Effect of Design Features and Operating Conditions on the Performance of a Bipolar Membrane-Based Acid/Base Flow Battery

In the context of renewable energy sources, storage systems have been proposed as a solution to the issues related to fluctuations in the production and consumption of electric power. The EU funded BAoBaB project is aimed at developing the Acid/Base Flow battery (AB-FB), an environment-friendly, cost-competitive, grid-scale battery storage system based on the cyclic coupling of Bipolar Membrane ElectroDialysis (BMED) and its reverse, the Bipolar Membrane Reverse ElectroDialysis (BMRED) (Pärnamäe et al., 2020). Bipolar membranes promote catalytically water dissociation, thus allowing the storage of electric power in the form of acidic and alkaline solutions (pH gradient), obtained from their corresponding salt (charging mode - BMED), which are then recombined to provide electrical power (discharging mode - BMRED). The membranes are key elements for the process performance; however, the energy conversion efficiency is also affected by the operating parameters of the process and the design features of the stack. In this work, we performed a sensitivity analysis by a mathematical multi-scale model previously developed (Culcasi et al., 2020a). The performance of AB-FB systems was predicted, focusing on the Round Trip Efficiency. Results showed that proper design features made the effect of parasitic currents negligible. Moreover, proper operating conditions maximized the RTE up to 66%.