Recent Advances in Developing Platinum Monolayer Electrocatalysts for the O2 Reduction Reaction Page: 3 of 6
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Recent Advances in Developing Platinum Monolayer Electrocatalysts for the 02
M. B. Vukmirovic, K. Sasaki, W-P. Zhou, M. Li, P. Liu, J.X. Wang, R. R. Adzic
For Pt, the best single-element catalyst for many reactions, the question of content
and loading is exceedingly important because of its price and availability. Using platinum
as a fuel-cell catalyst in automotive applications will cause an unquantifiable increase in
the demand for this metal. This big obstacle for using fuel cells in electric cars must be
solved by decreasing the content of Pt, which is a great challenge of electrocatalysis
Over the last several years we inaugurated a new class of electrocatalysts for the
oxygen reduction reaction (ORR) based on a monolayer of Pt deposited on metal or alloy
carbon-supported nanoparticles. The possibility of decreasing the Pt content in the ORR
catalysts down to a monolayer level has a considerable importance because this reaction
requires high loadings due to its slow kinetics. The Pt-monolayer approach has several
unique features and some of them are: high Pt utilization, enhanced (or decreased)
activity, enhanced stability, and direct activity correlations.
The synthesis of Pt monolayer (ML) electrocatalysts was facilitated by our new
synthesis method which allowed us to deposit a monolayer of Pt on various metals, or
alloy nanoparticles [1, 2] for the cathode electrocatalyst. In this synthesis approach Pt is
laid down by the galvanically displacing a Cu monolayer, which was deposited at
underpotentials in a monolayer-limited reaction on appropriate metal substrate, with Pt
after immersing the electrode in a K2PtCl4 solution.
The ORR is a complex multistep reaction involving the exchange of four
electrons, whose detailed mechanism still defies formulation . The overall four
electron reduction of 02 in acid aqueous solutions is
02 + 4H + 4e -- 2H20, (ENHE)298K=1.229 V
Irrespective of the microscopic mechanism, a four-electron process must involve the
breaking of an 0-0 bond and the formation of O-H bonds . Surfaces that strongly
bind an adsorbate tend to enhance the kinetics of bond-breaking steps. On the other hand,
surfaces that bind species weakly tend to facilitate the kinetics of bond-making steps.
In order to increase the activity of Pt monolayer for ORR, we synthesized three
types of Pt monolayer electrocatalysts for the ORR: (i) Pt on carbon-supported Pd
nanoparticles , (ii) mixed-metal Pt monolayers on Pd nanoparticles , and (iii) Pt
monolayers on noble/nonnoble core-shell nanoparticles .
A monolayer of Pt on Pd substrate had higher activity than the bulk Pt surface .
This increased activity is partly due to the decreased Pt-OH coverage in comparison with
bulk Pt (Pt-OH, derived from H20 oxidation on Pt, is a species blocking the ORR). In
addition, the small compression of a Pt deposit on a Pd substrate, causes a downshift of
the d-band center, thereby leading to the decreased reactivity of Pt (i.e. decline in the
interaction strength between Pt and ORR surface intermediates). Both effects enhance the
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Vukmirovic,M.B.; Sasaki, K.; Zhou, W.-P.; Li, M.; Liu, P.; Wang, J.X. et al. Recent Advances in Developing Platinum Monolayer Electrocatalysts for the O2 Reduction Reaction, article, September 15, 2008; United States. (https://digital.library.unt.edu/ark:/67531/metadc896051/m1/3/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.