Formulation of a simple analytical expression for irreversible electron transfer processes in linear sweep voltammetry and its experimental verification

A simple analytical expression for the current function has been formulated for irreversible electron transfer processes in linear sweep voltammetry (LSV). The equations pertaining to the surface concentrations of the reactants and products have been obtained using the current function. The parametric dependence of the diffusion layer thickness has also been derived and its significance pointed out. The reductive cleavage of carbon tetrachloride in N,N′-dimethylformamide (DMF) at glassy carbon electrodes is investigated for verifying the theoretical expressions.     

Analytical expressions for transient diffusion layer thicknesses at non uniformly accessible electrodes

Explicit analytical expressions for the diffusion layer thicknesses of disk and band electrodes of any size, under transient conditions have been deduced. We have applied these expressions to constant potential chronoamperometry and Linear Sweep Voltammetry (LSV). The analysis of the diffusion layer thickness and concentration profiles of electroactive species corresponding to the application of a constant potential have allowed us to characterise the evolution of the mass transport from linear (high sizes) to radial (microelectrodes). The influence of the time pulse, scan rate and the electrode radius has been analyzed, with limiting expressions corresponding to E ? E⁰ and E ? E⁰ were also deduced. The conditions required to attain a stationary state are discussed.     

Effect of oxygenation time on signal of a sensor based on ionic liquids

The paper presents an oxygen sensor based on ionic liquids and solid electrodes. The following ionic liquids have been employed: [BMIM][BF₄], [HMIM][Cl], [BMIM][N(CN₂)]. Minimum time of the sensor exposure to analyte, after which the signal (current intensity) was stable, has been evaluated. An impact of volumetric flow rate of analyte on the sensor exposure time and signal has been determined. A product of permeability coefficient and solubility of oxygen in ionic liquids has been estimated. A mechanism of oxygen reduction on a surface of the solid electrodes, in the ionic liquid environment has been presented. Overall cathodic coefficients of transition for the sensors with particular ionic liquids have been determined as a function of potential scan rate.     

Electrochemical behaviour of phenylethanolamine at gold in aqueous solution

The electrooxidation of phenylethanolamine (2-amino-1-phenylethanol) at a gold electrode in alkaline electrolyte has been studied. Measurement of the differential capacitance of the electric double layer versus the electrode potential has shown that the adsorption of phenylethanolamine at the gold-solution interface plays a significant role in the oxidation mechanism. The effect of amine concentration, electrolyte pH and potential scan rate on the electrooxidation is analysed.     

Electrocatalytic oxidation of methanol to soluble products on polycrystalline platinum: Application of convolution potential sweep voltammetry in the estimation of kinetic parameters

Irreversible oxidation of methanol on polycrystalline platinum leading to soluble products has been carried out by fast scan voltammetry, and the reaction has been studied under diffusion controlled process. The conventional analysis of current–potential data, viz. dependence of peak potential on scan rate and peak width measurements, resulted in the estimation of apparent diffusion coefficient of methanol and the anodic transfer coefficient of the electrode reaction. However, from the convolution potential sweep voltammetry, a more accurate and reliable kinetic data were obtained. Under the above conditions, methanol oxidation follows Butler–Volmer rate law with a linear variation of logarithmic heterogeneous rate constant with electrode potential. A constant apparent anodic transfer coefficient independent of electrode potential was observed pointing to the fact that the standard potential of the reaction cannot be determined from the voltammetric experiments. The experimental current–potential curve was compared with a theoretical voltammogram and further oxidation of products at the electrode surface has also been analyzed using limiting convolution current.     

Aptamer-based electrochemical detection of protein using enzymatic silver deposition

In this work an electrochemical protein detection based on enzymatic silver deposition has been proposed and applied to the detection of thrombin. The target protein, thrombin, was first captured by thrombin binding thiolated aptamer self-assembled monolayers (SAMs) on the gold electrode surface, and then sandwiched with another biotinylated thrombin binding aptamer for the association of alkaline phosphatase (Av-ALP). The attached Av-ALP enzymatically converts the nonelectroactive substrate p-aminophenyl phosphate (p-APP) to p-aminophenol (p-AP) which can reduce silver ions in solution leading to deposition of the metal onto the electrode surface. Finally, linear sweep voltammetry (LSV) is used to detect the amount of deposited silver. The peak current during the anodic scan was found to reflect the amount of the target protein captured into the sandwich configuration. The proposed approach has been successfully implemented for the detection of thrombin in the range of 0.1 nM to 1 μM. Therefore, the current work has demonstrated enzymatic silver deposition for detection at aptamer-modified electrode.     

Derivation of the explicit equation relating mass-transport-limited-current to voltage at the interface between two immiscible electrolyte solutions (ITIES)

The potential drop between two immiscible electrolyte solutions consists of the sum of that across the double layer and the diffusion barrier layer. A relation between these components has been proposed by Indenbom. We extended his approach to give a relation between the current density and the overall potential drop between the two bulk solutions. The final expression is mathematically similar to the Butler–Volmer equation for classical electrode kinetics.     

The simulation of the homogeneous catalytic reaction at a monolayer-film covered rotating disc electrode

A simple and fast numerical method for the simulation of linear scan voltammetric response of the homogeneous catalytic reaction at the electroactive-monolayer-film covered rotating disc electrodes has been developed. The linear relationship between the voltammetric peak current and the concentration of dissolved reactant ions has been predicted. The proportionality factor of this relationship is very similar to the one predicted for steady-state conditions. The voltammetric peak current is, also, linearly proportional to the square roots of scan rate and rotation rate of the disc electrode, but no cumulative relationship on these parameters is predicted.     

Application of channel flow double electrode to the study on platinum dissolution during potential cycling in sulfuric acid solution

The applicability of a channel flow double electrode (CFDE) as an in situ monitoring method of Pt dissolution during potential cycling in 0.5 M H₂SO₄ solution at 25 °C was investigated. In the CFDE, Pt ions (Ptⁿ⁺) dissolved from a platinum working electrode were detected by reducing them to Pt on a gold collector electrode which was placed at the downstream. The detection of the Pt dissolution by the collector current was confirmed by EPMA analysis of the collector electrode surface. In anodic scan, a rise of the collector current above 1.05 V clearly indicated the platinum dissolution. The collector current showed two different rates of dissolution, i.e. a lower rate from 1.05 to 1.3 V where only one layer of oxide (PtO) is formed and the higher rate from 1.3 to 1.46 V where two layers of oxides (probably PtO/PtO₂) are formed. The collector current, in the cathodic scan, clearly showed two different reduction peaks due to the Pt deposition, which was confirmed by EPMA analysis. On the basis of collector current, the rate and potential range of the Pt dissolution are discussed.     

Potentiodynamic estimation of sensitization of 347 grade SS superheater tubes Part I: Effect of surface finish,scan rate and solution temperature

A nondestructive electrochemical method for estimating the degradation of 347 stainless steel superheater tubes has been investigated using basic electrolytes. It was found that Cr/Fe concentration ratio and the anodic peak current density corresponding to dissolution of precipitates (carbides and sigma phases) in 1m NaOH increased with exposure time at elevated temperatures. The peak current density was observed to increase with electrode surface finish, electrolyte temperature and potential scan rate. A scan rate of 45 mV min^–1, temperature below 40° C and surface finish using 1200 grade SiC paper or a mirror finish (3 m diamond paste) is recommended.     

锌-空气电池Co-PPy-C复合催化剂的电化学性能研究

采用化学氧化聚合法合成了以碳为载体的钴-聚吡咯(PPy)配合物Co-PPy-C,作为气体扩散电极的氧还原催化剂。利用极化曲线、交流阻抗、计时电流等电化学方法测试了其在碱性介质中(6 mol/L KOH)氧气气氛条件下氧还原的催化性能。电极电位在-0.20 V vs.Hg/HgO时,催化剂电流密度达到158 mA/cm2,显示出优越的氧还原电催化性能;采取催化层/集流体/气体扩散层的排布方式,以纯锌为负极,6 mol/L的KOH为电解液,将气体扩散电极与锌负极组装成锌-空气电池。电池以80 mA/cm2进行恒流放电,放电电压为1.0 V,且性能稳定。     

Electrochemical and time-of-flight secondary ion mass spectrometry analysis of ultra-thin metal oxide (Al2O3 and Ta2O5) coatings deposited by atomic layer deposition on stainless steel

Ultra-thin (5–50 nm) layers of aluminium and tantalum oxides deposited by atomic layer deposition (ALD) on a stainless steel substrate (316L) for corrosion protection have been investigated by electrochemical methods (linear scan voltammetry, LSV, and electrochemical impedance spectroscopy, EIS) and time-of-flight secondary ion mass spectrometry, ToF-SIMS. The effects of the deposition temperature (250 °C and 160 °C) and coating thickness were addressed. ToF-SIMS elemental depth profiling shows a marked effect of the organic and water precursors used for deposition and of the substrate surface contamination on the level of C and OH trace contamination in the coating, and a beneficial effect of increasing the deposition temperature. The polarization data show a decrease of the current density by up to four orders of magnitude with increasing coating thickness from 5 to 50 nm. The 50 nm films block the pitting corrosion in 0.8 M NaCl. The uncoated surface fraction (quantified from the current density and allowing a ranking of the efficiency of the coating, also confirmed by the capacitance and resistance values extracted from the EIS data) was 0.03% with a 50 nm thick Al₂O₃ film deposited at 250 °C. The correlation between the porosity values of the coatings and the level of C and OH traces observed by ToF-SIMS points to a marked effect of the coating contaminants on the sealing performance of the coatings and on the corrosion resistance of the coated systems.     

高浓度氯离子环境中铜合金缓蚀的电化学研究

应用线性电位扫描(LSV)和Tafel实验等电化学测试技术,研究了苯并三氮唑(BTA)浓度、缓蚀剂的复配、温度对铜合金在高浓度氯离子(25%氯化钙溶液)环境中腐蚀行为的影响。结果表明:缓蚀剂浓度改变将引起缓蚀效果的变化,BTA浓度较低时,铜合金腐蚀电位随缓蚀剂浓度增大而升高,腐蚀速率降低;BTA浓度超过0.2%后,铜合金腐蚀电位和腐蚀速率趋于稳定;NaNO2、Na2MoO4、(NH4)2MoO4等缓蚀剂与BTA复配,对改善缓蚀效果有一定作用;温度对缓蚀效果有重要影响,铜合金在高浓度氯离子溶液中的腐蚀速率随温度的升高而加快,缓蚀剂的缓蚀效果随温度的升高而降低。     

Ultrafine Cu2ZnSnS4 quantum dots functionalized TiO2 nanotube arrays for potential optoelectronic applications

Tremendous progress has been made in power conversion efficiency (PCE) of thin-film photovoltaics over the past few years, yet most current high-efficient photoactive layer usually contains rare or toxic elements accompanied by expensive and complicated vacuum processes, which increases the cost and limits the scope of the applications in the long run. Here we present a synergistic effect of quantum effect of an earth-abundant and low toxic ultrafine Cu₂ZnSnS₄ (CZTS) quantum dots (QDs) and low charge recombination in one dimensional TiO₂ nanotube arrays for optoelectronic devices. By ligands exchange, the as-obtained ultrafine CZTS QDs have been robustly anchored to a highly ordered TiO₂ nanotube arrays (TNAs) to be served as a function layer in a simple QDs sensitized solar cells. Such ultrafine CZTS QDs based solar cells exhibit significant enhancement up to 457% in PCE compared to that of CZTS QDs with larger size. The CZTS QDs functionalized TNAs has also shown excellent charge transport capability with lower recombination rate than QDs sensitized TiO₂ nanoparticles and it is expected to be used as a low-cost environment-friendly function layer for various potential optoelectronic applications.     

Kinetic investigation of the chlorine reduction reaction on electrochemically oxidised ruthenium

The rate and mechanism of the electroreduction of chlorine on electrooxidised ruthenium has been investigated with focus on the effect of solution pH. Current/potential curves for the reduction process in solutions with constant chloride concentration of 1.0 mol dm⁻³ and varying H⁺ concentration have been obtained with the use of the rotating disk electrode technique (RDE). It was found that the chlorine reduction rate is highly inhibited in solutions with high H⁺ concentrations and that it can be satisfactorily described by the Erenburg mechanism, previously suggested for the chlorine evolution on RuO₂ and RTO. The expression of the kinetic current as a function of chlorine and H⁺ concentration was obtained by solving the elementary rate equations of the kinetic mechanism. The kinetic constants obtained from the correlation of the kinetic current expression to the experimental data were used to simulate the dependence of the surface coverages and elementary reaction rates on overpotential.     

Pitting corrosion of lead in sodium carbonate solutions containing NO3 ions

Pitting corrosion of Pb in Na₂CO₃ solutions (pH=10.8) containing NaNO₃ as a pitting corrosion agent has been studied using potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques, complemented with scanning electron microscopy (SEM) examinations of the electrode surface. In the absence of NO₃⁻, the anodic voltammetric response exhibits three anodic peaks prior to oxygen evolution. The first anodic peak A₁ corresponds to the formation of PbCO₃ layer and soluble Pb²⁺ species in solution. The second anodic peak A₂ is due to the formation of PbO beneath the carbonate layer. Peak A₂ is followed by a wide passive region which extends up to the appearance of the third anodic peak A₃. The later is related to the formation of PbO₂. Addition of NO₃⁻ to the carbonate solution stimulates the anodic dissolution through peaks A₁ and A₂ and breaks down the dual passive layer prior to peak A₃. The breakdown potential decreases with an increase in nitrate concentration, temperature and electrode rotation rate, but increases with an increase in carbonate concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases with increasing the applied anodic potential, nitrate concentration and temperature.     

An experimental study on cell-impedance-controlled lithium transport through Li1−δCoO2 film electrode with fractal surface by analyses of potentiostatic current transient and linear sweep voltammogram

The effect of the surface roughness on the cell-impedance-controlled lithium transport through the Li_1−δCoO₂ film electrode was experimentally investigated in a 1 M LiClO₄-PC solution by the analyses of the potentiostatic current transient (PCT) and the linear sweep voltammogram (LSV). The flat and fractal Li_1−δCoO₂ film electrodes were prepared on the Pt/polished Al₂O₃ substrate and the surface-modified Pt/unpolished Al₂O₃ substrate, respectively. From the ac-impedance spectra obtained from the flat and fractal electrodes, it is found that the apparent self-similar fractal dimension reduces the charge-transfer resistance. All the PCTs did not exhibit the generalised Cottrell behaviour until the characteristic time t_ch and all the power dependence of the peak current on the potential scan rate positively deviated from the generalised Randles-Sevcik behaviour above the characteristic scan rate ν_ch in the LSVs. From the analyses of the PCTs and the LSVs in terms of t_ch and ν_ch, furthermore, it is experimentally confirmed that the surface roughness plays a significant role in the kinetic facilitation of the interfacial charge-transfer reaction during the whole lithium intercalation and deintercalation processes.     

A study on the potentiostatic current transient and linear sweep voltammogram simulated from fractal intercalation electrode: diffusion coupled with interfacial charge transfer

Potentiostatic current transient and linear sweep voltammogram, theoretically calculated from the well-defined fractal profiles were analysed, with particular emphasis on hydrogen transport under the condition where hydrogen diffusion in the electrode is kinetically coupled with the charge-transfer reaction at the electrode/electrolyte interface. Under such a constraint of mixed control, the simulated current transient from the fractal electrode hardly exhibited the generalised Cottrell behaviour, and, especially, it displayed an inflexion point at the time that corresponds to the temporal outer cut-off of fractality (crossover time required for the fractal to flat transition). In the case of the linear sweep voltammogram computed from the fractal electrode, moreover, the power dependence of the peak current on the scan rate deviated negatively from the generalised Randles-Sev?ik behaviour, above the slow threshold scan rate (crossover scan rate needed for the fractal to flat transition). From the analyses of the current transients and the linear sweep voltammograms calculated with various values of the simulation parameters, it was further recognised that during the potential jump as well as the potential scan, the temporal cut-off ranges of fractality under the constraint of mixed control are crucially determined by the interfacial charge-transfer kinetics, even though the spatial cut-off range and the hydrogen diffusivity in the electrode are maintained constant.     

The influence of surface treatment on the anodizing of magnesium in alkaline solution

The mechanism of magnesium anodizing after mechanical polishing or HF pickling was studied. X-ray Photoelectron Spectroscopy and Photocurrent Spectroscopy were employed to characterize both the initial films formed on Mg soon after surface treatments and the anodic films grown in strongly alkaline solutions. Electrochemical and capacitance measurements were performed in order to study the oxidation process and to check if the kinetic of growth fits the Mott–Cabrera high field model. From Tafel plots it was possible to estimate the activation distance, while the simulation of the barrier layer growth as a function of the potential at high scan rate allowed to estimate the other kinetic parameters of Mott–Cabrera model. An influence of the initial layer composition on such parameters was evidenced.     

Piezoelectric resonator and high-frequency admittance study of viscosity and density changes in a thin water layer adjacent to the electrode surface

Analysis of the admittance of quartz resonator in contact with water has shown that the viscosity-density product of water at a metallic electrode surface decreases during the positive potential scan. This decrease is more pronounced when the electrode surface is coated by a thin layer of polymer. Literature data provide evidence that the density of water in the first layer attached to the surface increases when the potential is shifted into the positive direction. It is concluded that during such potential scan the decrease of viscosity is larger than the increase of density.