A novel hybrid Nafion-PBI-ZP membrane for direct methanol fuel cells

Abstract

Methanol crossover through proton conducting membranes represents one of the main drawbacks in DMFCs. This study presented a novel organic-inorganic hybrid membrane with several different compositions by casting mixtures of zirconium phosphate (ZP), polybenzimidazole (PBI) and Nafion dispersion in dimethylacetamide. The presence of PBI and ZP in the membranes was demonstrated with energy dispersive X-ray (EDX) analysis. From the scanning electron microscopy (SEM) analysis, it was observed that the hybrid Nafion-PBI-ZP membrane had the finest structure. This is because the synthesized films were homogeneous and therefore formed a dense membrane. The water content was higher in the hybrid membrane: 39.91% compared with 35.52% in Nafion117. The water content is important for the ion transportation in the membrane; therefore, a higher water uptake rate will contribute to a better fuel cell performance. It was determined that the proton conductivity of the hybrid membrane was 0.020 S cm−1, which was comparable with Nafion117, which had a proton-conductivity of 0.022 S cm−1. The methanol permeability of the hybrid membrane was 2.34 × 10−7 cm2 s−1, while the value for Nafion117 was 8.91 × 10−7 cm2 s−1. This showed that the methanol permeability of the hybrid membrane was almost 4 times lower than that of Nafion117. The selectivity factor for the Nafion-PBI 1%–ZP 1% membrane was 8.64 × 104 Scm−3, while that of Nafion117 was 2.48 × 104 S scm−3. From a thermogravimetry analysis (TGA), the addition of PBI and zirconium phosphate was shown to improve the thermal durability in the temperature range from room temperature to 450 °C over that of Nafion117. This study proofed that the Nafion-PBI 1%–ZP 1% performed better than commercial Nafion117 and other type of membranes. The membrane was tested on as single cell of DMFC. It gave the highest power density as compared to other type of membrane and proofed that it has potential to be used in DMFCs.