The Effect of Depassivation at Specific Crystal Facets on the State of Activation of Nickel Substrates for Electrodeposition

• Published in: Journal of the Electrochemical Society 1978-12, Vol.125 (12), p.1940-1945
• Main Authors: Tench, Dennis, Ogden, Cameron
• Format: Article
• Language: English
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.2131332

Changes in the surface structure of Ni substrates at open circuit in 65 wt.-% H sub 3PO sub 4 after an anodic etch treatment have been by electrode potential measurements as a function of time, by voltammetric repassivation in neutral sulfate and phosphoric acid solutions, and by microscopic examination. It was found that partial depassivation occurs at specific crystal facets within a few hundred seconds. Studies involving single crystals indicated that the {100} and {100} orientations within this time frame, whereas the passive film on the {111} surface is stable. The depassivation process is accelerated by Fe impurities in the substrate and this impurity effect is enhanced by the presence of dissolved O which also enhances the etching of depassivated areas. These data suggest poor activation of Ni substrates for electrodeposition can result from depassivation to form bare spots on the surface, through which appreciable cathodic current can pass without reducing the remaining oxide layer.13 refs.--AA