Performance of Advanced Pt-Ni Alloy Catalysts in Polymer-Electrolyte Fuel Cells

The cost of a Polymer-Electrolyte Fuel Cells (PEFC) system is still the primary barrier to commercialization, although it has decreased significantly over the past decade.  Platinum electrocatalysts are required due to the slow kinetics of the oxygen reduction reaction (ORR).  To reduce electrocatalyst cost, platinum alloys with higher ORR mass activity are being developed.^1,2  ORR activities exceeding DOE’s 2015 targets were reported by various research groups for carbon-supported Pt alloys and core-shell nanoparticles in rotating-disk electrode (RDE) tests.^3,4  However, it can be challenging to achieve similarly high mass activities for these electrocatalysts in membrane-electrode assemblies (MEAs), as evidenced by in-cell performance at low current densities (kinetically-controlled) region, and it is even more challenging to achieve improved cell performance at higher current densities with these advanced alloy catalysts.⁵

United Technologies Research Center (UTRC) is a part of an on-going DOE-supported research project, led by Argonne National Laboratory (ANL), focused on improving the understanding, performance, and durability of advanced Pt-alloy catalysts operating in complete PEFCs.  In the current study, advanced MEAs with high ORR activity Pt-Ni alloy catalysts are prepared by Johnson Matthey Fuel Cells (JMFC) and tested by UTRC in small PEFCs (12.5-cm² active area).  A variety of parameters, including: Pt-Ni catalyst composition and structure, catalyst-ink formulation, and MEA-fabrication procedures are being explored in order to develop MEAs with superior performance over the entire PEFC operating range relative to Pt-only MEAs.  A comparison of Pt-only and Pt-Ni MEAs, which have similar catalyst particle size and the same carbon support and electrode composition, are shown in Figure 1.  Results obtained from in-cell diagnostics will be used to explain the differences in the polarization curves, as well as project paths to future performance improvements.  The impact of Pt:Ni ratio on ORR activity and cell performance will also be reported.

Acknowledgements

The authors gratefully acknowledge funding from the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office (Nancy Garland, Technology Development Manager) under contract number DE-AC02-06CH11357.  The authors would also like to thank their DOE project colleagues at ANL and at JMFC for both their support of this work and for helpful discussions.

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