Coated anodes chlorine evolution reaction

If the Ru loss in the deactivated anode is a result of uniform dissolution across the entire coating layer, resulting in a Ru loading of less than 2 g m-2, the anode has to be recoated to regain its electrocatalytic activity for the chlorine evolution reaction. Under these conditions, the existing anode coating must be stripped prior to recoating. However, if surface depletion of Ru is the cause for increased anode potential, then replenishment of these surface sites should result in the rejuvenation of the deactivated anodes. 

Electrocatalysis of electrochemical chlorine evolution from Ru02-coated titanium anodes rests on the same grounds according to the so-called Krasil shchikov mechanism, which is schematically described by the reactions (8a) and (8b) for anodic chlorine evolution (9-/2) ... 

It is stated [22] that the %02 and the chlorate levels in the anolyte are functions of the nature and composition of the anode coating. It should, however, be emphasized that while the %02 is indeed a function of the anode coating composition, the ratio of the exchange current densities of the oxygen and chlorine evolution reactions and the surface pH at the anode. The rate of chlorate formation, F, is solely dictated by the bulk pH, pH [15,23], as given by the relationship (134), and as shown in Fig. 4.4.9. 

The increase in anode potential with decreasing Ru02 loading (at constant at% Ru in the coating) is a result of a change in the mechanism of the chlorine evolution reaction. 

Panic VV, Dekanski A, Milonjic 8K, Atanasoski RT, Nikolic BZ (1999) Ru02-Ti02 coated titanium anodes obtained by the sol-gel procedure and their electrochemical behaviour in the chlorine evolution reaction. Colloids 8urf A 157 269-274. doi 10.1016/ 80927-7757(99)00094-1... 

Chen, R. Y., V. Trieu, A. R. Zeradjanin et al. 2012. Microstructural impact of anodic coatings on the electrochemical chlorine evolution reaction. Phys. Chem. Chem. Phys. 14 7392-7399. 

The major electrochemical reaction at the anode surface is oxygen and chlorine evolution coupled with oxidation of the active carbon to carbon dioxide. Eventually all the carbon is removed from the anode coating and this allows perforation of the copper conductor leading to ultimate anode failure. 

Passage of 1.0 mol of electrons (one faraday, 96,485 A s) will produce 1.0 mol of oxidation or reduction—in this case, 1.0 mol of Cl- converted to 0.5 mol of Cl2, and 1.0 mol of water reduced to 1.0 mol of OH- plus 0.5 mol of H2. Thermodynamically, the electrical potential required to do this is given by the difference in standard electrode potentials (Chapter 15 and Appendix D) for the anode and cathode processes, but there is also an additional voltage or overpotential that originates in kinetic barriers within these multistep gas-evolving electrode processes. The overpotential can be minimized by catalyzing the electrode reactions in the case of chlorine evolution, this can be done by coating the anode with ruthenium dioxide. 

There are developments which could be interesting for realization in industry. Chlorine can be evolved from gaseous hydrogen chloride at an anode which is prepared as a coating of electro-catalytic active material directly on the surface of a Nation cation exchange membrane [9]. Also the cathode is a suitable coating on the opposite side of the membrane. In this case, hydrogen evolution is possible as the cathodic reaction from... 

The study of hydrous oxide systems is clearly of interest in many areas of electrochemistry. The unusually high level of activity of hydrous oxide-coated metal anodes for such industrially important reactions as oxygen and chlorine gas evolution... 

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