Transition metal doping of CeO2 boosts photo-assisted electrocatalytic oxygen evolution performance

Light causes Fermi level splitting, while Ni doping creates defect states close to the valence band. Upon illumination and application of potential, the Fermi level of the holes aligns with the redox potential for oxygen evolution reaction (OER), enabling fast hole transport and enhancing OER activity. Integrating electrocatalytic and photocatalytic functionalities into a single-component system offers a promising strategy for enhancing catalytic activity in photo-assisted electrocatalysis. This synergy is critical for advancing energy conversion efficiency, yet significant challenges persist, particularly in optimizing individual layers and minimizing charge recombination. In this work, we present a novel single-component photo-assisted electrocatalytic system based on Ni- or Co-doped CeO 2 , which simultaneously functions as a light absorber and electrocatalyst. We elucidate the critical relationship between bandgap engineering and d-band states, demonstrating that controlled modulation of dopant-derived 3 d states within the CeO 2 bandgap facilitates visible-light harvesting and optimizes the adsorption energetics of key reaction intermediates. Specifically, Ni-doped CeO 2 introduces additional 3 d states near the Fermi level, narrowing the bandgap from 3.0 to 2.7 eV. This modification not only enhances visible-light absorption but also improves charge transfer efficiency at the catalyst-electrolyte interface. Density functional theory (DFT) calculations and spectroscopic analyses reveal that Ni doping significantly enhances performance, achieving a 64 mV reduction in overpotential at 50 mA/cm 2 under illumination, while Co-doped CeO 2 exhibits a 35 mV reduction in 1 M NaOH. Our findings demonstrate that a simple doping strategy can tailor 3 d states to promote efficient charge carrier separation and intermediate transfer, offering a versatile and scalable approach to designing advanced electrocatalysts for water splitting.