Cationic Defect Engineering in Spinel NiCo2O4 for Enhanced Electrocatalytic Oxygen Evolution

Defect engineering is a promising method to solve the inherent low conductivity and limited number of reactive sites of metal oxides as electrocatalysts. High formation energy makes it challenging to controllably produce metal defects in metal oxides. In this study, abundant Co defects were preferentially produced on spinel NiCo2O4 by tuning the M–O bond length and interfering with ionization of the crystal surface. Theoretical calculations and experiments proved that Al doping elongated the Co–O bond and promoted ionization of Co under plasma treatment. Furthermore, Co ions in the crystal lattice were selectively taken away by adding NaOH to combine with surface-ionized metal ions, which facilitated the formation of cobalt defects. The Co defects induced electron delocalization, which effectively increased the carrier concentration and intrinsic conductivity of the catalysts, thereby enhancing the intrinsic OER catalytic activity of NiCo2O4.