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The electron density topology of carbon monoxide (CO) on dry and hydrated platinum is evaluated under the quantum theory of atoms in molecules (QTAIM) and by adsorbate orbital approaches. The impact of water co-adsorbate on the electronic, structural, and vibrational properties of CO on Pt are modelled by periodic density functional theory (DFT). At low CO coverage, increased hydration weakens C–O bonds and strengthens C–Pt bonds, as verified by changes in bond lengths and stretching frequencies. These results are consistent with QTAIM, the 5σ donation-2π* backdonation model, and our extended π-attraction σ-repulsion model (extended π-σ model). This work links changes in the non-zero eigenvalues of the electron density Hessian at QTAIM bond critical points to changes in the π and σ C–O bonds with systematic variation of CO/H2O co-adsorbate scenarios. QTAIM invariably shows bond strengths and lengths as being negatively correlated. For atop CO on hydrated Pt, QTAIM and phenomenological models are consistent with a direct correlation between C–O bond strength and CO coverage. However, DFT modelling in the absence of hydration shows that C–O bond lengths are not negatively correlated to their stretching frequencies, in contrast to the Badger rule: When QTAIM and phenomenological models do not agree, the use of the non-zero eigenvalues of the electron density Hessian as inputs to the phenomenological models, aligns them with QTAIM. The C–O and C–Pt bond strengths of bridge and three-fold bound CO on dry and hydrated platinum are also evaluated by QTAIM and adsorbate orbital analyses. [ABSTRACT FROM AUTHOR]

Laser-activated membrane introduction mass spectrometry (LAMIMS), a high-throughput screening method, evaluates heterogeneous catalysts under realistic reactor conditions. It is a precise, versatile system requiring no moving parts. The catalyst array is supported on carbon paper overlaid upon a silicone rubber membrane configured in a variation of membrane introduction mass spectrometry as introduced by Cooks. The carbon paper serves as a heat-dissipating gas diffusion layer that permits laser heating of catalyst samples far above the decomposition temperature of the polymer membrane that separates the array from the mass spectrometer vacuum chamber. A computer-controlled C[O.sub.2] bar code writing laser is used for fine-tune heating of the catalyst spots above the base temperature of the LAMIMS reactor. The detailed design and performance of LAMIMS is demonstrated on arrays of 'real world' bulk water--gas shift catalysts using natural and isotopically labeled reactor feed streams. A bulk catalyst array spot can be evaluated for activity and selectivity in as little as 1.5 min. All array screening results were confirmed by industrial microreactor evaluations.

Density functional theory (DFT) calculated spectra was used to correlate the operando infrared (IR) spectroscopy, polarization modulated IR spectroscopy (PM-IRRAS) of Pt-Nafion interfaces, and attenuated total reflectance IR spectroscopy of bulk Nafion to understand the Nafion functional group coadsorption responsible for the Stark tuning of [CO.sub.ads] on high surface area fuel cell electrodes. A model of the Nafion-Pt interface with appropriate dihedral and native bond angles which was consistent with experimental and calculated spectra indicated direct adsorption of the C[F.sub.3] and S[O.sub.3.sup.-] functional groups on Pt.

Electron spin resonance (ESR) is used for monitoring the local environment of 2,2,6,6-tetramethyl-4-piperidone N-oxide (Tempone) spin probe in water and methanol mixtures in solution and in [Li.sup.+] ion exchanged Nafion 117 membranes. The probe has displayed significant local ordering in the aqueous phase of Nafion membranes that is diminished with increasing methanol concentration.

The potential-dependent C[O.sub.2] exhaust from the cathode of an operating direct methanol fuel cell (DMFC) is monitored by online electrochemical mass spectrometry (ECMS) with air and with [H.sub.2] at the cathode. Electron spin resonance (ESR) measurements of the rotational diffusion rate of a nitroxide spin probe in Nafion have provided information concerning the effect of the [C.sub.MeOH] on the local state of the polymer.

The in situ X-ray absorption spectroscopy, ex situ X-ray fluorescence and X-ray powder diffraction have helped in the analysis of phase segregated nanostructured PtRu anode catalysts in an operating direct methanol fuel cell. The extended X-ray absorption fine structure analysis has showed that the Ru-O bond lengths are shorter than those reported for Ru-O of ruthenium oxides, indicating that the phases in which the Ru resides in the catalysts are not similar to oxides.

(super 195)Pt NMR spectroscopic and electrochemical measurements are carried out on commercial Pt-Ru alloy nanoparticle samples to investigate the effect of high temperature annealing in different vacuum/gas-phase environments. The results suggest that optimizing the amount of surface Ru by heat treatment at temperatures near 200 degree Celsius, in a hydrogen atmosphere, is utilized to produce Pt-Ru alloy nanoparticles with high methanol oxidation activity.