A novel in situ preparation method for nanostructured α-Fe2O3 films from electrodeposited Fe films for efficient photoelectrocatalytic water splitting and the degradation of organic pollutants

Abstract

A novel method has been developed for the preparation of nanostructured haematite (α-Fe₂O₃) films for use in photoelectrocatalytic (PEC) water splitting and the degradation of organic pollutants. The method has two stages, the electrodeposition of Fe films in alkalescent aqueous electrolyte with ferrous sulphate and ammonia, and the in situ thermal oxidation of the Fe films to α-Fe₂O₃. The thickness and crystallinity of the α-Fe₂O₃ films can be precisely controlled by adjusting the duration and the annealing conditions of the electrodeposition, respectively, avoiding the microstructural defects arising from the traditional electrodeposition of FeOOH films and the unwanted phases of FeO and Fe₃O₄ produced by thermal oxidation of Fe foils. This facilitates the generation, transportation and collection of photogenerated charges on the α-Fe₂O₃ film. The optimized α-Fe₂O₃ film, obtained from a Fe film deposited for 30 s and then annealed at 500 °C for 2 h, showed a stable PEC water oxidation current around 1.35 mA cm⁻² at 1.23 V vs. a reversible hydrogen electrode (RHE) under AM 1.5 irradiation. This was the highest current so far obtained using undoped α-Fe₂O₃ films produced by electrodeposition. When further coated with a cobalt phosphate (Co–Pi) co-catalyst, the optimized Co–Pi/α-Fe₂O₃ photoanode showed an incident photon-to-current conversion efficiency (IPCE) above 18% at 400 nm and a stable photocurrent of 1.89 mA cm⁻². The α-Fe₂O₃ film also showed excellent stability and degradation efficiency (rate constant 0.9372 h⁻¹) in the PEC degradation of methylene blue (MB) in neutral aqueous solution under a positive bias potential.