Electrochemical impedance spectroscopy as a probe for wet chemical silicon oxide characterization

The kinetics of the chemical growth of silicon oxide in H₂O₂-containing ammonia solutions and its break-up by dilute ammonia solutions was investigated using electrochemical techniques and more specifically electrochemical impedance spectroscopy. The recording of the open circuit potential (OCP), complemented by successive impedance diagrams, demonstrates clearly the build-up of a silicon oxide passivating layer when hydrophobic Si surfaces are immersed in NH₃+H₂O₂ solutions. The thickening of the chemical oxide coating mainly results in the decrease of the capacitance value together with the enhancement of the ohmic surface resistance. On the other hand, pure ammonia dilute solutions lead to the progressive destruction of this hydrophilic passivating surface oxide, which is revealed by the simultaneous decay of the real component of the impedance. Finally, we observed the break-up of the passive layer, characterized by a sudden drop of the OCP to a value quite identical to that obtained with a bare Si surface. This process resulted in a dramatic corrosion of the substrate surface. Electronic Publication     

Impedimetric immunosensor for human serum albumin detection on a direct aldehyde-functionalized silicon nitride surface

In this work we report the fabrication and characterization of a label-free impedimetric immunosensor based on a silicon nitride (Si₃N₄) surface for the specific detection of human serum albumin (HSA) proteins. Silicon nitride provides several advantages compared with other materials commonly used, such as gold, and in particular in solid-state physics for electronic-based biosensors. However, few Si₃N₄-based biosensors have been developed; the lack of an efficient and direct protocol for the integration of biological elements with silicon-based substrates is still one of its the main drawbacks. Here, we use a direct functionalization method for the direct covalent binding of monoclonal anti-HSA antibodies on an aldehyde-functionalized Si-p/SiO₂/Si₃N₄ structure. This methodology, in contrast with most of the protocols reported in literature, requires less chemical reagents, it is less time-consuming and it does not need any chemical activation. The detection capability of the immunosensor was tested by performing non-faradaic electrochemical impedance spectroscopy (EIS) measurements for the specific detection of HSA proteins. Protein concentrations within the linear range of 10⁻¹³–10⁻⁷ M were detected, showing a sensitivity of 0.128 Ω μM⁻¹ and a limit of detection of 10⁻¹⁴ M. The specificity of the sensor was also addressed by studying the interferences with a similar protein, bovine serum albumin. The results obtained show that the antibodies were efficiently immobilized and the proteins detected specifically, thus, establishing the basis and the potential applicability of the developed silicon nitride-based immunosensor for the detection of proteins in real and more complex samples.     

IMPEDANCE CHARACTERISTICS OF POLYFURAN FILMS

Electrochemical impedance spectroscopy (EIS) was first used for the characterization of polyfuran (PFu) films thathad been formed electrochemically on an Au electrode. The polyfuran was measured in high oxidation state, intermediateoxidation state and reduction state, respectively. As the oxidation level is increased, the ionic conductivity of PFu/BF4-increases. And impedance studies on PFu show that the anion BF4- appears to be mobile with a high diffusion coefficient of approximately 10-8 cm2·s-1.     

Capacitive performance of ordered mesoporous carbons with tunable porous texture in ionic liquid electrolytes

Ordered mesoporous carbons with tunable pore size and surface chemical properties are prepared by doping boric acid using a hard-templating method. The capacitive performance of these carbons is investigated in two common ionic liquids of EMImBF₄ and EMImTSFI. As demonstrated by the structure analysis, the pore size increases from 3.3 to 5.7 nm and the content of oxygenated groups on the carbon surface increases from 2.0 to 5.2 mol% with the increase of the boron doping from 0 to 50 mol%. In ionic liquid electrolyte, the carbons mainly show typical electric double layer capacitance, and the capacitance retention ratio and ion diffusion in the carbon channels is determined to the surface chemical property. The prepared carbons present visible pseudo-capacitance due to the rapid redox reactions of the oxygenated groups in hydrophilic EMImBF₄, reflecting by the increasing of the specific surface capacitance, while no visible pseudo-capacitive behavior was observed in hydrophobic EMImTSFI.     

离子液体添加剂[BMIM]HSO4对锌电积过程析氧反应动力学的影响

研究了1-丁基-3-甲基咪唑硫酸氢盐([BMIM]HSO₄)离子液体对锌电积过程析氧反应的影响. 研究工作借助于动电位极化, 电化学阻抗谱, 扫描电镜和X射线衍射等测试技术. 动电位极化曲线及对应的动力学参数分析表明, [BMIM]HSO₄对阳极析氧反应具有催化作用,可提高析氧反应速率常数. 电化学阻抗谱数据表明,[BMIM]HSO₄能显著降低阳极析氧电荷传递电阻,在所研究的1.85-2.10 V电位范围内添加5 mg·L^-1 [BMIM]HSO₄, 电阻值至少降低50%. 此外, 添加剂对阳极表面二次反应具有抑制作用, 其在阳极表面的吸附,阻碍了阴离子的阳极活化位点吸附过程. 电化学测试结果与长时间(120 h)阳极极化后所得阳极表面形貌和结晶取向分析结果相一致. [BMIM]HSO₄的添加能有效抑制中间产物β-PbO₂的形成,促进铅银电极表面大块且疏松多孔α-PbO₂的生成,加速阳极析氧的进行.     

Electrochemical impedance spectroscopy study of cuprous oxide films formed on copper: effect of pH and sulfate and carbonate ions

The semiconducting properties of anodic passive films formed potentiostatically on polycrystalline copper in aqueous borax solutions were studied using electrochemical impedance spectroscopy, photocurrent spectroscopy and ellipsometric measurements. The semiconducting nature of the cuprous passive layer was analysed as a function of pH (9.2>pH>7.4), electrode potential and with the addition of 3.5 mM Na₂CO₃ and 8 mM Na₂SO₄. The different growth conditions change the compactness and the defect or excess of cations accumulated in the compact inner cuprous layer, leading to different semiconducting properties. Electronic Publication     

Electrochemical impedance spectroscopy of diluted solutions of Bisphenol A

The electrochemical oxidation of bisphenol A was carried out using platinum, glassy carbon, titanium dioxide and polypyrrole modified working electrodes. Acetonitrile and water were evaluated as solvents; however, passivation could not be avoided due to the formation of insoluble oxidation products that adhere to the surface. The use of ultrasound did not show any improvement either. Finally, by using electrochemical impedance spectroscopy measurements at the open circuit potential it was possible to obtain a steady response of one of the components of the equivalent circuit proposed. This response is only dependent on the concentration of bisphenol A. At the same time it was demonstrated that the adsorption is a fundamental process that occurs more easily in water than in acetonitrile, this fact is reflected in the impedance spectra.     

Comparative Permeation Study of Different Types of Myoglobin Layer‐by‐Layer Films and the Effect of Film Permeability on Their Electrochemistry and Electrocatalysis

Three different types of myoglobin (Mb) layer‐by‐layer films were assembled respectively with TiO₂ sol‐gel by vapor‐surface deposition, TiO₂ nanoparticles, and poly(styrenesulfonate), designated as {SG‐TiO₂/Mb}_n, {NP‐TiO₂/Mb}_n, and {PSS/Mb}_n. The permeability of the films was studied and compared by rotating disk voltammetry (RDV) and electrochemical impedance spectroscopy (EIS) with different electroactive probes, showing a general permeability sequence of {SG‐TiO₂/Mb}_n>{NP‐TiO₂/Mb}_n>{PSS/Mb}_n. The electrochemical and electrocatalytic activity of Mb in these films were also investigated and compared by cyclic voltammetry (CV), RDV, and amperometry, indicating that among the three Mb films, {SG‐TiO₂/Mb}_n films demonstrated the highest maximum surface concentration of electroactive Mb and the best electrocatalytic performances toward reduction of H₂O₂. All these advantages could be attributed to the unique architecture and porous structure of {SG‐TiO₂/Mb}_n films, which could greatly facilitate the mass transport of small counterions and catalytic substrates within the films. The various influencing factors on the permeability, electrochemistry, and electrocatalysis of the Mb films were also investigated in detail.     

氢处理二氧化钛的光催化性能及电化学阻抗谱

通常可通过物理（浸渍法等）、化学方法（溶胶 -凝胶 ,电化学沉积法等）向光催化剂晶格中引入金属“小岛” ,以加速光生电子 -空穴的转移 ,提高改性后光催化剂的活性 [1].同时 ,运用物理和光电化学等手段研究半导体光催化剂的表面性质和光电化学性质 ,可以为评价这些改性光催化剂的活性和研究反应机理提供依据 [2,3].电化学阻抗谱 (EIS)方法是研究材料性质、化学 (特别是电化学 )过程和界面反应机理的有力工具 [4].本工作运用 EIS手段研究了纳米 TiO_2在氢气气氛下热处理后 TiO_2的阻抗谱特征同其光催化活性之间的关系 .1实验部分　　…     

Electrochemical behaviour of Ni-Co amorphous alloys in alkaline solutions

The dissolution processes of amorphous G15 (Ni₅₈Co₂₀B₁₂Si₁₀) and G16 (Ni₂₅Co₅₀B₁₀Si₁₅) alloys in carbonate-bicarbonate buffers (8.9≤pH≤10.5) have been studied using voltammetry and stationary polarization techniques combined with electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy (XPS) measurements. Results indicate that the electrochemical processes are dependent on the applied potential, the alloy composition, and the pH and ionic strength of the electrolyte. An enhancement of the corrosion processes is observed when the pH and the ionic strength are increased and when the Co content of the alloy diminishes. Furthermore, XPS provided information about the composition of the surface layer. Electronic Publication     

扫描电化学显微镜原位表征pH值对核电蒸汽发生器合金腐蚀行为的影响

用扫描电化学显微镜(SECM)和电化学阻抗谱(EIS)原位表征了溶液pH值对核电蒸汽发生器800 合金溶液中的腐蚀行为的影响. 实验结果表明：在酸性氯化钠溶液中,SECM探针渐进曲线为正反馈,表明800合金为活化阳极溶解,腐蚀电位下的EIS 图呈现完整的单容抗弧特征;而在中性或者碱性溶液中,SECM探针渐进曲线为负反馈,表明800 合金为自钝化,不同阳极电位下的EIS 图均呈现不完整的容抗弧特征,但随着阳极极化电位的增加,EIS 谱容抗弧半径减小,表明钝化膜的耐蚀性下降;SECM二维扫描图像结果显示探针电流增加,表明电极表面活性增加,即钝化膜的溶解速度增加. 而在中性或者碱性溶液中的SECM二维图像中均可观察到若干活性点,这可能与晶界或者金属夹杂物等有关.     

Aptamer-based biosensor for label-free detection of ethanolamine by electrochemical impedance spectroscopy

A label-free sensing assay for ethanolamine (EA) detection based on G-quadruplex-EA binding interaction is presented by using G-rich aptamer DNA (Ap-DNA) and electrochemical impedance spectroscopy (EIS). The presence of K⁺ induces the Ap-DNA to form a K⁺-stabilized G-quadruplex structure which provides binding sites for EA. The sensing mechanism was further confirmed by circular dichroism (CD) spectroscopy and EIS measurement. As a result, the charge transfer resistance (R_CT) is strongly increased as demonstrated by using the ferro/ferricyanide ([Fe(CN)₆]^3−/4−) as a redox probe. Under the optimized conditions, a linear relationship between ΔR_CT and EA concentration was obtained over the range of 0.16 nM and 16 nM EA, with a detection limit of 0.08 nM. Interference by other selected chemicals with similar structure was negligible. Analytical results of EA spiked into tap water and serum by the sensor suggested the assay could be successfully applied to real sample analysis. With the advantages of high sensitivity, selectivity and simple sensor construction, this method is potentially suitable for the on-site monitoring of EA contamination.     

贮氢电极电化学阻抗谱及其数学模型

从分析贮氢电极的放电过程着手,建立了具有明显物理意义贮氢电极电化学阻抗谱的数学模型,以该数学模型为基础,讨论了与电极材料性质和电极荷电状态相联系的一些参数。     

Study of the electrochemical behaviour of a carbon steel electrode in sodium sulfate aqueous solutions using electrochemical impedance spectroscopy

The study of a plain carbon steel (AISI 1020) in Na₂SO₄ aqueous solutions at different concentrations was carried out by electrochemical impedance spectroscopy (EIS) in order to determine the corrosion mechanism and to obtain representative corrosion rates of the system. EIS was used to measure corrosion current densities at high concentrations in the range 0.1–1 wt% Na₂SO₄, but in the low concentration range, from 0.001 to 0.01 wt%, a scattered Nyquist plot was obtained. Other electrochemical techniques, such as polarization resistance (PR), Tafel plots and electrochemical noise (EN), were also used in this analysis. The charge transfer resistance was determined and compared with the PR and noise resistance. Electronic Publication     

基于石墨烯化学修饰电极的适体传感器

采用石墨烯(RGO)作载体,凝血酶适体(TBA)作探针,凝血酶为目标蛋白,电化学阻抗谱(EIS)为检测技术,建立了检测蛋白质的新方法.由于RGO可增大电极有效表面积并提高电极表面电子传输速率以及TBA的特异性识别能力,此方法具有较高的灵敏度和良好的选择性.采用本方法检测凝血酶的线性范围为0.3～10 fmol/L,检出限为0.26 fmol/L.本研究将RGO应用于电化学适体传感器,证实了RGO修饰电极在电化学适体传感器领域中潜在的应用价值.