Take it to the Carnot limit: Perspectives and thermodynamics of dual-cell electrochemical heat engines

Abstract

In electrochemical dual-cell heat engines, the conduction of heat and electricity are fully decoupled, allowing their independent optimisation to maximise the conversion efficiency. Despite this advantage, the dual-cell electrochemical heat engine has only been explored superficially in previous studies. Here we address the in-depth thermodynamic aspects of the heat engines integrated with two electrochemical flow cells and assess the route to achieve a high heat-to-electricity conversion efficiency and system's power output. Our theoretical analysis revealed for the first time that in the dual-cell electrochemical system, the flow rate must be controlled as a response to the electrical current, and conversion efficiency no longer depend on the conventional thermoelectric figure-of-merit. Based on established principles and considering tremendous advancements for the past 10 years within thermogalavic materials and flow battery systems, our analysis presents that it is realistic to develop dual-cell electrochemical heat engines that can be operated at conversion efficiencies approaching the Carnot limit, reaching 10.1 % and 19.3 % at maximum power point and maximum conversion efficiency conditions, respectively, under the temperature gradient of 80 °C.