In situ quantification of the in-plane water content in the Nafion® membrane of an operating polymer-electrolyte membrane fuel cell using 1H micro-magnetic resonance imaging experiments

Spatial, quantitative, and temporal information regarding the water content distribution in the transverse-plane between the catalyst layers of an operating polymer-electrolyte membrane fuel cell (PEMFC) is essential to develop a fundamental understanding of water dynamics in these systems. We report 1H micro-magnetic resonance imaging (MRI) experiments that measure the number of water molecules per SO3H group, λ, within a Nafion®-117 membrane between the catalyst stamps of a membrane-electrode assembly, MEA. The measurements were made both ex situ, and inside a PEMFC operating on hydrogen and oxygen. The observed 1H MRI T2 relaxation time of water in the PEM was measured for several known values of λ. The signal intensity of the images was then corrected for T2 weighting to yield proton density-weighted images, thereby establishing a calibration curve that correlates the 1H MRI density-weighted signal with λ. Subsequently, the calibration curve was used with proton density weighted (i.e., T2-corrected) signal intensities of transverse-plane 1H MRI images of water in the PEM between the catalyst stamps of an operating PEMFC to determine λ under various operational conditions. For example, the steady state, transverse-plane λ was 9 ± 1 for a PEMFC operating at ∼26.4 mW cm−2 (∼20.0 mA, ∼0.661 V, 20 °C, flow rates of the dry H2(g) and O2(g) were 5.0 and 2.5 mL min−1, respectively).