Fully utilizing the organic and inorganic fractions in rice husk for electrode materials towards an excellent asymmetric solid-state supercapacitor

Rice husk is selected as the feedstock for the production of activated carbons (RHAC). The desilication process is performed to enhance its potential application in supercapacitors, meanwhile, cobalt silicates (Co/Si-x) are synthesized from recycled waste silica. To explain the effect of desilication processes on the characteristics of derived activated carbons, the desilication steps are carried out after carbonization and activation to produce two different types of desilicated RHAC (CD-RHAC and AD-RHAC). Results show that the specific surface area of CD-RHAC and AD-RHAC are 3404.5 and 3451.3 m2 g−1, which are both higher than that of untreated RHAC (2075.1 m2 g−1). Furthermore, Co/Si-x samples exhibit significantly different properties due to the various Co/Si ratios. In a three-electrode system, the capacitance of CD-RHAC and Co/Si-3 can achieve the capacitances of 264.5 and 400.3 F g−1 at the current density of 0.5 A g−1. The CD-RHAC//Co/Si-3 asymmetric solid-state supercapacitor shows an excellent capacitance retention of about 100 % after 6000 cycles and a high energy density of 19.0 Wh kg−1 at a power density of 176.8 W kg−1. Overall, the work offers a feasible pathway to fully utilize the organic and inorganic fractions of lignocellulosic biomass in the field of energy storage.