Hydrothermal synthesis of nitrogen-containing carbonaceous nanostructures from biomass for energy storage device

This research aimed to utilize enriched nitrogen carbonaceous material for energy storage. Spent coffee ground was selected as a precursor for the nitrogen-containing carbonaceous material (3.2 wt.%). The processes for synthesis consist of hydrothermal carbonization (HTC) and chemical activation by KOH. In HTC process, the precursor was hydrothermally carbonized with 0.5 M acetic acid at 200 C for 12 h. For the chemical activation, the derived material from HTC process (biochar) was mixed with different weight ratios between biochar and KOH in the ratio of 1:1 to 1:4, then carbonized at 800 C under nitrogen atmosphere. The optimum ratio of biochar to KOH was 1:2, providing the highly uniform porosity, ratio of micropore to mesopore volume of 3.4, surface area of 1300 m2 g-1, and nitrogen content of 3.4 wt.%. Moreover, the chemical species of this sample were analyzed by XPS technique. A-SCG 1:2 presented the pyridinic nitrogen species on the surface which plays important role in capacitance performance. This sample exhibited the highest specific capacitance in the range of 221-273 F g-1 at different scan rates from 20 to 100 mV s-1 in 6 M KOH electrolyte.