Parameter study in preparation of nitrogen-rich-activated carbon for supercapacitors' application using multilevel factorial design

Abstract

This research aims to study the effect of process parameters on hydrochar modification from biomass on physical and electrochemical properties. Hydrochar is produced by hydrothermal carbonization of biomass at 275 °C for 2 h using an activating agent of CaCl2. Hydrochar was modified by impregnation at a time variation (1 and 2 h) and doping type (urea, thiourea, and ammonium persulfate). The ratio of hydrochar to doping compound (1:1, 1:2, and 1:3). Activation is carried out by pyrolysis at 800 °C by flowing N2 and CO2 gases. The doping ratio and impregnation time significantly increase the yield of ​​activated carbon. The highest value is 39.97 percent for the sample with thiourea and a ratio doping of 1:3 at 2 h (ACT13-2). The main process parameter and the interaction of impregnation time with the doping type affect the surface area of ​​activated carbon. Porosity analysis indicates the product had a mesoporous structure with the largest surface area of ​​677.44 m2 g−1 for the sample with ammonium persulfate and a ratio of 1:1 at 2 h (ACA11-2). The process parameters significantly reduce electrolyte and charge transfer resistance and increase the specific capacitance. The cyclic voltammetry analysis shows the highest capacitance of the supercapacitor cell of 43.25F g−1 was obtained for the sample with urea and a ratio of 1:3 at 2 h (ACU13-2). The endurance test was carried out for 5000 cycles and showed that the supercapacitor cells were stable at 98 percent. Research findings indicate that the hydrochar impregnation method followed by activation can be an effective alternative to produce inexpensive nitrogen-rich activated carbon for supercapacitor applications.