Cross-linked fully aromatic sulfonated polyamide as a highly efficiency polymeric filler in SPEEK membrane for high methanol concentration direct methanol fuel cells

The current direct methanol fuel cells are still largely limited to the neat methanol operation due to the high methanol permeation of the currently used Nafion membranes. To achieve high methanol concentration DMFC application of the sulfonated poly(ether ether ketone) (SPEEK)-based proton exchange membrane, the neat SPEEK membrane is here modified by blending with the designed cross-linked fully aromatic sulfonated polyamide (Cr-fa-SPA). As the similar fully aromatic features of the SPEEK and the Cr-fa-SPA and the formed hydrogen bonding interactions between the SPEEK and the Cr-fa-SPA, the SPEEK/Cr-fa-SPA membranes show good compatibility, which is beneficial for the construction of the uniform and contact morphology of the membrane. In addition, the cross-linking network and the hydrogen bonding interactions in the SPEEK/Cr-fa-SPA membranes are favorable for enhancing the dimensional stability and reducing the methanol permeation. In particular, the lowest methanol permeability of 0.46 × 10⁻⁷ cm²/s is successfully obtained by blending 40 wt% Cr-fa-SPA in the SPEEK/Cr-fa-SPA membrane, which is almost two magnitudes lower than that of the Nafion 117 membrane. Finally, the SPEEK/Cr-fa-SPA DMFC devices were successfully demonstrated with the highly concentrated 20 M methanol fuels with remarkable performance.