Adsorption of dicarboxylic acids on lithiated nickel oxide electrode

Adsorption of dicarboxylic acids on NiO electrodes was studied by means of the galvanostatic transient method, mainly for oxalic acid. The oxalate or hydrogen oxalate anion or both were concluded to adsorb on the electrode. The adsorption was maximal at a potential less positive than the flat-band potential of the electrode, owing to preferential adsorption of hydroxyl anion in the region above the maximum adsorption potential. The quantity of adsorption was dependent on carrier concentration of the electrode, and high for the electrode of high carrier concentration. This phenomenon is connected to the charged condition of the electrode that when the maximum adsorption takes place, positively charged sites remain on the surface of the electrode which is charged negatively as a whole and the amount of the sites is much more different between the electrodes of different N than their bulk carrier concentrations. Adsorptions of malonic and succinic acid were distinctly low compared with that of oxalic acid. The adsorbability was in the order; oxalic acid>malonic acid>succinic acid. This order was in accord with the stability constants of nickel dicarboxylic acid chelates.     

On the adsorption of cadmium(II) ions on a HMDE from KF + thiourea aqueous solutions: A chronocoulometric study

The adsorption of cadmium(II) ions from thiourea aqueous solutions has been studied by double potential step chronocoulometry (DPSSC). The adsorption is strong on mercury electrodes and it has been studied as a function of thiourea concentration, cadmium(II) concentration and potential. A discrepancy between the double-layer charge values from either blank solutions or solutions containing reactant obtained by this technique has been found.     

Sb在Pt(100),Pt(110),Pt(111)及Pt(320)上不可逆吸附的电化学特性

研究了Sb在Pt(1 0 0 ) ,Pt(1 1 0 ) ,Pt(1 1 1 )和Pt(32 0 )单晶面上不可逆吸附的电化学特性 .发现当扫描电位的上限Eu≤ 0 .45V时 ,Sbad可以稳定地吸附在Pt(1 0 0 ) ,Pt(1 1 0 )和Pt(1 1 1 )表面 ,而Sbad在Pt(32 0 )表面稳定的电位较低 ,为Eu≤ 0 .40V .从饱和吸附Sb的铂单晶电极出发 ,通过改变电位扫描上限Eu 和电位扫描圈数可以获得不同Sb覆盖度 (θSb)的电极 .根据Sb和H在铂单晶电极表面共吸附的定量数据 ,对Sb在不同铂单晶面上饱和吸附的模型进行了初步探讨 .     

Adsorption of urea on a polycrystalline copper electrode

The adsorption of urea on a polycrystalline copper electrode from 0.01 M NaClO₄ solution has been studied by impedance spectroscopy and radiometric method. The dependence of the surface concentration of urea on the electrode potential and the bulk concentration was determined. From radiometric data, it follows that the adsorption of urea on the copper electrode takes place in the entire range of studied potentials where no faradaic processes occur. In this range, the process of adsorption is practically reversible with respect to the potential and the bulk concentration of urea. The experimental data were described by the Langmuir and the virial isotherms and the Gibbs energy of adsorption were calculated. The data of the urea adsorption on different electrodes have been compared and the role of the kind of the metal on the adsorption process was discussed.     

Catalytic activity of thiourea and its selected derivatives on electroreduction of In(III) in chlorates(VII)

It was found that thiourea, N-methylthiourea, N,N′-dimethylthiourea and N-allylthiourea accelerate the electroreduction process of In(III) ions in chlorates(VII). These substances are adsorbed on mercury from chlorates(VII). The relative surface excesses of thiourea and its derivatives increase with the increase of their concentrations and electrode charge. After adding thiourea, N-methylthiourea, N,N′-dimethylthiourea and N-allylthiourea to the solution an acceleration of the electroreduction process of In(III) ions occurs. This process depends on two factors: the adsorption of an accelerating substance on mercury and on the formation of complexes between a depolarizer and an accelerating substance on the electrode surface. The equilibrium of this complexing reaction determines the magnitude of the catalytic effect.     

Electrocatalytic oxidation of reduced nicotinamide adenine dinucleotide (NADH) at thick-film gold electrodes

Cyclic voltammetric and electrochemical impedance spectroscopic investigations of screen-printed, thick-film gold electrodes reveal significant differences when compared with conventional polished gold disk electrodes of comparable size. The rough and porous structure of the thick-film electrode surface leads to an actual electrode area which is increased six-fold compared to polished disk electrodes. Due to the catalytic properties of these surface structures it is possible to perform the electrochemical oxidation of reduced nicotinamide adenine dinucleotide (NADH) at relatively low overpotentials, i.e. +0.145 V vs. SCE. By operating electrodes at this potential, electrode fouling processes and interference from electroactive species, e.g. acetaminophen, are minimized. An amperometric glucose sensor based on polymer matrix-entrapped glucose dehydrogenase with a working potential of +0.145 V vs. SCE was successfully incorporated into a flow injection analysis (FIA) system.     

时间分辨表面增强拉曼光谱(TRSERS)研究硫脲衍生物与ClO4^-的共吸附行为

运用时间分辨表面增强拉曼光谱(TRSERS)结合电位双阶跃的方法, 研究了硫脲衍生物甲基硫脲(MTU)和烯丙基硫脲(ATU)在银电极表面与ClO4^-离子的共吸附行为, SERS强度-时间曲线表明它们各自相应的SERS谱峰强度随电位阶跃的响应速率不同, 离电极表面较近的基团的特征谱峰强度的响应速率较快; MTU以S端且垂直吸附在电极表面,ATU也以S端和表面发生化学吸附, 但整个分子斜躺吸附在电极表面上。     

Electrochemistry of the system Cu(II)Cu(I)Cu(0) in acidified thiocyanate solutions

The system Cu(II)Cu(I)Cu(0) in acidified thiocyanate medium was investigated at carbon, mercury, and copper amalgam electrodes using cyclic voltammetry, normal, differential and reverse pulse voltammetry, double potential step chronocoulometry, and exhaustive coulometry. Reduction of Cu(II) to Cu(I) on carbon electrodes proceeds quasireversibly. At moderate concentrations of Cu(II) and SCN^? the reduction of Cu(II) leads to three-dimensional precipitation of CuSCN which can be deposited at the electrode surface. At high concentration of SCN^? complexation dominates over precipitation and only soluble species are formed. At mercury and copper amalgam electrodes the situation is more complicated. The three- dimensional precipitation is preceded by strong thiocyanate-induced adsorption of Cu(I) which results in formation of a mono layer at potential well-separated from those where diffusing product is formed.     

Pt电极上CO的同位素取代吸附机理研究

本文依据偶极耦合理论和相干势近似方法,合理选择粗糙电极上吸附分子的频率分布函数、一氧化碳(CO)吸附层的结构参数以及偶极耦合作用常数,对13CO/12CO同位素取代过程记录的红外光谱进行了拟合.研究发现,只有在拟合过程中引入低频CO分子优先取代,就可成功地模拟整个同位素取代过程的红外光谱随表面吸附的13CO/12CO组分的变化,并由此提出了吸附驱动的脱附机理,COad的脱附不是热激发脱附,而是吸附到表面的CO分子为其邻近位置COad的脱附提供能量.伸缩振动频率较低的COad处于台阶或缺陷位等较开阔的位置(尽管其吸附能较高),周围有较大的空间,利于来自溶液的CO分子的吸附,因此在台阶或缺陷位优先发生同位素的取代.     

Electrocatalytic properties of Pt(111), Pt(332), Pt(331) and Pt(110) single crystal electrodes towards ethylene glycol oxidation in sulphuric acid solutions

In the present paper four platinum single crystal electrodes, two basal planes of Pt(111) and Pt(110) and two stepped surfaces of Pt(332) and Pt(331), were prepared and used in the study of electro-oxidation of ethylene glycol (EG). All of these Pt single crystal electrodes belong to the [1 0] zone of crystallography, and exhibit on their surface (111) symmetry sites or certain combinations of terraces of (111) symmetry with steps of (111) symmetry type. It has been found that as a result of a favourable steric matching of surface sites the Pt(110) electrode manifested a higher activity both for EG dissociative adsorption and oxidation than that of the Pt(111) electrode. The stepped surfaces of Pt(332) and Pt(331) operated with certain combinations of characteristics of Pt(111) and Pt(110). The best electrocatalytic properties have been obtained with a Pt(331) electrode, and this is attributed both to the configuration of the atomic arrangement and to the stability of this surface.In summary, the above results show that the performance of a given Pt single crystal electrode in EG oxidation at a potential below 1.0 V may be evaluated by three factors.

1. (1) The ability to resist self-poisoning (AB) which describes the difficulty of EG dissociative adsorption on the electrode surface.

2. (2) The activity for EG oxidation (AC). In considering that the threshold potential for EG oxidation on all electrodes is at 0.3 V and that the self-poisoning is encountered in PGPS, the activity for EG oxidation may be reasonably characterized by the intensity of the peak current acquired in NGPS near 0.6 V, which corresponds to the maximum current of EG oxidation on an activated (non-poisoned) surface of the electrode.

3. (3) The stability of activity during potential cycling (SA) between 0.05 and 1.0 V, which describes the resistance to the decrease of intensity of the EG oxidation current during voltammetric cycling.

For the two basal planes studied, the AB and SA of Pt(111) are higher than those of Pt(110), but its AC is much lower than that of Pt(110). These differences are clearly related to the surface atomic arrangement of the two electrodes. As has been discussed above, the surface of Pt(111) is atomically smooth and stable during voltammetric cycling. The surface of Pt(110) presents, however, atomic steps and is reconstructed under experimental conditions, i.e. certain steric configurations are encountered on the Pt(110) surface. The high AC and the low AB may be assigned to a favourite stereographic matching during EG adsorption and oxidation on Pt(110).The two electrodes with stepped surfaces, Pt(332) and Pt(331), contain different densities of (110) sites, which are formed on the border between terrace and step, as shown in Fig. 8. The AB of these two electrodes has been observed at a moderate range between that of Pt(111) and the AB of Pt(110). With a majority of (111) sites on its surface, the electrode of Pt(332) operates at a relatively higher AC than Pt(111) does, and its SA is not as good as that of Pt(111) but is much better than the SA of a Pt(110) electrode. In all cases the highest AC and SA are obtained with a Pt(331) electrode. It may be seen from the profile of a (331) plane (shown by the cross-section of A-A in Fig. 8) that all atoms on the top of the surface participated in forming (110) sites, and the atom on the step has two functions — one is to form a (110) site with an atom located in the terrace of second layer and the other is to form a (111) site in the terrace of the same layer. It has been mentioned in the above discussions that the Pt(110) electrode keeps a higher AC due to favourite stereographic matching in EG adsorption and oxidation, but its SA is the worst, due to the instability of the surface. The highest AC and SA obtained with Pt(331) may be ascribed not only to the high density of (110) sites existing on the surface, but also to the stabilization of these (110) sites, and moreover, the synergy generated by the atomic arrangement of the Pt(331) surface may also contribute to the performance of the Pt(331) electrode.     

Mechanism of nitrate electroreduction on Pt(100)

Kinetics and mechanism of nitrate anion reduction on the Pt(100) electrode in perchloric and sulfuric acid solutions are studied. Analysis of the results of electrochemical measurements (combination of potentiostatic treatment and cyclic voltammetry) and the data of in situ IR spectroscopy allow suggesting the following scheme of the nitrate reduction process on Pt(100) differing from that in the literature. If the potential of 0.85 V is chosen as the starting potential for a clean flame-annealed electrode surface and negativegoing (cathodic) potential sweep is applied, then an NO adlayer with the coverage of about 0.5 monolayer is formed on Pt(100) in the nitrate solution already at 0.6 V. The further decrease in the potential results in NO reduction to hydroxylamine or/and ammonia, desorbing products vacate the adsorption sites for nitrate and hydrogen adatoms. At E < 0.1 V, adsorbed hydrogen is mostly present on the surface. During positive-going (anodic) potential sweep, the process of nitrate reduction starts after partial hydrogen desorption, the cathodic peak of nitrate reduction to hydroxylamine or ammonia is observed at 0.32 V on cyclic voltammograms. The process of nitrate anion reduction continues up to 0.7 V; at higher potentials, the surface redox process with participation of hydroxylamine or ammonia (the anodic peak at 0.78 V) and nitrate (the cathodic peak at 0.74 V is due to nitrate reduction to NO on the vacant adsorption sites) occurs.     

生物小分子的电分析化学研究 Ⅱ.鸟嘌呤、腺嘌呤和次黄嘌呤在粗热解石墨电极上的分子定向和表面相互作用

本文讨论了鸟嘌呤、腺嘌呤和次黄嘌呤等嘌呤类生物小分子在几种电极上的反应活性,并选用粗热解石墨电极研究了它们的电化学性质.实验结果表明它们的电极过程是受吸附作用控制的.在粗热解石墨电极上鸟嘌呤以C(2)-NH~2、腺嘌呤以C(6)-NH~2、次黄嘌呤以N(1)-H基团按垂直方向吸附于电极表面,电极表面分子间存在着相斥的相互作用.鸟嘌呤、腺嘌呤和次黄嘌呤的吸附平衡常数分别为:(3.34±1.00)×10^5,和(4.38±1.20)×10^5和(4.13±1.21)×10^5;吸附能分别为:(31.5±0.77),(32.1±0.70)和(32.0±0.75)kJ/mol.这些数值表明它们在粗热解石墨电极上具有中等偏强的物理吸附作用.     

Adsorption of bromide at the Ag(100) electrode surface

The adsorption and phase formation of bromide on Ag(100) has been studied by chronocoulometry and surface X-ray scattering (SXS). With increasing electrode potential, bromide undergoes a phase transition from a lattice gas to an ordered c(2×2) structure (θ=0.5). The degree of lateral disorder was estimated by comparing the SXS- and the electrochemical measurements. Based on chronocoulometric experiments, a thermodynamic analysis of charge density data was performed to describe the bromide adsorption at the Ag(100) electrode. The Gibbs surfaces excess, electrosorption valencies, Esin–Markov coefficients, and the Gibbs energy of adsorption, lateral interaction energies as well as surface dipole moments have been estimated. The experimental θ versus E- isotherms are modeled employing (i) a quasi-chemical approximation as well as (ii) the results of a recent Monte Carlo simulation. An attempt is made to discuss the structure data and thermodynamic quantities of bromide adsorption on Ag(100) on the basis of the Grahame–Parsons model of the Helmholtz layer.     

The Comparative Study of “Adsorbed Co” Oxidation On the Rough and Smooth Pt Electrodes

Abstract

The oxidation of carbon monoxide adsorption products from rough and smooth platinum electrodes has been studied by cyclic voltammetry. It was found that the roughness of the electrode surface has strong influence on the composition and/or structure of the final adsorption products.     

Electrochemical behavior of hemoglobin in neutral surfactants with different poly(ethylene oxide) unit lengths adsorbed on an electrode

The direct electron transfer and adsorption behavior of hemoglobin(Hb) in a series of surfactants with different poly(ethylene oxide)(PEO) unit lengths on a glassy carbon electrode have been studied.With a surfactant of appropriate PEO unit length,the surfactant film-modified electrode exhibited a more stable adsorption state with a larger surface coverage of Hb and a more positive formal potential,which can be attributed to the effect of hydrogen bonding between proteins and surfactants.The electrochemical behavior of surfactants with different PEO unit lengths is discussed in detail.Moreover,UV-visible spectroscopy demonstrated that the structure of Hb was not destroyed in the surfactant films.The electrocatalytic activity of hydrogen peroxide on three neutral surfactant-modified electrodes has also been investigated.     

Pt纳米粒子修饰的多孔硅电极的制备及其电催化性能

通过循环伏安法电沉积使直径约为7 nm的Pt纳米粒子均匀地分散于多孔硅表面, 拟用作微型质子交换膜燃料电池的催化电极. 与刷涂法相比较, 电沉积Pt纳米粒子的多孔硅电极(Pt/Si)呈现出高的Pt利用率和增强的电催化活性. 当Pt载量为0.38 mg•cm−2时, 其电化学活性比表面积高达148 cm2•mg−1, 是刷涂相近质量的纳米Pt/C催化剂的多孔硅电极Pt-C/Si的2倍多；该修饰电极对甲醇氧化也呈现了增强的催化性能和好的稳定性, 在0.5 V(vs SCE)极化1 h后电流密度为4.52 mA•cm−2, 而刷涂了相近Pt量的Pt-C/Si电极的电流密度只有0.36 mA•cm−2.     

烷基链长对紫精分子在Cu(100)电极表面吸附结构的影响

用循环伏安法(CV)和原位扫描隧道显微镜(STM)研究了烷基取代的紫精分子在Cu(100)电极上的氧化还原行为及其吸附结构对电极电势的依赖性. 对乙基紫精(DHV)和庚基紫精(DEV)在含有KCl电解质溶液中进行循环伏安曲线的测定, 两者呈现出不同的氧化还原行为. 从STM所得图像观察, 二价庚基紫精在Cl-c(2×2)-Cu(100)电极上呈现出二维有序的点阵组装结构,而二价乙基紫精却未出现任何的吸附结构. 降低电极电势至单电子转移反应发生时, 形成的自由基庚基紫精在电极表面呈现出稳定的条带状组装结构, 而自由基乙基紫精出现的条带组装结构比较密集且不能稳定存在. 继续降低电极电势, 庚基紫精的吸附结构会随之出现明显的变化,而乙基紫精不会有吸附结构改变的响应.     

Studies of copper(II) sulphide ion-selective electrodes

Changes in liquid junction potentials in copper(II) solutions were measured when different reference electrodes were used. The slope and intercept of a calibration curve for a copper-selective electrode will depend on the selection of reference electrode. The condition of the electrode surface of an Orion copper-selective electrode was studied microscopically and the influence of redox potential on stability of the electrode against corrosion is discussed. Oxidizing solutions will produce pits at dislocations in the material and there will be a mixed electrode potential. The slope, stability, and speed of response are much lower when the surface contains pits. Diamond-polishing was shown to improve the electrode significantly.     

SERS study of the interaction of thiourea with a copper electrode in sulphuric acid solution

The electrochemical interaction of thiourea with a copper electrode in sulphuric acid solution was investigated using Fourier transform Raman and in situ surface-enhanced Raman scattering (SERS) spectroscopy. SERS spectra of thiourea at a copper electrode were obtained in solutions containing greater than 5 ppm thiourea; the spectra obtained were consistent with adsorption of the molecule on the copper electrode via the sulphur atom. The SERS spectra provide evidence of complex formation involving thiourea and sulphate species at the electrode surface.     

Adsorptionspolarisierte Elektroden zur Endpunktsindikation bei der potentiometrischen Titration

A novel indication model for potentiometric titrations has been presented, which is thought to be widely applicable. It is based on adsorption polarisation of indicator electrodes observable at very low concentration of measured ions. This concentration range depends on the surface quality of the indicator electrode. Combining two electrodes of the same kind, one of them with defective surface, a potential peak suitable for endpoint indication appears when passing through the concentration range in question. At all other concentrations the potential difference remains constant. The method has been examplified by the system Ag⁺/I^?.