Abstract
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 (Na2AQDS) 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/cm2 with an area resistance of 1 Ω.cm2. 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.
Highlights
Positive side1.6 M mixture of V3+ and V4+in 2 M H2SO4 flow rate of redox solutions, and concentration of redox species
One of the biggest challenges of further expansion of renewable PV and wind electricity is cost efficient storage
We recently demonstrated a semi-organic differential pH quinone-bromide battery based on bromide operated at pH∼2 on the positive side and anthraquinone-2,7disulfonate (AQDS) disodium operated at pH∼8 on the negative side that was successfully operated over a period of 30 days.[19]
Summary
1.6 M mixture of V3+ and V4+in 2 M H2SO4 flow rate of redox solutions, and concentration of redox species. The number of carbon papers was varied from 3 to 10 on each side of the cell; the performance of two proton exchange membranes with similar ion exchange capacity but different thickness (Nafion 117 and 212) was compared; the flow rate of positive and negative electrolytes was adjusted to 20, 50, 80 and 120 ml/min; and lastly, the effect of concentration of Na2AQDS and on cell resistance was studied. For comparison to EIS data, polarization curves were measured by charging and discharging the battery at constant current density. It consists of two Poco graphite plates with serpentine flow field provided from Fuel Cell Technologies (FCT). The differential pH quinone-bromide cell was charged at different current densities using upper cutoff voltage of 1.5 V and lower cutoff voltage of 0.4 V
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