Electrochemical Atomic-level Controlled Syntheses of Electrocatalysts for the Oxygen Reduction Reaction - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 157

of the U.S. Department of Energy's target for 2020, 2 and they possess ex-
cellent activity and performance stability. Furthermore, these catalysts have
a 100% Pt utilization, because of the nature of their processing, which
means that each Pt atom is accessible and is participating in the ORR.

d n 9 r 4 n g | 4

6.3.1 Electro-deposited Pd Nanostructures and Bimetallic Pd
Alloys on Functionalized Carbon Substrates: Advanced
Cores for Pt ML Shell Electrocatalysts
It has been reported recently that the morphology of the electro-deposited Pd
nanostructures on functionalized carbon nanoparticles from 1 mM PdCl 2
and 0.1 M NaCl solution, strongly depends from the applied over-potential. 32
Thus, Pd nanoparticles (Pd NP ) or nanorods (Pd NR ) or nanowires (Pd NW ) can
be easily electro-deposited directly on functionalized carbon support at
different over-potentials that have to be established. 20,32,33 Figure 6.5
presents the TEM images of electro-deposited Pd NP ,Pd NR and Pd NW at
different potentials. The elongated nanostructures obtained are excellent
cores for Pt ML shells electrocatalysts, because they possess smooth and
well-ordered facets with reduced number of low coordinating sites and de-
fects that are usually source of dissolution at fuel cell operation conditions.
The anisotropic growth of the one-dimensional Pd nanowires is ascribed to
the H under-potential deposition-mediated, layer-by-layer deposition of Pd.
The growth mode operates on the cluster's facets covered by adsorbed
hydrogen atoms, while, at these potentials, the chloride ions adsorbed only
on the edges of the Pd clusters, precluding growth in other directions. 32 In
addition, the surface structure of deposited nanowires is composed pre-
dominantly of (111)-oriented facets that facilitate the enhanced ORR activity
and stability of the Pt ML /Pd NW /C OX electrocatalysts.
In order to prepare Pt monolayer type catalysts, the surface of as electro-
deposited Pd nanostructures is modified by a monolayer of Pt, using the Cu

.

Figure 6.5 TEM images of electro-deposited Pd nanostructures at different over-
potentials: (a) at 0.25 V, (b) at 0.1 V, and (c) at 0.05 V. The HRTEM images
of nanoparticles, nanorods and nanowires are presented as insets. The
second inset in (c) shows the fast Fourier transform pattern of selected
area from the nanowires.