2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Ubiquitous low-grade thermal energy, which is typically wasted without use, can be extremely valuable for continuously powering electronic devices such as sensors and wearable electronics. A popular choice for waste heat recovery has been thermoelectric energy conversion, but small output voltage without energy-storing capability necessitates additional components such as a voltage booster and a capacitor. Here, a novel method of simultaneously generating a large voltage from a temperature gradient and storing electrical energy without losing the benefit of solid-state no-moving part devices like conventional thermoelectrics is reported. Thermally driven ion diffusion is used to greatly increase the output voltage (8 mV K1) with polystyrene sulfonic acid (PSSH) film. Polyaniline-coated electrodes containing graphene and carbon nanotube sandwich the PSSH film where thermally induced voltage-enabled electrochemical reactions, resulting in a charging behavior without an external power supply. With a small temperature difference (5 K) possibly created over wearable energy harvesting devices, the thermally chargeable supercapacitor produce 38 mV with a large areal capacitance (1200 F m2). It is anticipated that the attempt with thermally driven ion diffusion behaviors initiates a new research direction in thermal energy harvesting.
