基于超微电极的原位电化学拉曼光谱

原位电化学拉曼光谱是一种重要的光谱电化学技术.基于超微电极的原位电化学拉曼光谱将拉曼光谱反映的结构信息与电极表面的电化学过程从实验上严格对应和关联,为深刻理解电化学反应机理提供依据.本文综述了采用超微电极作为工作电极的原位电化学拉曼光谱的研究方法和应用进展,总结了应用超微电极作为工作电极开展电化学拉曼光谱实验的方法和具有表面增强拉曼活性的超微电极制备方法,展示了如何利用在超微电极表面获得的拉曼光谱与界面电化学过程的严格关联研究单个锌颗粒电化学氧化过程、吡啶分子在Au电极表面的电化学吸附过程,以及如何利用该技术能以高的信噪比和灵敏度同时测量光电流与分子反应这一特性研究对巯基苯胺选择性光氧化反应.采用超微电极作为工作电极的原位电化学拉曼光谱技术极大拓展了拉曼光谱技术的研究范围,有望成为探索(光)电化学反应的有力工具.     

拉曼光谱在燃料电池领域的应用

随着社会经济的快速发展,环境污染与能源短缺逐渐成为人们必须面对的热点问题。为实现人类社会的可持续发展,开发环境友好新型清洁能源技术成为二十一世纪的迫切任务。其中,燃料电池被认为是最具发展潜力的新型清洁能源技术之一。拉曼光谱作为一种无损的指纹识别的分子光谱技术,适用于燃料电池材料的研究,尤其是表面增强拉曼光谱技术(SERS)和壳层隔绝表面增强拉曼光谱技术(SHINERS)的发展,为研究燃料电池中反应的痕量中间物种,理解燃料电池实际反应机理提供了一种非常好的原位光谱实验平台,有助于合理设计更高效的催化剂及电极材料。本文主要对拉曼光谱以及SERS和SHINERS在燃料电池领域从电池材料层面和电极表面分子反应层面的应用及其发展前景进行相关讨论。     

电化学表面增强拉曼光谱—现状和展望

许多和能源、生命相关的过程都强烈依赖于电化学荷电界面的结构和性能.自从表面增强拉曼光谱效应发现后,就很快地被应用于电化学界面的原位研究,即从分子水平上深入表征各种表面(或界面)的结构和过程,如鉴别物种在表面的键合、构型和取向等.最近十年,纳米科技的飞速发展为SERS技术提供了丰富的基底以及检测和表征方法,从而推动了与纳米科学密切相关的电化学SERS领域令人瞩目的发展.本文系统介绍Au和Ag的SERS、过渡金属薄层SERS、纯过渡金属SERS、核壳结构SERS和已经可以应用于单晶表面研究的gap-modeSERS、TERS和SHINERS,其中穿插着介绍电化学SERS的历史发展、现状和存在的问题及其展望,为电化学SERS研究提供较为全面的详细的参考.     

粗糙铂电极上甲酸吸附氧化的电化学原位表面增强拉曼光谱研究

采用循环伏安法和电化学原位表面增强拉曼光谱（SERS）技术研究甲酸的解离 及附与氧化行为。首次报道了甲酸吸附、解离和氧化的电化学原位SERS谱，发现甲 酸在粗糙铂电极上能自发解离吸附；首欠成功地获得了粗糙铂电极上甲酸吸附解离 的强吸附中间体CO和活性中间体COOH的表面增强拉曼光谱，同时首次检测到甲酸氧 化最终产物CO_2的拉曼光谱信号，从分子水平证实甲酸解离吸附反应的双途径机理 。     

拉曼光谱测试技术在可充电铝离子电池储能机理的研究进展

拉曼光谱是一种无损的分析技术,可以提供样品化学结构和分子相互作用的详细信息。由光谱学方法与常规电化学方法相结合产生的电化学原位光谱是一种动态探测电极材料结构和相组成的强大技术,能够方便地提供电极界面分子的微观结构信息,这使得其在储能领域中有广阔的应用前景。拉曼光谱能够有效地原位表征可充电铝离子电池氯化铝基电解液中络合离子、不同正极材料在充放电过程中的变化规律。结合X射线衍射技术（XRD）或X射线光电子能谱技术（XPS）等表征技术,拉曼光谱能够有效地揭示可充电铝离子电池的储能机理,包括对电池电解液和电极材料的研究以及电极表面反应的原位监测,对电池材料和界面结构性质的研究可以为电池材料和微观结构的优化设计提供指导,对电极表面反应的原位监测,有助于对电极界面反应的机理进行深入的研究,从而指导正极材料结构改进,促进可充电铝离子电池的发展。     

暂态电化学表面增强拉曼光谱研究对硝基苯硫酚分子的电化学还原过程

对硝基苯硫酚是表面增强拉曼光谱研究中最常用的探针分子之一,对硝基苯硫酚在电极表面电化学还原反应的研究有助于对芳香族硝基化合物还原机理的认识. 本文应用暂态电化学-表面增强拉曼光谱技术,研究了对硝基苯硫酚在循环伏安和计时电流法过程中的表面增强拉曼光谱. 结果表明,实验实现了完全与电化学检测时间分辨率同步的表面增强拉曼光谱检测,以最快5毫秒的时间分辨率研究了对硝基苯硫酚分子在金电极表面的还原过程. 结果分析推测其此反应过程极快,在5毫秒的时间分辨率下仍难以捕获其中间物种. 本研究为人们更深层次研究和认识硝基苯类化合物电化学还原过程提供了参考和方向.     

寡聚脱氧核苷酸吸附状态随电位的变化

利用原位电化学及表面增强拉曼散射（SERS）光谱方法对寡聚脱氧核苷酸（26-mers ODN和13-mers ODN）在银电极表面上的吸附状态进行了研究. 实验表明, 单链寡聚脱氧核苷酸在银电极上有很好的SERS光谱,单链寡聚脱氧核苷酸在银表面上主要以碱基腺嘌呤（A）为吸附点,吸附状态随电位变化而变化, 链长较短的寡聚脱氧核苷酸在银电极表面的吸附态对电位变化较敏感.     

铂钌电极上乙醇解离吸附与氧化行为的原位SERS研究

应用电化学循环伏安法和原位表面增强拉曼光谱研究了乙醇在Pt-Ru电极上的解离吸附与氧化行为,首次获得了酸性介质中乙醇在Pt-Ru电极上解离吸附的表面拉曼光谱.实验表明:乙醇在粗糙铂和Pt-Ru电极上均能自发地解离出强吸附中间体CO,而且在Pt-Ru电极上,强吸附中间体CO氧化的过电位比在粗糙铂电极上降低了约140mV.初步证实酸性介质中乙醇在Pt-Ru电极上的氧化遵从双途径机理.本研究结果说明,表面增强拉曼光谱技术能拓展到有实用价值的电催化体系.     

甲酸在Pt-Ru/GC电极上氧化的SERS研究

采用循环伏安(CV)法、计时电流法和电化学原位表面增强拉曼散射光谱(SERS)技术研究了甲酸在Pt-Ru/GC电极上的氧化行为, 发现甲酸在Pt-Ru/GC电极上与在粗糙Pt电极上一样, 也能自发解离出强吸附中间体CO和活性中间体—COO－. 从分子水平证实钌的加入有利于提高电极对甲酸的电催化氧化活性, 当镀液中Pt：Ru的摩尔比从10∶1变化到1∶1, CO的氧化峰电位从0.41 V负移至0.35 V, 约负移了60 mV. Pt-Ru/GC(1∶1)电极与粗糙Pt电极相比, CO在电极表面氧化完毕的电位亦负移了约200 mV. 该研究结果表明, 电化学原位表面增强拉曼散射光谱技术可望成为研究电催化反应机理的普适谱学工具.     

电化学原位紫外可见反射光谱法

电化学原位（ｉｎ－ｓｉｔｕ）紫外可见反射光谱法是七十年代发展起来的一种光谱电化学方法。它对在分水平上电极界面结构和表面氧化，钝化，吸附，化学修饰等电化学过程具有独特的优越性。本文对电化学原位紫外可见反射光谱技术及其在电化学中的应用和发展趋势作了简要的叙述。     

Shell-isolated Nanoparticle-enhanced Raman Spectroscopy towards In-Situ Investigating of Interfacial Structure

Since the discovery of surface-enhanced Raman spectroscopy(SERS), it has been rapidly applied to the in situ study of electrochemical interfaces. Shell-isolated nanoparticle-enhanced Raman spectroscopy(SHINERS) stands out as one of the most powerful tools for the in situ study of interfacial structures, especially on well-defined single crystal surface. This perspective paper focuses on the study of interfacial structures with the SHINERS technique, including the electronic structure of heterogeneous metal surfaces, and the detection of molecules absorbed on the surface, as well as intermediate species, during electrochemical reactions. Finally, we present an outlook on future research and development of SHINERS for studying interfacial structures.     

In situ SERS and SHINERS study of electrochemical hydrogenation of p-ethynylaniline in nonaqueous solvents

Surface-enhanced Raman spectroscopy (SERS) studies of electrode/solution interfaces are important for understanding electrochemical processes. However, revealing the nature of reactions at well-defined single crystal electrode surfaces, which are SERS-inactive, remains challenging. In this work, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was used for the first time to study electrochemical adsorption and hydrogenation reactions at single crystal surfaces in nonaqueous solvents. A roughened Au surface was also studied for comparison. The experimental results show that the hydrogenation of adsorbed p-ethynylaniline (PEAN) on roughened Au electrode surfaces occurred at very negative potentials in methanol because of the catalytic effect of surface plasmon resonance (SPR). However, because “hot electrons” were blocked by the silica shell of Au@SiO₂ nanoparticles and aprotic acetonitrile was an ineffective hydrogen source, surface reactions at Au(111) were inhibited in the systems studied. Density functional theory (DFT) calculations revealed that the PEAN triple bond opened, allowing adsorption in a flat configuration on the Au(111) surface via two carbon atoms. This work provides an advanced understanding of electrochemical interfacial processes at single crystal surfaces in nonaqueous systems.     

Core-shell nanoparticle based SERS from hydrogen adsorbed on a rhodium(111) electrode

We present the first in situ surface Raman spectra of hydrogen on rhodium under electrochemical conditions using gold-core rhodium-shell (Au@Rh) nanoparticles for SERS or gold-core silica-shell (Au@SiO(2)) nanoparticles for SHINERS. The advantage of SHINERS lies in the versatility to study single crystal surfaces such as the H-Rh(111) system.     

Extraordinary enhancement of Raman scattering from pyridine on single crystal Au and Pt electrodes by shell-isolated Au nanoparticles

We used shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) to systematically study the adsorption of pyridine on low-index Au(hkl) and Pt(hkl) single crystal electrodes. Our gold-core silica-shell nanoparticles (Au@SiO(2) NPs) boost the intensity of Raman scattering from molecules adsorbed on atomically flat surfaces. The average enhancement factor reaches 10(6) for Au(110) and 10(5) for Pt(110), which is comparable to or even greater than that obtained for bare gold NPs (a widely adopted SERS substrate). 3D-FDTD simulations reveal that this large enhancement is due to the transfer of the "hotspots" from NP-NP gaps to NP-surface gaps. We also found that the SHINERS intensity strongly depends on the surface crystallographic orientation, with differences up to a factor of 30. Periodic DFT calculations and theoretical analysis of dielectric functions indicate that this facet-dependence is predominantly governed by the dielectric property of the surface. The results presented in this work may open up new approaches for the characterization of adsorbates and reaction pathways on a wide range of smooth surfaces.     

Synthesis, characterization, and 3D-FDTD simulation of Ag@SiO2 nanoparticles for shell-isolated nanoparticle-enhanced Raman spectroscopy

Au-seed Ag-growth nanoparticles of controllable diameter (50-100 nm), and having an ultrathin SiO(2) shell of controllable thickness (2-3 nm), were prepared for shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). Their morphological, optical, and material properties were characterized; and their potential for use as a versatile Raman signal amplifier was investigated experimentally using pyridine as a probe molecule and theoretically by the three-dimensional finite-difference time-domain (3D-FDTD) method. We show that a SiO(2) shell as thin as 2 nm can be synthesized pinhole-free on the Ag surface of a nanoparticle, which then becomes the core. The dielectric SiO(2) shell serves to isolate the Raman-signal enhancing core and prevent it from interfering with the system under study. The SiO(2) shell also hinders oxidation of the Ag surface and nanoparticle aggregation. It significantly improves the stability and reproducibility of surface-enhanced Raman scattering (SERS) signal intensity, which is essential for SERS applications. Our 3D-FDTD simulations show that Ag-core SHINERS nanoparticles yield at least 2 orders of magnitude greater enhancement than Au-core ones when excited with green light on a smooth Ag surface, and thus add to the versatility of our SHINERS method.     

Exploring interfacial electrocatalytic reactions by shell-isolated nanoparticle-enhanced Raman spectroscopy

The investigation of interfacial processes at the molecular level is an essential research area in electrocatalysis. To more clearly understand the electrocatalytic interfacial reaction mechanism, an in situ and highly sensitive surface investigation technique is required. Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) is a highly sensitive surface analysis approach that can gather spectral evidence of interfacial intermediates, which commonly have a short lifetime and trace amount that are difficult to be detected. In this review, we first cover the basics of the SHINERS and SHINERS-satellite strategies, including their principle, fabrication method, and features. We then summarized the applications of SHINERS and SHINERS-satellite strategies for the studies of interfacial electrocatalytic process in fuel cells, water electrolysis, and CO oxidation and reduction. Last but not least are the summary and outlook, in which the potential research prospects of SHINERS and SHINERS-satellite are proposed.     

Probing Interfacial Electronic and Catalytic Properties on Well‐Defined Surfaces by Using In Situ Raman Spectroscopy

Heterogeneous metal interfaces play a key role in determining the mechanism and performance of catalysts. However, in situ characterization of such interfaces at the molecular level is challenging. Herein, two model interfaces, Pd and Pt overlayers on Au single crystals, were constructed. The electronic structures of these interfaces as well as effects of crystallographic orientation on them were analyzed by shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) using phenyl isocyanide (PIC) as a probe molecule. A clear red shift in the frequency of the C≡N stretch (ν_NC) was observed, which is consistent with X‐ray photoelectron spectroscopy (XPS) data and indicates that the ultrathin Pt and Pd layers donate their free electrons to the Au substrates. Furthermore, in situ electrochemical SHINERS studies showed that the electronic effects weaken Pt?C/Pd?C bonds, leading to improved surface activity towards CO electrooxidation.     

In situ Spectroscopic Insight into the Origin of the Enhanced Performance of Bimetallic Nanocatalysts towards the Oxygen Reduction Reaction (ORR)

It is vital to understand the oxygen reduction reaction (ORR) mechanism at the molecular level for the rational design and synthesis of high activity fuel‐cell catalysts. Surface enhanced Raman spectroscopy (SERS) is a powerful technique capable of detecting the bond vibrations of surface species in the low wavenumber range, however, using it to probe practical nanocatalysts remains extremely challenging. Herein, shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) was used to investigate ORR processes on the surface of bimetallic Pt₃Co nanocatalyst structures. Direct spectroscopic evidence of *OOH suggests that ORR undergoes an associative mechanism on Pt₃Co in both acidic and basic environments. Density functional theory (DFT) calculations show that the weak *O adsorption arise from electronic effect on the Pt₃Co surface accounts for enhanced ORR activity. This work shows SHINERS is a promising technique for the real‐time observation of catalytic processes.