Synthesis and characterization of electron beam irradiated glutinous rice husk-derived biochar and activated carbon for aqueous electrochemical capacitors

Glutinous rice husk, an abundant agricultural biowaste in Thailand, was pretreated with high energy electron beam irradiation (EBI) at doses of 500 kGy, 1000 kGy, and 1500 kGy prior to fabrication into biochar by carbonization at 500℃ under nitrogen atmosphere. The biochar was then treated with KOH and subsequently heated at 800℃, yielding activated carbon (GAC). The physical, chemical, and electrochemical properties of the as-received biochar (GB) and activated carbon (GAC) were investigated. Scanning electron microscopic images (SEM) suggested that biochar irradiated with 1500 kGy (GB-1500) has the highest porosity compared to the other samples. The electrochemical properties of GB and GAC in 3 M H2SO4 using a three-electrode system indicated that EBI affects the electrochemical performance of the material. The specific capacitance of GB-1500 (6.15 F·g-1 at 0.05 A·g-1) is higher than that of the as-received biochar, and the improved performance of the former is potentially due to the formation of structural defects upon irradiation. Finally, we observed that the specific capacitances of the GAC were much higher than those of their corresponding GB with the same irradiation doses, and the capacitances of the GAC decrease with increasing EBI dose.