Electrochemically induced

One aspect that reflects the electronic configuration of fullerenes relates to the electrochemically induced reduction and oxidation processes in solution. In good agreement with the tlireefold degenerate LUMO, the redox chemistry of [60]fullerene, investigated primarily with cyclic voltammetry and Osteryoung square wave voltammetry, unravels six reversible, one-electron reduction steps with potentials that are equally separated from each other. The separation between any two successive reduction steps is -450 50 mV. The low reduction potential (only -0.44 V versus SCE) of the process, that corresponds to the generation of the rt-radical anion 131,109,110,111 and 1121, deserves special attention. 

Elofson and Gadallah (1971) showed that electrochemically induced Pschorr and related reactions give almost quantitative yields in several cases. 

Thus, as will be shown in this book, the effect of electrochemical promotion (EP), or NEMCA, or in situ controlled promotion (ICP), is due to an electrochemically induced and controlled migration (backspillover) of ions from the solid electrolyte onto the gas-exposed, that is, catalytically active, surface of metal electrodes. It is these ions which, accompanied by their compensating (screening) charge in the metal, form an effective electrochemical double layer on the gas-exposed catalyst surface (Fig. 1.5), change its work function and affect the catalytic phenomena taking place there in a very pronounced, reversible, and controlled manner. 

J. Poppe, A. Schaak, J. Janek, and R. Imbihl, Electrochemically Induced Surface Changes on Microstructured Pt Films on a solid YSZ Electrolyte, Ber. Buns. Phys. 

The first indication that NEMCA is due to electrochemically induced ion backspillover from solid electrolytes to catalyst surfaces came together with the very first reports of NEMCA Upon constant current application, i.e. during a galvanostatic transient, e.g. Fig. 5.2, the catalytic rate does not reach instantaneously its new electrochemically promoted value, but increases slowly and approaches asymptotically this new value over a time period which can vary from many seconds to a few hours, but is typically on the order of several minutes (Figure 5.2, galvanostatic transients of Chapters 4 and 8.)... 

X-ray photoelectron spectroscopic (XPS) studies of Ag63,64 and Pt6,56-62 films deposited on YSZ under positive current application conditions have confirmed the proposition2-4 that NEMCA with oxide ion conducting solid electrolytes is due to an electrochemically induced and controlled backspillover of oxide ions on the catalyst surface. 

Electrochemically induced and controlled Na backspillover is the origin of electrochemical promotion on metals interfaced with p"-Al203 solid electrolytes. 

The electrochemically induced creation of the Pt(lll)-(12xl2)-Na adlayer, manifest by STM at low Na coverages, is strongly corroborated by the corresponding catalyst potential Uwr and work function O response to galvanostatic transients in electrochemical promotion experiments utilizing polycrystalline Pt films exposed to air and deposited on (T -AbCb. 3637 Early exploratory STM studies had shown that the surface of these films is largely composed of low Miller index Pt(lll) planes.5... 

Figure 11.7 confirms that electrochemically induced and controlled O2 backspillover from the support to the metal film surface is the promoting mechanism both in the case of YSZ (Fig. 11.7a) and in Ti02 (Fig. 11.7b). These figures show the Ols spectrum of the Pt film deposited on YSZ and on TiC>2, first under open-circuit conditions (Fig. 11.7aC, 11.7bA) and then under positive current and potential application (Fig. 11.7aB, 11.7bB). Figures 11.7aC and 11.7bC show the difference spectra. In both cases, XPS clearly shows the presence of the O2 double layer, even under open-circuit conditions (Figs. 11.7aA, 11.7bA) and also clearly confirms the electrochemically controlled backspillover of O2 from the YSZ orTi02 support onto the catalyst surface. Note that the binding energy of the backspillover O species is in both cases near 529 eV, which confirms its strongly anionic (probably O2 ) state.31,32...

The electrochemically induced change in work function AO (eq. (1 1.6)) is related to the coverage 0j of the promoting species (e.g. O5 ) on the catalyst surface via the Helmholz equation ... 

It appears to be the electrochemically induced formation or destruction of surface oxides. 

Reactive radical ions, cations and anions are frequent intermediates in organic electrode reactions and they can serve as polymerization initiators, e.g. for vinylic polymerization. The idea of electrochemically induced polymerization of monomers has been occasionally pursued and the principle has in fact been demonstrated for a number of polymers But it appears that apart from special cases with anionic initiation the heterogeneous initiation is unfavorable and thus not competitive for the production of bulk polymers A further adverse effect is the coating of electrodes... 

Yamaguchi K, Yoshida T, Sugiura T, Minoura H (1998) A Novel approach for CdS thin-film deposition electrochemically induced atom-by-atom growth of CdS thin films from acidic chemical bath. J Phys Chem B 102 9677-9686... 

In the ruthenium frA-bipyridine system, an orange emission at 610 nm arises when the excited stated [Ru(bpy)32+] decays to the ground state. Ru(bpy)32+ is the stable species in the solution and the reactive species—Ru(bpy)33+—can be generated from Ru(bpy)32+ on the electrode surface by oxidation at about +1.3 V. Adding Ru(bpy)32+ to the electrolyte and using an end-column electrode to convert the Ru(bpy)32+ into the active Ru(bpy)33+ form allow a simple and sensitive ECL detection mode. The reaction lends itself to electrochemical control due to the electrochemically induced interconversion of the key oxidation states ... 

Ozntiltier, T. Erdogan, I. Demir, U. 2006. Electrochemically induced atom-byatom growth of ZnS thin films A new approach for ZnS co-deposition. Langmuir 22 4415 419. 

Pschorr s synthesis of phenanthrene (1893) in five steps with the essential dediazoniation and ring closure of 2-diazonio-a-phenylcinnamic acid giving, on addition of copper powder, phenanthrene-9-carboxylic acid, is today still the highest yielding one of all the reactions discussed in this section, Pschorr was able to get 93% yield, and today electrochemically induced Pschorr and related reactions141 give almost quantitative yields in several cases. 

It should be emphasized that the majority of electrochemically induced redox processes in inorganic chemistry proceed (or are assumed to proceed) through outer-sphere mechanisms. 

The first is the catalytic efficiency of the electrocatalytic process, which in the case of the electrochemically induced reaction is called coulombic efficiency. It is determined by the number of product molecules formed per electron consumed. In our example, the consumption of 0.02 electrons per molecule indicates a coulombic efficiency of 50 molecules produced per electron consumed. 

An example of electrochemically induced trans— cis isomerization is given by the macrocyclic complex rra j-[MnnI(cyclam)Cl2]+, the molecular structure of which is illustrated in Figure 9.9... 

Under similar reaction conditions, some ketones such as (53) gave products via an electrochemically induced Favorskii rearrangement (Eq. 10) [89, 90]. 

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