Multiscale honeycomb-structured activated carbon obtained from nitrogen-containing mandarin peel: high-performance supercapacitors with significant cycling stability

Abstract

Herein, a facile aqueous method was used to prepare multiscale honeycomb-structured activated carbon from mandarin peels using KOH and NaOH as activation agents, and the prepared multiscale honeycomb-structured activated carbon was carbonized under a nitrogen and argon atmosphere. All samples possessed nitrogen due to its natural abundance and exhibited enhanced specific capacitance, whereas metallic sodium (Na)-intercalated samples, which were formed due to NaOH activation, showed large pore size with increased intercalation capacitance although their surface area was reduced. Potassium has been additionally intercalated during cycling in a KOH solution and helped to sustain the micro/mesoporous honeycomb structure as well as increased the number of O–CO bonds with a concomitant reduction in the number of C–C and CC bonds. The honeycomb carbon retains up to 98% of its initial capacitance even after 7000 cycles. The presence of multiscale porosity in the interconnected carbon network structure enhances the reversible adsorption/desorption of ions in the Helmholtz double layer and hence results in high storage capacity and rate capability of the supercapacitors. The highest energy density of 10.92 W h kg⁻¹ at the power density of 240 W kg⁻¹ has been achieved and maintained up to 7.06 W h kg⁻¹ at the higher power density of 1740 W kg⁻¹. A detailed kinetic study has been employed to better understand the specific capacitance contribution in symmetrical supercapacitors.