Transition Metal Sulfide Cocatalysts: Applications and Challenges in Photocatalytic Hydrogen Production

Hydrogen (H2), as a pivotal zero-carbon energy carrier, plays a critical role in the global energy transition, with its efficient production being paramount. Photocatalytic water splitting, driven by solar energy to produce H2, is regarded as an ideal pathway for green hydrogen generation. However, its efficiency is still restricted by factors including narrow light-absorption spectra, elevated carrier recombination rates, and slow surface reaction kinetics. Among various strategies for enhancing photocatalytic activity, the development of cocatalyst loading has garnered significant attention due to its remarkable efficiency, stability, cost-effectiveness, and the ability to finely tune its performance. In the pursuit of optimizing catalysts for the green H2 production, researchers have delved into the design of cocatalysts by focusing on four pivotal aspects: band alignment and interfacial engineering, crystal phase modulation, precise regulation of active sites, and photothermal synergy effects. Transition metal sulfides (TMSs) have emerged as promising alternatives to noble metal cocatalysts, possessing unique electronic structures, tunable active sites, and interfacial synergistic effects. This review systematically summarizes recent advancements in TMS-based cocatalysts, including MoS2, NiS, WS2, and CuS, for photocatalytic H2 evolution. Furthermore, addressing practical challenges in TMS applications, we propose future research directions focusing on improving long-term material stability, developing environmentally friendly material designs, enabling low-cost, scalable synthesis, promoting interfacial charge transfer and advancing integrated device engineering. These efforts aim to provide theoretical foundations and technological breakthroughs for constructing efficient, economical, and sustainable solar-tohydrogen conversion systems.