Anodic Electrodissolution Research Articles

Bipolar electrochemical deposition of HKUST‐1 on carbon and its loading with polypyrrole for supercapacitor electrodes

AbstractUsing bipolar electrochemistry, carbon paper (CP) is asymmetrically coated with copper metal. Subsequent anodic electrodissolution in a solution containing trimesic acid linkers results in HKUST‐1 depositing on the carbon surface. The CP‐MOF (metal organic framework) composite is then soaked in a pyrrole/isopropanol solution for several hours before undergoing oxygen/Cu‐induced polymerization to fill the pores. Variations in the concentration and soaking time were investigated. X‐ray diffraction shows the successful synthesis of HKUST‐1 before and after pyrrole treatment. Scanning electron microscopy and optical microscopy suggest that the polymer is formed within HKUST‐1 rather than as a coating. Further characterization by Fourier transform infrared, X‐ray photoelectron spectroscopy, gas adsorption, and thermogravimetric analysis/differential thermal analysis were also carried out. Capacitance was found to increase with the concentration of pyrrole used to load HKUST‐1. Higher concentrations also lead to more leaching of copper. Differential pulse voltammetry (DPV), galvanostatic charge discharge, and electrochemical impedance spectroscopy electrochemically studied the redox peaks, capacitance retention, and resistivity of the electrodes.

Anodic electrodissolution: a low-cost alternative for carbon steel sample preparation for quantification of metals by ICP-MS.

A fast and low-cost method using electrolysis for sample preparation of carbon steel present in weld electrodes aiming to achieve quantification of heavy metals by inductively coupled plasma mass spectrometry (ICP-MS) was developed. Conditions of the electrolysis, such as pH and electrical charge were investigated to improve the solubility and concentration of the analytes in the electrolyte. The method showed high reproducibility, with a relative standard deviation (RSD) of less than 3.05%, and the recovery from 88.6 to 108.9% for the analytes demonstrates the accuracy of the developed method.

Low cost electrocoagulation process for treatment of contaminated water using aluminium electrodes from recycled cans

Electrocoagulation has been used to successfully treat diverse types of wastewaters. This treatment is carried out when there is an electro-dissolution of soluble anodes to form metal hydroxide flocks within the effluent. In this work an electrocoagulation setup was used to treat water from a contaminated stream. Aluminium anodes produced from recycled cans were used as electrodes. The contact time and voltage during electrocoagulation were varied and the corresponding effects on pH, Total Dissolved Solids (TDS), Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and electrode weight gain/loss were observed. The average TDS of the raw water before Electrocoagulation was 286.7 mg/L. At 10 V, 20 V and 30 V, the average TDS of 246.3 mg/L, 227.3 mg/L and 220.7 mg/L were obtained after 120 min of electrocoagulation. The reduction in TDS signified improved anode dissolution and thus improved water quality. The results show that optimum COD and BOD removal efficiencies of 90.7% and 97.67% were obtained at 10 V.

Sulfate (SO4 2−) removal by electrocoagulation process under combined electrical connection of electrodes

Inorganic compounds in water can have detrimental effects on human health and the environment due to the high toxicity level of these ionic contaminants. This study assessed the efficiency of electrocoagulation process for removing sulfate (SO4 2−). The technology of electrocoagulation depends mainly on electrical applied that produce coagulant species in a certain position via electro-dissolution of sacrificial anodes which are often made of iron or aluminum. EC process illustrated great potential as a vital method in eliminating numerous types of contaminants including inorganic contaminants at a lesser cost, and ecologically friendly technique. In the present study, aluminum materials were utilized in both cathode and anode electrodes. Water samples were obtained from Sawa Lake, Al-Muthanna Province located in Iraq. Electrocoagulation formations with static electrodes were used under mutual electrical connection. The effects of the different variables such as pH, current density, inter electrode distance, reaction time and stirring speed were scrutinized to obtain a higher removal of SO4 2−. Preliminary outcomes exhibited the following optimal and functional conditions; pH = 8, current density = 0.8A, reaction time (RT) = 80 min, IED = 1 cm, temperature = 27 °C and agitation speed = 500 rpm. The maximum removal efficiency of SO4 2− is 88 %. The present statistical rates proved the effectiveness of EC method in terms of removing salts from lake water.

Birhythmicity, intrinsic entrainment, and minimal chimeras in an electrochemical experiment.

The coexistence of limit cycles in a phase space, so called birhythmicity, is a phenomenon known to exist in many systems in various disciplines. Yet, detailed experimental investigations are rare, as are studies on the interaction between birhythmic components. In this article, we present experimental evidence for the existence of birhythmicity during the anodic electrodissolution of Si in a fluoride-containing electrolyte using weakly illuminated n-type Si electrodes. Moreover, we demonstrate several types of interaction between the coexisting limit cycles, in part resulting in peculiar dynamics. The two limit cycles exhibit vastly different sensitivities with respect to a small perturbation of the electrode potential, rendering the coupling essentially unidirectional. A manifestation of this is an asymmetric 1:2 intrinsic entrainment of the coexisting limit cycles on an individual uniformly oscillating electrode. In this state, the phase-space structure mediates the locking of one of the oscillators to the other one across the separatrix. Furthermore, the transition scenarios from one limit cycle to the other one at the borders of the birhythmicity go along with different types of spatial symmetry breaking. Finally, the master-slave type coupling promotes two (within the experimental limits) identical electrodes initialized on the different limit cycles to adopt states of different complexity: one of the electrodes exhibits irregular, most likely chaotic, motion, while the other one exhibits period-1 oscillations. The coexistence of coherence and incoherence is the characteristic property of a chimera state, the two coupled electrodes constituting an experimental example of a smallest chimera state in a minimal network configuration.

A review on industrial wastewater treatment via electrocoagulation processes

Every year, a large amount of wastewater is discharged from various industries into the environment, and various methods are used to treat wastewater to reduce the amount of pollutants. Electrocoagulation (EC) is an electrochemically based technique that generates coagulant species in situ from the electrodissolution of sacrificial anodes, usually made of iron or aluminum destabilizes suspended, dissolved, or emulsified pollutants by using an electric current. It has a potential in removing various kinds of pollutants including organic and inorganic contaminants for various types of wastewater. The effectiveness of EC process depends on various parameters including pH, electrode, operation time, and current density. The goal of this study is to review the most relevant literatures that were published recently. The main challenges associated with the EC process are electrode passivation and energy consumption. EC compared with other common methods has advantages such as reducing energy consumption and reducing operating costs.

Ultra-rapid fabrication of highly surface-roughened nanoporous gold film from AuSn alloy with improved performance for nonenzymatic glucose sensing

Using one-step anodization strategy, a nanoporous gold film (HNPG) with large surface area was rapidly fabricated on Au80Sn20 (wt%) alloy in just 80 s. The formation of highly surface-roughened nanoporous structures results from a complex process of electrochemical dealloying of Sn component from AuSn alloy, anodic electrodissolution, disproportion and deposition of Au component, and spontaneous redox reaction between electrodissolved Sn2+ and AuCl4－species at the applied anodic potential. As-prepared HNPG/AuSn shows enhanced electrochemical performance for glucose oxidation in alkaline electrolyte. At a low potential of 0.1 V (vs. SCE), it offers a short response time of 4 s, a wide linear detection range of 2 μM to 8.11 mM, an ultralow detection limit of 0.36 μM (S/N = 3), an ultrahigh sensitivity of 4374.6 μA cm−2 mM−1, and satisfactory selectivity and reproducibility. Specifically, after 6 weeks, no obvious loss of glucose amperometric signal was observed on HNPG/AuSn. The facile preparation and excellent sensing performance of HNPG/AuSn electrode make sure that it is a promising candidate for advanced enzyme-free glucose sensors.

Measurement and Analysis of Dynamic Impedance Spectra Acquired During the Oscillatory Electrodissolution of p‐Type Silicon in Fluoride‐Containing Electrolytes

AbstractUsing dynamic multifrequency analysis (DMFA), we investigated the oscillatory reaction dynamics that govern the anodic electrodissolution of p‐type silicon in fluoride‐containing electrolytes, in which the anodization of silicon is followed by the chemical etching of the oxide layer. By applying a constant voltage to the silicon electrode, stable oscillations are found in the presence of an external resistance. The dynamic impedance spectra acquired through DMFA were fitted to a suitable electrical equivalent circuit. In doing so, it was possible to investigate the temporal evolution of the kinetic parameters throughout the formation and dissolution of the silicon oxide.

Treatment of drilling fluids wastewater by electrocoagulation

Electrocoagulation has been successfully used to treat a variety of industrial wastewaters. The goal is to form flocks of metal hydroxides within the effluent to be cleaned by electro-dissolution of soluble anodes. The present work deals with the removal of petroleum organic matter such as diesel from drilling fluids wastewater by the electrocoagulation technique using a direct current (DC) electrolytic cell. The cell is consisted of a rectangular Plexiglass container of dimension 12*12*15cm equipped with varied number of parallel horizontal meshed Aluminum anodes (9*9cm) and 115.2cm2 effective area, stainless steel (9*9cm) cathode. The electrodes were connected to a digit DC power supply (40V) with a multi-range ammeter connected in series and voltmeter connected in parallel with the cell. The percentage of COD removal was studied under different conditions by varying the following parameters: (1) electrolysis time, from 5 to 45min, (2) current density, from 0.008 to 0.034A/cm2, (3) number of parallel horizontal meshed Al anodes, (4) electrolyte concentration. The new anode design of electrocoagulation cell permits high efficiencies with lower energy consumption in comparison with the other cell design used in previous studies.

Effect of temperature on precision of chaotic oscillations in nickel electrodissolution

We investigate the effects of temperature on complexity features of chaotic electrochemical oscillations using the anodic electrodissolution of nickel in sulfuric acid. The precision of the "period" of chaotic oscillation is characterized by phase diffusion coefficient (D). It is shown that reduced phase diffusion coefficient (D/frequency) exhibits Arrhenius-type dependency on temperature with apparent activation energy of 108 kJ/mol. The reduced Lyapunov exponent of the attractor exhibits no considerable dependency on temperature. These results suggest that the precision of electrochemical oscillations deteriorates with increase in temperature and the variation of phase diffusion coefficient does not necessarily correlate with that of Lyapunov exponent. Modeling studies qualitatively simulate the behavior observed in the experiments: the precision of oscillations in the chaotic Ni dissolution model can be tuned by changes of a time scale parameter of an essential variable, which is responsible for the development of chaotic behavior.

Copper corrosion and anodic electrodissolution mechanisms in naturally aerated stagnant 0.5 M [formula omitted

Mechanisms of copper corrosion and electrodissolution in naturally aerated, stagnant 0.5 M H 2 SO 4 were investigated by means of electrochemical techniques, compared with deaerated measurements. The role of dissolved oxygen was suggested, and three models were proposed in - 0.05 ∼ 0.15 V vs. SCE range. Near to corrosion potential, chemical redox between cuprous intermediate and oxygen reduction reaction (ORR) intermediate accelerated copper corrosion, and corrosion rate was controlled by a combined cathodic kinetic–anodic diffusion process. In low and high potential ranges, chemical redox, occurred between cuprous intermediate and oxygen molecule, synergistically accelerated the electrodissolution of copper.

Treatment of textile wastewater by a hybrid electrocoagulation/nanofiltration process

Untreated effluents from textile industries are usually highly coloured and contain a considerable amount of contaminants and pollutants. Stringent environmental regulation for the control of textile effluents is enforced in several countries. Previous studies showed that many techniques have been used for the treatment of textile wastewater, such as adsorption, biological treatment, oxidation, coagulation and/or flocculation, among them coagulation is one of the most commonly used techniques. Electrocoagulation is a process consisting in creating metallic hydroxide flocks within the wastewater by the electrodissolution of soluble anodes, usually made of iron or aluminium. This method has been practiced for most of the 20th century with limited success. In recent years, however, it started to regain importance with the progress of the electrochemical processes and the increase in environmental restrictions in effluent wastewater. This paper examines the use of electrocoagulation treatment process followed by nanofiltration process of a textile effluent sample. The electrocoagulation process was studied under several conditions such as various current densities and effect of experimental tense. Efficiencies of COD and turbidity reductions and colour removal were studied for each experiment. The electrochemical treatment was indented primarily to remove colour and COD of wastewater while nanofiltration was used to further improve the removal efficiency of the colour, COD, conductivity, alkalinity and total dissolved solids (TDS). The experimental results, throughout the present study, have indicated that electrocoagulation treatment followed by nanofiltration processes were very effective and were capable of elevating quality of the treated textile wastewater effluent.

Analysis of current transients for voltage pulse-modulated surface processing: Application to anodic electro-dissolution of copper for electrochemical mechanical planarization

The voltage pulse modulation technique is useful for electrochemical processing of metal and alloy surfaces by utilizing faradaic reactions like electro-deposition and electro-dissolution. A theoretical framework is presented here to facilitate quantitative analysis of experimental data (current transients) obtained in this approach. A typical application of this analysis is demonstrated for an experimental system involving electrochemical removal of copper surface layers, a relatively new process for abrasive-free electrochemical mechanical planarization of copper lines used in the fabrication of integrated circuits. Voltage pulse-modulated electro-dissolution of Cu in the absence of mechanical polishing is activated in an acidic solution of oxalic acid and hydrogen peroxide. The current generated by each applied voltage step shows a sharp spike, followed by a double-exponential decay, and eventually attains the rectangular shape of the potential pulses. The formulas presented here show excellent fits to these current transients, and help to probe the detailed electrochemistry of surface layer removal using a simple circuit model of the reactive interface.

Oscillatory Phenomena during Anodic Copper Electrodissolution in Trifluoroacetic Acid Solution

This work presents the current oscillation phenomena observed in an electrochemical Cu/0.5 M CF3COOH system. The dynamical response of this new oscillator was followed by both current density-potential (j-E) and current density-time (j-t) curves. The current oscillation phenomena of the investigated system were monitored over various potential scan rates and constant applied potentials as control parameters. The increase of potential scan rate significantly decreases both the potential range of current oscillations and the frequency of oscillations. At the j-t curves both the simple and the complex (period adding) oscillations were found. Moreover, with the increase of applied potential, the increase of period of oscillations and current oscillation amplitudes were observed. It appears that the period of current oscillations exponentially grows with applied potential.

Current Oscillations in Anodic Electrodissolution of Copper in Lithium-ion Battery Electrolyte

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Electrochemical Thinning of Thicker Gold Film with Qualified Thickness for Surface Plasmon Resonance Sensing

To meet the requirement of surface plasmon resonance (SPR) sensing, controlling the thickness of the gold film is very important. Here, we report an efficient and simple approach to prepare a SPR-active substrate when the thickness of the gold film is larger than the optimizing 50 nm and smaller than 100 nm. This method is based on anodic electrodissolution of gold in electrolyte containing chloride ions. Using this method, the thickness of gold films can be easily changed at a nanometer scale by controlling the number of potential scans and the concentrations of chloride ions in the electrolyte. At the same time, the influence of gold film thickness on the SPR signal is recorded by SPR in real time. To assess the change of the surface roughness and morphology of gold film through anodic electrodissolution, atomic force microscopy was used. The surface roughness of the same Au film before and after anodic electrodissolution is 1.179 and 2.767 nm, respectively. The change of the surface roughness of Au film brings out a slight angle shift of SPR. This indicates that surface electrodissolution of the gold does not affect the character of the original bulk film and this film can be used for SPR experiments. To confirm our expectation, a simple adsorption experiment of cytochrome c (Cyt c) on the gold film treated with anodic electrodissolution modified by 11-mercaptoundecanic acid was carried out. The angle shift of SPR confirmed the adsorption of Cyt c, and the cyclic voltammetry of Cyt c provided a complementary confirmation for the adsorption of Cyt c. These results show that this approach provides a good way to change the thicker gold film to an optimized thickness of SPR sensing. The great advantage brought by this approach is in that it can convert the waste gold films with greater thicknesses fabricated by the vacuum deposition method or other methods into useful materials as active SPR substrates.

Current oscillations in anodic electrodissolution of copper in lithium-ion battery electrolyte

Current oscillations were observed during electrodissolution of copper in nonaqueous lithium-ion battery electrolyte under potentiostatic conditions using copper foil electrodes. Mixed-mode oscillations were observed over certain ranges of stir rate and applied potential. A nonlinear dynamics technique (return map) was applied to characterize the oscillations. The dynamic stir conditions of the electrolyte influenced the frequency and pattern of the oscillations. The amplitude of the oscillations increased with increasing potential. Also, cyclic voltammetry (CV) showed that the oscillatory current was correlated to the oxidation of the copper electrode.

Photoelectrochemical investigation of film formation at titanium and niobium anodes in acid fluoride media

The properties of the surface oxide films during electrodissolution of titanium and niobium anodes in acid fluoride media are investigated by photoelectrochemical and impedance techniques. In slow voltammetries a linear dependence of photocurrent signal on applied potential is observed, consistent with a constant film formation ratio; an estimate of the latter is given on the basis of capacity data. Phenomena of depassivation observed at the Nb anode during voltammetric and potential step experiments are characterised and attributed to instability of the oxide film. The photocurrent spectra of both surface oxides change in shape under polarisation, showing a limited decrease of the photoresponse for penetrating wavelengths close to the bandgap and a marked decay for the shorter, strongly absorbed wavelengths. The phenomenon may be attributed to formation of a duplex oxide film, with a compact photoactive layer in contact with the metal substrate and an outer layer at the film ∣ solution interface, rich in defects and possibly porous/hydrated, which acts as an optical filter.

Eletrodissolução anódica em sistema de injeção em fluxo: uma alternativa rápida e eficiente para dissolução de ligas metálicas

Anodic electrodissolution procedure in a flow injection system for determination of constituents in alloys is discussed. This approach implement sample preparation procedure by using a chamber and a DC power supply with constant direct current. Solid sample was attached to chamber as anode. In this review a general overview of these procedure is presented. The procedure presented a good performance characterized by a high sample throughput determinations, good accuracy and relative standard deviation.

Expanding the working concentration range for the direct analysis of metallic alloys by on-line anodic electrodissolution and electrothermal atomic absorption spectrometry

The behavior of several absorption lines under different atomization conditions (from tube wall, L’vov platform and with and without modifier) and the maintenance of the carrier gas flow during atomization were studied with the objective of expanding the working concentration range in the determination of Sn, Ni and Fe in brass alloy samples by on-line anodic electrodissolution and electrothermal atomic absorption spectrometry (ETAAS). The employment of several lines and atomization conditions does not seem to affect the precision with any of the investigated metals. The upper working limit for Sn, Ni, and Fe is approximately 1.5, 3.5 and 4.0 times higher, respectively, under stop gas flow conditions using the less sensitive line than under the most sensitive condition. When combined with the use of resonance lines, non-stop gas flow could be a promising alternative especially for Ni and Fe. The use of non-stop gas flow in combination with non-resonance lines should be avoided. The detection limit and the sensitivity can be adjusted better by employing elevated currents in the electrodissolution step.