High Performance of Anion Exchange Blend Membranes Based on Novel Phosphonium Cation Polymers for All-Vanadium Redox Flow Battery Applications

Muthumeenal Arunachalam; Alessandro Sinopoli; Farida Aidoudi; Stephen E Creager; Rhett Smith; Belabbes Merzougui; Brahim Aïssa

doi:10.1021/acsami.1c10872

High Performance of Anion Exchange Blend Membranes Based on Novel Phosphonium Cation Polymers for All-Vanadium Redox Flow Battery Applications

ACS Appl Mater Interfaces. 2021 Sep 29;13(38):45935-45943. doi: 10.1021/acsami.1c10872. Epub 2021 Sep 17.

Authors

Muthumeenal Arunachalam¹, Alessandro Sinopoli¹, Farida Aidoudi¹, Stephen E Creager², Rhett Smith², Belabbes Merzougui¹, Brahim Aïssa¹

Affiliations

¹ Qatar Environment & Energy Research Institute (QEERI), Hamad Bin Khalifa University (HBKU), Qatar Foundation, Doha 34110, Qatar.
² Department of Chemistry and Center for Optical Materials Science and Engineering Technology, Clemson University, 105 Sikes Hall, Clemson, South Carolina 29634, United States.

PMID: 34533936
DOI: 10.1021/acsami.1c10872

Abstract

The deployment of alkaline anion exchange membranes (AEMs) in flow battery applications has the advantage of a low cationic species crossover rate. However, the alkaline stability conjugated to the low conductivity of hydroxide ions of anion exchange membranes (AEMs) still represents a major drawback for the large deployment of such technology. In this study, three types of tetraarylpolyphosphonium (pTAP)-based copolymers (namely, CP1, CP2, and CP3) are synthesized and blended with chitosan and polyvinylidene fluoride (PVDF) for the fabrication of AEMs. Chitosan, a green biopolymer, was employed as a blend to enhance the water uptake of the base ionomer matrix. It is proposed that the abundancy of hydroxyl groups in chitosan improves considerably the ionic conductivity, water transport, and ion selectivity of the membrane, together with facilitating the dispersion of the chitosan in the pTAP copolymer matrix. The purpose of blending PVDF is instead to provide stable mechanical strength to the composite blend. The chemical, mechanical, and thermal stabilities of the three fabricated composite-blend membranes (i.e., CM1, CM2, and CM3) were characterized. All the membranes exhibited a high water retaining capacity of up to 36.26% (recorded for CM2) along with a hydroxyl ion conductivity of 17.39 mS cm^-1. Due to the strong interactions between pTAP copolymers, chitosan, and PVDF polymers (confirmed also by Fourier transform infrared spectroscopy), the studied anion exchange membranes are able to retain up to 97% of the original OH conductivity after 1 M KOH treatment at room temperature for 100 h. The three membranes, namely, CM1, CM2, and CM3, have vanadium ion permeabilities measured at 20 °C of 1.775 × 10^-8, 1.718 × 10^-8, and 1.648 × 10^-8 cm²/s, respectively, which are lower than that for the commercially available Nafion. The good stability and remarkable cell performance of the composite-blend membranes reported here make them definitely excellent candidates for the future generation of vanadium redox flow batteries.

Keywords: all-vanadium redox flow battery; anion exchange membrane; chemical stability; ion permeability; phosphonium copolymer.