Towards efficient continuous thermally regenerative electrochemical cycle: Model-based performance map and analysis

Abstract

Continuous thermally regenerative electrochemical cycle (TREC), which could convert heat to power and realize the continuous power output, is a promising technology for low-grade heat harvesting. However, the mechanism elucidation and performance analysis of continuous TREC are still incomplete, which hinders its performance improvement and practical applications. In this study, a pseudo-two-dimensional flow and electrochemical coupled model for continuous TREC is developed to investigate its performance. Based on the model, the polarization mechanism is revealed, and the effects of operating parameters and physical properties of electrolytes on the cycle performance are analyzed in detail. The results indicate that the concentration polarization is the major contributor to the system overpotential, especially at low electrolyte flow velocities. Regarding operating parameters, although temperatures of heat source and heat sink and electrolyte flow velocity determine the power density, the heat recuperation efficiency shows a decisive effect on the efficiencies. With perfect recuperation, the thermal efficiency and exergy efficiency could reach 8.3 % and 57.5 %, respectively. Regarding physical properties of electrolytes, the electrolyte concentrations affect the power density by changing the limiting current density. In addition, the temperature coefficient significantly affects the power density at any electrolyte flow velocity, while the internal resistance does so only at high flow velocities. With a temperature difference of 50 °C, a high power density of 4.33 W m−2 is expected if the temperature coefficient is increased to 4.0 mV K−1 and the area specific resistance is reduced to 1.0 Ω cm2. Based on the results, beneficial recommendations are put forward for further optimizing the system configuration and screening electrolytes for continuous TREC.