Robust 2D-SnSe2/TiO2 S-scheme heterostructure for efficient neutral-pH oxygen evolution: experiments and DFT insights

Abstract Designing chemically robust photoanodes capable of efficient oxygen evolution reaction (OER) in neutral media remains a central challenge for practical photoelectrochemical (PEC) water splitting. By experiment and theory herein we report the PEC OER functionality of a durable and mechanistically well-defined 2D-SnSe ₂ /mesoporous TiO ₂ heterostructure photoanode operating at pH 7. Highly crystalline 2D-SnSe ₂ nanosheets (1.8 ± 0.1 μm lateral size and 100 ± 5 nm thickness) were solvothermally grown over mesoporous TiO ₂ films, forming a layered 2D-SnSe ₂ /TiO ₂ heterojunction, with efficient carrier transport and strong interfacial adhesion, solving the common delamination problem of 2D/TiO ₂ systems. Under solar illumination, the 2D-SnSe ₂ /TiO ₂ photoanode delivers a 16-fold higher current density than its single counterparts (0.80 mA/cm ² at 1.7 V vs RHE), together with excellent operational stability ( < 3% decay over 3 × 16 h continuous irradiation). Combining Mott–Schottky, valence-band XPS, and optical bandgap measurements with density functional theory (DFT), we reconstruct a defect-driven S-scheme charge-transfer mechanism, where oxygen vacancies in (110) TiO ₂ shift band edges to promote selective electron–hole recombination at the interface. Finally, differential free adsorption energies calculations of the four OER intermediates over oxygen defective (110) TiO ₂ , indicate the OH* → O* transition as the potential-determining step. These results establish 2D-SnSe ₂ /TiO ₂ as a stable, visible-light-responsive S-scheme heterostructure for neutral-pH OER, broadening the OER applications of group-IV chalcogenides MX ₂ (M = Sn, Ge; X = S, Se)/TiO ₂ photoanodes in neutral electrolytes.