Oxygen solution electrodes

SepaDB, VojnovicMV, VracarLj. M, Damjanovic A. 1986a. Apparent enthalpies of activation of electrodic oxygen reduction at platinum in different current density regions—1. Acid solution. Electrochim Acta 31 91-96. 

Such an electrochemical arrangement can also be used to transport oxygen from one electrode to the other by the imposition of an externally applied potential. This technique, known as coulometric titration , has been used to prepare flowing gas mixtures of oxygen/argon with a controlled oxygen partial pressure, to vary the non-stoichiometry of oxides, to study the thermodynamics of dilute oxygen solutions in metals, and to measure the kinetics of metal oxidation, as examples. 

Figure 20 Cyclic voltammograms recorded at a platinum electrode in a MeCN solution of [Ir(triphos) (DBcat) J+ (a) deaerated solution (b) oxygenated solution. Scan rate 0.2 Vs. T= -20 °C... 

This is not the only subject of debate the nature of the adsorbed forms of oxygen and reaction products on the electrode surface has been widely discussed, as well as the various steps of ORR. Very often, for conditions apparently similar, for example, the same electrode and solution, observations made by two research groups are different and so are, of course, the deductions and the pathways for the electrode reaction. There are so many possible steps, reactions and species that various combinations can be envisaged moreover, as other methods for observing the species or intermediates involved in the electrode reaction are rare, electrochemistry is often the only source of experimental facts. As for other multiparametric problems, when a plausible explanation is found, there is no certainty that this is the only possibility and the correct solution. Moreover, experimental conditions that look identical are not really exactly similar the problem... 

In Fig. 13(a), the occurrence of two simultaneous redox reactions at an electrode surface has been considered. However, in most corrosion problems, more than two reactions may take place and both forward and backward individual electrode reactions may not take place at significant rates in the potential range where the mixed potential is observed, due to the slow kinetics of the participating reactions under those conditions. Figure 13(b) illustrates the corrosion of two metals, M and M, in aqueous aerated (oxygenated) solutions. 

The electrolytic aluminium rectifier includes an aluminium electrode and mother electrode of carl ion, iron or load. Both electrodes are suspended so that they face one another and are immersed in a solution of alkali borates, phosphates or carbonates. In a tantalum rectifier a solution of potassium carbonate, ammonium carbonate or sulphuric acid is used the othev electrode being made of lead. The maximum voltage of the alternating current to be rectified must of course be lower than the breakdown voltage of the rectifier. When the rectifier cell is working, hydrogen is evolved at the tantalum or aluminium electrode while at the lead electrode oxygen is liberated. 

Dissolved oxygen in solutions can strongly affect OCP of silicon electrodes. Bertagna ef a/. " found that (DCP of both /7-Si and n-Si in 5% HF solution shifts to more positive values, by 100-150 mV, in oxygenated solution as shown in Table 2 1 7 146,968 rpjjg Qf oxygen can readily be explained by the change involved in the... 

The E/pH diagram for the Pb/H2S04/H20 system is calculated for an overall activity of hso4 + so - = 1- dashed lines delimit the regions of stability of Pb +, HPbO and Pb03 ions in the solution, and the dashed-and-dotted lines mark the dependencies of the equilibrium potentials of the hydrogen and oxygen electrodes on solution pH. 

A variation of this type of methodology is also used to measure blood flow rates. In this case appropriate anodic potentials are applied to implanted platinum electrodes. A solution of ascorbic acid is then injected into the vein or artery at a location of choice. Blood flow rate between the location of the platinum wire and injection site is determined from the time of injection to the time of a marked increase in oxidation current. Similar techniques using cathodic potentials can be used to monitor blood flow and oxygen levels during cardiac surgery. 

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