Synergistic Ni and Co Doping in Manganese Oxide for Enhanced Oxygen Evolution

A series of Ni and Co codoped manganese dioxide catalysts with varying Ni/Co ratios were prepared via a two-step hydrothermal-assisted calcination process, in which Birnessite-type δ-MnO2 precursors were first synthesized hydrothermally and then calcined at different temperatures. The optimally performing Ca-NCMO11–500 (Ni/Co = 1:1, calcined at 500 °C) was identified. Systematic investigations revealed that bimetallic doping modulates the local structure and electronic states of the manganese oxide framework. The Ca-NCMO11–500 catalyst exploits Ni–Co synergistic effects to activate lattice oxygen and promote O–O coupling, resulting in superior oxygen evolution reaction activity. Electrochemical measurements demonstrate that Ca-NCMO11–500 achieves 50 mA cm–2 at an overpotential of 237 mV and maintains excellent durability with negligible activity loss over 300 h at 400 mA cm–2. This study elucidates the microscopic mechanism by which Ni and Co codoping strengthens metal–oxygen bonds and enhances lattice oxygen reactivity, providing a rational basis for the design of high-performance manganese-based electrocatalysts.