Sulfonated poly(ether ether ketone) membrane for quinone-based organic flow batteries

Abstract

Over the past few years, organic flow batteries have gained immense attention owing to their potential for large-scale energy storage applications and modifiable properties. Organic redox couples usually involve only one type of counter-ion for ion exchange membranes, and hence provide opportunities to use low-cost membranes in organic flow batteries. In this study, we prepared a sulfonated poly (ether ether ketone) (sPEEK) membrane for application in acidic flow batteries of 1,2-dihydroxybenzene-3,5-disulfonic acid/anthraquinone-2-sulfonic acid. The proton conductivity of the prepared sPEEK membrane was 50% lower than that of Nafion-212 membrane. However, the Coulombic efficiency of the sPEEK cell was similar to that of Nafion cell, and the voltage efficiency was 0.99%–2.66% higher than that of Nafion cell at different current densities. The cell using the sPEEK membrane also exhibited long-term stability, retaining 96.93% reversible capacity after 100 charge/discharge cycles at the current density of 100 mA cm−2. The results of symmetric cell cycling indicated that the decay of reversible capacity in this organic flow battery system was mainly due to the instability of organic compounds in the positive electrolyte, which was also confirmed by the self-discharge measurements of the sPEEK cell. These results demonstrate that the sPEEK membrane is highly suitable for organic flow batteries. These results will be helpful for realizing cost-effective energy storage systems.