Non-Pre-Treated Sulfonated Poly(Ether Ether Ketone) Membrane as an Efficient Alternative for Nafion in Acidic Aqueous Organic Redox Flow Batteries

Aqueous organic redox flow batteries (AORFBs) based on tryptanthrin sulfonic acid (TRYP-SO 3 H) or alizarin red S, 3,4-dihydroxy-9,10-anthaquinone-2-sulfonic acid (ARS) as anolytes and 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt monohydrate (BQDS) as catholyte, were studied in acidic medium, using pre-treated or non-pre-treated sulfonated poly(ether ether ketone) (SPEEK) membranes and further compared with the performance obtained with a commercial Nafion® 115 membrane. The cell tests using the non-pre-treated SPEEK membrane presented higher performance and capacity retention than that of the cells using the pre-treated Nafion membrane. The study highlights the great potential of using inexpensive membranes without pre-treatment and low-cost active materials for application in AORFBs