Ball-milling route to design hierarchical nanohybrid cobalt oxide structures with cellulose nanocrystals interface for supercapacitors

Nanocellulose materials are promising sustainable and environmentally friendly candidates for green and renewable energy storage applications. Herein, hierarchical Co₃O₄@CNC nanohybrid structure was fabricated in conjunction with cobalt acetate tetrahydrate and cellulose nanocrystals (CNC) as a bio-carbon source using green ball-milling pathway for the first time. For comparison, pristine Co₃O₄ nanostructure was prepared using a similar method without adding CNC. The structural and morphological characteristics of nanohybrid composites were investigated using X-ray diffractometer (XRD), Raman, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer-Emmett-Teller (BET) techniques. Furthermore, the electrochemical properties of the nanohybrid composites evaluated using cyclic voltammetry (CV), Galvanostatic Charge-Discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques. The hierarchical Co₃O₄@CNC nanohybrid electrode showed the highest specific capacitance of 396 F/g that of pristine Co₃O₄ nanostructure electrode (was 268 F/g) at a current density of 1.0 A/g for a three-electrode assembly. The hierarchical Co₃O₄@CNC nanohybrid electrode showed appreciable capacitive behavior with 96% cyclic retention even after 5,000 cycles at 1.0 A/g with energy density of 12.5 Wh k⁻¹ at a power density of 230.5 W k⁻¹. Thus, it is suitable for improving and/or designing active electrocatalysts for enhanced supercapacitor applications.