Kim Young-Geun, Soriaga Manuel P.
Department of Chemistry, Texas A&M University, College Station, Texas, 77843
J Colloid Interface Sci. 2001 Apr 1;236(1):197-199. doi: 10.1006/jcis.2001.7443.
The benzoquinone/hydroquinone (Q/H(2)Q) redox reaction has been studied by electrochemical-scanning tunneling microscopy (EC-STM) at a Pd(111)-(square3xsquare3)R30 degrees -I electrode surface in a solution that contained 10(-4) M H(2)Q in 0.05 M H(2)SO(4); iodine-pretreatment of the Pd(111) surface was to prevent chemisorption of organic-derived species. The molecule-resolved EC-STM images indicated that: (i) at a potential where only H(2)Q is present in solution, a self-assembled (square21xsquare21)R10.9 degrees -eta(6)-H(2)Q monolayer is produced in which the H(2)Q molecules are oriented parallel to the surface; (ii) at a potential where partial oxidation (to Q) occurs, a self-assembled (square21xsquare21)R10.9 degrees -eta(6)-QH adlayer is generated, where QH represents quinhydrone, an equimolar mixture of Q and H(2)Q; in this structure, the Q and H(2)Q molecules are oriented vertically, face-to-face, and arranged alternately along a given row, reminiscent of the crystal structure of quinhydrone. The partial oxidation-induced molecular reorientation, which is reversible, most likely arises from favorable Q-H(2)Q face-to-face interactions; that is, complete oxidation would yield only flat-oriented Q species. Unfortunately, at potentials where only Q would be present in solution, I-catalyzed corrosion of the Pd starts to occur, which leads to noise-laden EC-STM images. Copyright 2001 Academic Press.
通过电化学扫描隧道显微镜（EC-STM）在含有10⁻⁴ M对苯二酚（H₂Q）的0.05 M硫酸（H₂SO₄）溶液中，于钯（Pd）(111)-(√3×√3)R30°-I电极表面研究了苯醌/对苯二酚（Q/H₂Q）氧化还原反应；对Pd(111)表面进行碘预处理是为了防止有机衍生物种的化学吸附。分子分辨的EC-STM图像表明：（i）在溶液中仅存在H₂Q的电位下，会形成一种自组装的(√21×√21)R10.9°-η⁶-H₂Q单层，其中H₂Q分子与表面平行排列；（ii）在发生部分氧化（生成Q）的电位下，会生成一种自组装的(√21×√21)R10.9°-η⁶-QH吸附层，其中QH代表醌氢醌，即Q和H₂Q的等摩尔混合物；在这种结构中，Q和H₂Q分子垂直面对面排列，并沿给定的行交替排列，这让人联想到醌氢醌的晶体结构。这种可逆的部分氧化诱导的分子重排最有可能源于有利的Q-H₂Q面对面相互作用；也就是说，完全氧化只会产生平面取向的Q物种。不幸的是，在溶液中仅存在Q的电位下，Pd开始发生碘催化的腐蚀，这导致EC-STM图像充满噪声。版权所有2001年学术出版社。
