Inorganic matter in rice husk derived carbon and its effect on the capacitive performance

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Journal of Energy Chemistry


Porous carbons were obtained from rice husk using two different chemical activation methods and they were investigated as supercapacitors. Their properties were studied using X-ray photoelectron spectroscopy, thermal analysis, potentiometric titration, and nitrogen adsorption isotherm. The specific capacitance measured in both H2SO4 and KOH electrolytes in two-electrode cell was up to ~150 F/g. The activation method used affected the resulting carbons' features. As expected, the dependence of the capacitance on porosity was found. The ash content reached 36 wt.% and that inorganic mater blocked some pores and limited their accessibility to electrolyte ions and increased the charge transfer resistance. Nevertheless, the main ash constituents such as CaCO3, MgCO3, Ca3(PO4)2 (or P2O5), and Fe- and Zn- containing species did not affect the specific capacitance to a large extent. Especially SiO2, even in a relatively large amount (~20 wt.%), did not play a detrimental role in the capacitance behavior. The results showed that in spite of a high ash content, carbon can exhibit a good capacitive performance provided that it has a favorable porosity and is rich in sp2 configurations.