Size effects and odd–even effects on hydrogen adsorption on Janus MoSSe nanosheets: first-principles studies

Abstract

Nanosheets of molybdenum dichalcogenides have been widely explored for their catalytic applications including hydrodesulfurization and hydrogen evolution reactions, in which the adsorption of hydrogen plays a key role in determining the catalytic efficiency. Herein, we studied the nanosize effects of triangular Janus MoSSe nanosheets as well as their odd–even effects on hydrogen adsorption using first-principles calculations. It is found that, after structural relaxation, the Janus MoSSe nanosheets form an arch structure bending toward the S layer because of the structural asymmetry, which is unlike the case of molybdenum disulfide, MoS₂. Moreover, the calculated changes of the Gibbs free energy for the hydrogen adsorption exhibit an odd–even oscillation as the size number (n) of the nanosheets changes from an odd number to an even number. These results highlight the unique structural and catalytic properties of two-dimensional Janus transition-metal chalcogenide nanostructures.