Single-atomic ruthenium dispersion promoting photoelectrochemical water oxidation activity of CeOx catalysts on doped TiO2 nanorod photoanodes

Abstract

Recently, various single-atom (SA) catalyst-coupled TiO₂ nanostructures have been designed for photocatalytic hydrogen evolution. However, TiO₂ is a well-established photoanode capable of solar-driven oxygen evolution reaction (OER). Selection and design of suitable oxygen evolution catalysts (OECs) boost the photoelectrochemical (PEC) water oxidation performance of TiO₂. Various single-atom catalysts (SACs) are designed mainly for the electrochemical OER, while atomically dispersed SAs on TiO₂ photoanodes for the photoelectrochemical (PEC) OER are still to be explored. Here, we demonstrate a rational and effective design of stabilizing Ru SAs dispersed on the CeO_x catalyst (Ru:CeO_x) coupled with one-dimensional (1D) Sb-doped TiO₂ nanorods (Sb–TiO₂ NRs) for remarkably enhanced PEC water oxidation activity. The role of Ru SAs in the electronic structure, separation, and transfer of photogenerated charge carriers and water oxidation pathways of the CeO_x catalyst coupled photoanode has been investigated. Along with improved visible light absorption, the Ru:CeO_x catalyst serves as an efficient hole extraction layer, inducing large interfacial band bending, large photovoltage generation, and shrinkage of the depletion layer, eventually accelerating the photogenerated hole transportation. DFT simulation demonstrates that Ru SA incorporation increases the conductivity of the catalyst, improving photocarrier transfer. Reduced photocarrier recombination, along with enhanced photocarrier transfer and injection rate enhance the photocurrent yield of the photoanode. DFT studies further confirm that Ru SAs significantly reduce the water oxidation overpotential of the neighboring active Ce atom sites, promoting the photoelectrochemical water oxidation activity of the CeO_x catalyst. The optimal photoanode delivers a photocurrent density of 1.96 mA cm⁻² (at 1.23 V vs. the reversible hydrogen electrode (RHE)), extremely low on-set potential (0.05 V_RHE), peak ABPE value of 0.54%, and charge separation efficiency of 61.5% at 1.23 V_RHE. This work provides an effective strategy to promote the water oxidation activity of metal oxide-supported SA catalysts to boost the overall performance of photoanodes.