Electrochemical formation

PH3 is formed by cathodic reduction of white phosphorus under nitrogen. Polarographic investigations (mercury drop electrode) show that in protic media (methanol or ethanol solution containing benzene) the irreversible cathode reaction 

A black phosphorus electrode [7, 30] has a low hydrogen overvoltage, and electrolysis in aqueous solution is accompanied by reduction of the cathode material with formation of phosphane. The largest PH3 yield of 27.5% (calculated from the loss of the electrode weight) at 12.5% current efficiency was obtained in 1M K2HPO4 (pH 7.5) at a current density of 0.07 to 0.09 A/cm2 and at 20 C. Altering the pH to either the acidic or basic side reduces the PH3 yield. An increase in catholyte temperature from 20 to 55 0 lowers the PH3 yield by a factor of 5 to 6. Decreasing the current density also lowers the current efficiency [30]. 

Cathodic polarization of /7-type InP single crystals in 1N H2SO4 leads to phosphane and metallic indium [31] according to InP + 3H+ + 3e PH3 + In. In IN KOH or IN KF, formation of PH3 and indium is only observed at current densities 10 A/cm. Anodic dissolution of p-InP in KOH solution yields PH3, probably by disproportionation of the intermediately formed H3PO3. Phosphane also forms in acidic (1N H2SO4,1N NH4F HF, 1N HF) or neutral electrolytes (0.8N KF, IN NH4F) [31]. 

Phosphinic acid, H3PO2, or phosphonic acid, H3PO3, can be reduced at zinc, mercury, or lead cathodes (3 to 6 V, 1 to 11 mA/cm ) to give PH3 [32]. 

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In most cases, the impregnation process is followed by an electrochemical formation where the plaques are assembled into large temporary cells filled with 20—30% sodium hydroxide solution, subjected to 1—3 charge—discharge cycles, and subsequentiy washed and dried. This eliminates nitrates and poorly adherent particles. It also increases the effective surface area of the active materials. 

Figure 6. Simplified scheme showing the stage formation during electrochemical formation of lithiated graphite. Left schematic galvanosta-tic curve. Right schematic voltam-metric curve. Prepared with data from 192, 100, 104, 105, 110], For a more detailed discussion, see text.

Furthermore, the molecular size of the Li+ -solvating solvents may affect the tendency for solvent co-intercalation. Crown ethers [19, 152-154, 196, 197] and other bulky electrolyte additives [196] are assumed to coordinate Li+ ions in solution in such a way that solvent co-intercalation is suppressed. The electrochemical formation of binary lithiated graphites Li tC6 was also reported for the reduction... 

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

T. Chao, K.J. Walsh, and P.S. Fedkiw, Cyclic voltammetric study of the electrochemical formation of platinum oxide in a Pt/yttria-stabilized zirconia cell, Solid State Ionics 47, 277-285 (1991). 

Works on the electrochemical formation of copper sulfide have been reported mainly in connection with the fabrication of CujS/CdS junctions for solar cells [159-161]. 

Bouroushian M, Kosanovic T, Loizos Z, Spyrellis N (2002) Electrochemical formation of ZnSe from acidic aqueous solutions. J Solid State Electrochem 6 272-278... 

Bouroushian M, Kosanovic T (2006) Electrochemical formation and composition analysis of ZnxCdi-xSe sohd solutions. J Sohd State Electrochem 10 223-229... 

Lukinskas A, Jasulaitiene V, Lukinskas P, Savickaja I, Kahnauskas P (2006) Electrochemical formation of nanometric layers of tin selenides on Ti surface. Electrochim Acta 51 6171-6178... 

Alanyahoglu M, Demir U, Shannon C (2004) Electrochemical formation of Se atomic layers on Au(lll) surfaces the role of adsorbed selenate and selenite. J Electroanal Chem 561 21-27... 

In the past it had been a popular belief that the electrochemical reduction of any inorganic or organic substance involves the primary electrochemical formation of a special, active form of hydrogen in the nascent state (in statu nascendi) and subsequent chemical reaction of this hydrogen with the substrate. However, for many reduction reactions a mechanism of direct electron transfer from the electrode to the substrate could be demonstrated. It is only in individual cases involving electrodes with superior hydrogen adsorption that the mechanism above with an intermediate formation of adsorbed atomic hydrogen is possible. 

The main idea of a lattice model is to assume that atomic or molecular entities constituting the system occupy well-defined lattice sites in space. This method is sometimes employed in simulations with the grand canonical ensemble for the simulation of surface electrochemical proceses. The Hamiltonians H of the lattice gas for one and two adsorbed species from which the ttansition probabilities 11 can be calculated have been discussed by Brown et al. (1999). We discuss in some detail MC lattice model simulations applied to the electrochemical double layer and electrochemical formation and growth two-dimensional phases not addressed in the latter review. MC lattice models have also been applied recently to the study the electrox-idation of CO on metals and alloys (Koper et al., 1999), but for reasons of space we do not discuss this topic here. 

Electrochemical oscillation during the Cu-Sn alloy electrodeposition reaction was first reported by Survila et al. [33]. They found the oscillation in the course of studies of the electrochemical formation of Cu-Sn alloy from an acidic solution containing a hydrosoluble polymer (Laprol 2402C) as a brightening agent, though the mechanism of the oscillatory instability was not studied. We also studied the oscillation system and revealed that a layered nanostructure is formed in synchronization with the oscillation in a self-organizational manner [25, 26]. 

Very recently, a sandwich assay for prostatic acid phosphatase antigen was carried out using two cascaded enzyme reactions to provide amplification of the immunochemical event. In one format, an optical readout was used whereby a forma-zan dye was generated by reaction of a dye precursor and NADH generated from the second enzyme cycle. In the electrochemical format, the NADH generated in the second enzyme cycle was used to reduce Fe(CN) to FeCCN) " which was then detected amperometrically. While the use of Fe(CN) in ECIA has appeared in the... 

X-ray photoelectron spectroscopy (XPS) of electrodes was first applied to the oxidation of noble metal electrodes. Kim and Winograd investigated in 1971 the electrochemical formation of anodic oxides on Pt [10] and later on Au electrodes [60]. The electrochemical parameters of oxide formation on these noble metal electrodes were well characterized and enabled a direct correlation between ex situ XPS and in situ electrochemical analysis. 

CA in which many filled cells execute a random walk but never interact with one another, cannot give rise to stable pattern formation since the cells will move at random forever. However, if cells can interact when they meet, so that one diffusing cell is allowed to stick to another, stable structures can be created. These structures illustrate the modeling of diffusion-limited aggregation (DLA), which is of interest in studies of crystal formation, precipitation, and the electrochemical formation of solids. 

Dehalogenating reduction Salt elimination Disproportionation Electrochemical formation Dehydrogenative catalytic coupling... 

There have been a number of studies directed toward the electrochemical formation of CuInSe2, CIS, over the last 17 years [40, 71, 193-203], Several electrodeposition methodologies have been used, including codeposition and multiple two stage methodologies. The impetus has been the excellent photovoltaic properties of CIS. 

Wade, T. L. Vaidyanathan, R. Happek, U. Stickney, J. L. 2001. Electrochemical formation of a III-V compound semiconductor superlattice InAs/InSb. J. Electroanal. Chem. 500 322-332. 

Electrochemical formation of allylnickel species and their addition to aldehydes were reported. a Allylnickel(i) species generated via one-electron reduction of 3-allylnickel(ii) intermediates are considered as active nucleophilic species. 

Preparative electrochemical reduction of aryltrimethylsilanes in methyl-amine in the presence of LiCl gives the Birch-type products, 1,4-cyclohexan-dienes (Scheme 34) [6], A mechanism involving the electrochemical formation of lithium metal which chemically reduces the substrate has been suggested. The hydrogen atom is introduced on the carbon adjacent to the silicon preferentially. This regioselectivity is consistent with the spin density of the anion radical determined by ESR spectroscopy (Sect. 2.2.1). 

The most common evaluation of aromaticity via energetic criteria is done using calculations either a type of isodesmic reaction (34) or comparison of two isomers that differ only through the aromaticity of one (3). We were interested in the possibility of evaluating stability experimentally and the electrochemical formation of dications such as 8 was attractive. In this approach, the redox potential for formation of the dication would be compared to the redox potential for formation of dications which could not be antiaromatic. If 8 was antiaromatic, its redox potential should be larger and more positive than that of the reference system. This approach was applied to the evaluation of the antiaromaticity of 9... 

To understand the electrochemical behavior of silicon, however, the formation and the properties of anodic oxides are important The formation of an anodic oxide on silicon electrodes in HF and HF-free electrolytes will therefore be discussed in detail in this chapter. The formation of native and chemical oxides is closely related to the electrochemical formation process and will be reviewed briefly. The anodic oxidation of porous silicon layers is closely related to the morphology and the luminescent properties of this material and is therefore discussed in Section 7.6. 

According to the macropore formation mechanisms, as discussed in Section 9.1, the pore wall thickness of PS films formed on p-type substrates is always less than twice the SCR width. The conductivity of such a macroporous silicon film is therefore sensitive to the width of the surface depletion layer, which itself depends on the type and density of the surface charges present. For n-type substrates the pore spacing may become much more than twice the SCR width. In the latter case and for macro PS films that have been heavily doped after electrochemical formation, the effect of the surface depletion layer becomes negligible and the conductivity is determined by the geometry of the sample only. The conductivity parallel to the pores is then the bulk conductivity of the substrate times 1 -p, where p is the porosity. 

The electrochemical formation of porous structures is also observed for III—V semiconductors like GaP [Anl, Erl], GaN [Pe7, Myl], InP [Ki2, Kol6, Tal3, LalO] or GaAs [Be5, Fa4, Scl5]. Structural dimensions in the macroporous regime are observed for n-type GaAs of moderate doping (1017 cm4) anodized in KOH in the... 

Fig. 5.15 (a) Schematic of a standard three-electrode cell with (b) general procedure for the electrochemical formation of NPs on nanocarbon electrodes. 

Rust is a hydrated iron(III) oxide, Fe203 XH2O. The electrochemical formation of rust occurs in small galvanic cells on the surface of a piece of iron, as shown in Figure 11.28. In each small cell, iron acts as the anode. The cathode is inert, and may be an impurity that exists in the iron or is deposited onto it. For example, the cathode could be a piece of soot that has been deposited onto the iron surface from the air. 

Magnesium alloys are very lightweight, and are being used in the aerospace industry. Because they are very reactive, these alloys need to be protected from corrosion. Dr. Birss holds a patent on a new approach to the electrochemical formation of protective oxide films on magnesium alloys. Dr. Birss also works on developing new catalysts for fuel cells, and studies the factors that lead to the breakdown of fuel cells. 

One of the major benefits of the ECALE methodology is that it breaks compound electrodeposition into a series of identical cycles and each cycle into a set of individual steps. Each step is examined and optimized independently, resulting in increased control over deposit structure, composition, and morphology. Better understanding of the individual steps in the deposition mechanism should allow the electrochemical formation of high-quality thin films of compound semiconductors. 

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