Carbon hollow spheres as electrochemical capacitors: Mechanistic insights

Abstract

Carbon hollow spheres with similar sizes and surface functionalities but different specific surface areas and shell thickness are prepared to investigate the insight mechanism of energy storage in carbon hollow spheres as electrochemical capacitors utilizing Step Potential Electrochemical Spectroscopy. In 0.5 M Na2SO4 electrolyte carbon hollow spheres provide much better overall capacitance values as compared to high surface area activated carbon due to the better surface area utilization particularly at large scan rates. Carbon hollow spheres exhibited 74% more specific surface area utilization for energy storage as an electrode material in comparison to activated carbon in 0.5 M Na2SO4 solution. When, overall capacitance is divided in to the fragment capacitances in terms of geometric, porous and diffusional contents; morphology of hollow spheres played an important role while in the non-aqueous solutions specific capacitance values remained dependent on the specific surface area of the carbon material. Diffusional fragment of capacitance values in carbon hollow spheres remained limited because of limited thickness of the hollow shells. In this study, at 1 mV s−1 carbon hollow spheres with 29 nm shell thickness and with a specific surface area of 1523 m2 g−1 exhibited a specific capacitance values of 105 F g−1 and 127 F g−1 as compared to 85 and 121 F g−1 for activated carbon with a specific surface area of 1895 m2 g−1 in 0.5 M sodium sulfate and 1.0 M TEABF4 respectively.