The Effects of Cerium Migration on PEM Fuel Cell Performance

Cerium is an additive which improves polymer electrolyte membrane (PEM) fuel cell durability, however, its migration can be an issue. Ce migration was induced in PEMs using in situ hydrogen pump experiments. In these experiments, Ce was measured to be in ionic equilibrium between the PEM and the catalyst layer (CL) ionomer; Ce migration due to water and proton flux did not significantly alter the ionic equilibrium. As a result, cathode CL proton conductivity, measured with impedance spectroscopy, was not affected. Ex situ experiments on ionomer films exchanged with Ce concentrations greater than ionic equilibrium, however, do demonstrate significant losses caused by reduced proton conductivity and oxygen diffusion to active sites of the Pt catalyst, measured using microelectrode studies.