Electrochemical Redox Mechanism Research Articles

Electrochemical Properties and Redox Mechanism of Na2Ni0.4Co0.6[Fe(CN)6] Nanocrystallites as High-Capacity Cathode for Aqueous Sodium-Ion Batteries

Nickel-based ferrocyanides have attracted wide interest as cathode for aqueous sodium-ion batteries in fields of sustainable energies such as wind and solar, owing to excellent cycling stability and high-rate capability. However, they suffer from low specific capacities (∼60 mAh g–1). Herein, Na2Ni0.4Co0.6[Fe(CN)6] nanocrystallites are reported for the first time as high-capacity cathode for aqueous sodium-ion batteries. Its electrochemical properties and redox mechanism have been understood by combining the X-ray diffraction technique, Fourier-transform infrared spectroscopy, cyclic voltammetry, electrochemical impedance microscopy, and charge/discharge measurements. It is revealed that the material undergoes a reversible three-step single-phase reaction mechanism during Na extraction through sequential electrochemical oxidation of nitrogen-coordinated Co2+ ions and carbon-coordinated Fe2+ ions and achieves superior electrochemical performance with a high reversible capacity of 85 mAh g–1 at 0.5 C, an av...

A voltammetry sensor platform for baicalein and baicalin simultaneous detection in vivo based on Ta2O5-Nb2O5@CTS composite

Baicalein and baicalin are the major flavonoids found in Scutellariae Radix, an essential herb which has had a presence in traditional Chinese medicine (TCMs) for more than two thousands of years. Owing to their similar characteristics and physiochemical properties, sensitive, it is a great challenge to detect both of them simultaneously. In this work, a novel, facile and sensitive electrochemical method was proposed based on tantalum oxide (Ta2O5), niobium oxide (Nb2O5) particles and antiseptic chitosan modified carbon paste electrode (Ta2O5-Nb2O5@CTS-CPE). Scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) were used to characterize the properties and investigate the electrochemical response of the sensor. The electrochemical behaviors and redox mechanisms of two analytes were investigated at the target electrode. Under the optimum conditions, the highly sensitive and simultaneous determination of baicalein and baicalin was successfully achieved with a linear response range of 0.08–8.0μM for both of them. The obtained detection limits for baicalein and baicalin were of 0.05 and 0.03μM (S/N=3), respectively. Furthermore, the proposed sensor displayed high sensitivity, excellent stability and satisfactory results in Scutellariae Radix samples analysis and hydrolysis process analysis of baicalin in vivo.

Synthesis, pH dependent photometric and electrochemical investigation, redox mechanism and biological applications of novel Schiff base and its metallic derivatives

A novel Schiff base, 1-((2, 4-dimethylphenylimino)methyl)naphthalen-2-ol abbreviated as (HL) and its four metallic complexes were synthesized and confirmed by 1H and 13C NMR, FTIR, TGA and UV–Visible spectroscopy. Schiff base was also characterized by X-ray analysis. The photometric and electrochemical responses of all the synthesized compounds were investigated in a wide pH range. Structures of the compounds were optimized computationally for the evaluation of different physico-chemical parameters. On the basis of electrochemical results the redox mechanistic pathways of the compounds were proposed. The cytotoxicity analysis on Hela cells revealed that HL and its complexes inhibit cell growth as revealed from their IC50 values (HL):106.7μM, (L2VO): 40.66μM, (L2Sn): 5.92μM, (L2Zn): 42.82 and (L2Co): 107.68μM. The compounds were tested for anti-diabetic, triglyceride, cholesterol, anti-microbial, anti-fungal and enzyme inhibition activities. The results revealed that HL and its complexes are promising new therapeutic options as these compounds exhibit strong activity against cancer cells, diabetics, fungal and microbial inhibition.

The Electrochemical Redox Mechanism and Antioxidant Activity of Oleanolic Acid Based on Multi-walled Carbon Nanotuber Screen-printing Electrode

The Electrochemical Redox Mechanism and Antioxidant Activity of Oleanolic Acid Based on Multi-walled Carbon Nanotuber Screen-printing Electrode

Facile Synthesis and Electrochemical Evaluation of Coumarin‐Tagged Pyridine and Thiophene Derivatives

AbstractA series of coumarin pyridinethiones and pyridinones has been synthesized employing a range of substituted cyanothioacetamides and cyanoacetamides intermediates. Coumarin pyridinethiones and pyridinones bear different substituents including electron donating groups such as methyl, methoxy dimethylamine in addition to chloro, bromo and nitro as electron withdrawing groups were chosen to study the structure/electrochemical relationship. The influence of electron donating group and electron withdrawing group on different positions of coumarin scaffold was studied utilizing cyclic voltammetry and controlled potential electrolysis at platinum and glassy carbon electrodes. The electrochemical redox mechanisms of synthesized coumarins were proposed and the oxidation and reduction pathways were determined. Data for cyclic voltammetry and controlled potential electrolysis proved that amine center served as the oxidation center, while thiocarbonyl and carbonyl groups were identified as the reduction centers.

Synthesis and electrochemical study of new 3-(hydroxyphenyl)benzo[f]coumarins

New hydroxyl substituted 3-arylbenzo[f]coumarins (compounds 6–10) have been designed and synthesized. Their electrochemical redox mechanisms, and the influence of one or two hydroxyl groups, in different positions on the coumarin scaffold, was investigated by cyclic, differential pulse and square wave voltammetry, at a glassy carbon electrode, at different pHs, and a comparative study was performed. The structural information obtained enabled a better understanding of the structure/electrochemical relationship of hydroxyl substituted 3-arylbenzo[f]coumarins, compounds with important antioxidant properties.

Correction: Preparation, characterization and analytical application of an electrochemical laccase biosensor towards low level determination of isoprenaline in human serum samples

A novel electrochemical biosensor has been developed based on the immobilization of multiwalled carbon nanotubes (MWCNT) on to a glassy carbon electrode (GCE) and subsequent casting of silica sol–gel (SiSG) entrapped laccase (Lac) enzyme on to the MWCNT/GCE. The catalytic activity of laccase biosensor was found to be good enough for sensitive determination of isoprenaline (ISP) with the aid of voltammetric techniques and we have also demonstrated the detailed electrochemical redox mechanism of ISP. From the effect of the pH, we have optimized the optimum pH as 6.5, and from effect of scan rate we have evaluated the kinetic parameters, heterogeneous rate constant, charge transfer coefficient and diffusion coefficient values. Furthermore the limit of detection (LOD) and limit of quantification (LOQ) values were found to be 1.8 × 10−7 M and 6.0 × 10−7 M, respectively. The simultaneous determination of ISP in the presence of uric acid (UA) and ascorbic acid (AA) was successfully carried out. The surface nature of the biosensor was characterized by using electrochemical impedance spectroscopy. Finally the validation of the proposed method was verified by the recovery of injection (ISP) in serum samples and their recoveries were found to be in a satisfactory range. The proposed method was found to have good repeatability, reproducibility and stability with low relative standard deviation (RSD) values.

Electrochemical redox mechanism of Co–B–H anode material and its optimization by a novel electrolyte additive

Electrochemical redox mechanism and cycling stability are two important points for the research of the anode of alkaline rechargeable Ni/Co batteries. Herein, we report an amorphous Co–B–H anode material, which shows a multistep reaction in the initial discharge and the reaction of Co/Co(OH)2 in the subsequent cycles instead of hydrogen storage. The severe capacity decay of the anode caused by the dissolution during cycling is substantially limited by a novel electrolyte additive of NaS2O3, which is also beneficial to achieving a long term store of Ni/Co batteries and thus markedly boost the application of the battery.

New hydroxylated 3-arylcoumarins, synthesis and electrochemical study

A selected series of new different substituted 3-arylcoumarins have been designed, synthesized, and evaluated their electrochemical redox mechanisms. The relevant structural information about coumarins was considered in order to better understand the structure/electrochemical relationship. The influence of bromine, methyl or other hydroxyl groups in different positions of the coumarin scaffold, by cyclic, differential pulse and square wave voltammetry at a glassy carbon electrode at different pHs was investigated. A comparative study of differently substituted 8-hydroxy-3-arylcoumarins was performed.

Electrochemical characteristics of cis-jasmone in acid media at multi-wall carbon nanotube-Nafion composite film modified electrode and its analytical application

cis-Jasmone is a plant activator in terms of production of defence-related volatile semiochemicals. The redox and quantitative analysis of cis-jasmone are practically significant for the investigation of physiological processes in plants. In this work, the electrochemical characteristics of cis-jasmone in different acid media were investigated at a multi-wall carbon nanotube/Nafion composite film modified glassy carbon electrode (MWNT/Nafion/GCE) by cyclic voltammetry, chronocoulometry and infrared spectroscopy. The redox mechanism of cis-jasmone in strong acid media, i.e., a remarkable catalytic oxidation process for the reduction product of cis-jasmone at MWNT/Nafion/GCE, was demonstrated to be completely different from the cases in weakly acidic or neutral solution. The standard rate constant k0, the diffusion coefficient D and the surface coverage Γ were calculated and discussed. The sensitive anodic stripping voltammetric response of cis-jasmone was employed to determine its content in the extract of rice spikelet. The electrochemical redox and quantitative analysis of cis-jasmone are therefore of great significance for studying not only the physiological processes of cis-jasmone in plants but also the electrochemical redox mechanism of other α,β-unsaturated ketones.

Electrochemical Redox Mechanism in 3.5 V Li2-xFeP2O7 (0 ≤ x ≤ 1) Pyrophosphate Cathode

Li2FeP2O7 pyrophosphate is the latest phosphate-based polyanionic cathode material operating at 3.5 V (vs Li+/Li). Capable of two-dimensional Li+-ion diffusion, the pyrophosphate has a complex three-dimensional crystal structure, rich in Li–Fe antisite defects. The electrochemical (de)lithiation of pristine Li2FeP2O7 involves permanent structural rearrangement, as reflected by the voltage drop between the first and subsequent charging segments. The current article presents the structural analysis of the electrochemical redox mechanism of Li2FeP2O7 cathode coupling in situ and ex-situ structural characterization. Contrary to previous reports, it involves a single-phase redox reaction during (de)lithiation cycles involving a minimal <2% volume expansion. Further, it forms a rare example of cathode showing positive expansion upon delithiation similar to LiCoO2. The mechanism of single-phase (de)lithiation and related (ir)reversible structural arrangement is elucidated.

Redox behaviour of (Z)-2-(5-ethoxycarbonylmethyl-N-methyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone in aprotic medium: Spectroelectrochemical study and theoretical modelling

Electrochemical and spectroelectrochemical study of the reduction of (Z)-2-(5-ethoxycarbonylmethyl-N-methyl-4-oxothiazolidin-2-ylidene)-1-phenylethanone in an aprotic solvent (dimethylsulfoxide (DMSO)) has been presented. The results indicate an ECCEE reaction sequence, whereby the chemical step is a protonation of the anion radical electrogenerated in the first electron transfer step by the enol tautomer of the substrate. The gas phase and solvent dependent PM3 semiempirical modelling allowed further rationalization of experimental data pertinent to the suggested electrochemical redox mechanism and the reactivity of the intermediate species involved.

The Electrochemical Behavior of Acetaminophen on Multi‐Walled Carbon Nanotubes Modified Electrode and Its Analytical Application

A multi‐walled carbon nanotubes modified glassy carbon electrode (MWNTs/GCE) was fabricated, and the electrochemical behaviors of acetaminophen (ACOP) were investigated on the MWNTs/GCE. The results showed that MWNTs exhibited excellent electrocatalytic effects on the reaction of ACOP by accelerating the electron transfer rate. Cyclic voltammetry (CV) was used to explore the electrochemical redox mechanism of ACOP on the MWNTs/GCE and differential pulse voltammetry (DPV) was taken to determine ACOP in samples, respectively. The results showed that the oxidative peak currents were linear with the concentration of ACOP in the range of 4.0×10−7–1.5×10−4 mol l−1 with the detection limit 1.2×10−7 mol l−1. The MWNTs/GCE showed satisfactory stability, selectivity, and it can be used to quantify ACOP in effervescent dosage real samples.

Voltammetrische Charakterisierung des elektrochemischen Redoxverhaltens von N-Thiocarbamoyl-benzamidinen und 1,2,4-Thiadiazoliumsalzen

The electrochemical redox behaviour of N-(diethylamino-thiocarbamoyl)-benzamidines Et2N-C(S)-N*C-(NHR)-Ph (1: R=H; 2: R=n-C3H7; 3: R=Ph) and 2,3-diphenyl-5-diethylamino-1,2,4-thiadiazolium iodide (4) as well as of its perchlorate (5) was studied by cyclic voltammetry in ethanolic solution at a glassy carbon electrode between −1.2 V and +1.5 V vs. Ag/AgCl. The mechanisms for the irreversible anodic oxidation of the benzamidines 1–3 and the formed products (1,2,4-thiadiazolium cations or 1,2,4-thiadiazole) are influenced directly by the substituents bound to the terminal benzamidine nitrogen atom. In the cathodic potential range, an irreversible reductive cleavage of the benzamidines 1–3 occurs which also depends on the N-bound substituents. The products of this reduction, which are identified indirectly electrochemically by comparing voltammogramms, can be adsorbed on the electrode surface and reoxidized in the following anodic scan. The 1,2,4-thiadiazolium cation of 4 and 5 is redox inert in the investigated anodic potential range. The obtained anodic peaks in the case of 4 result from redox reactions of the iodide counter ions only. However, the 1,2,4-thiadiazolium cation is also subject of a reductive cleavage in a similar way to the mechanism which is proposed for the N-thiocarbamoyl-benzamidines 1–3. The discussed electrochemical redox mechanisms of the characterized compounds 1–5 are compatible with known results of synthesis.

Solid-State Light-Emitting Devices Based on the Trischelated Ruthenium(II) Complex. 1. Thin Film Blends with Poly(ethylene oxide)

Thin-film solid-state light-emitting devices have been fabricated by using blends of a trischelated complex of ruthenium(II) with 4,7-diphenyl-1,10-phenanthroline disulfonate ligands and lithium triflate complexed poly(ethylene oxide). Charge injection occurs via an electrochemical redox mechanism and the mechanism of light production is similar to electrogenerated chemiluminescence. Orange-red light is emitted with a turn-on voltage of 2.5−3.0 V. At 6 V, devices reach luminance levels of about 100 cd/m2 with an external quantum efficiency of 0.02% photons/electron. The admixed PEO acts both as a film processing aid, giving uniform, homogeneous, and reproducible devices, and as a polymer electrolyte for ruthenium complex and counterion diffusion. Devices reach about 50% of their maximum luminance within a few seconds, and reach maximum luminance in about a minute. This behavior can be realized without the need of elaborate charging schemes involving the use of elevated temperatures or solvent treatments that enhance ionic conductivity. Devices of this type can be fabricated via conventional processing routes and conditioned to high light ouput with a few simple voltage scans.

Electrochemical quartz crystal microbalance characterization of I - and its amperometric detection by microelectrode

The electrochemical redox mechanism of I − ion under different concentrations on gold electrodes was studied in detail using the EQCM technique (a combination of the QCM technique and cyclic voltammetry). The redox behavior of the I − ion on a gold microelectrode when no supporting electrolyte was added was compared with a conventional gold microelectrode. Due to the small current and the very low solution iR drop of the microelectrode, the actual oxidation potential of I − on the microelectrode was much more negative than that of the conventional electrode and its anodic peak was better defined. Therefore the gold microelectode was employed for the determination of I − . A linear range of 1.0×10 −5–0.1 mol l −1 with a detection limit of 1.0×10 −6 mol l −1 was obtained on the microelectrode in pure KI aqueous solution. Two samples were measured using this method and the results were in good agreement with those indicated or calculated..

Effects of solvent and electrolyte on the electrochromic behavior and degradation of chemically prepared polyaniline‐poly(vinyl alcohol) composite films

AbstractEffects of solvent and electrolyte on the electrochromic behavior and degradation of polyaniline in nonaqueous aprotic media, as well as its electrochemical redox and degradation mechanisms, were investigated with chemically prepared polyaniline‐poly (vinyl alcohol) composite films and polyaniline homogeneous films. Visible and FT‐IR absorption spectra of the polyaniline films, oxidized electrochemically at various polarization potentials, showed that the mechanisms in aprotic media involved two successive oxidation processes. In contrast to aqueous systems, the higher oxidation process involved further anion insertion without deprotonation, and the degradation was due to partial formation of the electrochemically inactive quinonediimine structure at excessive polarization potentials. From investigations of solvent and electrolyte effects, it is suggested that the electrochromic behavior and degradation of polyaniline are influenced by the electron‐donating and accepting ability of solvents, acceptor strength of electrolyte cations, and the nucleophilic character of electrolyte anions. It was also suggested that some anions like $\[ PF_6^ - , BF_4^ - , \] and $ $\[ CIO_4^ - , \] $ as well as protons, are constrained in the PVA matrix by specific electrostatic interactions and steric effects to improve the stability of polyaniline in the highly oxidized state. © 1994 John Wiley &amp; Sons, Inc.

The role of ion exchange in the redox processes of polypyrrole/dodecyl sulfate films as studied by electrogravimetry using a quartz crystal microbalance

The electrochemical redox mechanism of a dodecyl sulfate-doped polypyrrole was studied in detail by electrogravimetry using a quartz crystal microbalance. In order to distinguish the nature of the inserted/deinserted species, different salts were used as aqueous electrolytes. A quantitative analysis of the results indicated that the surfactant counter anion was trapped in the polymer matrix and that both anions and cations of the electrolyte play an important role in the redox processes. Quantitative calculations showed that the hydration sphere of these ions must be taken into account when dealing with the redox processes of conductive polymers adhered to the surface of electrodes.

Electrochemical Redox Mechanism of Polyaniline Analyzed by X-ray Photoelectron Spectroscopy

Electrochemical Redox Mechanism of Polyaniline Analyzed by X-ray Photoelectron Spectroscopy

Polyaniline films. Electrochemical redox mechanisms

The different redox mechanisms proposed in the literature concerning the electron and proton transfers that occur in polyaniline (PANi) films are presented and discussed. The electrochemical behaviour of PANi usually shows two pairs of current peaks on cyclic voltammetry curves in aqueous or organic medium. In situ spectroelectrochemical and EPR studies of PANi synthesized in NH 4F, 2.3HF were carried out in association with cyclic voltammetry. The results are discussed in terms of the redox reaction mechanisms. We propose that the complete redox mechanism involves four one-electron steps and two polaron-bipolaron states in PANi films.