Ou Yang Liang-Yueh, Bensliman Fahd, Shue Chia-Haw, Yang Yaw-Chia, Zang Ze-Haw, Wang Li, Yau Shueh-Lin, Yoshimoto Soichiro, Itaya Kingo
Faculty of Engineering, Tohoku University, 6-6-04 Aoba, Sendai 980-8579, Japan.
J Phys Chem B. 2005 Aug 11;109(31):14917-24. doi: 10.1021/jp0511101.
In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were employed to examine the underpotential deposition (UPD) of cadmium on a rhodium(111) electrode in sulfuric and hydrochloric acids. The (bi)sulfate and chloride anions in the electrolytes played a main role in controlling the number and arrangement of Cd adatoms. Deposition of Cd along with hydrogen adsorption occurred near 0.1 V (vs reversible hydrogen electrode) in either 0.05 M H2SO4 or 0.1 M HCl containing 1 mM Cd(ClO4)2. These coupled processes resulted in an erroneous coverage of Cd adatoms. The process of Cd deposition shifted positively to 0.3 V and thus separated from that of hydrogen in 0.05 M H2SO4 containing 0.5 M Cd2+. The amount of charge (80 microC/cm2) for Cd deposition in 0.5 M Cd2+ implied a coverage of 0.17 for the Cd adatoms, which agreed with in situ STM results. Regardless of [Cd2+], in situ STM imaging revealed a highly ordered Rh(111)-(6 x 6)-6Cd + HSO4- or SO42- structure in sulfuric acid,. In hydrochloric acid, in situ STM discerned a (2 x 2)-Cd + Cl structure at potentials where Cd deposition commenced. STM atomic resolution showed roughly one-quarter of a monolayer of Cd adatoms were deposited, ca. 50% more than in sulfuric acid. Dynamic in situ STM imaging showed potential dependent, reversible transformations between the (6 x 6) Cd adlattices and (square root 3 x square root 7)-(bi)sulfate structure, and between (2 x 2) and (square root 7 x square root 7)R19.1 degrees -Cl structures. The fact that different Cd structures observed in H2SO4 and HCl entailed the involvement of anions in Cd deposition, i.e. (bi)sulfate and chloride anions were codeposited with Cd adatoms on Rh(111).
采用原位扫描隧道显微镜（STM）和循环伏安法（CV）研究了镉在铑（111）电极上于硫酸和盐酸中的欠电位沉积（UPD）。电解质中的（亚）硫酸根和氯离子在控制镉吸附原子的数量和排列方面起主要作用。在含有1 mM Cd(ClO4)2的0.05 M H2SO4或0.1 M HCl中，镉的沉积以及氢的吸附在0.1 V（相对于可逆氢电极）附近发生。这些耦合过程导致镉吸附原子的覆盖度出现误差。在含有0.5 M Cd2+的0.05 M H2SO4中，镉的沉积过程正向移动至0.3 V，从而与氢的沉积过程分离。0.5 M Cd2+中镉沉积的电荷量（80微库仑/平方厘米）意味着镉吸附原子的覆盖度为0.17，这与原位STM结果一致。无论[Cd2+]如何，原位STM成像显示在硫酸中存在高度有序的Rh(111)-(6×6)-6Cd + HSO4-或SO42-结构。在盐酸中，原位STM在镉开始沉积的电位下辨别出(2×2)-Cd + Cl结构。STM原子分辨率显示大约沉积了四分之一单层的镉吸附原子，比在硫酸中多约50%。动态原位STM成像显示在(6×6)镉晶格和（根号3×根号7）-（亚）硫酸根结构之间以及(2×2)和（根号7×根号7）R19.度数-Cl结构之间存在电位依赖的可逆转变。在H2SO4和HCl中观察到的不同镉结构这一事实表明阴离子参与了镉的沉积，即（亚）硫酸根和氯离子与镉吸附原子共沉积在Rh(111)上。
