Influence of graphene on enhancing supercapacitance characteristics of tungsten oxide based composite

Graphene and tungsten oxide (WO₃) quantum dots (QDs) are known for their unique characteristics and their mixture has good potential for supercapacitor applications. To date, most of the reported processes for the synthesis of WO₃ QDs are either expensive or require high capital investment and are performed at elevated temperatures. This study uses WO₃ QDs produced by electrochemical oxidation of WC-6Co scrap at room temperature, followed by a microwave treatment resulting in the formation of partially dehydrated WO₃·H_0.5 QDs. The dehydration of WO₃ QDs changed their crystal structure, reduced band gap, and increased vacancy concentrations which make them useful for energy storage applications. The primary objective of this study was to improve the supercapacitance performance of WO₃ QDs by mixing them with electrochemically exfoliated graphene nanoplatelets. The graphene platelets were synthesized at room temperature via electrochemical exfoliation of graphite sheet at low voltage (3–4 V) using KOH solution as electrolyte of low concentration (0.05 M). These exfoliated graphene nanoplatelets had very low defect concentration. The synthesis of graphene was confirmed using transmission electron microscopy and Raman spectroscopy. The graphene-WO₃ composite powder was prepared by manually mixing 1, 3, and 5 wt% of graphene with WO₃ QDs. The addition of 3 wt% graphene nanoplatelets to WO₃ QDs increased their specific capacitance value from 412 Fg⁻¹ to 560 Fg⁻¹ at 10 mVs⁻¹ scan rate. Results from the chronopotentiometry test showed a progressive decrease in both charging and discharging times of graphene-WO₃ composite powder with the increase in the amount of graphene owing to the high electrical conductivity of graphene.