Multifunctionality exploration of NiCo2O4–rGO nanocomposites: photochemical water oxidation, methanol electro-oxidation and asymmetric supercapacitor applications

Different weight percentages of NiCo2O4-rGO nanocomposites were prepared via a facile hydrothermal method. The prepared nanocomposites were structurally and morphologically characterized by X-ray diffraction, Raman spectroscopy, and electron microscopy. The structural studies show the formation of rGO-NiCo2O4 nanocomposites by embedment of porous NiCo2O4 rods on rGO sheets. The effect of the NiCo2O4 content on photochemical water oxidation was investigated. It revealed that the catalysts NiCo2O4-rGO with 1 : 26 ratio (NCO26) and 1 : 13 ratio (NCO13) are efficient in generating oxygen under light illumination. It proves that NCO26 works far more effectively as a photocatalyst compared to NCO13. Methanol electro-oxidation of the NCO26 nanocomposite shows a current density of 24 mA cm-2 at a potential of 0.45 V in cyclic voltammetry and maintains the current for 3600 s at 0.45 V in chronoamperometry. An onset potential of 0.344 V was observed for 0.5 M methanol oxidation. The specific capacitance values were found to be 354.75 F g-1 and 375.32 F g-1 at 1 mV s-1 and 1 A g-1, respectively, for NCO26 in supercapacitor studies. The charge stored via capacitive and diffusion-controlled processes was determined using Power's law and Trasatti plot. An asymmetric supercapacitor device shows a specific capacitance of 122.2 F g-1 at a current density of 1 A g-1 and exhibits a retention of 74.3% after 5000 cycles. An energy density of 67.89 W h kg-1 and a power density of 1 kW kg-1 at a current density of 1 A g-1 are observed.