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

ABSTRACT

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.