Rapid Surface Reconstruction of In₂S₃ Photoanode via Flame Treatment for Enhanced Photoelectrochemical Performance

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 (In₂S₃) is demonstrated via a high-temperature flame treatment to improve its charge collection properties. The flame process selectively transforms the In₂S₃ surface into a diffusionless In₂O₃ layer with high crystallinity. Additionally, it controllably generates bulk sulfur vacancies within a few seconds, leading to surface-reconstructed In₂S₃ (sr-In₂S₃). When using those sr-In₂S₃ as photoanode for photoelectrochemical water splitting devices, these dual functions of surface In₂O₃/bulk In₂S₃ reduce the charge recombination in the surface and bulk region, thus improving photocurrent density and stability. With optimized surface reconstruction, the sr-In₂S₃ 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 In₂S₃ (3.5 mA cm^-2). More importantly, the sr-In₂S₃ 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.