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

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 CeO₂, 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 3d states within the CeO₂ bandgap facilitates visible-light harvesting and optimizes the adsorption energetics of key reaction intermediates. Specifically, Ni-doped CeO₂ introduces additional 3d 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/cm² under illumination, while Co-doped CeO₂ exhibits a 35 mV reduction in 1 M NaOH. Our findings demonstrate that a simple doping strategy can tailor 3d states to promote efficient charge carrier separation and intermediate transfer, offering a versatile and scalable approach to designing advanced electrocatalysts for water splitting.