ELECTRODEPOSITION PROCESSES OF PALLADIUM AND RHODIUM MONOLAYERS ON PT(111) AND PT(100) ELECTRODES STUDIED BY IR REFLECTION-ABSORPTION SPECTROSCOPY

The electrodeposition of palladium on Pt(111) of Pt(100) single-crystal electrodes, and of rhodium on a Pt(111) electrode was carried out in 0.5 M sulfuric acid aqueous solutions containing 1 x 10(-4) M Pd2+ or Rh3+. Cyclic voltammograms showed the growth of the new sets of adsorption and desorption peaks at 0.22 V (vs. the standard hydrogen electrode) and 0.22 V for Pd/Pt(111), 0.10 and 0.12 V for Pd/Pt(100), and 0.14 and 0.19 V for Rh/Pt(111) respectively. The IR spectra of carbon monoxide on the surfaces during deposition gave evidence for the formation of two-dimensional islands of palladium and rhodium, respectively, by showing the bridge and the threefold absorption bands of carbon monoxide on those atoms. The epitaxial growth of palladium or rhodium monolayers in pseudomorphic (111) structures on Pt(111) and Pt(100) was suggested.