Through-plane water content distribution in a polymer electrolyte membrane (PEM) and water flux across the membrane were measured under different water permeation conditions using magnetic resonance imaging (MRI) and a dew point measurement system. We placed the PEM by itself or as a catalyst coated membrane (CCM) in an experimental cell, and we subjected them to several water permeation conditions that had different water activities across the membrane. We compared the water content distribution and water flux of samples, and the results showed the membranes exhibited different water content distribution between the PEM and the CCM. The differences suggest that the rate-determining process of the water transport phenomena across the membrane, which are diffusion through the membrane and interfacial transport across the membrane-gas interface, changed according to whether the membrane is used by itself or as a CCM.

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