The behavior of individual positive and negative electrodes of the sintered‐plate nickel‐cadmium battery system in the presence of foreign ions in KOH solutions has been examined. Carbonate choke: The variation of electrochemical capacity as a function of carbonate contamination of the electrolyte, temperature, and current density was measured for both positive and negative electrodes. The effect of carbonate on the negative cadmium electrode is much greater than on the positive. The general mechanism and the role of intermediate complexes are discussed. Nitrate shuttle: Self‐discharge occurs in cells containing nitrate, as a result of reduction of NO3− to NO2− at the cadmium electrode with subsequent reoxidation to NO3− at the nickel hydroxide electrode. Cations on the positive: Addition of Li+, Ag+ Sb+3, Al+3, and As+3 to the electrolyte had effects on capacity and on charge‐retention of well‐formed nickel hydroxide positive electrodes. Lithium promoted the highest average oxidation, particularly at high temperatures (55°C). Arsenic was the best inhibitor of loss of charge. Possible mechanisms are discussed.
T h e n a t~l r e and concentration of the cadmium-containi~~g ions i n potassiuln hydroxide and potassium carbonate solutions have been studied polarographically. The co-ordinatior~ nurnber for the hydroxide-cadmiuln complex is 4 and its dissociation constant 2X10-r0. The coordination number for the carbonate-cadmium cornples is :3 and its dissociation constant 6 X 10-l.
INTRODCC'L'IOSFrom a study of the electrolytic oxidation of cadmium in carbonate and hydroxide solutions (1) it became apparent that cadmium must exist in solution as an intermediate step in the oxidation. According t o Latimer (2) the solubility products of Cd(0H)a and CdCOn are 2 X10-l4 and 5 X lo-'? respectivelj.. These data show t h a t no appreciable concentration of cadmium can exist in these solutions as a simple Cd+? ion.The object of this work was to measure the concentration of cadmium in potassium hydroxide and potassium c a r b o~~a t e solutions in equilibrium with solid CdO, Cd(OH)2, and CdCOs and to determine the nature and properties of the cadmium-containing ion.The method used was that described by Lingane (3). After it was established t h a t the reduction of the complexes was reversible, measurements of half-wavk potential as a function of concentration of complexing ion were made. From these results co-ordination numbers and dissociation constants were calculated.
Preparation of Saturated SolutiozsSolutions of I
Cadmium oxidizes anodically in hydroxide solutions to form films of reaction products which control the subsequent anodic processes. The electrometrics of film formation and reduction were determined, and various other definitive experiments were done which permit an interpretation of the general mechanism of oxidation to be made. The film forms as CdO which is converted into Cd(OH).~ at a rate dependent upon various experimental factors.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 128.192.114.19
Cadmium electrodes under anodic oxidation in hydroxide and carbonate electrolytes have been examined by analysis of the decay of overpotential after current interruption.After passivation while oxygen is being evolved, except for a small instantaneous (<1 msec) ohmic drop, the potential decays logarithmically with time in the manner usually found for the decay of activation overpotential of a gas electrode. Before passivation while the metal is actively being oxidized, however, except for the small ohmic drop, the potential decays exponentially with time in two steps. This behavior is not described by activation theory.Determinations were made of the capacitance of both the oxidizing and the passivated cadmium, both from potential decay curves and from superimposed a.c. All the a‐c values correspond to those of a normal double layer, as do those obtained from decay measurements after passivation has occurred. However, the values obtained from decay curves before passivation are two orders of magnitude higher early in the oxidation but drop rapidly toward the a‐c values as oxidation proceeds.It is proposed that next to the Helmholtz double‐layer at the normalCdO ‐electrolyte interface, there exists a highly polarized inner double‐layer in which the reaction OH−→O=+H+ takes place. When the field strength across the inner double layer becomes high enough for the reaction OH−→OH+e− to take place instead, oxygen is evolved and the electrode passivates.The roles of adsorption of OH− to form the Helmholtz layer and of interference by CO3= are discussed in terms of the results.
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