扫描电化学显微镜在光电能源研究领域的应用

作为一种扫描探针技术,扫描电化学显微镜(SECM)在金属防腐、材料表征、生物医学和新能源技术等领域的研究中扮演着重要角色。本文简要介绍了SECM的基本工作原理和常用的两种工作模式:反馈模式和收集/产生模式;综述了SECM在太阳能电池和太阳光解水制氢两个光电能源研究领域的应用进展,同时结合课题组的工作基础,特别是近期利用SECM筛选合适金属离子掺杂改性WO₃光阳极的工作,对SECM在筛选半导体电极材料方面的应用特点进行了实例展示介绍,最后简要总结了SECM在光电能源研究领域的发展及方向。     

扫描电化学显微镜沉积六氰合铁酸盐微阵及其催化活性成像

采用扫描电化学显微技术在玻碳电极表面沉积出K₂Cu[Fe(CN)₆]和K₂Fe[Fe(CN)₆]微阵, 并对所得的微阵结构进行了可视化表征. 铜微电极和镀铁铂微电极阳极化产生金属离子, 然后与玻碳电极(基底电极)上还原产生的[Fe(CN)₆]^4－在微区生成六氰合铁酸盐沉淀, 操纵探针以跳跃沉积方式可以得到沉淀的点阵结构. 通过改变K₃[Fe(CN)₆]的浓度和沉积时间可以调整沉淀斑的直径和厚度. 扫描电化学显微镜成像表明微阵结构对多巴胺的氧化和过氧化氢的还原有明显的电催化作用.     

Scanning Electrochemical Cell Microscopy Investigation of Single ZIF‐Derived Nanocomposite Particles as Electrocatalysts for Oxygen Evolution in Alkaline Media

“Single entity” measurements are central for an improved understanding of the function of nanoparticle‐based electrocatalysts without interference arising from mass transfer limitations and local changes of educt concentration or the pH value. We report a scanning electrochemical cell microscopy (SECCM) investigation of zeolitic imidazolate framework (ZIF‐67)‐derived Co?N‐doped C composite particles with respect to the oxygen evolution reaction (OER). Surmounting the surface wetting issues as well as the potential drift through the use of a non‐interfering Os complex as free‐diffusing internal redox potential standard, SECCM could be successfully applied in alkaline media. SECCM mapping reveals activity differences relative to the number of particles in the wetted area of the droplet landing zone. The turnover frequency (TOF) is 0.25 to 1.5 s^?1 at potentials between 1.7 and 1.8 V vs. RHE, respectively, based on the number of Co atoms in each particle. Consistent values at locations with varying number of particles demonstrates OER performance devoid of macroscopic film effects.     

Alternating Current Measurements in Scanning Electrochemical Microscopy,Part 2: Detection of Adsorbates

A scanning electrochemical microscope (SECM) in ac mode is used for the characterisation of the adsorption process during the hydrogen evolution reaction (HER) in sulfuric acid solution. It is shown that this technique allows quantitative analysis of the adsorption process, and measurements of the differential capacitance with the frequency as parameter are obtained. The time constant for relaxation of adsorbed hydrogen (H_ads) is approximately 2 Hz, and analysis of the Nyquist plot allows direct evaluation of the charge involved. In addition, the direct comparison of the usual electrochemical impedance data and ac‐SECM results obtained simultaneously permits characterisation of processes occurring at the surface and in solution.     

Analytical Expressions for Quantitative Scanning Electrochemical Microscopy (SECM)

Scanning electrochemical microscopy (SECM), is a recent analytical technique in electrochemistry, which was developed in the 1990s and uses microelectrodes to probe various surfaces. Even with the well‐known disc microelectrodes, the system geometry is not as simple as in regular electrochemistry. As a consequence even the simplest experiments, the so‐called positive and negative feedback approach curves, cannot be described with exact analytical expressions. This review gathers all the analytical expressions available in the SECM literature in steady‐state feedback experiments. Some of them are claimed as general expressions, other are presented as approximate. Their validity is discussed in the light of the current understanding and computer facilities.     

扫描电化学显微镜技术近期进展

本文较详细地介绍了扫描电化学显微镜技术的近期进展,引用参考文献77篇。     

Alternating‐Current Measurements in Scanning Electrochemical Microscopy,Part 1: Principle and Theory

The development of the scanning electrochemical microscope in ac mode is presented from both experimental and theoretical point of views. The experiments are performed with the ferri/ferrocyanide redox mediator as model system. Based on analysis of the frequency‐dependent collection efficiency, diffusion between the probe and the substrate is investigated, and analysis of time constants allows evaluation of the size of the sensing area under investigation. The experimental results are in good agreement with numerical simulations.     

扫描电化学显微镜及其最新进展

对扫描电化学显微镜技术的基本原理,仪器设备,最新的研究进展和发展展望进行了评述。     

扫描电化学显微镜直接电沉积法构建葡萄糖氧化酶微米点

利用自制的凹形电极在铂基底电极上直接构建了葡萄糖氧化酶微米点. 首先, 将电聚合和电化学刻蚀法相结合制备了凹形铂微米电极. 然后将此种电极作为参比及辅助电极, 基底铂电极作为工作电极, 利用葡萄糖氧化酶在合适的条件下(浓度、一定量Triton X-100存在、电极电位等)由于电极表面pH的降低可以在铂电极上电沉积这一特性, 将酶固定在铂基底电极上, 微修饰得到了具有活性的葡萄糖氧化酶微米点. 最终用扫描电子显微镜和扫描电化学显微镜对所得微米点进行了表征. 所得微米点直径约20 μm, 且具有催化活性. 该方法简便, 干扰因素较少.     

Investigating Localized Electrochemical of Ferrocenyl-Imidazolium in Ionic Liquid Using Scanning Electrochemical Microscopy Configuration

In the present work, the localized electrochemical behavior of redox molecule in ionic liquid has been investigated using scanning electrochemical microscopy. The electrochemical response of ferrocenyl-imidazolium redox mediator was studied by recording approach curves over a conducting and insulating substrate in an undiluted ionic liquid. The SECM approach curve over the conducting substrate displays a positive feedback, as observed in classical solvent. However, in the case of the insulating substrate, the approach curve reveals different shapes, depending on the used approach speed. In this configuration, low approach speed is necessary to reach the expected negative feedback. Interestingly, at a very close distance between the UME and the insulating substrate, a thin film behavior is revealed. In addition, the approach curves on both insulator and conducting substrates can be reconstructed from punctual responses at different distance tip-substrate. The latter match perfectly with the expected theoretical curves over conducting and insulating under diffusion control.     

Non‐destructive Patterning of Carbon Electrodes by Using the Direct Mode of Scanning Electrochemical Microscopy

Patterning of glassy carbon surfaces grafted with a layer of nitrophenyl moieties was achieved by using the direct mode of scanning electrochemical microscopy (SECM) to locally reduce the nitro groups to hydroxylamine and amino functionalities. SECM and atomic force microscopy (AFM) revealed that potentiostatic pulses applied to the working electrode lead to local destruction of the glassy carbon surface, most likely caused by etchants generated at the positioned SECM tip used as the counter electrode. By applying galvanostatic pulses, and thus, limiting the current during structuring, corrosion of the carbon surface was substantially suppressed. After galvanostatic patterning, unambiguous proof of the formation of the anticipated amino moieties was possible by modulation of the pH value during the feedback mode of SECM imaging. This patterning strategy is suitable for the further bio‐modification of microstructured surfaces. Alkaline phosphatase, as a model enzyme, was locally bound to the modified areas, thus showing that the technique can be used for the development of protein microarrays.     

Progress in Scanning Electrochemical Microscopy by Coupling with Electrochemical Impedance and Quartz Crystal Microbalance

Scanning electrochemical microscopy (SECM) is a powerful technique for performing quantitative measurements at a local scale. This paper covers the development of combinations of SECM with electrochemical impedance spectroscopy (EIS) and electrochemical quartz crystal microbalance (EQCM). Basic aspects are described and potential applications reported by several research groups are covered. The unique advantages of the coupled techniques—with additional information being obtained from each coupling—are also discussed.     

In Situ Scanning Tunneling Microscopy of Cobalt‐Phthalocyanine‐Catalyzed CO2 Reduction Reaction

We report a molecular investigation of a cobalt phthalocyanine (CoPc)‐catalyzed CO₂ reduction reaction by electrochemical scanning tunneling microscopy (ECSTM). An ordered adlayer of CoPc was prepared on Au(111). Approximately 14 % of the adsorbed species appeared with high contrast in a CO₂‐purged electrolyte environment. The ECSTM experiments indicate the proportion of high‐contrast species correlated with the reduction of Co^IIPc (?0.2 V vs. saturated calomel electrode (SCE)). The high‐contrast species is ascribed to the CoPc‐CO₂ complex, which is further confirmed by theoretical simulation. The sharp contrast change from CoPc‐CO₂ to CoPc is revealed by in situ ECSTM characterization of the reaction. Potential step experiments provide dynamic information for the initial stage of the reaction, which include the reduction of CoPc and the binding of CO₂, and the latter is the rate‐limiting step. The rate constant of the formation and dissociation of CoPc‐CO₂ is estimated on the basis of the in situ ECSTM experiment.     

Imaging Local Proton Fluxes through a Polycarbonate Membrane by Using Scanning Electrochemical Microscopy and Functionalized Alkanethiols

A new application of scanning electrochemical microscopy (SECM) to probe the transport of protons through membranes is described. Herein, a probe ultramicroelectrode (UME) is modified with a self‐assembled monolayer (SAM) of 11‐mercaptoundecanoic acid to qualitatively image areas within different pH regions above a track‐etched membrane. The current response of the modified electrode in the presence of potassium hexacyanoferrate as electroactive component is different in acidic and alkaline solutions. Depending on the pH value of the solution, the SAM‐covered electrode exposes either a neutral or a negatively charged insulating monolayer at pH 3 or 7, respectively, which leads to an increase/decrease in the faradaic current due to electrostatic interactions between the neutral/charged surface and the charged redox mediator. Therefore, local pH changes in the close vicinity of a membrane‐like substrate lead to different current responses recorded at the tip electrode when scanning above the surface.     

Monitoring Tyrosinase Expression in Non‐metastatic and Metastatic Melanoma Tissues by Scanning Electrochemical Microscopy

Although tremendous progress has been made in the diagnosis of melanoma, the identification of different stages of malignancy in a reliable way remains challenging. Current strategies rely on optical monitoring of the concentration and spatial distribution of specific biomarkers. State‐of‐the‐art optical methods can be affected by background‐color interference and autofluorescence. We overcame these shortcomings by employing scanning electrochemical microscopy (SECM) to map the prognostic indicator tyrosinase (TyR) in non‐metastatic and metastatic melanoma tissues by using soft‐stylus microelectrodes. Electrochemical readout of the TyR distribution was enabled by adapting an immunochemical method. SECM can overcome the limitations of optical methods and opens unprecedented possibilities for improved diagnosis and understanding of the spatial distribution of TyR in different melanoma stages.     

Localized Visualization of Chemical Cross-Talk in Microsensor Arrays by Using Scanning Electrochemical Microscopy

 An investigation of an array of four Pt microband electrodes 25 μm wide and spaced 25 μm apart was performed with the scanning electrochemical microscope (SECM). Where possible the SECM measurements were confirmed with conventional electrochemical measurements. It is shown how the sensiti- vity of the SECM recycling current to the activity of the underlying surface can be used to probe the homogeneity of enzyme-modified microelectrodes. The diffusion of H₂O₂ between these micro enzyme- electrodes and unmodified electrodes was investigated and it was demonstrated how the SECM can be a powerful tool in the elucidation of the properties of these electrodes. Received June 8, 1998. Revision November 12, 1998.     

The Study on the Self-assembled Monolayer （SAMs） of Porphyrin with Different Chain Length by Scanning Electrochemical Microscopy （SECM）

Self-assembled monolayers (SAMs) have become a subject of intense interest in materials science and molecular technologies, because they provided highly ordered structures on the surfaces. SAMs, comprising hydrocarbons bound to the gold surface via a S-Au…     

Development of a Temperature-pulse Enhanced Electrochemical Glucose Biosensor and Characterization of its Stability via Scanning Electrochemical Microscopy

Glucose oxidase (GOx) is an enzyme frequently used in glucose biosensors. As increased temperatures can enhance the performance of electrochemical sensors, we investigated the impact of temperature pulses on GOx that was drop-coated on flattened Pt microwires. The wires were heated by an alternating current. The sensitivity towards glucose and the temperature stability of GOx was investigated by amperometry. An up to 22-fold increase of sensitivity was observed. Spatially resolved enzyme activity changes were investigated via scanning electrochemical microscopy. The application of short (<100 ms) heat pulses was associated with less thermal inactivation of the immobilized GOx than long-term heating.     

Characterization of Inherently Chiral Electrosynthesized Oligomeric Films by Voltammetry and Scanning Electrochemical Microscopy (SECM)

A voltammetric and scanning electrochemical microscopy (SECM) investigation was performed on an inherently chiral oligomer-coated gold electrode to establish its general properties (i.e., conductivity and topography), as well as its ability to discriminate chiral electroactive probe molecules. The electroactive monomer (S)-2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bibenzothiophene ((S)-BT₂T₄) was employed as reagent to electrodeposit, by cyclic voltammetry, the inherently chiral oligomer film of (S)-BT₂T₄ (oligo-(S)-BT₂T₄) onto the Au electrode surface (resulting in oligo-(S)-BT₂T₄-Au). SECM measurements, performed in either feedback or competition mode, using the redox mediators [Fe(CN)₆]⁴⁻ and [Fe(CN)₆]³⁻ in aqueous solutions, and ferrocene (Fc), (S)-FcEA, (R)-FcEA and rac-FcEA (FcEA is N,N-dimethyl-1-ferrocenylethylamine) in CH₃CN solutions, indicated that the oligomer film, as produced, was uncharged. The use of [Fe(CN)₆]³⁻ allowed establishing that the oligomer film behaved as a porous insulating membrane, presenting a rather rough surface. This was inferred from both the approach curves and linear and bidimensional SECM scans, which displayed negative feedback effects. The oligomer film acquired semiconducting or fully conducting properties when the Au electrode was biased at potential more positive than 0.6 V vs. Ag|AgCl|KCl. Under the latter conditions, the approach curves displayed positive feedback effects. SECM measurements, performed in competition mode, allowed verifying the discriminating ability of the oligo-(S)-BT₂T₄ film towards the (S)-FcEA and (R)-FcEA redox mediators, which confirmed the results obtained by cyclic voltammetry. SECM linear scans indicated that the enantiomeric discriminating ability of the oligo-(S)-BT₂T₄ was even across its entire surface.     

纳米尺度扫描电化学显微镜的探针制备及在电催化氧和氢反应研究中的应用

扫描电化学显微镜是一种在检测样品表面物理形貌的同时能提供丰富的电化学信息的扫描探针技术,由于超微电极的引入,它可以高时空分辨率地探究各类样品的物理形貌和电化学性能之间的构效关系. 随着现代纳米科技的不断发展,扫描探针的尺寸也逐渐从亚微米发展到纳米级别. 与此同时,高效优选各类氧反应和氢反应电催化材料,明晰其电化学反应过程和性能是二十一世纪绿色新能源转换存储系统（如可再生燃料电池、金属空气电池等）的重要研究方向. 本文首先概括了可应用于扫描电化学显微镜的纳米级扫描探针的制备及发展,之后着重介绍了近四年纳米尺度扫描电化学显微镜在电催化氧反应和氢反应研究中的一些最新研究进展. 最后以点窥面,对未来纳米尺度扫描电化学显微镜的未来发展趋势作了展望.