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This study explores the changes in bulk composition/ structure and oxygen reduction activity of two alloys, Pt 7 IrCo 7 and PtCo, caused by Co leaching during electrochemical cycles and as a result of membrane electrode assembly (MEA) fabrication procedures. Exposure to liquid electrolyte and electrochemical cycles in a rotating disc electrode (RDE) environment resulted in substantial Co loss and no stabilization from the low levels of Ir used in the ternary material. The true composition of the ternary material was determined as Pt 8 IrCo 3 following initial exposure to 0.1 M HClO 4 (before cycling) and Pt 11 IrCo 4 after 5000 cycles. Density functional theory (DFT) modeling of the cycled catalyst compositions indicated that structures with Pt-rich upper layers would show the highest stability; however, addition of 0.25 ML oxygen adsorption favored Co segregation from second and third atomic layers. The high initial activities (>0.44A/mgPt) achieved in the RDE environment decreased with cycles and were not reproduced in MEAs. X-ray diffraction (XRD) analysis revealed a measurable increase in lattice parameter caused by the MEA preparation procedure, consistent with Co (and some Ir) leaching into the ionomer phase and relaxation of the lattice. MEA fabrication procedures and cycling in 1 M H 2 SO 4 at 80 • C showed greater changes to catalyst structure and increased Ir and Co loss compared to exposing the catalyst to RDE like conditions (0.1 M HClO 4 , RT) explaining the observed discrepancy in activity between RDE and MEA.

OBJECTIVES Develop structurally and compositionally advanced supported alloy catalyst system with loading < 0.3 mg platinum group metal (PGM)/cm 2 . Optimize catalyst performance and decay parameters through quantitative models.  Demonstrate 5,000 cyclic hours below 80°C with less than 40% loss of electrochemical surface area and catalyst mass activity. TECHNICAL BARRIERSThis project addresses the following technical barriers from the Fuel Cells section (section 3.4. SUMMARYAchieving DOE's stated 5000-hr durability goal for light-duty vehicles by 2015 will require MEAs with characteristics that are beyond the current state of the art. Significant effort was placed on developing advanced durable cathode catalysts to arrive at the best possible electrode for high performance and durability, as well as developing manufacturing processes that yield significant cost benefit. Accordingly, the overall goal of this project was to develop and construct advanced MEAs that will improve performance and durability while reducing the cost of PEMFC stacks. The project, led by UTC Power, focused on developing new catalysts/supports and integrating them with existing materials (membranes and gas diffusion layers (GDLs)) using state-of-the-art fabrication methods capable of meeting the durability requirements essential for automotive applications. Specifically, the project work aimed to lower platinum group metals (PGM) loading while increasing performance and durability. Appropriate catalysts and MEA configuration were down-selected that protects the membrane, and the layers were tailored to optimize the movements of reactants and product water through the cell to maximize performance while maintaining durability. A brief summary of accomplishments from FY2008-FY2012 is provided below FY2008:The atomistic modeling work guiding the synthesis project was providing fundamental activity and durability controlling information. Preliminary samples synthesized on the project exceeded the DOE 2010 targets for mass activity when normalized to mass of Pt. However, further work is needed to achieve the PGM based mass activity targets. FY2009:Mass activities of almost 0. Pt ML catalyst prepared using scalable chemistries and characterized by a range of techniques showed strong evidence for a core-shell structure. However, a key challenge for the core-shell catalysts was their poor durability towards potential cycling due to non-uniform Pt layer on the core structures. Various scalable methods specifically geared towards achieving uniform Pt coatings were completed. FY2010:Mass activities of~0.15 A/mg PGM in subscale MEA testing have been reproduced and verified for a scaled-up 30% Pt 2 IrCr and was down-selected as the dispersed alloy catalyst system for full scale fuel cell demonstration. The Pt 2 IrCr alloy was chosen, over the PtIrCo alloy, based on the higher durability of Cr over Co in the alloy catalysts under the MEA fabrication process. Key barriers to overcome for the incorporation of the 30% Pt 2 IrCr in an MEA such as the low...