Cerium in-plane transport in PEM fuel cells during real-world automotive operations: experimental and dynamic modelling analysis

Abstract

Cerium is an additive adopted in polymer electrolyte membrane fuel cells to extend membrane lifetime, but its mobility remains a challenge. A cerium transport model accounting for diffusion, migration and water activity gradient is developed. Diffusion coefficient is calibrated on literature data, as the effect of Ce ion-exchange fraction on protonic conductivity and membrane water uptake; Einstein relation is used for the migration coefficient. Validation is conducted on migration profiles obtained via hydrogen pump tests, quantified through X-ray fluorescence. Trends under different temperatures, relative humidities and initial cerium contents are reproduced. Tailored tests investigate how the water activity gradient affects Ce transport. Furthermore, a 1+1D fuel cell performance model is exploited to determine the initial and time-integral mean values of the operating variables that characterize the current steps of a dynamic load cycle, then provided to the Ce transport model. The experimentally measured planar radical scavenger redistributions, after hundreds of hours of single-cell automotive-representative operations, are predicted from air-inlet to outlet. Cerium accumulates towards air-inlet and depletes at middle/outlet; the modelling analysis identifies the building-up in the region of lowest ionic potential and water content. Succeeding in predictions, this model can support the development of strategies to improve durability.