Functionalization of carbon nanotubes grown on heavy oil fly ash for enhanced symmetric supercapacitor performance

The increasing global population is increasing energy demand, thereby rendering efficient energy storage solutions crucial for the management of excess energy. In this study, carbon nanotubes (CNTs) were produced via chemical vapor deposition (CVD) using heavy oil fly ash (HOFA) and subsequently treated with two different acids to enhance their electrochemical properties. Nitric acid treatment increased the specific capacitance to 181.7 F/g in a three-electrode configuration (at 0.1 A/g) and 101.1 F/g in a two-electrode setup (at 0.5 A/g). Hydroquinone (HQ) addition further increased the performance to 213.1 F/g at 1 A/g with a 0.05 M HQ concentration. The resulting symmetric supercapacitor delivered a maximum energy density of 9.02 Wh/kg at a power density of 799.8 W/kg. Even at its highest power density (7,985.5 W/kg), the device maintained an energy density of 3.55 Wh/kg. The assembled device exhibited excellent cycling stability, retaining 114% of its capacitance after 5,000 cycles. Density Functional Theory (DFT) simulations were conducted to provide a theoretical basis for the increased wettability of functionalized CNTs compared to pristine versions. This study presents a novel approach to synthesising functionalized CNTs from a low cost, eco-friendly carbon source, aimed at enhancing the performance of symmetric supercapacitors (SCs). • CNTs of oil fly ash were functionalized and evaluated as supercapacitor electrodes. • They showed excellent performance mainly after their treatment with nitric acid. • They recorded specific capacitance of 213.1 F /g at 1 A /g after adding Hydroquinone. • The delivered max. power density is 7985.5 W/kg and energy density of 3.55 Wh/kg. • Excellent cycling stability is noticed, and the results were theoretically simulated.