Hybrid thermoelectrochemical and concentration cells for harvesting low-grade waste heat

Abstract

Thermoelectrochemical cells (TECs) are promising platforms for thermal energy conversion. However, their widespread use is limited because of their low Seebeck coefficient and low conversion efficiency. We demonstrate a hybrid thermoelectrochemical and concentration cell based on carbonate solvents with a I3−/I− redox couple (referred to as i-TCC), which outperforms the current best n-type TEC employing an aqueous Fe3+/2+ redox couple. As the temperature of the hot side of i-TCC increases above 40 °C, dimethyl carbonate solvent reacts with iodide anions to form a porous Li2CO3-matrix near the hot electrode, which sustains long-lasting iodide-concentration gradient across the cell. The thermally driven concentration difference boosts the performance of the TEC to yield a remarkably high Seebeck coefficient (+7.7 mV K−1), figure of merit (ZT = 0.114), and Carnot efficiency (5.2%) for a temperature difference of 35 °C (25 °C and 60 °C for cold and hot temperatures, respectively). i-TCC demonstrated here thus provides a new perspective in harvesting low-grade waste heat.