Preparation and performance control of PVA proton exchange membrane incorporating ionic liquids with varying ΔpKa for direct methanol fuel cells

The proton exchange membrane (PEM) constitutes a pivotal component of the fuel cell, with its property frequently serving as a determining factor in the overall performance of the fuel cell. In this study, a composite membrane with excellent comprehensive properties for direct methanol fuel cells (DMFC) is obtained by doping a highly conductive proton-ionic liquid (PIL) into a polyvinyl alcohol (PVA) crosslinked membrane. The physicochemical properties of three PILs with different ΔpK a are characterized, and the relationship between their structure and properties is researched and the proton conduction mechanism of different PILs is clarified. Subsequently, the PIL exhibiting the optimal comprehensive performance is doped into the PVA crosslinking system, thereby introducing further proton conduction groups into the original system and enhancing the proton conductivity of PEMs. When the content of the PIL was 20 wt%, the CPVA/IL-20 composite membrane exhibits the most favorable comprehensive performance, with a proton conductivity of 53.5 mS/cm at 80 °C, and a peak power density of 42.7 mW/cm 2 at 80 °C with 100 % RH, which is 1.7 times that of CPVA without PIL. The methanol permeability and selectivity at room temperature are 6.5 × 10 −7  cm 2  s −1 and 3.75 × 10 4  S s cm −3 , respectively.