Comprehensive Understanding of the Spatial Configurations of CeO₂ in NiO for the Electrocatalytic Oxygen Evolution Reaction: Embedded or Surface-Loaded

Introducing cerium (Ce) species into electrocatalysts has been recently developed as an effective approach to improve their oxygen evolution reaction (OER) performance. Importantly, the spatial distribution of Ce species in the hosts can determine the availability of Ce species either as additives or as co-catalysts, which would dictate their different contributions to the enhanced electrocatalytic performance. Herein, the comprehensive investigations on two different catalyst configurations, namely CeO₂-embedded NiO (Ce-NiO-E) and CeO₂-surface-loaded NiO (Ce-NiO-L), are performed to understand the effect of their specific spatial arrangements on OER characteristics. The Ce-NiO-E catalysts exhibit a smaller overpotential of 382 mV for 10 mA cm⁻² and a lower Tafel slope of 118.7 mV dec⁻¹, demonstrating the benefits of the embedded configuration for OER, as compared with those of Ce-NiO-L (426 mV and 131.6 mV dec⁻¹) and pure NiO (467 mV and 140.7 mV dec⁻¹), respectively. The improved OER property of Ce-NiO-E originates from embedding small-sized CeO₂ clusters into the host for the larger specific surface area, richer surface defects, higher oxygen adsorption capacity, and better optimized electronic structures of the surface active sites, as compared with Ce-NiO-L. Above findings provide a valuable guideline for and insight in designing catalysts with different spatial configurations for enhanced catalytic properties.