Charging-free redox flow battery for continuous high-power electricity generation from low-grade heat

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.