Insights into the Thermopower of Thermally Regenerative Electrochemical Cycle for Low Grade Heat Harvesting

The thermally regenerative electrochemical cycle (TREC) is a promising technology for converting low-grade heat (<100 °C) to electrical power. In this work, the TREC with the NiHCF cathode and Zn anode achieves a markedly high thermopower (α) of -1.575 mV K^-1 and a heat-to-electricity efficiency of 2.41% at the temperature difference of 30 °C (equivalent to 25.15% of Carnot efficiency), surpassing all the existing TREC systems. For the first time, the mixed membranes with mixed pH electrolytes are introduced in the TREC systems to boost α to a record-high value of -2.270 mV K^-1. The proposed thermodynamic framework advances the understanding on the origin of α and electrochemical potential, which will guide people to engineer TRECs.