Redox flow batteries (RFBs) have a great potential to be a next generation energy storage system in that they can be flexibly configured according to the power demand because power and enegy capacity are separated in the system. Various types of RFB have been studied according to the active materials such as all vanadium, zinc/bromine, iron/crome, etc. Most of such RFBs use metal redox pairs, which are expensive and have potential problems such as metral dendrites. Therefore, metal-free organic aqueous flow batteries are getting attention to replace expensive metals. As a result, low-cost quinone-bromine flow battery was proposed by Brian but it has toxicity and corrosion problem since it operates under acidic condition [2]. Instead, alkaline quinone flow battery can be considered to resolve those problems and replace the metal-based flow batteries. One of imporant issues of developing a RFB is to minimize the active mateial crossover through the separator, which gradually degrades the battery capacity by contaminating the electrolytes. When the anode and cathode share the same active material such as the all vanadium redox flow battery, the battery capacity can be recovered by regularly reblancing the anolyte and catholyte. However, the alkaline quinone flow battery has two different active mateials that should not be mixed by crossove phenomena. Therefore, it is important to identify the stability of the electrolyte and peformance of the alkaline quinone flow battery through a long time operation.

To invesigate the effect of the crossover phenomena in the alkaline quinone flow battery, we completely mixed the anolyte and catholyte, and conducted electrochemical characterization of the battery. The mixed electrolyte was made by mixing a solution of 0.5 M 2,6-dihydroxyanthraquinone (2,6-DHAQ) dipotassium salt and a solution of 0.4 M potassium ferrocyanide with 1 M potassium hydroxide at a volume ratio of 1:1. First, CV test confirmed the redox reaction at the positive electrode and the negative electrode as shown in figure 1. Second, we conducted a cell cycling to examine the long-time stability of the electrolyte and observed that the cell capacity was rapidly degraed as shown in figrue 2. Dismentling the cell after the cycling test, it was observed that the electrolyte precipitation was formed and it blocked the flow channels in both positive and negative electrode (figure 3).

References

[1] M. Skyllas-Kazacos, M. H. Chakrabarti, S. A. Hajimolana, F. S. Mkalli, M. Saleem, J. Electrochem. Soc 158 (2011) R55-R79

[2] Brian Huskinson, Michael P. Marshak, Changwo Suh, Suleyman Er, Michael R. Gerhardt, Cooper J. Galvin, Xudong Chen, Alan Aspuru-Guzik, Roy G. Gordon, Michael J. Aziz, Nature 505 (2014) 195-198

[3] Kaixiang Lin, Qing Chen, Michael R. Gerhardt, Liuchuan Tong, SangBok Kim, Louise Eisenach, Alvaro W. Valle, David Hardee, Roy G. Gordon, Michael J. Aziz, Michael P. Marshak, Sience 349 (2015) 1529-1532