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

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.