A comparative study of electrochemical Brayton cycle and thermally regenerative electrochemical cycle

Abstract

Both the emerging thermally regenerative electrochemical cycle (TREC) and electrochemical Brayton cycle (EBC) harvest low-grade heat by utilizing the temperature effect of electrode potential. Their key difference lies in the cycle configurations, the Stirling cycle and the Brayton cycle, respectively. Determining which cycle configuration performs better could indicate the direction of thermodynamics for further research. However, this remains an open question to be investigated. To address this, a performance comparison of EBC and TREC using KI/KI3 and K3Fe(CN)6/K4Fe(CN)6 solutions as electrolytes is conducted based on an improved system configuration and a two-dimensional model coupling mass transfer and electrode kinetics. Multi-objective optimization results show that there is no significant difference in performance between EBC and TREC. Under a given temperature difference of 50 °C, the power density and exergy efficiency of optimized EBC are respectively 5.28 W m−2 and 16.6%, compared with 5.93 W m−2 and 15.6% of optimized TREC. The corresponding temperature drops of heat sources are 14.49 °C and 12.26 °C, respectively, indicating that EBC is more suitable for heat sources with large temperature variations. The concentration overpotential is found to be the main contributor to entropy generation in both EBC and TREC besides heat transfer. Their power density and exergy efficiency can be further improved by approximately 50% and 40% by eliminating overpotentials, respectively. This study is expected to provide beneficial insights into the performance optimization and electrolyte improvement of EBC and TREC.