Electrochemical Atomic-level Controlled Syntheses of Electrocatalysts for the Oxygen Reduction Reaction - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 160

more than 20 times and 25% higher than that of Pt/C and Pt ML /Pd/C, re-
spectively. The electrochemical measurements pointed out that the enhanced
ORR kinetics observed on Pt ML /PdIr/C electrocatalysts originated from a de-
creased Pt-OH coverage. 34 This has been rationalized by self-consistent DFT
calculations of the binding energy of OH on various relevant model systems.
Clearly, the existence of a PdIr 2 monolayer located right below a Pt ML /Pd ML
bilayer and above the Pd(111) crystal leads to the destabilization of the surface
OH compared to that already shown on a Pt ML /Pd(111).
Pd 0.9 Au 0.1 and Pd 0.9 Ir 0.1 alloys nanoparticles are co-electro-deposited at
constant potential from solution containing PdCl 2 and HAuCl 4 or IrCl 3 salts
in presence of 0.1 M NaCl. The ratio between the salts in the solutions is
chosen to give a deposit containing 90 at.% Pd and 10 at.% of Au or Ir. Al-
though the deposition potential has been applied in the range where an-
isotropic growth of Pd nanowires is taking place, Pd 0.9 Au 0.1 and Pd 0.9 Ir 0.1
nanorods are obtained. It seems that due to the atomic size difference be-
tween Pd and Au or Ir atoms the proposed mechanism is not enough e-
cient to grow nanowires. After the deposition the surface of the Pd 0.9 Au 0.1
and Pd 0.9 Ir 0.1 nonorods is modified by Pt ML, and the activity and stability of
these electrocatalysts is studied by measuring their polarization curves. In
Figure 6.7, the TEM image of the electro-deposited Pd 0.9 Au 0.1 nanoroads is
presented along with the polarization curves for the ORR of the Pt ML /
Pd 0.9 Au 0.1 /C electrocatalysts measured in 0.1 M HClO 4 solution at 1600 rpm.
The mass activity of this electrocatalyst, as calculated from the polar-
ization curves, exceeds by an order of magnitude the DOE's targets for mass
activity of electrocatalysts for the ORR for 2020. Also, it is seen from
Figure 6.7a that the polarization curve measured after 15,000 accelerated

d n 9 r 4 n g | 4

.

Figure 6.7 (a) ORR polarization curves, measured in 0.1 M HClO 4 acid solution at

1600 rpm, and (b) TEM image of the Pd 0.9 Au 0.1 nanorods.