Redox Mediation Involving Oxide Films as Examined by Surface-Enhanced Raman Spectroscopy: Peroxodisulfate Reduction at Oxide-Modified Gold Electrodes

摘要

The influence of peroxodisulfate on the potential dependent state of oxidation of gold and nickel oxide coated gold electrodes in alkaline aqueous solution has been examined by means of surface enhanced Raman spectroscopy (SERS). For a gold electrode in 1 M KOH containing 1-20 micro moles S2O8, the SERS metal surface oxygen band at about 560 cm which diagnoses the presence of an oxidized gold surface (associated with a gold hydroxide film) survives to markedly (0.3 to 0.4 V) more negative electrode potentials than in the absence of S2O8. This chemically induced change in the state of surface oxidation is attributed to the oxidation of OH by S2O8 to form gold oxide; the latter undergoes electroreduction resulting in the mediated reduction of S2O8. This mechanism is discussed on the basis of electrochemical kinetic data for the reduction of S2O8 and gold oxide, obtained using rotating disk and linear-sweep voltammetry. Peroxodisulfate is also observed to influence the potential-dependent redox state of thin nickel oxide films on gold in alkaline solutions. Keywords: Surface enhanced raman spectroscopy, Oxide films, Redox mediation, Rotating disk linear-sweep voltammetry.