In Situ 2D-XAS Imaging and Modeling Analysis of Cerium Migration in Proton Exchange Membrane Fuel Cells

In-situ two-dimensional X-ray absorption spectroscopy (XAS) imaging was employed to analyze cerium ion (Ce 3+ ) migration in the through-plane direction in proton exchange membrane fuel cells (PEMFCs), offering fundamental insights supporting improvement of their power density and membrane durability. The transport of Ce 3+ was visualized in both unreinforced thick Nafion membranes (Nafion 115, 127 μm) and reinforced thin (12 μm) perfluorosulfonic acid (PFSA) membranes under either an electrical potential gradient or a water activity gradient. The diffusion coefficients of Ce 3+ were ascertained based on its behavior after removal of these gradients in both membrane types. Additionally, using a one-dimensional cation transport model, the mobility and electroosmotic drag coefficients of Ce 3+ were derived from experimentally obtained data of the thick Nafion membrane. Our measurements also demonstrate that the migration of Ce 3+ in the thick membranes was notably impeded by the presence of ferrous ion (Fe 2+ ) impurities. Because Fe 2+ is known to accelerate membrane degradation by promoting hydroxyl radical formation, this effect might further exacerbate membrane degradation. It therefore warrants careful consideration.