Mesoscopic degradation effects of voltage cycled cathode catalyst layers in polymer electrolyte fuel cells

The first successful imaging of Pt/C and fluorine containing ionomer phases in pristine and degraded cathode catalyst layers is performed using transmission electron microscopy with elemental mapping to investigate the degradation effects caused by high voltage excursions in polymer electrolyte fuel cells. Through high resolution elemental mapping, the distributions of ionomer and Pt/C phases are identified at beginning-of-test. Loss of carbon through corrosion paralleled by Pt and ionomer segregation is diagnosed using elemental maps of the degraded material. The observed fuel cell performance decrement is attributed to the absence of electrically conducting carbon, agglomerated and isolated active platinum, and irregularly redistributed ionomer with a significant mass transport barrier due to voltage cycling. (C) 2016 Elsevier B.V. All rights reserved.