The use of organic molecules such as quinone/hydroquinone in a redox flow battery (RFB) is a promising path toward inexpensive grid-scale electricity storage [1,2]. Because of their relatively large size, the molecules also provide the opportunity to mitigate capacity loss associated with active material crossover that is encountered in RFBs that utilize vanadium ions or bromine. Here we first discuss the effect of crossover on cell performance metrics, including current efficiency, energy efficiency, and capacity retention. We quantitatively compare the impacts from crossover and other loss mechanisms, such as leakage and molecule decomposition in a quinone-bromide RFB [3]. By using UV-Vis spectroscopy in a concentration-driven crossover cell, the crossover rates of different quinone molecules through ion-selective membranes are measured. The rate of crossover is shown to depend on the molecular structure and net charge of the migrating species. The results provide valuable insights with regard to molecule and membrane selection enabling molecular crossover through ion-selective membranes to be effectively minimized.

References:

1. B. Huskinson, M. P. Marshak, C. Suh, S. Er, M. R. Gerhardt, C. J. Galvin, X. Chen, A. Aspuru-Guzik, R. G. Gordon, and M. J. Aziz, Nature, 505, 195–8 (2014).

2. K. Lin, Q. Chen, M. R. Gerhardt, L. Tong, S. B. Kim, L. Eisenach, A. W. Valle, D. Hardee, R. G. Gordon, M. J. Aziz, and M. P. Marshak, Science, 349, 2013–2016 (2015).

3. Q. Chen, L. Eisenach, and M. J. Aziz, J. Electrochem. Soc., 163, A5057–A5063 (2016).