ELLIPSOMETRY OF NICKEL-HYDROXIDE ELECTRODES FORMED BY EX SITU CHEMICAL PRECIPITATION - POTENTIAL ROUTINE AND TIME EFFECTS

Ellipsometric and reflectivity data combined with voltammetric data have been obtained at 546.1 nm for different nickel hydroxide electrodes in 0.01 M NaOH at 25-degrees-C. The electrodes were prepared by ex situ chemical precipitation on a polished platinum substrate. The influence of the potential routine applied to the nickel hydroxide electrode on the corresponding optical parameters and time effects for both the oxidized and reduced forms of the active material kept at constant potential have been investigated. The nickel hydroxide layer is described as a mixture of nickel(II) hydroxide, nickel(III) hydroxide and electrolyte-water domains. The kinetic effects are discussed through a complex reaction pathway involving different nickel(II) and nickel(III) hydroxide species, the processes starting preferentially at the borders of the different domains.