Electrocatalysis, single-crystal

Lamy C, Leger JM, Claviher J, Parsons R. 1983. Structural effects in electrocatalysis A comparative study of the oxidation of CO, HCOOH and CH3OH on single crystal Pt electrodes. J Electroanal Chem 150 71-77. 

Clues for the Molecular-Level Understanding of Electrocatalysis on Single-Crystal Platinum Surfaces Modified by p-Block Adatoms... 

It has been often stressed that low eoordinated atoms (defeets, steps, and kink sites) play an important role in surfaee ehemistry. The existenee of dangling bonds makes steps and kinks espeeially reaetive, favoring the adsorption of intermediate species on these sites. Moreover, smdies of single-crystal surfaces with a eomplex geometry have been demonstrated very valuable to link the gap between fundamental studies of the basal planes [Pt( 111), Pt( 100), and Pt(l 10)] and applied studies of nanoparticle eatalysts and polycrystalline materials. In this context, it is relevant to mention results obtained with adatom-modified Pt stepped surfaces, prior to discussing the effect of adatom modification on electrocatalysis. 

Gasteiger HA, Markovic NM, Ross PN Jr. 1996. Structural effects in electrocatalysis Electrooxidation of carbon monoxide on Pt3Sn single-crystal surfaces. Catal Lett 36 1-8. 

Friedrich KA, Geyzers KP, Dickinson AJ, Stiimning U. 2002. Fundamental aspects in electrocatalysis From the reactivity of single-crystals to fuel cell electrocatalysis. J Electroanal Chem 524/525 261-272. 

Adzic RR, Tripkovic AV, Markovic NM. 1983. Structural effects in electrocatalysis oxidation of formic acid and oxygen reduction on single-crystal electrodes and the effects of foreign metal adatoms. J Electroanal Chem 150 79-88. 

Markovic NM, Adzic RR, Cahan BD, Yeager EB. 1994. Structural effects in electrocatalysis— Oxygen reduction on platinum low-index single-crystal surfaces in perchloric-acid solutions. J Electroanal Chem 377 249-259. 

Adzic RR, Markovic NM, Vesovic, VB. 1984. Structural effects in electrocatalysis Oxygen reduction on the Au(lOO) single crystal electrode. J Electroanal Chem 165 105-120. 

Alvarez-Rizatti M, Jiittner K. 1983. Electrocatalysis of oxygen reduction by UPD of lead on gold single-crystal surfaces. J Electroanal Chem 144 351-363. 

As mentioned in Section 5.1, adsorption of components of the electrolysed solution plays an essential role in electrode processes. Adsorption of reagents or products or of the intermediates of the electrode reaction or other components of the solution that do not participate directly in the electrode reaction can sometimes lead to acceleration of the electrode reaction or to a change in its mechanism. This phenomenon is termed electrocatalysis. It is typical of electrocatalytic electrode reactions that they depend strongly on the electrode material, on the composition of the electrode-solution interphase, and, in the case of single-crystal electrodes, on the crystallographic index of the face in contact with the solution. 

In the following section, we focus on imaging single-crystal electrode surfaces that are of relevance to electrocatalysis. We will first deal with flat, defect-free terraces as well as with more real surfaces with monoatomic high steps as the most common active sites. We will then explore various strategies for nano structuring surfaces, for example, by repetitive oxidation-reduction cycles (ORCs). 

A remarkable progress has been made in the last several years in electrocatalysis on single crystal surfaces. This parallels the progress in surface science and it has been partly stimulated by developments in that field, mostly regarding the preparation and characterization of surfaces. New advances in preparation of surfaces outside of high vacuum, achieved in electrocatalytic studies, also helped this trend. 

Identification of Peaks for Hydrogen Adsorption on the Disordered Low Index Planes. Besides the major objective for studying electrocatalysis on single crystal stepped surfaces mentioned above, these studies offer a wealth of information on the behaviour of polycrystalline surfaces, of preferentially oriented surfaces and, as we suggested recently (12), of disordered low-index surface. 

Electrodes modified by underpotential deposition of metal were subjected as electrocatalysts to reduction of oxygen,oxidation of formic acid, and other processes in which polycrystalline metal substrates were used (see review in Ref. 151). Electrocatalysis of single-crystal electrodes modified by underpotential deposition was also investigated, as reviewed by Ad2iC. ... 

Electrocatalysis is manifested when it is found that the electrochemical rate constant, for an electrode process, standardized with respect to some reference potential (often the thermodynamic reversible potential for the same process) depends on the chemical nature of the electrode metal, the physical state of the electrode surface, the crystal orientation of single-crystal surfaces, or, for example, alloying effects. Also, the reaction mechanism and selectivity 4) may be found to be dependent on the above factors in special cases, for a given reactant, even the reaction pathway [4), for instance, in electrochemical reduction of ketones or alkyl halides, or electrochemical oxidation of aliphatic acids (the Kolbe and Hofer-Moest reactions), may depend on those factors. 

In the case of Pt3Ni(M0 surfaces UPS results (Fig. 3.2) show that the d-band density of states (DOS) shifts from -2.70 eV on Pt3Ni(110) to -3.10 eV on Pt3Ni(lll) to -3.14 eV on Pt3Ni(100). Furthermore, the DOS of the alloy surfaces are quite different from corresponding pure Pt single crystals the d-band center is downshifted by approximately 0.16, 0.24, and 0.33 eV, respectively. We have had six different single-crystal systems that could be studied specifically for the elusive electronic effect in electrocatalysis. 

The book is divided into six parts theory of nanoparticle catalysis and electrocatalysis model systems from single crystals to nanoparticles synthetic approaches in nanoparticle catalysis and electrocatalysis advanced experimental concepts particle size, support, and promotional effects and advanced electro-catalytic materials. This facilitates access to the general reader s interests. Each chapter begins with a summary and a table of contents to provide an overview of its scope. 

STM is ideally suited to characterize the morphology of nanostructures grown on single-crystal substrates. The self-organization of nanoclusters with a preferential size distribution on semiconductor surfaces is being exploited to form quantum dots, and a huge number of studies in this technologically important field have been conducted. Here, however, we provide two examples that relate to catalysis and electrocatalysis. 

Electrocatalysis at Single-Crystal Platinum Alloy Surfaces... 

ELECTROCATALYSIS AT SINGLE-CRYSTAL PLATINUM ALLOY SURFACES... 

The bond strength measured or estimated at a constant temperature or at a specified facet of single-crystal planes are, of cause, important factors in the discussion of electrocatalysis. But, if they are obtained under different conditions from the practical ones, the conclusion might not be correct. The author believes that the general understanding on the size effect still needs further experimental and theoretical studies. Particularly careful attention should be paid to the operation temperature, the coagulation of nanoparticles during the experiment, or the territory. Of course, evaluation on the stability of such small particles is essential in the practical application. 

P. N. Ross Jr, Oxygen reduction reaction on smooth single crystal electrodes, in Handbook of Fuel Cells, Electrocatalysis, John Wiley and Sons, Chichester, 2003, Vol. 2. 

Korzeniewski, C. (2006) Recent advances in in-situ infrared spectroscopy and applications in single-crystal electrochemistry and electrocatalysis, in Diffraction and Spectroscopic Methods in Electrochemistry (eds R.C. Alkire, D.M. Kolb, J. Lipkowski, and P.N. Ross), Wiley-VCH Verlag GmbH, Weinheim, pp. 233-268. 

The specific catalytic properties of polyciystalline and single crystal surfaces have prompted extensive research on their oxidation in electrochemical- and gas- pliase environments. Recent developments in fuel cell technology have renewed efforts to improve Pt-Ru electrocatalysis for both reformate hydrogen- and methanol-oxidation. In the following Section, we discuss the oxidation of single crystal surfaces in both UHV- and electro-chcmical-cnvi ronments. 

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