XPS STUDY AND ELECTROCHEMICAL-BEHAVIOR OF THE NICKEL HEXACYANOFERRATEFILM ELECTRODE UPON TREATMENT IN ALKALINE-SOLUTIONS

This paper describes the X-ray photoelectron spectroscopy (XPS) charac terisation and voltammetric behaviour of nickel hexacyanoferrate (NiHC F) film electrodes. Glassy carbon was used as a substrate and was modi fied by cycling the potential between -0.1 and +0.9 V vs. SCE in fresh 0.5 M KCl solutions containing 0.25 mM NiCl2 and 0.25 mM K3Fe(CN)(6). Subsequent electrochemical cycling of the NiHCF film in alkaline solu tions induces significant changes, yielding a modified electrode that is primarily composed of hydrated Ni(II) oxide/hydroxide with a single set of well-defined Ni(II)/(III) voltammetric peaks. Such induced cha nges are irreversible, and the XPS investigation was very useful for v erifying the electrode modifications occurring. Iron present in the Ni HCF film suffered the most changes. The absolute intensity of the Fe2p and N:K elemental ratio were especially useful in evaluating the modi fications occurring, providing a clear indication of the extent to whi ch NiHCF film was converted. The implications of these findings are di scussed.