strain reduces (enlarges) the value of Δ G H . • Within the strain range from −2% to 2%, Δ G H of 1S-MoSSe_VSe keeps in the catalytic window.