Novel porous thermosensitive gel electrolytes for wearable thermo-electrochemical cells

Abstract

Thermo-electrochemical cells (TECs) represent an efficient and low-cost heat-harvesting device that can directly convert human body heat energy into electricity. However, the flexible, solid-state gelled electrolytes used in wearable thermocell devices suffer from poor mass transport of electrolyte. Here, a novel porous gel is developed via sodium acetate (NaAc) templates and freeze-drying treatment that is applied in p-type gelled electrolyte: poly-acrylamide (PAM) - K3/4[Fe(CN)6] and integrated into platinum (Pt) electrodes for wearable devices. Moreover, the guanidinium ([Gdm]+) is initially introduced into gelled electrolytes, and the p-type cell effectively boosts the maximum power density from 4.01 to 7.68 mW m−2 at ΔT = 10 °C, and exhibits a quick thermosensitive response under a broad temperature range (15 – 55 °C), which is sufficient for working conditions of wearable devices. The optimised porous gel host was also utilized in series with an n-type: PAM-FeCl2/3-HCl gelled electrolyte. The multiple thermocells (12 pairs) were further fabricated into a device by alternating p- and n-type cells in series. This device was found to output nearly 0.23 V at ΔT = 10 °C, and was manufactured into a flexible wearable device that was demonstrated to successfully harvest human body heat by both charging a supercapacitor (100 mF), and illuminating an LED, demonstrating the potential of actual application of our n-p-type in series devices.