XPS study and electrochemical behaviour of the nickel hexacyanoferrate film electrode upon treatment in alkaline solutions

Abstract

This paper describes the X-ray photoelectron spectroscopy (XPS) characterisation and voltammetric behaviour of nickel hexacyanofer-rate (NiHCF) film electrodes. Glassy carbon was used as a substrate and was modified by cycling the potential between −0.1 and + 0.9V vs. SCE in fresh 0.5M KCl solutions containing 0.25 mM NiCl 2 and 0.25 mM K 3Fe(CN) 6. Subsequent electrochemical cycling of the NiHCF film in alkaline solutions 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 changes are irreversible, and the XPS investigation was very useful for verifying the electrode modifications occurring. Iron present in the NiHCF film suffered the most changes. The absolute intensity of the Fe2p and N:K elemental ratio were especially useful in evaluating the modifications occurring, providing a clear indication of the extent to which NiHCF film was converted. The implications of these findings are discussed.