Advances in transition metal sulfides: Synthesis, properties, and modification strategies for electrocatalysis and energy conversion applications

Transition metal sulfides (TMSs) are compounds composed of sulfur anions and one or more transition metal cations. They are characterized by having multiple crystal phases and electronic structures, including metallic, semiconducting, and insulating states. These tunable and controllable polycrystalline phases and electronic structures endow TMSs with unique physical and electrochemical properties, making them highly promising for energy-sector applications. Even though significant progress has been made in this field, most studies remain confined to idealized systems with only half-reactions, lacking a systematic understanding of the relationship between the intrinsic properties of materials and catalytic mechanisms, and ignoring the essential differences between half-reactions and complete reaction systems. To fully exploit the potential advantages of TMSs, it is necessary to clarify their mechanism of action in different catalytic processes systematically to establish a clear correlation between structural characteristics, intrinsic properties, and catalytic activity to gradually shift from qualitative studies focusing on single half-reactions to full-reaction application research in order to promote their practical development at the industrial and commercial scales. This review systematically summarizes recent advances in TMS-based electrocatalysts, covering preparation methods, structural features, and modification strategies, to establish a framework for rational structural design. Then elucidates the key electrocatalytic mechanisms that correlate catalytic performance with structural characteristics, thereby guiding the development of efficient catalysts. Finally, the review critically evaluates the application of TMS-based electrocatalysts in energy conversion devices beyond isolated half-reaction studies, identifies current challenges in practical implementation and commercialization, and outlines potential directions for future development.