High yield low temperature biocompatible activation of biochar for sustainable supercapacitors

Abstract

This study presents a sustainable and efficient method for producing activated carbon from biomass-derived biochar for use in electrochemical supercapacitors. Biochar sourced from wood chips supplied by Carbofex Ltd., a European Biochar Certificate (EBC) certified biomass producer renowned for carbon-negative biochar, was hydrothermally activated using potassium bicarbonate (KHCO3) at 200 °C for 36 h. This simplified activation method achieved a yield of approximately 90 %, in contrast to the 30–70 % typically obtained with conventional activation methods such as KOH or CO2, where extensive carbon burn-off is common. Beyond yield, the process enhanced the BET-specific surface area from ∼420 to ∼1006 m2/g and improved thermal stability by removing volatile fractions, generating a microporous network with structural robustness and ion-accessible porosity. Electrochemical characterization showed that the activated carbon achieved a specific capacitance of 27.13 F/g at 0.08 A/g, which is comparable to commercially available activated carbon YP80-F (30 F/g) and retained 85 % of its capacitance after 10,000 cycles. The activated carbon device performed on par with commercial materials, indicating its promise for practical supercapacitor use. This mild, non-corrosive activation process using sustainable precursors offers a scalable alternative to conventional methods, avoiding the environmental and safety risks associated with agents like KOH.