A Solid-State and Flexible Supercapacitor That Operates across a Wide Temperature Range

Electrochemical properties of most supercapacitor devices degrade quickly when the operating temperature deviates from room temperature. To exploit the potential of rGO in supercapacitors at extreme temperatures, a resilient electrolyte that is functional over a wide temperature range is also required. In this study, we have implemented a flexible, low-resistant solid-state electrolyte membrane (SSEM) into symmetric rGO electrodes to realize supercapacitor devices that operate in the temperature range −70 to 220 °C. The SSEM consists of a polycation–polybenzimidazole blend that is doped with phosphoric acid (H3PO4), and this material displays uniquely high conductivity values that range from 50 to 278 mS cm–1 in the temperature range −25 to 220 °C. The fabricated supercapacitor produced a maximum capacitance of 6.8 mF cm–2 at 100 °C. Energy and power densities ranged from 0.83 to 2.79 mW h cm–2 and 90 to 125 mW cm–2, respectively. The energy storage mechanism with a SSEM occurs by excess H3PO4 migrating from the membrane host into the electrochemical double layer in rGO electrodes. The high-temperature operation is enabled by the polycation in the SSEM anchoring phosphate type of anions preventing H3PO4 evaporation. Low-temperature operation of the supercapacitor with the SSEM is attributed to the PC–PBI matrix depressing the freezing point of H3PO4 to maintain structural proton diffusion.