Thao Ngo1 Chengjun Sun2 Michael Pape2 Hong Yang1

1, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
2, Argonne National Laboratory, Lemont, Illinois, United States

One major challenge hindering the large-scale utilization of high-performing polymer electrolyte membrane fuel cells (PEMFCs) is the durability of catalysts for the cathodic oxygen reduction reaction (ORR). In catalytic systems that show enhanced activity such as faceted platinum-transition metal (Pt-M) bimetallic catalysts (M = Fe, Co, Cu and Ni), continuous leaching of the non-noble, more reactive metals during long-term stability tests contributes to degradation in mass activity. A previous study by the Yang group had demonstrated that carbon-supported truncated octahedral Pt3Ni electrocatalysts lost 21% of its initial electrochemical surface area (ECSA) and 40% of its mass current density (from 0.55 to 0.33 A/mgPt) of commercial catalysts [1]. To control metal leaching and improve catalytic performance and durability, it is essential to understand the underlying mechanism and kinetics of metal leaching in faceted Pt-M bimetallic electrocatalysts. In this study, in situ x-ray absorption spectroscopy (XAS) was used to probe the changes in the electronic structure of Pt-Ni electrocatalysts during accelerated durability tests. Real time data acquisition was enabled by an aqueous electrochemical cell, which was designed and made in house. Current results suggest the catalysts underwent restructuring during the accelerated durability test, as evidenced by an increased to a maximum level of oxidation of Ni after 2500 potential cycles and a strengthening of the Pt-Pt bond over time.

[1] Wu, J.; Yang, H. ChemCatChem 2012, 4 (10), 1572-1577.