Fu Jia-Ying, Li Xiao-Chong, Yu Zhou, Huang-Fu Xu-Nan, Fan Jian-Ang, Zhang Zhi-Qi, Huang Sheng, Zheng Ju-Fang, Wang Ya-Hao, Zhou Xiao-Shun
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Institute of Physical Chemistry, Zhejiang Normal University, Jinhua 321004, China.
Langmuir. 2022 May 17;38(19):6209-6216. doi: 10.1021/acs.langmuir.2c00703. Epub 2022 May 4.
Probing the adlayer structures on an electrode/electrolyte interface is one of the most important tasks in modern electrochemistry for clarifying the electrochemical processes. Herein, we have combined cyclic voltammetry and electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy techniques to explore the potential-dependent adlayer structures on Au(111) in a room-temperature ionic liquid of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF) without or with pyridine (Py). It is clearly found that the BMI cations strongly adsorb on the negatively charged surface with a flat-lying orientation, leaving a little space for Py adsorption. Upon increasing the potentials of the electrode, the variations of Raman band intensities and frequencies reveal that the interaction between the BMI cations and the Au surface becomes weak; meanwhile, the Py adsorption becomes strong, and its geometry turns from flat, tilted to vertical. Finally, BMI cations desorb and leave plenty of surface sites for Py adsorption in bulk solution, and a N-bonded compact Py adlayer is formed on the very positively charged surface. This causes obvious anodic peaks in cyclic voltammograms, and the peak currents increase with the square root of the scanning rate. The present work provides a fair molecular-level understanding of electrochemical interfaces and molecular adsorption of Py in ionic liquids.
探究电极/电解质界面上的吸附层结构是现代电化学中阐明电化学过程的最重要任务之一。在此，我们结合循环伏安法和电化学壳层隔离纳米粒子增强拉曼光谱技术，来探索在无吡啶或有吡啶（Py）存在的1-丁基-3-甲基咪唑六氟磷酸盐（BMIPF）室温离子液体中，Au(111)上电位依赖的吸附层结构。清楚地发现，BMI阳离子以平躺取向强烈吸附在带负电荷的表面上，为Py吸附留下少许空间。随着电极电位增加，拉曼谱带强度和频率的变化表明，BMI阳离子与Au表面之间的相互作用变弱；同时，Py吸附变强，其几何构型从平躺、倾斜变为垂直。最后，BMI阳离子解吸，在本体溶液中留下大量表面位点供Py吸附，在带非常正电荷的表面上形成了N键合的致密Py吸附层。这在循环伏安图中导致明显的阳极峰，且峰电流随扫描速率的平方根增加。本工作为离子液体中电化学界面和Py的分子吸附提供了合理的分子水平理解。
