Ce-Substituted Spinel CuCo2O4 Quantum Dots with High Oxygen Vacancies and Greatly Improved Electrocatalytic Activity for Oxygen Evolution Reaction

Exploring effective electrocatalysts for oxygen evolution reaction (OER) is a crucial requirement of many energy storage and transformation systems, involving fuel cells, water electrolysis, and metal-air batteries. Transition-metal oxides (TMOs) have attracted much attention to OER catalysts because of their earth abundance, tunable electronic properties, and so forth. Defect engineering is a general and the most important strategy to tune the electronic structure and control size, and thus improve their intrinsic activities. Herein, OER performance on spinel CuCo₂O₄ was greatly enhanced through cation substitution and size reduction. Ce-substituted spinel CuCe_δCo_2-δO_x (δ = 0.45, 0.5 and 0.55) nanoparticles in the quantum dot scale (2-8 nm) were synthesized using a simple and facile phase-transfer coprecipitation strategy. The as-prepared samples were highly dispersed and have displayed a low overpotential of 294 mV at 10 mA·cm^-2 and a Tafel slope of 57.5 mV·dec^-1, which outperform commercial RuO₂ and the most high-performance analogous catalysts reported. The experimental and calculated results all confirm that Ce substitution with an appropriate content can produce rich oxygen vacancies, tune intermediate absorption, consequently lower the energy barrier of the determining step, and greatly enhance the OER activity of the catalysts. This work not only provides advanced OER catalysts but also opens a general avenue to understand the structure-activity relationship of pristine TMO catalysts deeply in the quantum dot scale and the rational design of more efficient OER catalysts.