Novel Proton Exchange Membrane with Long-Range Acid–Base-Pair Proton Transfer Pathways Based on Functionalized Polyethyleneimine

Mass transport in proton exchange membrane fuel cells (PEMFCs) is critical to their efficiency and energy output, especially the transfer of protons and water that occurs in the PEM. Here, we describe designing and fabricating a novel composite PEM based on perfluorosulfonic acid (PFSA) and polyethyleneimine functionalized with methylphosphonic acid (PEIMPA), with the aim of constructing efficient mass transfer pathways using long-range acid–base pairs. Improvements in water absorption/retention, proton conductivity, and single-cell performance resulted from these long-range transfer pathways, as the acid–base pairs and abundant water-retaining groups in the membrane enhanced the connectivity of the hydrophilic zone, forming new proton and water transport pathways. These improvements in water and proton transport also gave the PFSA/PEIMPA composite membranes higher reversal tolerance. Their excellent physical and chemical properties make these membranes promising candidates for PEMFC applications by reducing dependency on water content, enhancing fuel cell performance at low relative humidity, and improving the fuel cell's tolerance toward reversal.