Thermodynamic and electrochemical performance analysis for an electrochemical refrigeration system based on iron/vanadium redox couples

Abstract

Alternative refrigeration systems have been explored due to the limitations of vapor compression refrigeration system on theoretical efficiency and environmental friendliness. In this study, an electrochemical refrigeration system based on the endothermic effect of electrochemical reactions was proposed to realize continuous refrigeration. This electrochemical refrigeration system mainly comprised endothermic and exothermic cell stacks, regenerator, heat exchangers, and pumps. Fe2+/Fe3+ and VO2+/VO2+ redox couples were employed to establish a refrigeration cycle due to their large entropy change and no phase change during reaction processes. A thermodynamic model with polarization loss analysis was established for system performance evaluation. Through quantitative analysis of polarization losses, optimal operating conditions of the system and key factors affecting the system performance were determined. The results indicated that the coefficient of performance (COP) of the system under ideal conditions was close to that of the reverse Carnot cycle. In actual situations, polarization losses led to system performance degradation. The electrochemical refrigeration system achieved comparable or better COP than the vapor compression refrigeration system when the current density was within 60 A m−2. The impact analysis of state of charge (SOC) showed that the actual refrigerating capacity and COP reached the peak values when the SOC was about 0.43 and 0.5, respectively. Increasing the flow rate and operating temperature improved the system performance by decreasing concentration and activation polarization losses, respectively. Furthermore, the activation polarization loss accounted for the largest proportion of system losses. Thus, improving electrode catalysis is critical to enhance the system performance.