Fabrication of MIL-100(Fe)-GO Filler-Infused Sulfonated Polyether Ether Ketone Membrane for Room-Temperature Direct Methanol Fuel Cell Applications with Enhanced Selectivity

This study reports the preparation of MIL-100(Fe)-GO composites by a one-pot synthesis approach at room temperature, assisted by ultrasonication. The synthesized MIL-100(Fe)-GO composites were utilized as a filler for the preparation of a sulfonated polyether ether ketone (SPEEK)-based proton exchange membrane (PEM). The in situ development of MIL-100(Fe) on GO creates a strong interaction between GO and MIL-100(Fe), which enhances the surface roughness (confirmed from the AFM study) of the SPEEK membrane with its incorporation as a filler. The resulting SPEEK membrane containing MIL-100(Fe)-GO exhibits a hydrophobic-hydrophilic phase-separated structure, delivering impressive performance as a PEM. Notable characteristics include high proton conductivity, low methanol crossover, high selectivity, and high power density compared with pure SPEEK membranes. Specifically, the composite membranes, particularly SPEEK with 3% (w/w) MIL-100(Fe)-GO (SMGO3), demonstrate reduced methanol crossover (0.22 × 10^-6 cm²/s) and enhanced proton conductivity (10.90 mS/cm), resulting in superior selectivity of 4.9 × 10⁴ S·s·cm^-3 over Nafion-117 (0.65 × 10⁴ S·s·cm^-3) benchmark membranes. Durability experiments and Fenton's test for the oxidative stability of the SMGO3 membrane were also performed. In direct methanol fuel cell applications, the SPEEK/MIL-100(Fe)-GO membrane significantly outperforms pristine SPEEK, indicating its potential as a promising candidate for PEMs.