Although the application of capacitance measurements to studies of metal solution interfaces as a function of potential are numerous, they have rarely been useful in the study of metal deposition, due to complications arising from faradaic reactions. Graphical methods I or complex instrumentation 2 have usually been necessary to attain adequate separation. In this present work, the electrical double layer (edl) capacitance of the electrodeposited zinc substrate was determined using a galvanostatic pulse technique. Preliminary investigations were concerned with the potential dependence of the edl capacitance of the initial zinc substrate in order to ascertain at which potential the edl capacitance should be determined. Following this, further deposition of zinc from alkaline zincate solutions was done and the change in edl capacitance (measured in the absence of OH-and zincate) was observed with respect to deposition time.
From work elsewhere 3'4 well defined differences in the edl capacitance~Seposition time behavior, above and below the critical initiation overpotential for dendrites, are to be expected.
Previous work 5'6'7 on the potential dependence of the zinc capacitance in, for example, potassium chloride presents a somewhat confusing picture. The results of Chuang-Hshin Cha and Iofa 5 with zinc single crystals has shown that the addition of the large organic cation (C4H9)N + produces a large decrease in the capacitance, at potentials slightly cathodic of the reversible potential, from approximately 20 to < 5 #F cm -2. The authors 5 have stated that the desorption potential of this cation lies at -1.0 V (with respect to zero charge potential) for both zinc and mercury ; these authors s have also stated that the adsorption equilibration time is long, and from their data it may be said that the relaxation time is > 10 -4 s. Brown et al. 6 in some work with single crystal (0001) and polycrystalline zinc in KC1 reported results essentially similar to those of Cha and Iofa 5 for systems containing KC1 and the cation (C4H9)N + ; however, no mention was made of possible impurity effects, even though substantial changes in capacitance occurred prior to H 2 evolution.
Capacitance measurements of zinc in alkaline zincate solutions have also been reported 7'8. Here the situation is much more complex than in KC1, due to the adsorption of the OH-ion. A potential dependence study of the zinc electrode capaci-