Impact on the ionic channels of sulfonated poly(ether ether ketone) due to the incorporation of polyphosphazene: a case study in direct methanol fuel cells

Blend membranes are fabricated from sulfonated poly(ether ether ketone) (SPEEK) and poly[bis(phenoxy)phosphazene] (POP). The effect of POP content on the distribution of ionic channels is investigated by atomic force microscopy (AFM). The water uptake and methanol permeability for the blend membranes are also investigated. The blend membranes are characterized in terms of their thermal and mechanical properties in conjunction with their ionic conductivity. The proton conductivity of the blend membranes slightly decreased with increasing POP content in comparison with the pristine SPEEK membrane. The hydrophobic nature of POP blocks the ionic channels in the SPEEK matrix, subsequently decreasing its water uptake and methanol permeability. The blend membranes showed higher power density compared to a pristine SPEEK membrane in direct methanol fuel cells (DMFCs).