Synergistic Fluorine Doping and Oxygen Vacancy Formation in Hematite Photoanodes via Solid-State Thermite Defect Engineering

Defect engineering such as doping is a crucial strategy to overcome the sluggish charge transfer kinetics of metal oxide photoanodes. Fluorine doping of metal oxide photoanodes, such as hematite (α-Fe 2 O 3 ), conventionally relies on fluorine-containing solutions, which often causes severe surface etching. Herein, we report a solid-state thermite defect engineering strategy to simultaneously induce F-doping and oxygen vacancies in hematite using fluororubber-coated aluminum (Al@F2311). Upon heating to 400 °C, the decomposing fluororubber effectively strips the inert Al oxide shell, triggering a localized interfacial thermite reaction. This process extracts lattice oxygen and substitutes fluorine into the near-surface region without disrupting the bulk structure. The resulting dual-defect Hem-AlF photoanode achieves a photocurrent density of 1.13 mA cm –2 at 1.23 V vs RHE, which is a 5.65-fold enhancement over pristine hematite. This improvement originates from a synergistically increased donor density, minimized interfacial charge transfer resistance, and reaction-induced surface hydrophilicity (contact angle of 49.7°). This solvent-free paradigm successfully pioneers the integration of energetic material kinetics into semiconductor defect engineering.