Enhancement of Nafion-Based Ionomeric Membranes by Using ATRP Sulfonated Polymer Grafted on Reduced Graphene Oxide Fillers

Graphene is a widely utilized filler in Nafion ionomeric membranes due to its sheet-like structure and exceptional thermal and chemical-mechanical stability, which address the challenges associated with methanol permeability in direct methanol fuel cells (DMFCs). However, Nafion composite membranes incorporating graphene and its derivatives often suffer from reduced proton conductivity due to uneven dispersion, dilution of sulfonic acid groups (−SO₃H), and the introduction of convoluted paths for proton transport at the interface. In this study, atom transfer radical polymerization (ATRP) was used to graft sulfonated polymeric brushes derived from poly(3-sulfopropyl methacrylate potassium salt) (PSPMA) onto the surface of reduced graphene oxides (rGO), aiming to enhance the dispersion of graphene derivatives within Nafion membranes. PSPMA, with its −SO₃H groups, not only enhanced the interfacial compatibility between rGO and Nafion but also contributed to increasing the proton conductivity by increasing the −SO₃H concentrations and optimizing the ionomer cluster network. Consequently, the proton conductivity of Nafion containing 2.0 wt % of rGO modified with PSPMA increased by 1.2-fold compared to pristine Nafion, while methanol permeability was reduced by a significant factor of 8. This PSPMA-rGO/Nafion composite membrane demonstrates promising potential for DMFC applications by effectively balancing proton conductivity and methanol permeability, with a value of selectivity equal to 6.47 × 10⁵ S cm^-3 when the content of filler is equal to 2.0 wt %.