Platinum Monolayer Electrocatalysts for O₂ Reduction:  Pt Monolayer on Pd(111) and on Carbon-Supported Pd Nanoparticles

Abstract

The kinetics of oxygen reduction was studied in acid solutions on Pt monolayers deposited on a Pd(111) surface and on carbon-supported Pd nanoparticles using the rotating disk-ring electrode technique. These electrocatalysts were prepared by a new method for depositing Pt monolayers involving the galvanic displacement by Pt of an underpotentially deposited Cu monolayer on a Pd substrate and characterized by scanning tunneling and transmission electron microscopies. The kinetics of O 2 reduction shows a significant enhancement at Pt monolayers on Pd(111) and Pd nanoparticle surfaces in comparison with the reaction on Pt(111) and Pt nanoparticles. The four-electron reduction, with a first-charge transfer-rate determining step, is operative on both surfaces. The observed increase in the catalytic activity of Pt monolayer surfaces compared with Pt bulk and nanoparticle electrodes may reflect decreased formation of PtOH. An enhanced atomic scale surface roughness and low coordination of some atoms may contribute to the observed activity. The results illustrate that placing a Pt monolayer on a suitable metal nanoparticle substrate is an attractive way of designing better O 2 reduction electrocatalysts. Also, by using this method the Pt content is reduced to very low levels. The Pt mass-specific activity of the Pt/Pd/C electrode is 5-8 times higher than that of the Pt/C electrocatalyst. The noble metal (Pt + Pd) mass-specific activity is two times higher than that of Pt/C.

In situ X-ray probing reveals fingerprints of surface platinum oxide

“…This appears to be the case in the Pt/Rh(111) system studied here, for which lower ORR activity and increased H 2 O 2 formation in comparison to Pt(111) was found 41 . L 3 -edge spectra of pure Pt nanoparticles 6,[8][9][10][11][12] exhibit a strong increase and broadening of the white-line, similar to what we observe on Pt/Rh(111), already at lower onset potentials of around 0.8 V but with less intensity since bulk Pt atoms also contribute significantly to the L-edge peak. The similarities between our data and previously reported spectra of Pt nanoparticles suggest a re-interpretation of the latter, with the generally observed white-line increase being due to oxide formation rather than OH or O chemisorption.…”

“…Such a case could be the modification of Pt nanoparticles with Au clusters 7 , which was shown to significantly enhance the stability of Pt against oxidation while retaining almost identical ORR half-wave potentials. Improved ORR activities were also found on Ptalloy and bimetallic core-shell nanoparticles 5,6,9,43 , concomitantly with a suppression of Pt oxidation at high potentials 5,6,9 . HERFD XAS applied to bimetallic systems could, as demonstrated in the present work, elucidate details of the inhibition mechanism for Pt oxide growth, especially when suitable absorption edges of both metal components are studied.…”

Nanostructured Pt-alloy electrocatalysts for PEM fuel cell oxygen reduction reaction

“…For example, when a Pt monolayer was deposited on the surface of bulk Pd(111) single crystals, 10 the ORR activity, characterized using rotating ring disk electrode in a 0.1 M HClO 4 solution, revealed a very positive onset potential for the ORR (0.95-1 V vs. NHE), as well as a half-wave potential of 0.838 V. When such a Pt monolayer was deposited on the carbon-supported Pd nanoparticles, even higher activity was observed, with a half-wave potential at 0.853 V. In addition, the ring current was insignificant, indicating that the ORR catalyzed by this catalyst was a complete four-electron process on the disk electrode from O 2 to H 2 O. In their further studies, a Pt monolayer was also deposited on Au/Ni, Pd/Co and Pt/Co nanoparticles 96 to form core-shell Pt/Au/Ni, Pt/Pd/Co and Pt/Pt/Co nanoparticles, which were more active than Pt/C electrocatalyst.…”

Metal Oxide‐Supported Platinum Overlayers as Proton‐Exchange Membrane Fuel Cell Cathodes

“…The principal approach to achieve this is to alloy platinum with some non-noble transition metal such as V, Cr, Fe, Ni, Co, Cu [1,2,3,4,5] or similarly, deposit thin metal overlayers onto less noble metal substrates [6,7,8]. Readily, great activity enhancements for the oxygen reduction reaction (ORR) have been reported for such catalysts.…”