Rice husk-derived sodium hydroxide activated hierarchical porous biochar as an efficient electrode material for supercapacitors

Abstract

In this study, one-step pyrolysis technique and NaOH chemical activation method were used to synthesize hierarchical porous biochar from rice husk. The existence of carbonaceous structure in biochar samples was confirmed by X-ray diffraction, field-emission scanning electron microscopy, elemental mapping, Raman spectroscopy, Brunauer-Emmett-Teller surface area, and X-ray photoelectron spectroscopy analysis. Activation of NaOH in rice husk biochar (ARB) sample suggested seven-fold enhancement of BET specific surface area (307.42 m2 g−1) as compared to rice husk biochar (RB). The NaOH activation also provides the enhancement of specific capacitance in RB. The boosting of supercapacitors (SCs) performance of ARB was proved by a larger loop in cyclic voltammetry and triangular shape along with a longer discharge time in galvanostatic charge-discharge curves as compared to RB. The electrode revealed excellent cyclic stability up to 4000 cycles with 94% retention. Furthermore, electrochemical impedance spectroscopy and galvanostatic charge-discharge curves showed evidence of electrode stability. The mechanisms related NaOH activation and enhancement of supercapacitor performance were well explained. These results suggest that NaOH treated RB could be promising low-cost electrode material for SCs application.