A CoHCF system with enhanced energy conversion efficiency for low-grade heat harvesting

Thermally regenerative electrochemical cycles (TRECs) have drawn plenty of attention recently as an efficient and low-cost approach to convert heat to electricity. In this work, we report the application of cobalt hexacyanoferrate (CoHCF)-based materials in TRECs. When the battery is charged at a high temperature (T-H) and discharged at a low temperature (T-L), the discharge voltage is higher than the charge voltage due to the dependence of battery voltage on temperature, and thus low-grade heat can be converted into electricity. The temperature coefficient and specific heat of the material determine the energy conversion efficiency of the battery. When complexed with helical carbon nanotubes (HCNTs), the CoHCF/HCNTs show a higher absolute temperature coefficient and lower specific heat than pure CoHCF. Consequently, the heat-to-electricity conversion efficiency is greatly increased. It is suggested that moderately changing the temperature coefficient and specific heat is an effective strategy to further improve thermogalvanic performance of CoHCF-based materials.