(Invited) Porous Hollow PtNi/C Nanoparticles and Their Many Facets

Tuesday, 3 October 2017: 14:20
National Harbor 2 (Gaylord National Resort and Convention Center)
T. Asset (Univ. Grenoble Alpes, LEPMI, F-38000 Grenoble, France, CNRS, LEPMI, F-38000 Grenoble, France), R. Chattot (Univ. Grenoble Alpes, LEPMI, F-38000 Grenoble, France, CNRS, LEPMI, F-3800 Grenoble, France), O. Le Bacq, A. Pasturel (Univ. Grenoble Alpes, SIMAP, F-38000 Grenoble, France, CNRS, SIMAP, F-38000 Grenoble, France), J. Drnec (European Synchrotron Radiation Facility (ESRF)), P. Bordet (Univ. Grenoble Alpes, Inst. Néel, 38000 Grenoble, France, CNRS, Inst. Néel, 38000 Grenoble, France), J. Nelayah (MPQ - Paris), L. Dubau, and F. Maillard (Univ. Grenoble Alpes, LEPMI, F-38000 Grenoble, France, CNRS, LEPMI, F-38000 Grenoble, France)
Porous hollow PtM/C electrocatalysts (where M is a 3d transition metal element) have proven to enhance remarkably the oxygen reduction reaction (ORR) kinetics in proton exchange membrane fuel cells. However, their mechanism of formation, the nature of adequate alloying elements and carbon supports as well as the rationale for their interesting electrocatalytic properties remain open questions.

Herein, we describe the mechanism of formation and growth of porous hollow PtNi/C NPs using operando wide angle X-ray scattering, scanning transmission electron microscopy and X-ray energy dispersive spectroscopy 1. The results show that Ni-rich NPs covered by a NixByOz shell form first before acting as a sacrificial template for the deposition of Pt2+ ions via galvanic replacement (Figure 1). Finally, the solid Ni-rich core@Pt-rich shell NPs are transformed into alloy hollow PtNi/C NPs via the nanoscale Kirkendall effect (a vacancy mediated interdiffusion mechanism). Density Functional Theory (DFT) calculations were then used to gain insights on the impact of atomic vacancies on the surface structure and the reactivity of the porous hollow PtNi/C nanoparticles 2. The DFT and experimental results show that porous hollow PtM/C nanoparticles feature unique catalytic advantages (i) open percolated structure exposing two catalytic surfaces (inner and outer), and (ii) structural defects that distort the metal lattice and produce catalytic sites that are highly active for both electrooxidation (COadsmonolayer electrooxidation, methanol and ethanol electrooxidation) and electroreduction (ORR) reactions.

1. R. Chattot, T. Asset, J. Drnec, P. Bordet, J. Nelayah, L. Dubau, F. Maillard, Nano Lett. (2017). DOI: 10.1021/acs.nanolett.7b00119

2. O. Le Bacq, A. Pasturel, R. Chattot, B. Previdello, J. Nelayah, T. Asset, L. Dubau, F. Maillard, ChemCatChem. (2017). DOI: 10.1002/cctc.201601672

Figure 1. Conventional and scanning transmission electron microscopy images and elemental maps of the different intermediate nanostructures forming during the synthesis of hollow PtNi/C nanoparticles.