ADSORBATE-CATALYZED LAYER-BY-LAYER METAL DISSOLUTION IN HALIDE-FREE SOLUTIONS - PD(111)(ROOT-3X-ROOT-3)R3-DEGREES-I

The anodic dissolution of Pd in inert (halide-free) solution (0.05 M H 2SO4), catalyzed by a single adsorbed layer of iodine, was studied wit h a well-ordered, single-crystal electrode surface, Pd(111)(square-roo t 3 x square-root 3)R30-degrees-I. Experimental measurements were base d upon a combination of electrochemistry (voltammetry and coulometry) and electron spectroscopy (low-energy electron diffraction and Auger e lectron spectroscopy). The significant results were as follows: (i) Pd dissolution occurred only when iodine was present on the surface, (ii ) the amount of adsorbed iodine was not affected by the dissolution pr ocess, and (iii) the interfacial structure of the iodine adlattice rem ained highly ordered even after prolonged corrosion. These observation s strongly suggest an adsorbate-catalyzed layer-by-layer anodic dissol ution process.