Defect-Engineered MoS ₂ Supported Transition Metal Clusters for Electrochemical Reactions

Electrochemical reactions such as hydrogen and oxygen evolution, as well as carbon dioxide reduction, are central to renewable energy conversion and storage technologies. The development of efficient and earth-abundant catalysts remains crucial for improving these processes. In this study, we employed density functional theory calculations combined with the computational hydrogen electrode model to investigate the catalytic behavior of transition-metal (TM) tetramer clusters (Fe4, Co4, Ni4, Cu4) supported on pristine and defected (sulfur vacancies) MoS2 monolayers. The results reveal distinct reactivity trends driven by both the metal identity and the presence of sulfur vacancies, as well as their synergistic effects on cluster stability and activity. Except for Ni4, the TM4 clusters preferentially anchor near sulfur vacancies, where most clusters maintain their compact tetrahedral geometries, although Cu4 exhibits noticeable distortions when located away from the vacancy sites. In the hydrogen evolution reaction, Fe4@MoS2 near a sulfur vacancy exhibits the most favorable activity, highlighting the beneficial role of defect sites in stabilizing adsorbates and tuning electronic properties (synergistic effects). For the oxygen evolution reaction, overpotentials spread from 0.95 to 2.0 V, with Co4@MoS2 positioned close to a vacancy emerging as the most active configuration. Regarding CO2 reduction, only limited activity is observed, primarily for Co4 and Cu4 clusters located away from vacancies; however, the competing hydrogen evolution and surface poisoning by OH intermediates significantly hinder selectivity. Overall, these findings establish clear activity trends across different reactions and emphasize the synergistic role of cluster composition and defect engineering in tailoring the catalytic landscape of non-noble-metal MoS2-based electrocatalysts.