Skoltech researchers and their staff have developed, synthesized and evaluated new compounds that can serve as catholytes and anolytes for organic redox flow batteries to bring this promising technology closer to large-scale implementation. The two works were published in the Journal of Materials Chemistry A. and Chemical communication.
Energy storage is an essential part of a more environmentally friendly energy system of the future based on renewable sources. Batteries have to be supplemented by wind and solar parks and have to be scalable, safe and flexible in terms of design and service life. Redox flow batteries (RFBs) are all of these things, but a major obstacle to commercialization has been their low specific capacity. Therefore, much research is focused on developing better battery components to overcome this hurdle.
“The main advantage of redox flow batteries is their scalability. The capacity of the battery is only limited by the volume of the electrolyte. Therefore, it is the ideal design for large-scale energy storage. Today we work with organic redox-active materials that are dissolved in organic solvents (non-aqueous organic RFBs). The main advantages for non-aqueous organic RFB are high cell voltage (up to 5 V versus around 1.6 V for water-based systems), a variety of organic redox-active molecules that can be applied cold, and potential low temperature operability. regardless of freezing below 0 ° C. This work therefore offers considerable progress in the development of such RFBs, ”explains Skoltech doctoral student Elena Romadina, the first author of both papers.
In the two papers, Elena Romadina and her colleagues describe promising catholyte and anolyte materials for RFBs – materials based on triarylamine and a phenazine derivative, respectively. The seven highly soluble redox-active triarylamine-based compounds were designed, synthesized and tested for solubility and electrochemical properties. One of them was selected as the most promising candidate for further studies. The authors emphasize that the developed compounds showed nearly unlimited solubility in polar organic solvents such as acetonitrile, making them promising for high-capacity RFBs. In the other study, a phenazine derivative with oligomeric ethylene glycol ether substituents was synthesized in a two-step process and showed solid performance as an RFB anolyte.
“A non-aqueous organic redox flow battery, which is referred to as a phenol-based anolyte and the most promising catholyte based on triarylamine, showed a high cell voltage of 2.3 V, a high capacity, a Coulomb efficiency of> during the 50 cycles 95% and good charge-discharge cycle stability, ”the authors write in the ChemComm Paper.
“As a result of our work, we introduced a novel class of compounds that can be used in RFBs. So far, polytriarylamines have been investigated as cathode material for metal ion cells, but this class of compounds has not been investigated in redox flow batteries. A new and promising core structure was opened up to us and other scientists. Triarylamines have a stable and fully reversible redox potential and can be easily modified to provide different redox potentials and physical properties. In addition, we have found that triarylamine-based compounds can maintain their electrochemical properties even in the presence of water in organic solvents, which reduces solvent production requirements and costs, ”adds Romadina.
“We are actually examining both ends of the battery to increase the operational cell voltage and prevent any other breakdown of catholytes and anolytes. To make organic RFBs commercially viable, we also need to conduct research in areas such as the cost-effective, scalable synthesis of highly soluble redox-active molecules. the development of high performance membranes that are good ion conductors but inhibit the crossing of anolytes and catholytes during charging and discharging; and the scaling of larger device configurations at cell and stack level to enable energy storage on a network scale, ”says Professor Keith Stevenson, Skoltech-Provost and co-author of the work.
Other organizations involved in this research are the Institute for Problems in Chemical Physics of the Russian Academy of Sciences and the D. Mendeleev University of Chemical Technology in Russia.