RHODIUM-MODIFIED GOLD POLYCRYSTALLINE SURFACE AS ANODE MATERIAL IN ALKALINE MEDIUM: AN ELECTROCHEMICAL AND XPS INVESTIGATION.

Abstract

A gold polycrystalline electrode modified with rhodium species was characterized by electrochemical and XPS (X-ray photoelectron spectroscopy) techniques in moderately alkaline medium. The Au/Rh electrodes were prepared utilizing a spontaneous deposition process (SDP) of rhodium adlayer on the gold surface. In particular, rhodium deposition was obtained in non-deaerated 50 mM HClO4 solution containing 10 mM RhCl3 at open circuit for a given time. The modified gold electrode with adsorbed rhodium species (Au/ Rh) exhibit higher electrochemical activity for the oxygen evolution reaction. The effects on the electrochemical activity of the Au/Rh electrode such as: rhodium coverage, pH, electrolyte composition and applied potentials were critically evaluated and discussed. An optimized pulsed chronoamperometric detection technique for the analytical determination of several mono- and di-protic organic acids such as acetic, tartaric, oxalic, malic, etc., was successfully proposed. An average film composition of AU93(+/- 1) Rh-7 +/- 1 was evaluated by XPS technique. The film composition remains unchanged after various electrode treatments such as cycling of potentials and/or polarization conditions for long times in alkaline medium. Thus, the adsorbed rhodium oxide particles show a good chemical and mechanical stability despite the conditions of electrochemical treatment of the electrode surface