Polarization studies of silver Galvanostatic charging of electropolished silver electrodes was carried out at room temperature in 1.0 and 3.0 M aqueous KOH (not presaturated with Ag20; cf. ref. 1) at current densities of 0.25 mAcm-z. The results are summarized in Fig. for 3.0 M KOH but it is relevant to state that essentially the same results were obtained with runs in 1.0 M KOH. In the absence of KIO4, the classical potentialtime curves reported first by Luther and Pokorny 2 were obtained. When 10 -4 M KIO 4 was added, the Ag20/AgO transition peak showed noticeable broadening and the AgO plateau became shorter. Ultimately, at a concentration of 10-2 M KIO 4 both the Ag20/AgO transition peak and the AgO plateau disappeared completely. The sequence of polarization curves shown in Fig. ) is remarkably simila~ to those previously published 1 using Ag20 presaturated 0.1 M KOH solutions at decreasing temperature intervals from 40 ยฐ to 0ยฐC. The addition of K10 4 resulted in the formation of a yellow cotour streaming downward in the vicinity of the electrode and the first appearance of a yellow tinge occurred at the Ag20/AgO transition potential. The intensity of the yellow colour increased with increasing KIO 4 addition.
Figure (c) depicts the spectrum of a chemically prepared solution of 5 x 10-5 M K3H4Ag(IO6)2 in water with three characteristic bands at 213, 255 and 362 nm in agreement with that published by Pappalardo and Los?. The original solution 'containing 5 x 10-5 M KaH4Ag(IO6)2 was made 1.0 M KOH, and after equilibration gave the spectrum shown in Fig. ). The 213 nm band was obscured but apart from changes in absorbance heights, the other two maxima were shifted respectively to 250 and 352 nm. The spectrum of the electrochemically prepared 'solution shown in Fig. ) is similar to that of Fig. ) except for the masking of the 250 nm band, which may be due to a strong absorption by the excess periodate 4. These effects have not hitherto been reported. We conclude that the electrochemical product in 1.0 M KOH may contain a mixture of Ag(IO6) 7-and small amounts of other complexes. From the results shown in Fig. it is tempting to suggest that at sufficiently high KOH concentrations, there may be significant exchange of periodate by hydroxyl ions in the Ag(III) complexes to form some Ag(OH)4 which absorbs at 271 nm 5.