Proton conductivity enhancement of SPEEK membrane through n-BuOH assisted self-organization

• Excellent SPEEK/n-BuOH PEM was achieved with n-BuOH assisted self-organization.
• Multiple hydrogen bonds facilitate the clustering of hydrophilic domains.
• SPEEK/n-BuOH exhibits a proton conductivity as high as 0.314 S cm−1 at 80 °C.
• Proton conductivities higher than Nafion at low relative humidity were obtained.

Non-fluorinated proton exchange membranes are limited by poor proton conductivity due to weak phase separation and narrow hydrophilic channels. In this research, SPEEK membrane with high proton conductivity was fabricated by introducing self-organization inducer (n-BuOH). Multiple hydrogen bonds between SPEEK and n-BuOH facilitate the clustering of hydrophilic domains, and increase the ionic clusters from 1 nm to 3 nm. At 80 °C, SPEEK/n-BuOH membrane (IEC=1.5 mmol g−1) exhibits a proton conductivity as high as 0.314 S cm−1, yielding enhancements of 161% and 88% on pristine SPEEK and Nafion 115 membranes respectively. To the best of our knowledge, this is the highest proton conductivity among SPEEK based PEMs. Furthermore, SPEEK/n-BuOH exhibits proton conductivities even higher than Nafion at low relative humidity (from 40% to 90%). The modulus and tensile strength of SPEEK/n-BuOH are increased by 32% and 35% as well. Finally, a selectivity of 122×104 S s cm−3 is achieved for SPEEK/n-BuOH membrane, which is comparable to the reported highest value among SPEEK based PEMs (130×104 S s cm−3).