Thermally Regenerable Redox Flow Battery for Exploiting Low-Temperature Heat Sources

Harvesting energy from low-temperature heat sources (<100°C) would enable the exploitation of currently untapped renewable sources. Recently proposed techniques fail to reach suitable efficiencies. We propose here a redox flow battery that can be recharged by a thermal process, distillation. The electrochemical cell produces electrical energy from the mixing free energy of two sodium iodide aqueous solutions at different concentrations. The electrochemical cell is based on the technology of sodium ion-conducting ceramics and is coupled with a liquid-liquid extraction process, performed by an unconventional device, the “through-liquid-exchanger.” Our technique bypasses the bottleneck of other similar techniques by working with solutions at very high concentrations. Our initial experiments prove an unprecedented energy efficiency (ratio between the electrical work produced and the incoming heat necessary to restore the initial solutions concentrations) of 3% from a heat source <100°C and a power density of 10 W/m2, with the possibility of further improvements. © 2020 The Author(s) The flow battery described by Facchinetti et al. can be recharged by distillation with heat sources <100°C. It enables the efficient exploitation of currently untapped clean and renewable heat sources (e.g., low-concentration solar heat collectors). The design is based on a solid-state ion conductor and includes an unconventional device based on liquid-liquid exchange.