Valence engineering via double exchange interaction in spinel oxides for enhanced oxygen evolution catalysis

The design of spinel-oxide-based catalysts with high activity and long-term durability for oxygen evolution reaction (OER) confronts grand challenges that may be well tackled by maneuvering the electronic structure of surface catalytic sites within spinel oxides. Herein, we harness a double exchange interaction (DEI) triggered by the synergistic effects of Schottky junction and oxygen vacancies (V_O) to generate high proportions of octahedrally coordinated Ni³⁺ and Co²⁺ (highly active sites) in the edge-sharing [Ni_xCo_1−XO₆] octahedra. Specifically, Schottky junction is formed between metallic Cu nanowires and semiconducting NiCo₂O₄ via a core-shell structure, and abundant V_O sites are created in NiCo₂O₄ via H₂ thermal treatment. As expected, the Cu@V_O-NiCo₂O₄ electrocatalyst allows a significantly boosted OER performance, with a low overpotential of 214 mV at 10 mA cm^-2 and a small Tafel slope of 64.9 mV dec^-1, which outperforms the state-of-the-art RuO₂ catalyst and most of reported Ni-Co based OER catalysts. Our work provides some inspirations for designing high-performance spinel-oxide-based electrocatalysts towards OER via DEI engineering.