Suppression of Charge Recombination by Growth of a TiOx Passivation Layer on Ti-Doped Hematite Photoanodes for Boosted Photoelectrochemical Water Oxidation

Abstract

Hematite (α-Fe₂O₃) represents a photoelectrode material that holds high potential to realize efficient and stable photoelectrochemical (PEC) hydrogen production due to its narrow bandgap for efficient solar absorption and good stability in alkaline electrolytes. However, pure α-Fe₂O₃ has been plagued by its poor conductivity with low carrier mobility and rapid charge recombination, which greatly hinder its photoelectrochemical applications. Herein, a hybrid photoanode is rationally designed by growing an amorphous TiO_x overlayer on a Ti-doped α-Fe₂O₃ nanorod photoanode to passivate surface states for improved PEC performance. Consequently, the photocurrent achieved by the composite photoanode (Ti–Fe₂O₃/TiO_x) is around 1.24 mA·cm^–2 at 1.23 V vs RHE, up to about 1.7 and 62.0 times that of Ti-doped Fe₂O₃ (0.74 mA·cm^–2) and untreated α-Fe₂O₃ (0.02 mA·cm^–2) photaonodes, respectively. The intensive study of charge dynamics reveals that the improved PEC response of the composite photoelectrode can be ascribed to the Ti doping and TiO_x passivation effect greatly suppressing the charge recombination kinetics constant (k_rec) and promoting the charge transfer efficiency (η_tran), which resulted in accelerated charge separation and enhanced PEC activity. This work emerges as a feasible approach to designing the Fe₂O₃-based photoelectrode for enhanced solar water oxidation activity.