Enhancement of Nafion-Based\nIonomeric Membranes by\nUsing ATRP Sulfonated Polymer Grafted on Reduced Graphene Oxide Fillers

Graphene is a widely utilized filler in Nafion ionomeric\nmembranes\ndue to its sheet-like structure and exceptional thermal and chemical-mechanical\nstability, which address the challenges associated with methanol permeability\nin direct methanol fuel cells (DMFCs). However, Nafion composite membranes\nincorporating graphene and its derivatives often suffer from reduced\nproton conductivity due to uneven dispersion, dilution of sulfonic\nacid groups (−SO<sub>3</sub>H), and the introduction of convoluted\npaths for proton transport at the interface. In this study, atom transfer\nradical polymerization (ATRP) was used to graft sulfonated polymeric\nbrushes derived from poly(3-sulfopropyl methacrylate potassium salt)\n(PSPMA) onto the surface of reduced graphene oxides (rGO), aiming\nto enhance the dispersion of graphene derivatives within Nafion membranes.\nPSPMA, with its −SO<sub>3</sub>H groups, not only enhanced\nthe interfacial compatibility between rGO and Nafion but also contributed\nto increasing the proton conductivity by increasing the −SO<sub>3</sub>H concentrations and optimizing the ionomer cluster network.\nConsequently, the proton conductivity of Nafion containing 2.0 wt\n% of rGO modified with PSPMA increased by 1.2-fold compared to pristine\nNafion, while methanol permeability was reduced by a significant factor\nof 8. This PSPMA-rGO/Nafion composite membrane demonstrates promising\npotential for DMFC applications by effectively balancing proton conductivity\nand methanol permeability, with a value of selectivity equal to 6.47\n× 10<sup>5</sup> S cm<sup>–3</sup> when the content of\nfiller is equal to 2.0 wt %.