Stabilizing Lattice Oxygen through Mn Doping in NiCoO Spinel Electrocatalysts for Efficient and Durable Acid Oxygen Evolution.

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) and form the Mn-O structure adjacent octahedral sites in spinel NiCoO (NiMnCoO), which highly enhanced the activity and stability of spinel NiCoO with a low overpotential (η) of 280 mV at j=10 mA cm 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 NiMnCoO 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) of NiCoO 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.