Reorientation of magnetic graphene oxide nanosheets in crosslinked quaternized polyvinyl alcohol as effective solid electrolyte

This work aims to clarify the effect of magnetic graphene oxide (GO) reorientation in a polymer matrix on the ionic conduction and methanol barrier properties of nanocomposite membrane electrolytes. Magnetic iron oxide (Fe₃O₄) nanoparticles were prepared and dispersed on GO nanosheets (GO-Fe₃O₄). The magnetic GO-Fe₃O₄ was imbedded into a quaternized polyvinyl alcohol (QPVA) matrix and crosslinked (CL-) with glutaraldehyde (GA) to obtain a polymeric nanocomposite. A magnetic field was applied in the through-plane direction during the drying and film formation steps. The CL-QPVA/GO-Fe₃O₄ nanocomposite membranes were doped with an alkali to obtain hydroxide-conducting electrolytes for direct methanol alkaline fuel cell (DMAFC) applications. The magnetic field-reoriented CL-QPVA/GO-Fe₃O₄ electrolyte demonstrated higher conductivity and lower methanol permeability than the unoriented CL-QPVA/GO-Fe₃O₄ membrane or the CL-QPVA film. The reoriented CL-QPVA/GO-Fe₃O₄ nanocomposite was used as the electrolyte in a DMAFC and resulted in a maximum power density of 55.4 mW·cm^-2 at 60°C, which is 73.7% higher than that of the composite without the magnetic field treatment (31.9 mW·cm^-2). In contrast, the DMAFC using the CL-QPVA electrolyte generated only 22.4 mW·cm^-2. This research proved the surprising benefits of magnetic-field-assisted orientation of GO-Fe₃O₄ in facilitating the ion conduction of a polymeric electrolyte.