Oxygen evolution reaction lead oxide

An increasing amount of attention is being given to oxides as possible anodes for oxygen evolution because of the importance of this reaction in water electrolysis. In this connection, numerous studies have been carried out on noble metal oxides, spinel and perovskite type oxides, and other oxides such as lead and manganese dioxide. Kinetic parameters for the oxygen evolution reaction at a variety of single oxides and mixed oxides are shown in Table 3. 

What is the effect of silver on the anodic corrosion of lead It is revealed hy the rate of oxidation of the metal expressed in current density units (Fig. 2.45). Let us consider the case when the polarization is carried out at a constant potential (e.g., 1500 mV). When Ag ions are introduced into the solution, the oxygen over-voltage decreases. When silver is alloyed in the metal, a weaker effect on the rate of oxygen evolution is observed, but the corrosion rate of the lead—silver alloy is considerably reduced. Hence, the introduction of silver by both methods accelerates the oxygen evolution reaction, but it affects differently the anodic corrosion of the metal. 

The oxygen reactions occur at potentials where most metal surfaces are covered by adsorbed or phase oxide layers. This is particularly true for oxygen evolution, which occurs at potentials of 1.5 to 2.2 V (RHE). At these potentials many metals either dissolve or are completely oxidized. In acidic solutions, oxygen evolution can be realized at electrodes of the platinum group metals, the lead dioxide, and the oxides of certain other metals. In alkaline solutions, electrodes of iron group metals can also be used (at these potentials, their surfaces are practically completely oxidized). 

Lead azide, like hydrazoic acid, is liable to undergo oxidation and reduction reactions. It is partially decomposed by atmospheric oxygen to form free hydrazoic acid, nitrogen and ammonia. This reaction is promoted by the presence of carbon dioxide in the air. When boiled in water, lead azide undergoes slow decomposition with the evolution of hydrazoic acid. 

Diamond film electrode has an inert character with weak adsorption properties (Martin et al. 1996 Swain et al. 1998 Pleskov 1999). Weak interactions of D ( OH) lead to low anode activity toward oxygen gas evolution [Reaction (3.3)] and high oxidation reactivity to the organic pollutants incineration [Reaction (3.2)]. Due to the high oxidizing power of the radicals, highly persistent pollutants, which cannot be decomposed with bioremediation method, advanced oxidation process, or even electrooxidation process with other kinds of electrodes, can be successfully degraded with the diamond film electrode. 

There is a need to develop new types of oxide electrodes for reactions of technological importance with emphasis on both high electrocatalytic activity and stability. For example, pyrochlore-type oxides, e.g. lead or bismuth ruthenates, have shown excellent catalytic activity for the oxygen evolution and reduction reactions and should be further investigated to elucidate the reasons for such high activity. The long term stability of such ruthenate electrodes is questionable, however. 

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. 

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