Cold-Resistant Nitrogen/Sulfur Dual-Doped Graphene Fiber Supercapacitors with Solar-Thermal Energy Conversion Effect.

Although graphene fiber-based supercapacitors are promising for wearable electronic devices, the low energy density of electrodes and poor cold resistance of aqueous electrolytes limit their wide application in cold environments. Herein, porous nitrogen/sulfur dual-doped graphene fibers (NS-GFs) are synthesized by hydrothermal self-assembly followed by thermal annealing, exhibiting an excellent capacitive performance of 401 F cm-3 at 400 mA cm-3 because of the synergistic effect of heteroatom dual-doping. The assembled symmetric all-solid-state supercapacitor with polyvinyl alcohol/H2 SO4 /graphene oxide gel electrolyte exhibits a high capacitance of 221 F cm-3 and a high energy density of 7.7 mWh cm-3 at 80 mA cm-3 . Interestingly, solar-thermal energy conversion of the electrolyte with 0.1 wt % graphene oxide extends the operating temperature range of the supercapacitor to 0 °C. Furthermore, the photocatalysis effect of the dual-doped heteroatoms increases the capacitance of NS-GFs. At an ambient temperature of 0 °C, the capacitance increases from 0 to 182 F cm-3 under 1 sun irradiation because of the excellent solar light absorption and efficient solar-thermal energy conversion of graphene oxide, preventing the aqueous electrolyte from freezing. The flexible supercapacitor exhibits a long cycle life, good bending resistance, reliable scalability, and ability to power visual electronics, showing great potential for outdoor electronics in cold environments.