Performance Optimization of Differential pH Quinone-Bromide Redox Flow Battery

It is of paramount importance to operate redox flow batteries (RFB) at high power densities in order to minimize the stack and associated costs. With published data from our recent study [ J. Mater. Chem. A, 5, 21875 (2017)], the cell potential of semi-organic, quinone-based RFB, was increased from 0.86 to 1.3 V by operating it in differential pH mode. The differential pH RFB uses bromine at pH ∼2 on the positive side and anthraquinone-2,7-disulfonate disodium (Na 2 AQDS) operated at pH ∼ 8 on the negative side. In the present work we have evaluated how the thicknesses of carbon paper and membrane, electrolyte flow rate, and redox species concentration affect the cell resistance and peak galvanic power density. The optimized cell delivered a maximum peak galvanic power density of 0.45 W/cm 2 with an area resistance of 1 Ω.cm 2 . The peak power density of differential pH battery was compared to those of acidic quinone-bromide and both are benchmarked against vanadium RFB tests in the same cell. It is shown that under identical conditions, the peak galvanic power density of the differential pH battery is 12% higher than acidic quinone-bromide, however lower than that of vanadium RFB tests.