Preparation and fuel cell performances of SPI/S-BEA composite proton exchange membranes

Sulfonated porous zeolite (S-BEA) composite sulfonated polyimide (SPI) proton exchange membranes were prepared by mixing inorganic nanoparticles S-BEA with SPI solution. Scanning electron microscopy showed that inorganic particles S-BEA were fairly uniform dispersed in the SPI PEM, when the S-BEA content was 10% (H1). The agglomerated inorganic particles increased with the content up to 20% (H2), the macro-phase interface separation was clearly observed. The ion exchange capacity (IEC) value of S-BEA composite PEM H1 was decreased by 12% when compared to that of M1 without composite, the water uptake of H1 barely decreased due to the existence of hydrophilic S-BEA. The number of sorbed water molecules per sulfonic acid group increased from 23 for M1 to 26 for H1. No obvious increase of membrane size change in dry/wet environment was observed for SPI/S-BEA composite PEMs due to the hydrogen bonding interaction of the hydroxyl groups on the inorganic particles surface with the polymer chain. These composited PEMs also showed excellent mechanical properties. The proton conductivity under low humidity for H1 with lower IEC value was comparable to that of M1. However, when the S-BEA content increased to 20%, the obvious macro-phase separation interface hindered the proton conducting in the PEM matrix, thus the proton conductivity of H2 decreased on the contrary. The proton exchange membrane fuel cell performance test showed H1 did not have clearly higher fuel cell performances than that of M1 at 90°C. When the fuel cell temperature increased to 110°C, due to the water retention property of inorganic particles S-BEA, H1 showed clearly better fuel cell performances than those of M1. For example, the maximum power output of SPI/S-BEA composite PEM H1 was 0.61 W cm^-2, which was 30% higher than that of M1.