Investigations of Performance and Durability of PtNi-Alloy Based MEAs Utilizing In-Cell Diagnostics
Authors: Yang Zhiwei , Darling Robert M. , Perry Mike L. 
Published: February 2020

The successful commercialization of Polymer Electrolyte Fuel Cells (PEFCs) system requires highly active oxygen-reduction reaction (ORR) electrocatalysts to meet the cost, performance, and durability targets for automotive applications. Although significant progress has been made in the past decade, Pt/C catalyst has the limitation of high material cost and insufficient ORR activity. Platinum-nickel alloy catalysts with core-shell structure have been demonstrated by multiple research groups to have higher intrinsic ORR activity, which can exceed the U.S. DOE 2015 ORR activity target, and also have promising stability in PEFC conditions [1, 2]. Additionally, Membrane Electrode Assemblies (MEAs) with low loadings of highly active Pt-group metal (PGM) catalysts have already been demonstrated to exceed the high-efficiency target of > 0.3 A/cm2 at 0.8 V [3]; however, the rated-power target of 1 W/cm2 cannot be met with these MEAs due to transport losses that are unique to MEAs with ultra-low catalyst loadings [4, 5].

United Technologies Research Center (UTRC) is a part of a 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 and ultra-low Pt loading (total ~ 0.13 mg-Pt/cm2) are prepared by Johnson Matthey Fuel Cells (JMFC) and tested by UTRC.

The focus of this talk will be on using a variety of in-cell diagnostics and analysis methods to investigate both the initial performance and durability of these state-of-the-art MEAs. One example diagnostic that will be utilized are Polarization Change Curves (PCCs), which were originally developed for durability studies [6], but can also be used to investigate changes in performance due to operating conditions or MEA composition. For example, Fig 1a is a PCC comparison of the initial performance of the PtNi MEA and a Pt-only MEA, which have similar average catalyst particle size and the same carbon support, metal/carbon ratio, and ionomer/carbon ratio. Clearly, in addition to the differences in catalyst activity, there are also differences in the transport losses between these two different electrocatalysts. The durability of ultra-low Pt loading MEAs will also be discussed. Fig. 1b is a durability example of a PCC result, which is after applying a recent DOE-suggested AST protocol (0.6V-0.95V trapezoid potential cycle, with 700mV/s ramp rate and 6s/cycle). Other diagnostics and analysis beyond PCCs will also be included. The results obtained from these in-cell diagnostics will be used to hypothesize the potential mechanisms responsible for the differences in polarization curves, as well as project possible pathways to future performance and durability improvements.

Acknowledgements

This work is partially funded by the U. S. Department of Energy (DOE) under contract number DE-AC02-06CH11357. The authors would like to thank their DOE-project colleagues, especially those at ANL and JMFC.

References

1. V. R. Stamenkovic, et al. Science, 315, 493 (2007).

2. B. Han, et al, Energy Environ. Sci.,
8, 258, (2015)

3. D. Myers, et. al., DOE AMR, ID# FC106 (2015).

4. W. Yoon & A. Z. Weber, J. Electrochem. Soc., 158, B1007 (2011).

5. A. Kongkanand, et al., ACS Catalysis, 6, 1578 (2016).

6. R. Darling, et al., Modern Topics in Polymer Electrolyte Fuel Cell Degradation, Chap. 7, M. Mench, et.al., Ed.; Elsevier, Denmark (2011).

Figure 1