Oxidation of Silver Electrodes in CsOH Solutions

Abstract

Sintered Ag electrodes were cycled under several conditions in aqueous CsOH or KOH solutions. Over a wide range of charge rates the capacity accepted at the Ag/Ag20 potential plateau increased as electrolyte concentration decreased, but charge acceptance at the Ag20/AgO plateau increased as concentration increased and was larger in CsOH than in KOH. Polarization was greater in CsOH than in KOH of the same concen.tration. Cross sections through electrodes were examined by optical microscopy. The structures that formed in CsOH tended to be similar to those that formed in a more concentrated KOH. After several cycles the average Ag particle size became larger in KOH than was typical in CsOH. Results indicated that concentration gradients were higher in. CsOH.The charge and discharge reactions are well known for the Ag electrode in alkaline solutions. First, Ag is oxidized to Ag20 and then to AgO during charge. The opposite reactions take place during discharge. The work reported in the literature has been done most often in aqueous KOH solutions and less often in NaOH solutions. The products of charge and discharge are the same in both electrolytes. Nevertheless, electrolyte concentration has a definite effect on the characteristics of Ag electrodes (1-5).Variations between results in different KOH concentrations may be effects of changes in ionic mobility or in the amount of free water. Dirkse has pointed out the importance of the mobility of OH-ions and of hydration of the various ions in the electrolyte (2). Comparison of results in different KOH concentrations can indicate the influence of water concentration.Another factor that may have an influence on the characteristics of Ag electrodes is the particular alkaline metal cation involved. The cation can have a noticeable effect even though it does not enter into an electrode reaction. For example, the capacity obtained when sheet Zn was oxidized in KOH was a little larger than in CsOH or RbOH, an effect probably related to solubility of Zn oxidation products (6).The use of CsOH instead of KOH should indicate if the cation of the electrolyte has a strong effect on the Ag electrode. The atomic weight of Cs is 3.4 times that of K. CsOH and KOH solutions having the same molar concentration of cation will contain different amounts of water. The ionic radius of Cs (as measured in crystals) is about 1.26 times as large as K, but hydration of the ions decreases this size difference. A recent review points out the considerable disagreement among various workers as to the actual solvation numbers of most ions (7). It seems reasonable, however, to consider the ionic radius of hydrated Cs to be approx~ imately 1.19 times as large as hydrated K. Thus, it is of interest to determine some of the characteristics of Ag electrodes in aqueous CsOH solutions because results may differ significantly from those obtained in KOH solutions of the same concentration. A better understanding of the behavior of Ag electrodes in alkaline solutions can result in improvements in high energy ba...

Electrochemical formation and reduction of silver oxides in alkaline media

“…In the charging situation, the Ag/Ag20 plateau does not persist as long as the Ag20/AgO level, especially at higher current density [24,32,34,35,41,43]. This has led to the conclusion that the layer of AgO is thicker than that of Ag20 [2,3,4,7].…”

Reduction of the Silver Oxide Electrode in CsOH Solutions

“…2). At cycle 1 a new sintered Ag electrode always accepted more capacity in 3.6M CsOH t h a n in 8.4M CsOH (9). It was concluded that formation of an u n u s u a l l y large amount of AgO resulted in a smoother AgO having a smaller surface area, since oxygen evolution potentials were about 80 mV higher than in other electrolytes, although formation of Ag20 and AgO had taken place at normal potentials.…”

“…3), indicating that reduction in KOH took place under conditions that were closer to equilibrium. Earlier work showed that oxidation of Ag also occurred closer to equilibrium in KOH than in CsOH (9). This difference probably occurred because conductivity in 8.4M CsOH was lower and viscosity was higher t h a n in 8.41VI KOH.…”

“…A previous paper has described the oxidation of sintered silver electrodes in CsOH solutions (9). The present work is concerned with reduction or discharge of these electrodes and gives the effect of CsOH on electrical characteristics and on electrode structure.…”

“…The results given in Table I were calculated from data taken from Ref. (7) and (9) and the present work. Rates of loss tended to be highest in the most dilute solutions.…”