Coordination enhanced high-seebeck coefficient n-type gel-based thermocells for low-grade energy harvesting and n-p type connected devices

Thermocells (TECs) have shown potential for commercial applications in low-grade heat harvesting, but the development of n-type TECs has always been lagging behind p-type TECs, hindering the practical utilization of integrated devices. Here, n-type and p-type TECs of polyacrylic acid (PAA) and bacterial cellulose (BC) composite hydrogel are developed, respectively. By coordinating Fe3+ with carboxyl groups, the thermal entropy difference between Fe2+ and Fe3+ increases, resulting in a record high Seebeck coefficient (S) of 2.51 mV K−1 of Fe3+/Fe2+ redox couple in n-type TEC. In p-type TEC, a S of −1.29 mV K−1 based on [Fe(CN)6]4‒/[Fe(CN)6]3‒ redox couple is achieved. The 22-pair n-p type connected device generated a voltage of 1.8 V at a temperature difference of 30 K, which is enough to power a calculator and light up an LED without an amplifier. This work offers a fresh perspective for enhancing the performance of n-type TECs and promoting the practical application of n-p type connected devices.