Enhanced photoelectrochemical water splitting of In-doped TiO2 nanorods with oxygen vacancies: synergistic effects of band structure and charge carrier dynamics engineering

Titanium dioxide (TiO₂) is a widely studied photocatalyst for photoelectrochemical (PEC) water splitting due to its excellent stability, low cost, and non-toxicity. However, conventional doping strategies to enhance TiO₂ performance often increase light absorption and carrier concentration at the expense of introducing carrier recombination centers. In this study, we propose a simple one-step hydrothermal method to synthesize In-doped TiO₂ nanorods, where In³⁺ doping synergistically stabilizes oxygen vacancies through charge compensation mechanisms. This dual modification optimizes the band structure, significantly increases charge carrier density, and reduces charge transfer resistance, leading to enhanced oxygen evolution reaction (OER) kinetics and overall PEC efficiency. The optimized In-doped TiO₂ nanorods achieve a photocurrent density of 1.4 mA cm⁻² at 1.23 V vs. RHE, 2.8 times higher than that of pristine TiO₂. Density functional theory (DFT) calculations further reveal that In³⁺ doping lowers the energy barrier of the rate-determining step (*OH → *O) by modulating the electronic structure of Ti active sites. This work demonstrates a synergistic strategy of combining element doping and oxygen vacancy engineering to design high-performance TiO₂-based photoanodes for solar energy conversion.