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MoSH is a representative example of a Janus two-dimensional monolayered system consisting of a molybdenum atomic layer sandwiched between sulfur and hydrogen atomic layers. Extensive experimental and theoretical efforts have suggested the great promise of the MoSH material, but the validity of the MoSH model (with a Mo–S–H ratio of 1:1:1) remains uncertain. While various experiments have established the Mo-to-S ratio to be close to 1:1, the hydrogen content has remained elusive even with the use of state-of-the-art characterization techniques due to its lightweight nature. In this study, we present a theoretical investigation aiming to determine the positions and ratios of the hydrogen atoms on MoSHx (with x ranging from 0 to 3) as well as assess their structural stability. By evaluating the energetic, mechanical, and thermodynamic properties, we confirm the existence of stable MoSHx structures within a critical range of hydrogen atom ratios, specifically 0.5 ≤ x ≤ 2.0. Additionally, as the hydrogen atom ratio increases, we observe a transition in the preferred adsorption sites of hydrogen atoms from the center of the hexagonal ring composed of molybdenum and sulfur atoms to the upper region of the molybdenum atoms. This study offers critical insight into the structural characteristics and stability of Janus monolayer MoSHx, contributing to the advancement and application of Janus MoSHx in various fields. [ABSTRACT FROM AUTHOR]

Single transition‐metal atom coordinated graphite carbon nitride, including the metal atom doped g‐C3N4 system, displays catalytic activity comparable to that of the noble metal Pt catalyst with outstanding performance. Herein, we investigate the single atom catalytic performance of g‐C3N3 embedded by a single transition metal atom (M−C3N3; M=Mn, Fe, Co, Ni, Cu, Rh, Pd, Ag, and Pt) for hydrogen evolution reaction (HER) using density functional theory (DFT) calculations. The results indicate that all the M−C3N3 catalysts are thermally and dynamically stable systems. By comparing the Gibbs free energies, we found that the Rh−C3N3 catalyst exhibits the best HER electrocatalytic performance among the investigated systems. Subsequently, analysis of electronic structure indicates that the Rh−C3N3 system displays a metallic behavior, which is a beneficial feature for an adequate HER electrocatalyst. Finally, the charge density difference of the Rh−C3N3 structure further supports the rationality of our results. This study provides a new candidate of low‐cost, high‐performance, and highly active non‐noble metal electrocatalysts. [ABSTRACT FROM AUTHOR]