Rapid Carbothermal Shock Enhances the Double-Layer Response of Graphene Oxide–Carbon Nanotube Electrodes

Abstract

Graphene oxide and carbon nanotube composites are considered to be an ideal electrode for electrochemical energy storage and conversion. Herein, we prepare electrodes via a green synthesis that yields a binderless, flexible, and free-standing electrode. To improve the performance of these electrodes comprising graphene oxide and carbon nanotubes (GO–CNT), we carry out carbothermal shock (CTS), which reduces graphene oxide in a rapid (millisecond time scale) and tunable manner (1000–2000 K). When CTS is employed, the specific capacitance of GO–CNT increases by 50%, from 30 to 45 F g–1, for reduced GO–CNT (GO–CNT_CTS). When benchmarking against activated carbon, both GO–CNT and GO–CNT_CTS outperform in terms of capacitance and rate capability. We then examine impedance spectroscopy data in the form of two-dimensional color-mapped surface plots to analyze the dependence of the real and imaginary capacitance and the phase angle as a function of both frequency and potential. This analysis provides key mechanistic insight into the electrochemical double-layer response, such as the characteristic relaxation time and charge-transfer resistance. This analysis shows that, upon CTS, the relaxation times of GO–CNT-based electrodes are 70% faster than that of activated carbon and charge-transfer resistances are reduced dramatically.