▎ 摘　　要

The development of cost-effective and high-performance electrocatalysts for oxygen evolution reaction (OER) is essential for sustainable energy storage and conversion processes. This study reports a novel and facile approach to the hierarchical-structured sheet-on-sheet sandwich-like nanocomposite of CoNiOx/reduced graphene oxide as highly active electrocatalysts for water oxidation. Notably, the as-prepared composite can operate smoothly both in 0.1 and 1.0 M KOH alkaline media, displaying extremely low overpotentials, fast kinetics, and strong durability over long-term continuous electrolysis. Impressively, it is found that its catalytic activity can be further promoted by anodic conditioning owing to the in situ generation of electrocatalytic active species (i.e., metal hydroxide/(oxy)hydroxides) and the enriched oxygen deficiencies at the surface. The achieved ultrahigh performance is unmatched by most of the transition-metal/nonmetal-based catalysts reported so far, and even better than the state-of-the-art noble-metal catalysts, which can be attributed to its special well-defined physicochemical textural features including hierarchical architecture, large surface area, porous thin nanosheets constructed from CoNiOx nanoparticles (approximate to 5 nm in size), and the incorporation of charge-conducting graphene. This work provides a promising strategy to develop earth-abundant advanced OER electrocatalysts to replace noble metals for a multitude of renewable energy technologies.