Journal
APPLIED CATALYSIS B-ENVIRONMENTAL
Volume 152, Issue -, Pages 300-308Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.apcatb.2014.01.034
Keywords
Proton exchange membrane fuel cell; Oxygen reduction reaction; Pt-Co/C nanoparticles; Electrocatalyst degradation mechanisms; Atomic-scale spectroscopic imaging
Funding
- Oseo-AII through the H2E project
- MECD Spanish Ministry [EX2010-1135]
- French University Institute (IUF)
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The oxygen reduction reaction (ORR), which is the cathodic reaction in a proton-exchange membrane fuel cell (PEMFC) and in several other important processes, is a widely studied reaction. From the kinetics viewpoint, Pt is the best electrocatalyst and its activity can be increased upon alloying with a 3d-transition metal (Co, Ni, Fe, Cu). Aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy prove that the structural and compositional changes of Pt3Co/C nanoparticles during real-life PEMFC operation are much richer than previously thought from accelerated stress tests. Four different nanostructures are observed after 3422 h of operation in stationary mode: Pt, Pt-Co/C hollow, Pt-Co core-shell and Pt bulk nanoparticles. The presence of hollow nanoparticles in the aged catalytic layer is accounted for by the nanoscale Kirkendall effect, a vacancy-mediated diffusion mechanism in binary alloys where one species diffuses faster than the other. The oxygen reduction reaction specific activity of the hollow nanostructures is 1.5-fold that of the fresh Pt3Co/C cathode catalyst and 3-fold that of Pt/C nanoparticles, thereby offering a new route to synthesize highly active and durable PEMFC electrocatalysts. (C) 2014 Elsevier B.V. All rights reserved.
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