Optimization study of acid-base flow battery stacks with monopolar and bipolar membranes

The Acid-Base Flow Battery (AB-FB) is a novel technology for energy storage. It is based on reversible electrodialytic techniques with ion-exchange membranes. The kye elements are the bipolar membranes, which convert electrical energy in the form of pH gradients and vice versa. Despite the promising results of few experimental studies, the AB-FB potential has been poorly explored so far. This work presents an optimization study of the AB-FB. It was performed by a multi-scale process model previously developed (gPROMS Model Builder® environment) and experimentally validated. A two-objective optimization was conducted by maximizing the Net Round Trip Efficiency and the Net Power Density in the discharge phase. By the ε-constraint method, curves of Pareto optimal solutions were predicted under several scenarios by assessing systematically the effect of decision variables. In a closed-loop configuration (solutions recirculation), optimized operating conditions and design features yielded a maximum NRTE of 64% and a maximum NPD of 19.5 Wm-2. Improved membrane properties increased these quantities to 76.2% and 23.2 Wm-2, respectively. Finally, open-loop operations were beneficial for the process performance. These promising results will drive the AB-FB technology towards future developments and competitive configurations.