Preparation of porous biochar and its application in supercapacitors

Abstract

In this study, economical porous biochar was prepared from an apricot shell and used as an electrode material for a supercapacitor, showing excellent capacitance, cycling stability and rate performance. KOH was used as the activator for preparing the biochar, and the effects of different activator concentrations on the specific surface area, pore volume, morphology and the electrochemical properties of the prepared biochar material were investigated. The results showed that increasing the KOH concentration from 0 mol L⁻¹ to 4 mol L⁻¹ changed the surface morphology of the prepared biochar from a smooth and non-porous structure to a porous honeycomb structure. The specific surface area and pore volume of the porous biochar increased first and then decreased and reached a maximum value (2452.7 m² g⁻¹, and 1.613 cm³ g⁻¹) at a KOH concentration of 3 mol L⁻¹. After assembling the supercapacitor with the prepared biochar, the specific capacitance (C_s) was 216 F g⁻¹ at 0.5 A g⁻¹ and the C_s could still reach a high capacity of 189 F g⁻¹ at 20 A g⁻¹, which was 87.5% of the C_s at 0.5 A g⁻¹. Meanwhile, the assembled supercapacitor showed a high capacity retention rate of 99.5% after 10 000 cycles of charging and discharging at 5 A g⁻¹ and a high energy density of 7.48 W h kg⁻¹ at 125 W kg⁻¹ power density.