Enhancing the selectivity of Nafion membrane by incorporating a novel functional skeleton molecule to improve the performance of direct methanol fuel cells

Abstract

Conventional fillers have limitations on the modification of proton exchange membranes because of differences in the sizes and physicochemical properties of matrix molecules. Designing skeleton molecules is a vital way to address the limitations by enabling precise distribution in the matrix and inducing automatic nanoscale aggregation and separation of hydrophilic–hydrophobic phases. In this work, a novel SDF-PAEK polymer was synthesized with a rigid hydrophobic backbone, short high-density trifluoromethyl side chains and long flexible aliphatic pendant side chains as a skeleton molecule for the Nafion membrane. Due to the unique molecular interaction selectivity during the membrane formation process, SDF-PAEK automatically matches the Nafion molecular conformation by self-assembly. Combining an improved solution formulation and membrane-casting method, the degree of composition can therefore rise to 20%, which can effectively reduce the cost. Morphological studies show that there is a certain degree of bicontinuous phase microcrystalline domains, and the proton transport channels are highly concentrated. In contrast to the Nafion membrane, SDF-PAEK@Nafion-15% exhibits better performances with higher selectivity (9.73 × 10⁴ S s cm⁻³) and single-cell maximum power density (PD_max–139 mW cm⁻², at 80 °C), which demonstrates the feasibility of SDF-PAEK as a novel PEM skeleton molecule for fuel cell applications.