Lattice Oxygen Redox Engineering in Mn/Ni-Coordinated Spinel Cobalt Oxides for Robust Acidic Oxygen Evolution

Developing highly active and durable nonprecious-metal catalysts for acidic oxygen evolution reaction (OER) is crucial for optimizing hydrogen production in proton exchange membrane water electrolysis. However, substantial challenges remain in achieving this goal. In this study, a synergistic Mn/Ni codoping strategy is proposed to fabricate a spinel-type Co 2 Mn 0.5 Ni 0.5 O 4 (CMN) catalyst, which requires a low OER overpotential of 273 mV to reach 10 mA cm −2 and demonstrates an excellent stability for over 430 h in 0.5 M H 2 SO 4, outperforming pristine Co 3 O 4 . This superb performance could be attributed to Mn/Ni codoping in Co 3 O 4, which introduces structural defects, generates oxygen vacancies, and increases the Co 3+ /Co 2+ ratio. Furthermore, differential electrochemical mass spectrometry and in situ Raman studies reveal that CMN activates an additional lattice oxygen mechanism (LOM) pathway, thus accelerating the OER rate, with quantitative analysis showing that LOM contributes approximately 22.4% to the overall reaction. Partial density of states analysis confirms that Ni effectively narrows the energy-level separation between Co 3d and O 2p orbitals, strengthens their electronic coupling, and thereby facilitates lattice oxygen activation. Additionally, Bader charge analysis confirms that Mn enhances the Mn–O bond, thereby stabilizing the crystal structure and preventing structural collapse. These findings demonstrate the potential of Mn/Ni coregulation for balancing lattice oxygen activity and structural stability in Co-based spinel catalysts.