Vibrational Recognition of Adsorption Sites for Carbon Monoxide on Platinum and Platinum-Ruthenium Surfaces

We have studied the vibrational properties of CO adsorbed on platinum and platinum-ruthenium surfaces using density-functional perturbation theory within the Perdew-Burke-Ernzerhof generalized-gradient approximation. The calculated C-O stretching frequencies are found to be in excellent agreement with spectroscopic measurements. The frequency shifts that take place when the surface is covered with ruthenium monolayers are also correctly predicted. This agreement for both shifts and absolute vibrational frequencies is made more remarkable by the frequent failure of local and semilocal exchange-correlation functionals in predicting the stability of the different adsorption sites for CO on transition metal surfaces. We have investigated the chemical origin of the C-O frequency shifts introducing an orbital-resolved analysis of the force and frequency density of states, and assessed the effect of donation and backdonation on the CO vibrational frequency using a GGA + molecular U approach. These findings rationalize and establish the accuracy of density-functional calculations in predicting absolute vibrational frequencies, notwithstanding the failure in determining relative adsorption energies, in the strong chemisorption regime.Comment: 21 pages, 9 figure

Catalytic Nanoparticles for DMFC and DFAFC: Reaction Rates, Local Densities of States, and Oxygen Shuttling Pathways

The object of this project has been to combine novel synthetic methods to produce much more active anode catalysts for fuel cells, and the use of spectroscopy to develop a molecular-level understanding of chemical physics principles of the fuel cell catalyst operation. We have made tremendous recent progress as evidenced by our 25 journal articles and 6 patents listed in Section 3.7 page 7. We have developed the most active catalysts for Direct Formic Acid Fuel Cells and discovered a correlation between spectroscopy (Pd 3d binding energy) and performance. We have observed the largest effect of particle size on fuel cell performance found to date where 3 nm palladium particles give an order of magnitude higher steady state current per exposed metal atom than 6 nm particles. We discovered a series of as yet unexplained support effects where Pd on V{sub 2}O{sub 5} gives an order of magnitude more current than pure palladium. We have verified the results in operating fuel cells and are closing in on the DOE targets of anode catalysts for portable fuel cells (costing less than $1/watt). Table 1 page 2 summarizes where these findings are described in the proposal for the reviewers reference. Generally, our approach will be to correlate spectroscopy (XPS, NMR, and STM) to kinetic (CA, CV and VI) measurements as summarized. We already have noticed a correlation between XPS binding energy and activity. We propose expanding this correlation to see if we can explain the effects of particle size and support on performance. We also propose expanding the effort using in situ STM,and EC-NMR to better characterize the changes in the catalysts as we change the support so that we can develop a fundamental understanding for catalyst design. As a second thrust of the work, we will continue of our efforts to develop novel synthetic methods to prepare electrochemical catalysts. In particular we will extend the spontaneous deposition methodology developed in previous grant cycles to the production of metal coated conducting oxide supports so we can turn the Pd on/metal oxide films that show high activity into practical catalysts

Underpotential deposition of Cu on Au(111) in sulfate-containing electrolytes: a theoretical and experimental study

We study the underpotential deposition of Cu on single-crystal Au(111) electrodes in sulfate-containing electrolytes by a combination of computational statistical-mechanics based lattice-gas modeling and experiments. The experimental methods are in situ cyclic voltammetry and coulometry and ex situ Auger electron spectroscopy and low-energy electron diffraction. The experimentally obtained voltammetric current and charge densities and adsorbate coverages are compared with the predictions of a two-component lattice-gas model for the coadsorption of Cu and sulfate. This model includes effective, lateral interactions out to fourth-nearest neighbors. Using group-theoretical ground-state calculations and Monte Carlo simulations, we estimate effective electrovalences and lateral adsorbate--adsorbate interactions so as to obtain overall agreement with experiments, including both our own and those of other groups. In agreement with earlier work, we find a mixed R3xR3 phase consisting of 2/3 monolayer Cu and 1/3 monolayer sulfate at intermediate electrode potentials, delimited by phase transitions at both higher and lower potentials. Our approach provides estimates of the effective electrovalences and lateral interaction energies, which cannot yet be calculated by first-principles methods.Comment: 36 pages, 14 Postscript figures are in uufiles for

Coverage dependence of co surface diffusion on pt nanoparticles: An ec-nmr study

We have studied the effects of CO surface coverage on the diffusion rates of CO adsorbed on commercial Pt-black in sulfuric acid media by using 13 C electrochemical nuclear magnetic resonance (EC-NMR) spectroscopy in the temperature range 253-293 K. The temperature range chosen for these measurements was such that the electrolyte is in a liquid-like and liquid environment. For CO coverage between θ ) 1.0 and 0.36, the CO diffusion coefficients (D CO ) follow a typical Arrhenius behavior and both the activation energies (E d ) as well as the pre-exponential factors (D CO 0 ) show CO coverage dependence. For partially CO covered samples, E d decreases linearly with increasing CO coverage, indicating that the repulsive CO-CO interactions exert a stronger influence on the coverage dependence of the activation energy than does the nature of the CO adlayer structure. On the other hand, D CO 0 shows an exponential decrease with increasing CO coverage, consistent with the free site hopping model [Gomer, R. Rep. Prog. Phys. 1990, 53, 917] as the major mechanism for surface diffusion of CO at partial coverages, unlike the situation found with a fully CO covered surface [Kobayashi et al., J. Am. Chem. Soc., 2005, 127, 14164]. Overall, these results are of interest since they improve our understanding of the surface dynamics of molecules at electrochemical interfaces, and may help facilitate better control of fuel cell reactions in which the presence of surface CO plays a crucial role in controlling electrocatalytic reaction rates

Fat and Sugar—A Dangerous Duet. A Comparative Review on Metabolic Remodeling in Rodent Models of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a common disease in Western society and ranges from steatosis to steatohepatitis to end-stage liver disease such as cirrhosis and hepatocellular carcinoma. The molecular mechanisms that are involved in the progression of steatosis to more severe liver damage in patients are not fully understood. A deeper investigation of NAFLD pathogenesis is possible due to the many different animal models developed recently. In this review, we present a comparative overview of the most common dietary NAFLD rodent models with respect to their metabolic phenotype and morphological manifestation. Moreover, we describe similarities and controversies concerning the effect of NAFLD-inducing diets on mitochondria as well as mitochondria-derived oxidative stress in the progression of NAFLD