In situ FTIR spectroscopic studies of CO adsorption on electrodes with nanometer-scale thin films of ruthenium in sulfuric acid solutions

A nanometer-scale thin film of ruthenium supported on glassy carbon (nm-Ru/ GC) was prepared by electrochemical deposition under cyclic voltammetric co nditions. Scanning tunneling microscopy (STM) was used to investigate the s tructure and to measure the thickness of the thin film. It has been found t hat the Ru thin film is composed of layered Ru crystallites that appear in a hexagonal form with dimensions of about 250 nm and thickness around 30 nm . In situ FTIR spectroscopic studies demonstrated that such a nanostructure d Ru thin film exhibits abnormal infrared effects (AIREs) for CO adsorption (G.Q. Lu et al., Langmuir 16 (2000) 778). In comparison with CO adsorbed o n a massive Pt electrode, the IR absorption of COad on nm-Ru/GC was signifi cantly enhanced. Moreover, the direction of COad bands is inverted and the full width at half maximum of COad bands is increased. It has been revealed that the enhancement factor of IR absorption of CO adsorbed on nm-Ru/GC el ectrodes depends strongly on the thickness of the Ru film. An asymmetrical volcano relationship between the enhancement factor and the thickness of th e Ru film has been obtained. The maximum value of the enhancement factor wa s measured as 25.5 on a nm-Ru/GC electrode of Ru film thickness around 86 n m. The present study has contributed to exploration of the particular prope rties of nanostructured Ru film material and to the origin of the abnormal infrared effects. (C) 2001 Elsevier Science B.V. All rights reserved.