Reversible potentials chlorine electrode

The influence of the relative values of the transference numbers, affecting the resultant value of the EMF of the concentration cell without transference, is clearly to be seen from the equation (VI-29) should t.. > <+ then eK is positive and in a concentration cell reversible with respect to cations the liquid junction potential is added to the sum of the electrode potentials should, however, < t+, then the liquid junction potential will lower the resultant EMF. In a concentration cell reversible with respect to anions (e. g. in a cell with chlorine electrodes) the EMF is decreased when ( >(+, and increased when t. < t+. 

The theoretical decomposition voltage of chlorides can be calculated from the value of equilibrium oxidation potential of the chlorine electrode e t. cia1 ci-in the anolyte and the reversible reduction potential of the hydrogen electrode 7Toh- Ha. pt in alkaline catholyte. If we apply the Nemst equations for the corresponding electrochemical processes [see (XI-9) and (XI-10)] we obtain the... 

The theoretical decomposition voltage of sodium chloride may be calculated as the sum of the reversible oxidation potential of the chlorine electrode and the reversible reduction potential of the amalgam electrode. 

Amalgam Cell Starting with the chlorine electrode, the reversible standard potential is +1.37 V (all potentials are given versus NHE), due to the sodium concentration of 6 mol L-1 we have to note +1.33 V. The current-overpotential curve represents an unhindered process... 

Table 3.2 lists the reversible potentials for the four electrode reactions which must be considered in brine electrolysis. The data are given for the pH s which prevail at the anodes and cathodes in the various cells. Qiloride ion is always oxidized in slightly acid solution to prevent hydrolysis of chlorine to hypochlorite while the pH at the cathode will, with the exception of the mercury cell, be at least 14. Two factors emerge immediately. First, in a mercury cell where the electrode reactions are A and D, the term - E/ ) of equation (3.5) is —3.25 V, a value... 

When the two electrodes of a cell are interconnected by an external circuit, however, the cell reaction will only occur spontaneously if the free energy change associated with the net cell reaction is negative. This is not the case in a cell for the production of chlorine and caustic soda, i.e. the free energy of reaction (1.11) is positive, and for reaction (T.ll) to occur it will be necessary to supply energy by applying a potential between the two electrodes. This potential must certainly be greater than the difference between the reversible potentials of the cathode and anode in the cell, ( - e ), calculated from... 

The electrode thus behaves like a reversible chlorine electrode the electrode potential, E, depends on the concentration of the potassium chloride solution and the temperature, T/K ... 

The silver-silver chloride electrode, used as a reference electrode, consists of a strip or disc of silver, on which is deposited a film of silver chloride. It behaves as a reversible chlorine electrode, with a potential given by... 

Turning now to the acidic situation, a report on the electrochemical behaviour of platinum exposed to 0-1m sodium bicarbonate containing oxygen up to 3970 kPa and at temperatures of 162 and 238°C is available. Anodic and cathodic polarisation curves and Tafel slopes are presented whilst limiting current densities, exchange current densities and reversible electrode potentials are tabulated. In weak acid and neutral solutions containing chloride ions, the passivity of platinum is always associated with the presence of adsorbed oxygen or oxide layer on the surface In concentrated hydrochloric acid solutions, the possible retardation of dissolution is more likely because of an adsorbed layer of atomic chlorine ... 

Based upon the concepts of the adsorption of the anode reaction product, the share of the anodic curve, on which the carbamide oxidation processes is reflected as a wave, can be explained. It may be assumed that the adsorption of the reaction product inhibits the direct oxidation of carbamide. To verify this conclusion, the anode was polarized to the electrolysis product formation potential, and the reverse sweep was stopped before the electrolysis product was reduced at the electrode. Then the carbamide oxidation process was completely inhibited on the subsequent forward sweep, and the curve exhibited only a current increase at the chlorine ion oxidation potential. 

A method for the preparation of thin films of Fe4[Ru(CN)6]3 ( ruthenium purple ) involving electrochemical reduction of K3[Ru(CN)6] in a solution of Fe2(S04)3 has been developed.28 This ruthenium purple modified electrode is claimed to be one of the best catalysts for evolution of oxygen and chlorine. Electrochemical studies on polyammonium macrocyclic complexes of [Ru(CN)6]4 indicate a 1 1 stoichiometry with a monoelectronic, reversible, oxidation for these complexes this illustrates the control of redox potential of anions by complexation with appropriate receptor molecules.29 The kinetics of oxidation of [Ru(CN)6]4 by [Mn04] in HC104 have been investigated by stopped-flow techniques. It is found that [Ru(CN)6]4" is quantitatively oxidized to [Ru(CN)6]3 in accordance with equation (1) and that two protonated intermediates [RuH(CN)6]3 and [RuH2(CN)6]3 are involved in the oxidation process.30... 

The partial pressure pi of chlorine was kept low to diminish the effects of hydrolysis of the dissolved gas, but later workers have aj parently found that precaution unnecessary. Similar measurements were made by Kameyma, Yamamoto, and Oku,47 except that they substituted saturated potassium chloride for the hydrochloric add. Since both electrodes used are presumably reversible to the chloride ion constituent die potentials of such cells should be independent of the nature of the positive ion constituent and of the concentration. In both cells the reaction is... 

---