全钒液流单电池充放电行为及特性研究

建立具有外置双饱和甘汞参比电极及双液流电池的实验装置系统.使用该装置可在同一时刻同时测定小型液流单电池充放电时的电池电压、电池正负极电位及正负极开路电位,进而计算充放电过程电池的欧姆内阻降(iR)及其正负极过电位.以石墨毡为电极、Nafion 117作隔膜的全钒液流单电池,在60 mA.cm-2电流密度下,每一充放电循环的平均iR降约占总电压损耗的74%,表明该电池的电压效率受制于电池的欧姆内阻.充放电曲线显示,电池放电终点之所以出现主要是由于电池负极电位在放电末期的快速上升而引起的.本文设计的全钒单电池于60 mA.cm-2下工作时,其电压及能量效率分别达89%和85%,表明该电池结构合理,且石墨毡是钒电池合适的电极材料.     

Ultrafast cyclic voltammetry: performing in the few megavolts per second range without ohmic drop

A new concept of a three-electrode potentiostat involving positive feedback compensation of ohmic drop is used to investigate nanosecond time scales by allowing the recording of ohmic drop-free voltammograms at scan rates of a few megavolts per second. This range of scan rates corresponds to the development of diffusion layers whose widths are only a few nanometers thick. Independent tests on dummy cells (Bode plots) demonstrated that the potentiostat behaved excellently in the megavolt per second range. Examination of the well-established voltammetric reduction of anthracene in highly concentrated (0.9 M) supporting electrolyte confirmed that this potentiostat allowed the recording of undistorted ohmic drop-free voltammograms up to 2.25 MV s⁻¹.     

Deposition of polyaniline on RVC electrodes: effect of substrate thickness

Polyaniline films, obtained by either chemical or electrochemical deposition on reticulated vitreous carbon (RVC), were investigated as a function of the substrate thickness. The electrochemical properties of these RVC/Pani electrodes were assessed by cyclic voltammetry and electrochemical impedance spectroscopy (EIS), whereas the morphology of the Pani films on RVC was analyzed by scanning electron microscopy (SEM). The cyclic voltammetric results revealed that the oxidation/reduction charges for electrodeposited polyaniline decrease as the RVC thickness is increased. Conversely, the charge densities for the chemically deposited films do not present a significant dependence on the substrate thickness. Two time constants, appearing in all the EIS spectra, indicate that an ohmic drop effect within the RVC substrate affects the polymer electrodeposition and the electrochemical behavior of the obtained electrodes. Therefore, an electric equivalent circuit considering the different electrochemical environments at the outer and inner RVC surfaces was proposed to analyze the EIS data.     

Oscillatory regime of titanium anodization under voltage control

Regular current oscillations during anodization of titanium in potentiostatic conditions were postulated in the literature but never documented experimentally. We here report emergence of such oscillatory anodization on Ti submitted previously to the activation procedure. Activation consisted in remaining the specimen under open circuit conditions in the electrolyte containing fluoride ions. The sign of the activation end point was fast drop of the electrode potential to negative values, well below the potential of the cathodic hydrogen evolution. At the active state titanium exposed to the electrolyte its surface free of oxides and subsequent anodization occurred on the bare metal and not on the metal covered with native oxide.Oscillations were observed in 1 M H₂SO₄ in the voltage range from 6 to 30 V in both voltage scan and step experiments. Their amplitude, shape and spectral character changed with anodization voltage. Electrolyte mixing had no influence on oscillations suggesting no role played by the transport in the electrolyte bulk. At elevated temperature oscillations were more regular and similar was the influence of mixture of H₂SO_4aq with ethylene glycol. The latter introduced however strong ohmic voltage drop in the electrolyte this causing the change of the shape and periods of oscillations.     

Characteristics of the dropping mercury electrode below the limiting current: Part II. Drop time and scan rate effects

A mathematical model of the dropping mercury electrode that includes the effects of electrochemical kinetics, ohmic potential drop, and mass transfer is used to examine the influence of scan rate and drop time on the shape of the polarographic wave. The system behavior is described in terms of three characteristic dimensionless parameters. For certain parameter values, the half-wave potential predicted for a metal deposition reaction is dependent on the drop time and scan rate used to obtain the polarogram.     

The Influence of Water Vapor on the Electrochemical Shift of an Ionic Liquid Measured by Ambient Pressure X-ray Photoelectron Spectroscopy

Ionic liquids (ILs) are considered to be one of the steppingstones to fabricate next generation electrochemical devices given their unique physical and chemical properties. The addition of water to ILs significantly impact electrochemical related properties including viscosity, density, conductivity, and electrochemical window. Herein we utilize ambient pressure X-ray photoelectron spectroscopy (APXPS) to examine the impact of water on values of the electrochemical shift (S), which is determined by measuring changes in binding energy shifts as a function of an external bias. APXPS spectra of C 1s, O 1s and N 1s regions are examined for the IL 1-butyl-3-methylimidazolium acetate, [C₄mim][OAc], at the IL/gas interface as a function of both water vapor pressure and external bias. Results reveal that in the absence of water vapor there is an IL ohmic drop between the working electrode and quasi reference electrode, giving rise to chemical specific S values of less than one. Upon introducing water vapor, S values approach one as a function of increasing water vapor pressure, indicating a decrease in the IL ohmic drop as the IL/water mixture becomes more conductive and the potential drop is driven by the electric double layer at the electrode/IL interface.     

Studies of coupling effects and ohmic potential drops at ring-disc electrodes

The total ohmic potential drop at rotating ring-disc electrodes (RRDE) has been studied for primary current distribution conditions with iron electrodes in slightly alkaline solutions (pH 8.4). It will be shown that the total ohmic potential drop consists of two parts, namely the “normal” IR-drop and a coupling influence caused by superposition of the individual potential fields of both the electrodes (ring or disc). On the basis of known potential fields near the single electrodes, theoretical considerations will be given in order to calculate or estimate the total IR-drop for a given RRDE system in dependence on the position of the Luggin capillary. Furthermore, it will be shown that an optimum compromise can be reached between “normal” IR-drop and coupling effect by appropriate positioning of the Luggin capillary. Conclusions for experimental work will be drawn.     

多壁纳米碳管空气电极的交流阻抗研究

研究了多壁纳米碳管、活性炭和石墨等空气电极的交流阻抗特性.结果表明,纳米碳管空气电极的阻抗谱由两个半圆组成,高频区半圆对应欧姆极化阻抗,低频区半圆对应电化学极化阻抗.催化剂Pt以纳米颗粒的形式沉积在碳管的外表面,明显减小了电极的欧姆阻抗和电化学极化阻抗,提高了氧还原反应的电催化活性.活性炭电极除存在电化学阻抗外,还存在薄液膜扩散阻抗(Nernst扩散),石墨电极形成的薄液膜反应区域较小,电极反应呈Warburg扩散阻抗特征,相应的电催化活性较低.采用交流阻抗等效电路分析方法,对拟合的动力学数据进行了解释.     

微电极的稳态可逆极化曲线

微电极具备一些常规尺寸电极所没有的优点,例如:(1)半径很小的微电极在不对溶液进行搅拌的情况下就具备与高速旋转的圆盘电极类似的性质,即在电位扫描速率较低时,可获得稳态伏安曲线.这一特点使微电极能方便地用于稳态测量.与暂态测量相比,稳态测量精度较高(实验曲线几乎不受充电电流干扰),实验方法较简单,实验结果的数学处理较容易.(2)微电极体系的时间常数(溶液电阻和双层电容的乘积)正比于电极面积的平方根.若在     

Ultrafast double potential step chronoamperometry with the time window down to submicrosecond.

Ultrafast double potential step chronoamperometry at an ultramicroelectrode was achieved through decreasing the ohmic drop by positive feedback compensation, and the lower limit of the time window was extended to the submicrosecond level. With the reduction of anthracene in acetonitrile as a test system, the validity of this instrumentation was demonstrated by comparing between experimental and simulated curves. The capability in kinetic studies of the technique was then approved.     

Determination of the Tafel slope for oxygen evolution on boron-doped diamond electrodes

It has been reported that the oxygen evolution reaction (OER) on boron-doped diamond (BDD) electrodes appears at high overpotential and results in unusually high Tafel slope. In this work, we have studied the OER in 1 M HClO₄ on BDD macroelectrode and microelectrodes-array (MEA). The correction of the anodic polarization curve for ohmic drop has been performed on BDD macroelectrode taking into account the total uncompensated resistance of the studied system. On BDD MEA, no correction of the polarization curve was necessary due to the small contribution of ohmic drop to the measured potential. At low overpotential (<1.2 V), abnormally high Tafel slopes (340 and 680 mV dec⁻¹ on BDD MEA and BDD, respectively) have been observed. Such high slopes may result from the presence of surface redox couples/functional groups which act as a barrier for OER on BDD. In this potential region, the Tafel slope depends strongly on the state of the electrode surface. In the high overpotential region (>1.2 V), the Tafel slope has been found equal to 120 mV dec⁻¹, which is the theoretical value considering a first or a second electron transfer step as the rate determining step.     

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     

指数扩展的网络方法模拟超快循环伏安曲线

将指数扩展格原理用于网络模拟方法,给出了模拟受欧姆降歪曲的超快伏安曲线的电路网络模型,利用电路模拟软件ＰＳＰＩＣＥ给出该电路的瞬态响应曲线,并与数值解进行对比,结果表明这一模拟算法准确而稳定,而且计算速度比等格网络法提高１０倍以上。     

Macroscopically uniform nanoperiod alloy multilayers formed by coupling of electrodeposition with current oscillations

The electrodeposition from an acidic solution containing Cu(2+), Sn(2+), and a cationic surfactant gave a negative differential resistance (NDR) and a current oscillation in a narrow potential region of about 20 mV lying slightly more negative than the onset potential for Sn-Cu alloy deposition. Scanning Auger microscopic inspection has indicated that alloy films deposited during the oscillation have a clear alternate multilayer structure composed of two alloy layers of different compositions. The multilayer had the period of thickness of 40-90 nm and was uniform over a macroscopically wide area of about 1 mm x 1 mm. Detailed investigations have revealed that the NDR arises from adsorption of a cationic surfactant (acting as an inhibitor for diffusion of metal ions) on the alloy surface, and the oscillation comes from coupling of the NDR with the ohmic drop in the electrolyte.     

用于现场FTIR及UV/Vis光谱电化学的高质量简单结构的光透薄层电化学池

设计制作了一种应用于紫外可见、红外电谱电化学的新型光透薄层电化学池(OTTLE),并以铁氰化钾水溶液、二茂铁乙腈溶液体系进行了表征。池腔几何结构的合理设计使电位降和边缘效应降至最低。该池有良好的伏安响应特性并可用它得到高质量的UV/Vis和IR光谱。由于简单的结构及低廉的造价使适用于光谱电化学研究的电化学池变得更容易得到。     

Impedance modelling of two-phase solid-state ionic conductors. Part I—theoretical model and computer simulations

An equivalent circuit model is introduced to account for the impedance properties of solid state ionic conductors, composed of two distinct phases. The model is developed on the basis of physical arguments, regarding the micrometer-scale structure of the two-phase material system and the comparison of different possible equivalent circuit representations. The final equivalent circuit reduces to two simpler circuits, suitable for fitting experimental impedance spectra. Computer simulations are provided to demonstrate the non-Arrhenius behaviour, which is observed in the temperature dependence of the ohmic elements of the equivalent circuits used for data analysis. This complex dual-slope behaviour of the Arrhenius plot is in agreement with the predictions of the model. Finally, with the aid of mathematical calculations and illustrated by computer simulations, a modified Arrhenius plot evaluation procedure was developed to derive correctly the electrical properties of the individual constituent phases from impedance measurements.     

Ultrafast cyclic voltammetry with asymmetrical potential scan

Based on the perfect ohmic drop compensation by online electronic positive feedback, ultrafast cyclic voltammetry with asymmetrical potential scan is achieved for the first time, with the reduction of anthracene acting as the test system. Compared with the traditional cyclic voltammetry utilizing symmetrical triangular waveform as the excitation one, the new method allows a simpler approach to mechanistic analysis of ultrafast chemical reactions coupled with a charge transfer. And perhaps more important, it also provides a way to eliminate the interference of the adsorbed product in dynamic monitoring. 2007 Zhi Yong Guo. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.     

La0.8Sr0.2MnO3／YSZ高温电极交流阻抗研究

用交流阻抗方法研究了Ｌａ０．８Ｓｒ０．２ＭｎＯ３电极上进行的氧化电化学还原反应。实验表明反应速度控制步骤随反应温度，氧分压及过电位发生显著变化，近平衡下反应的ｒｄｓ为氧的解离吸附过程。强阳极极化下，电解质表面产生大量电子空穴；强阴极极化下，ＬＳＭ电极表面形成大量氧空位，二者的结果均使界面电导增加，电化学反应区扩展。     

启动工况下质子交换膜燃料电池动态性能仿真分析

本文以等效电路模型为基础模型,结合动态气体压力模型和动态热传输模型建立了集总参数模型,在SIMULINK环境下,利用建立的模型模拟了电池启动过程,发现了电压的下冲现象,且电压的响应时间与电池温度的响应时间基本一致,说明启停过程中电池温度对电池的动态性能影响很大. 进一步从温度角度对模型中决定电池输出电压大小的热力学电动势、活化过电势、欧姆过电势和浓差过电势的动态响应情况进行了分析,发现启动过程电压的下冲现象主要由电池活化过电势和欧姆过电势的过冲引起;当以阶跃信号形式输入温度时,启动过程电池输出电压响应很快且未发生下冲现象,说明提高电池温度的响应速度能够改善电池的动态性能.     

Determination of heavy metals in real samples by anodic stripping voltammetry with mercury microelectrodes : Part 2. Application to Rain and Sea Waters

Differential-pulse anodic stripping voltammetry at a mercury microelectrode is applied to determine labile and total zinc, cadmium, lead and copper in samples of rain and sea water. The low ohmic drop associated with microelectrodes permits reliable measurements in rain water without addition of supporting electrolyte. The values found in a typical sample were 0.95 μg l^?1 Cu, 0.38 μg l^?1 Pb, 0.01 μg l^?1 Cd and 0.95 μg l^?1 Zn, with relative standard deviations in the range 4–18%. The small effects of organic matter at microelectrodes, compared with those at a hanging mercury drop electrode, allow sensitive and reliable measurements of labile metals in surface sea water. Total metal concentrations are determined after acidification to pH 1.5 with hydrochloric acid. The results are compared with those obtained with atomic absorption spectrometry and with differential-pulse anodic stripping voltammetry at conventional mercury electrodes. Satisfactory results were obtained for a reference sea water.