157
© Springer Nature Switzerland AG 2020
R. Adzic, N. Marinkovic, Platinum Monolayer Electrocatalysts,
https://doi.org/10.1007/978-3-030-49566-4_10
Chapter 10
Palladium Monolayer Electrocatalysts
In principle, other metals, not only Pt, can serve as monolayer electrocatalysts, if
supported by adequate cores, they can have high stability, and can be used in electrolyte solutions with various pH. A recent increase of interest in the alkaline fuel
cells will be coupled with the interest for Pd as non-platinum catalyst that can have
high stability, activity, and selectivity. The applications of these catalysts can be
expected in oxidation and reduction of organic compounds and syntheses of pharmaceuticals, where these properties have high importance.
Oxygen reduction reaction on Pd monolayers on various surfaces and on Pd
alloys was studied to obtain a substitute for Pt and to elucidate the origin of their
activity [1, 2]. The activity of Pd monolayers (STM image Fig. 10.1a), supported on
Ru(0001), Rh(111), Ir(111), Pt(111), and Au(111), increased in the following
order: Pd/Ru(0001) < Pd/Ir(111) < Pd/Rh(111) < Pd/Au(111) < Pd/Pt(111)
(Fig. 10.1b). Their activity was correlated with their d-band centers, which were
calculated using density functional theory (DFT). The volcano-type dependence of
activity on the energy of the d-band center of Pd monolayers, with Pd/Pt(111) at the
top of the curve, was found (Fig. 10.2) [1].
The electrocatalytic activity of intrinsic Pd and Pt surfaces and Pd and Pt overlayers on several substrates with their electronic properties shows the volcano-type
dependence of O 2 reduction activity on the binding energy of oxygen and the d-band
center of the top metal layer. Intrinsic Pd and Pt surfaces bind oxygen too firmly to
allow efficient removal of the adsorbed reaction intermediates. Therefore, they do
not have the highest activity and are not on the top of the volcano plot. A Pd overlayer on a Pd 3 Fe(111) alloy was predicted to lie on top of the volcano plot, and thus,
it appears to be the most active catalyst among investigated ones because of its
moderate interaction with oxygen [3].
A descriptor of surface reactivity again was the calculated Pd d-band center (relative to the Fermi level), ε d . The closer the position of ε d toward the Fermi level, the
stronger the interactions with adsorbates. These calculations also show a linear correlation between the O binding energies and the d-band position of the Pd atom on
M surfaces (Fig. 10.2a). Pd/Ru(0001), Pd/Ir(111), and Pd/Rh(111) have a low ε d
© Springer Nature Switzerland AG 2020
R. Adzic, N. Marinkovic, Platinum Monolayer Electrocatalysts,
https://doi.org/10.1007/978-3-030-49566-4_10
Chapter 10
Palladium Monolayer Electrocatalysts
In principle, other metals, not only Pt, can serve as monolayer electrocatalysts, if
supported by adequate cores, they can have high stability, and can be used in electrolyte solutions with various pH. A recent increase of interest in the alkaline fuel
cells will be coupled with the interest for Pd as non-platinum catalyst that can have
high stability, activity, and selectivity. The applications of these catalysts can be
expected in oxidation and reduction of organic compounds and syntheses of pharmaceuticals, where these properties have high importance.
Oxygen reduction reaction on Pd monolayers on various surfaces and on Pd
alloys was studied to obtain a substitute for Pt and to elucidate the origin of their
activity [1, 2]. The activity of Pd monolayers (STM image Fig. 10.1a), supported on
Ru(0001), Rh(111), Ir(111), Pt(111), and Au(111), increased in the following
order: Pd/Ru(0001) < Pd/Ir(111) < Pd/Rh(111) < Pd/Au(111) < Pd/Pt(111)
(Fig. 10.1b). Their activity was correlated with their d-band centers, which were
calculated using density functional theory (DFT). The volcano-type dependence of
activity on the energy of the d-band center of Pd monolayers, with Pd/Pt(111) at the
top of the curve, was found (Fig. 10.2) [1].
The electrocatalytic activity of intrinsic Pd and Pt surfaces and Pd and Pt overlayers on several substrates with their electronic properties shows the volcano-type
dependence of O 2 reduction activity on the binding energy of oxygen and the d-band
center of the top metal layer. Intrinsic Pd and Pt surfaces bind oxygen too firmly to
allow efficient removal of the adsorbed reaction intermediates. Therefore, they do
not have the highest activity and are not on the top of the volcano plot. A Pd overlayer on a Pd 3 Fe(111) alloy was predicted to lie on top of the volcano plot, and thus,
it appears to be the most active catalyst among investigated ones because of its
moderate interaction with oxygen [3].
A descriptor of surface reactivity again was the calculated Pd d-band center (relative to the Fermi level), ε d . The closer the position of ε d toward the Fermi level, the
stronger the interactions with adsorbates. These calculations also show a linear correlation between the O binding energies and the d-band position of the Pd atom on
M surfaces (Fig. 10.2a). Pd/Ru(0001), Pd/Ir(111), and Pd/Rh(111) have a low ε d