Electrochemical Atomic-level Controlled Syntheses of Electrocatalysts for the Oxygen Reduction Reaction - Atomically-Precise Methods for Synthesis of Solid Catalysts - page 155

performed in a 'one-cell configuration'. According to the authors, the ad-
vantages of this protocol over the other SLRR protocols are: (i) easier
handling; (ii) better control and uniformity of oxygen-free environment; (iii)
better uniformity of the deposit, and (iv) easier adaptation and scaling up of
systems with practical importance. It is demonstrated that with only one
SLRR event of Pb UPD it is possible to form Pt ML film on Au that behaves
like pure Pt in the H UPD reaction. The Pt film grows in 2D mode with no
roughness increase up to 10 redox replacement cycles. An e ciency of 1 Pt
ML per cycle (1 : 1 exchange Pb:Pt ratio) is achieved. As obtained Pt films
consist of small clusters that show very similar size and distribution for
different thicknesses. Interestingly, an amount of Pt above stoichiometry
depositing per replacement event has been detected once the bare Au sur-
face is platinized. This anomaly is attributed to the presence of extra re-
duction power that could be associated with the oxidative adsorption of
OH ads and/or to H adsorption/desorption phenomena, both reported to take
place along with the UPD of Pb layers on Pt surfaces. In addition, a com-
positional analysis of the Pt layers grown by SLRR suggested incorporation of
a minimum 4 atom% Pb and 13 atom% Cu when these metals are used as
sacrificial ones in the deposition process.

d n 9 r 4 n g | 4

6.2.2.3 Hydrogen Adsorption and Absorption as a Surface-
limited Reaction for Synthesis of Pt ML Catalysts
A viable SLRR protocol for the growth of Pt MLs, and as well as thin films on
Pt and Pd (including Pd nanocubes) substrates, based on adsorbed H or also
called under-potentially deposited H (H-UPD), has been most recently pro-
posed. 19 In contrast to the previously reported studies on SLRR deposition,
this work presents the first application of the SLRR protocol in a one-cell
configuration using a nonmetal UPD system. Thus, any possible mediator
metal incorporation, reported in standard Pt SLRR protocols, is precluded
herein. The growth of Pt using H UPD via SLRR method is conducted in
tetra-chloro-platinate [PtCl 4 ] 2 solution containing perchlorite ions as a
supporting electrolyte. The protocol consist of repeating elementary steps of
H UPD formation by potential impulse for 1 s followed by redox replacement
step that takes place at OCP. It is reported that as grown Pt films feature
steady roughness evolution and the growth is in the realm of quasi-2D
growth mode that generates uniform Pt films. In addition, it is confirmed
that no side reactions are taking place during the redox exchange, and the
exchange Pt:H ratio is 1 : 2. The generality of the proposed approach is val-
idated by growth of Pt films on two types of Pd surfaces: Pd ultra-thin films
on Au (Pd/Au) and Pd nanocubes. The Pt over-layers grown by 30 replace-
ments on Pd structures have been characterized by H-UPD and their catalytic
activity examined by formic acid oxidation reaction.
A method for producing Pt surface monolayer on palladium or palladium
alloy nanoparticles having low Pt loading coupled with catalytic activity for

.