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 (Se), and ease of device integration. However, current strategies of developing high-performance I-/I3 --based thermocells usually result in substantial imbalance between Se 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 Se. 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 Se 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.