Compositional segregation in shaped Pt alloy nanoparticles and their structural behaviour during electrocatalysis

Abstract

Shape-selective monometallic nanocatalysts offer activity benefits based on structural sensitivity and high surface area. In bimetallic nanoalloys with well-defined shape, site-dependent metal surface segregation additionally affects the catalytic activity and stability. However, segregation on shaped alloy nanocatalysts and their atomic-scale evolution is largely unexplored. Exemplified by three octahedral PtxNi1−x alloy nanoparticle electrocatalysts with unique activity for the oxygen reduction reaction at fuel cell cathodes, we reveal an unexpected compositional segregation structure across the {111} facets using aberration-corrected scanning transmission electron microscopy and electron energy-loss spectroscopy. In contrast to theoretical predictions, the pristine PtxNi1−x nano-octahedra feature a Pt-rich frame along their edges and corners, whereas their Ni atoms are preferentially segregated in their {111} facet region. We follow their morphological and compositional evolution in electrochemical environments and correlate this with their exceptional catalytic activity. The octahedra preferentially leach in their facet centres and evolve into ‘concave octahedra’. More generally, the segregation and leaching mechanisms revealed here highlight the complexity with which shape-selective nanoalloys form and evolve under reactive conditions.

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Figure 1: Atomic-scale Z-contrast STEM images and composition profile analysis of PtxNi1−x octahedral nanoparticles.
Figure 2: Electrochemical studies on carbon-supported PtxNi1−x octahedra.
Figure 3: STEM-EELS analysis of Pt1.5Ni and PtNi octahedra after 25 potential cycles.
Figure 4: HRTEM images of PtxNi1−x octahedra after stability tests.
Figure 5: Morphology and surface structural changes of PtxNi1−x octahedra.

References

  1. 1

    Arico, A. S., Bruce, P., Scrosati, B., Tarascon, J. M. & Van Schalkwijk, W. Nanostructured materials for advanced energy conversion and storage devices. Nature Mater. 4, 366–377 (2005).

    CAS  Article  Google Scholar 

  2. 2

    Sasaki, K. et al. Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction. Nature Commun. 3, 1–5 (2012).

    Article  Google Scholar 

  3. 3

    Yu, W. T., Porosoff, M. D. & Chen, J. G. G. Review of Pt-based bimetallic catalysis: From model surfaces to supported catalysts. Chem. Rev. 112, 5780–5817 (2012).

    CAS  Article  Google Scholar 

  4. 4

    Watanabe, M., Tsurumi, K., Mizukami, T., Nakamura, T. & Stonehart, P. Activity and stability of ordered and disordered Co-Pt alloys for phosphoric-acid fuel-cells. J. Electrochem. Soc. 141, 2659–2668 (1994).

    CAS  Article  Google Scholar 

  5. 5

    Rabis, A., Rodriguez, P. & Schmidt, T. J. Electrocatalysis for polymer electrolyte fuel cells: Recent achievements and future challenges. ACS Catal. 2, 864–890 (2012).

    CAS  Article  Google Scholar 

  6. 6

    Debe, M. K. Electrocatalyst approaches and challenges for automotive fuel cells. Nature 486, 43–51 (2012).

    CAS  Article  Google Scholar 

  7. 7

    Wagner, F. T., Lakshmanan, B. & Mathias, M. F. Electrochemistry and the future of the automobile. J. Phys. Chem. Lett. 1, 2204–2219 (2010).

    CAS  Article  Google Scholar 

  8. 8

    Stephens, I. E. L. et al. Tuning the activity of Pt(111) for oxygen electroreduction by subsurface alloying. J. Am. Chem. Soc. 133, 5485–5491 (2011).

    CAS  Article  Google Scholar 

  9. 9

    Toda, T., Igarashi, H., Uchida, H. & Watanabe, M. Enhancement of the electroreduction of oxygen on Pt alloys with Fe, Ni, and Co. J. Electrochem. Soc. 146, 3750–3756 (1999).

    CAS  Article  Google Scholar 

  10. 10

    Greeley, J. et al. Alloys of platinum and early transition metals as oxygen reduction electrocatalysts. Nature Chem. 1, 552–556 (2009).

    CAS  Article  Google Scholar 

  11. 11

    Snyder, J., Fujita, T., Chen, M. W. & Erlebacher, J. Oxygen reduction in nanoporous metal–ionic liquid composite electrocatalysts. Nature Mater. 9, 904–907 (2010).

    CAS  Article  Google Scholar 

  12. 12

    Liu, Z., Yu, C., Rusakova, I. A., Huang, D. & Strasser, P. Synthesis of Pt3Co alloy nanocatalyst via reverse micelle for oxygen reduction reaction in PEMFCs. Top. Catal. 49, 241–250 (2008).

    CAS  Article  Google Scholar 

  13. 13

    Stamenkovic, V. R. et al. Improved oxygen reduction activity on Pt3Ni(111) via increased surface site availability. Science 315, 493–497 (2007).

    CAS  Article  Google Scholar 

  14. 14

    Stamenkovic, V. R. et al. Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces. Nature Mater. 6, 241–247 (2007).

    CAS  Article  Google Scholar 

  15. 15

    Carpenter, M. K., Moylan, T. E., Kukreja, R. S., Atwan, M. H. & Tessema, M. M. Solvothermal synthesis of platinum alloy nanoparticles for oxygen reduction electrocatalysis. J. Am. Chem. Soc. 134, 8535–8542 (2012).

    CAS  Article  Google Scholar 

  16. 16

    Zhang, J., Yang, H., Fang, J. & Zou, S. Synthesis and oxygen reduction activity of shape-controlled Pt3Ni nanopolyhedra. Nano Lett. 10, 638–644 (2010).

    CAS  Article  Google Scholar 

  17. 17

    Wu, J. B., Gross, A. & Yang, H. Shape and composition-controlled platinum alloy nanocrystals using carbon monoxide as reducing agent. Nano Lett. 11, 798–802 (2011).

    CAS  Article  Google Scholar 

  18. 18

    Wu, J. et al. Truncated octahedral Pt3Ni oxygen reduction reaction electrocatalysts. J. Am. Chem. Soc. 132, 4984–4985 (2010).

    CAS  Article  Google Scholar 

  19. 19

    Wu, Y., Cai, S., Wang, D., He, W. & Li, Y. Syntheses of water-soluble octahedral, truncated octahedral, and cubic Pt–Ni nanocrystals and their structure–activity study in model hydrogenation reactions. J. Am. Chem. Soc. 134, 8975–8981 (2012).

    CAS  Article  Google Scholar 

  20. 20

    Gasteiger, H. A. & Markovic, N. M. Just a dream-or future reality? Science 324, 48–49 (2009).

    CAS  Article  Google Scholar 

  21. 21

    Gan, L., Heggen, M., Rudi, S. & Strasser, P. Core-shell compositional fine structures of dealloyed PtxNi1−x nanoparticles and their impact on oxygen reduction catalysis. Nano Lett. 12, 5423–5430 (2012).

    CAS  Article  Google Scholar 

  22. 22

    Strasser, P. et al. Lattice-strain control of the activity in dealloyed core-shell fuel cell catalysts. Nature Chem. 2, 454–460 (2010).

    CAS  Article  Google Scholar 

  23. 23

    Van der Vliet, D. F. et al. Mesostructured thin films as electrocatalysts with tunable composition and surface morphology. Nature Mater. 11, 1051–1058 (2012).

    CAS  Article  Google Scholar 

  24. 24

    Colon-Mercado, H. R. & Popov, B. N. Stability of platinum based alloy cathode catalysts in PEM fuel cells. J. Power Sources 155, 253–263 (2006).

    CAS  Article  Google Scholar 

  25. 25

    Wang, D. S., Zhao, P. & Li, Y. D. General preparation for Pt-based alloy nanoporous nanoparticles as potential nanocatalysts. Sci. Rep. 1, 1–5 (2011).

    Article  Google Scholar 

  26. 26

    Snyder, J., McCue, I., Livi, K. & Erlebacher, J. Structure/processing/properties relationships in nanoporous nanoparticles as applied to catalysis of the cathodic oxygen reduction reaction. J. Am. Chem. Soc. 134, 8633–8645 (2012).

    CAS  Article  Google Scholar 

  27. 27

    Wu, Y. et al. A strategy for designing a concave Pt–Ni alloy through controllable chemical etching. Angew. Chem. Int. Ed. 51, 12524–12528 (2012).

    CAS  Article  Google Scholar 

  28. 28

    Oezaslan, M., Heggen, M. & Strasser, P. Size-dependent morphology of dealloyed bimetallic catalysts: linking the nano to the macro scale. J. Am. Chem. Soc. 134, 514–524 (2011).

    Article  Google Scholar 

  29. 29

    Strasser, P. Dealloyed core-shell fuel cell electrocatalysts. Rev. Chem. Eng. 25, 255–295 (2009).

    CAS  Article  Google Scholar 

  30. 30

    Wang, C. et al. Correlation between surface chemistry and electrocatalytic properties of monodisperse PtxNi1−x nanoparticles. Adv. Funct. Mater. 21, 147–152 (2011).

    Article  Google Scholar 

  31. 31

    Wang, G. F., Van Hove, M. A., Ross, P. N. & Baskes, M. I. Monte Carlo simulations of segregation in Pt–Ni catalyst nanoparticles. J. Chem. Phys. 122, 024706 (2005).

    Article  Google Scholar 

  32. 32

    Urban, K. W. Studying atomic structures by aberration-corrected transmission electron microscopy. Science 321, 506–510 (2008).

    CAS  Article  Google Scholar 

  33. 33

    Van der Vliet, D. F. et al. Unique electrochemical adsorption properties of Pt-skin surfaces. Angew. Chem. Int. Ed. 51, 3139–3142 (2012).

    CAS  Article  Google Scholar 

  34. 34

    Colon-Mercado, H. R., Kim, H. & Popov, B. N. Durability study of Pt3Ni1 catalysts as cathode in PEM fuel cells. Electrochem. Commun. 6, 795–799 (2004).

    CAS  Article  Google Scholar 

  35. 35

    Antolini, E., Salgado, J. R. C. & Gonzalez, E. R. The stability of Pt-M (M = first row transition metal) alloy catalysts and its effect on the activity in low temperature fuel cells—a literature review and tests on a Pt–Co catalyst. J. Power Sources 160, 957–968 (2006).

    CAS  Article  Google Scholar 

  36. 36

    Chen, S., Gasteiger, H. A., Hayakawa, K., Tada, T. & Shao-Horn, Y. Platinum-alloy cathode catalyst degradation in proton exchange membrane fuel cells: Nanometer-scale compositional and morphological changes. J. Electrochem. Soc. 157, A82–A97 (2010).

    CAS  Article  Google Scholar 

  37. 37

    Snyder, J. & Erlebacher, J. Kinetics of crystal etching limited by terrace dissolution. J. Electrochem. Soc. 157, C125–C130 (2010).

    CAS  Article  Google Scholar 

  38. 38

    Dubau, L., Maillard, F., Chatenet, M., Andre, J. & Rossinot, E. Nanoscale compositional changes and modification of the surface reactivity of Pt3Co/C nanoparticles during proton-exchange membrane fuel cell operation. Electrochim. Acta 56, 776–783 (2010).

    CAS  Article  Google Scholar 

  39. 39

    Dubau, L. et al. Further insights into the durability of Pt3Co/C electrocatalysts: Formation of ‘hollow’ Pt nanoparticles induced by the Kirkendall effect. Electrochim. Acta 56, 10658–10667 (2011).

    CAS  Article  Google Scholar 

  40. 40

    Wang, C. et al. Design and synthesis of bimetallic electrocatalyst with multilayered Pt-Skin surfaces. J. Am. Chem. Soc. 133, 14396–14403 (2011).

    CAS  Article  Google Scholar 

  41. 41

    Wang, D. et al. Structurally ordered intermetallic platinum–cobalt core–shell nanoparticles with enhanced activity and stability as oxygen reduction electrocatalysts. Nature Mater. 12, 81–87 (2013).

    CAS  Article  Google Scholar 

  42. 42

    Zhang, J., Vukmirovic, M. B., Xu, Y., Mavrikakis, M. & Adzic, R. R. Controlling the catalytic activity of platinum-monolayer electrocatalysts for oxygen reduction with different substrates. Angew. Chem. Int. Ed. 44, 2132–2135 (2005).

    CAS  Article  Google Scholar 

  43. 43

    Cui, C. H., Li, H. H., Liu, X. J., Gao, M. R. & Yu, S. H. Surface composition and lattice ordering-controlled activity and durability of CuPt electrocatalysts for oxygen reduction reaction. ACS Catal. 2, 916–924 (2012).

    CAS  Article  Google Scholar 

  44. 44

    Kolb, D. M. Reconstruction phenomena at metal-electrolyte interfaces. Prog. Surf. Sci. 51, 109–173 (1996).

    CAS  Article  Google Scholar 

  45. 45

    Cui, C. et al. Octahedral PtNi nanoparticle catalysts: Exceptional oxygen reduction activity by tuning the alloy particle surface composition. Nano Lett. 12, 5885–5889 (2012).

    CAS  Article  Google Scholar 

  46. 46

    Heggen, M., Oezaslan, M., Houben, L. & Strasser, P. Formation and analysis of core–shell fine structures in Pt bimetallic nanoparticle fuel cell electrocatalysts. J. Phys. Chem. C 116, 19073–19083 (2012).

    CAS  Article  Google Scholar 

  47. 47

    Mayrhofer, K. J. J., Juhart, V., Hartl, K., Hanzlik, M. & Arenz, M. Adsorbate-induced surface segregation for core-shell nanocatalysts. Angew. Chem. Int. Ed. 48, 3529–3531 (2009).

    CAS  Article  Google Scholar 

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Acknowledgements

We thank the Zentraleinrichtung für Elektronenmikroskopie (Zelmi) of the Technical University Berlin for their support with TEM and energy-dispersive X-ray spectra techniques. This work was supported by US DOE EERE award DE-EE0000458 via subcontract through General Motors. P.S. acknowledges financial support through the cluster of excellence in catalysis (UniCat).

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P.S. and C.C. conceived and designed the experiments. C.C. carried out the chemical synthesis and the electrochemical experiments and analysed the results. L.G. and M.H. performed the HRTEM and STEM-EELS experiments, evaluated and analysed the results. P.S. and C.C. aggregated the figures and co-wrote the manuscript. All authors discussed the results, drew conclusions and commented on the manuscript.

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Correspondence to Peter Strasser.

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Cui, C., Gan, L., Heggen, M. et al. Compositional segregation in shaped Pt alloy nanoparticles and their structural behaviour during electrocatalysis. Nature Mater 12, 765–771 (2013). https://doi.org/10.1038/nmat3668

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