Engineering thermally activated NiMoO₄ nanoflowers and biowaste derived activated carbon-based electrodes for high-performance supercapatteries

In the recent development of electrochemical capacitors, battery-type electrode materials are considered to be promising materials owing to their comparable energy density and the ability to deliver significant power compared to batteries. Herein, we report the applicability of nickel molybdate (NiMoO₄) nanostructures as battery-type positive electrodes for the development of supercapatteries. The nickel molybdate nanostructures were synthesized by a facile coprecipitation technique and the structural and electrochemical properties were modified with appropriate heat treatment. The sample heat treated for 500 °C shows good crystallization of the NiMoO₄ phase with a partial flower-like nanostructure compared with as-synthesized (bare) and 400 °C heat-treated samples. Moreover, the 500 °C sample-based electrode shows better battery-like electrochemical performances with a maximum specific capacity of 554 C g^-1, which is higher compared to the other two electrodes. The supercapattery designed using the 500 °C NiMoO₄ sample as the positive electrode and heteroatom enriched biowaste activated carbon as the negative electrode exhibited excellent electrochemical performances. The resultant supercapattery exhibited a maximum specific capacity value of 341 C g^-1 at 1 A g^-1 discharge specific current and showed an excellent specific energy of ∼64.07 W h kg^-1 for a specific power of 0.676 kW kg^-1 with <100% specific capacity retention even after 5000 charge/discharge cycles.