Expanding the range of supercapacitor operation to temperatures above 100 °C is important because this would enable capacitors to operate under the severe conditions required for next-generation energy storage devices. In this study, we address this challenge by the fabrication of a solid-state supercapacitor with a proton-conducting Sn(0.95)Al(0.05)H(0.05)P(2)O(7) (SAPO)-polytetrafluoroethylen...