The parameter space for scalable integration of atomically thin graphene with Nafion for proton exchange membrane (PEM) applications

Selective proton permeation through atomically thin graphene while maintaining impermeability to even small gas atoms i.e. He or hydrated ions, presents potential for advancing proton exchange membranes (PEMs) across a range of energy conversion and storage applications. The incorporation of graphene into state-of-the-art proton conducting polymers e.g. Nafion can enable improvements in PEM selectivity as well as mitigate reactant crossover. The development of facile integration approaches are hence imperative. Here, we systematically study the parameters influencing the integration of monolayer graphene synthesized via scalable chemical vapor deposition (CVD) on polycrystalline Cu foils with a model proton conducting polymer (Nafion) via a facile hot-press process. The hot-press time (t), temperature (T) and pressure (P) are found to not only influence the quality of graphene transfer but can also introduce additional defects in the CVD graphene. Graphene transfers to Nafion performed below the optimum temperature (T_opt ∼ 115 °C) remain patchy with ruptures, while transfers above T_opt showed defect features, and transfers near T_opt show minimal ruptures and defect features. We demonstrate Nafion|graphene|Nafion sandwich membranes using the optimal transfer conditions that allow for ∼50% reduction in hydrogen crossover (∼0.17 mA cm⁻²) in comparison to Nafion control membranes (∼0.33 mA cm⁻²) while maintaining comparable proton area specific resistance < 0.25 Ω cm² (areal conductance ∼ 4-5 S cm⁻²), that are adequate to enable practical PEM applications such as fuel cells, redox flow batteries, and beyond.