Atomically thin CVD graphene-integrated proton exchange membrane electrode assemblies: fabrication parameter space...

Proton selective, atomically thin two-dimensional (2D) materials interfaced with state-of-the-art proton exchange membranes (PEMs) enable overcoming the inherent trade-off between proton conductance and gas crossover. Monolayer graphene-integrated PEMs show significantly reduced gas crossover with negligible impact on proton conductance. However, the influence of fabrication methods on membrane-electrode assemblies (MEAs) using PEMs interfaced with monolayer graphene (synthesized via chemical vapor deposition (CVD)) via an ultra-thin (∼700 nm) ionomer carrier layer remains elusive. Here, we systematically investigate three MEA fabrication processes: gas diffusion electrode (GDE), directly sprayed catalyst-coated membrane (DS-CCM), and decal transfer catalyst-coated membrane (DT-CCM) using monolayer CVD graphene-integrated with perfluorosulfonic acid (PFSA) PEMs (∼12-25 μm thick). Although the GDE process minimizes processing or impact on PEM properties, the rough surface of the GDE could damage CVD graphene coated with the ∼700 nm ionomer carrier layer, limiting the suppression of H₂ crossover. The DS-CCM approach exposes the PEM to solvents, resulting in degradation and diminished performance. DT-CCM emerges as the most effective route, with minimal graphene damage, yielding a pronounced reduction (∼25-44%) in H₂ crossover without impacting proton conductance. Notably, the decal approach remains effective even for thinner (∼12 μm thick) PEMs with inherently higher proton conductance, where reduced crossover can enable enhanced membrane durability and fuel cell efficiency. These findings establish fabrication-sensitive design rules for integrating 2D materials into MEAs and highlight the advantages of the decal-transfer approach for next-generation PEMs.