Improving the efficiency of Nafion-based proton exchange membranes embedded with magnetically aligned silica-coated Co3O4 nanoparticles

Abstract

In this study, Nafion proton exchange membranes with incorporated silica-coated Co3O4 nanoparticles (Nafion/CT) were prepared. The nanoparticles were synthesized and characterized using FT-IR spectroscopy, XRD, magnetic measurements, TEM, SEM, and EDX spectroscopy. Thereafter, the nanoparticles were employed as an effective additive so as to improve the Nafion/CT properties. To do so, the spherical core-shell nanoparticles (Co3O4 diameter 12 nm; SiO2 layer thickness 20 nm) were aligned by a magnetic field in the Nafion matrix during solution casting and solvent evaporation. The thus obtained nanocomposite membranes, including control samples without particles or with particles but without alignment, were investigated with respect to their structure by SEM, EDX, and XPS analyses, and also with regard to their water uptake, proton conductivity, and methanol permeability. Overall, the aligned nanocomposite membranes showed much better performance than that of randomly dispersed nanocomposite membranes. The data indicate that regarding aligned structure, the proton transfer channels in the membrane matrix become less tortuous so that proton transfer through the membrane occurs faster while at the same time methanol transfer is partially blocked. The Nafion/CT nanocomposite membrane containing 1 wt% of CT exhibited a proton/methanol selectivity at 25 °C of 6.04 × 104 S s−1 cm−3, whereas the pristine Nafion membrane showed a selectivity of 4.2 × 104 S s−1 cm−3. The nanofiller alignment by magnetic field improved the proton conductivity at 90 °C from 0.14 S cm−1 (no field) to 0.18 S cm−1.