Prompt Thermal Transfer Across the sp3–sp2 Interfaces for the Enhanced Electrochemical Performance of Aqueous Carbon-Based Supercapacitors

The local thermal accumulation induced by the charging process of the aqueous supercapacitors will facilitate water splitting, which seriously decreases the energy density and safety of aqueous supercapacitors. Therefore, it is necessary to evacuate the heat from the active sites and identify the types of side reactions. In this study, we employ a self-assembly strategy to successfully synthesize a highly thermally conductive three-dimensional nanodiamond-reduced graphene oxide (NDs-rGO) aerogel. The NDs-rGO aerogel is used as the electrode material, which can expand the operating voltage of alkaline aqueous symmetric supercapacitors to 1.1 V, much higher than that of previously reported carbon-based symmetric supercapacitors (≤1.0 V). Moreover, we have, for the first time, utilized scanning electrochemical microscopy to confirm the beneficial role of materials with thermally conductive interfaces in dissipating heat during the charging process of supercapacitor electrodes. As a result, the aqueous NDs-rGO supercapacitor device exhibits excellent reversibility (100% capacitance retention after 10,000 cycles) and achieves an energy density of 12.2 W h kg–1 at a high working voltage of 1.1 V. The excellent electrochemical performance may be ascribed to the fact that the redox self-assembly process in NDs-rGO creates high thermal-conductivity heterogeneous interfaces between sp2–sp3 structures, enabling rapid heat dissipation during the charging process, suppressing water splitting, and thus increasing the working voltage of the supercapacitors.