Intrinsically high-performance n-type copper (I/II) chloride thermocells

Abstract

Thermocells are attracting growing interest as a promising thermoelectric technology for low-grade heat harvesting. However, the scarcity of high-performance redox couples featuring intrinsically high thermopower (S_e) and fast redox kinetics hinders the rapid development of thermocells. Identifying potential intrinsically high-performance redox couples remains a significant challenge. This work introduces a novel n-type copper (I/II) chloride (CuCl/CuCl₂) redox couple with intrinsically high performance. Through tailored electrolyte design, long-term stability was significantly improved by reducing proton concentration to suppress cuprous ion photo-oxidation, while ammonium chloride solvation enhanced cuprous ion solubility. The resulting system achieves a S_e value closely aligned with theoretical predictions and exhibits rapid redox kinetics. Consequently, the optimized CuCl/CuCl₂ intrinsic system demonstrated a high S_e of 1.52 mV K⁻¹ and a record-high normalized power density P_max (ΔT)⁻² of 0.399 mW m⁻² K⁻², surpassing previously reported intrinsic n-type thermocells and rivaling the performance of p-type pristine 0.4 M ferri/ferrocyanide systems. A prototype module comprising 30 p-n units successfully powered a line of light-emitting diodes or a thermohygrometer. This work introduces a valuable redox couple for further advancing high-performance thermocells and demonstrates a viable strategy for developing novel redox systems.