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

Abstract

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.