Iron-Based Thermally Regenerative Flow Battery Recharged by Distillation of Acetone

Thermo-electrochemical conversion systems can convert abundant low-grade heat into electricity. In particular, thermally regenerative flow batteries (TRFBs) have gained significant attention owing to their high power density compared to other thermo-electrochemical conversion systems. However, the variety of redox species is limited in previous studies. To provide an alternative option for the redox species, we newly propose using Fe, and investigate the performance of an Fe-based TRFB called the solvation difference flow battery (SDFB). In this study, the SDFB uses [Fe(CN)6]4-/3- as the redox species and can be recharged by the distillation of acetone. The maximum power density was 40 W m-2 and the thermal efficiency was estimated to be 0.20% at an average power density of 16 W m-2. In addition, we discuss the challenges for future improvements. The cell voltage should be enhanced by optimizing the electrolyte components, such as solvents and counterions. For the cell design, the cell resistance is reduced by improving the flow fields of the electrolytes to enhance the mass-transfer properties. Moreover, a membrane that satisfies both a high ion conductivity and low crossover rate of the solvents is required. This study provides new options for the redox species in TRFBs. Iron was newly used as a redox species of the thermally regenerative flow battery. The iron-based flow battery can be recharged by distillation of acetone. Maximum power density reached 40 W m-2. Technical challenges for the electrolyte and cell designs were discussed.