Cerium Migration in Polymer Electrolyte Membranes

Cerium migration was induced in polymer electrolyte membranes (PEMs) and subsequently characterized using X-ray fluorescence. The effects of proton flux and relative humidity on cerium migration were evaluated using H2 pump operation in a standard conductivity cell. After 6 Coulombs of charge transfer, cerium in the region between the cell electrodes was reduced by > 75% and was increased in the region under the counter electrode by a factor of 8. In addition to charge transfer, a secondary PEM hydration effect is discussed. Proton/water flux resulted in rapid migration compared to the effects of concentration gradients. Reversible migration is also demonstrated in an uncatalyzed PEM, however, the presence of catalyst layers results in cerium stabilization in the electrodes.