Electrodeposition Of Ultrathin Pd Co And Bi Films On Well Defined Noble Metal Electrodes

Download or read book Electrodeposition of Ultrathin Pd, Co and Bi Films on Well-defined Noble-metal Electrodes written by Jack Hess L Baricuatro and published by . This book was released on 2006 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Three illustrative cases involving the electrodeposition of ultrathin metal films of varying reactivities onto noble-metal substrates were investigated: (I) Pd on Pt(111), a noble admetal on a noble-metal surface; (II) Bi on Pd(111), a less noble admetal on a noble-metal surface; and (III) Co on polycrystalline Pd and Pd(111), a reactive metal on a noble-metal surface. The interfacial electrochemistry of these prototypical systems was characterized using a combination of electrochemical methods (voltammetry and coulometry) and ultrahigh vacuum electron spectroscopies (Auger electron spectroscopy, AES; low energy electron diffraction, LEED; and X-ray photoelectron spectroscopy, XPS). Potential-controlled adsorption-desorption cycles of aqueous bromide exerted surface smoothening effects on ultrathin Pd films with defect sites (steps). This procedure, dubbed as electrochemical (EC) annealing, constituted a nonthermal analogue to conventional annealing. EC-annealed ultrathin Pd films exhibited long-range surface order and remained free of oxygen adspecies. Pd adatoms occupying step-sites were selectively dissolved and/or rearranged to assume equilibrium positions in a well-ordered (1x1) film. Electrodeposition of Co was found to be highly surface-structure sensitive. While virtually no Co electrodeposition transpired on a clean Pd(111) surface, Co was voltammetrically deposited on (I) a Pd(111) electrode roughened by oxidation-reduction cycles; and (II) thermally annealed polycrystalline Pd, which is a composite of the (111) and (100) facets. Electrodeposition of Co was also observed to be kinetically hindered and slow potential scan rates (0.1 mV/s) were required. Well-defined ultrathin Bi films were potentiostatically electrodeposited onto Pd(111); a Stranski-Krastanov growth mode was indicated. The electrochemical reactivity of ultrathin Bi films was characterized using two surface probes: aqueous iodide and D-glucose. (I) Exposure of the prepared Biadlayers ([theta] Bi>̲ 0.33) to aqueous iodide gave rise to ([unable to replicate] 3x[unable to replicate] 7) I-on-Bi superlattice. The same superlattice was obtained if Bi was electrodeposited onto Pd(111) ([unable to replicate]3x [unable to replicate] 3) R30°-I. (II) With respect to electrooxidation of D-glucose on Pd(111), the presence of Bi adlayers inhibited the by-product-induced "surface poisoning" of Pd(111) but reduced its electrocatalytic efficiency.