Ionic-Nanophase Hybridization of Nafion by Supramolecular Patching for Enhanced Proton Selectivity in Redox Flow Batteries

Abstract

Nafion, as the mostly used proton exchange membrane material in vanadium redox flow batteries (VRFBs), encounters serious vanadium permeation problems due to the large size difference between its anionic nanophase (3–5 nm) and cationic vanadium ions (∼0.6 nm). Bulk hybridization usually suppresses the vanadium permeation at the expense of proton conductivity since conventional additives tend to randomly agglomerate and damage the nanophase continuity from unsuitable sizes and intrinsic incompatibility. Here, we report the ionic-nanophase hybridization strategy of Nafion membranes by using fluorinated block copolymers (FBCs) and polyoxometalates (POMs) as supramolecular patching additives. The cooperative noncovalent interactions among Nafion, interfacial-active FBCs, and POMs can construct a 1 nm-shrunk ionic nanophase with abundant proton transport sites, preserved continuity, and efficient vanadium screeners, which leads to a comprehensive enhancement in proton conductivity, selectivity, and VRFB performance. These results demonstrate the intriguing potential of the supramolecular patching strategy in precisely tuning nanostructured electrolyte membranes for improved performance.

Efficient and durable vanadium flow batteries enabled by high-performance fluorinated poly(aryl piperidinium) membranes

“…This result is consistent with the values reported in the literature. 55,56 Notably, the migration of water and vanadium ions across the membrane cannot be avoided, and the negative electrolyte is easily oxidized by the air in the actual application of VFBs. 57,58 When the sealing of the pipeline system (including electrolyte storage tanks) is poor, the oxidation of some V 2+ will lead to an imbalance of the positive and negative electrolytes, which will cause the capacity decay of the battery.…”

“…The gradual decay of the cell capacity during cycling can be attributed to electrolyte crossover, the polarization of the active substance, or a combination of these issues. 55,60 Therefore, the small volume of electrolyte, in this case, needs to be refreshed at regular intervals. After exchanging, the cell capacity fully recovered, and the CE, VE and EE remained stable, with the PFDP-90 membrane demonstrating an impressive cycling performance.…”

Polyoxometalate-based reticular materials for proton conduction: from rigid frameworks to flexible networks

“…For instance, embedding POMs into polymer matrices can create composite proton exchange membranes with stable conducting properties and good processability for fuel cell and redox flow battery applications. 24–27…”

High-performance ultrathin perfluorinated sulfonic acid membranes with thermo-morphology control for a vanadium redox flow battery

“…As straightforward approaches, to enhance the ion selectivity of PFSA membranes, various studies have been conducted to reduce the channel size by introducing foreign moieties into the channels, such as inorganic 12–14 and 2D materials, 15–17 and amine-based oligomers. 18 Although the fillers suppress the permeation of the active species, they simultaneously act as barriers for proton conduction, resulting in proton conductivity reduction. On the other hand, since the membrane properties are closely related to the morphology, there have been a few attempts to directly tune the ion transportation behavior of PFSA membranes by aligning hydrophilic channels with mechanical deformation or electromagnetic field-assisted casting.…”