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.

Low-grade heat (< 100 °C) is abundant in the environment, which is the key to alleviating the potential energy crisis of modern society through reasonable heat energy conversion and storage. Most thermal regenerative electrochemical cycle systems (TREC) rely on external power for charging, resulting in additional energy loss. Here, we report a charging-free redox flow battery for continuous high-power, low-grade heat harvesting based on thermosensitive crystallization-boosted TREC. Using molecular dynamics (MD) and density functional theory (DFT), we analyzed the mesoscopic intermolecular interactions, radial distribution, and solvation structure variations of [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ across varying temperatures. These insights elucidate the mechanism of thermosensitive crystallization evolution and its influence on entropy change during the thermodynamic cycle. By rationally adjusting redox activity at various temperatures, the system achieves an impressive temperature coefficient of −3.72 mV/K and a full-cell coefficient averaging –2.78 mV/K, exceeding the highest value of reported charging-free TRECs. The maximum power density also exceeds 3 times the best-reported charging-free TREC.