Enhanced electrochemical cooling through a cascade Brayton refrigeration cycle: theoretical and practical insights

Effective and eco-friendly refrigeration technologies have been sought for years because vapor compression contributes largely to the global warming potential. Electrochemical refrigeration is a promising alternative due to the merits of zero-GWP, high efficiency, direct electrical-to-heat conversion, etc. However, it falls short of ultralow temperatures with significant temperature lift (ΔT). Here, we propose a novel cascade electrochemical Brayton refrigeration cycle that effectively enhances electrochemical deep refrigeration by cascading thermocells, integrating regenerative heat exchange, charging and discharging, and heat absorption and dissipation to increase ΔT, which is unique in utilizing the inherent entropy change of redox couples for refrigeration. Mathematical formulas and analytical models based on experimental data are derived and developed. Results show that with six cells cascaded and optimized parameters, the temperature lift of electrochemical cooling is enhanced from 16.27 to 109.79 K. More cells, higher regenerative efficiency, lower current, and larger temperature coefficient favor ΔT values of 30.52 K, 85.05 K, 30.54 K, and 109.79 K, respectively. Temperature coefficient affects the most on ΔT. This research broadens the scope for electrochemical deep refrigeration and provides a clear framework for optimization.