Lab-scale experiments on a novel acid/base electrodialytic flow battery with bipolar membranes

Electrical energy storage has a key role in the development and diffusion of renewable energy technologies. The Acid/Base Flow Battery is an innovative process to store electrical energy in the form of pH and salinity gradients via electrodialytic reversible techniques based on the use of bipolar membranes. During the charge phase, the unit produces acid and alkaline solutions by applying an electric field, during the discharge phase, converts the pH gradient into electrical energy. In this work, several experimental tests were performed in a 10×10 cm2 laboratory-scale unit fed with HCl, NaOH and NaCl solutions, in order to characterize the battery and assess its performance. The effect of acid/base concentration, feed velocity and the number of repetitive units (triplets) was studied. Results showed that the Open Circuit Voltage obtainable with 1 M acid/base solutions increases from 4.2 V in a stack equipped with 5 triplets to only 16.5 V in a stack equipped with 38 triplets, due to significant effects of shunt currents, with a maximum power density of about 53 W/m2 in the discharge phase. Other important limitations originate from co-ion leakages. This work was performed in the framework of the BAoBaB project, funded by the EU H2020 program.