Stabilizing Lattice Oxygen through Mn Doping in NiCo2O4‐δ Spinel Electrocatalysts for Efficient and Durable Acid Oxygen Evolution

Abstract Design the electrocatalysts without noble metal is still a challenge for oxygen evolution reaction (OER) in acid media. Herein, we reported the manganese (Mn) doping method to decrease the concentration of oxygen vacancy (V O ) and form the Mn−O structure adjacent octahedral sites in spinel NiCo 2 O 4‐δ (NiMn 1.5 Co 3 O 4‐δ ), which highly enhanced the activity and stability of spinel NiCo 2 O 4‐δ with a low overpotential ( η ) of 280 mV at j =10 mA cm −2 and long‐term stability of 80 h in acid media. The isotopic labelling experiment based on differential electrochemical mass spectrometry (DEMS) clearly demonstrated the lattice oxygen in NiMn 1.5 Co 3 O 4‐δ is more stable due to strong Mn−O bond and shows synergetic adsorbate evolution mechanism (SAEM) for acid OER. Density functional theory (DFT) calculations reveal highly increased oxygen vacancy formation energy (E VO ) of NiCo 2 O 4‐δ after Mn doping. More importantly, the highly hydrogen bonding between Mn−O and *OOH adsorbed on adjacent Co octahedral sites promote the formation of *OO from *OOH due to the greatly enhanced charge density of O in Mn substituted sites.