A vanadium-cerium redox flow battery with an anion-exchange membrane separator

Cardo-poly(etherketone)-based anion-exchange membranes (AEMs) were prepared and employed as separators in a vanadium-cerium redox flow battery (V-Ce RFB). V-Ce RFBs with AEM separators yielded energy efficiencies (EEs) ranging from 67 to 84-% at current densities between 20 and 80mA-cm^-2. V-Ce RFBs using Nafion212 as the separator had EEs ranging from 50 to 84-% and displayed a capacity and efficiency loss as a result of cation intermixing. Over 20charge/discharge cycles, the RFB with the AEM separator yielded unchanged efficiencies and capacity, whereas the loss of capacity was 50-% with the Nafion separator. There was no substantial change in the ionic conductivity, ultimate tensile strength, and Young's modulus of AEMs after 50charge/discharge cycles. This suggests that AEMs are promising candidates as V-Ce RFB separators that: 1)are chemically and mechanically stable during cycling, and 2)act as efficient barriers that preclude the intermixing of vanadium and cerium cations. Membranes in charge: Quaternized cardo-poly(etherketone) (QPEK-C) anion-exchange membranes (AEMs) have been prepared and employed as a separator in a redox flow battery [carbon felt|V³⁺, V²⁺ (0.5-M)||carbon felt|Ce⁴⁺, Ce³⁺ (0.5-M)]. The low cation permeability of the AEM together with its good mechanical and chemical stability give this material improved coulombic efficiency (CE) and energy efficiency (EE) during cycling (see figure).