Highly Conductive Polymer Electrolyte Membranes with Polyoxometalate Hybrid Nanodomains for High-Temperature Fuel Cells

Phosphoric acid (PA)-doped polymer electrolyte membranes represent the most widely used high-temperature proton exchange membranes (HT-PEMs) in fuel cells. However, these materials face a significant challenge in achieving high proton conductivity under low PA content. Here, we report the fabrication of highly conductive nanodomains in HT-PEMs to solve this issue. A comb polymer with poly(ethylene glycol) (PEG) side chains was assembled with polyoxometalate nanoclusters (POMs) and PA, forming hybrid membranes with continuous nanodomains and dense hydrogen-bonding networks, which enabled efficient proton conduction and suppressed PA leaching. These membranes exhibited superior proton conductivity (109 mS cm^-1 at 180 °C) and high cell performance (1287 mW cm^-2 at 160 °C, 2.2 times of commercial PBI/PA membrane) at low PA uptake (160%). Additionally, POMs acted as electrostatic cross-linkers, enhancing both mechanical strength and PA retention. This work demonstrates the potential of POM-polymer hybridization strategy in developing advanced HT-PEMs for energy applications.