Synergistic effect between the iron (III) oxyhydroxide and Gd-Fe2O3 photoanode interface resulted in an ultra-low onset potential for photoelectrochemical water oxidation

The onset potential is an important descriptor of the photoelectrochemical water oxidation performance of photoanodes. Herein, we prepared Gd-doped hematite (Gd-Fe2O3)/iron (III) oxyhydroxide (FeOOH) core-shell photoanodes by in-situ isovalent doping and secondary hydrothermal treatment. This Gd-Fe2O3/FeOOH photoanode shows a record alkaline water oxidation onset potential (0.59 V vs. reversible hydrogen electrode) in hematite-based photoanodes and a 2.4-fold increase in photocurrent density over pristine hematite. Detailed studies demonstrate that the origin of the ultra-low onset potential is mainly attributed to the synergistic effect of isovalent Gd-doping and FeOOH cocatalyst. Specifically, Gd doping enhances donor density and reduces charge transport resistance, and FeOOH cocatalyst significantly improves water oxidation kinetics. In addition, the strong interfacial coupling of FeOOH and Gd-Fe2O3 promotes electron flow, which also improves the charge separation remarkably. This work gives hope for the achievement of stable and bias-free hematite-based photoanodes.