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-MX₂ 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 (ΔG_H) of non-Janus 1S-MoS₂ and 1S-MoSe₂ with point vacancies reduce to 35 and −105 meV, respectively. Due to the atomic asymmetry of Janus structure, ΔG_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-MoS₂ with S vacancy are comparable while 1S-MoSSe is much better than 1S-MoSe₂ with Se vacancy. Additionally, ΔG_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.

基于密度泛函理论，系统地研究了方相Janus MoSSe单分子膜的产氢反应（HER）的催化性能。类似于2H相过渡金属二卤化物，原始1S- MX ₂和1S- MXY（M：Mo; X / Y：S / Se）的基面是催化惰性的。通过引入空位缺陷，可以激活基面的催化性能。计算得出的非Janus 1S-MoS ₂和1S-MoSe ₂的点空位的吉布斯自由能差（ΔG _H）分别减小到35和-105 meV。由于Janus结构的原子不对称性，ΔG _HS-和Se-空位缺陷的1S-MoSSe单层的层数分别为-53和-28 meV。定性地，具有S空位的1S-MoSSe和1S-MoS ₂的催化活性相当，而具有Se空位的1S-MoSSe则比1S-MoSe ₂好得多。此外，具有-1％硒原子的1S-MoSSe的ΔG _H在-2％–2％双轴应变下保持在±50 meV以内，证明了对应变的催化活性具有很高的鲁棒性。结果表明方相Janus MoSSe单层作为单层HER催化剂的选择的潜力。