Phosphonated Ionomers of Intrinsic Microporosity with Partially Ordered Structure for High-Temperature Proton Exchange Membrane Fuel Cells.

Abstract

High mass transport resistance within the catalyst layer is one of the major factors restricting the performance and low Pt loadings of proton exchange membrane fuel cells (PEMFCs). To resolve the issue, a novel partially ordered phosphonated ionomer (PIM-P) with both an intrinsic microporous structure and proton-conductive functionality was designed as the catalyst binder to improve the mass transport of electrodes. The rigid and contorted structure of PIM-P limits the free movement of the conformation and the efficient packing of polymer chains, resulting in the formation of a robust gas transmission channel. The phosphonated groups provide sites for stable proton conduction. In particular, by incorporating fluorinated and phosphonated groups strategically on the local side chains, an orderly stacking of molecular chains based on group assembly contributes to the construction of efficient mass transport pathways. The peak power density of the membrane electrode assembly with the PIM-P ionomer is 18-379% greater than that of those with commercial or porous catalyst binders at 160 °C under an H2/O2 condition. This study emphasizes the crucial role of ordered structure in the rapid conduction of polymers with intrinsic microporosity and provides a new idea for increasing mass transport at electrodes from the perspective of structural design instead of complex processes.