The effect of ultrasonic and HNO3 treatment of activated carbon from fruit stones on capacitive and pseudocapacitive energy storage in electrochemical supercapacitors

The effect of ultrasonic treatment and modification with nitric acid of activated carbon obtained from fruit stones, on the parameters of electric double-layer (EDL) as well as on farad–volt characteristics of its boundary with electrolyte 7.6 m KОН, 4 m KI and 2 m ZnI2 aqueous solutions has been studied by means of precision porometry, cyclic voltamperometry, electrochemical impedance spectroscopy and computer simulation methods. It is shown that HNO3 treatment results in an increase of the electrostatic capacitance up to 202 F/g in 7.6 m KОН-solution as well as pseudocapacitance up to 1250 F/g in 4 m KI. This increase is supposed to be related both with hydrophilicity and with an increase of the density of states on Fermi level. The ultrasonic treatment enables one to significantly increase (more than 200 times) the density of states on Fermi level which in turn causes both quantitative and qualitative changes in farad–volt dependences. A hybrid supercapacitor with specific capacitance of 1100 F/g and specific energy of 49 Wh/kg per active mass of two electrodes was developed.