Improvement of proton conductivity of magnetically aligned phosphotungstic acid-decorated cobalt oxide embedded Nafion membrane

Abstract

The fabrication of proton exchange membranes with a short conduction pathway in the direction of membrane thickness is desirable for fuel cell applications. In this study, a new nanohybrid additive (Co3O4-NH2/H3PW12O40; CAW) is synthesized, by anchoring phosphotungstic acid (H3PW12O40; HPW) on aminopropylsiloxane-functionalized cobalt oxide, and then it is incorporated into the Nafion (NF) matrix to prepare nanocomposite membranes by film casting from CAW dispersions in NF solutions. To obtain short-pathway proton-conducting channels, through the nanocomposite membranes drying process, a magnetic field is employed to align the nanohybrid particles in transversal (thickness) direction of the NF matrix. Furthermore, the alignment of nanohybrids is observed directly by scanning electron microscopy, and estimated indirectly by proton conductivity and methanol permeability values. It is found that alignment of nanohybrids in the NF matrix elevates the conductivity of proton as well as the permeability of methanol. The aligned NF/CAW nanocomposite membrane with 1 wt% of CAW reveals the highest proton conductivity of 211 mS cm−1 at 90 °C and 95% relative humidity, which is 39% higher than that of pure NF (152 mS cm−1). Interestingly, through the orientation of CAW, 76% improvement in the selectivity of the membranes is observed.