Overpotential for oxygen evolution

The presence of iron in nickel oxyhydroxide electrodes has been found to reduce considerably the overpotential for oxygen evolution in alkaline media associated with the otherwise iron free material.(10) An in situ Mossbauer study of a composite Ni/Fe oxyhydroxide was undertaken in order to gain insight into the nature of the species responsible for the electrocatalytic activity.(IT) This specific system appeared particularly interesting as it offered a unique opportunity for determining whether redox reactions involving the host lattice sites can alter the structural and/or electronic characteristics of other species present in the material. 

Smooth platinum, lead dioxide and graphite are anode materials commonly used in electrooxidation processes. All show large overpotentials for oxygen evolution in aqueous solution. Platinum coated titanium is available as an alternative to sheet platinum metal. Stable surfaces of lead dioxide are prepared by electrolytic oxidation of sheet lead in dilute sulphuric acid and can be used in the presence of sulphuric acid as electrolyte. Lead dioxide may also be electroplated onto titanium anodes from lead(Il) nitrate solution to form a non-porous layer which can then be used in other electrolyte solutions [21],... 

Platinum and carbon are frequently used as counter electrode materials for both anode and cathode. Platinum is resistant to corrosion while carbon is cheap and can be discarded after use. Nickel is a suitable counter cathode material in aqueous solution because of the low overpotential for hydrogen evolution. Titanium coated with platinum and then over coated with mthenium dioxide is a stable counter anode material with a low overpotential for oxygen evolution. 

Furthermore, BDD anodes have a high overpotential for the oxygen evolution reaction compared with the platinum anode (Fig. 1.3). This high overpotential for oxygen evolution at BDD electrodes is certainly related to the weak BDD-hydroxyl radical interaction, what results in the formation of H202 near to the electrode s surface (1.14), which is further oxidized at the BDD anode (1.15) ... 

The presence of Ir02 nanoparticles on the BDD surface causes a considerable decrease in the overpotential for oxygen evolution, in the inhibition of sulfate to peroxodisulfate oxidation, and in the modification of the mechanism of organic oxidation. 

Fig. 25 Volcano plot of the overpotential for oxygen evolution versus the enthalpy of the lower-to-higher oxide transition (°) alkaline and ( ) acidic solution.

The reversible standard potential of the anodic reaction (8) is 1.19 V (please remember that all potentials are noted versus NHE). This is in the near neighborhood to water oxidation (1.23 V). So anode materials possessing high overpotentials for oxygen evolution have to be used, for instance platinum, platinum coated materials like titanium, or lead dioxide. 

The use of less expensive (Pb02) anode materials results in less overpotentials for oxygen evolution, that is, less current efficiencies. Nevertheless, this can be more economically compared with using platinum materials, as the loss of platinum from the electrodes can amount to 7 g per ton perchlorate generated [10]. 

Figure 3 - Overpotential for Oxygen Evolution on the SCA and the General Zone of the Lead-Silver Alloy Anode in Zinc Electrolyte at 38°C and 45 mA/cm ...

Chromium passivates strongly in acid sulphate media. Hence an inert anode is always employed in chromium plating. It is generally a lead alloy which immediately covers with lead dioxide on positive polarization in the electrolyte. The alloying elements are tin, antimony and silver which are added to the lead to improve its mechanical properties and to reduce the overpotential for oxygen evolution. 

The kinetic stability of A OH at these anodes is attributed to their high overpotential for oxygen evolution ... 

Organic Pollutants, Oxidation on Active and Non-Active Anodes, Table 1 Oxidation potentials for water oxidation and overpotentials for oxygen evolution at different anodes... 

Reactions (4.21) and (4.22) serve to reduce the overpotential for oxygen evolution. An additional benefit of the Co(ii) is a reduced dissolution rate of Pb-Sb anodes, leading to a lower lead contamination of the copper deposit (to a level <10mgkg ). 

There is great interest in electrochemical treatment of waste water using diamond electrodes. In addition to the stability of these electrodes in corrosive electrolytes, they also exhibit a large overpotential for oxygen evolution. This permits the production of strong oxidants, such as ozone and hydroxyl radical [32-36]. 

Boron-doped diamond has a high overpotential for oxygen evolution, in contrast to traditional anodes. This high overpotential can allow the formation of the active hydroxyl radical (OH°) by water discharge, according to the following reaction (eq. 21.1) ... 

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