Trivial Transfer Graphene for PFSA Membranes - Forschungszentrum Jülich, 2023

Maier, M. et al. (2023). A comprehensive study on the ionomer properties of PFSA membranes with confocal Raman microscopy. *Journal of Membrane Science*. https://doi.org/10.1016/j.memsci.2022.121244

Journal of Membrane Science · 2023

Researchers at Forschungszentrum Jülich used ACS Material Trivial Transfer Graphene as a single-layer interlayer in Nafion composite membranes imaged by confocal Raman microscopy.

About this research

Researchers at Forschungszentrum Jülich (Helmholtz-Institute Erlangen-Nürnberg, IEK-11) used ACS Material Trivial Transfer Graphene as a single-layer graphene (SLG) interlayer in a Nafion composite membrane, demonstrating that confocal Raman microscopy (CRM) can resolve atomically thin features inside multi-layer perfluorinated sulfonic acid (PFSA) membranes. The study provides a comprehensive demonstration that CRM can quantify equivalent weight (EW), thickness, swelling, and water uptake for all three common PFSA ionomers—Nafion, Aquivion, and 3M Ionomer—in a contact-free, non-destructive manner. Beyond standard membranes, the work shows CRM can image composite membranes containing either a monolayer graphene interlayer or a polymeric nanofiber reinforcement, distinguishing each phase by its characteristic Raman signature.

Proton exchange membranes are central to electrochemical energy systems including PEM fuel cells, water electrolyzers, and redox flow batteries. Their performance and longevity depend on membrane hydration, thickness, ion exchange capacity, and resistance to chemical degradation. Conventional analysis methods such as NMR, neutron scattering, and X-ray scattering suffer from limited spatial resolution, small sample volumes, or radiation damage to susceptible polymers. IR spectroscopy is limited by poor spatial resolution and strong water absorption. Confocal Raman microscopy overcomes many of these drawbacks: it is less sensitive to water, operates in the visible range for sub-2-micron lateral resolution, and works on hydrated or immersed samples. The open challenge addressed here is establishing a single universally applicable spectroscopic toolkit that can simultaneously evaluate multiple PFSA properties and image composite membrane architectures, which are increasingly used to improve mechanical and chemical stability.

ACS Material Trivial Transfer Graphene was used to fabricate the SLG-interlayer composite membrane. The product is a single-layer graphene deposited on a polymeric substrate and coated with a thin layer of polymethylmethacrylate (PMMA), ordered in a 2.5 cm × 2.5 cm format. Following the supplier's transfer protocol, the SLG was detached by wetting the polymeric substrate and transferring the film to deionized water, where the PMMA-coated SLG floated for two hours. The PMMA-coated graphene was then collected on top of a Nafion NR211 membrane by lifting the membrane through the floating film. The composite was dried at room temperature for one hour, then at 80 °C for 20 minutes, and the PMMA coating was removed by immersing the membrane in ethyl acetate for one minute. A second NR211 membrane was hot-pressed (155 °C, 5 min, 2.5 MPa) on top to form a sandwich structure with the SLG embedded in the center. This composite served as a model multi-layer membrane to test whether CRM could resolve an atomically thin interlayer, alongside a separately fabricated PVDF-HFP nanofiber-reinforced Nafion membrane.

The study produced clear quantitative results. Calibration curves relating side-chain to backbone Raman intensity ratios against the inverse number of backbone repeat units per sulfonyl group yielded excellent linear fits, with coefficients of determination (R²) between 0.969 and 0.996 across Aquivion, 3M Ionomer, and Nafion. For the long-side-chain ionomer Nafion, water volume fractions ranged from about 0.39 (D2021) to 0.49 (DE2029). The confocal setup achieved a spectral resolution near 3 cm⁻¹ and axial resolution of 1.6 μm with the 63×/1.0 water-immersion objective and 3.0 μm with the 50×/0.55 objective, giving lateral resolution under 2 μm. For composite imaging, high-resolution scans of 6000 spectra over a 20 × 30 μm² area were acquired in roughly five minutes. The single-atom-thick SLG interlayer appeared as a band approximately 1.5 μm wide—reflecting the optical point-spread function rather than the true monolayer thickness—yet was clearly detected because of its strong Raman signal. Individual sub-micron PVDF-HFP nanofibers were also partially resolved. The 3M Ionomer Raman spectrum was analyzed in detail for the first time, revealing distinct peak positions and areas despite chemical similarity to Nafion and Aquivion.

This work enables non-destructive, spatially resolved characterization of ionomer membranes for fuel cells, water electrolysis, and redox flow batteries. The ability to image embedded interlayers and reinforcement meshes makes CRM valuable for designing advanced membrane electrode assemblies with improved mechanical and chemical stability. Because interlayers like the graphene used here can act as spatial markers, CRM also opens routes to monitoring membrane degradation during operation or post-mortem. The authors point to extending the EW quantification approach to other ionomeric materials and to aging studies across diverse PFSA types, broadening applicability from fuel cell research into electrolysis and flow-battery development.

For researchers working on 2D-material composites or membrane engineering, the Trivial Transfer Graphene used in this study is available from ACS Material in convenient pre-mounted, PMMA-coated formats with a straightforward wet-transfer protocol. The product performed as intended here, providing a clean monolayer interlayer that could be embedded in a polymer membrane and unambiguously detected by Raman imaging, making it a practical option for building model multi-layer membranes and van der Waals heterostructures.

How ACS Material products were used

• Trivial Transfer® Graphene (Trivial Transfer Series)  — “Trivial Transfer Graphene, which is a SLG deposited on a polymeric substrate and coated with a thin layer of polymethylmethacrylate (PMMA), was ordered from ACS Material with a dimension of 2.5 cm × 2.5 cm.”

Product Performance in this Study

The single-layer graphene from ACS Material was successfully transferred onto a Nafion NR211 membrane to form a SLG interlayer composite, which confocal Raman microscopy could clearly resolve as a distinct phase despite its atomic thickness.

Related product categories

• Trivial Transfer Series

Frequently asked questions

What is Trivial Transfer Graphene used for in composite membranes?

In this study, Trivial Transfer Graphene served as a single-layer graphene interlayer embedded in a Nafion membrane. The PMMA-coated monolayer was wet-transferred onto a Nafion NR211 sheet and sandwiched with a second membrane. It acted as a model thin feature to test whether confocal Raman microscopy could resolve atomically thin layers inside multi-layer ionomer membranes.

How does confocal Raman microscopy measure PFSA membrane equivalent weight?

Confocal Raman microscopy quantifies equivalent weight by comparing side-chain to backbone Raman band intensity ratios. These ratios plot linearly against the inverse number of backbone repeat units per sulfonyl group. The study reported excellent linear calibration fits with R² values from 0.969 to 0.996 across Nafion, Aquivion, and 3M Ionomer, enabling accurate determination of unknown PFSA equivalent weights.

Why can Raman microscopy detect a single graphene layer thinner than its resolution limit?

Confocal Raman microscopy can detect features smaller than its diffraction-limited resolution when they produce a strong Raman signal. Single-layer graphene has a characteristic 2D band near 2680 cm⁻¹. In the membrane images the monolayer appeared roughly 1.5 μm wide, reflecting the optical point-spread function rather than its true atomic thickness, yet it was clearly identified.