Thermally chargeable supercapacitor using a conjugated conducting polymer: Insight into the mechanism of charge-discharge cycle

Abstract

Ubiquitous temperature-difference thermally energy, which is typically ignored without use, can be extremely valuable for mobile energy storage devices in environments with large temperature differences. A valuable choice for this low-grade thermally energy recovery has been thermoelectric energy storage or conversion, but small output energy storage necessitates sensitive supercapacitor component such as a suitable electrode material and electrolyte. In this work, a novel conjugated all-conducting polymer is synthesized, namely PDAQ-BC via Buchwald-Hartwig coupling method between 2,6-diaminoanthraquinone (DAQ) and 3,6-dibromo-9-(4-bromophenyl)carbazole (DBC). The PDAQ-BC exhibits specific capacitance of 180.5 F g−1 at a current of 1 A g−1 retaining 84% capacitances and about 95% coulombic efficiency upon 5000 cycles at a current density of 5 A g−1. Furthermore, a thermally chargeable supercapacitor (TCS) assembled by PDAQ-BC electrode and polystyrene sulfonic acid film (PSSH) solid electrolyte, which shows a greatly output potential of 6.67 mV K−1 and stable potential retention over 30 h. With a small temperature gradient of 10.8 and 5.2 °C, the TCS produce 72 and 43 mV, respectively. More interestingly, the output potential of TCS is related to temperature gradient and PDAQ-BC electrode, but not to the thickness of the PSSH electrolyte.