Facile synthesis of nanorod-like NiCo2O4 particles via PVP-assisted hydrothermal processing for high-performance supercapacitors

Nanorod-like NiCo₂O₄ powders were synthesized for supercapacitor applications. Hydrothermal treatment of oxalate precipitates with different amounts of polyvinylpyrrolidone (PVP) surfactant (0-8 mmol) led to the formation of NiCo₂O₄ particles with rectangular-like to nanorod-like morphologies. Variations in electrochemical properties with changes in PVP amount were evaluated. Due to the nanorod-like morphology of the NiCo₂O₄ powders, the effective surface area increased from 36.3 to 67.7 m² g^-1. At an appropriate PVP content, the specific capacitance increased from 981 to 2,717 F g^-1 (at a current density of <i>1 A g</i> ^<i>-1</i> ) with a rate capability of 71.2% by increasing the current density up to <i>10 A g</i> ^<i>-1</i> . The contribution of capacitive-controlled process was initially decreased with the addition of low PVP content, but subsequently increased at higher PVP dosage. The supercapacitor fabricated from NiCo₂O₄ and activated carbon, at the current density of <i>1 A g</i> ^<i>-1</i> , exhibited 25.4 Wh·kg^-1 energy density at 1,428 W kg^-1 power density.