Electrochemical oxidation of phenol on boron-doped diamond electrode

The process of phenol oxidation on a boron-doped diamond electrode (BDD) is studied in acidic electrolytes under different conditions of generation of active oxygen forms (AOFs). The scheme of phenol oxidation known from the literature for other electrode materials is confirmed. Phenol is oxidized through a number of intermediates (benzoquinone, carboxylic acids) to carbon dioxide and water. Comparative analysis of phenol oxidation rate constants is performed as dependent on the electrolysis conditions: direct anodic oxidation, with oxygen bubbling, and addition of H₂O₂. A scheme is confirmed according to which active radicals (OH^·, HO₂^·, HO₂⁻) are formed on a BDD anode that can oxidize the substrate which leads to formation of organic radicals interacting with each other and forming condensation products. Processes with participation of free radicals (chain-radical mechanism) play an important role in electrochemical oxidation on BDD. Intermediates and polymeric substances (polyphenols, quinone structures, and resins) are formed. An excess of the oxidant (H₂O₂) promotes a more effective oxidation of organic radicals and accordingly inhibition of the condensation process.     

Indirect electrosynthesis of peracetic acid using hydrogen peroxide generated in situ in a gas diffusion electrode

Indirect electrochemical oxidation of acetic to peracetic acid in aqueous solutions using hydrogen peroxide generated in situ from O₂ in a gas diffusion electrode was studied. The use of sulfuric acid and ammonium molybdate as catalysts accelerated the formation of peracetic acid during the electrolysis, and the use of both catalysts allowed us to prepare 0.02 M solutions. The limiting stage of the electrosynthesis of peracetic acid was the chemical interaction of the substrate with the generated H₂O₂. The desired product mainly formed during the storage of the reaction mixture after the electrosynthesis. In electrolytes with more than 3.5 M acetic acid, the electrochemical activity of the gas-diffusion cathode decreased.     

Crosslinking of poly(vinylpyrrolidone) activated by electrogenerated hydroxyl radicals: A first step towards a simple and cheap synthetic route of nanogel vectors

A facile electrosynthesis route for the preparation of polymer nanogels based on the in situ production of hydroxyl radicals is reported for the first time. Electro-Fenton process with continuous H₂O₂ electrogeneration and Fe^2 + regeneration performs better than electro-oxidation with a boron-doped diamond or dimensionally stable anode for promoting crosslinking of poly(vinylpyrrolidone).     

Opportunities and challenges of thin-film boron-doped diamond electrochemistry for valuable resources recovery from waste: Organic,inorganic, and volatile product electrosynthesis

Thin-film boron-doped diamond (BDD) electrochemistry has made a tremendous progress in electrochemical synthesis/recovery of high-added value products from aqueous and gaseous waste streams. The distinguished electrochemical characteristic of this electrode has made this material emerging and successfully used in electrosynthetic transformations, besides its destructive and powerful performance in disinfection and detoxification of wastewaters. Organic electrosynthesis is achieved by the oxyl radical oxidation formed at BDD, peroxo compounds electrosynthesis is attained by oxidation of corresponding anions at the BDD surface, whereas electrochemical conversion of SO₂, CO₂, NO₃^?, and NH₃ to value-added products occurs by BDD cathodic reduction process. There are still some challenges needed to address for seamless scale-up and translation into application of this future technology.     

Electrochemical performance of Li4Ti5O12/carbon nanofibers composite prepared by an in situ route for Li-ion batteries

A Li₄Ti₅O₁₂/carbon nanofibers (LTO/CNFs) composite has been synthesized by solid-state reaction with the in situ growth of CNFs using the chemical vapor deposition method in N₂/C₂H₂. The nanocomposite is characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, Raman spectrum, and nitrogen adsorption/desorption isotherms, and is investigated as an anode material for lithium-ion (Li-ion) batteries. The underlying mechanism for the improvement is analyzed by cyclic voltammetry and electrochemical impedance spectroscopy. The in situ synthesized composite shows better electrochemical performance than the bare LTO. The in situ formation of CNFs not only supply an efficient electronic conductive network but also reduce the particle size of LTO and increase in specific surface area, leading to increased electrical conductivity and rapider Li-ion diffusion in electrode/electrolyte interface and bulk electrode.     

Aqueous electrosynthesis of carbonyl compounds and the corresponding homoallylic alcohols in a divided cell

An aqueous paired electrosynthesis is studied in a divided cell. On graphite anode Br⁻ was oxidized to Br₂ and this generated Br₂ oxidized alcohols to the corresponding carbonyl compounds while Sn²⁺ was reduced to Sn⁰ on graphite cathode. Then the produced metallic tin mediated allylation of the carbonyl compounds with allyl bromide to generate the corresponding homoallylic alcohols. In the reaction the mediators (Sn and Br₂) were generated in situ and could be reused via the electrolysis. Both working electrode and the counter electrode were utilized to generate useful products without the sacrifice of the electrode materials.     

Boosting Hydrogen Peroxide Electrosynthesis via Modulating the Interfacial Hydrogen-Bond Environment

Designing highly efficient and stable electrode-electrolyte interface for hydrogen peroxide (H₂O₂) electrosynthesis remains challenging. Inhibiting the competitive side reaction, 4 e⁻ oxygen reduction to H₂O, is essential for highly selective H₂O₂ electrosynthesis. Instead of hindering excessive hydrogenation of H₂O₂ via catalyst modification, we discover that adding a hydrogen-bond acceptor, dimethyl sulfoxide (DMSO), to the KOH electrolyte enables simultaneous improvement of the selectivity and activity of H₂O₂ electrosynthesis. Spectral characterization and molecular simulation confirm that the formation of hydrogen bonds between DMSO and water molecules at the electrode-electrolyte interface can reduce the activity of water dissociation into active H* species. The suitable H* supply environment hinders excessive hydrogenation of the oxygen reduction reaction (ORR), thus improving the selectivity of 2 e⁻ ORR and achieving over 90 % selectivity of H₂O₂. This work highlights the importance of regulating the interfacial hydrogen-bond environment by organic molecules as a means of boosting electrochemical performance in aqueous electrosynthesis and beyond.     

Electrocatalytic carboxylation of aliphatic halides at silver cathode in acetonitrile

A simple and efficient electrocarboxylation reaction of aliphatic halides has been developed using silver as cathode, magnesium as anode and CH₃CN saturated CO₂ as solvent in an undivided cell. The influence of some key factors (such as the nature of electrode materials, supporting electrolytes and temperature) on this reaction was investigated. Under the optimized condition, the corresponding carboxylic acids were obtained in moderate to good yields (22-89%). The electrochemical behaviour was studied at different electrodes (Ag, Cu, Ni and Ti) by cyclic voltammetry, which showed significant electrocatalytic effect of the silver electrode towards the reductive carboxylation of aliphatic halides.     

Use of MEA technology in the synthesis of pharmaceutical compounds: The electrosynthesis of N-acetyl-l-cysteine

The electrosynthesis of N-acetyl-l-cysteine (NAC) from the electroreduction of N,N-diacetyl-l-cystine (NNDAC) using a Polymer Electrolyte Membrane Electrochemical Reactor (PEMER) has been carried out. The Membrane Electrode Assembly (MEA) was formed by a cathode with a catalyst layer made of Pb/C 20 wt% supported on Toray Paper and a catalyst loading of 0.5 mg Pb cm^?2. The anode was a 2 mg Pt cm^?2 gas diffusion anode fed with H₂. The main advantages of this process are: (1) the electrochemical reactor allows to carry out the electrosynthesis without supporting electrolyte, improving in this way the NAC purification and (2) a pronounced decrease of the electrosynthesis energy consumption due to both, the small internal resistance of the PEMER (electrode gap very small and electrolyte very conductive) and the choice of the H₂ oxidation as anodic reaction in stead of the oxygen evolution reaction from water oxidation. The large number of pharmaceutical applications of NAC, as well as the high versatility of the PEMER for electrosynthesis processes, makes interesting the use of MEAs for electroorganic synthesis.     

Future perspectives for the advancement of electrochemical hydrogen peroxide production

Hydrogen peroxide (H₂O₂)is an important chemical with multiple uses across domestic and industrial settings. With a global need for wider adoption of green synthetic methods, there has been a growing interest in the electrochemical synthesis of H₂O₂ from oxygen reduction or water oxidation. State-of-the-art catalyst and reactor developments are beginning to advance to a stage where electrochemical synthesis is discussed as a viable alternative to current industrial methods. In this review, we highlight some of the most promising candidates for H₂O₂ electrosynthesis technologies and what further advancements are needed before the electrochemical route could challenge the ubiquitous anthraquinone process.     

Understanding the High-Performance Anode Material of CoC2O4⋅2 H2O Microrods Wrapped by Reduced Graphene Oxide for Lithium-Ion and Sodium-Ion Batteries

Metal oxalate has become a most promising candidate as an anode material for lithium-ion and sodium-ion batteries. However, capacity decrease owing to the volume expansion of the active material during cycling is a problem. Herein, a rod-like CoC₂O₄⋅2 H₂O/rGO hybrid is fabricated through a novel multistep solvo/hydrothermal strategy. The structural characteristics of the CoC₂O₄⋅2 H₂O microrod wrapped using rGO sheets not only inhibit the volume variation of the hybrid electrode during cycling, but also accelerate the transfer of electrons and ions in the 3 D graphene network, thereby improving the electrochemical properties of CoC₂O₄⋅2 H₂O. The CoC₂O₄⋅2 H₂O/rGO electrode delivers a specific capacity of 1011.5 mA h g⁻¹ at 0.2 A g⁻¹ after 200 cycles for lithium storage, and a high capacity of 221.1 mA h g⁻¹ at 0.2 A g⁻¹ after 100 cycles for sodium storage. Moreover, the full cell CoC₂O₄⋅2 H₂O/rGO//LiCoO₂ consisting of the CoC₂O₄⋅2 H₂O/rGO anode and LiCoO₂ cathode maintains 138.1 mA h g⁻¹ after 200 cycles at 0.2 A g⁻¹ and has superior long-cycle stability. In addition, in situ Raman spectroscopy and in situ and ex situ X-ray diffraction techniques provide a unique opportunity to understand fully the reaction mechanism of CoC₂O₄⋅2 H₂O/rGO. This work also gives a new perspective and solid research basis for the application of metal oxalate materials in high-performance lithium-ion and sodium-ion batteries.     

Degradation of florfenicol in a flow-through electro-Fenton system enhanced by wood-derived block carbon (WBC) cathode

The flow-through electro-Fenton (EF-T) reactor with WBC cathode was designed to remove florfenicol (FF). The activated WBC cathode was prepared by facile carbonization and activation methods, and featured high specific surface area, natural multi-channel structure, abundant oxygen-containing groups, good hydrophilicity, and excellent O₂ reducing capacity. WBC cathode was located above Ti/Ru-IrO₂ mesh anode. O₂ evolved at the anode was carried to the inner wall of channel of WBC by the force of buoyancy and water flow, which increases oxygen source of H₂O₂ generation at the cathode. The flow-through system by using WBC electrode promote the mass transfer of O₂ and FF. The production amount of H₂O₂ at activated WBC was 32.2 mg/L, which was almost twice as much as that at non-activated WBC (15.0 mg/L). FF removal ratio in EF-T system was 98%, which was much higher than that of traditional flow-by electro-Fenton (EF-B, 33%) or single electrooxidation system (EO, 16%). EF-T system has the lowest energy consumption (4.367 kWh/kg) among the three electrochemical systems. The cathodic adsorption, anodic electrooxidation, and EF reaction are responsible for the degradation of FF. After five consecutive cycle experiments, FF removal ratio was still 98%, indicating WBC has the good stability.     

High‐Yield Electrosynthesis of Hydrogen Peroxide from Oxygen Reduction by Hierarchically Porous Carbon

H₂O₂ production by electroreduction of O₂ is an attractive alternative to the current anthraquinone process, which is highly desirable for chemical industries and environmental remediation. However, it remains a great challenge to develop cost‐effective electrocatalysts for H₂O₂ synthesis. Here, hierarchically porous carbon (HPC) was proposed for the electrosynthesis of H₂O₂ from O₂ reduction. It exhibited high activity for O₂ reduction and good H₂O₂ selectivity (95.0–70.2 %, most of them >90.0 % at pH 1–4 and >80.0 % at pH 7). High‐yield H₂O₂ generation has been achieved on HPC with H₂O₂ concentrations of 222.6–62.0 mmol L^?1 (2.5 h) and corresponding H₂O₂ production rates of 395.7–110.2 mmol h^?1 g^?1 at pH 1–7 and ?0.5 V. Moreover, HPC was energy‐efficient for H₂O₂ production with current efficiency of 81.8–70.8 %. The exceptional performance of HPC for electrosynthesis of H₂O₂ could be attributed to its high content of sp³‐C and defects, large surface area and fast mass transfer.     

Electrosynthesis of hydrogen peroxide in solutions of salts that form molecular addition products (peroxo solvates) with it

The possibility of electrosynthesis of hydrogen peroxide in the electroreduction of oxygen in a gas-diffusion electrode in solutions of salts that form the molecular addition products (peroxo solvates) with H₂O₂ was studied. In KF and potassium and sodium phosphate solutions, H₂O₂ was obtained at concentrations of 2.3–3.6 M at current densities of 0.1–0.15 A/cm² and current efficiencies of 75–92%. The resulting solutions were concentrated to 11–27 M to give solid peroxo solvates with high hydrogen peroxide contents (22–50%). These results demonstrate that the application of gas-diffusion electrodes for electrosynthesis of inorganic products can be significantly expanded.     

A Carbon–Air Battery for High Power Generation

We report a carbon–air battery for power generation based on a solid‐oxide fuel cell (SOFC) integrated with a ceramic CO₂‐permeable membrane. An anode‐supported tubular SOFC functioned as a carbon fuel container as well as an electrochemical device for power generation, while a high‐temperature CO₂‐permeable membrane composed of a CO₃^2? mixture and an O^2? conducting phase (Sm_0.2Ce_0.8O_1.9) was integrated for in situ separation of CO₂ (electrochemical product) from the anode chamber, delivering high fuel‐utilization efficiency. After modifying the carbon fuel with a reverse Boudouard reaction catalyst to promote the in situ gasification of carbon to CO, an attractive peak power density of 279.3 mW cm^?2 was achieved for the battery at 850 °C, and a small stack composed of two batteries can be operated continuously for 200 min. This work provides a novel type of electrochemical energy device that has a wide range of application potentials.     

Electrochemical Properties and Sodium‐Storage Mechanism of Ag2Mo2O7 as the Anode Material for Sodium‐Ion Batteries

Silver molybdate, Ag₂Mo₂O₇, has been prepared by a conventional solid‐state reaction. Its electrochemical properties as an anode material for sodium‐ion batteries (SIBs) have been comprehensively examined by means of galvanostatic charge–discharge cycling, cyclic voltammetry, and rate performance measurements. At operating voltages between 3.0 and 0.01 V, the electrode delivered a reversible capacity of nearly 190 mA h g^?1 at a current density of 20 mA g^?1 after 70 cycles. Ag₂Mo₂O₇ also demonstrated a good rate capability and long‐term cycle stability, the capacity reaching almost 100 mA h g^?1 at a current density of 500 mA g^?1, with a capacity retention of 55 % over 1000 cycles. Moreover, the sodium storage process of Ag₂Mo₂O₇ has been investigated by means of ex situ XRD, Raman spectroscopy, and HRTEM. Interestingly, the anode decomposes into Ag metal and Na₂MoO₄ during the initial discharge process, and then Na⁺ ions are considered to be inserted into/extracted from the Na₂MoO₄ lattice in the subsequent cycles governed by an intercalation/deintercalation mechanism. Ex situ HRTEM images revealed that Ag metal not only remains unchanged during the sodiation/desodiation processes, but is well dispersed throughout the amorphous matrix, thereby greatly improving the electronic conductivity of the working electrode. The “in situ” decomposition behavior of Ag₂Mo₂O₇ is distinct from that of chemically synthesized, metal‐nanoparticle‐coated electrode materials, and provides strong supplementary insight into the mechanism of such new anode materials for SIBs and may set a precedent for the design of further materials.     

Oxygen isotope exchange between the gas-phase and the electrochemical cell O<Subscript>2</Subscript>, Pt | YSZ | Pt,O<Subscript>2</Subscript> under conditions of applied potential difference

The kinetics of oxygen isotope exchange between gas-phase oxygen and the electrochemical cell O₂, Pt | ZrO₂ + 10 mol % Y₂O₃ (YSZ) | Pt, O₂ with applied potential difference (ΔU = ±1.2 V) is studied in the temperature range of 600–800°С and the oxygen pressure interval of 3–13 kPa. An original design of a vacuum electrochemical cell with the separated gas space is put forward for studying how the potential difference on the electrochemical cell influences the kinetics of interaction of gas-phase oxygen with the gas electrode O₂, Pt | YSZ in the electrochemical cell. It is shown that the oxygen interphase exchange rate is the higher the more negative the charge on the electrode studied; moreover, the mechanism of gas-phase oxygen exchange with the gas electrode O₂, Pt | YSZ in the electrochemical cell depends fundamentally on the electrode charge sign. The possible reasons for the revealed differences are discussed; the corresponding models are proposed.     

High-efficiency ozone generation via electrochemical oxidation of water using Ti anode coated with Ni–Sb–SnO<Subscript>2</Subscript>

Ozone (O₃) has been generated on Ni–Sb–SnO₂/Ti electrode as anode immersed in acidic media at 25 °C by electrochemical process. The anode was electrochemically characterized by cyclic voltammetry and morphologically characterized by scanning electron microscopy (SEM) and X-ray diffraction. The concentration of dissolved ozone was determined by a UV/Vis spectrophotometer. The type of electrode with different times coating on the titanium mesh and different acid type and various concentrations (C _acid) were used, and the stability of the electrode was investigated under the experimental conditions by SEM images. Results shows that higher efficiency (53.7%) for O₃ generation by electrochemical oxidation of water were obtained in HClO₄ (1 M) and an applied potential of 2.4 V vs. Ag/AgCl in 150 ml volume undivided electrochemical cell.     

Mediatorless Hydrogen Peroxide Biosensor Based on Horseradish Peroxidase Immobilized on 4‐Carboxyphenyl Film Electrografted on Gold Electrode

A novel method to fabricate a third‐generation hydrogen peroxide biosensor was reported. The electrode was first derivatized by electrochemical reduction of in situ generated 4‐carboxyphenyl diazonium salt (4‐CPDS) in acidic aqueous solution yielded stable 4‐carboxyphenyl (4‐CP) layer. The horseradish peroxidase (HRP) enzyme was then covalently immobilized by amidation between NH₂ terminus of enzyme and COOH terminus of 4‐CP film making use of the carbodiimide chemistry. Electrodeposition conditions used to control electrode functionalization density and film electron transfer kinetics were assessed by chronoamperometry and electrochemical impedance spectroscopy. The immobilized HRP displayed excellent electrocatalytic activity towards the reduction of hydrogen peroxide (H₂O₂) without any mediators. The effect of various operational parameters was explored for optimum analytical performance. The reported biosensor exhibited fast amperometric response (within 5 s) to H₂O₂. The detection limit of the biosensor was 5 μM, and linear range was from 20 μM to 20 mM. Furthermore, the biosensor exhibited high sensitivity, good reproducibility, and long‐term stability.     

Elektrochemische Methode zur quantitativen und kontinuierlichen Bestimmung von Ozon in Gasgemischen

The method is based on the measurement of the diffusion controlled limiting current obtained with the cathodic reduction of ozone according to O₃ + 2H⁺ + 2e^? → H₂O + O₂ in sulphuric acid. The electrolyte is vigorously mixed with the gas containing ozone and circulated through the electrolytic cell by the ascending gas flow operating as a gas-lift pump. The solution saturated with ozone moves along a cylindric electrode consisting of a smooth platinum foil in laminar flow. A constant potential is maintained at the electrode by means of a potentiostat in such a way, that the electrochemical reaction is proceeding under limiting current conditions. A lead anode of high capacitiy is used as a counter- and reference electrode. The current recorded continuously is directly proportional to the concentration of ozone in gas.