context: In addition to the room-temperature performance investigation, we also explored the possibility of operating the hybrid supercapacitor at low temperatures. Our previous research studies have demonstrated that rechargeable batteries using H3O+ ions as charge carriers can operate even at a low temperature of −70 °C. Therefore, it is highly possible that this hybrid supercapacitor can operate well in such cold environments. To illustrate this assumption, we evaluated its electrochemical performance at a low temperature of −70 °C. It can be observed from Fig. S19† that the acid electrolyte containing Mn2+ has frozen at −70 °C. However, the hybrid supercapacitor still displays a discharge specific capacitance of 163.6 F g−1 at 0.1 A g−1 and 62.2 F g−1 at 0.5 A g−1 (Fig. 5a). Additionally, the Ragone plot in Fig. 5b shows that the hybrid supercapacitor exhibits a maximum energy density of 27.4 W h kg−1 and power density of 605 W kg−1 at −70 °C. More surprisingly, the specific capacitance of the hybrid supercapacitor can maintain approximately 100% of the original capacitance over 1000 cycles at −70 °C (Fig. 5c). Such excellent low-temperature performance of the hybrid supercapacitor is associated with the high ionic conductivity of the electrolyte. The DSC measurements show that the freezing point of the acid electrolyte containing Mn2+ is −40.2 °C (Fig. S20†), which is lower than that of the 2 M MnSO4 solution (−11 °C, Fig. S21†). Surprisingly, it is found that this acid electrolyte containing Mn2+ can still show a decent ionic conductivity at −70 °C (2.6 mS cm−1), obtained from EIS data displayed in Fig. S22 (see the related calculations in the ESI†).