Oxygen defect-mediated NiCo₂O₄ nanosheets as the electrode for pseudocapacitors with improved rate capability

Transition metal oxide-based supercapacitors have attracted much attention due to their high theoretical specific capacitances. However, due to an insufficient utilization ratio and poor intrinsic conductivity of active materials, the rate performance of these electrodes is usually low. Herein, oxygen defect-mediated NiCo₂O₄ nanosheets with enhanced electrical conductivity (1.9 S m^-1vs. 0.2 S m^-1 of original NiCo₂O₄ NSs) are fabricated using a post NaBH₄ reduction strategy (denoted as r-NiCo₂O₄ NSs). The derived r-NiCo₂O₄ materials have sheet-like morphology, increased oxygen defects and low valence metal species, and an unprecedented rate capability comparable to that of carbon-based electrode materials, with a satisfactory capacitance of 1812 F g^-1 and 91.5% retention at 20 A g^-1. The general strategy can be extended to other transition metal oxides to construct enhanced conductivity electrodes for related energy storage and conversion devices.