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电化学Stark效应是指电极溶液界面的吸附物或金属-吸附物之间的化学键的振动频率随电极电势而发生变化的现象.研究该效应,可以更好地理解吸附物与基底的相互作用(如吸附构型、吸附取向和覆盖度等随电位的变化),也可反过来推断电极基底的电子构型及其随电势的变化规律,对理解电化学双电层的结构以及电催化反应的构效关系都很有帮助.多年以来,电极表面吸附CO的电化学Stark效应广受关注,是由于CO为很多小分子氧化的中间产物,研究CO的谱学行为,可加深对CO以及其它能产生CO中间物有机小分子的电催化氧化机理和动力学的理解;另一方面,CO与过渡金属之间普遍存在σ给电子以及π反馈电子作用,因此CO也可作为探针分子,通过考察CO_(ad)以及M–CO_(ad)的振动频率的变化,可推断相应条件下基底的电子与几何结构等信息.本文使用电化学原位表面增强拉曼技术,在一个大的电势范围内考察了Au@Pd纳米粒子薄膜电极上饱和吸附CO的振动光谱行为,以期更好地理解CO_(ad)与基底的成键作用与电极电势之间的关系.由于纯Pd电极表面的拉曼信号太弱,实验使用具有核壳结构的Au@Pd纳米粒子薄膜作为模型电极,并利用Au核的拉曼增强特性.宽广的电势范围约–1.5到0.55V vs.NHE,通过使用酸性、中性以及碱性电解质得以实现.实验考察的电势上限由COad氧化起始电位决定,而下限由强烈氢析干扰测量所限制.结果表明,在检测的电势范围内,C–OM(M指在电极表面的桥式吸附CO和穴位吸附CO所形成的谱带重叠)和Pd–COM键的振动频率可以分为三段:dνC–O_M/d E在–1.5~–1.2 V范围内是185～207 cm~(–1)/V,在–1.2~–0.15 V是83～84 cm~(–1)/V,在–0.2～0.55 V是43 cm~(–1)/V;而dν_(Pd–COM)/d E在–1.5~1.2 V范围内是–10～–8 cm~(–1)/V,在–1.2~–0.15 V是–31~–30 cm~(–1)/V,在–0.2～0.55 V是–15 cm~(–1)/V.与同时记录的极化曲线对比,认为在中性和碱性介质中所观察到dν_(C–OM)/d E在–1.2 V附近的急剧变化与电极表面发生了强烈的析氢反应有关.另外,结合密度泛函理论模型计算,认为共吸附的H减少了CO_(ad)从桥式构型到穴位构型的转变,在酸性介质中这种变化不明显,可能是由于对应的电势较高,桥式吸附的CO比例越大,桥式向穴位的转变本身相对较少.
Electrochemical Stark effect refers to the phenomenon that the vibration frequency of the chemical bond between the adsorbate or the metal-adsorbate at the interface of the electrode solution changes with the potential of the electrode, so as to better understand the interaction between the adsorbate and the substrate Such as the adsorption configuration, adsorption orientation and coverage with potential changes), can also be inferred from the electrode substrate electronic configuration and its potential with the law of change, to understand the structure of the electrochemical double layer and the electrocatalytic reaction The structure-activity relationship is very helpful.For many years, the electrochemical Stark effect of adsorbing CO on the electrode surface has drawn much attention due to the fact that CO is an intermediate product of many small-molecule oxidation. Studying the spectral behavior of CO can deepen the CO and other energy On the other hand, there exist ubiquitous sigma-electron and π-feedback electrons between CO and transition metal, so CO can also be used as a probe molecule to investigate the electrocatalytic oxidation mechanism and kinetics of small molecules of CO intermediates. CO_ (ad) and M-CO_ (ad), we can deduce the electronic and geometric information of the substrate under the corresponding conditions.In this paper, electrochemical in-situ surface-enhanced Raman scattering In a large potential range, the vibrational behavior of CO adsorbed on the Au @ Pd nanoparticle film electrode was investigated in order to better understand the relationship between CO_ (ad) and substrate bonding and electrode potential. The Raman signal on the surface of the electrode is too weak, the Au @ Pd nanoparticle film with core-shell structure is used as the model electrode and the Raman enhancement of Au core is utilized. The wide potential range is about -1.5 to 0.55V vs. NHE, This is achieved by using acidic, neutral and alkaline electrolytes.The upper limit of the potential investigated experimentally is determined by the COad oxidation initiation potential and the lower limit is limited by the intense hydrogen precipitation interference measurement.The results show that C-OM (M refers to the overlap of the band formed by bridge adsorption CO and CO adsorbed on the electrode surface) and the vibration frequency of the Pd-COM bond can be divided into three sections: dνC-O_M / d E in the range of -1.5 to -1.2 V Is 185 ~ 207 cm -1 / V in the range of -1.2 ~ -0.15 V and is 83 ~ 84 cm -1 / V in the range of -0.2 ~ 0.55 V, which is 43 cm -1 / V ; And dν_ (Pd-COM) / d E is -10 -8 cm -1 / V in the range of -1.5 to 1.2 V and -31 to -30 cm -1 in -1.2 to -0.15 V -1) / V, at -0 .2 to 0.55 V is -15 cm -1 / V. In contrast to the polarimetric curves recorded simultaneously, it is considered that the dν_ (C-OM) / d E observed in neutral and alkaline media is between -1.2 The abrupt change around V is related to the intense hydrogen evolution reaction on the electrode surface. In addition, with the help of density functional theory (DFT) model calculations, it is considered that co-adsorbed H reduces the transition of CO_ (ad) from the bridge configuration to the acupoint configuration. This change in acid medium is not obvious, probably due to the higher corresponding potential, the larger the proportion of CO adsorbed on the bridge, the relatively small change of bridge acupoint itself.