Mechanism of Polysulfone-Based Anion Exchange Membranes Degradation in Vanadium Flow Battery

Abstract

The stability of hydrocarbon ion exchange membranes is one of the critical issues for a flow battery. However, the degradation mechanism of ion exchange membranes has been rarely investigated especially for anion exchange membranes. Here, the degradation mechanism of polysulfone based anion exchange membranes, carrying pyridine ion exchange groups, under vanadium flow battery (VFB) medium was investigated in detail. We find that sp(2) hybrid orbital interactions between pyridinic-nitrogen in 4,4'-bipyridine and benzylic carbon disrupt the charge state balance of pristine chloromethylated polysulfone. This difference in electronegativity inversely induces an electrophilic carbon center in the benzene ring, which can be attacked by the lone pair electron on the vanadium(V) oxygen species, further leading to the degradation of polymer backbone, while leaving the 4,4'-bipyridine ion exchange groups stable. This work represents a step toward design and construction of alternative type of chemically stable hydrocarbon ion exchange membranes for VFB.

A Bunch-Like Tertiary Amine Grafted Polysulfone Membrane for VRFBs with Simultaneously High Proton Conductivity and Low Vanadium Ion Permeability

“…The superior chemical stability of the prepared membranes is mainly attributed to the special grafting mode of the polymer and to the protection to the polymer backbone. [42] Figure 4d shows that the VRFB assembled with the TT-PSF-68% membrane exhibited much better capacity retention than the Nafion 212-based VRFB. The dischargecapacity loss of the VRFB with TT-PSF-68% is 25.0% lower than that of the Nafion 212-based VRFB, and the value is even better than reported in the literature.…”

“…Furthermore, only slight changes are observed in the 1 H NMR signal integrations for the TT‐PSF‐68% membrane over 240 h even under strong oxidizing environments at 35 °C (Figure S14, Supporting Information), verifying the chemical stability of the designed bunch‐like tertiary amine membrane. The superior chemical stability of the prepared membranes is mainly attributed to the special grafting mode of the polymer and to the protection to the polymer backbone …”

Membranes with Well‐Defined Selective Layer Regulated by Controlled Solvent Diffusion for High Power Density Flow Battery

“…[5][6][7][8][9][10] A common role of a membrane is to separate molecules or substances with different properties, size in particular. [11][12][13] The separation performance is ultimately determined by membrane morphologies. [14][15][16][17][18] For a membrane, one of the most troublesome and common issues is the trade-off between the selectivity and flux.…”

Recent Development in Composite Membranes for Flow Batteries

“…[43] Commonly,t he performance of ac omposite membranei s limited by its interfacial properties. Although the interface is commonly customized to meet basic demands,atoo dense selective layer can restrict ion transport, resulting in poor ionic conductivity.E specially in some applicationss uch batteries and desalination devices,adense top layer normally utilizes ion-exchange groups such as ÀSO 3 H, [18] ÀCOOH, [44] and pyridine [45] to create effective ion transport paths. Therefore, the structure of the polymerc hain is highly important.…”