Analytical expression for transient chronoamperometric current at ultramicroband electrode

Analytical solution of non-steady state chronoamperometric current at ultramicroband electrode is derived. The analytical expression for current (Padé approximant), valid for entire time domain is compared with the analytical and digital simulation data. A satisfactory agreement with the available limiting cases of analytical expressions and digital simulation data is noted. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 10, pp. 1244–1250. The text was submitted by the authors in English.     

High‐Performance Electrocatalytic Activity of Palladium‐Copper Nanoalloy towards Methanol Electro‐oxidation in an Alkaline Medium

Nanoalloy of PdCu were synthesized with three different stoichiometry ratio (3 : 1, 1 : 1, 1 : 3) by simple co‐reduction process at 5 °C with Triton X‐100 as surface modifier. Morphology and composition of the synthesized catalyst were characterized by X‐ray diffraction (XRD), X‐ray photo electron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X‐ray analysis (EDAX) with selected area electron diffraction (SAED) techniques. Electrocatalytic activity and stability of the catalysts towards methanol oxidation reaction were verified in alkaline medium by cyclic voltammetry (CV) and chronoamperometry (CA). Observed results emphasis that PdCu nanoalloy in the 3 : 1 stoichiometric ratio shows better catalytic activity (778.98 mA mg⁻¹) and stability not only in the initial state (93.73 mA mg⁻¹) but also after 1800 s (8.61 mA mg⁻¹) among all other prepared catalysts.     

Understand the Degradation Mechanism of Electrochromic WO3 Films by Double‐step Chronoamperometry and Chronocoulometry Techniques Combined with in situ Spectroelectrochemical Study

In this paper, we demonstrate that the double‐step chronoamperometry and chronocoulometry techniques are efficient tools for characterizing the basic electrochromic performance of WO₃ films (i. e., coloration/bleaching conversion, charge capacity and coloration efficiency). In combination with in situ spectroelectrochemical study, the variations in the optical modulation and charge capacity of the WO₃ film under different potential windows were attributed to different ion diffusion depths and the quantity of WO₃ sites participating in the redox reaction. Moreover, the double‐step techniques have distinctive advantages for analyzing the cyclic mechanism of the WO₃ film. When the inserted Li⁺ ions in the coloration process cannot be completely extracted from the film in the next bleaching process, these ions accumulate in the film upon cycling, leading to the degradation of the electrochromic performance. Here the accumulated ions are referred to as “unrecoverable ions”. The abundant formation of unrecoverable ions may be due to incomplete reduction of a portion of Li_x WO₃, which is caused by collapse of the Li⁺ ion diffusion channels in the deep of film after repeated cycles. All these results support that the double‐step chronoamperometry and chronocoulometry techniques have significant advantages to analyze the cyclic stability and explore the degradation mechanism of electrochromic WO₃ films.     

Study of the Electrochemical Behavior of Biodiesel Microemulsion

Microemulsions have become a widely employed technique for the control of biodiesel quality but are still poorly understood as regard to their electrochemical behavior. In this work, we report the fundamental importance associated with the knowledge of electrochemical behavior of microemulsions composed of water in the presence of a supporting electrolyte, soybean biodiesel and propan‐1‐ol as consolute, along with the ferrocyanide–ferricyanide redox system applied as probe. The voltammetric results showed that for different compositions of microemulsions, variation in peak currents and change in system reversibility as well as in the electron transfer process were clearly noted. Furthermore, through the study of the diffusion coefficient, three different types of microemulsions including Oil/Water, Bicontinuous, and Water/Oil were successfully identified. Electrochemical impedance spectroscopy studies were also carried out aiming at obtaining more information regarding the electrode/solution interface. All the studies performed demonstrated that different types of microemulsions were formed upon exerting a direct influence on the electrochemical behavior of the redox probe. These results, in essence, point to the possibility of choosing a more suitable and advantageous microemulsion type for the development of an analytical method, as in the case, for example, of the microemulsions ME‐2 and ME‐3 which presented high voltammetric response in redox probe oxidation.     

n型半导体硅电极表面Au的电化学成核机理

在成功实现半导体硅表面电沉积致密金膜的柠檬酸盐镀金实际应用体系中,运用循环伏安和电位阶跃法研究了Au在n型Si(111)电极表面的电沉积过程和成核机理.结果表明,在该体系中, Au在Si表面呈现不可逆电极过程,成核过电位达到250 mV;根据Cottrell方程求得扩散系数D = (1.81 ± 0.14) × 10^-4 cm₂·s^-1;运用Scharifker-Hills (SH)理论模型对比分析拟合实验结果,表明Au在n型Si表面遵循扩散控制下的三维连续成核机理;通过扫描电子显微镜观察Au初期成核、生长形貌,进一步证实了Au的三维连续成核机制,并讨论了阶跃电位和阶跃时间对Au核形貌和密度的影响.     

Cr2O3粉末在CaCl2熔盐中直接电化学还原的金属通腔电极研究

应用金属通腔电极研究Cr2O3粉末于熔盐中的电化学行为,验证了900℃下Cr2O3粉末在含镁量<0.005%氯化钙熔盐中的分步还原机理,估算其电化学还原动力学参数;并由扫描电镜观察产物形貌,分析电解电位和时间对金属颗粒尺寸的影响.     

Electrocatalytic Acitivity of rGO/PEDOT : PSS Nanocomposite towards Methanol Oxidation in Alkaline Media

Increasing demand of alternative energy sources leads to the development of new electrocatalytic materials for fuel cells. In present work, we report the synthesis of rGO/PEDOT : PSS (reduced graphene oxide/ Poly (3,4‐ethylenedioxythiophene) : Polystyrene sulfonate) nanocomposite by in‐situ polymerization method using EDOT as precursor and the nanocomposite is used as anode catalyst for methanol oxidation. Structural and chemical characterizations such as XRD, FTIR and Micro‐Raman confirm the formation of the nanocomposite. From TEM image, growth of nanofibrous PEDOT : PSS on rGO nanosheets is observed. Electrochemical characterizations of rGO/PEDOT : PSS/ITO electrode are performed by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and Chronoamperometry (CA) measurements. Methanol oxidation reactions are performed in 0.5 M NaOH solution. The anodic current of the nanocomposite coated ITO is found be 37.5 mA at 0.59 V due to methanol electro‐oxidation and retentivity of the electrode is 92 % of initial scan after 800 cycles. The chronoamperometric results reveal that the nanocomposite modified electrode exhibits better stability with retention factor of 42.4 % up to 3000 seconds. The rGO/PEDOT : PSS/ITO electrode exhibits enhanced electrocatalytic activity towards methanol oxidation reaction due to larger surface area and excellent conductivity of rGO nanosheet.     

The Determination of Timolol Maleate Using Silver/Tannic Acid/Titanium Oxide Nanocomposite as an Electrochemical Sensor in Real Samples

Herein, a portable and cost-effective electrochemical sbased on Silver/tannic acid/titanium dioxide/glassy carbon electrode (Ag/TA@ TiO₂/GCE) was fabricated to determine timolol(TM) assay. The Ag/TA@TiO₂/GCE offered an irreversible oxidation peak at +0.99 V, and exhibited an extraordinary electrochemical performance with a wide linear working ranges from 0.01–0.84 and 0.84–49.0 μM and a low detection limit of 5.2 nM. The detection of TM in the presence of interfering agents and real samples was also analyzed. The sensor‘s selectivity was studied by comparing the binding of TM, propranolol, nebivolol, and metoprolol. The developed electrochemical sensing platform could have promising potential for the determination of TM in clinical samples.     

Rate and Extent of Carbon Dioxide Uptake In Room Temperature Ionic Liquids: A New Approach Using Microdisc Electrode Voltammetry

A simple method is introduced which enables the simultaneous determination of both the maximum CO₂ concentration and kinetics of CO₂ uptake and release by a room temperature ionic liquid. This method is based upon the analysis of chronoamperometry recorded in bulk ionic liquid at intervals during exposure to CO₂ and subsequent exposure to vacuum to remove the dissolved CO₂. Comparing experimental data with a numerical model reveals the rate‐limiting factors for both uptake and release of CO₂.     

微环电极上双电位阶跃计时电流和计时库仑法可逆波理论及其验证

推导了微环电极上双电位阶跃计时电流和计时库仑法可逆波理论方程式，并得到了解析表达式。对其电流电量曲线的特性进行了讨论。在亚铁氰化钾－氯化钾体系中，用金微环电极在自制的微机多功能电化学仪器上进行了实验验证，实验结果与理论相符。