The crucial role of the supporting electrolyte in Redox Flow Battery performances.

Abstract

Renewable energy sources are being adopted more widely around the world. This is due to the increasing energy demand, and by the fact that countries have set targets to reduce carbon emissions and solar and wind energy are intermittent by nature. This means that reliable, large-scale storage solutions are needed urgently. Redox flow batteries (RFBs) are proving to be leading candidates in this field, as they decouple power and energy capacities, enabling highly scalable and modular installations. One of the key parameters of RFB performances relies in the supporting electrolyte. It can affect ionic conductivity (IC), redox stability, membrane selectivity and cycle life. In this review we present a comparison of supporting electrolyte's role in both aqueous and non-aqueous RFBs. A comparison between traditional inorganic salts (e.g. H2SO4, Na2SO4, KCl) and novel neutral organic electrolytes such as ionic liquids (ILs) and deep eutectic solvents (DES) are assessed. Here we highlight how those latter are able to improve the properties of the electroactive solution in term of increasing solubility, conductivity and thermal and electrochemical stability. In addition, a cost analysis of those novel organic electrolytes is presented, alongside future hybrid electrolytes