Electrochemical Oxidation Step Research Articles

Driving Force of the Initial Step in Electrochemical Pt(111) Oxidation

The first step of electrochemical surface oxidation is extraction of a metal atom from its lattice site to a location in a growing oxide. Here we show by fast simultaneous electrochemical and in situ high-energy surface X-ray diffraction measurements that the initial extraction of Pt atoms from Pt(111) is a fast, potential-driven process, whereas charge transfer for the related formation of adsorbed oxygen-containing species occurs on a much slower time scale and is evidently uncoupled from the extraction process. It is concluded that potential plays a key independent role in electrochemical surface oxidation.

Electrochemical Oxidation for Treatment of PFAS in Contaminated Water and Fractionated Foam-A Pilot-Scale Study.

Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic contaminants that are present globally in water and are exceptionally difficult to remove during conventional water treatment processes. Here, we demonstrate a practical treatment train that combines foam fractionation to concentrate PFAS from groundwater and landfill leachate, followed by an electrochemical oxidation (EO) step to degrade the PFAS. The study combined an up-scaled experimental approach with thorough characterization strategies, including target analysis, PFAS sum parameters, and toxicity testing. Additionally, the EO kinetics were successfully reproduced by a newly developed coupled numerical model. The mean total PFAS degradation over the designed treatment train reached 50%, with long- and short-chain PFAS degrading up to 86 and 31%, respectively. The treatment resulted in a decrease in the toxic potency of the water, as assessed by transthyretin binding and bacterial bioluminescence bioassays. Moreover, the extractable organofluorine concentration of the water decreased by up to 44%. Together, these findings provide an improved understanding of a promising and practical approach for on-site remediation of PFAS-contaminated water.

Electrochemical oxidation assisted with the 1,3-dipolar cycloaddition for the synthesis of the new substituted triazole

The electrochemical reaction of 4-ethynylaniline (4-EA) in the presence of sodium azide in buffered solutions with the various pHs (buffer solution /acetonitrile (80/20 v/v)) was investigated for the first time. Our electrochemical data assert that the product of oxidation of 4-ethynylaniline enters the chemical reaction with azide ion. In continues, after the 1,3 dipolar cycloaddition, electrochemical oxidation, dimerization, and third step electrochemical oxidation a triazole ring was produced as the desired product in a simple undivided cell and using carbon anode. The critical aim of this study was applying a non-catalytic procedure for the synthesis of triazole ring at room temperature that was successfully achieved.

Facile Detection of Vitamin B12 with Copper Oxide Nanocrystal Graphenic Composite Electrode

Vitamin B12 (VB12) is applied as the cofactors in various important enzymatic reactions and is involved in gene expression regulation mediated by B12-riboswitch and the VB12-dependent photoreceptor. Rapid detection VB12 concertation in a given environment may provide insights in the evaluation of micronutrient levels and the physiological and ecological performances of organisms under the relevant condition. This study demonstrating an amperometric approach to quantify the VB12 in biological samples without complicated sample pretreatment. The electrochemical oxidation step was conducted with a plain graphenic electrode to convert all nitrogen groups within the VB12 molecules to NO3− at 1.3 V vs. Ag/AgCl for 15 min. VB12 was quantified stoichiometrically according to the oxidized nitrate anions, which were reduced with copper oxide nanocrystal decorated graphenic electrode. Cathodic polarization was conducted with a graphite rod electrode before nitrate reduction to eliminate the potential interferences. Under optimized experimental conditions, the presented approach gave a wide detection linear range of 0.15–7378 nmol L−1 and the detection limit was 0.59 nmol L−1. The results for biological samples were comparable to those of the HPLC method. These results indicated that successively combined anodic and cathodic polarization enhanced the detection sensitivity and efficiency of the electrode towards VB12. The proposed electrode shows potential in terms of efficiency, reliability and accuracy for rapid determination of VB12 in biological samples.

Electrochemical Oxidation Assisted with the 1,3-Dipolar Cycloaddition for the Synthesis of the New Substituted Triazole

The electrochemical reaction of 4-ethynylaniline ( 4-EA ) in the present of sodium azide in buffered solutions with the various pHs (buffer solution /acetonitrile (80/20 v/v)) was investigated for the first time. Our electrochemical data assert that the product of oxidation of 4-ethynylaniline enter in the chemical reaction with azide ion. In continues, after the 1,3 dipolar cycloaddition, electrochemical oxidation, dimerization and third step electrochemical oxidation a triazole ring was produced as a desired product in a simple undivided cell and using carbon anode. The critical aim in this study was applying a non-catalytic procedure for the synthesis of triazole ring in the room temperature that successfully achieved.

Rapid Electrochemical Methane Functionalization Involves Pd-Pd Bonded Intermediates.

High-valent Pd complexes are potent agents for the oxidative functionalization of inert C-H bonds, and it was previously shown that rapid electrocatalytic methane monofunctionalization could be achieved by electro-oxidation of PdII to a critical dinuclear PdIII intermediate in concentrated or fuming sulfuric acid. However, the structure of this highly reactive, unisolable intermediate, as well as the structural basis for its mechanism of electrochemical formation, remained elusive. Herein, we use X-ray absorption and Raman spectroscopies to assemble a structural model of the potent methane-activating intermediate as a PdIII dimer with a Pd-Pd bond and a 5-fold O atom coordination by HxSO4(x-2) ligands at each Pd center. We further use EPR spectroscopy to identify a mixed-valent M-M bonded Pd2II,III species as a key intermediate during the PdII-to-PdIII2 oxidation. Combining EPR and electrochemical data, we quantify the free energy of Pd dimerization as <-4.5 kcal/mol for Pd2II,III and <-9.1 kcal/mol for PdIII2. The structural and thermochemical data suggest that the aggregate effect of metal-metal and axial metal-ligand bond formation drives the critical Pd dimerization reaction in between electrochemical oxidation steps. This work establishes a structural basis for the facile electrochemical oxidation of PdII to a M-M bonded PdIII dimer and provides a foundation for understanding its rapid methane functionalization reactivity.

Performance of ultrafiltration as a pre-concentration stage for the treatment of oxyfluorfen by electrochemical BDD oxidation

The present work deals with the use of ultrafiltration as a pre-concentration stage in the electrochemical degradation of a non-polar organochlorine compound (oxyfluorfen) with boron-doped diamond (BDD) anodes. The first stage of the work consisted in evaluating the performance of a pilot scale ultrafiltration unit to concentrate a solution of a commercial formulation of oxyfluorfen (Barre®) at total recirculation mode. The ultrafiltration membrane exhibited a total rejection of oxyfluorfen, around 70% rejection of TOC and a permeate flux of 285.1 L h−1 m−2 at 4 bar and 25 °C. The rejection of oxyfluorfen is higher than expected due to the presence of surfactant compounds in the commercial formulation selected, which promotes a mechanism of micellar enhanced ultrafiltration. Next, a discontinuous ultrafiltration test was performed, maintaining this high rejection of oxyfluorfen and observing a limited contribution of fouling mechanisms, according to the adjustment of the data to fouling models. Regarding the electrochemical oxidation of the concentrate with BDD anodes, it was observed an increase in the specific power consumption from 590 kWh kg−1 for the raw solution to 882 kWh kg−1 for the concentrate. This unexpected result can be explained due to the limited rejection of the soluble fraction in the ultrafiltration stage, what produced a lower concurrence of oxidants in the electrochemical oxidation step. According to these results, it can be stated that it is worth using ultrafiltration as a concentration stage for commercial formulations of non-polar organochlorines with both high rejection and flux, although it should be combined with degradation technologies different from electrochemical oxidation.

Electrochemical oxidation of flavonoids: PM6 and DFT for elucidating electronic changes and modelling oxidation potential

A set of 14 flavonoids and their cation and radical forms involved in the first electrochemical oxidation step, Ep1, were optimized using semi-empirical PM6 and DFT in vacuo methods. For the differences in Net atomic charges (ΔNACCat.-Neut.), by which we previously used to determine active OH oxygens by PM6 in water (which were in agreement with the literature), both PM6 and DFT gave doubtful results in some cases. In accordance with our previous research, the sum of Atomic orbital spin populations on carbon atoms in the skeleton of radicals (ΣsCAOSPRad.) calculated using both PM6 and DFT, is lower for flavonoids more prone to oxidation. Although the models for the estimation of Ep1 based on ΣsCAOSPRad. calculated by PM6 method gave somewhat better statistics than those calculated using DFT, the statistics obtained by both methods in vacuo were worse than those obtained by PM6 in water calculations.

Electrochemical degradation of naproxen from water by anodic oxidation with multiwall carbon nanotubes glassy carbon electrode.

Naproxen (NPX) degradation was investigated by anodic oxidation both at constant potential and by cyclic voltammetry, using this last technique for optimizing reaction conditions and catalyst properties. Three multiwall carbon nanotubes (MWCNTs)-promoted electrodes were used (MWCNT, MWCNT-COOH and MWCNT-NH2) and a two steps oxidation process was observed in all the cases. At the optimized conditions (volume of MWCNT = 15 μL), the influence of the scan rate indicates the diffusion-adsorption control of the process. Likewise, the kinetic study of NPX degradation at fix potential, considering two different stirring speeds (250 and 500 rpm), indicates that degradation rate increases with the stirring speed. After 20 h, NPX is degraded even an 82.5%, whereas the mineralization reaches almost 70%, as it was obtained from total organic carbon analysis. The pH effect was also analysed, in the range 5-11, observing a positive effect at low pH. Concerning the surface chemistry of the electrode, MWCNT-NH2, with the highest isoelectric point (4.70), is the most promising material due to the improved interactions with the reactant. From these observations, a pathway is proposed, which includes two steps of electrochemical oxidation followed by subsequent oxidation steps, until mineralization of the NPX, attributed mainly to active chlorine species and ·OH.

Self-Supported Hydrous Iridium–Nickel Oxide Two-Dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts

Oxygen evolution reaction (OER) electrocatalysts with high activity, high stability, and low costs are needed for proton-exchange membrane (PEM) electrolyzers. Based on the high cost and limited supply of iridium, approaches that result in iridium-based OER catalysts with increased catalytic activity are of significant interest. We report a carbon-free, self-supported hydrous iridium–nickel oxide two-dimensional nanoframe structure synthesized by thermal treatment of iridium-decorated nickel oxide nanosheets under reducing conditions and subsequent chemical leaching in acid. The catalyst nanoarchitecture contains an interconnected network of metallic iridium–nickel alloy domains with hydrous iridium oxide and nickel oxide located in the surface region. The electrochemical oxidation step maintains the three-dimensional nanoarchitecture and results in a thin (∼5 A) oxide/hydroxide surface layer. The temperature used for thermal reduction was found to strongly affect the catalyst surface structure and OER ac...

Changes in electronic structures of flavonoids upon electrochemical oxidation and a theoretical model for the estimation of the first oxidation potential

This paper studies the electronic structures of the 14 flavonoids and their cation and radical forms involved in the first electrochemical oxidation step, associated with the oxidation peak appearing at potential Ep1. The sum of differences in Net atomic charges on atoms in skeleton of cations and neutral flavonoids (Σs(C)ΔNACCat.-Neut.) and the sum of Atomic orbital electron and spin populations on atoms in skeleton of radicals (Σs(C)AOEP and Σs(C)AOSP) revealed that electron distribution between skeleton atoms and active OH oxygen is more evenly distributed in cations and radicals of flavonoids that are more prone to oxidation. Those less susceptible to oxidation are more polarized, i.e. the skeleton becomes more positively charged. Also, Σs(C)AOSP proved to be an excellent descriptor for modelling the first oxidation potential, especially in combination with Σs(C)pzAOEP (common model for pH = 3 and 7 yielded R2 = 0.978 and S.E. = 0.43).

A Stable and Electrocatalytic Iron Electrode for Oxygen Evolution in Alkaline Water Electrolysis

Iron electrodes disintegrate in alkali at the anodic potentials needed for oxygen evolution. Hence, relatively expensive nickel-based electrodes and substrates have been the workhorse of materials for industrial water electrolysis. We report here a novel surface-modification method that transforms iron into an electrocatalytically-active and robust oxygen evolution electrode for alkaline water electrolysis. This surface modification consists of an electrochemical oxidation step followed by a thermal decomposition step. The electrochemical oxidation of the iron substrate in alkali transformed the surface to high surface area iron(II) hydroxide with a coral-like morphology that converted to magnetite upon heat treatment. On this high-surface area substrate an electrocatalytic layer of amorphous nickel hydroxide was produced by the thermal decomposition step. Such a surface-modified iron electrode exhibited an extremely low overpotential of 195 mV at 10 mA/cm2 and a low Tafel slope of 43 mV/decade. The electrochemical oxidation step during preparation results in doubling of the electrochemically active area. Even after 1500 h of oxygen evolution at 10 mA/cm2, there was no noticeable change in the electrode potential, morphology, or surface composition of these iron electrodes. This durability was attributed to the conductive oxide layer of magnetite that protects iron surface at the anodic potentials of oxygen evolution. The remarkable electrocatalytic activity was attributed to the amorphous layer of nickel hydroxide. Development of such a robust and electrochemically-active iron electrode presents a unique opportunity for the advancement of alkaline water electrolysis.

Electrochemical Properties of Chlorogenic Acids and Determination of Their Content in Coffee Using Differential Pulse Voltammetry

The electrochemical properties of nine chlorogenic acids (CGAs) isomers: three caffeoylquinic acids, CQAs (5-CQA, 4-CQA, 3-CQA), three dicaffeoylquinic acids, diCQAs (3,4-diCQA, 3,5-diCQA, 4,5CQA) and three feruloylquinic acids, FQAs (5-FQA, 4-FQA, 3-FQA) were studied by differential pulse voltammetry (DPV) method. The study has shown that electrochemical properties of CQAs and diCQAs are strongly dependent on their chemical structure and electronic properties, particularly on presence of electron-donating –OH and –CH=CH– groups, and a strong electron-withdrawing effect of ester (–COOR) group presented in their structures. The electrochemical properties of FQAs were additionally influenced by the presence of methoxy group (–OCH3) attached on the aromatic ring. DPV measurements show that electrochemical oxidation of CQAs and diCQAs at a GCE is reversible, pH dependent, two- electron-two- proton process occured on catechol moiety in the structure of these molecules. Electrochemical oxidation of FQAs proceeded by an EC mechanism. In the first, electrochemical oxidation step, a phenoxy radical was formed by irreversible one-electron-one-proton process. In the second, chemical step, phenoxy radical undergoes hydrolysis generated a new more electroactive compound with methoxy-catechol moiety in the structure. This compound was reversible oxidised to methoxy-ortho-quionone structure by two-electron-two-proton process. The electrochemical properties of 5-CQA (main CGAs in coffee) were investigated more in detail. It was observed that anodic oxidation peak current of 5-CQA show its maximum in PBS solution of pH 7 and linear relationship within the concentration range of 5-50 mol L -1 , with LOD of 1.2·10 -6 mol L -1 . DPVs of coffee show that electrochemical properties of coffee extracts were very similar to that of investigated CGAs. Therefore, DPV was used for characterization of CGAs in coffees. It was shown that DPV is a very sensitive and selective method for determination of total CGAs content in coffee.

Influence of controlled surface oxidation on the magnetic anisotropy of Co ultrathin films

We studied the influence of controlled surface-limited oxidation of electrodeposited epitaxial Co(0001)/Au(111) films on their magnetic anisotropy energy using real time in situ magneto optical Kerr effect and density functional theory (DFT) calculations. We investigated the Co first electrochemical oxidation step which we demonstrate to be completely reversible and determined the structure of this oxide layer. We show that the interface magnetic anisotropy of the Co film increases by 0.36 erg/cm2 upon Co surface oxidation. We performed DFT calculations to determine the different surface structures in a wide potential range as well as the charge transfer at the Co surface. Our results suggest that the magnetic anisotropy change is correlated with a positive charge increase of 0.54 e− for the Co surface atom upon oxidation.

Why palladium cathodes can bear resistance to methanol but not platinum cathodes

Methanol crossover on the cathodes causes significant performance loss in direct methanol fuel cells, and the parasitic current induced by the electrochemical oxidation of methanol on the cathodes is believed to be the cause. Palladium cathodes are known to bear resistance to methanol but not platinum cathodes. By means of the density functional theory (DFT), the distorted molecular structure of the adsorbed methanol on platinum was revealed, and this distorted molecular structure indicates that platinum makes methanol has a tendency toward the elimination of the first hydrogen (involved in the first step of electrochemical oxidation of methanol) in electric neutrality, and loss of an electron can reinforce this tendency. However, palladium cannot distort the molecular structure of the adsorbed methanol, even in the loss of electron condition. The activation energies and the reaction energies calculated by means of DFT also show that after losing an electron, the elimination of the first hydrogen on platinum is more kinetically and thermodynamically favourable than that on palladium. These computational results can explain the experimental findings that no parasitic current is induced at palladium cathodes, but not at platinum cathodes; therefore, palladium cathodes have a methanol-resistance property.

Study of the oxidation mechanisms associated to new dimeric and trimeric esters of ferulic acid

The electrochemical behaviour of new ferulic acid derivatives, three dimeric and one tripodal esters as well as the monomeric benzylic ester, is described. All of them follow an ECE (electrochemical–chemical–electrochemical) oxidation mechanism. Electrografting processes were observed too, except in the case of the monomeric ester. Interestingly, topology seems to play an important role in their capacity of being adsorbed by the electrode, which suggest that a greater reactivity of the bi- and tri- radicals, probably generated during the first steps of electrochemical oxidation of this type of compounds or an increase of the van der Waals interactions between huge molecules and the electrode surface, could be the main responsible. In addition, electrodonating power, as that defined within the density functional theory, was estimated for the benzylic ester, one dimeric ester, the tripodal ester, and the ferulic acid. This quantity was compared with the corresponding experimental values of the oxidation potential. Results show that monomers are more effective for the process of donating electrons; however, a higher number of ferulic units increases the ability of the bis and tris structures to increase their electrodonating power.

Electrochemically Active L-Cysteine Gold Modified Electrodes

Gold electrodes were easily modified using MPA (3- mercaptopropionic acid) to produce a self assemble monolayer, SAM, in which electrochemically active cysteine molecules were anchored to produce Au/MPA and Au/MPA/CSH electrodes. The functional groups, present on the modified electrode surfaces, were identified using cyclic voltammetry and ferricyanide ions, an electrochemical probe, at variable pH values. The steps which describe the global electrode process were identified and characterized using cyclic voltammetry. It involves the deprotonation of the R-SH superficial groups; production of R-S free radicals from R-S- electrochemical oxidation and attack and of R-S free radicals to the RSH adjacent molecules on the electrode surface, followed by the second electrochemical oxidation step to produce RSSR. The Au/MPA/CSH electrode showed electrocatalytic activity toward oxidation of quercetin in the range of 0.50 to 12.2μmolL−1 with a detection limit of 0.15μmolL−1.

Electrochemical Characterization and Evaluation of the Analytical Potentialities of Glassy Carbon Electrodes Modified with Extracted Lignin from Black (Kraft) Liquor

The electrochemical behavior of Kraft Lignin Glassy Carbon Modified electrodes, GCE-LIG, was studied. The modified electrode was prepared by recovering the glassy carbon surfaces with 10 μL of 1.0 and 0.01 g L-1 lignin in DMF. The polymeric film produced showed electrochemical activity due the quinone / hydroquinone (Q/HQ) redox couple produced from lignin by a mechanism involving an electrochemical oxidation step followed by a coupled chemical reaction. The GCE-LIG is stable at negative potentials up to - 1.5 V in pH range of 2.0 to 8.0, but the lignin polymeric film is leached from the electrode surface at potentials higher than + 0.8 V. The modified electrodes showed resistive behavior, which increased with the film thickness. Another interesting characteristic of the GCE-LIG is its selectivity to coordination complexes since the electrochemical activity increases as function of the major complexes lability.

Synthesis and electrochemical, optical, and thermal properties of polycarbosilanes with silylene–vinylene–phenylene–vinylene backbones and triphenylamine or carbazole unit-containing side chains

Polycarbosilanes with silylene–vinylene–phenylene–vinylene backbones and triphenylamine or carbazole unit-containing side chains were conveniently prepared by Pd-catalyzed one-pot reactions of a trihydrosilane (phenylsilane) with aromatic diynes (p- and m-diethynylbenzene) and triphenylamine or carbazole-unit containing acetylenes. Cyclic voltammetry of these polycarbosilanes suggested that dimerization processes of the pendant units took place during the electrochemical oxidation steps. In UV/vis absorption and emission spectra, the p-phenylene or triphenylamine unit-containing polymers showed λmax peaks at longer wavelength regions than the corresponding m-phenylene or carbazole unit-containing polymers. An energy transfer process from the backbone to the side chain was suggested in the polycarbosilane possessing m-phenylene and triphenylamine units. Photoluminescence quantum yields of these polymers ranged from 0.16 to 0.34 with the m-phenylene and triphenylamine units-containing polymer exhibiting the highest value. DSC analyses revealed that the p-phenylene polymers showed higher glass transition points (148–180 °C) than the corresponding m-phenylene polymers (129–158 °C). In TGA, the 5% weight loss temperatures were in the range of 382–444 °C, suggesting considerably high thermal stability of these polycarbosilanes. Ionization potentials were estimated by atmospheric photoelectron spectroscopy at 5.6–5.9 eV with the values of carbazole polymers being higher than those of the triphenylamine polymers.

Amperometric detection of cholesterol using an indirect electrochemical oxidation method

The indirect electrochemical oxidation method using bromine species in an organic media for measuring cholesterol was developed. The electrochemical behaviors of cholesterol were examined by cyclic voltammetry in a potential range of −0.5 to 2.0 V (vs. Ag/AgCl/saturated KCl). The polarization curve of the steady-state current in the applied potential range of 0–2.0 V is reported. The obtained kinetic parameters for the catalytic oxidation of cholesterol support the assumption that positive bromine species can be generated from bromine by undergoing two consecutive electrochemical oxidation steps. The positive bromine acts both as electron mediators and as electrocatalysts. Amperometric detection with an anodic current was investigated, and the calibration curve exhibited a linear relationship between the steady-state current and the concentration of cholesterol in the range of 30–200 μM, from which the sensitivity was calculated to be about 0.2 μA/cm 2/μM. Moreover, the amperometric current followed Michaelis–Menten’s enzymatic model for cholesterol concentrations in the range of 30 μM to 5 mM, which can be applied for cholesterol rapid detection in processed foods.