Enhancing thermoelectric conversion efficiency of hydrogel-based supercapacitors by the three-dimensional ion channels hydration

Abstract

Ionic thermoelectric (i-TE) supercapacitors are capable of converting low-grade heat directly into electricity, which has enormous potential for wearable power sources and the Internet of Things. However, the low thermoelectric conversion efficiency limits their applications. Here, we report a method for forming polar corona in a three-dimensional (3D) network based on chitosan-polyacrylamide‑silicon dioxide (PACS) hydrogel, significantly increasing the maximum thermogalvanic power density of 187.2 mW m−2 at a temperature difference (ΔT) of 5 K. The abundant functional groups on PACS confine free H2O molecules to the polymer network, forming polar corona, reducing the volume of thermally diffused ions, and enabling rapid conduction of lithium ions (Li+) in unsaturated coordination. In addition, demonstrating an impressive ionic conductivity of 50.2 mS cm−1 as well as a maximum thermal charging voltage of 200 mV (ΔT of 8 K), this work provides a new strategy for broadening applications of ionic thermally chargeable supercapacitors in harvesting low-grade heat and wearable devices.