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

Abstract Proton exchange membranes with high selectivity are urgently required in energy and electronic technologies. Although Nafion represents the state‐of‐the‐art commercial proton exchange membrane material,it still suffers from the permeation of undesirable substances, like hydrogen in fuel cells and vanadium ions in redox flow batteries, due to the unmatched sizes between its ionic domains (3–5 nm) and these substances. In this work, we present a supramolecular modification strategy that simultaneously enhances the proton conductivity and selectivity of Nafion. We employ fluoroalkyl‐grafted polyoxometalate (POMs) nanoclusters as supramolecular additives to modify Nafion via co‐assembly. These POMs can precisely and robustly decorate at Nafion ionic domains, with their fluoroalkyl chains anchoring into the perfluorinated matrix while their inorganic clusters stay in the ionic regions. The hybrid membranes, with continuous proton hopping sites and nanoscale steric hindrance offered by POMs, exhibit a 56 % increase in proton conductivity and a 100 % improvement in proton/vanadium selectivity. This leads to significantly enhanced power density and energy efficiency in fuel cells and vanadium flow batteries, respectively. These results underscore the intriguing potential of molecular cluster additives in improving the functions of ion‐conducting membranes.