Nanocomposites from Polymer Brushes and Metal Oxide Clusters for Fabrication of High‐Temperature Fuel Cell Proton Exchange Membranes

Abstract High‐temperature proton exchange membranes (HT‐PEMs) are highly desired for fuel cells with high energy density; however, the requirements in balanced anhydrous proton conductivity, mechanical/structural stability, processability and gas‐barrier property impose great difficulty for molecular design. Herein, the supramolecular complexation of brush polymers and super acidic metal oxide cluster (H 3 PW 12 O 40 , abbreviation PW 12 ) affords HT‐PEMs with comprehensive performance that contributes to the robust performance of high energy density fuel cells. The polymers brush topology enables the decoupling of mechanical properties and proton conduction: the polyethylene glycol (PEG) side chains possess high affinity to PW 12 for proton transport while the rigid backbones help maintain structural stability and mechanical strengths up to 250 °C. The PW 12 clusters can be homogeneously dispersed in PEG with high loadings (≈80 wt.%) and it facilitates proton hopping among the crowded PW 12 for promising anhydrous proton conduction, e.g., 2 × 10 −3 S cm −1 at 200 °C. Their dense supramolecular bonds contribute to enhanced mechanical strength, flexibility and gas barrier property with mitigating hydrogen permeation current as 0.73 mA cm −2 , enabling the feasible processability of PEMs and stable operation of fuel cells. The devices show high power density as 218 mW cm −2 at 180 °C with long‐term stable operation.