Constructing High-Power N-Type Thermocells via Fluoride-Mediated Imidazole-Iodine Coordination

I^-/I₃ ^--based thermocells show great potential for low-grade heat harvesting because of their affordability, adjustable electrochemical Seebeck coefficient (S_e), and ease of device integration. However, current strategies of developing high-performance I^-/I₃ ^--based thermocells usually result in substantial imbalance between S_e and ultimate output power due to deteriorated ion transportation and replenishment. Herein, we propose a novel fluoride-mediated coordination strategy to break this trade-off. By introducing potassium fluoride and 1-(2-hydroxyethyl)imidazole (HEI) into the electrolyte, we engineer in situ formation of thermosensitive HEI-I₂F^- coordinated complexes. These complexes undergo reversible temperature-dependent precipitation and dissociation, creating a significant concentration ratio gradient, thereby remarkably increasing S_e. Concurrently, the introduced ligand ions disrupt the original hydrogen bonding of water molecules, facilitating superior ion transport for increased output current. Consequently, the optimized thermocell achieves a high S_e of 1.53 mV K^-1 and a maximum power density of 124.74 mW m^-2 at ΔT = 30 K. This work provides a versatile and effective pathway toward high-power thermocells for low-grade heat harvesting.