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A new method for the preparation of Pt-Ru and similar bimetallic electrocatalysts is reported. It involves a spontaneous deposition of Pt submonolayers on metallic Ru nanoparticles, which yields electrocatalysts with a considerably lower Pt loading and higher CO tolerance than the commercial Pt-Ru alloy electrocatalysts. The method offers a unique possibility to place the Pt atoms onto the surface of Ru nanoparticles, which very likely makes almost all of them available for hydrogen oxidation, in contrast to the Pt-Ru alloy catalysts that have Pt throughout the nanoparticles. Thus, an ultimate reduction of Pt loading can be achieved. It also facilitates a fine-tuning of the electrocatalyst's activity and selectivity by changing the coverage ͑the cluster size͒ of Pt for optimal performance under required CO tolerance levels.

The work exploring the stoichiometry of Pt deposition via surface-limited redox replacement of the underpotentially deposited ͑UPD͒ Cu monolayer on Au͑111͒ is presented. The Cu UPD monolayer is formed from 10 −3 M Cu 2+ + 0.1 M HClO 4 solution, whereas the Pt deposition via surface-limited redox replacement reaction is carried out in 10 −3 M ͕PtCl 6 ͖ 2− + 0.1 M HClO 4 solution at open-circuit potential. Our results indicate that the Pt submonolayers have two-dimensional morphology and linear dependence of their coverage on the amount ͑coverage͒ of the replaced Cu UPD monolayers. Our analysis shows that the oxidation state of Cu during redox replacement reaction is 1+, suggesting that four Cu UPD adatoms are replaced by each deposited Pt adatom. This work stresses the general importance of the anions, determining the stoichiometry of metal deposition reaction via surface-limited redox replacement of the UPD monolayers.

Using the binding energy of OH* and CO* on close-packed surfaces as reactivity descriptors, we screen bulk and surface alloy catalysts for methanol electro-oxidation activity. Using these two descriptors, we illustrate that a good methanol electro-oxidation catalyst must have three key properties: (1) the ability to activate methanol, (2) the ability to activate water, and (3) the ability to react off surface intermediates (such as CO* and OH*). Based on this analysis, an alloy catalyst made up of Cu and Pt should have a synergistic effect facilitating the activity towards methanol electro-oxidation. Using these two reactivity descriptors, a surface PtCu 3 alloy is proposed to have the best catalytic properties of the Pt-Cu model catalysts tested, similar to those of a Pt-Ru bulk alloy. To validate the model, experiments on a Pt(111) surface modified with different amounts of Cu adatoms are performed. Adding Cu to a Pt(111) surface increases the methanol oxidation current by more than a factor of three, supporting our theoretical predictions for improved electrocatalysts.

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Novel insights in the synthesis–structure–catalytic activity relationships of nanostructured trimetallic Pt–Rh–Sn electrocatalysts for the electrocatalytic oxidation of ethanol are reported. In particular, we identify a novel single-phase Rh-doped Pt–Sn Niggliite mineral phase as the source of catalytically active sites for ethanol oxidation; we discuss its morphology, composition, chemical surface state, and the detailed 3D atomic arrangement using high-energy (HE-XRD), atomic pair distribution function (PDF) analysis, and X-ray photoelectron spectroscopy (XPS). The intrinsic ethanol oxidation activity of the active Niggliite phase exceeded those of earlier reports, lending support to the notion that the atomic-scale neighborhood of Pt, Rh, and Sn is conducive to the emergence of active surface catalytic sites under reaction conditions. In situ mechanistic Fourier transform infrared (in situ FTIR) analysis confirms an active 12 electron oxidation reaction channel to CO₂ at electrode potentials as low as 450 mV/RHE, demonstrating the favorable efficiency of the PtRhSn Niggliite phase for C–C bond splitting

Hydrogen oxidation kinetics without and with trace amounts of CO in H 2 were investigated for carbon-supported catalysts consisting of Pt submonolayers on Ru nanoparticles prepared by spontaneous deposition and commercial Pt, Ru, and PtRu alloy catalysts. Thin catalyst layers were deposited onto a glassy carbon rotating disk electrode without using Nafion film to stabilize them. Nonlinear fittings of the entire polarization curves at several rotation rates were used to determine the exchange current, the Tafel slope, and the Levich slope. To ensure full utilization of the catalyst, the mass-specific activity was determined by finding the minimum Pt loading needed to have all three kinetic parameters close to those found for a polycrystalline Pt electrode. For the PtRu 20 , PtRu 10 , and PtRu 5 samples prepared by spontaneous deposition of 1/9 to 4/9 monolayer Pt on Ru, the minimum loading is 5 nmol/cm 2 (1 g Pt /cm 2). This is only one-third of that for Pt or PtRu ͑E-TEK͒ catalysts and only double the atomic density of a Pt͑111͒ surface, indicating that the high activity of Pt metal for hydrogen oxidation is retained when the atomic assemblies are reduced to submonolayer level on Ru. The enhanced CO tolerance was studied at low potentials by correlating the loss of the activity in 0.1% CO/H 2 with the CO coverage on Pt and Ru sites.