Needle-type ultra micro silver/silver chloride reference electrode for use in micro-electrochemistry.

A needle-type ultra micro silver/silver chloride reference electrode having a micro capillary with outer and inner diameters of 1.0 microm and 0.5 +/- 0.2 microm, respectively, was constructed. This micro reference electrode can be stuck into a living cell, and is applicable to use in very small environments, such as an electrochemical cell of an electrochemical scanning tunneling microscope or the detection portion of a micro-TAS. Excellent stability and repeatability of the micro reference electrode potential could be obtained by filling the micro capillary with agar gel containing 3.33 mol/L potassium chloride as a salt bridge, by covering the bare part of the silver wire on which silver chloride was deposited, and by electromagnetic shielding of the measurement cell and wire lead from the electromagnetic waves. The electrode showed stable potential for 7 days after its fabrication using 3.3 mol/L potassium chloride aqueous solution containing silver chloride as an internal electrolyte solution. The electrode exhibited constant electrode potential and excellent stability in test solutions of pH 5-9. The electrode potential of a commercial pH glass electrode measured against the micro reference electrode in standard pH buffer solutions was in good accordance with the Nernst equation.     

The In-cell iR Compensation Using a Four-electrode System

It is well known that the iR compensation is very important in electrochemistry, especially in fast, ultra-fast and transient voltammetry for kinetic and mechanistic studies. The modern design of potentiostat is usually of the three-electrode system, in w…     

Destruction of butyraldehyde isomers using silver catalyzed electrochemical oxidation

The destruction of butyraldehyde isomers has been studied using a silver catalyzed electrochemical oxidation technique. The destruction rates of nand iso-butyraldehydes were measured as a function of the concentrations of butyraldehyde isomers, silver and nitric acid in aqueous solutions, anode potential and temperature. More than 99% of n-butyraldehyde in 3M nitric acid was destroyed within 50 minutes by electrochemical oxidation at the anode potential of 1.6V versus a reference saturated calomel electrode (SCE). The process was found to be applicable to the destruction of butyraldehyde isomers in nitric acid solutions.     

Improvement of the silver/silver chloride reference electrode and its application to pH measurement

When a silver/silver chloride (Ag AgCl ) reference electrode was used continuously in a low conductivity solution or reductive solution, it was often observed that stability of the liquid junction potential was lost. This phenomenon was remarkable with a Ag AgCl reference electrode compared to a calomel reference electrode. We found that 340 mg l(-1) of silver was dissolved in 3 M potassium chloride (KCl) internal solution as silver complex ions (AgCl(-(x-1))(x)) for x = 2 or 3. However, only 1.93 mg l(-1) of silver chloride (AgCl) can theoretically be dissolved in water. The complex ion that effused into the sample solution through the liquid junction clogged the liquid junction (e.g. porous ceramic) as AgCl, or as metallic silver (Ag) in reducing solution. Therefore, the constant effusion of KCl internal solution was inhibited, and the liquid junction potential became unstable or fluctuating. A new reference electrode was developed, which can eliminate AgCl(-(x-1))(x) in 3 M KCl internal solution by the use of chelating resins. A combination of this reference electrode with a pH electrode made long-term stable pH measurements possible.     

集成化金膜阵列电极的制作研究

以聚乙烯不干胶掩膜版法结合金属溅射沉积技术在FR-4玻璃纤维版上制作了由6个金膜工作电极(1 mm×2 mm)、1个大面积金膜对电极(2 mm×13 mm)和1个厚膜Ag/AgCl参比电极构成的集成化金膜阵列电极系统,并利用电化学手段对阵列电极系统进行了考察。研究结果表明,K3Fe(CN)6在厚膜Ag/AgCl/1.0 mol/L NaCl参比电极上的式电位与商业Ag/AgCl/3.0 mol/L NaCl参比电极相差0.067 V;参比电极放置1个月后,测量电位未发生明显变化。利用扫描电化学显微镜对工作电极表面平整度进行考察,结果表明工作电极表面具有较好的平整度。通过测量H2SO4还原峰面积评价了工作电极电化学面积的批内、批间一致性;通过K3Fe(CN)6在电极上的Ipa/Ipc比值评价了工作电极电化学特性的批内、批间一致性。结果表明,阵列电极面积和电化学特性具有良好的批内和批间一致性。对集成化金膜阵列电极系统的研究结果表明,聚乙烯不干胶掩膜版法结合金属溅射沉积技术制作的阵列电极能够满足电化学电极的要求,可作为电化学生物传感器的基础电极。     

A Reference Electrode System for Electrochemical Measurements in Pure Water

A reference hydrogen electrode systems is constructed by employing a strip of proton‐type Nafion membrane as an ion‐conducting “bridge” to connect a reversible hydrogen electrode (RHE) in an acidic solution to an electrochemical system using pure water as electrolyte, in which the working electrode (WE) is placed. Using such a reference electrode system, the potential at the “WE/pure water” interface is equal to the equilibrium hydrogen electrode potential in pure water when the potential difference between RHE and WE is zero, irrespective of the pH value of the acidic solution in the RHE compartment. The accuracy and reproducibility of the WE potential measurements are within 1–2 mV.     

一种铂网栅薄层光谱电化学池的制作及表征

以铂网栅电极作工作电极,设计制作了一种应用于紫外-可见光谱电化学研究的新型光透薄层电化学池（OTTLE）,并以铁氰化钾-亚铁氰化钾体系对此光谱化学池进行了表征。铁氰化钾-亚铁氰化钾体系在该池中有良好的循环伏安特性,并可获得良好的紫外-可见光谱。测得的克式量电位E^0,电子转移数n与文献结果一致。     

The renovated silver ring electrode

In this preliminary note, a new type of working electrode – the renovated silver ring electrode (RSRE) – is presented. The main constituents of the RSRE: a specially constructed silver ring electrode, a silver sheet used as silver counter/quasi-reference electrode and a silicon O-ring are fastened together in a polypropylene body. The renovation of this electrode is carried out through mechanical removal of solid contaminants and electrochemical activation in the electrolyte which fills the RSRE body. The effectiveness of the renovation procedure was tested by designating the RF and E_pzc and by recording C_d–t curves. As shown on selected examples, RSRE exhibits good performance in underpotential deposition stripping voltammetry (UPD-SV) applied for the determination of Pb(II) traces in certified reference materials.     

A combined μ-mercury reference electrode/Au counter-electrode system for microelectrochemical applications

Different types of mercury-based μ-reference electrodes (Hg/Hg₂SO₄/Na₂SO₄, Hg/Hg₂(CH₃COO)₂/NaCOOCH₃) have been developed following the concept of agar-based μ-reference electrodes. Mercury was electrochemically deposited onto a gold wire to form an amalgam. The corresponding mercury salt was formed electrochemically at the surface. This electrode can be inserted into a capillary that is filled with the electrolyte of interest. To simplify the handling of this μ-reference electrode, to reduce diffusion and to avoid leakage, the electrolyte was immobilised with agar. A 250-nm-thick gold layer on the outer surface of the capillary of the reference electrode served as counter-electrode. The electrochemical behaviour of reference electrodes and counter-electrodes were proven by micro-polarisation curves, electrochemical impedance spectroscopy, potential transients and cyclic voltammetry.     

The microporous structure of silver/silver chloride electrodes and the implications for Harned cell operation

The stability of silver/silver chloride reference electrodes when moved between different electrolyte solutions is limited by the small amount of solution transferred. The time required for the Ag/AgCl electrode potential to stabilize has been shown to increase with electrode size in an empirical fashion. The results presented suggest the presence of a microporous structure in the electrodes that limits the rate at which traces of any previous solutions are diluted by any new solution environment. Operational implications for the stability and accuracy of the Harned Cell used as the primary standard for pH measurements and the certification of primary reference buffers are discussed. Presented to the CCQM Electrochemical Analysis Working Group, Paris, April 2004.     

The study of PVP/Pd/IrO(2) modified sensor for amperometric determination of sulfur dioxide

A novel electrochemical sensor for the detection of sulfur dioxide in both gas and solution is described. The chemically modified electrode was constructed by polymerizing (4-VP), palladium and iridium oxide (PVP/Pd/IrO(2)) onto a platinum microelectrode which exhibits excellent catalytic activity toward sulfite with an oxidation potential of +0.50 V. The SO(2) gas sensor is based on the PVP/Pd/IrO(2) modified electrode as working electrode, Ag/AgCl electrode as reference electrode, Pt electrode as counter electrode and a porous film, which is in direct contact with the gas-containing atmosphere. The effect of different internal electrolyte solutions of hydrochloric acid, sulfuric acid, phosphates buffer solution, mixed solution of dimethyl sulfoxide and sulfuric acid to the determination of SO(2) was also studied. The sensor was found to have a high current sensitivity, a short response time and a good reproducibility for the detection of SO(2). It has good potential to be used in the field of environmental monitoring and controlling.     

基于纳米银/碳纳米纤维复合材料的增强效应电化学测定多贝斯

将银纳米粒子(AgNPs)电沉积在碳纳米纤维(CNFs)修饰玻碳电极表面制备纳米银/碳纳米纤维修饰玻碳电极(AgNPs/CNFs/GCE).采用扫描电镜考察其表面形态,在K3[Fe(CN)6]-K4[Fe(CN)6]体系中用循环伏安法和电化学阻抗法研究AgNPs/CNFs/GCE的电化学行为.采用循环伏安法和方波伏安法...     

Surface-enhanced Raman scattering at the silver electrode/ionic liquid (BMIPF6) interface

This is the first report of in situ SER spectra of chemical species adsorbed on a Ag/room temperature ionic liquid (RTIL) interface. We have investigated the dependence of the SERS intensity of the RTIL derived from 1-n-butyl-3-methylimidazolium hexafluorophosfate (BMIPF6) adsorbed on a silver electrode. It has been shown that the BMI+ adsorbs on the silver electrode for potentials more negative than -0.4 V vs a Pt quasireference electrode (PQRE). In the -0.4 to -1.0 V potential range the SER spectra are similar to the Raman spectrum of the RTIL BMIPF6. At potentials more negative than -1.0 V some imidazolium ring vibrational modes and N-CH3 vibrations are enhanced, suggesting that the imidazolium ring is parallel to the surface and for potentials <-2.8 V the BMI+ is reduced to the BMI carbene. The potential dependence of the SERS intensities of Py adsorbed on a silver electrode in BMIPF6 has also been investigated. The results have shown that at potentials less negative than -0.8 V (vs PQRE) Py adsorbs at an end-on configuration forming an Ag-N bond. In the -0.9 to -1.4 V potential range Py molecules lie flat on the electrode surface and at potentials <-1.4 V Py is replaced by the BMI+. The electrochemical and SERS results have shown that Py has the effect of changing the oxidation of silver in that medium as well as the reduction of BMI+ to the BMI carbene. In the presence of Py the BMI+ reduction is observed at potentials near -2.4 V. The Ag electrode has presented SERS activity from 0.0 to -3.0 V.     

Carbon electrode for electrochemical studies in cryolite-alumina melts at 700–960°C

The paper presents the results of tests of different carbon electrode designs for electrochemical studies in cryolite-alumina melts in the temperature range of 700?C960°C. Operation of the electrode and its applicability as the reference electrode is analyzed. The theoretical value of the maximum possible instability of its potential related to instability of the gas composition is calculated. A new design of the carbon electrode is suggested in which the gas composition is much more stable. It is shown that the suggested electrode is suitable for application as the reference electrode in cryolite-alumina melts in the temperature range of 750°C and above. The electrode can be used for a prolonged time. Herewith, its potential remains stable and reproducible.     

Electrochemical Sensing Platform Integrated with Solid-state Reference Electrode Based on Indium Tin Oxide Interdigitated Array Electrodes

We present a new strategy for the fabrication of a fully integrated electrochemical platform. The three-electrode system consists of an indium tin oxide interdigitated array as working electrode, a solid-state reference electrode, and an electrodeposited Pt counter electrode that are placed in microfluidic channel. By controlling the electrodeposition conditions, such as the applied potential and time, the stability and uniformity of the films can be optimized. A solid-state reference electrode was fabricated on the nanoporous Pt via electropolymerization of poly-1,3-phenylenediamine. This system provides a simple method for the fabrication of three-electrode system and opens the possibility for an electroanalytical platform.     

Simple electrochemical method for deposition and voltammetric inspection of silver particles at the liquid-liquid interface of a thin-film electrode

A novel experimental methodology for depositing and voltammetric study of Ag nanoparticles at the water-nitrobenzene (W-NB) interface is proposed by means of thin-film electrodes. The electrode assembly consists of a graphite electrode modified with a thin NB film containing decamethylferrocene (DMFC) as a redox probe. In contact with an aqueous electrolyte containing Ag(+) ions, a heterogeneous electron-transfer reaction between DMFC((NB)) and Ag(+)((W)) takes place to form DMFC(+)((NB)) and Ag deposit at the W-NB interface. Based on this interfacial reaction, two different deposition strategies have been applied. In the uncontrolled potential deposition protocol, the electrode is immersed into an AgNO(3) aqueous solution for a certain period under open circuit conditions. Following the deposition step, the Ag-modified thin-film electrode is transferred into an aqueous electrolyte free of Ag(+) ions and voltammetrically inspected. In the second protocol the deposition was carried out under controlled potential conditions, i.e., in an aqueous electrolyte solution containing Ag(+) ions by permanent cycling of the electrode potential. In this procedure, DMFC((NB)) is electrochemically regenerated at the electrode surface, hence enabling continuation and voltammetric control of the Ag deposition. Hence, the overall electrochemical process can be regarded as an electrochemical reduction of Ag(+)((W)) at the W-NB interface, where the redox couple DMFC(+)/DMFC acts as a mediator for shuttling electrons from the electrode to the W-NB interface. Ag-particles deposited at the W-NB interface affect the ion transfer across the interface, which provides the basis for voltammetric inspection of the metal deposit at the liquid-liquid interface with thin-film electrodes. Voltammetric properties of thin-film electrodes are particularly sensitive to the deposition procedure, reflecting differences in the properties of the Ag deposit. Moreover, this methodology is particularly suited to inspect catalytic activities of metal particles deposited at the liquid-liquid interface toward heterogeneous electron-transfer reactions occurring at the at the liquid-liquid interface.     

Crystallic silver amalgam--a novel electrode material

A crystallic silver amalgam was found to be a suitable working electrode material for voltammetric determination of electrochemically reducible organic nitro-compounds. Optimum conditions for crystal growth were found, the crystal surface was investigated by atomic force microscopy in tapping mode and single crystals were used for the preparation of quasi-cylindrical single crystal silver amalgam electrode (CAgAE). An electrochemical behavior of this alternative electrode material was investigated in aqueous media by direct current voltammetry, cyclic voltammetry (CV), differential pulse voltammetry (DPV) and adsorptive stripping voltammetry (AdSV) using 4-nitrophenol as a model compound. Applicable potential windows of the CAgAE were found comparable with those obtained at a hanging mercury drop electrode, providing high hydrogen overpotential, and polished silver solid amalgam electrode. Thanks to the smooth single crystal electrode surface, the effect of the passivation is not too pronounced, direct DPV determination of 100 μmol l(-1) of 4-nitrophenol at CAgAEs in 0.2 mol l(-1) acetate buffer pH 4.8 provides a RSD around 1.5% (n = 15). DPV calibration curves of 4-nitrophenol are linear in the whole concentration range 1-100 μmol l(-1) with a limit of quantification of 1.5 μmol l(-1). The attempt to increase sensitivity by application of AdSV was not successful. The mechanism of 4-nitrophenol reduction at CAgAE was investigated by CV.     

Simple and rapid voltammetric determination of morphine at electrochemically pretreated glassy carbon electrodes

A simple and rapid method for morphine detection has been described based on electrochemical pretreatment of glassy carbon electrode (GCE) which was treated by anodic oxidation at 1.75 V, following potential cycling in the potential range from 0 V to 1.0 V vs. Ag|AgCl reference electrode. The sensitivity for morphine detection was improved greatly and the detection limit was 0.2 μM. The reproducibility of the voltammetric measurements was usually less than 3% RSD for six replicate measurements. Moreover, this method could readily discriminate morphine from codeine. And an electrochemical detection of morphine in spiked urine sample was succeeded with satisfactory results.     

应用扫描电化学显微镜研究极化液/液界面上的电子转移反应

将含有氧化还原电对的水溶液滴涂在铂盘电极表面, 然后将该电极插入到1,2-二氯乙烷溶液中, 形成稳定的油/水界面. 液滴中的K3Fe(CN)6和K4Fe(CN)6氧化还原电对既可以作为水相中的参比电对参与控制液/液界面上的电势差, 同时又可以作为水相的电子授受体参与界面上的电子转移反应. 结合扫描电化学显微镜电化学系统的特点, 利用其双恒电位仪分别控制界面电势差和现场扫描的优点, 通过扫描电化学显微镜的渐进曲线得到了不同界面电势差控制的电子转移反应速率常数. 实验结果表明, 应用此方法获得的液/液界面可以被外加电位极化, 在一定的电势差范围内, 反应速率常数与界面电势差的关系遵守Butler-Volmer公式.     

Study of an Au colloid self-assembled electrode and its application to the determination of carbon monoxide

A novel electrochemical sensor has been developed for the detection of carbon monoxide. The chemically modified electrode, prepared by reaction of cysteine and then an Au colloid of size approximately 15 nm with a platinum microelectrode, has excellent catalytic activity toward carbon monoxide, with an oxidation potential of +600 mV relative to the Ag/AgCl electrode. The CO gas sensor is based on an Au colloid self-assembled modified electrode as working electrode, an Ag/AgCl electrode as reference electrode, a Pt electrode as counter electrode, and a porous film which is in direct contact with the gas-containing atmosphere. The effects on the determination of CO of different internal electrolyte solutions of perchloric acid, hydrochloric acid, sulfuric acid, nitric acid, and phosphate buffer of different concentrations were also studied. The sensor is characterized by a short response time and highly reproducible detection of CO. This sensor can be used in the field of environmental monitoring and control.