Development of nafion/ palladium nanofiller as nanocomposite membrane for fuel cell applications

Abstract

The nanocomposite membranes were fabricated by incorporating palladium nanoparticles into Nafion® matrix to develop suitable membrane to be used as polymer electrolyte membrane (PEM) in Direct Methanol Fuel Cell (DMFC). The effect of palladium loading was studied to explore a suitable membrane for DMFC. The recast method was used to synthesize the nanocomposites membranes. Commercial palladium nanoparticles were used as reference for synthesized palladium nanoparticles and palladium nanocomposite membranes. The synthesized palladium nanoparticles by sol-gel method were characterized by TEM, UV-vis, FTIR and DLS. The morphology and crystalline structure of nanocomposite membranes were characterized by FESEM, XRD, FTIR. The distribution of palladium nanoparticles within Nafion® membrane was confirmed by EDS. The thermal properties were analysed by TGA and DSC. The mechanical properties were also investigated. To evaluate suitability of palladium nanocomposite membranes as polymer electrolyte membranes (PEMs) in DMFC properties such as water uptake (WU), water contact angle, methanol permeability, ion exchange capacity (IEC), proton conductivity and selectivity were determined. The palladium nanocomposite membranes indicated the lowest water uptake of 0.37% at 25°C and highest water uptake of 14.8% at 100°C. The results of water uptake indicated hydrophobic behaviour which corresponds to water contact angle. The highest water contact angle of 100.3° and lowest water contact angle of 84°were recorded for nanocomposite membrane. v The mechanical properties of nanocomposite membranes such as tensile strength, elastic modulus (stiffness) and elongation at break were improved for all nanocomposite membranes. The methanol permeability of nanocomposite membranes was improved with reduced methanol permeability of 3.5 × 10-7 cm-1s-1 for commercial PdNps/Nafion®, 3.6 × 10-7 cm-1s-1 for PdEG22/Nafion®, 3.8 × 10-7 cm-1s-1 for PdEG33/Nafion®, 4.5 × 10-7 cm-1s-1 for PdEG11/Nafion® compared to 9.12 × 10-7 cm-1s-1 of pristine recast Nafion® membrane at temperature of 80°C. The ion exchange capacity recorded values were 1.28 mm/g for PdEG22/Nafion®, 1.32 mm/g for PdEG33/Nafion®,1.47 mm/g for PdEG11/Nafion®,2.18 mm/g commercialPdNps/Nafion® compared to 0.81mm/g of pristine Nafion®. The proton conductivity of 0.6 Scm-1 (PdEG11/Nafion®), 0.41 Scm-1 (PdEG22/Nafion®), 0.28 Scm-1 (PdEG33/Nafion®), 0.26 Scm-1 (commercial PdNps/Nafion®) was achieved comparable to pristine Nafion® with 0.25 Scm-1.The membrane selectivity of palladium nanocomposite membranes showed the membranes are suitable to be used as PEM in DMFC due to their selectivity values recorded as 1.33 × 106 Sc cm-3 for PdEG11/Nafion®, 1.14 × 106 Sc cm-3 for PdEG22/Nafion®, 7.4 × 105 Sc cm-3 for both PdEG33/Nafion® and commercial PdNps/Nafion® compared to pristine Nafion® (2.7 × 105 Sc cm-3) and their ability to reduce methanol crossover.