Carbon sequestration through hydrothermal carbonization of expired fresh milk and its application in supercapacitor

Abstract This study investigated the production of natural nitrogen-doped carbon from expired fresh milk for use in a supercapacitor electrode. The material was prepared by hydrothermal carbonization followed by sequential KOH–H3PO4 activation. Carbon modified with KOH at a ratio of 1:1 had the largest Brunauer-Emmett-Teller surface area of 465 m2/g. Furthermore, the presence of surface functional groups played an important role in determining the specific capacitance. The highest specific capacitance of 186.3 F/g was obtained from carbon modified with C:KOH at 1:1 and 50 wt% H3PO4. An electrochemical impedance study suggested that charge storage resembled a modified Randles circuit. Carbon derived from expired milk and exposed to sequential KOH and H3PO4 modification was shown to be a promising candidate material for use as electrodes in electric double-layer supercapacitors, while simultaneously reducing food waste.