Anodic oxidation inert electrodes

In the first group the titrant is generated either directly from a participating or active electrode, or indirectly from an inert or passive electrode, in which case it is necessary to add previously an auxiliary substance that generates the titrant by either cathodic reduction or anodic oxidation the end-point detection is usually potentiometric or amperometric. The following selected examples are illustrative of the first group in non-aqueous media ... 

Direct electrochemical reduction and oxidation treatment of pollution involving a mass-free reagent - the electron - is a very attractive idea, because it is a uniquely clean process, as (1) the reduction and oxidation take place at inert electrodes and (2) there is no need to add chemicals. The techniques of cathodic reduction/anodic oxidation of wastewaters containing dyes are relatively new and have drawn the attention of investigators in Japan, China, USA and Russia [55]. 

Write the oxidation half-reaction, the reduction half-reaction, and the overall cell reaction for each of the following galvanic cells. Identify the anode and the cathode in each case. In part (h), platinum is present as an inert electrode. 

In addition to the above thermodynamic consideration, kinetics also play an important role in determining the anodic stability of these salts. For example, some salts whose decomposition products are polymeric moieties were found to passivate the electrode surface effectively." Therefore, although the intrinsic oxidation potentials for these anions were not as high ( 4.0 V), they showed stability up to 4.50 V in subsequent scans. It should be cautioned here, though, as the passivation was only observed on an inert electrode surface, whether similar passivations would occur on an actual cathode surface... 

In nonalkaline and nonfluoride aqueous solutions, silicon substrates behave as essentially inert electrodes due to the presence of a thin oxide film. Even in alkaline solutions, silicon is passivated by an oxide film at anodic potentials beyond the passivation peak. Very small current can pass through the passivated silicon surface of n- or p-type materials in the dark or under illumination. Depending on the pH of the electrolyte, oxidized surface sites Si—OH are more or less ionized into anionic species Si—0 owing to the acido-basic properties of such radicals so that the passivation current can vary in a wide range from a few... 

Application of direct electric currents in saturated soils results in electrolysis reactions at the electrodes. If inert electrodes (such as graphite) are used, water oxidation generates an acid (H+) and oxygen gas at the anode while water reduction produces a base (OH-) and hydrogen gas at the cathode (Acar and Alshawabkeh, 1993),... 

Molecular hydrogen (H2 AHDBE, 435 kJ mol-1) is resistant to electrochemical oxidation at inert electrodes (glassy carbon or passivated metals Ni, Au, Hg, Cu). At passivated Pt and Pd dissolved H2 exhibits only broad, diffuse, anodic voltammetric peaks with irreproducible peak currents that are not proportional to the partial pressure of dissolved H2 (PH2). However, with freshly preanodized Pt and Pd electrodes well-defined oxidation peaks for H2 are obtained, which have peak currents that are proportional to P (Figure 8.3).14 The surface... 

Anodic oxidation using a large-aiea inert electrode. 

No systematic study of inert electrode materials has taken place to date and nothing is known about the anodic processes taking place in ionic liquids. It is probable that noble metal oxide coatings should be suitable but processes such as chlorine evolution will clearly have to be avoided for eutectic-based ionic liquids. The breakdown products of most cations are unknown but it is conceivable that some of them could be potentially hazardous. 

One of the drawbacks of DMFCs is the relatively slow rate of the anodic oxidation of methanol even on highly active platinum electrodes. It was shown that the Pt-Ru system is much more catalytically active than pure platinum (pure ruthenium is inert towards this reaction) (-> platinum-ruthenium -> electrocatalysis). The so-called bifunctional mechanism is broadly accepted to describe this synergistic effect, according to which organic species are chemisorbed predominantly on platinum centers while ruthenium centers more readily adsorb species OH, required for the oxidation of the organic intermediates. Usually the composition of such alloys is Pto.sRuo.s and the metal loading is 2-4 mg cm-2. 

In many cases the surface of the anode is oxidized to lead oxide, which thus is the real anode material. Titanium anodes coated with lead oxide have been found to have a long lifetime [154,155]. In some cases the lead dioxide, a strong oxidant in acid solution, reacts chemically with the substrate [156] and is continuously regenerated whereas it acts as an inert electrode in other oxidations. A review of the basic electrochemistry of Pb02, mainly in relation to the lead battery, has been published [157]. 

In another electrochemical approach we used inert electrodes and a transition metal salt such as PtCl2 as the source of metal [38]. Reduction of Pt at the cathode has to be compensated by some oxidative process at the anode. Therefore, we substituted tetraalkylammonium halides by the analogous acetates R4N CH3C02, hoping that they would fulfill three purposes, namely to function as the electrolyte, as the stabilizer and as the reductant (Kolbe-like) ... 

The electrochemical fihn formation by oxypolymerization was discussed for inert electrodes Uke Pt or Au. A stable and adherent film can be formed on inert metals. But on metals Uke iron undergoing anodic dissolution during the anodic oxidation process the preparation is more complicated. 

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