Additive-free macroscopic-scale synthesis of coral-like nickel cobalt oxides with hierarchical pores and their electrocatalytic properties for methanol oxidation

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.

Nickel foam supported mesoporous NiCo2O4 arrays with excellent methanol electro-oxidation performance

Schematic of the electro-oxidation reaction process of NiCo₂O₄ nanocloth arrays on nickel foam. The unique morphological features can afford efficient 3D electron transport during the redox reaction.