1 3
Topics in Current Chemistry (2019) 377:11
increase In a series of Pt/Ir/Rh/Sn catalysts, the highest activity for ethanol oxidation showed the ternary catalyst having Pt:Ir:Sn = 1:1:1 atomic ratio. Of the catalysts
containing both Rh and Ir, the highest CO 2 production was found for the catalyst
with atomic ratio Pt:Ir:Rh:Sn = 1:1:1:1. Nevertheless, even the best catalyst containing Ir was inferior in comparison to the optimized Pt–Rh–SnO 2 /C. We ascribe this
phenomenon to the inability of SnO 2 to keep the Ir and Pt in metallic state, unlike its
behavior in Pt–Rh–SnO 2 catalysts [31].
5 Platinum Monolayer Electrocatalysts for Ethanol Oxidation
Adzic et al. developed a new approach for designing and synthesizing electrocatalysts that can dramatically reduce the required Pt content, while affording possibilities to enhance their catalytic performance [112]. These electrocatalysts consist of
a monolayer (one atom thick) of Pt on extended or supported nanoparticle metal
or metal-alloy surfaces. The Pt-monolayer (Pt ML ) approach has several attractive
features: (a) Close to complete Pt utilization since all Pt atoms are present on the
surface and participate in catalytic reactions; (b) Tailored electrocatalytic properties consequent upon the combined geometric effect (substrate-induced strain)
and ligand effect (the electronic interaction between Pt ML and the substrate); (c)
enhanced stability because of the decreased oxidation of the Pt ML resulting from the
interaction with the suitable substrate; (d) direct activity correlations between catalytic and physical properties of the Pt ML as all Pt atoms involved in the reaction are
sampled by the measuring technique [112].
Such Pt ML electrocatalysts can be synthesized by depositing a Pt monolayer on
different substrates via the galvanic displacement of an underpotentially deposited (UPD) Cu monolayer (Fig. 17). Scanning tunneling microscopy (STM) study
of the resulting Pt ML /Ru(1010) surface revealed that Pt was deposited as a small
three-dimensional (3D) island on Ru [113]. In some other Pt-M binary systems, for
instance, Pt on Pd, a pseudomorphic monolayer of Pt was formed by the displacement of a Cu UPD layer [112]. EXAFS data on monolayer of Pt (Pt ML ) deposited on
Pd revealed that the structure is indeed pseudomorphic, as the coordination numbers
N(Pt–Pt) and N(Pt–Pd) were 5.8 ± 0.8 and 2.7 ± 0.7, respectively. These coordination numbers are close to that expected on a flat Pt ML on Pd(111), as an atom of Pt
at the surface of (111) structure has six Pt nearest neighbors in the plane of the monolayer, and three Pd nearest neighbors below the surface. On a curved surface as in
nanoparticles, those coordination numbers may differ slightly due to the presence of
edges and vertices [79].
The Pt ML electrocatalysts were systematically studied for the electrooxidation
of methanol and ethanol. Pt ML was deposited on different substrates via the galvanic displacement of a Cu UPD monolayer employing five single-crystal surfaces
[Au(111), Pd(111), Ir(111), Rh(111), and Ru(0001)] as substrates. Because of the
larger lattice, Au exerts on Pt a tensile strain in Pt ML /Au(111); in other Pt ML /M(111)
surfaces (M = Pd, Ir, Rh, and Ru) Pt is under compressive strain as the metals
have smaller lattice constants. Interestingly, a significant enhancement in the catalytic activity associated with the tensile strain, and decreased activity associates
Reprinted from the journal
29
Topics in Current Chemistry (2019) 377:11
increase In a series of Pt/Ir/Rh/Sn catalysts, the highest activity for ethanol oxidation showed the ternary catalyst having Pt:Ir:Sn = 1:1:1 atomic ratio. Of the catalysts
containing both Rh and Ir, the highest CO 2 production was found for the catalyst
with atomic ratio Pt:Ir:Rh:Sn = 1:1:1:1. Nevertheless, even the best catalyst containing Ir was inferior in comparison to the optimized Pt–Rh–SnO 2 /C. We ascribe this
phenomenon to the inability of SnO 2 to keep the Ir and Pt in metallic state, unlike its
behavior in Pt–Rh–SnO 2 catalysts [31].
5 Platinum Monolayer Electrocatalysts for Ethanol Oxidation
Adzic et al. developed a new approach for designing and synthesizing electrocatalysts that can dramatically reduce the required Pt content, while affording possibilities to enhance their catalytic performance [112]. These electrocatalysts consist of
a monolayer (one atom thick) of Pt on extended or supported nanoparticle metal
or metal-alloy surfaces. The Pt-monolayer (Pt ML ) approach has several attractive
features: (a) Close to complete Pt utilization since all Pt atoms are present on the
surface and participate in catalytic reactions; (b) Tailored electrocatalytic properties consequent upon the combined geometric effect (substrate-induced strain)
and ligand effect (the electronic interaction between Pt ML and the substrate); (c)
enhanced stability because of the decreased oxidation of the Pt ML resulting from the
interaction with the suitable substrate; (d) direct activity correlations between catalytic and physical properties of the Pt ML as all Pt atoms involved in the reaction are
sampled by the measuring technique [112].
Such Pt ML electrocatalysts can be synthesized by depositing a Pt monolayer on
different substrates via the galvanic displacement of an underpotentially deposited (UPD) Cu monolayer (Fig. 17). Scanning tunneling microscopy (STM) study
of the resulting Pt ML /Ru(1010) surface revealed that Pt was deposited as a small
three-dimensional (3D) island on Ru [113]. In some other Pt-M binary systems, for
instance, Pt on Pd, a pseudomorphic monolayer of Pt was formed by the displacement of a Cu UPD layer [112]. EXAFS data on monolayer of Pt (Pt ML ) deposited on
Pd revealed that the structure is indeed pseudomorphic, as the coordination numbers
N(Pt–Pt) and N(Pt–Pd) were 5.8 ± 0.8 and 2.7 ± 0.7, respectively. These coordination numbers are close to that expected on a flat Pt ML on Pd(111), as an atom of Pt
at the surface of (111) structure has six Pt nearest neighbors in the plane of the monolayer, and three Pd nearest neighbors below the surface. On a curved surface as in
nanoparticles, those coordination numbers may differ slightly due to the presence of
edges and vertices [79].
The Pt ML electrocatalysts were systematically studied for the electrooxidation
of methanol and ethanol. Pt ML was deposited on different substrates via the galvanic displacement of a Cu UPD monolayer employing five single-crystal surfaces
[Au(111), Pd(111), Ir(111), Rh(111), and Ru(0001)] as substrates. Because of the
larger lattice, Au exerts on Pt a tensile strain in Pt ML /Au(111); in other Pt ML /M(111)
surfaces (M = Pd, Ir, Rh, and Ru) Pt is under compressive strain as the metals
have smaller lattice constants. Interestingly, a significant enhancement in the catalytic activity associated with the tensile strain, and decreased activity associates
Reprinted from the journal
29