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.