Utilization of novel alginate membranes developed for quinone based aqueous redox flow batteries

Abstract

Alginate (Alg)-based mambranes are explored for use in aqueous redox flow batteries (ARFBs). Alg is a cheap natural material of low toxicity. To improve the properties of pristine Alg membranes, they are ionically crosslinked with calcium chloride (CaCl2) or alternatively treated with organic solvents. While the effect of CaCl2 is negligible, membranes treated with tetrahydrofuran (THF) or chloroform (THF-Alg and Chlor-Alg) show higher tensile strength and Young’s modulus than Alg and Ca-Alg membranes. All four membranes are tested in ARFBs including TironA and 2,7-anthraquinone disulfonic acid as redox couple. A significant increase in voltage efficiency (VE) is observed with the organic solvent-treated membranes (70.9, 70.6, 73.0 and 74.3 % for Alg, Ca-Alg, Chlor-Alg and THF-Alg membranes), while VE of ARFB including Nafion 117 is 73.0 %, meaning that ARFB including THF-Alg shows a better VE. This is partly due to the area specific resistance (ASR). More specifically, when ASR of 70 μm thick THF-Alg and 200 μm thick Nafion 117 membranes submerged in 2 M sulfuric acid is measured, they show 76.7 and 100.6 mΩ cm2. This difference in ASR promotes the rapid increase in VE of ARFB including THF-Alg membrane.