VOLTAMMETRIC AND XPS INVESTIGATION OF NICKEL HYDROXIDE ELECTROCHEMICALLY DISPERSED ON GOLD SURFACE ELECTRODES.

A chemically modified electrode composed of mixed hydroxide and oxyhydroxide nickel film (6-8 nmol cm(-2)) on the gold substrate (Au \ Ni) was characterized by cyclic voltammetry and XPS techniques. The gold substrate electrodes were firstly electrochemically conditioned in 0.2 M NaOH by cycling the potential between -0.25 and 0.6 V versus SCE, then modified by cathodic electrodeposition of nickel hydroxide films. These nickel films were obtained either by voltage cycling (50 mV s(-1)) between 0.0 and -0.5 V (SCE) or at constant potential of -0.3 or -0.5 V using non-deaerated 50 mM Ni(NO3)(2) solutions. X-ray photoelectron spectroscopy (XPS) characterisation and voltammetric behaviour of Au \ Ni electrodes in alkaline solutions are described. Continuous electrochemical cycling of the Au \ Ni electrodes induces significant changes of the nickel films in terms of crystallographic structures and chemical composition. Combination of XPS and electrochemical methodologies have demonstrated the ability to follow the morphological and chemical changes in alkaline solutions upon cycling potentials. Angular-dependent XPS measurements have demonstrated that electrochemical treatment induces the formation of a uniform film layer with the following chemical distribution: Au \ Ni(OH)(2) \ NiOOH. The electrocatalytic activity of the Au \ Ni electrodes is investigated in alkaline medium using glucose as a model compound. The favourable combination of active species such as gold and nickel leads to a sensing electrode with strong catalytic activity over a wide range of applied potentials.