Acid substitutions for WO3 nanostructures synthesis by the hydrothermal route and its effect on physio-chemical and electrochemical properties for supercapacitors

In this study, we have developed a feasible and eco-friendly electrode material for supercapacitor (SCs) application by effectively synthesizing different morphological structures of tungsten oxide nanostructures (WO3NSs). The concentrated acids play a crucial role in the synthesis of WO3-NSs and are employed to evaluate the electrochemical activity. The stable phase formation and the crystal structures of WO3-NSs were confirmed by thermogravimetric and X-ray analysis. From the field emission scanning electron microscope (FE-SEM), the hexagonal-shaped nanosheets, one-dimensional nanorods (1D NRs), and heterogeneous non-uniform agglomerated nanosheets were observed for the WO3-NSs. The presence of functional groups and the stretching-bending vibrations of W-O bonds were detected by Fourier transform infrared, and Raman spectroscopy respectively. The transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) offers a more in-depth morphological, structural, and elemental composition and electronic states investigation of the optimized WO3NRs. Additionally, the electrochemical properties of the WO3-NSs have been examined in 1 M KOH electrolyte using Nickel Foam (NF) as a current collector. Furthermore, the M-WO3-NF electrode reveals higher specific capacity (Csp) and gravimetric capacitance (Cg) of 72 mAh/g and 600 F/g with high energy density (Ed) of 17 Wh/kg, and power density (Pd) of 321 W/kg as well as the superior Columbic efficiency (96.9 %) at 5 mA/cm2. The M-WO3 electrode exhibits 91 % capacitive retention over 5000 cycles. The M-WO3-NF is used as the cathode and activated carbon (AC) as the anode in the design of an aqueous hybrid supercapacitor (AHSC) device. Notably, the M-WO3-NF//AC-NF device offers a Pd of 1060 W/kg at an Ed of 9 Wh/kg and remarkable electrochemical stability of 80 % over 3000 charge-discharge cycles. These results highlight the excellent electrochemical functionality and advantages of the M-WO3-NRs as a promising cathode for practical energy-storage systems.