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We report the first combined application of solid-state electrochemical NMR (EC NMR), cyclic voltammetry (CV), and potentiostatic current generation to investigate the topic of the ruthenium promotion of MeOH electro-oxidation over nanoscale platinum catalysts. The CV and EC NMR results give evidence for two types of CO: CO on essentially pure Pt and CO on Pt/Ru islands. There is no NMR evidence for rapid exchange between the two CO populations. CO molecules on the primarily Pt domains behave much like CO on pure Pt, with there being little effect of Ru on the Knight shift or on Korringa relaxation. In sharp contrast, COs on Pt/Ru have highly shifted (13)C NMR resonances, much weaker Korringa relaxation, and, at higher temperatures, they undergo thermally activated surface diffusion. For CO on Pt, the correlation observed between the 2pi* Fermi level local density of states and the steady-state current suggests a role for Ru in weakening the Pt-CO bond, thereby increasing the CO oxidation rate (current). The combined EC NMR/electrochemistry approach thus provides new insights into the promotion of CO tolerance in Pt/Ru fuel cell catalysts, in addition to providing a novel route to investigating promotion in heterogeneous catalysis in general.

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A modified radioactive labeling method was used to study bisulfate and sulfate anion adsorption on a Pt(111) electrode from aqueous HClO 4 /H 2 SO 4 media. The highest surface concentration of the anion is 3.2 × 10 14 ions/cm 2 , which corresponds to a coverage (packing density) of 0.21 ( 0.01monolayer. Overall, the coverage data confirm our previous results reported in J. Electroanal. Chem. 1993, 348, 451. We found fast adsorption kinetics and a semilogarithmic anion adsorption isotherm. In the "butterfly" electrode potential range [that is, in the range where anomalous anion adsorption was found on the Pt(111) electrode (Clavilier, J. J. Electroanal. Chem. 1980, 107, 211)], the charge on the anion and, consistently, electrosorption valency vary with the electrode potential, demonstrating progress in bisulfate dissociation to sulfate, with the increase in potential. On the plateau of the surface concentration-electrode potential plot, we conclude that the adsorbate is a partially discharged (or neutralized) sulfate anion, which displays a net charge of -1.7 e. We also conclude that the species coadsorbed with sulfate are predominantly water molecules rather than hydronium cations. A brief review of the theory of anion adsorption on metal surfaces is presented and a model of sulfate-platinum bonding is proposed.

The potential- and coverage-dependent infrared absorption spectroscopy (IRAS) of linearly bound CO on single-phase polycrystalline arc-melted Pt, PtRu(1/1), PtRu(8/2), PtOs(8/2), PtRuOs(8/1/1), PtRuOs(65/25/10), and Ru electrodes in 0.5 M H2SO4 are correlated with the potential-dependent X-ray photoelectron spectroscopy (XPS) of the PtRu(1/1), PtOs(8/2), and PtRuOs(65/25/10) substrates. The CO stretching frequencies decrease as the mole fraction of Pt in the alloy is decreased. The CO oxidation onset on pure Pt at 100.0% CO coverage is 0.5 V vs a reversible hydrogen electrode and shifts negatively as the alloy mole fraction of Pt is reduced. At CO dosing conditions that yield 100% coverage on pure Pt, the CO bandwidths increase with decreasing Pt mole fraction:  on pure Pt the bandwidths increase as the CO coverage is reduced. The effects of CO coverage and bulk alloy composition on the Stark tuning rates (STRs) have been systematically examined on Pt, and a series of binary and ternary alloy surfaces. The XPS data confirm a potential-dependent surface distribution of oxides and no significant surface segregation of the alloying components. The systematic displacement, to lower frequencies, of the linear STRs as the mole fraction of Pt is reduced suggests no significant island formation on the arc-melted alloy surfaces. The XPS data also suggest that the alloying metals, rather than Pt, are responsible for activation of the water required for methanol oxidation in the direct methanol fuel cell potential window.