Performance enhancement of hematite photoanode with oxygen defects for water splitting

[Display omitted] •Methanol solvothermal treatment induces a hydroxylated surface on Fe2O3:Ti.•HCl hydrothermal treatment induces more chemisorbed oxygen on Fe2O3:Ti.•Surface hydroxylation enhances the photocurrent and chemisorbed oxygen reduces the onset potential of Fe2O3:Ti.•A synergistic effect is achieved by oxhydryl and chemisorbed oxygen.•The photocurrent density of Fe2O3:Ti is optimized to 3.0 mA cm−2 at 1.23 VRHE. Two types of oxygen defects are created on the Fe2O3:Ti photoanode and their acting roles on prompting the photoelectrochemical performance are clarified. Methanol solvothermal treatment is discovered to expediently import hydroxyl oxygen on Fe2O3:Ti. Accordingly, the charge carrier density is multiplied and surface hydrophilicity is dramatically improved, resulting in inhibition of surface transfer recombination and enhancement of the photocurrent density. In addition, HCl hydrothermal treatment can induce surface defects with chemisorbed oxygen, which barely affects the surface hydrophobicity or the carrier density. HCl hydrothermal treatment behaves on promoting the charge transfer in surface states as well as suppressing the bulk charge recombination, thus moderately enhancing the photocurrent density and lowering the onset potential. By combining two treatment processes, both defects are formed simultaneously with synergistic effectiveness. In addition, the FeCoW oxy–hydroxide electrocatalyst is incorporated for further accelerating the surface charge transfer. As a result, by compositing the strategies of methanol solvothermal, HCl hydrothermal, and FeCoW deposition, the photocurrent density of Fe2O3:Ti photoanode is significantly enhanced to 3.0 mA cm−2 at 1.23 VRHE with an onset potential of as low as 0.67 VRHE.