Sulfonated poly (ether ether ketone)/MOF hybrid polymer electrolyte membrane with ultra‐low methanol permeability for enhanced direct methanol fuel cell performance

Abstract A novel hybrid polymer electrolyte membrane (PEM) was developed for direct methanol fuel cell (DMFC) applications by incorporating sulfonated poly (ether ether ketone) (SPEEK) with a chromium‐based metal–organic framework (MOF), namely, BUT‐8(Cr). The incorporation of BUT‐8(Cr) significantly improved the dispersion of the MOF within the SPEEK matrix, leading to alterations in surface morphology and the creation of hydrophilic channels, as confirmed by SEM. Furthermore, the presence of an excess of sulfonic groups and the flexible structure of the MOF enhanced the physicochemical properties of the membrane, such as water uptake, proton conductivity and ion exchange capacity. Importantly, well‐defined rigid coordination structure of MOF effectively blocks methanol migration, resulting in a notably low methanol permeability value of 1.6 × 10 −7 cm 2 s −1 , compared to Nafion 117 (20 × 10 −7 cm 2 s −1 ). For practical DMFC operation, the hybrid membrane (~0.75 wt.% MOF) exhibited a maximum power density of 88.6mWcm −2 with current density of 434.04 mAcm −2 , outperforming Nafion 117 (73.4mWcm −2 and 380 mAcm −2 respectively) at same conditions. Our results suggest that the prepared SPEEK‐0.75 hybrid membrane holds a great promise as a PEM material for DMFC applications.