Combinatorial Studies on Wet-Chemical Synthesized Ti-Doped α-Fe₂O₃: How Does Ti⁴⁺ Improve Photoelectrochemical Activity?

Hematite (α-Fe₂O₃)-based photoanode for photoelectrochemical water oxidation has been intensively studied for decades. Doping with isovalent or aliovalent ions is one way to mitigate several intrinsic drawbacks of bare hematite. While addition of Ti in the bulk has been reported for improving photoresponse, several aspects of effects of Ti impregnation have not been justified. In this work, Ti:Fe₂O₃ nanoellipsoids synthesized by a facile one-pot hydrothermal process present improved photoelectrochemical response. Tuned symmetry of Fe-O and Fe-Fe (Fe-Ti) with less recombination during charge transportation, tuned electron configuration of O_2p-Fe_4s4p hybridization in Ti-adjoining regime with enhanced electron relaxation within Fe₂O₃ lattice, suppressed O₂/H₂O back reaction (reduction of O₂), and inhibit formation of surface defects during hydrothermal synthesis were attested by X-ray absorption spectroscopy, Mott-Schottky analysis, and photoelectrochemical impedance spectroscopy. Additionally, Ti:Fe₂O₃ showed enhanced light absorption. Hydrogen evolution rate of 11.76 μmol h^-1 cm^-2 under illumination was observed while using Ti:Fe₂O₃ as the working electrode. Additional experiments on Mn⁴⁺ and In³⁺ incorporation showed mixed effects. This study provides insights and clarification toward "Ti-doping" of the hematite photoanode for solar hydrogen production from water.