EC-NMR Under Potential Control

We found that the C spectra of adsorbed CO and CN on R nanoparticle electrodes depend on the value of the electrode potential. For EC-NMR under direct potential control, again, a few hundred milligrams of powdered Pt (fuel cell grade platinum black) was used as the working electrode in a three-electrode NMR electrochemical cell. The cell was positioned inside the NMR coil with the leads connected to an external potentiostat. The NMR electrochemical cell also incorporates 

In the field of FTIR of electrode surfaces, it is well known that the C-0 vibrational frequency, Vco. decreases when the electrode potential becomes more negative. This variation of the vibrational frequency with electrode potential is referred to as the vibrational Stark effect. The Stark effect can now be considered in the context of our NMR 

Correlation Between Clean Surface f-LDOS of Metals and the Adsorbate Knight Shift 

the value was 203 20 ppm. These calculated values are in surprisingly good agreement with available experimental data. The standard deviations account for uncertainties due to use of different functionals and basis sets. The clean smface ErLDOS for Pd was estimated based on the changes in magnetic susceptibility of small Pd particles with respect to their bulk value. 

Effect of Surface Charge on the Chemisorption Bond CO Chemisorption on Pd 

Comparison of the NMR Parameters of CO Produced from CO Gas and Methanol Oxidation on a Nanocrystalline Platinum 

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This originates from the changes in Ef-LDOS at the nanocrystalline metal surface and at the adsorbate, induced by electrochemical potential control [142]. A layer model analysis is used to describe the Pt NMR spectrum of nanoscopic materials [144]. It is also possible to correlate the electronegativity of the adsorbates with the Knight shift associated with the Pt nanoparticles [138]. The orientation of adsorbates on metallic substrates under potential control conditions has also been explored [122, 131]. Tong and co-workers have recently demonstrated the use of EC-NMR to investigate the electronic environment of the core of MPCs [145]. 

EC-NMR has made considerable progress during the past few years. It is now possible to investigate in detail metal-liquid interfaces under potential control, to deduce electronic properties of electrodes (platinum) and of adsorbates (CO), and to study the surface diffusion of adsorbates. The method can also provide information on the dispersion of commercial carbon-supported platinum fuel cell electrocatalysts and on electrochem-ically generated sintering effects. Such progress has opened up many new research opportunities since we are now in the position to harness the wealth of electronic, Sp-LDOS as well as dynamic and thermodynamic information that can be obtained from NMR experiments. As such, it is to be expected that EC-NMR will continue to thrive and may eventually become a major characterization technique in the field of interfacial electrochemistry. 

Exploring various phenomena at metal/solution interfaces relates directly to heterogeneous catalysis and its applications to fuel cell catalysis. By the late 1980s, electrochemical nuclear magnetic resonance spectroscopy (EC-NMR) was introduced as a new technique for electrochemical smface science. (See also recent reviews and some representative references covering NMR efforts in gas phase surface science. ) It has been demonstrated that electrochemical nuclear magnetic resonance (EC-NMR) is a local surface and bulk nanoparticle probe that combines solid-state, or frequently metal NMR with electrochemistry. Experiments can be performed either under direct in situ potentiostatic control, or with samples prepared in a separate electrochemical cell, where the potential is both known and constant. Among several virtues, EC-NMR provides an electron-density level description of electrochemical interfaces based on the Eermi level local densities of states (Ef-LDOS). Work to date has been predominantly conducted with C and PtNMR, since these nuclei... 

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