Platinum-Alloy Cathode Catalyst Degradation in Proton Exchange Membrane Fuel Cells: Nanometer-Scale Compositional and Morphological Changes

Electrochemical measurements showed an Pt surface area loss and an specific activity loss for a membrane electrode assembly (MEA) cathode with acid-treated " " catalyst particles in a proton exchange membrane fuel cell after voltage cycling between 0.65 and vs reversible hydrogen electrode. Transmission electron microscopy, scanning transmission electron microscopy, associated X-ray energy dispersive spectroscopy, and high angle annular dark-field techniques were used to probe the microstructural changes of the MEA cathode and the compositional changes along the MEA cathode thickness and within individual nanoparticles before and after voltage cycling. Further Co dissolution from acid-treated particles that leads to an increased thickness of a Pt-enriched surface layer and the development of core/shell particles was largely responsible for the reduction in the specific activity of nanoparticle after potential cycling. The Pt weight loss associated with the formation of Pt crystallites near the cathode/membrane interface largely contributed to the measured electrochemical surface area loss, while particle growth of the particles via Ostwald ripening played a lesser role.