Surface engineered doping of hematite nanorod arrays for improved photoelectrochemical water splitting

Given the narrow band gap enabling excellent optical absorption, increased charge carrier density and accelerated surface oxidation reaction kinetics become the key points for improved photoelectrochemical performances for water splitting over hematite (α -Fe₂O₃) photoanodes. In this study, a facile and inexpensive method was demonstrated to develop core/shell structured α-Fe₂O₃ nanorod arrays. A thin, Ag-doped overlayer of ∼2-3 nm thickness was formed along α-Fe₂O₃ nanorods via ultrasonication treatment of solution-based β2-FeOOH nanorods in Ag precursor solution followed by high temperature annealing. The obtained α-Fe₂O₃/Ag_xFe_2-xO₃ core/shell nanorod films demonstrated much higher photoelectrochemical performances as photoanodes than the pristine α-Fe₂O₃ nanorod film, especially in the visible light region; the incident photon-to-current efficiency (IPCE) at 400 nm was increased from 2.2% to 8.4% at 1.23 V vs. RHE (Reversible hydrogen electrode). Mott-Schottky analysis and X-ray absorption spectra revealed that the Ag-doped overlayer not only increased the carrier density in the near-surface region but also accelerated the surface oxidation reaction kinetics, synergistically contributing to the improved photoelectrochemical performances. These findings provide guidance for the design and optimization of nanostructured photoelectrodes for efficient solar water splitting.