(Invited) Pt Alloy Octahedral Nanoparticle Catalysts from Screening Studies to Fuel Cell Measurements

Abstract

In proton exchange membrane fuel cells (PEMFCs) hydrogen is oxidized at the anode and oxygen is reduced at the cathode, where Pt-based catalysts represent the state of the art. Due to the sluggish oxygen reduction reaction (ORR) kinetics, Pt loadings per vehicles are still rather high when compared to platinum-group metal (PGM) loadings in combustion engine cars ( ~ 5 gPGM/vehicle in light-duty internal combustion engine vehicles),1 impacting the cost of fuel cell electric vehicles.Octahedral PtNi nanoparticles have been reported to achieve extremely high ORR mass activity in rotating disk electrode (RDE) experiments,2 which would allow for a significant decrease of Pt loadings in fuel cells. In addition, the introduction of a third metal (X) as a surface dopant has been recently shown to have beneficial effects on the RDE performance, enhancing both activity and stability.3 However, despite these promising steps toward shape-stable PtNiX octahedral nanoparticles, the morphological stability and the performance in membrane electrode assembly (MEA)-based fuel cell measurements still needs to be improved to match and surpass the state of the art Pt and de-alloyed Pt alloy catalysts.4 In this contribution, we will show the results of our recent investigations that were aimed at improving the performance of PtNi based octahedral nanoparticle catalysts towards integration in low Pt loading cathodes for PEMFCs. These include exploration of different dopants, Pt loadings and carbon supports. Preliminary screening by RDE identified promising dopants (i.e. Mo4 and other transition metals) and Pt:Ni atomic ratios. The activity and stability of the PtNiX octahedral nanoparticles were then investigated in a comparative study by using different carbon supports, including high surface area porous carbon. Finally, selected catalysts were investigated in MEA-based fuel cells and their activity compared with state-of-the art reference Pt and PtNi alloy materials, measured under the same conditions. References A. Kongkanand and M. F. Mathias, J Phys Chem Lett, 2016, 7, 1127-1137.P. Strasser, Science, 2015, 349, 379-380.X. Q. Huang, Z. P. Zhao, L. Cao, Y. Chen, E. B. Zhu, Z. Y. Lin, M. F. Li, A. M. Yan, A. Zettl, Y. M. Wang, X. F. Duan, T. Mueller and Y. Huang, Science, 2015, 348, 1230-1234.F. Dionigi, C. C. Weber, M. Primbs, M. Gocyla, A. M. Bonastre, C. Spöri, H. Schmies, E. Hornberger, S. Kühl, J. Drnec, M. Heggen, J. Sharman, R. E. Dunin-Borkowski and P. Strasser, Nano Lett, 2019, 19, 6876-6885. Acknowledgements The GAIA project has received funding from the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 826097. This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe Research.