Activated carbon derived from rice husks enhanced by methylene blue and gamma irradiation for supercapacitor applications†

Electrodes for supercapacitors were developed from activated carbon (GAC) derived from glutinous rice husk (GRH). The production of GAC involved the chemical activation of GRH with potassium hydroxide (KOH), followed by carbonization at 800 °C for 2 hours under a N₂ atmosphere. The pseudocapacitive effects of the GAC were enhanced through N/S doping by adsorption of methylene blue, followed by post-treatment. Two post-treatment methods were employed in this study: gamma irradiation at doses of 25 kGy (GAC-25), 50 kGy (GAC-50), and 100 kGy (GAC-100), and hydrothermal treatment (GAC-Hdt). Among all samples, GAC-25 exhibited the highest specific capacitance of 127.9 F g⁻¹ at 0.5 A g⁻¹, an 84.8% enhancement compared to GAC alone, attributed to pseudocapacitive effects. GAC-25 shows pseudocapacitor behavior, while GAC-Hdt shows EDLC characteristics at an increased scan rate. GAC-Hdt possessed a specific capacitance value of 0.5 A g⁻¹, about four-fold higher than that of GAC-25, due to its larger specific surface area of 1846 m² g⁻¹. These results highlight the potential use of gamma irradiation as an alternative post-treatment method for developing supercapacitor electrodes.