87
The deposit consists of two-dimensional interconnected Pt islands. With a small
difference between the Pt and Rh lattice constants, these islands are expected to be
epitaxial with the Rh(111) substrate. There are a certain number of holes between
the islands and also a few sites with Pt atoms in the second layer.
Implementation of this deposition method can be accomplished without potentiostat by short circuiting Pd support to a copper foil or wire in the same electrolyte.
This brings the Pt potential to a reversible Cu/Cu
2+
value and facilitates the UPD of
Cu above that potential. Removing Cu metal from the cell upon completion of a Cu
monolayer and adding Pt
2+
in solution will replace Cu monolayer by Pt. This may
be a simple method for producing large batches.
Initial studies are best performed using single-crystal surfaces, rather than complex nanoparticles on carbon supports. The use of single-crystal vicinal surfaces
enabled decoupling of electronic and surface structure effects resulting from the
crystallographic orientation alone and structural features such as terraces, steps,
and kinks.
Controlled epitaxial deposition of Pt is a challenge. Due to the very high surface
energy and low diffusivity, Pt growth, regardless of the method of deposition, is
nonuniform and proceeds via 3D island formation (Volmer Weber growth, which
proceeds when the atoms of the deposit are more strongly coupled with each other
than with the substrate) [8]. Very quickly the method has become one of the most
exploited to design 2-dimensional (2D) and nanoparticle Pt-bimetallic systems. In
the recent papers regarding metal electrodeposition, the process has been designated as the surface limited redox replacement (SLRR) deposition method that
enabled for the first time successful epitaxial deposition of Pt films and nanoclusters
with atomic scale control on to other metal surfaces. Additional deposition protocols involve steps same as above with surface covered by adlayer.
The second protocol involves a similar routine but with a stagnant substrate; the
solutions for metal UPD monolayer formation and Pt deposition are exchanged in a
single SLRR cycle (solution shuffling approach) [4, 9]. Finally, the latest developed
protocol adopts a one-solution, one-cell experimental design [10].
7.3 Other Syntheses of Pt Monolayer Electrocatalysts
It is generally accepted that the shape and composition of nanoparticles play a crucial role in determining their catalytic activity. Consequently, the shape and composition of cores will affect the core-shell interaction, that is the catalytic properties of
a Pt ML shell. Electrochemical deposition on carbon fibers and functionalized carbon
nanoparticles was used to obtain two interesting types of cores: (i) Pd NWs, and
nanorods, (ii) nanoparticles of refractory metal alloy (W + Ni) from aqueous solutions (Fig. 7.5) [11]. This is a simpler procedure than various chemical routes. A
co-deposition of W and Ni can take place in aqueous solutions. These particles, as
cores, can provide a stable support (W passivates at high potentials and precludes
7.3 Other Syntheses of Pt Monolayer Electrocatalysts
The deposit consists of two-dimensional interconnected Pt islands. With a small
difference between the Pt and Rh lattice constants, these islands are expected to be
epitaxial with the Rh(111) substrate. There are a certain number of holes between
the islands and also a few sites with Pt atoms in the second layer.
Implementation of this deposition method can be accomplished without potentiostat by short circuiting Pd support to a copper foil or wire in the same electrolyte.
This brings the Pt potential to a reversible Cu/Cu
2+
value and facilitates the UPD of
Cu above that potential. Removing Cu metal from the cell upon completion of a Cu
monolayer and adding Pt
2+
in solution will replace Cu monolayer by Pt. This may
be a simple method for producing large batches.
Initial studies are best performed using single-crystal surfaces, rather than complex nanoparticles on carbon supports. The use of single-crystal vicinal surfaces
enabled decoupling of electronic and surface structure effects resulting from the
crystallographic orientation alone and structural features such as terraces, steps,
and kinks.
Controlled epitaxial deposition of Pt is a challenge. Due to the very high surface
energy and low diffusivity, Pt growth, regardless of the method of deposition, is
nonuniform and proceeds via 3D island formation (Volmer Weber growth, which
proceeds when the atoms of the deposit are more strongly coupled with each other
than with the substrate) [8]. Very quickly the method has become one of the most
exploited to design 2-dimensional (2D) and nanoparticle Pt-bimetallic systems. In
the recent papers regarding metal electrodeposition, the process has been designated as the surface limited redox replacement (SLRR) deposition method that
enabled for the first time successful epitaxial deposition of Pt films and nanoclusters
with atomic scale control on to other metal surfaces. Additional deposition protocols involve steps same as above with surface covered by adlayer.
The second protocol involves a similar routine but with a stagnant substrate; the
solutions for metal UPD monolayer formation and Pt deposition are exchanged in a
single SLRR cycle (solution shuffling approach) [4, 9]. Finally, the latest developed
protocol adopts a one-solution, one-cell experimental design [10].
7.3 Other Syntheses of Pt Monolayer Electrocatalysts
It is generally accepted that the shape and composition of nanoparticles play a crucial role in determining their catalytic activity. Consequently, the shape and composition of cores will affect the core-shell interaction, that is the catalytic properties of
a Pt ML shell. Electrochemical deposition on carbon fibers and functionalized carbon
nanoparticles was used to obtain two interesting types of cores: (i) Pd NWs, and
nanorods, (ii) nanoparticles of refractory metal alloy (W + Ni) from aqueous solutions (Fig. 7.5) [11]. This is a simpler procedure than various chemical routes. A
co-deposition of W and Ni can take place in aqueous solutions. These particles, as
cores, can provide a stable support (W passivates at high potentials and precludes
7.3 Other Syntheses of Pt Monolayer Electrocatalysts