Na-β-Alumina as a Separator in the Development of All-Vanadium Non-Aqueous Tubular Redox Flow Batteries: An Electrochemical and Charging-Discharging Examination Using a Prototype Tubular Redox Flow Cell

Abstract

© The Author(s) 2018. The non-aqueous redox flow battery (N-ARFB) is in the development stages with aim to produce high power density storage systems. In addition to the development of N-ARFBs, this study examined the applicability of a sodium beta alumina (Na-β-Al2O3) membrane in the development of a N-ARFB through an analysis of the electrochemical processes, redox active species migration, and charging/discharging at room temperature (25 ± 3◦C). Through impedance analysis, the ionic conductivity of the Na-β-Al2O3 was 2.97 × 10−2 S cm−1 which is slightly higher than the literature value. UV-Visible analysis showed no migration of the vanadium acetylacetonate (V(acac)3) ion from one compartment to another, either during the charging or discharging process. In addition, the lack of a change in the morphology of the spent membrane revealed not only stability, but also confirmed no permeation of V(acac)3 species. The maximum applied current density for charging and discharging was 0.01 mA cm−2 and 0.0015 mA cm−2, respectively. The charging/discharging of V(acac)3 enables voltage and current efficiencies of almost 16% and 11% respectively, at the state of charge of 15%. This demonstrates that the Na-β-Al2O3 membrane can be improved for use in N-ARFB after optimizing the conditions.