Improving the Durability of Pt-Alloy Nanoparticles for the Oxygen Reduction Reaction in Acidic Media Via Encapsulation

The Oxygen Reduction Reaction (ORR) is the desired cathode reaction in Proton Exchange Membrane Fuel Cells (PEMFCs). Carbon-supported platinum alloy (PtM/C) nanoparticles such as PtCo/C are by far the most effective ORR catalysts in PEMFCs. However, the durability of PtM/C is not satisfying, partly owing to the dissolution of the second transition metal M. In this study, by conducting accelerated stress tests (ASTs) on a commercial PtCo/C catalyst in both a rotating disk electrode and a PEMFC, we identified that a significant fraction of the electrochemical surface area (ECSA) loss of the PtCo/C upon the AST was recoverable. This recoverable ECSA loss was tentatively ascribed to the poisoning of the Pt surface by the sulfate ions either from the H 2 SO 4 electrolyte in a RDE or the Nafion in a PEMFC. We further demonstrated that this poisoning effect can be largely suppressed without compromising the activity by encapsulating PtCo/C into thin functionalized carbon overlayers that were tuned to be permeable to H + , O 2 , and H 2 O, but not to sulfate ions. The encapsulation may also alleviate the poisoning of ionomer during on the Pt surface during PEMFC operation. Acknowledgement This work was supported by Massachusetts Clean Energy Center Catalyst Award Program G00006319 and the US Department of Energy under award number DE-EE0008416 and DE-EE0008075. This research used beamline 8-ID (ISS) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. The authors declare no competing financial interests. Vielstich, W.; Lamm, A.; Gasteiger, H. A., Handbook of fuel cells: fundamentals technology and applications . Wiley New York: 2003; Vol. 2. Chung, D. Y.; Jun, S. W.; Yoon, G.; Kwon, S. G.; Shin, D. Y.; Seo, P.; Yoo, J. M.; Shin, H.; Chung, Y. H.; Kim, H.; Mun, B. S.; Lee, K. S.; Lee, N. S.; Yoo, S. J.; Lim, D. H.; Kang, K.; Sung, Y. E.; Hyeon, T., Highly Durable and Active PtFe Nanocatalyst for Electrochemical Oxygen Reduction Reaction. J Am Chem Soc 2015, 137 (49), 15478-85.