Microporous expanded polytetrafluoroethylene layer functionalized hydrophilic groups for excellent mechanical durability and superior performance in proton exchange membrane fuel cell

Introducing hydrophilic groups and increasing the compatibility of the ionomer and reinforcement layer can have a significant impact on the proton conductivity and cell performance of a proton exchange membrane (PEM) under lower relative humidity (RH). In this work, a novel PEM containing expanded polytetrafluoroethylene (ePTFE) functionalized with amino and hydroxyl groups is designed and fabricated to enhance the PEM's proton conductivity and electrochemical performance at low RH, and to improve its mechanical stability. The introduction of the hydrophilic groups and the generation of stable acid–base pairs yield a PFSA ionomer that has better compatibility with and adhesion to the hydrophilic functionalized ePTFE membrane, thereby significantly improving the prepared membrane's proton conductivity, H2 crossover current density, and single-cell performance. In addition, generated water is retained inside the PEM, keeping its cell performance high at low RH. The PEM's mechanical durability is also improved by the increased dimensional stability and compatibility of the ionomer and reinforcement layer. This work provides a promising way to improve the proton conductivity and cell performance of PEMs at low RH and has great application potential for creating PEM fuel cells with high mechanical durability.