Crystalline Fe₂O₃/Fe₂TiO₅ heterojunction nanorods with efficient charge separation and hole injection as photoanode for solar water oxidation

Highlights: • First report of crystalline Fe₂O₃/Fe₂TiO₅ heterojunction for solar water splitting. • Higher photocurrent density c.a 1.4 mA/cm² at 1.23V_RHE as compared to pristine oxides. • High surface charge separation efficiency of around 85% at 1.23V_RHE. • Enhanced performance due to efficient surface states mediated hole transfer process. We have constructed a Fe₂O₃/Fe₂TiO₅ heterojunction based photoanode deposited on Fluorine Doped Tin Oxide (FTO) substrate by initially fabricating hematite (Fe₂O₃) nanorods and subsequently pseudobrookite (Fe₂TiO₅) nanoporous thin film on top of them. Comparatively lower annealing temperature of 650 °C (usually 750 °C or above) was used to avoid degradation of FTO. The crystalline Fe₂O₃/Fe₂TiO₅ heterojunction shows a considerable enhancement in photocurrent density ca. 1.4 mA/cm² and high surface charge separation efficiency of 85% at operating voltage of 1.23 V vs RHE as compared to its constituents. The crystalline heterojunction showed overall improvement in performance due to enhanced charge separation owing to the favorable band alignment with Fe₂O₃ nanorods and efficient injection of photogenerated holes through surface states into the electrolyte observed through Electrochemical Impedance Spectroscopy.