Stabilizing Lattice Oxygen through Mn Doping in NiCo2O4−d 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 doping method to decrease the concentration of oxygen vacancy (Vo) and form the Mn−O structure adjacent octahedral sites in spinel NiCo2O4−δ (NiMn1.5Co3O4−δ), which highly enhanced the activity and stability of spinel NiCo2O4−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 NiMn1.5Co3O4−δ is more stable due to strong Mn‐O bond and synergetic adsorbate evolution mechanism (SAEM) for acid OER. Density functional theory (DFT) calculations reveal highly increased oxygen vacancy formation energy (EVO) of NiCo2O4−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.