Electrode Reaction Rate Research Articles

Solution voltammetry of 4 nm magnetite iron oxide nanoparticles.

The voltammetry of solution-dispersed magnetite iron oxide Fe3O4 nanoparticles is described. Their currents are controlled by nanoparticle transport rates, as shown with potential step chronoamperometry and rotated disk voltammetry. In pH 2 citrate buffer with added NaClO4 electrolyte, solution cyclic voltammetry of these nanoparticles (average diameter 4.4 ± 0.9 nm, each containing ca. 30 Fe sites) displays an electrochemically irreversible oxidation with E(PEAK) at ca. +0.52 V and an irreversible reduction with E(PEAK) at ca. +0.2 V vs Ag/AgCl reference electrode. These processes are presumed to correspond to the formal potentials for one-electron oxidation of Fe(II) and reduction of Fe(III) at their different sites in the magnetite nanoparticle structure. The heterogeneous electrode reaction rates of the nanoparticles are very slow, in the 10(-5) cm/s range. The nanoparticles are additionally characterized by a variety of tools, e.g., TEM, UV/vis, and XPS spectroscopies.

Electrochemically reduced graphene oxide-based electrochemical sensor for the sensitive determination of ferulic acid in A. sinensis and biological samples

An electrochemically reduced graphene oxide (ERGO) modified glassy carbon electrode (GCE) was used as a new voltammetric sensor for the determination of ferulic acid (FA). The morphology and microstructure of the modified electrodes were characterized by scanning electron microscopy (SEM) and Raman spectroscopy analysis, and the electrochemical effective surface areas of the modified electrodes were also calculated by chronocoulometry method. Sensing properties of the electrochemical sensor were investigated by means of cyclic voltammetry (CV) and differential pulse voltammetry (DPV). It was found that ERGO was electrodeposited on the surface of GCE by using potentiostatic method. The proposed electrode exhibited electrocatalytic activity to the redox of FA because of excellent electrochemical properties of ERGO. The transfer electron number (n), electrode reaction rate constant (ks) and electron-transfer coefficient (α) were calculated as 1.12, 1.24s−1, and 0.40, respectively. Under the optimized conditions, the oxidation peak current was proportional to FA concentration at 8.49×10−8molL−1 to 3.89×10−5molL−1 with detection limit of 2.06×10−8molL−1. This fabricated sensor also displayed acceptable reproducibility, long-term stability, and high selectivity with negligible interferences from common interfering species. The voltammetric sensor was successfully applied to detect FA in A. sinensis and biological samples with recovery values in the range of 99.91%-101.91%.

Electrochemical behavior and voltammetric determination of p-methylaminophenol sulfate using LiCoO2 nanosphere modified electrode

In this study, LiCoO2 nanoparticles were synthesized by the hydrothermal method and characterized by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction analyses, which exhibited flower-like nanospheres composed of uniform nanosheets. The synthesized LiCoO2 nanospheres were further used for the modification of 1-hexylpyridinium hexafluorophosphate based carbon ionic liquid electrode (CILE). The electrochemical performance of the modified electrode, LiCoO2/CILE, was studied by cyclic voltammetry and electrochemical impedance spectroscopy. Electrooxidation of p-methylaminophenol sulfate (metol) on the modified electrode was further tested and electrochemical responses of metol were significantly enhanced owing to the presence of LiCoO2 nanospheres with large surface area and fast electron transfer rate. The electrochemical parameters such as the charge transfer coefficient, the number of electron transferred, the standard electrode reaction rate constant, and the apparent diffusion coefficient for metol electrooxidation were calculated as 0.51, 0.91, 0.92s−1 and 7.06×10−5cm2/s, respectively. Under the optimized conditions, metol can be linearly detected in the concentration range from 0.4 to 400.0μmol/L with a detection limit of 2.46×10−7mol/L (3σ). The optimized method was further applied to the detection of metol content in artificial wastewater samples with satisfactory results.

Interplay Between Structure and Conductivity in Imidazolium-Based Ionic Liquids As Electrolytes for Magnesium Batteries

The search for new electrolytes is one of the most challenging aspects in the development of secondary batteries based on Li and Mg ions [1].The state of the art for Mg electrolytes is mainly constituted by organo-Mg compounds; in general, they show good Mg deposition and dissolution performance, high Coulombic efficiency and in some cases a wide electrochemical stability window [2-3]. The main drawback of this class of materials is associated with their dissolution in ethereal-based solvents characterized by a high vapor pressure and flammability. Nevertheless, the use of high-boiling solvents is known to lead to: (a) a decrease in the electrolyte conductivity; and (b) a decrease in the electrode reaction rate, which limits their practical applicability [2].Ionic liquids (ILs) are salts that are molten at room temperature [4]. ILs are also characterized by: (a) negligible vapor pressure; (b) high thermal stability; and (c) low flammability.Only a few examples of the applicability of ILs as electrolytes for secondary Mg batteries are reported in the literature [5]. Several issues regarding the conductivity mechanisms, formation of the solid-electrolyte interface (SEI) and long-term performance of these systems are still open questions.From a fundamental point of view, the interplay between the ILs nanostructure and the conductivity is a crucial point to clarify the effect of the IL matrix on the migration mechanism of Mg2+ ions.In this report, a comparison between two Mg electrolytes based on Ethyl-methylimidazolium tetrafluoroborate (EMImBF4) and Ethyl-methylimidazolium chloride/AlCl3 (EMImCl/(AlCl3)1.5) ILs is proposed. Both ionic liquids are doped with different amounts of δ-MgCl2, to achieve a sufficient conductivity of Mg2+ ions.The correlation between structure, thermal properties and conduction mechanism of the resulting EMImBF4/(δ-MgCl2)x and [EMImCl/(AlCl3)1.5]/(δ-MgCl2)x is investigated by a variety of techniques: (a) FT-MIR and FIR at different temperatures; (b) differential scanning calorimetry (DSC); and (c) broadband electrical spectroscopy (BES).Figure 1 shows a plot of σDC of EMImBF4 vs. 1/T. The observed trend of σDC is strongly correlated to the thermal features detected by DSC. A decrease in σDC of six orders of magnitude is evidenced at temperatures higher than the crystallization temperature (Tc). This phenomenon is investigated as a function of: (a) Mg concentration; and (b) the different anions in the ILs.BES measurements were undertaken to elucidate the electrical response of the electrolytes in terms of dielectric and polarization phenomena. At T < Tm (Tm = melting temperature) three dielectric relaxations are present, associated with the rotational motions of EMIm+ cations; at T > Tm, three and four interdomain polarization events are detected respectively for EMImBF4 and [EMImCl/(AlCl3)1.5]. These polarization events are associated with the presence of cation and anion nanocluster aggregates with different permittivities.

Charge Transport and Transfer in Ionic Liquids for Advanced Electrochemical Devices

A new family of ionic liquids can be obtained by simply mixing glyme (triglyme (G3) or tetraglyme (G4)) with lithium bis(trifluoromethylsulfonyl)amide (Li[TFSA]) in a molar ratio of 1:1 [1-4]. The equimolar complex [Li(G3 or G4)1][TFSA] maintains a stable liquid state over a wide temperature range and can be regarded as a solvate ionic liquid consisting of a [Li(glyme)1]+ complex cation and a [TFSA]- anion, exhibiting high self-dissociativity (ionicity) at room temperature [1, 4]. The electrochemical oxidation of [Li(glyme)1][TFSA] takes place at the electrode potential of ~5 V vs. Li/Li+, while the oxidation of solutions containing excess glyme molecules ([Li(glyme)x][TFSA], x > 1) occurs at lower than 4 V [2]. This enhancement of oxidative stability is due to the donation of lone pairs of ether oxygen atoms to the Li+ cation, resulting in the highest occupied molecular orbital (HOMO) energy level lowering of a glyme molecule, which is confirmed by ab initio molecular orbital calculations. The solvation state of a Li+ cation and ion conduction mechanism in the [Li(glyme)x][TFSA] solutions is elucidated by means of NMR and electrochemical methods. The experimental results strongly suggest that Li+ cation conduction in the equimolar complex takes place by the migration of [Li(glyme)1]+ cations, whereas the ligand exchange mechanism is overlapped when interfacial electrochemical reactions of [Li(glyme)1]+ cations occur. The ligand exchange conduction mode is typically seen in a lithium battery with a configuration of [Li anode | [Li(glyme)1][TFSA] | LiCoO2 cathode] when the discharge reaction of a LiCoO2 cathode, i.e., de- solvation of [Li(glyme)1]+ and insertion of the resultant Li+ into the cathode, occurs at the electrode-electrolyte interface. The battery can be operated for more than 200 charge-discharge cycles in the cell voltage range of 3.0–4.2 V, regardless of the use of ether-based electrolyte, because the ligand exchange rate is much faster than the electrode reaction rate [2].Protic ionic liquid as a proton conductor for a fuel cell is another topic to be discussed here. The characterization of a protic ionic liquid, diethylmethylammonium trifluoromethanesulfonate ([dema][TfO]), and the fabrication of a membrane-type fuel cell system using [dema][TfO] under non-humidified conditions at intermediate temperatures are described in detail [5-8]. In terms of physicochemical and electrochemical properties, [dema][TfO] exhibits high activity for fuel cell electrode reactions (i.e., the hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR)) at a Pt electrode, and the open circuit voltage (OCV) of a liquid fuel cell is 1.03 V at 150 °C [5]. However, diethylmethylammonium bis(trifluoromethane sulfonyl)amide ([dema][NTf2]) has relatively low HOR and ORR activity, and thus, the OCV is ca. 0.7 V, although [dema][NTf2] and [dema][TfO] have an identical cation ([dema]) and similar thermal and bulk-transport properties. Proton conduction occurs mainly via the vehicle mechanism in [dema][TfO] and the proton transference number (t +) is 0.5~0.6. This relatively low t + appears to be more disadvantageous for a proton conductor than for other electrolytes such as hydrated sulfonated polymer electrolyte membranes (t + = 1.0). However, fast proton-exchange reactions occur between ammonium cations and amines in a model compound. This indicates that the proton-exchange mechanism contributes to the fuel cell system under operation, where de-protonated amines are continuously generated by the cathodic reaction, and that polarization of the cell is avoided [6]. Six-membered sulfonated polyimides in the diethylmethylammonium form exhibit excellent compatibility with [dema][TfO]. The composite membranes can be obtained up to a [dema][TfO] content of 80 wt% and exhibit good thermal stability, high ionic conductivity, and mechanical strength and gas permeation comparable to those of hydrated Nafion. H2/O2 fuel cells prepared using the composite membranes can successfully operate at temperatures from 30 °C to 140 °C under non-humidified conditions, and a current density of 400 mA cm−2 is achieved at 120 °C [7]. The protic ionic liquid and its composite membrane are a possible candidate for an electrolyte of a H2/O2 fuel cell that operates under non-humidified conditions.

Electrochemical characterization of electrodes in the electrochemical Bunsen reaction of the sulfur–iodine cycle

In the electrochemical Bunsen reaction, SO2 is oxidized to H2SO4 at the anode while I2 is reduced to HI at the cathode. Both electrodes were electrochemically characterized using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The effects of H2SO4 concentration in the anolyte, as well as HI concentration and I2/HI molar ratio in the catholyte, were explored. The cyclic voltammograms of platinum electrode shift with rising scan rate, indicating the irreversibility of two electrode reactions. The equivalent circuit for the cathode reaction impedance consists of an ohmic resistance of the solution, in series with a parallel combination of a charge transfer resistor and a constant phase element, yet the impedance spectra for the anode reaction can be modeled using a parallel combination of a charge transfer resistor and a constant phase element. The electrode reaction kinetics was also analyzed using the exchange current density (j0) and the standard reaction rate constant (k0). The results indicate that a high electrode reaction rate in the cell can be obtained for a HI concentration of 8 mol/kgH2O and an I2/HI molar ratio of 0.5 in the catholyte and a H2SO4 concentration of 13 mol/kgH2O in the anolyte.

Effective improvement of interface modified strontium titanate based solid oxide fuel cell anodes by infiltration with nano-sized palladium and gadolinium-doped cerium oxide

The development of low temperature solid oxide fuel cell (SOFC) anodes by infiltration of Pd/Gd-doped cerium oxide (CGO) electrocatalysts in Nb-doped SrTiO3 (STN) backbones has been investigated. Modification of the electrode/electrolyte interface by thin layer of spin-coated CGO (400–500 nm) contributed to a significant improvement in performance of the STN backbones and infiltrated electrodes. The improvement is due to the result of CGO enrichment at the interface. The impedance analysis showed that addition of Pd further increased the electrode reaction rate with a factor 10 with respect to the CGO electrocatalysts. Very low electrode polarization resistances of 0.055 Ω cm2 (after excluding the gas diffusion limitation contribution) and 1.2 Ω cm2 at 600 °C and 400 °C, respectively, have been obtained in 3% H2/H2O. A gradual decrease in polarization resistance was achieved with increasing loading of Pd-CGO electrocatalyst. The microstructural analysis of the infiltrated Pd-CGO electrocatalyst on STN revealed a homogenous coating of Pd and CGO nanoparticles.

Accelerated azo dye removal by biocathode formation in single-chamber biocatalyzed electrolysis systems

Biocatalyzed electrolysis systems (BES) have been the topic of a great deal of research. However, the biocathodes formed in single-chamber BES without extra inocula have not previously been researched. Along with the formation of biocathodes, the polarization current increased to 1.76 mA from 0.35 mA of abio-cathodes at -1.2 V (vs. SCE). Electrochemical impedance spectroscopy (EIS) results also indicated that the charge transfer resistance (Rct) was decreased to 148.9 Ω, less than 1978 Ω of the abio-cathodes cleared. The performance of the biocathodes was tested for azo dye decolorization, and the dye removal efficiency was 13.3±3.2% higher than abio-cathodes with a 0.5 V direct current (DC) power supply. These aspects demonstrate that biocathode accelerates the rate of electrode reaction in BES and comparing with noble metal catalysts, biocathodes have low toxicity or non-toxic and reproducible properties, which can be widely applied in bioelectrochemical field in the future.

Electrochemical study and application on shikonin at poly(diallyldimethylammonium chloride) functionalized graphene sheets modified glass carbon electrode

The electrochemical behaviors of shikonin at a poly(diallyldimethylammonium chloride) functionalized graphene sheets modified glass carbon electrode(PDDA-GS/GCE) have been investigated. Shikonin could exhibit a pair of well-defined redox peaks at the PDDA-GS/GCE located at 0.681 V(E pa) and 0.662 V(E pc)[vs. saturated calomel electrode(SCE)] in 0.1 mol/L phosphate buffer solution(pH=2.0) with a peak-to-peak separation of about 20 mV, revealing a fast electron-transfer process. Moreover, the current response was remarkably increased at PDDA-GS/GCE compared with that at the bare GCE. The electrochemical behaviors of shikonin at the modified electrode were investigated. And the results indicate that the reaction involves the transfer of two electrons, accompanied by two protons and the electrochemical process is a diffusional-controlled electrode process. The electrochemical parameters of shikonin at the modified electrode, the electron-transfer coefficient(α), the electron-transfer number(n) and the electrode reaction rate constant(k s) were calculated to be as 0.53, 2.18 and 3.6 s−1, respectively. Under the optimal conditions, the peak current of differential pulse voltammetry(DPV) increased linearly with the shikonin concentration in a range from 9.472×10-8 mol/L to 3.789×10-6 mol/L with a detection limit of 3.157×10−8 mol/L. The linear regression equation was I p=0.7366c+0.7855(R=0.9978; I p: 10−7 A, c: 10−8 mol/L). In addition, the modified glass carbon electrode also exhibited good stability, selectivity and acceptable reproducibility that could be used for the sensitive, simple and rapid determination of shikonin in real samples. Therefore, the present work offers a new way to broaden the analytical application of graphene in pharmaceutical analysis.

A Binuclear Iron–Thiolate Catalyst for Electrochemical Hydrogen Production in Aqueous Micellar Solution

The substituted iron-thiolate complex [Fe(2)(μ-bdt)(CO)(4){P(OMe)(3)}(2)] (bdt=benzenedithiolate) is an active catalyst for electrochemical hydrogen production in aqueous sodium dodecyl sulfate solution, with a high apparent rate constant of 4×10(6) M(-1) s(-1). The half-peak potential for catalysis of proton reduction is less negative than -0.6 V versus the standard hydrogen electrode at pH 3. Voltammetric data are consistent with the rate of electrode reaction controlled by diffusion. A mechanism that begins with the rapid protonation of the iron-thiolate catalyst is proposed. The Faradaic efficiency in diluted HCl solutions is close to 100%, but the catalytic activity decayed after about twelve turnovers when electrolysis was carried out in the presence of acetic acid.

Investigation on the Photoelectrocatalytic Activity of Well-Aligned TiO2Nanotube Arrays

Well-aligned TiO2nanotube arrays were fabricated by anodizing Ti foil in viscous F−containing organic electrolytes, and the crystal structure and morphology of the TiO2nanotube array were characterized and analyzed by XRD, SEM, and TEM, respectively. The photocatalytic activity of the TiO2nanotube arrays was evaluated in the photocatalytic (PC) and photoelectrocatalytic (PEC) degradation of methylene blue (MB) dye in different supporting solutions. The excellent performance of ca. 97% for color removal was reached after 90 min in the PEC process compared to that of PC process which indicates that a certain external potential bias favors the promotion of the electrode reaction rate on TiO2nanotube array when it is under illumination. In addition, it is found that PEC process conducted in supporting solutions with low pH and containing Cl−is also beneficial to accelerate the degradation rate of MB.

Effects of Various Boundary Conditions on the Response of Poisson–Nernst–Planck Impedance Spectroscopy Analysis Models and Comparison with a Continuous-Time Random-Walk Model

Various electrode reaction rate boundary conditions suitable for mean-field Poisson-Nernst-Planck (PNP) mobile charge frequency response continuum models are defined and incorporated in the resulting Chang-Jaffe (CJ) CJPNP model, the ohmic OHPNP one, and a simplified GPNP one in order to generalize from full to partial blocking of mobile charges at the two plane parallel electrodes. Model responses using exact synthetic PNP data involving only mobile negative charges are discussed and compared for a wide range of CJ dimensionless reaction rate values. The CJPNP and OHPNP ones are shown to be fully equivalent, except possibly for the analysis of nanomaterial structures. The dielectric strengths associated with the CJPNP diffuse double layers at the electrodes were found to decrease toward 0 as the reaction rate increased, consistent with fewer blocked charges and more reacting ones. Parameter estimates from GPNP fits of CJPNP data were shown to lead to accurate calculated values of the CJ reaction rate and of some other CJPNP parameters. Best fits of CaCu(3)Ti(4)O(12) (CCTO) single-crystal data, an electronic conductor, at 80 and 140 K, required the anomalous diffusion model, CJPNPA, and led to medium-size rate estimates of about 0.12 and 0.03, respectively, as well as good estimates of the values of other important CJPNPA parameters such as the independently verified concentration of neutral dissociable centers. These continuum-fit results were found to be only somewhat comparable to those obtained from a composite continuous-time random-walk hopping/trapping semiuniversal UN model.

Oxidative-Stability Enhancement and Charge Transport Mechanism in Glyme–Lithium Salt Equimolar Complexes

The oxidative stability of glyme molecules is enhanced by the complex formation with alkali metal cations. Clear liquid can be obtained by simply mixing glyme (triglyme or tetraglyme) with lithium bis(trifluoromethylsulfonyl)amide (Li[TFSA]) in a molar ratio of 1:1. The equimolar complex [Li(triglyme or tetraglyme)(1)][TFSA] maintains a stable liquid state over a wide temperature range and can be regarded as a room-temperature ionic liquid consisting of a [Li(glyme)(1)](+) complex cation and a [TFSA](-) anion, exhibiting high self-dissociativity (ionicity) at room temperature. The electrochemical oxidation of [Li(glyme)(1)][TFSA] takes place at the electrode potential of ~5 V vs Li/Li(+), while the oxidation of solutions containing excess glyme molecules ([Li(glyme)(x)][TFSA], x > 1) occurs at around 4 V vs Li/Li(+). This enhancement of oxidative stability is due to the donation of lone pairs of ether oxygen atoms to the Li(+) cation, resulting in the highest occupied molecular orbital (HOMO) energy level lowering of a glyme molecule, which is confirmed by ab initio molecular orbital calculations. The solvation state of a Li(+) cation and ion conduction mechanism in the [Li(glyme)(x)][TFSA] solutions is elucidated by means of nuclear magnetic resonance (NMR) and electrochemical methods. The experimental results strongly suggest that Li(+) cation conduction in the equimolar complex takes place by the migration of [Li(glyme)(1)](+) cations, whereas the ligand exchange mechanism is overlapped when interfacial electrochemical reactions of [Li(glyme)(1)](+) cations occur. The ligand exchange conduction mode is typically seen in a lithium battery with a configuration of [Li anode|[Li(glyme)(1)][TFSA]|LiCoO(2) cathode] when the discharge reaction of a LiCoO(2) cathode, that is, desolvation of [Li(glyme)(1)](+) and insertion of the resultant Li(+) into the cathode, occurs at the electrode-electrolyte interface. The battery can be operated for more than 200 charge-discharge cycles in the cell voltage range of 3.0-4.2 V, regardless of the use of ether-based electrolyte, because the ligand exchange rate is much faster than the electrode reaction rate.

The Influence of Potential on Electrodeposition of Silver and Formation of Silver Nanoparticles in Some Ionic Liquids

Electrodeposition of Ag was studied in several ionic liquids. When the potential applied more negative than −0.25 V vs. Ag | Ag(I), the cathodic current density reached in the diffusion-controlled region. The surface morphology of Ag deposits, the initial stage of nucleation and crystal growth behavior and the apparent current efficiency changed depending on the applied potential. These results indicate that the applied potential affects the electrodeposition processes of Ag under diffusion-controlled region. Since the electrode reaction rate is controlled by diffusion, the change of the surface morphology may be caused by the change of the double layer structure, which is expected to depend on the applied potential. In addition, Ag nanoparticles were obtained in the ionic liquid after potentiostatic cathodic reduction, suggesting a part of reduced Ag was dispersed in the ionic liquid.

Scrap cast iron and copper‐modified cast iron for reductive degradation of 2,4‐dinitrotoluene

AbstractBACKGROUND: Little attention has been paid to the use of large‐sized scrap cast iron for reduction of refractory organic pollutants at neutral pH and in the presence of dissolved oxygen (DO).RESULTS: Scrap cast iron and copper‐modified cast iron with fresh surfaces have a high reactivity towards the reduction of 2,4‐dinitrotoluene (2,4‐DNT). The extent of conversion reached around 80% and 97% respectively, though it gradually decreased with repeated reactions to relatively stable values of 63% and 72%, and recovered once the reacted filings were cleaned by dilute acid. After 50 days reaction, no dissolved copper appeared in the copper‐modified cast iron process. The mass loss of copper due to physical detachment reached 1.1% of the total coated copper within the initial 20 reaction days, and only 0.3% appeared in the next 30 days. 2,4‐DNT oxidizes scrap cast iron to generate mainly FeFe2O4 with DO, however, it oxidizes scrap copper‐modified cast iron to generate mainly γ‐FeO(OH) and α‐FeO(OH).CONCLUSION: Both samples of cast iron were successfully applied in the treatment of neutral wastewater containing 2,4‐DNT with high reactivity and good repeatable efficiency. Electrode reaction rate was enhanced by the deposited copper, which has strong chemical and physical stability. Copyright © 2011 Society of Chemical Industry

Research on Polarization Curve and Anode Discharge Mechanism in Electrolysis Cells for Preparation of Al-Li Alloys

At 953K, anodic over voltage by electrolyzing LiCl and Li2CO3 were measured respectively by continuous pulse oscillograph method in a mixture fused salt of LiCl-LiF in a laboratory electrolyte cell and the change of polarization curve obtained was studied as well. According to kinetics of electrode process theory, we calculated and analyzed anode reaction mechanism and reaction rate-determining step. The results indicate that when over voltage entered into the Tafel zone with current density in range of 0.1 to 0.3A·cm-2, electrode reaction of LiCl is controlled by electrochemical polarization but electrode reaction of Li2CO3 is controlled by chemical polarization. With current density increase further beyond the Tafel zone (i&gt;0.4A·cm-2), electrode reaction is changing gradually from dual control influenced by electrochemistry or chemistry united with concentration polarization to single concentration polarization. While electrolyzing Li2CO3, it is complexing oxygen ions discharging on carbon anode slowly that determine the whole electrode reaction rate.

The Influence of Potential Under Diffusion-Controlled Region on Electrodeposition of Silver in an Amide-Type Ionic Liquid

The electrodeposition of Ag was studied in several ionic liquids. When the potential applied more negative than −0.25 V vs Ag/Ag(I), current density reached the diffusion-controlled region. The surface morphology of electrodeposited Ag changed depending on the applied potential. This result indicates that the applied potential affects the processes of Ag electrodeposition under diffusion-controlled region. Surface morphology was considered related closely to the crystal growth process. Since the electrode reaction rate is controlled by diffusion, the change of the surface morphology may be caused by the change of the double layer structure, which is expected to depend on the applied potential.

Electrocatalytic oxidation of quinine sulfate at a multiwall carbon nanotubes-ionic liquid modified glassy carbon electrode and its electrochemical determination

The electrocatalytic oxidation of quinine sulfate (QS) was investigated at a glassy carbon electrode, modified by a gel containing multiwall carbon nanotubes (MWCNTs) and room-temperature ionic liquid of 1-Butyl-3-methylimidazolium hexafluorophate (BMIMPF6) in 0.10 M of phosphate buffer solution (PBS, pH 6.8). It was found that an irreversible anodic oxidation peak of QS with Epa as 0.99 V appeared at MWCNTs-RTIL/glassy carbon electrode (GCE). The electrode reaction process was a diffusion-controlled one and the electrochemical oxidation involved two electrons transferring and two protons participation. Furthermore, the charge-transfer coefficient (α), diffusion coefficient (D), and electrode reaction rate constant (kf) of QS were found to be 0.87, 7.89 × 10−3 cm2⋅s−1 and 3.43 × 10−2 s−1, respectively. Under optimized conditions, linear calibration curves were obtained over the QS concentration range 3.0 × 10−6 to 1.0 × 10−4 M by square wave voltammetry, and the detection limit was found to be 0.44 μM based on the signal-to-noise ratio of 3. In addition, the novel MWCNTs-RTIL/GCE was characterized by the electrochemical impedance spectroscopy and the proposed method has been successfully applied in the electrochemical quantitative determination of quinine content in commercial injection samples and the determination results could meet the requirement.

Synthesis and electroreduction of 2-[(8-hydroxyquinoline-5-yl)azo]benzo[c]cinnoline in DMSO–H2O (1:1) medium

2-[(8-Hydroxyquinoline-5-yl)azo]benzo[c]cinnoline (HQAB) was prepared and characterized by elemental analysis, MS, FTIR and 1H NMR techniques. The electrochemical reduction of HQAB has been investigated by cyclic voltammetry, chronoamperometry and controlled potential electrolysis at mercury pool electrode in the pH range 3.5–9.4. The number of electrons transferred in the electrode reaction, diffusion coefficients and standart rate constants were calculated. In acidic medium, cyclic voltammograms display four cathodic peaks, with the total exchange of 6 e– and 6 H+. By contrast, the reverse scan displays two anodic peaks. Constant potential electrolysis at –1.0 V and TLC analysis of the product reveals that the reduction of azo group (in the bridge) in HQAB does not stop at the hydrazo stage but goes further through the cleavage of –NH–NH– linkage to give amino compounds as the final products. The voltammograms recorded in basic medium exhibit two cathodic peaks corresponding to 4 e–, 4 H+ and two reverse anodic peaks, and thus the reduction stopped at hydrazo stage. A tentative mechanism for the reduction has been suggested.

Determination of Rutin on the Poly(p-aminobenzene sulfonic acid) Modified Glassy Carbon Electrode

The electrochemical behaviors of rutin at a poly(p-aminobenzene sulfonic acid) modified glassy carbon electrode (PABSA/GC) have been investigated. Rutin can generate a pair of well-defined redox peaks at the PABSA/GC located at 0.440 V (E(pa)) and 0.396 V (E(pc)) (vs. saturated calomel electrode (SCE)), respectively. The results indicate that the reaction involves two electrons transfer, accompanied by two protons and the electrochemical process is controlled by adsorption. The electrochemical parameters of rutin on the modified electrode were calculated with the results of the charge transfer coefficient (alpha), the number of electron transfer (n) and the electrode reaction rate constant (k(s)) as 0.61, 2.08 and 2.18 s(-1), respectively. Under the selected conditions, the oxidation peak current was linear to the rutin concentration over the range of 2.5x10(-7)-1.0x10(-5) M with a detection limit of 1.0x10(-7) M. The proposed method has been successfully applied to the determination of compound rutin tablets with no interference from the coexisting ascorbic acid.