AC Electrolysis Research Articles

Augmentation of Pd-catalysed oxidative C–H/C–H carbonylation through alternating current electrosynthesis

Unsymmetrical-waveform AC electrolysis facilitates Pd-catalysed oxidative C–H/C–H carbonylation. This methodology highlights the substantial benefits conferred by Pd-catalysed conversions in comparison to traditional DC electrolysis.

Elucidating the Underlying Reactivities of Alternating Current Electrosynthesis by Time‐Resolved Mapping of Short‐Lived Reactive Intermediates

AbstractAlternating current (AC) electrolysis is an emerging field in synthetic chemistry, however its mechanistic studies are challenged by the effective characterization of the elusive intermediate processes. Herein, we develop an operando electrochemical mass spectrometry platform that allows time‐resolved mapping of stepwise electrosynthetic reactive intermediates in both direct current and alternating current modes. By dissecting the key intermediate processes of electrochemical functionalization of arylamines, the unique reactivities of AC electrosynthesis, including minimizing the over‐oxidation/reduction through the inverse process, and enabling effective reaction of short‐lived intermediates generated by oxidation and reduction in paired electrolysis, were evidenced and verified. Notably, the controlled kinetics of reactive N‐centered radical intermediates in multistep sequential AC electrosynthesis to minimize the competing reactions was discovered. Overall, this work provides direct evidence for the mechanism of AC electrolysis, and clarifies the underlying reasons for its high efficiency, which will benefit the rational design of AC electrosynthetic reactions.

Alternating Current Techniques for a Better Understanding of Photoelectrocatalysts

Several spectroscopic and electroanalytical techniques are in use when it comes to the investigation of interfaces in photoelectrocatalysis (PEC). Among them, AC techniques are the least used ones except for electrochemical impedance analysis despite having several advantages over DC electroanalytical techniques. Though AC electrolysis of water was known in the early years of the 20th century, it was not given significant attention either. In this Perspective, we discuss how these barely used yet powerful AC techniques, namely, (1) Mott–Schottky in impedance and photoelectrochemical impedance analyses (equivalent circuit analysis, capacitance spectroscopy), (2) intensity-modulated photocurrent spectroscopy (IMPS), (3) FS-HA-FT-AC voltammetry, and (4) paired electrolysis, can lead us ahead in the way of further fathoming interfaces in PEC with highlights on prospects of these AC techniques for energy conversion reactions.

Synthesis of Chloroauric Acid from Gold Electrodes in Alkali Halide Salt Solution by AC Electrolysis and the Sequential Formation of Gold Nanoparticles by Turkevich Method

Abstract Gold nanoparticles have been commonly made by a wet process from chloroauric acid or dry process using vacuum evaporation to solid surfaces. Here, we have shown a method to make gold particle from gold electrodes in potassium chloride solution by AC electrolysis and the following Turkevich method. The developed AC electrolysis method provides an environment-friendly process to produce gold particles from gold electrodes without using any strong acids such as aqua regia or hydrochloric acid.

Methods to Determine the Current Efficiency in AC Electrolysis

The paper presents several methods (analytical, electromechanical and electronic) for determining the cathodic current efficiency of the metal deposition processes carried out by AC or pulse current. Based on the results of own experimental researches (for indium, cadmium, nickel, tin and zinc), the appropriate equations are given and the distribution of both faradaic and non-faradaic parts of charge (charging of the electrode double layer) is calculated.

Influence of joule heat and heat of electric arc on the vortex flow in DC arc furnace

The paper devoted to the numerical simulation of processes in DC electric arc furnaces with the bottom electrode. These furnaces have shown higher efficiency, low heat loss, lower components wear and higher quality of steel production. The biggest disadvantage of such furnaces is a high rate of fettle wear near the bottom electrode that connected with electrovortex flow. Electrovortex flows appearing under electromagnetic forces as a result of non-homogeneous distribution of the current density through the liquid conductor. This effect can be observed in many technological processes: electro slag remelting process (including DC and AC metallurgical furnaces, electrolysis cells and submerged-resistor induction furnaces), arc welding, processes of semiconductor crystals growing, electro vortex engines etc.

Preparation of nanosized porous oxide layers on titanium by asymmetric AC electrolysis in sulfuric acid

Abstract

Hydrogen･oxygen Nanobubbles Generation by Anomalous High Frequency AC Electrolysis

Hydrogen･oxygen nanobubbles were generated in 0.1-1.0 m mol/L Na2SO4 solutions using anomalous high-frequency AC electrolysis （-pole and ±poles, 30 kHz）. The bubble size distribution was 20-600 nm. The maximum bubble number density was about 4 million per milliliter at the size distribution position of 100 nm. The bubble number density of the solution boiled for 2 min did not decrease, but instead increased slightly. After 26 days, the nanobubbles were found to exist almost stably.

Inkjet printing and nanoscale electrocrystallization: Complete fabrication of organic microcrystals-based devices under ambient conditions

We report the first successful attempt at complete device fabrication under ambient conditions using inkjet printing and nanoscale electrocrystallization. Three different electrode patterns—parallel-type, multiparallel, and multitip patterns—are prepared using inkjet patterning. The printed electrodes, which have gaps of ∼20μm, are produced using a material printer. Indium tin oxide and gold inks are used for printing, and the electrodes are printed on silicon and glass substrates. Next, using these printed electrodes, micro- or nanocrystals are synthesized through nanoscale electrocrystallization. Owing to the surface roughness of the electrodes, the manner of crystal growth is slightly different from that in the case of lithographically formed electrodes; however, the morphology of the grown crystals is similar. In addition, the nanocrystals-based bridge structure formed between the two electrodes by AC electrolysis is similar to that obtained using lithographically formed electrodes. Further, the two-terminal device shows ohmic characteristics, indicating that there is good contact between the electrode and obtained crystal.

Phase composition and pore structure of nanoparticulate tin oxides prepared by AC electrochemical synthesis

The effect of current density and sodium chloride concentration in solution on the phase composition and pore structure of the products of ac electrolysis of metallic Sn has been studied using X-ray diffraction, thermogravimetry, differential scanning calorimetry, electron microscopy, and low-temperature nitrogen adsorption measurements. The results demonstrate that the synthesis products consist of tin(II) and tin(IV) oxides and hydroxides, whose percentages depend on electrolysis conditions, and have a large specific surface area and mesoporous structure. The average particle size ranges from 10 to 30 nm.

Alternating‐Current Electrolysis for the Production of Phenol from Benzene

Works both ways: phenol was produced by both anodic and cathodic benzene oxidations over the V(x)O(y)-Sn(0.9)In(0.1)P(2)O(7) electrode in an electrochemical cell, thus allowing the use of AC electrolysis for phenol production. AC electrolysis was found to be more efficient and selective toward phenol production than DC electrolysis.

Preparation of the Bioactive Porous Layer on Titanium by AC Electrolysis in Sulfuric Acid

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ChemInform Abstract: A New Electrochemical Method to Prepare Mesoporous Titanium(IV) Oxide Photocatalyst Fixed on Alumite Substrate.

A TiO2 film was deposited onto alumite using an electrochemical technique, where the initial electrodeposition was carried out by ac electrolysis in (NH4)2[TiO(C2O4)2] solution, followed by pulse electrolysis in TiCl3. This is a new method to prepare a mesoporous TiO2 photocatalyst film consisting of nanosized particles and to directly fix them onto the alumite substrate (Al/Al2O3). The sizes of the TiO2 particles in the prepared film were about 5 nm, and they consisted of mixtures of the anatase, rutile, and amorphous phases. This film had a high catalytic activity for the decomposition of acetaldehyde even under fluorescent lamp illumination. Moreover, the preparation cost is very low compared with other methods. Therefore, the prepared Al/Al2O3/TiO2 plate is very useful for the practical photodecomposition of chemical contaminants in the atmosphere. The mechanisms of the TiO2 deposition and the photocatalysis are discussed.

Low-voltage DC/AC electrolysis of water using porous graphite electrodes

Abstract Using DC and AC electrolysis of water, experimental current density–voltage curves were determined using graphite electrodes in an electrolyte of 5 mol of NaOH per liter. It was found that certain aspects of the DC curves could not be accounted for, using a model based on modern electrochemical theory. However, the experimental data could be explained using a revised model which incorporated the adsorption of hydrogen and oxygen by the graphite electrodes. The AC curves had to be explained via a more complex model based on current flowing in the outside circuit. During AC electrolysis, little or no gas was formed via current through the cell. If the electrodes are of a different area, hydrogen and oxygen are formed on the small-area electrode only at a relatively low potential; at a higher potential, both gases are formed at both electrodes. According to the model, the current does not cross the electrolysis cell either above or below the decomposition potential, but flows through the low-impedance outside circuit. Using these models, the experimental features of both DC and AC electrolysis of water can be explained.

交直ハイブリッド電解法により構造制御したポーラスアルミナをテンプレートとしたニッケルナノピラーの作製

Aluminum was anodized in an oxalic acid bath using AC and DC hybrid electrolysis at a frequency of 0.1-1000 Hz and with DC galvanostatic electrolysis. Palladium was electrodeposited as a catalyst into pores of the anodized films using AC potentiostatic electrolysis. Electroplating was prepared continuously on anodized films of aluminum. Then the anodized film was dissolved in 5 mol dm−3 NaOH aqueous solution at room temperature to obtain nickel nanopillar aggregate (about 50-90 nm diameter).Results of SEM evaluation showed that the pore diameter and number (structure) of anodized films were governed by the impressed frequency. The frequency and the pore diameter showed an inverse relation. In addition, nickel nanopillars were prepared from an anodized film template. Results show that the pillar diameter accorded with the pore diameter of the anodized film.

Peculiarities of Bi 0 nanowire arrays growth within the alumina template pores by ac electrolysis

A stable aqueous solution, well-compatible with the template material, was developed with interest to synthesize densely packed arrays of pure phase Bi 0 nanowires (nws) in micrometer length using various alumina templates and a simple alternating current (ac) deposition protocol. Structural, morphological and optical features exhibited by Bi 0 nw arrays were studied ex-situ for several alumina templates with average ∅ pore from 10 to 100 nm. The blue-shift effect in the absorption energy of the Bi 0 nw arrays with decrease in ∅ Bi is demonstrated. Cyclic voltammograms recorded in-situ in the studied solution for polycrystalline Au, Pt, Bi and nano-Bi 0/alumina electrodes are also presented, composed and discussed.

Effect of Environmentally Friendly Anodization on the Mechanical Properties and Microstructure of AZ91D Magnesium Alloy

Die-cast plates of ASTM (American Society for Testing and Materials) AZ91D magnesium alloy were anodized by DC or AC electrolysis in a solution of phosphate and ammonium salt in which the anodized layer is formed by local discharge, followed by rapid solidification. Salt spray tests of the anodized specimens showed that AC electrolysis increases corrosion resistance and the anodized layers become denser compared with that for DC electrolysis. Tensile strength, elongation, and hardness were also improved by anodization, but higher anodizing bias and the resulting heating caused grain coarsening and a decrease in these properties. For the specimens that displayed remarkable improvement in mechanical properties, a decrease in network precipitates of the β phase was observed. Improvement of mechanical properties is considered to be due to the fine precipitation of β inside the grains of the a phase at moderate temperature.

陽極酸化 Al-Mg 合金の電解着色後の色調に及ぼす連続ねじり加工の影響

Al-Mg alloys treated by continuous rotation evolutional control (CREO) were anodized and colored by means of AC electrolysis at 10 V in sulfate solutions of 303 K containing Cu, Sn, Ni or Co. The anodized Al-Mg alloys were colored rufous (Cu), yellow to gold (Sn), or red brown (Ni and Co) by the electrolysis. The lightness of the colored Al-Mg alloys was significantly enhanced by CREO, regardless of the metals deposited. The gloss of the Al-Mg alloys decreased-probably due to an increase in surface waviness resulting from CREO. The enhancement of the lightness of colored Al-Mg alloys treated by CREO is attributed to the decrease in the glossiness. SEM images showed that the density of the micro-pores in anodic oxide films on Al-Mg alloys decreased as a result of CREO. The decrease in the density of the micro-pores may be assumed to have enhanced the lightness of the colored Al-Mg alloys treated by CREO.

Template synthesis, characterization and transformations of iron nanowires while aging

Densely packed arrays of various materials demonstrating enhanced magnetic properties remain of great interest nowadays. In this study, transmission electron microscopy (TEM), Mössbauer spectroscopy (MS) and powder X-ray diffraction (XRD) were used to characterize the morphology, composition and phase of iron nanowires ( nws) deposited from the developed solution within alumina template pores of the average diameter of ca.15 nm by the alternating current (ac) electrolysis protocol. The same investigations were performed after Fe nws storage in the air for several months. Characterization of the as-grown product shows the formation of the crystalline α-Fe nws array with a preferred [1 1 0] nw growth direction. The aging of samples leads to the corrosion of Fe nws mainly from the template top side while aging of Fe nws liberated from the template and kept for several months under ambient conditions results in the corrosion of nws along their full length producing catkin-twig shapes.

The influence of the alumina barrier-layer thickness on the subsequent AC growth of copper nanowires

In order to reveal the role of the alumina barrier-layer thickness, δb, on the copper nanowires electrochemical growth within the alumina pores, the experiments varying porous alumina template parameters and subsequent AC electrolysis conditions were performed. A linear dependence of δb on the final anodizing voltage, Ua,fin, was verified from 40 to 5V by the electrochemical impedance spectroscopy technique. The further decrease in Ua,fin was not followed by the concomitant decrease in δb presumably due to uneven formation of the native aluminum oxide in a reaction between the aluminum and ambient oxygen. The spectrometric analysis of deposited copper content has shown that the range of AC voltages used for copper nanowires growth within the alumina pores sharply increases with decrease in the Ua,fin and so, in the δb. The most favourable Ua,fin range for the uniform growth of copper nanowires is 15–7.0V. This is because: (i) the decrease in Ua,fin below 7V results in the alumina framework peeling off from the Al surface, during subsequent AC electrolysis; (ii) the AC filling of template with δb>20nm (Ua,fin>20V) leads to the breakdown of alumina.