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 H2SO4), catalyzed by a single adsorbed layer of iodine, was studied with a well-ordered, single-crystal electrode surface, Pd(111)(square-root 3 x square-root 3)R30-degrees-I. Experimental measurements were based upon a combination of electrochemistry (voltammetry and coulometry) and electron spectroscopy (low-energy electron diffraction and Auger electron 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 process, and (iii) the interfacial structure of the iodine adlattice remained highly ordered even after prolonged corrosion. These observations strongly suggest an adsorbate-catalyzed layer-by-layer anodic dissolution process.