Recycling of biomass wastes from amarula husk by a modified facile economical water salt method for high energy density ultracapacitor application

In this study, we are reporting for the first time the activated carbon from amarula seed husk (AMH) produced by a modified facile synthesis method producing low-cost, high porosity materials through impregnation of raw materials with water salt. The water salt treatment resulted from the salt formed by a mixture of calcium chloride and phosphoric acid. Calcium influences the catalytic of dehydroxylation and desiccation while phosphate groups stimulates the pyrolytic transformation of the raw material which increases the expansion of pores on the surface of the carbon materials thus prevents destruction of the carbon structure and produce a high yield. The treated AMH with water salt displayed high specific surface area with a maximum specific capacitance of 275 F g⁻¹ at 0.5 A g⁻¹ in a three-electrode configuration. The fabricated symmetric device presented a specific energy and power of 16 Wh kg⁻¹ and 450 W kg⁻¹ at 0.5 A g⁻¹, and retained 10 Wh kg⁻¹ and 18 kW kg⁻¹ at 20 A g⁻¹. The symmetric device retained a capacitance retention of 94.3 % noted after 13,000 cycling and 88.5 % for up to 20,000 cycling at 5 A g⁻¹. An exceptional increase in specific energy from 15.5 to 38.3 Wh kg⁻¹ at 1 A g⁻¹ was noted after 200 h floating time. The results propose the potential synthesis progress for recycling and transforming economical biomass waste for developing high performing energy storage device. The approach used in this work is simple and cost-efficient compared to other method that comprises of high temperature and organic chemicals, which are poisonous and corrosive to the environment.