Coherent anti-Stokes Raman scattering spectroscopy system for observation of water molecules in anion exchange membrane.

[Display omitted] • Coherent anti-Stokes Raman scattering spectroscopy for anion exchange membranes. • Vibration spectroscopy with high time (0.2 s) and spatial (0.9 µm) resolution. • The number of OH species in an anion exchange membrane is a minimum of 7. • H-bonded OH species change with hydration, non-H-bonded species do not. • 785 nm CARS is suitable for both anion and proton exchange membranes. Anion exchange membrane fuel cells (AEMFCs) provide one of the most feasible remedies to fuel cells' dependency on the dwindling Pt group catalysts. Nevertheless, AEMFCs still suffer reduced durability, which requires an in-depth understanding of their membranes. The low thermal endurance of the anion exchange membranes (AEMs) usually limits the direct application of powerful techniques, such as Raman spectroscopy. We sought to establish a system for coherent anti-Stokes Raman scattering (CARS) spectroscopy capable of taking measurements inside an AEM rapidly and accurately without photodamage. A 785 nm CARS system was newly developed to study the water species in an AEM (QPAF-4) located vertically in a fuel cell. From the results of water measurement in a QPAF-4 membrane, the OH-related region was deconvoluted into nine Gaussian peaks: Five H-bonded OH peaks, non-H-bonded OH, OH–, and two CH peaks. The H-bonded species increased with increasing relative humidity, but the other species remained constant. These results open unlimited possibilities for studying and comparing different AEMFCs, enabling more rapid technology optimization. [ABSTRACT FROM AUTHOR]