Improving the charge separation efficiencies of ternary metal sulfides for photocatalytic hydrogen production

Ternary metal sulfides represent a pivotal advancement in photocatalysis for solar-driven hydrogen production, offering tunable bandgaps, visible-light responsiveness, and superior stability over binary analogs. However, their efficiency is constrained by rapid charge recombination, suboptimal interfacial charge transfer, and sluggish surface kinetics. This review systematically explores mechanisms to enhance charge separation, with a primary focus on built-in electric fields (BIEFs). The dual origins of BIEFs (interfacial and polarization-induced) are elaborated, along with their role in establishing directional charge migration pathways to mitigate recombination. Advanced characterization techniques for probing charge dynamics are critically evaluated. Strategies to engineer BIEFs are analyzed, encompassing structural design (e.g., heterojunctions, core-shell architectures), defect engineering, and crystal phase modulation. Additionally, the synergistic effects of external fields (electric, thermal, and ultrasonic) are highlighted in amplifying BIEFs or generating dynamic fields for sustaining charge separation. This work provides a comprehensive framework for improving charge separation efficiencies of advancing ternary sulfide photocatalysts.