In situ crosslinking of polyoxometalate-polymer nanocomposites for robust high-temperature proton exchange membranes

Supramolecular Modifying Nafion with Fluoroalkyl‐Functionalized Polyoxometalate Nanoclusters for High‐Selective Proton Conduction

Fluoroalkyl-grafted polyoxometalate nanoclusters are used as supramolecular additives to precisely modify the ionic domains of Nafion, which can increase the proton conductivity and selectivity simultaneously. The resulting hybrid membranes show significantly enhanced power density in fuel cells and improved energy efficiency in vanadium flow batteries.

Semi-Solid Supramolecular Ionic Network Electrolytes Formed by Zwitterionic Liquids and Polyoxometalate Nanoclusters for High Proton Conduction

Flexible electrolytes with solid self-supporting properties are highly desired in the fields of energy and electronics. However, traditional flexible electrolytes prepared by doping ionic liquids or salt solutions into a polymer matrix pose a risk of liquid component leakage during device operation. In this work, the development of supramolecular ionic network electrolytes using polyoxometalate nanoclusters as supramolecular crosslinkers to solidify bola-type zwitterionic liquids is reported. The resulting self-supporting electrolytes possess semi-solid features and show a high proton conductivity of 8.2 × 10-4 S cm-1 at low humidity (RH = 30%). Additionally, the electrolytes exhibit a typical plateau region in rheological tests, indicating that their dynamic network structures can contribute mechanical behavior similar to the entangled networks in covalent polymer materials. This work introduces a new paradigm for designing flexible solid electrolytes and expands the concept of reticular chemistry to noncrystalline systems.

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

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.

Supramolecular Anchoring of Polyoxometalate Amphiphiles into Nafion Nanophases for Enhanced Proton Conduction

Advanced proton exchange membranes (PEMs) are highly desirable in emerging sustainable energy technology. However, the further improvement of commercial perfluorosulfonic acid PEMs represented by Nafion is hindered by the lack of precise modification strategy due to their chemical inertness and low compatibility. Here, we report the robust assembly of polyethylene glycol grafted polyoxometalate amphiphile (GSiW₁₁) into the ionic nanophases of Nafion, which largely enhances the comprehensive performance of Nafion. GSiW₁₁ can coassemble with Nafion through multiple supramolecular interactions and realize a stable immobilization. The incorporation of GSiW₁₁ can increase the whole proton content in the system and induce the hydrated ionic nanophase to form a wide channel for proton transport; meanwhile, GSiW₁₁ can reinforce the Nafion ionic nanophase by noncovalent cross-linking. Based on these synergistic effects, the hybrid PEMs show multiple enhancements in proton conductivity, tensile strength, and fuel cell power density, which are all superior to the pristine Nafion. This work demonstrates the intriguing advantage of molecular nanoclusters as supramolecular enhancers to develop high-performance electrolyte materials.