Concentration-driven enhancement of low-grade thermal energy harvesting in electrochemical systems

Thermal regenerative electrochemical cycles (TRECs) represent a highly promising technology for the direct conversion of low-grade thermal energy (<373 K) into electrical energy. This study investigates the impact of electrolyte concentration on the electrochemical performance and thermoelectric conversion efficiency of nickel hexacyanoferrate (NiHCF) electrodes. The findings demonstrate that decreasing the electrolyte concentration not only increases the reaction entropy, but also reduces the interstitial water content within the NiHCF lattice, thereby amplifying the vibrational energy of the cyanide ligands. Ultimately, the synergistic effect of these two mechanisms yields an enhanced temperature coefficient (α). Leveraging the theory of concentration-driven temperature coefficients, a highly efficient TREC Zn–NiHCF flow cell was developed. Notably, this study represents the first elucidation of how supporting electrolyte concentration influences Prussian blue analogues in thermal energy recovery applications, offering a critical insight into the viability of TREC systems and establishing new avenues for optimizing their energy-harvesting capabilities.