On the Relevance of Static Cells for Fast Scale-Up of New Redox Flow Battery Chemistries

The search for organic electroactive molecules suitable in Aqueous Organic Flow Batteries requires great efforts not only from an electrochemical perspective (weeks of testing), but also from an organic synthesis viewpoint. This work focuses on the relevance of static cells for accelerating the search and helping understand degradation mechanisms. After disclosing an easy-to-make and reliable static cell, its validation is carried out using a few milligrams of model materials, i.e. ferrocyanide-based electrolyte. A simple but effective approach is proposed to investigate active species in the absence of air, which is based on the use of a cheap lunch box (Ar-box) in contrast to the expensive Ar-filled glovebox. The relevance of the proposed strategy is demonstrated by investigating two case studies. The 2,6-dihydroxantraquinone/K4Fe(CN)6 in alkaline is studied with and without Ar-box. The air leakage in our static cell in the Ar-box is neglectable, so an Ar-filled glovebox is not needed. Interestingly, the use of Ar-box leads to higher capacity fading (1.3 vs 2.5%day-1) since a very small leakage of air prevents the formation of dimers. In neutral pH, the total absence of air using 1,1-bis[3-sulfonatopropyl]-4,4-bipyridinium/K4Fe(CN)6 static cell in the Ar-box leads to an increase in capacity fading (0.2%day-1) compared to reported values using Ar-filled glovebox.