Stability of Platinum-Based Alloy Cathode Catalysts in Pem Fuel Cells
Hector R. Colon-Mercado, Savannah River National Laboratory, Aiken, SC 29808 and Branko Popov, Department of Chemical Engineering, University of South Carolina, 301 Main Street, Swearingen Engineering Center, Columbia, SC 29208.
The search for more active and less expensive electrocatalysts for oxygen reduction reaction (ORR) with higher stability than Pt has resulted in the development of Pt-based binary or ternary alloys. It has been reported that alloying Pt with transition metals such as Co, Cr, V, Ni and Fe, enhances the catalytic activity for ORR. The improvement in the ORR activity of Pt alloys has been attributed to various structural changes caused by alloying, including the shortening of the Pt-Pt interatomic distance, the exposure of more active planes and the interplay between the electronic Pt d-vacancy and Pt coordination number. In this study, corrosion and stability of the Pt-based catalysts (Pt, Pt-Co and Pt-Ni) supported on carbon were evaluated using an accelerated durability test (ADT) . The experimental results obtained using the ADT were correlated to the performance of the Pt-based catalysts in the fuel cell. The Pt catalyst exhibited loss of active surface area due to particle agglomeration, and a resulting decrease in the ORR activity was observed. On the other hand, the dissolution of transition metals from the alloys was responsible for loss in the ORR activity of the Pt alloy catalysts. Cross-sectional studies by electron probe micro-analysis of the membrane-electrode assembly after fuel cell testing revealed the Co dissolution followed by diffusion into the membrane.
 H.R. Colon-Mercado, H. Kim, B.N. Popov, Electrochem. Commun., 6 (2004) 795.