Carbon material produced by hydrothermal carbonisation of food waste as an electrode material for supercapacitor application: A circular economy approach

This study aims to use landfill leachate (LL) as an aqueous medium during hydrothermal carbonisation (HTC) of food waste to produce hydrochar (FWH-LL-C), which could be used as an electrode material in energy storage devices. The structural properties and electrochemical performance of the hydrochar were compared to that obtained using distilled water as a reaction medium (FWH-DW-C). The results showed that there is a difference in Brunauer-Emmett-Teller (BET) surface area of FWH-LL-C (220 m² gm^-1) and FWH-DW-C (319 m² gm^-1). The electrochemical properties were comparable, with FWH-LL-C having 227 F g^-1 specific capacitance at 1 A g^-1 current density and FWH-DW-C having 235 F g^-1 specific capacitance at 1 A g^-1 current density. Furthermore, at a power density of 634 W kg^-1, FWH-DW-C achieved the highest energy density of 14.4 Wh kg^-1. The energy retention capacity of the electrode was 98% which indicate that the material has an excellent energy storage capacity. The findings suggested that LL could be used as an alternative source of aqueous media during the HTC of food waste to produce hydrochar which could be used as an effective electrode material in supercapacitors.