Photo-induced dissolution of zinc in alkaline solutions

The passive behaviour of zinc in an alkaline pH 13.0 solution under dark an d illumination conditions has been studied using de polarization and ac imp edance techniques. Illumination with polychromatic light in the wavelength region 200-900 nm caused significant dissolution of anodically formed passi ve layers on zinc. This was evident from increased anodic currents, a ten-f old decrease in the charge transfer resistance and an increase in the capac itance of the passive layer. The photo-induced dissolution effect was only slightly evident under open-circuit conditions, where a precipitated or ads orbed layer forms on the electrode. These results are explained in terms of the n-type semi-conducting properties of ZnO. (C) 2000 Elsevier Science Lt d. All rights reserved.