Hydrous Oxide Film Growth on Amorphous Ni‐Co Alloys

The electrochemical behavior of a Ni 51 Co 23 Cr 10 Mo 7 Fe 5.5 B 3.5 (weight percent) amorphous alloy ribbon has been investigated in alkaline solutions. When the metal is initially subjected to anodic potentials, an enriched Cr (and possibly B) surface layer is dissolved. Following this, a hydrous oxide film can be readily formed on the electrode surface by a continuous potential cycling method, to a thickness of up to ca. one micron. The film, which has an electrochemical signature which is very similar to the Ni(II)/Ni(III) transition, is electrochromic in nature and displays interference colors when still thin. The maximum growth rate of the film per cycle of potential has been found to be 0.15 to 0.20 mC/cm 2 , achieved by optimization of the magnitude and time spent at the upper and lower potential limits.