Application of N- and B-doped CVD diamond layers for cyclic voltammetry measurements

Conductive polycrystalline diamond layers prepared by the CVD process have received attention from electrochemists owing to such superior electrochemical properties as the wide potential window, the very low background current, the stability of chemical and physical properties.In this paper, the cyclic voltammetry application using N- and B-doped diamond electrodes was studied. Diamond layers, doped with boron and nitrogen, were synthesized on a silicon substrate in a hot-filament CVD reactor. The obtained diamond layers were characterized using Raman spectroscopy and scanning electron microscopy (SEM).The electrochemical properties of diamond layers were measured in KCl and NaCl basic solutions to gain knowledge about their potential application as an electrode material.It was found that boron doped diamond electrodes showed potential windows up to about 7 V which were almost twice wider than those observed for conventional Pt electrodes.     

微机自动控制电化学测试系统的研制

研制了一套由ＩＢＭ－ＰＣ机为上位机、单片机为前端机的电化学测试系统．结合恒电位仪，成功地实现了实验条件控制、数据采集和结果处理的自动化，该测试系统具有速度快、精度高、操作方便及参数修改灵活等特点．用于实际体系的电化学测量，取得了较好的效果．     

Zr－4合金中第二相Zr（Fe，Cr）_2的电化学分离

通过测定Ｚｒ－４合金和Ｚｒ（Ｆｅ，Ｃｒ）２：合金在各种电解液中的阳极极化行为，和对阳极产物的电子显微镜和Ｘ射线衍射分析，得到了一种适合分离Ｚｒ－４合金中第二相Ｚｒ（Ｆｅ，Ｃｒ）２的电解液：乙醇：正丁醇：高氯酸＝２５：３：２；室温条件下，控制电位为－０．４５￣－０．８０Ｖ（ＳＣＥ）．     

Aspects of the development of a copper electrowinning cell based on reactive electrodialysis

This paper reports work aimed at developing a new copper electrowinning cell based on reactive electrodialysis (RED) which uses Fe²⁺→Fe³⁺+e as anodic reaction. In this lab-scale cell, the anolyte (aqueous FeSO₄+H₂SO₄) and the catholyte (aqueous CuSO₄+H₂SO₄) are kept separate by an anion membrane which prevents cation and water transport between the electrolytes. Both solutions are agitated by recirculation. The kinetics of the anodic reaction have been studied via potentiodynamic experiments on various anode materials (lead, platinum, ruthenium oxide, iridium oxide and graphite). The highest oxidation rate was obtained on platinum and the lowest one on lead, whereas the remaining materials showed satisfactory performance. Results in the lab-scale RED cell show that, depending on experimental conditions, for a cell current density of , the cell voltage ranges from 1.81 to , the cathodic current efficiency from 97.2% to 98.3% and the specific energy consumption, from 1.53 to of deposited copper.     

Electrochemical investigation and characterization of thin-film porosity

In thin-film applications it is necessary to control film properties such as homogeneity and porosity to obtain high-quality coatings. Electrochemistry can be a very helpful tool since it can provide information about processes taking place at the interface between substrate and coating. Different thin carbon-based coatings were deposited via physical vapour deposition methods and vapour phase polymerization on pure iron substrates: fullerene films, which were modified by an ion bombardment and thin films of poly(p-xylylene), which is a very good insulating polymer. The film porosity and stability of the film/substrate system against aqueous corrosion were investigated and compared using cyclic voltammetry. The dependence of porosity and film stability on various deposition process parameters such as film thickness and plasma conditions was measured via the dissolution current density and the open circuit potential shift of the substrate material. It could be shown that the two measurements, current density I_crit. and open circuit potential E_ocp. can provide useful complementary information about film porosity that can lead to a better understanding of the coatings properties and the deposition process as well.     

Modeling of Electrochemistry and Heat/Mass Transfer in a Tubular Solid Oxide Steam Electrolyzer for Hydrogen Production

A finite‐volume based mathematical model has been developed for modeling hydrogen production by a tubular cell of solid oxide steam electrolyzer (SOSE), taking into account the electrochemical reactions and heat/mass transfer effects. The model is composed of three systems of nonlinear equations that govern the electric current density, energy balance in the solid SOSE cell, and energy balance in the flow of steam and hydrogen. The simulated hydrogen production rate proportional to the applied potential agreed well with the experimental measurements published in the literature. The intermediate modeling results indicated that the activation effect dominate the overall cell overpotential due to low exchange current density through the SOSE cell electrodes. Thus, higher electrode activity was identified as an important factor for enhancing cell performance. Parametric modeling analyses were conducted to gain better understanding of the SOSE characteristics. It was found that low‐temperature gas intake would cause a high temperature gradient in the tubular cell material at the inlet, possibly leading to a thermal expansion problem. The risk could be reduced by increasing the gas inlet temperature. It was also found that energy‐efficient SOSE hydrogen production can be achieved by reducing the hydrogen content in the steam intake and regulating the steam intake flow rate to an optimum that minimizes the overall electrical and thermal requirements. More parametric modeling results are discussed in this paper. The tubular SOSE cell model developed in this study can easily be expanded to accomplish tubular SOSE stack analysis for comprehensive system design optimization.     

Electrochemical surface plasmon spectroscopy—Recent developments and applications

A survey is given on recent developments and applications of electrochemical techniques combined with surface plasmon resonance (SPR) spectroscopy. Surface plasmon spectroscopy (SPS) and optical waveguide mode spectroscopy make use of evanescent waves on metal-dielectric interfaces and can be conveniently combined with electrochemical methods. Selected examples of applications of high-pressure surface electrochemical plasmon resonance spectroscopy to study supramolecular architectures such as layer-by-layer films of conducting polymers or thin composite films will be presented. Then a combination of SPS with the electrochemical quartz crystal microbalance (EQCM) will be introduced and illustrated with a study on doping/de-doping process of a conducting polymer. This combination allows for simultaneous electrochemical, optical and microgravimetric characterization of interfaces. Finally, new technical developments including integration of SPS into microfluidic devices using a grating coupler and surface plasmon enhanced diffraction will be discussed.     

Sensitivity of positive ion mode electrospray ionization mass spectrometry (ESI MS) in the analysis of purine bases in ESI MS and on-line electrochemistry ESI MS (EC/ESI MS)

A cone-shaped MS inlet and on-line electrochemistry (EC) were used to enhance the ionization efficiency in electrospray ionization mass spectrometry (ESI MS) of purine bases. A pathway of positive ion mode ESI may involve oxidation of purine bases, guanine, adenine, xanthine and hypoxanthine, by 1e⁻, 1H⁺ processes. The electrospray process generates dimers of purine bases that are detected in ESI MS as protonated ions, except for xanthine, for which a protonated radical dimer is detected. Thus electrochemical oxidation of purine bases during ESI may generate reactive radicals that can subsequently dimerize. Dimer formation is facilitated in ESI MS when the carrier solution pH is high. The positive ion mode ESI MS ionization is consistent with the reactivity of the bases toward oxidation. Furthermore, the formation of the protonated ions, and Na⁺ and K⁺ adducts of the bases, expected in positive ion ESI MS, are observed. In addition, unusual H-bonding of purine bases guanine and xanthine is confirmed by ESI MS. Application of low EC voltage to the on-line EC cell in EC/ESI MS improves the sensitivity and correlates with the decrease of the intensity of the dimers, possibly as a result of their further oxidation.     

Electrochemistry of anodic etching of 4H and 6H–SiC in fluoride solution of pH 3

Electrochemical etching of single-crystal SiC rotating disk electrodes in fluoride solution was studied at pH 3. Anodic dissolution and passivation are observed for p-type electrodes in the dark and for n-type electrodes under illumination. The dissolution of p-type (0 0 0 1) 4H–SiC is found to be under mixed transport/kinetic control; the diffusion current is first order in fluoride concentration. Polishing of p-type electrodes can be achieved at rates up to 5.8 μm/min. Porous etching was not observed in this case. The surface finish of n-type (0 0 0 1) 4H and 6H–SiC depends on the experimental conditions; both uniform and porous etching are observed. The results are compared with those of Si under comparable conditions.