Improvement of safe bromine electrolytes and their cell performance in H2/Br2 flow batteries caused by tuning the bromine complexation equilibrium

Hydrogen bromine redox flow batteries utilize electrolytes in their positive half cell, offering capacities larger than 100 Ah L?1. Addition of quaternary ammonium compounds, so-called complexing agents (BCA), may increase safety as they reduce the vapour pressure posolyte. However, have not been applied so far. They (a) interact with perfluorosulfonic acid membranes leading to significant reduction membrane conductivity and (b) form a low conductive ionic liquid polybromides, high overvoltage if formation happens at electrode. In this work solution problem is proposed by an excess addition Br2 these electrolytes. The leads permanent fused salt phase tank. Bromine formed cell stays aqueous transfer between two phases Transfer without [BCA]+ cations exists phases, while [C2Py]+ remain do influence performance. For first time posolyte capacity 179.6 L?1 based on 7.7 M hydrobromic BCA achieved compared previous investigations e.g. 53.9