Ren Jindong, Wang Yanan, Zhao Jin, Tan Shijing, Petek Hrvoje
Department of Physics and Astronomy and Pittsburgh Quantum Institute , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States.
Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics , University of Science and Technology of China , Hefei , Anhui 230026 , China.
J Am Chem Soc. 2019 Mar 13;141(10):4438-4444. doi: 10.1021/jacs.8b13843. Epub 2019 Feb 25.
Alkali atoms are known to promote or poison surface catalytic chemistry. To explore alkali promotion of catalysis and to characterize discharge species in alkali-oxygen batteries, we examine coadsorption of K and O on Au(111) surface at the atomic scale by scanning tunneling microscopy (STM) and density functional theory (DFT). On a clean Au(111) surface, O molecules may weakly physisorb, but when Au(111) is decorated with K ions, they chemisorb into structures that depend on the adsorbate concentrations and substrate templating. At low K coverages, an ordered quantum lattice of KO complexes forms through intramolecular attractive and intermolecule repulsive interactions. For higher K and O coverages, the KO complexes condense first into triangular islands, which further coalesce into rhombohedral islands, and ultimately into incommensurate films. No structures display internal contrast possibly because of high structural mutability. DFT calculations explain the alkali-promoted coadsorption in terms of three center, cation-π interactions where pairs of K coordinate the π-orbitals on each side of O molecules, and in addition O forms a covalent bond to Au(111) surface. The K promoted adsorption of O is catalyzed by charge transfer from K atoms to Au(111) substrate and ultimately to O molecules, forming O in a redox state between the peroxo and superoxo. Tunneling d I/d V spectra of KO complexes exhibit inordinately intense inelastic progression involving excitation of the O-O stretching vibration, but absence of a Kondo effect suggests that the magnetic moment of O is quenched.
已知碱金属原子会促进或毒化表面催化化学。为了探究碱金属对催化的促进作用并表征碱氧电池中的放电物种，我们通过扫描隧道显微镜（STM）和密度泛函理论（DFT）在原子尺度上研究了K和O在Au(111)表面的共吸附。在清洁的Au(111)表面上，O分子可能会弱物理吸附，但当Au(111)用K离子修饰时，它们会化学吸附形成取决于吸附质浓度和衬底模板的结构。在低K覆盖度下，通过分子内吸引和分子间排斥相互作用形成了KO络合物的有序量子晶格。对于更高的K和O覆盖度，KO络合物首先凝聚成三角形岛，这些岛进一步聚结成菱形岛，最终形成不匹配的薄膜。没有结构显示出内部对比度，可能是因为结构的高度可变性。DFT计算从三中心阳离子-π相互作用的角度解释了碱金属促进的共吸附，其中一对K配位O分子两侧的π轨道，此外O与Au(111)表面形成共价键。K促进的O吸附是由从K原子到Au(111)衬底并最终到O分子的电荷转移催化的，形成处于过氧和超氧之间氧化还原状态的O。KO络合物的隧道d I/d V光谱表现出异常强烈的非弹性进程，涉及O-O伸缩振动的激发，但没有近藤效应表明O的磁矩被淬灭。
