Rapid Surface Reconstruction of In ₂ S ₃ Photoanode via Flame Treatment for Enhanced Photoelectrochemical Performance

Abstract Surface reconstruction, reorganizing the surface atoms or structure, is a promising strategy to manipulate materials' electrical, electrochemical, and surface catalytic properties. Herein, a rapid surface reconstruction of indium sulfide (In ₂ S ₃ ) is demonstrated via a high‐temperature flame treatment to improve its charge collection properties. The flame process selectively transforms the In ₂ S ₃ surface into a diffusionless In ₂ O ₃ layer with high crystallinity. Additionally, it controllably generates bulk sulfur vacancies within a few seconds, leading to surface‐reconstructed In ₂ S ₃ (sr‐In ₂ S ₃ ). When using those sr‐In ₂ S ₃ as photoanode for photoelectrochemical water splitting devices, these dual functions of surface In ₂ O ₃ /bulk In ₂ S ₃ reduce the charge recombination in the surface and bulk region, thus improving photocurrent density and stability. With optimized surface reconstruction, the sr‐In ₂ S ₃ photoanode demonstrates a significant photocurrent density of 8.5 mA cm ⁻² at 1.23 V versus a reversible hydrogen electrode (RHE), marking a 2.5‐fold increase compared to pristine In ₂ S ₃ (3.5 mA cm ⁻² ). More importantly, the sr‐In ₂ S ₃ photoanode exhibits an impressive photocurrent density of 7.3 mA cm ⁻² at 0.6 V versus RHE for iodide oxidation reaction. A practical and scalable surface reconstruction is also showcased via flame treatment. This work provides new insights for surface reconstruction engineering in sulfide‐based semiconductors, making a breakthrough in developing efficient solar‐fuel energy devices.