Process modelling of a novel acid-base flow battery based on bipolar-membranes

The storage of electrical energy is crucial for a deeper penetration of renewable energies with intermittent nature, e.g. solar and wind energy. The Acid/Base Flow Battery (AB-FB) is a novel, sustainable, environmental-friendly storage technology with high energy density of the electrolyte solutions. The process is based on reversible electrodialytic techniques with bipolar membranes, which convert the electrical energy in the chemical energy associated to pH gradients and vice versa. The charge phase is a bipolar membrane electrodialysis process, while the discharge phase is a bipolar membrane reverse electrodialysis process. The stack consists of several repetitive units, called triplets, made up of an anion-exchange membrane, a bipolar membrane, and a cation-exchange membrane, separated by spacers forming the channels where the acid, base and salt solutions flow. This work presents a sensitivity analysis performed by an experimentally validated AB-FB process model. The model is built by a multi-scale approach, integrating four different dimensional scales (channel, triplet, stack, hydraulic circuit) within a comprehensive simulation tool with distributed parameters. The model was validated against experimental results collected under different operating conditions, showing a good agreement. A wide sensitivity analysis was performed in order to explore the behavior and performance of the AB-FB in different scenarios. The model outcome illustrates how stack geometry, operating conditions and battery flow layouts (e.g. open-loop vs closed-loop operations) can affect the process performance. By adopting some measures to tackle the shunt currents flowing via manifolds and taking thermodynamic advantages from open-loop operations, the round trip efficiency reached values up to 70%