Effect of defect-rich Co-CeO OER cocatalyst on the photocarrier dynamics and electronic structure of Sb-doped TiO nanorods photoanode.

This work demonstrates the in-depth mechanism of enhanced photoelectrochemical (PEC) water oxidation of Sb-doped rutile TiO nanorods (NRs) photoanode coupled with oxygen vacancy defect-rich Co-doped CeO (Co-CeO) oxygen evolution reaction (OER) cocatalyst. The defect-rich Co-CeO cocatalyst modification improves the conductivity, light absorption, charge transfer efficiency, and surface photovoltage generation of the Co-CeO/Sb-TiO hybrid NRs photoanode. The Co-CeO cocatalyst also serves as the surface passivating overlayer for the Sb-TiO photoanode, which suppresses the surface states mediated recombination of electron-hole pairs in the NRs. The PEC studies further indicate that Co-CeO cocatalyst induces remarkably large band bending at the semiconductor/electrolyte interface and shortens the carrier diffusion length and depletion layer width, facilitating the rapid separation and transportation of the photocarriers for the surface PEC reactions. The experimental and theoretical studies confirm that the Co-doping in CeO cocatalyst enhances the surface oxygen vacancy defects, which provides active catalytic sites for OH adsorption and charge transportation for enhanced OER kinetics. The density functional theory (DFT) calculations demonstrate a higher conductivity of the Co-CeO cocatalyst, advantageous for rapid charge transfer capability during PEC reactions. The synergy between all these merits helps the optimized Co-CeO/Sb-TiO photoanode to deliver a maximum photocurrent density of 1.41 mA cm at 1.23 V vs. reversible hydrogen electrode (V) and an ultra-low turn on potential (V) of 0.1 V under AM 1.5G solar illumination compared to the Sb-TiO NRs (0.96 mA cm at 1.23 V and V = 0.42 V). This work demonstrates the design of an efficient defect-rich cocatalyst modified photoanode for solar energy harvesting.