International Journal of Energy Research, Vol.44, No.7, 5385-5396, 2020
Potassium sulphate (K2SO4) activation of chestnut shell to oxygen-enriched porous carbons with enhanced capacitive properties
Noncorrosive K2SO4 is found to be able to activate the chestnut shell carbon to oxygen-enriched porous carbons. Chestnut shells are activated by K2SO4. The structure, texture, chemical state of surface of samples and morphology are analyzed via X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, transmission electron microscopy and scanning electron microscopy, respectively. With the optimum amount of K2SO4 (m(K2SO4)/m(C) = 1.8), higher specific surface area (SSA, 1412 m(2) g(-1)) and total pore volume (0.75 m(2) g(-1)) are obtained. The prepared carbon samples exhibit a hierarchical textural structure making up of micropores, mesopores and macropores. More importantly, a large amount of oxygen defects, as high as 37.7%, and a small amount of sulfur element (0.31%-0.79%) are successfully introduced on the surface of the carbons. The activation mechanism of K2SO4 is also investigated via thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC), which put it down to the high-temperature redox reaction between C and K2SO4. Owing to the high SSA, the composition of pore, and the abundant surface defects, the activated porous carbons originated from chestnut shell carbon possess highly enhanced capacitive properties. At 0.1 A/g, the specific capacitance reaches 265 F/g, and retains 92% of its starting value after 10 000 cycles at 10 A/g. In general, K2SO4 is a promising noncorrosive alternative to the conventional KOH activator.