In-situ crossover diagnostics to assess membrane efficacy for non-aqueous redox flow battery

Abstract

The redox species crossover through the membrane is problematic since it leads to capacity loss and lower coulombic efficiency. It needs to be readily quantified before any commercial application of the non-aqueous redox flow battery (NAqRFB). An in-situ electrochemical method is introduced and further validated through an ex-situ method and performance characterization. The feasibility of ferrocene is checked and reported as a model probing species. Among ion exchange membranes, a lower crossover molar flux rate is obtained from Nafion 117 & FAPQ-375-PP (2.18 & 0.75 µmol⋅h−1⋅cm−2). The model redox species – V(acac)3 – was used for the performance assessment of NAqRFB. The coulombic efficiency was 86.6% and potential efficiency of 65.8%. The ohmic and mass transport overpotentials affecting the performance of NAqRFB were 0.46 V and 1.44 V. The crossover rate obtained from the LSV technique concerns materials and cells under real working conditions. This technique has the potential to become a reference testing method to determine the crossover and aid selecting the best performing membrane, in the RFB field. As membrane diagnosis tool, this technique allows in-situ determination of crossover without the need for disassembling the devices.