Oxy-sulfide semiconductors for hydrogen production from pure water: materials design, performance, and stability

Oxy-sulfides have emerged as a versatile class of mixed-anion semiconductors capable of bridging the complementary strengths of oxides (structural stability) and sulfides (narrow band gap, enhanced conductivity) for hydrogen production from pure water. This review summarises recent progress in their application as both photocatalysts and electrocatalysts, with emphasis on mixed-anion electronic structure, band-edge engineering, and charge-carrier dynamics. Layered titanate oxy-sulfides, exemplified by Y₂Ti₂O₅S₂, are highlighted as benchmarks for visible-light-driven overall water splitting; key findings regarding cocatalyst loading effects, band-tail states, and interfacial selectivity are critically assessed. Electrocatalytic systems—notably NiFe-based oxy-sulfides—are also reviewed, with attention to the role of sulfur content, in situ reconstruction, and active-phase evolution. Degradation mechanisms including photocorrosion, surface reconstruction, and compositional drift are discussed alongside mitigation strategies. Despite substantial progress, solar-to-hydrogen efficiencies in pure-water systems remain well below levels required for practical deployment. Future directions involving operando characterisation, first-principles-guided materials design, and scalable synthesis are outlined.