Nanocomposite proton conducting membranes based on sulfonated polystyrene/imidazole-2-acetic acid blend for direct methanol fuel cell application

Nanocomposite polyelectrolyte membranes based on sulfonated polystyrene (SPS) /imidazole-2-acetic acid (Im) blend (SPSIm), incorporated with halloysite nanotubes (HNTs) were studied for direct methanol fuel cell (DMFC) applications. Firstly, PS was sulfonated at various degrees of sulfonation (DS), and the optimum DS was selected based on hydrolytic stability. Then, SPS was blended with Im as new proton conducting sites. In addition to increasing proton conductivity, methanol permeability decreased due to the attractive interaction between Im and -SO3H groups in SPS. In the next step, to introduce tortuous diffusion pathways and hence decrease the methanol crossover, halloysite nanotubes were incorporated into the SPSIm matrix. The results show that the methanol permeability of the membrane incorporated with 1 wt% HNT (SPSIm/HNT) was around 0.527 x 10(-7) cm(2) s(-1), which showed a significant decrease compared to SPS, causing an improvement in the membrane selectivity parameter in comparison to pristine SPS membrane. Furthermore, the thermal properties, ion exchange capacity (IEC), water uptake behavior, and performance of the membranes were evaluated. Based on the results, owing to the reduced methanol permeability, acceptable power density, ease of preparation, as well as low cost, SPSIm/HNT could be considered for DMFC applications.