Dual Cross-Linked Poly(vinyl alcohol)-Based Anion Exchange Membranes with High Ion Selectivity for Vanadium Flow Batteries

Abstract

As a widely used, low-cost, and environmentally friendly carbohydrate polymer, poly(vinyl alcohol) (PVA) is employed to prepare dual cross-linked anion exchange membranes (AEMs) for vanadium flow batteries (VFBs). Tertiary amine group functionalized PVA (i.e., poly(vinyl acetal) (PVAc)) is first synthesized via the acetalization reaction between 4dimethylaminobenzaldehyde (DMABA) and PVA. Then (5-bromopentyl)-trimethylammonium bromide (BPTMA) is used as the quaternary ammonium reagent, while α,α′-dibromo-p-xylene (DBPX) is adopted as the first cross-linker. Meanwhile, glutaraldehyde (GA) is used as the second cross-linker to further improve the dimensional stability of AEMs. The formed dual cross-linked PVAc-BPTMA-DBPX-GA membranes display enhanced sulfonic acid (SA) uptake and low area resistance (AR), and maintain low VO 2+ permeability and suitable mechanical strength simultaneously. For example, the PVAc-0.5BPTMA-0.5DBPX-GA membrane shows a low AR of 0.27 Ω cm 2 and an ultralow vanadium ion permeability of 8.09 × 10 −8 cm 2 min −1 . Therefore, the above membrane exhibits a significant ion selectivity of 5.95 × 10 5 S min cm −3 , which is nearly 2 orders of magnitude higher than that of Nafion 115 (i.e., 6.66 × 10 3 S min cm −3 ). The VFB based on PVAc-0.5BPTMA-0.5DBPX-GA displays a higher energy efficiency of 85.2% at 100 mA cm −2 than the cell with Nafion 115 (71.1%). Meanwhile, the battery also maintains a stable performance in a long-term operation of 150 cycles.

Hollow Cuboidal Metal Oxide-Based Asymmetric Electrode Configuration for High-Performance Anion Exchange through Quaternized Pyridine-Poly(vinyl alcohol) @ Metal Hydroxide Nanosheets for Water Dissociation

“…After calculation, it is observed approximately 41% degree of grafting for pyridine side chain over PVA and 37% for the quaternization degree of pyridine by bromoethane. 51 To benchmark our grafting percentage, we refer to relevant literature, specifically the study by Tong et al, who utilized 4-dimethylaminobenzaldehyde (DMABA) for PVA functionalization, yielding a grafting percentage of 35%. Additionally, Li et al introduced a novel series of membranes featuring covalent self-cross-linking with a branch structure, resulting in a observed cross-linking degree of 14%.…”

“…We have also undertaken the calculation of the degree of grafting (DG %) for the pyridine side chain into PVA and the quaternization degrees of pyridine groups by bromoethane from the NMR data (Supporting Information Section 16). After calculation, it is observed approximately 41% degree of grafting for pyridine side chain over PVA and 37% for the quaternization degree of pyridine by bromoethane . To benchmark our grafting percentage, we refer to relevant literature, specifically the study by Tong et al, who utilized 4-dimethylaminobenzaldehyde (DMABA) for PVA functionalization, yielding a grafting percentage of 35%.…”