Preparation of carbon materials for supercapacitors in energy storage by direct hydrothermal carbonization of cellulose and pyrazine

In this study, cohydrothermal carbonization (co-HTC) of cellulose and pyrazine for the production of supercapacitor carbon was investigated at heating of 240 °C for 1 h. The effect of pyrazine loading on the yield of the resulting solid product (hydrochar, HC) and the properties of the activated hydrochar (AHC) were studied. The HC yield increased from 54.3 wt% to 67.2 wt% as the pyrazine loading increased from 4 wt% to 20 wt%. Further increasing the pyrazine loading had little effect on the HC yield. Adding acrylic acid (AA) to the reaction co-HTC system further increased the yield of HC, and the higher the amount of AA added, the higher the yield of hydrochar was. The results also showed that the presence of pyrazine improved the physical properties of the HC by increasing the proportion of functional groups and the specific surface area and promoting the pore-forming process of micropores. At 20 wt% pyrazine loading, the activated hydrochar (AHC) by KOH showed a specific capacitance of 195.8 F/g at a current density of 1 A/g. At a current density of 5 A/g, after 20,000 charge–discharge cycles, the capacity retention remained at 99.96 %. After addition of AA, the proportion of functional groups and the specific surface area of the resulting HC were further improved; however, the specific capacitance of the AHC decreased.