Effect of temperature on the chemical activation of carbon nanospheres and their efficiency in supercapacitors

Abstract

We report the synthesis of carbon spheres (CSs) by pyrolysis of soybean oil and their chemical activation employing acid baths at different temperatures. This allows to study the effect of these experimental parameters on the efficiency of these materials for their use as supercapacitor electrodes. The CSs were characterized by SEM, Raman, XRD, FT-IR, BET, and TEM to reveal the relationship between the electrochemical properties and the structure. Using nitric acid as the activating agent causes the formation of micropores and a high density of oxygenated functional groups in the CSs. In contrast, the mixture of sulfuric and nitric acids destroys the CSs, producing coalescence. The capacitance of the CSs was ~103 F g−1 at 5 mV s−1, and the contribution of electrical double-layer capacitance and pseudocapacitance was determined using cyclic voltammograms. Moreover, it is observed that after 1000 galvanostatic charge-discharge cycles at 2 A g−1, the CSs with the larger electrochemical capacitance increase their capacitive performance up to 38 %, maintaining the electrical double-layer capacitance contribution constant. Therefore, we show that controlling the density of oxygenated functional groups anchored through an increase in temperature during acid treatment and generating high surface areas are key parameters to obtain high capacitance.