Exploring the effect of concentration on hydrothermally synthesized mesoporous spherical nanoflowers of bismuth tungstate for hybrid supercapacitor and water-splitting applications

Abstract

This paper describes how the synergistic effect of concentration changes the electrode conductivity and enhances the electrochemical and electrocatalytic activities of bismuth tungstate nanoflowers (BWO NFs). This research mainly aims to develop mesoporous spherical BWO NFs using a hydrothermal route. The structural analysis of the BWO NFs revealed the presence of an orthorhombic phase with a regular atomic arrangement. Scanning electron microscopy revealed that the different BWO NFs samples had nonuniform spherical NFs, which play an important role in supercapacitor and electrocatalytic applications. The identification of functional groups and stretching–bending vibrations of Bi–W–O bonds are revealed by FT-IR and Raman spectroscopy respectively. Additionally, the transmission electron microscopy and X-ray photoelectron spectroscopy confirmed the morphological, structural, and electronic states of the BWO NFs. Furthermore, the supercapacitive and electrocatalytic activity of BWO–nickel foam (NF) electrodes were investigated using an aqueous 1 M KOH electrolyte. The results revealed that the BWO-2 electrode exhibited an improved specific capacity (Csp) of (647 F/g) 72 mAh/g and excellent capacitive retention of 81 % over 5000 cycles. An asymmetrical hybrid device was fabricated using a two-electrode cell with BWO–NF and reduced graphene oxide acting as the positive and negative electrodes, respectively. The device demonstrated favorable electrochemical properties: a Csp of 52 mAh/g at 5 mV/s as well as a Csp of 46 mAh/g, the highest energy density of 32 Wh/kg, and the highest power density of 2330 W/kg at 5 mA/cm2. Furthermore, the BWO NFs were investigated for water-splitting activity, and the BWO-2 electrode was found to exhibit better electrocatalytic performance (overpotential: 328 mV, Tafel slope: 80.9 mV/dec, and electrochemical surface area: 41.2 cm2) and stability than the other electrodes. The designed asymmetric structure offers a suitable cathode material for energy storage and electrocatalytic applications.