Fluorine-surface-modified tin-doped hematite nanorod array photoelectrodes with enhanced water oxidation activity

Severe charge recombination and sluggish water oxidation reaction (OER) kinetics significantly limit the practical application of hematite in photoelectrochemical (PEC) water-splitting devices. In this study, fluorine-surface-modified tin-doped hematite (F/Sn:Fe2O3) photoelectrodes have been fabricated by a hydrothermal method incorporated impregnation annealing process. The grown FeOOH nanorods coated with NH4F solution are annealed first at 550 °C in the vacuum to modify the hematite surface and then at 750 °C in argon to promote the diffusion of tin atoms from the fluorine-doped tin oxide (FTO) glass substrate to the hematite structure. The synergistic effect of F-modification and Sn-doping on Fe2O3 electrode considerably enhances its PEC water oxidation performance, resulting in the highest photocurrent density of 3.64 mA cm−2 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5 G illumination. Both effects increase the carrier concentration in the photoelectrode, which improves its transport efficiency. Moreover, the surface-localized F species promote the OER process on the electrode surface and improve the charge separation at the electrode/electrolyte interface by increasing its hole supply rate under the increased electric field. This work may open a new avenue for fabricating novel photoelectrodes with high PEC water splitting efficiency.