Electrode potential multiple electron transfer

The difference in - peak potentials observed in -> cyclic voltammetric or - AC voltammetric responses in cyclic and/or higher harmonic forms for an -> analyte in bulk solution or attached to the electrode surface. In the case of corresponding anodic and cathodic peaks, a value of AEp greater than the value predicted for reversible electron transfer may be attributed to quasireversibility of the electron transfer, to uncompensated resistance (see - uncompensated IR drop), and/or to coupled chemical processes [i—iv]. In the case of multiple peaks associated with sequential multiple electron transfers for a single analyte or for several analytes, AEp can also denote the difference in the peak potentials of individual electron-transfer steps. 

Recently, it was reported that loading small amount of platinum onto tungsten(VI) oxide enhances the visible-light photocatalytic activity significantly and this is caused by the catalytic action of platinum to induce multiple-electron transfer to oxygen 44). Reactions of two and four-electron transfer processes are as follows (potential in parentheses is standard electrode potential versus standard hydrogen electrode at pH 0). 

The standard electrode potentials are far more anodic than that of one-electron transfer process, -0.284 V (SHE) and the visible-light photocatalytic activity of platinum-loaded tungsten(VI) oxide could be interpreted by enhanced multiple-electron transfer process by deposited platimun (45), since it is well known that platinum and the other noble metals catalyze such multiple-electron transfer processes. Similar phenomena, cocatalyst promoted visible-light photocatalytic activity, have been reported with palladium 46) and copper oxide (47). Thus, change of reaction process seems beneficial to realize visible-light photocatalytic activity. 

On a glassy carbon electrode, the Tafel slope was observed to be 60 mV/dec in alkaline solutions, and at pH < 10, the Tafel slope was 120 mV/dec. These values are in accordance with the proposed mechanisms. In the case of 120 mV/dec, the first electron transfer is the rate determining step. In the case of 60 mV/dec, the current-potential relationship observed from the multiple-electron transfer process of ORR on carbon electrodes was expressed as Equation 2.27, given by Taylor and Humffray [14, 17] ... 

By tradition, electrochemistry has been considered a branch of physical chemistry devoted to macroscopic models and theories. We measure macroscopic currents, electrodic potentials, consumed charges, conductivities, admittance, etc. All of these take place on a macroscopic scale and are the result of multiple molecular, atomic, or ionic events taking place at the electrode/electrolyte interface. Great efforts are being made by electrochemists to show that in a century where the most brilliant star of physical chemistry has been quantum chemistry, electrodes can be studied at an atomic level and elemental electron transfers measured.1 The problem is that elemental electrochemical steps and their kinetics and structural consequences cannot be extrapolated to macroscopic and industrial events without including the structure of the surface electrode. 

At low light flux, the semiconductor sensitization is constrained to one electron routes, since the valence band hole is annihilated by a single electron transfer. Presumably after decarboxylation the resulting alkyl radical can be reduced to the observed monodecarboxylate more rapidly than it can transfer a second electron to form the alkene. In a conventional electrochemical cell, in contrast, the initially formed radical is held at an electrode poised at the potential of the first oxidation so that two-electron products cannot be avoided and alkene is isolated in fair chemical yield. Other contrasting reactivity can be expected for systems in which the usual electrochemistry follows multiple electron paths. 

A dendrimer consisting of multiple identical and non-interacting redox units, able to reversibly exchange electrons with another molecular substrate or an electrode, can perform as a molecular battery [64, 65]. The redox-active units should exhibit chemically reversible and fast electron transfer processes at easily accessible potential difference and chemical robustness under the working conditions. 

Electrochemical detectors were reported used by 21% of the respondents to the detector survey (47). Electron transfer processes offer highly sensitive and selective methods for detection of solutes. Various techniques have been devised for this measurement process, with the most popular being based on the application of a fixed potential to a solid electrode. Potential pulse techniques, scanning techniques, and multiple electrode techniques have all been employed and can offer certain advantages. Two excellent reviews of electrochemical detection in flowing streams have appeared (59,60), as well as a comprehensive chapter in a series on liquid chromatography (61). 

Interfacial electron transfer at solid-liquid interfaces, photoinduced and/or in the presence of an applied potential bias, as in the case of water oxidation on semiconducting metal oxide electrodes involves, as will be discussed in the next section, multiple electron and proton transfer steps. The energy cost associated with charge transfer across the interface will translate into overpotentials for driving the (photo)electrochemical reactions. This is particularly significant in... 

The typical IL system could be considered as a solvent-free system, in which it can simplify the EIS analysis significantly which spurs its wide use in the characterization of the IL-electrode interface. However, due to low mobility of ions in an IL and multiple molecular interactions present in an IL, more time is needed to reach to a steady state of IL-electrode interface structure and arrangement, when a potential is applied. Furthermore, the electron-transfer process in ILs is different from that in traditional solvents containing electrolytes. Thus, the interfacial structures of IL are more complex than other systems. Even the electrode geometry could affect the EIS results of IL systems. It is noted that the bulk ILs could not be simply described by a resistor (R ) as in classic electrochemical systems. And the electrode double layer in IL electrolyte couldn t be simply depicted as a capacitor. So the Randle equivalent circuit is not sufficient to describe an IL system. Significant efforts have been made to illustrate the properties of diffusion layer and the bulk ILs with equivalent circuits. However, currently there is no general equivalent circuit model to describe the interface of an IL system. 

Faradaic in nature and therefore is different farm Pseudocapacitance usually originates from electrosorption (specific adsorption) processes and related partial electron transfer or surface charging (Section 5-5). On metal oxide "supercapacitor" types of electrodes (such as iridium and ruthenium oxides) possessing several oxidation states, pseudocapacitance originates from potential dependence of multiple oxidation/reduction couples that are active on the surfaces of the materials. Another coiiunon source of pseudocapacitance is charging-discharging of redox-active polymers such as polyaniline and polypyrrole. 

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