Indirect Electrochemical Oxidation Research Articles

Redox Relay-Induced C-S Radical Cross-Coupling Strategy: Application in Nontraditional Site-Selective Thiocyanation of Quinoxalinones.

Oxidative cross-coupling is a powerful strategy to form C-heteroatom bonds. However, oxidative cross-coupling for constructing C-S bond is still a challenge due to sulfur overoxidation and poisoning transition-metal catalysts. Now, electrochemical redox relay using sulfur radicals formed in situ from inorganic sulfur source offers a solution to this problem. Herein, electrochemical redox relay-induced C-S radical cross-coupling of quinoxalinones and ammonium thiocyanate with bromine anion as mediator is presented. The electrochemical redox relay comprised initially the formation of sulfur radical via indirect electrochemical oxidation, simultaneous electrochemical reduction of the imine bond, electro-oxidation-triggered radical coupling involving dearomatization-rearomatization, and the reformation of the imine bond through anodic oxidation. Applying this strategy, various quinoxalinones bearing multifarious electron-deficient/-rich substituents at different positions were well compatible with moderate to excellent yields and good steric hindrance compatibility under constant current conditions in an undivided cell without transition-metal catalysts and additional redox reagents. Synthetic applications of this methodology were demonstrated through gram-scale preparation and follow-up transformation. Notably, such a unique strategy may offer new opportunities for the development of new quinoxalinone-core leads.

Selective recovery of lithium from spent LiFePO4 powders with electrochemical method

In recent years, with the flourishing of new energy vehicles, the lithium iron phosphate (LFP) batteries are vigorously developed due to their low cost and high stability. Meanwhile, it leads to an increase in large-scale retirement of batteries. Therefore, it is crucial to develop a green and efficient recycling method. In this work, an indirect electrochemical oxidation has been proposed for selective leaching of Li ions. An electrochemical system using boron-doped diamond electrode (BDD) with high oxygen evolution potential as anode and RuO2/Ti as cathode has been built to generate oxidizing species and enhance the oxidative reaction contact for an indirect oxidation of LFP. The operating conditions were optimized to a current density of 110 mA/cm2, Na2SO4 electrolyte concentration of 0.225 M, pH of 1.7, solid–liquid ratio of 16 g/L. The leaching efficiency of Li ions reached up to 95.53 % and the leaching efficiency of Fe ions was less than 0.01 % at room temperature. A purity of lithium carbonate product of 99.93 % was obtained after precipitation of the leaching solution. This proposed method could realize efficient and rapid selective leaching of Li and Fe ions by indirect oxidation, realizing selective leaching and significantly reducing the usage of acid.

Electrocatalytic degradation of octadecylamine and 4-dodecylmorpholine by the Ti/SnO2-Sb/β-PbO2 anode at high salinity conditions: Activity and mechanism insights

Increased levels of octadecylamine (ODA) and 4-dodecylmorpholine (DMP) in the aqueous, primarily utilized as flotation agents in the worldwide production of potash fertilizer, imperil the stability of ecosystems and the downstream production of high-end chemicals. Nevertheless, there is a dearth of exhaustive studies pertaining to the elimination of ODA and DMP. Herein, the Ti/SnO2-Sb/β-PbO2 anode was fabricated by a thermal decomposition-electrodeposition technique for the electrocatalytic degradation of ODA and DMP. The degradation efficiency of ODA and DMP can achieve complete degradation, reaching 100%, after treatment periods of 10 min and 120 min, respectively. Meanwhile, the TOC removal efficiency of ODA and DMP is up to 85% and 61% at 30 min and 120 min, respectively. In particular, sulphate exhibits inhibitory degradation activity of ODA and DMP in comparison to chloride salt. The recycling and accelerated lifetime tests indicate excellent stability and recyclability of the Ti/SnO2-Sb/β-PbO2 electrode. The mechanism of electrocatalytic degradation involves indirect electrochemical oxidation mediated by free radicals. The primary reactive species responsible for the degradation of DMP and ODA, as determined through scavenger quenching experiments and ESR, are ·OH and Cl·. The degradation of the ODA and DMP commences with the elimination of N element, leading to the formation of the NO3-. The carbon chain subsequently undergoes the breakdown. The degradation pathways of ODA and DMP were also proposed based on the GC–MS and H-NMR analyses, respectively. Moreover, the Ti/SnO2-Sb/β-PbO2 anode performed excellently in the removal of ODA and DMP in real samples, TOC removal from ODA and DMP in natural samples was 56% and 52%, respectively, within 180 min. This study provides the first exploration of electrocatalytic degradation mechanisms and pathways of ODA and DMP based on the Ti/SnO2-Sb/β-PbO2 anode.

Synthesis of defective Ni-Mn layered double hydroxides nanosheets via alkali-assisted Mo doping for urea electro-oxidation

Urea oxidation reaction (UOR) with favorable thermodynamic potential provides a good application prospect in renewable energy infrastructure. However, the sluggish kinetics caused by 6e- transfer greatly hinders the usage of urea as fuel, efficient catalysts are urgently needed in consequence. In response, alkali-assisted Mo doped into Ni-Mn layered double hydroxides (Mo-NiMnLDH-OH) with laminate structure is synthesized via one-pot hydrothermal method. The alkali-assisted Mo doping contributes the modified morphology and microstructure, the tuned chemical states of Ni and Mn species, simultaneously generates defects and more active sites. The existence of alkali plays a vital role in promoting the Mo doping. Without alkali, the Mo doping should damage the laminate structure, and the chemical states of active sites cannot be efficiently tuned. When used as catalyst for UOR, the current density of 45.3 mA cm−2 and a specific current activity of 1132.8 mA cm−2 mg−1 for Mo-NiMnLDH-OH can be achieved at the potential of 1.623 V (vs. RHE), which is 4-fold higher than that for Ni-Mn layered double hydroxides without doping. Both indirect electrochemical and direct urea oxidation processes occur when using Mo-NiMnLDH-OH as catalyst, and the existence of Mo species will facilitate the occurrence of direct urea oxidation process. This work paves an effective way to synergistically engineer of Mo doping and defects into Ni-based layered double hydroxides for UOR.

Quinone-mediated hydrogen anode for non-aqueous reductive electrosynthesis.

Electrochemical synthesis can provide more sustainable routes to industrial chemicals1-3. Electrosynthetic oxidations may often be performed 'reagent-free', generating hydrogen (H2) derived from the substrate as the sole by-product at the counter electrode. Electrosynthetic reductions, however, require an external source of electrons. Sacrificial metal anodes are commonly used for small-scale applications4, but more sustainable options are needed at larger scale. Anodic water oxidation is an especially appealing option1,5,6, but many reductions require anhydrous, air-free reaction conditions. In such cases, H2 represents an ideal alternative, motivating the growing interest in the electrochemical hydrogen oxidation reaction (HOR) under non-aqueous conditions7-12. Here we report a mediated H2 anode that achieves indirect electrochemical oxidation of H2 by pairing thermal catalytic hydrogenation of an anthraquinone mediator with electrochemical oxidation of the anthrahydroquinone. This quinone-mediated H2 anode is used to support nickel-catalysed cross-electrophile coupling (XEC), a reaction class gaining widespread adoption in the pharmaceutical industry13-15. Initial validation of this method in small-scale batch reactions is followed by adaptation to a recirculating flow reactor that enables hectogram-scale synthesis of a pharmaceutical intermediate. The mediated H2 anode technology disclosed here offers a general strategy to support H2-driven electrosynthetic reductions.

Combination of electrochemically activated persulfate process and electro-coagulation for the treatment of municipal landfill leachate with low biodegradability

To handle complex wastewater with limited biodegradability, hybrid treatment systems are necessary. The current study represents the combined effectiveness of sulfate-radical associated electro-chemical advanced oxidation process (SR-EAOP) and electro-coagulation (EC) for the treatment of stabilized landfill leachate. For SR-EAOP, Pt/Ti was employed as the anode and an iron plate as the cathode; while EC treatment was performed by switching the polarity. Hence, both electrochemical treatment was carried out in single reactor. Initially, the effects of pH, applied voltage, persulfate and Fe2+ dosage, on the performance of SR-EAOP was examined. Sulfate radical was generated in the electrolytic system via cathodic reduction of persulfate (PS) and ferrous (Fe2+) ion activation. Auxiliary processes such as anodic oxidation via Pt/Ti anode and indirect electro-chemical oxidation were also contributed for pollutant degradation. Combined process SR-EAOP followed by EC (SR-EAOP + EC) has better leachate treatment efficacy in comparison with EC + SR-EAOPs. The SR-EAOP + EC based combined treatment mechanism achieved an efficient COD reduction of 88.67% than that of EC + SR – EAOP process (74.51% COD reduction). Characterization studies have been carried out for post-treated dried-sludge using Field Emission scanning electron microscope (FE-SEM) and X-ray powder diffraction (XRD) techniques. The combined process treatment (SR-EAOP + EC) can be applied as pre-treatment for leachate decontamination.

Electrochemical Degradation of Phenol in Aqueous Solutions Using Activated Carbon-ZnO Composite

Olive mill wastewater (OMWW) has high added-value compounds namely phenolic alcohols, phenolic acid, flavonoids, and lignans. OMWW causes a certain amount of toxicity/phytotoxicity because of its phenolic compounds, which demands removal to acceptable levels before being discharged into water bodies. Therefore, the treatment of phenolic compounds of OMWW is very much needed. Actually, electrochemistry method is becoming a substitute method for wastewater treatment using modified carbon as an electrode. The modification of granular activated carbon with zinc oxide (ZnO) nanoparticles was done based on the deep-coating procedure. Electrochemistry degradation of phenol, with a molecular formula C6H5OH, was studied using an activated carbon modified by ZnO as an electrode. The composite activated carbon-ZnO was characterized by Scanning Electron Microscope, X-ray Diffraction, Transformer Fourier Infrared Spectroscopy, and the measure of pHPZC. The techniques used in this work confirmed that ZnO was immobilized onto activated carbon surface. The morphology and the chemical composition of activated carbon have been changed after the ZnO grafting. Electrochemical performances of the electrochemical process were determined under different conditions, like pH, nature, and concentration of the supporting electrolyte. In this work, NaCl is used as a supporting electrolyte; phenol groups were oxidized by indirect electrochemical oxidation. The degradation of 95% of phenol was achieved after 30 min at the optimal operating conditions (pH = 2 in 3% NaCl). It was concluded that electrochemical oxidation using activated carbon-ZnO is a promising process for the destruction of all phenolic compounds present in OMWW. This opens new perspectives in the field of adsorbent materials, to prepare very efficient carbon for environmental phenol remediation.

A Review of the Use of Electrolytic Cells for Energy and Environmental Applications

There is a significant push to reduce carbon dioxide (CO2) emissions and develop low-cost fuels from renewable sources to replace fossil fuels in applications such as energy production. As a result, CO2 conversion has gained widespread attention as it can reduce the accumulation of CO2 in the atmosphere and produce fuels and valuable industrial chemicals, including carbon monoxide, alcohols, and hydrocarbons. At the same time, finding ways to store energy in batteries or energy carriers such as hydrogen (H2) is essential. Water electrolysis is a powerful technology for producing high-purity H2, with negligible emission of greenhouse gases, and compatibility with renewable energy sources. Additionally, the electrolysis of organic compounds, such as lignin, is a promising method for localised H2 production, as it requires lower cell voltages than conventional water electrolysis. Industrial wastewater can be employed in those organic electrolysis systems due to their high organic content, decreasing industrial pollution through wastewater disposal. Electrocoagulation, indirect electrochemical oxidation, anodic oxidation, and electro-Fenton are effective electrochemical methods for treating industrial wastewater. Furthermore, bioenergy technology possesses a remarkable potential for producing H2 and other value-added chemicals (e.g., methane, formic acid, hydrogen peroxide), along with wastewater treatment. This paper comprehensively reviews these approaches by analysing the literature in the period 2012–2022, pointing out the high potential of using electrolytic cells for energy and environmental applications.

Selective indirect electrochemical oxidation of sulfides and thiols using DDQ as an efficient and cost-effective electrocatalyst

The efficient oxidation of sulfides to sulfoxides and the oxidative coupling of thiols to disulfides was performed electrochemically in the presence of DDQ as an electrocatalyst. The electrochemical reactions were conducted in a mixture of water and acetonitrile as solvent under constant potential (0.6 V vs Ag/AgCl) for regeneration of DDQ at room temperature and the products were selectively produced in good to high yields. The electrocatalytic properties of the applied electrocatalyst for the oxidation of substrates and the proposed electrocatalytic mechanism were investigated by the cyclic voltammetry (CV) technique. The proposed electrochemical regeneration of DDQ can be developed for the synthesis of different organic compounds in a single operation under mild conditions

NaClO-ს მიღება NaCl-ის დაბალი კონცენტრაციის წყალხსნარების ელექტროლიზით

The work aims to develop a method for producing NaClO by electrolysis of 20–25 g/L NaCl aqueous solution under conditions other than optimal, ensuring the maintenance of competitive technical and economic indicators of this product, primarily in terms of specific electric energy consumption. NaClO produced by electrolysis of a low concentration NaCl aqueous solution is used in the process of modifying zeolite with MnO2 by indirect electrochemical oxidation, where the mediator is the redox system NaCl – NaClO. Optimal conditions for producing NaClO by electrolysis of aqueous solution of 20–25 g/L NaCl are determined: concentration of available chlorine in the solution produced by electrolysis – 2.0–2.3 g/L; Anodic current density – 200–300 A/m2 ; Electrolyte temperature – 20–250C. Under these conditions, the available chlorine yield is 74.8–82.5%, and the specific electric energy consumption is 5.12–7.61 kWh/kg, which is equal to the value of a similar characteristic obtained under optimal industrial conditions.

New insights into the cleaning mechanisms of conductive membrane by NaClO and electric field in terms of protein and polysaccharide degradation

Membrane fouling can be effectively alleviated by using conductive membrane and external electric field in membrane bioreactor. However, the transformation and removal mechanism of foulants during the electrochemical process needs to be further explored. The present work investigated the degradation mechanisms and cleaning efficiency of organic foulants by electric field and sodium hypochlorite (NaClO) on the composite conductive microfiltration membranes. The results show that the electrochemical oxidation obtained a great degradation efficiency of bovine serum albumin (BSA) at current densities of 40 and 80 A/m2, which was equivalent to that of high-dose NaClO (160 mg/L). However, the degradation efficiency of sodium alginate (SA) was much lower than that of BSA under the same cleaning strategy, due to its strong antioxidant activity. It was also found that NaClO oxidation can decompose BSA macromolecules into small molecules instead of mineralization, while electrochemical oxidation can convert dissolved BSA into foams and flocs by electrocoagulation, thus reducing the BSA concentration in the solution. During the electrochemical cleaning, indirect electrochemical oxidation through the formation of strong oxidants played an important role in the degradation of BSA and SA, and the role of OH· was more significant than that of O2·-. The combination of electric fields and NaClO showed great membrane cleaning efficiency. Moreover, the combination of electrochemical cleaning could not only prevent a large number of precursors from being converted to halogenated by-products, but also shorten the chlorination time and reduce the chlorine concentration, which can alleviate the secondary pollution of cleaning solution.

Electrochemical Mn-Promoted Radical Selenylation of Boronic Acids with Diselenide Reagents

A powerful and environmentally friendly electrochemical manganese-promoted free radical selenylation reaction between boronic acids and diselenide reagents was established. This electrochemical protocol provides a practically applicable way to a series of valuable organoselenium compounds with the use of easy available materials. Mechanistic experiments implied that the seleno-radical formed via direct or indirect electrochemical oxidation of diselenide may be involved as a key species in this transformation.

Comparative Degradation Studies of Carmine Dye by Photocatalysis and Photoelectrochemical Oxidation Processes in the Presence of Graphene/N-Doped ZnO Nanostructures

The goal of this study was to synthesize a UV-light-active ZnO photocatalyst by modifying it with nitrogen and graphene, then applying it to the degradation of carmine dye utilizing two promising technologies: photocatalysis and electrochemical oxidation (E.O.). Different techniques were used to analyze the prepared photocatalysts, such as Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). According to XRD measurements, the produced nanocomposite possesses a hexagonal wurtzite structure, indicating ZnO and markedly crystalline. For photocatalytic applications, the results revealed that the 0.001 g of G/N-doped ZnO catalyst achieved 66.76% degradation of carmine and kinetic degradation rates of 0.007 min−1 within 185 min by photocatalysis under UV light irradiation. In comparison, the same sample reached 100% degradation of carmine and kinetic degradation rates of 0.202 min−1 within 15 min using the electrochemical oxidation method. The improved photocatalytic activity of as-produced nanocomposites can be attributed to intermediate levels in the prohibited bandgap energy and the enhanced oxygen vacancies caused by nitrogen doping. The electrolyte (NaCl) on the degradation of the carmine dye was tested, and the findings indicated that the dye molecules were photodegraded by the 0.001 g of G/N-doped ZnO nanocomposite after a 15 min time interval. The data presented in this work for the carmine breakdown in water give intriguing contrasts between photocatalytic, indirect electrochemical oxidation, and photoelectrochemical oxidation. The action of chlorinated oxidative species, predominantly HClO, which were electrogenerated at the electrode surface due to the chloride ion’s oxidation in solution, induced indirect electrochemical oxidation degradation. This study also revealed that the modifications made to ZnO were beneficial by improving its photocatalytic activities under UV light, as well as a comparison of photocatalysis and electrochemical oxidation processes to determine which technique is best for treating carmine in effluents with high chloride ions.

Decomplexation of Cu-1-hydroxyethylidene-1,1-diphosphonic acid by a three-dimensional electrolysis system with activated biochar as particle electrodes

The feasibility of decomplexation removal of typical contaminants in electroplating wastewater, complexed Cu(II) with 1-hydroxyethylidene-1,1-diphosphonic acid (Cu-HEDP), was first performed by a three-dimensional electrode reactor with activated biochar as particle electrodes. For the case of 50 mg/L Cu-HEDP, Cu(II) removal (90.7%) and PO43− conversion (34.9%) were achieved under the conditions of electric current 40 mA, initial pH 7, acid-treated almond shell biochar (AASB) addition 20 g/L, and reaction time 180 min, with second-order rate constants of 1.10 × 10−3 and 1.94 × 10−5 min−1 respectively. The growing chelating effect between Cu(II) and HEDP and the comprehensive actions of adsorptive accumulation, direct and indirect oxidation given by particle electrodes accounted for the enhanced removal of Cu-HEDP, even though the mineralization of HEDP was mainly dependent on anode oxidation. The performance attenuation of AASB particle electrodes was ascribed to the excessive consumption of oxygen-containing functionalities during the reaction, especially acidic carboxylic groups and quinones on particle electrodes, which decreased from 446.74 to 291.48 µmol/g, and 377.55 to 247.71 µmol/g, respectively. Based on the determination of adsorption behavior and indirect electrochemical oxidation mediated by in situ electrogenerated H2O2 and reactive oxygen species (e.g., •OH), a possible removal mechanism of Cu-HEDP by three-dimensional electrolysis was further proposed.

Indirect Electrooxidation of Methane to Methyl Bisulfate on a Boron‐Doped Diamond Electrode

AbstractAlthough highly desired and studied for decades, direct methane functionalization to liquid products remains a challenge. We report an electrochemical system using a boron‐doped diamond (BDD) anode in concentrated sulfuric acid that is able to convert methane to methyl bisulfate and methanesulfonic acid without the use of a catalyst by indirect electrochemical oxidation. Due to its high material stability, BDD can be operated at high current densities. High temperature (140 °C) and pressure (70 bar) support the formation of methyl bisulfate to concentrations as high as 160 mM in 3 h and methanesulfonic acid to concentrations of up to 750 mM in 8 h. We present a novel way of catalyst‐free electrochemical methane oxidation and show general trends and limitations of this reaction.

Shifts of surface-bound •OH to homogeneous •OH in BDD electrochemical system via UV irradiation for enhanced degradation of hydrophilic aromatic compounds

Indirect electrochemical oxidation by hydroxyl radicals is the predominant degradation mechanism in electrolysis with a boron-doped diamond (BDD) anode. However, this electrochemical method exhibits low reactivity in removal of hydrophilic aromatic pollutants owing to mass transfer limitation. In this study, the combination of ultraviolet light and BDD electrolysis could increase the degradation rate of hydrophilic aromatic pollutants by approximately 8–10 times relative to electrolysis alone. According to the results of the scavenging experiments and identification of benzoic acid oxidation products, surface-bound hydroxyl radical (•OH(surface)) was the primary reactive species degrading aromatic pollutants in the BDD electrolysis process, whereas freely-diffusing homogeneous hydroxyl radical (•OH(free)) was the major reactive species in the UV-assisted BDD electrolysis process. Cyclic voltammetry revealed that UV light decomposed H2O2 formed on the BDD anode surface, thus retarding O2 evolution and facilitating •OH(free) generation. This work also explored the potential application of UV-assisted BDD electrolysis in removing COD from bio-pretreated landfill leachate containing high concentrations of hydrophilic aromatic pollutants. This study shed light on the importance of the existing state of •OH on removal of pollutants during BDD electrolysis, and provided a facile and efficient UV-assisted strategy for promoting degradation of hydrophilic aromatic pollutants.

Electrochemically driven synthesis of phosphorothioates from trialkyl phosphites and aryl thiols

A facile and elegant protocol for synthesis of phosphorothioates from trialkyl phosphites and aryl thiols via indirect electrochemical oxidation mediated by KI has been successfully developed. KI as a redox mediator, enabled the reaction of trialkyl phosphites and aryl thiols effectively at low potential. Cyclic voltammetry and in situ FTIR were applied to investigate the electrocatalytic activity of KI for the cross-coupling of trialkyl phosphites with aryl thiols. A variety of phosphorothioates were obtained in good to excellent yields under the optimal conditions. This strategy provided an expedient access to construct P–S bond with good functional group compatibility and a broad substrate scope.

Indirect electrochemical oxidation of blood in the treatment of patients with surgical diseases of the abdominal organs on the background of diabetes mellitus

Indirect electrochemical oxidation of blood in the treatment of patients with surgical diseases of the abdominal organs on the background of diabetes mellitus

Optimal pH for indirect electrochemical oxidation of isopropyl alcohol with Ru-Ti anode and NaCl electrolyte

When the levels of human waste exceed an ecosystem’s native purification capacity, pollution causes large, long-term damage. Therefore, to prevent wastewater spillage from damaging the environment and raising external cost to the society, industries are required to degrade pollutants in wastewater to an acceptable level according to local regulations before emission. This investigation uses an electrochemical system to degrade isopropanol—a common pollutant found in wastewater—and find the optimal pH level at which the highest degradation of isopropanol takes place. We hypothesized that by decreasing the pH value due to an increase in the amount of HClO (a strong oxidant) in the solution, the degradation of isopropanol (IPA) into acetone should increase. The result supports the hypothesis and shows the electrochemical system under acidic conditions has a higher efficiency than alkaline conditions. Under pH 5–6, NaCl concentration of 2%, initial IPA concentration of 500 ppm total organic carbon, and a current of 1 ampere, the electrochemical system degrades 98.6% of IPA into acetone and other intermediate compounds in under 180 minutes. Furthermore, with such a high transfer rate, the system demonstrates its potential to degrade isopropanol to generate acetone, which is a commonly-used agent found in a variety of products ranging from lab cleaning products to nail varnish.

Dip coating deposition of manganese oxide nanoparticles on graphite by sol gel technique for the indirect electrochemical oxidation of methyl orange dye: Parameter’s optimization using box-behnken design

Textile industries produce large quantity of toxic effluents, very loaded and hardly biodegradable. In this work, MnO2 was synthetized by sol-gel method and coated on graphite rods which were obtained from used batteries and tested as electrodes for the degradation of anionic dye. Physical and chemicals characteristics of the material were determined by Fourier transform infrared and X-ray diffraction spectroscopies. The electrochemical properties of the elaborated material were carried out using linear sweep voltammetry and electrochemical impedance spectroscopy. During this study, experiments were carried out an electrochemical cell where C/MnO2 electrode was employed as cathode and anode. Box-Behnken design was used to design the experiments and find the optimal conditions for the degradation of Methyl Orange (MO) synthetic solution. The results also show that indirect anodic oxidation of MO using sodium chloride as supporting electrolyte was effective for MO degradation. However, the optimum conditions were 25 ​mg/L of initial dye concentration, 5 ​g/L of NaCl concentration, 5.6 ​h of electrolysis time, and 108 ​mA/cm2 of current density, where 77.0% degradation would be achieved from proposed model. According to these results, indirect anodic oxidation using manganese dioxide electrode in an electrochemical cell is efficient in the degradation of MO synthetic solutions.