共查询到20条相似文献,搜索用时 62 毫秒
1.
Amar Prasad Yadav Atsushi Nishikata Tooru Tsuru 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2005,585(1):142-149
The mechanism of oxygen reduction on the as-polished and corroded zinc specimens has been studied using a rotating ring disc electrode (RRDE) system. On the as-polished surface, oxygen was reduced into two distinct steps. In the first step, about 44% of O2 was reduced to H2O2 in a 2-electron reaction with the rest being reduced to OH? in a 4-electron reaction. On the other hand, in the second step, with the increase of overpotential O2 was almost exclusively reduced to OH? in a 4-electron reaction. The first step reduction occurred on an air-formed oxide-covered surface at more positive potential than ?1.2 V vs. Ag/AgCl and the second step reduction (E < ?1.2 V) took place on a semi-uniformly active surface. On the corroded surface, the second step was not distinctly observed on the polarization curve, because reduction of the zinc corrosion products simultaneously took place around ?1.2 V. The O2 reduction in the first step was inhibited by deposition of the corrosion products, though the ratio of amount of O2 reduced to OH? in a 4-electron reaction was larger than that on the as-polished surface. The mechanism of oxygen reduction is discussed on the basis of results obtained from the RRDE experiment. 相似文献
2.
Shaojun Dong Xiaodan Xi Min Tian 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》1995,385(2):227-233
Three couples of reversible redox waves of the SiW12O4?40 anion which are composed of two one-electron and one two-electron processes occur in the potential range +0.1 to ?0.7 V in aqueous solutions. The first (most positive) and third (most negative) redox waves exhibit good electrocatalytic activities for nitrite reduction in acid solutions with pH < 2 for the former and with for the latter. The behavior of the third catalytic wave, which is quite unusual, was studied in detail. The rate constant governing the reduction of NO?2 by the first wave of SiW12O4?40 was measured by an ultramicrodisk electrode as 3.73 × 103 M?1 s?1. 相似文献
3.
Yasushi Hasebe Tingting Gu 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2005,576(1):177-181
A DNA–Cu(II) complex was effectively utilized as a novel electrocatalyst for an H2O2-sensing electrode. The DNA–Cu(II) complex was immobilized onto the surface of a glassy carbon (GC) electrode by polyion complex formation with poly(allylamine) (PAA). Cyclic voltammetry revealed that the copper ion embedded in the DNA/PAA layer exhibited a pair of well-defined redox peaks which is due to the Cu(II)/Cu(I) redox couple. The resulting DNA–Cu(II)/PAA/GC electrode showed excellent electrocatalytic activity for H2O2 reduction. The amperometric response to H2O2 obtained at ?0.2 V (vs. Ag∣AgCl) was rapid and highly sensitive. A calibration curve obtained in air-saturated buffer (pH 5) was linear in the concentration range from 0.1 to 135 μM with a detection limit of 0.05 μM (S/N = ca. 3). Moreover, this sensor showed long term-storage stability of more than 30 days under dry conditions 4 °C. 相似文献
4.
Noriaki Wakabayashi Masayuki Takeichi Masayuki Itagaki Hiroyuki Uchida Masahiro Watanabe 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2005,574(2):339-346
The temperature dependence of the oxygen reduction reaction (orr) activity at a platinum electrode in 0.1 M HClO4 electrolyte solution was investigated with a channel flow double electrode at 20–90 °C. We demonstrate that an apparent rate constant (kapp) for the orr can be evaluated from the hydrodynamic voltammograms by correcting the oxygen concentration in the electrolyte solution. The apparent activation energy for the kapp was found to be 38 kJ/mol at ?0.525 V vs. E0 (0.760 V vs. RHE at 30 °C). Production of H2O2 was not detected at potentials more positive than 0.3 V in the temperature region examined. One capacitive semicircle was observed in electrochemical impedance spectroscopy for the orr, suggesting the fast complete reduction of intermediates to H2O following the rate determining step of the first electron-transfer. 相似文献
5.
B.B Lalabekyan N. Tetlow R. Moonesinghe D. Martin E. Burdett J. Otto D. Wyndham E. Bettini N. Kalavrezos R.C.M. Stephens 《The British journal of oral & maxillofacial surgery》2021,59(3):297-302
Cardiopulmonary exercise testing (CPET) is used as a risk stratification tool for patients undergoing major surgery. In this study, we investigated the role of CPET in predicting day five cardiopulmonary morbidity in patients undergoing head and neck surgery. This observational cohort study included 230 adults. We recorded preoperative CPET variables and day five postoperative cardiopulmonary morbidity. Full data from 187 patients were analysed; 43 patients either had incomplete data sets or declined surgery/CPET. One hundred and nineteen patients (63.6%) developed cardiopulmonary morbidity at day five. Increased preoperative heart rate and duration of surgery were independently associated with day five cardiopulmonary morbidity. Those with such morbidity also had lower peak V?O2 11.4 (IQR 8.4-18.0) vs 16.0 (IQR 14.0-19.7) ml.kg-1.min-1, P<0.0001 and V?O2 at AT 10.6 (IQR 9.1-13.1) vs 11.5 (IQR 10.5-13.0) ml.kg-1.min-1, p=0.03. Logistic regression model containing peak V?O2 and duration of surgery demonstrated that increased peak V?O2 was associated with a reduction in the likelihood of cardiopulmonary complications OR 0.92 (95%CI 0.87 to 0.96), p=0.001. The area under the receiver operating characteristic curve for this model was 0.75(95%CI 0.68 to 0.82), p<0.0001, 64% sensitivity, 81% specificity. CPET can help to predict day five cardiopulmonary morbidity in the patients undergoing head and neck surgery. A model containing peak V?O2 allowed identification of those with such complications. 相似文献
6.
T. Thomberg E. Lust 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2000,485(1):89-93
Electroreduction of peroxodisulfate anion on an electrochemically polished Cd(0001) plane in aqueous NaF solution with different additions of Na2S2O8 was studied by rotating disc voltammetry. The rate of electroreduction of S2O2?8 depends on the electrode potential and base electrolyte concentration, i.e. on the thickness of the diffuse layer. The kinetic current densities at E=const have been obtained by the Koutecký–Levich method and used for the determination of the apparent rate constant values of electroreduction of S2O82? anion. The ψ0 potential values obtained according to the Gouy–Chapman–Grahame (GCG) model have been used for the construction of corrected Tafel plots, which were linear at E?ψ0<?1.1 V (SCE). The value of the charge transfer coefficient α decreases somewhat with the concentration of the base electrolyte solution (0.18≤α≤0.22), but the value of α is practically independent of the concentration of S2O82? ions if cNaF=const. 相似文献
7.
Shen-Ming Chen Chia-Ming Chan 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2003,543(2):161-173
Copper(II)hexacyanoferrate films have been prepared from various electrolyte aqueous solutions using consecutive cyclic voltammetry. The cyclic voltammograms recorded the direct deposition of copper(II)hexacyanoferrate films from the mixing of Cu2+ and Fe(CN)63? ions from solutions of ten cations: Li+, Na+, K+, Rb+, Mg2+, Ca2+, Sr2+, Ba2+, H+ and Al3+. An electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry were used to study the in situ growth of the copper(II)hexacyanoferrate films. The copper(II)hexacyanoferrate film showed a single redox couple that exhibited a cation effect (Li+, Na+, K+, Rb+ and Cs+) and an anion effect (F?, Cl? and Br?) in the cyclic voltammograms and formal potential of the redox couple. The electrochemical and EQCM properties of the film indicate that the redox process was confined to the immobilized copper(II)hexacyanoferrate, and the interaction between the copper(II)hexacyanoferrate film with K+ (monovalent cation) and Ca2+ (divalent cation). The electrocatalytic oxidation properties of NADH, NH2OH, N2H4, SO32? and S2O32? were also determined. The electrocatalytic reduction properties of SO52? and S2O82? by monolayered iron, nickel, and cobalt hexacyanoferrate films, and by bilayered metal–copper hexacyanoferrate films were determined. Two-layered modified electrodes and hybrid films composed of a copper(II)hexacyanoferrate film with iron(II)hexacyanoferrate, cobalt(II)hexacyanoferrate, or nickel(II)hexacyanoferrate film were prepared, and these films caused the electrocatalytic reduction of SO52? and S2O82?. 相似文献
8.
Nicolas Alonso-Vante Sandro Cattarin Marco Musiani 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2000,481(2):200-207
Composite layers consisting of a polyaniline (PANI) matrix and a molybdenum-doped ruthenium selenide (MRS) dispersed phase have been tested as cathodes for O2 reduction in 0.5 M H2SO4. The investigation, carried out on rotating disc electrodes using steady-state techniques, shows that a 4-electron reduction of O2 is efficiently carried out on PANI+MRS composites. The onset potential is close to 0.5 V (SCE) and a current plateau is observed at E<0.1 V (SCE). The overall process is under mixed control. Besides the charge transfer and mass transport in solution, either O2 diffusion in the film or partial blockage of the electrode are possible limiting factors. The performance of PANI+MRS electrodes becomes better than that of Pt in 0.5 M H2SO4 in the presence of methanol. Diminished current densities are obtained at higher pH due to a decreased O2 solubility, the conductivity of the PANI matrix being always good at pH<3. 相似文献
9.
S.Abraham John Takeyoshi Okajima Takeo Ohsaka 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》1999,466(1):67-74
This paper describes the dimerization of self-assembled monolayers (SAMs) of N-ethyl-N′-octadecylviologen (1) on GC and Au electrode surfaces in the presence of 0.1 M NH4PF6 aqueous solutions. The ‘wet’ and ‘dry’ SAMs of 1 showed multiple redox peaks for the first reduction of 1 in the presence of NH4PF6, in contrast to the case of other supporting electrolytes (typically KCl, NaNO3, Na2SO4 and NaClO4) where both wet and dry SAMs of 1 exhibited a single redox wave for the first reduction. The dry SAM showed a well defined reduction peak at ?0.57 V along with a shoulder reduction peak at ?0.50 V and two oxidation peaks at ?0.50 and ?0.42 V. On the contrary, the wet SAM gave a very sharp reduction peak at ?0.50 V and a small shoulder peak at ?0.57 V in addition to two oxidation peaks like those observed for the dry SAM. The reduction peak of ?0.50 V was ascribed to the reduction of strongly hydrated dications of 1, while the reduction peak at more negative potential (?0.57 V) was attributed to the reduction of the dehydrated dications of 1. The two oxidation peaks at ?0.50 and ?0.42 V were ascribable to the oxidation of the usual radical cation monomer and the radical cation dimer, respectively. In the case of the wet SAM, upon continuous potential cycling, the sharp reduction peak of ?0.50 V clearly decreased, whereas the more negative reduction peak of ?0.57 V was highly stable. In this case, in the oxidation process, the monomer peak of ?0.50 V increased, while the dimer peak of ?0.42 V decreased. Thus it is reasonably assumed that in the wet SAM, initially the radical cations of 1 feel an aqueous environment in the monolayer where the dimerization is highly favored and at subsequent potential cycles, due to the entry of hydrophobic anions of PF6? into the monolayer, the pre-existent water molecules are expelled from the monolayer and under this circumstance the radical cations of 1 may feel the environment very similar to non-aqueous media where the dimerization is totally suppressed. The adsorption tendency of 1 on the electrode surface was also studied using the SAMs prepared by dissolving 1 in water+ethanol mixtures of different ratios. The appearance of multiple peaks was found to depend significantly on the alkyl chain length of asymmetric viologen. The inclusion/expulsion of solvents and anions into/from the SAM during the redox reaction were studied by the electrochemical quartz crystal microbalance (EQCM). It was found that in the presence of SO42? ions ca. 17 water molecules per one SO42? ion were transported to the SAM of 1 during the oxidation, whereas ca. five water molecules were transported in the presence of PF6? ions. 相似文献
10.
Karl-Heinz Lubert Markus Guttmann Lothar Beyer 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》1999,462(2):174-180
The electrochemical behaviour of the unmodified carbon paste electrode (CPE) in the presence of [PdCl4]2? in chloride solutions of different pH (in the range from 3 to 7) is studied by cyclic voltammetry (CV). During cathodic treatment or cycling, Pd(0) is deposited in situ on the electrode surface. Results obtained at negative potentials as a function of the concentrations of Pd(II) and protons in the solution are presented. It is concluded that hydrogen ions are reduced in different ways: first, the reduction at deposited Pd(0) or the simultaneous reduction of H+ and [PdCl4]2?, respectively, which occurs during the whole cathodic cycle; second, the reduction in the potential range from about ?0.5 to ?1.0 V versus SCE, where surface groups are reduced at the unmodified CPE. The second pathway is the prevailing reduction at lower pH, which occurs at the carbon surface probably via protonated chloropalladate complexes adsorbed at the electrode surface. Potentiostatic pretreatment in the voltammetric range between 0 and +0.2 V leads in solutions of pH 5 to a pronounced increase of the H+ reduction current caused by an increase of the sorption capacity of the electrode or by the accumulation of protons at the electrode surface. Protons could be accumulated at the electrode surface by formation of protonated chloropalladate complexes at the CPE. 相似文献
11.
Michael E. Hyde Richard G. Compton 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2005,581(2):224-230
The utility of a recently derived model [M.E. Hyde, O.V. Klymenko, R.G. Compton, J. Electroanal. Chem. 534 (2002) 13] for the potentiostatic nucleation and three dimensional growth of deposits on an electrode surface under hydrodynamic conditions is demonstrated. 2.1 mM Pb2+ solution is used as the depositing species, and a wall-tube and stirred cell are used to generate conditions in which the diffusion layer thickness is in the range 10–40 μm. It is shown that the model provides excellent fits to the experimental data. The nucleation parameters N0, the number of active sites, and A, the nucleation rate are derived from analysis of the transients. These values are compared to those extracted from experiments under quiescent conditions, and also to previously reported data in which ultrasound was used to induce hydrodynamic flow. 相似文献
12.
I.G. Casella M. Gatta 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2000,494(1):12-20
A novel procedure of anodic electrodeposition of copper oxides and hydroxides on glassy carbon and noble metals electrodes in an alkaline medium is described. The deposited films have been investigated by electrochemical and by X-ray photoelectron spectroscopy (XPS) techniques. The copper films are deposited on the electrode surface as Cu(OH)2 and CuO after the dissociation of the Cu(CN)n1?n complex caused probably by the formation of CuIII species at relatively high applied potentials (i.e. 0.5 V). The resulting active copper films, independently of the electrochemical procedure adopted (i.e. potentiostatic or potentiodynamic conditions), appear to be uniform, smooth and with a good degree of adhesion on the electrode surface The electrocatalytic properties of the copper deposited films were investigated in an alkaline medium for the electrooxidation of several classes of organic compounds. 相似文献
13.
Shen-Ming Chen Sheh-Hung Hsueh 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2004,566(2):291-303
Polynuclear mixed-valent ruthenium oxide/ruthenocyanide (ruthenium oxide/hexacyanoruthenate or mvRuO/RuCN) films were prepared using consecutive cyclic voltammetry directly from the mixing of Ru3+ and Ru(CN)64? ions from solutions of two divalent cations (Ba2+ and Ca2+), and seven monovalent cations (H+, Li+, Na+, K+, Rb+, Cs+, and Ga+). The films exhibited three redox couples with Ba(NO3)2 or BaCl2 aqueous solutions, and the formal potentials of the redox couples showed a cation and pH effect. An electrochemical quartz crystal microbalance (EQCM), cyclic voltammetry, UV–visible spectroscopy, and the stopped-flow method (SFM) were used to study the growth mechanism of the mvRuO/RuCN films. The results indicated that the redox process was confined to the immobilized ruthenium oxide/ruthenocyanide. The EQCM results showed a Ba2+ ion exchange reaction for the two most negative redox couples. The electrocatalytic reduction properties of SO52?, and S2O82? by the ruthenium oxide/ruthenocyanide films were determined. The electrocatalytic oxidation of NADH and dopamine were also determined, and revealed two different types of properties. The electrocatalytic oxidations of SO32?, S2O32?, and N2H4 were also investigated. The electrocatalytic reactions of the ruthenium oxide/ruthenocyanide films were investigated using the rotating ring-disk electrode method. 相似文献
14.
Chi-Feng Cheng Ching-lun Hung Y.Oliver Su Shu-Hua Cheng 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2004,566(1):169-175
A water-soluble chromium porphyrin, [CrIIITF4TMAP]5+ (chromium(III) meso-tetrakis(2,3,5,6-tetrafluoro-N,N,N-trimethyl-4-anilinium)yl) porphyrin) was synthesized and the spectral and electrochemical properties were examined. In aqueous solution, [CrIIITF4TMAP]5+ exhibits two pKas at 7.04 and 10.07. The cyclic voltammogram showed that a reversible reduction wave appeared at ?0.84 V in pH 5.0 buffer solution, which is assigned as the CrIII/II redox couple. The oxidation formal potentials were obtained by spectroelectrochemistry. With suitable control of the oxidation potentials and solution conditions, the high valent oxo-CrIV and oxo-CrV porphyrins were obtained. The ligand trans to the oxygen atom is either H2O or OH?, depending on the pH of the solution. In this paper, oxo-CrVTF 4TMAP is thus the first reported water-soluble CrV porphyrin that can be generated electrochemically and chemically. Electrogenerated oxo-CrV porphyrin species catalyzed the oxidation of cyclopent-2-ene-1-acetic acid to cyclopent-2-ene-4-one-1-acetic acid in the presence of dioxygen and returned to oxo-CrIV porphyrin, which is not reactive toward the substrate. 相似文献
15.
Hua Cui Zhi-Feng Zhang Gui-Zheng Zou Xiang-Qin Lin 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2004,566(2):305-313
The behavior of luminol electrochemiluminescence (ECL) at a polycrystalline gold electrode was studied under conventional cyclic voltammetric (CV) conditions. At least six ECL peaks were observed at 0.28 (ECL-1), 0.56 (ECL-2), 0.95 (ECL-3), 1.37 (ECL-4), ?0.43 (ECL-5) and 1.00 (ECL-6, a broad wave after the reverse scan from +1.66) V (vs. SCE), respectively, on the curve of ECL intensity versus the potential. These ECL peaks were found to depend on the presence of O2 and N2, the pH of the solution, KCl concentration, scan rate, and potential scan ranges. The emitter of all ECL peaks was identified as 3-aminophthalate by analyzing the CL spectra. It is believed that ECL-1 at 0.28 V was correlated to luminol radicals produced by the electro-oxidation of luminol anion and ECL-2 at 0.56 V was caused by the reaction of luminol radical anions with gold oxide formed on the electrode surface. ECL-1 and ECL-2 could be strongly enhanced by O2 and O2?. ECL-3 at 0.95 V was likely to be due to the reaction of luminol radical anions with O2 oxidized by OH?. ECL-4 at 1.37 V suggested that OH? was electro-oxidized to HO2? at this potential and then to O2?, which reacted with luminol radical anions to produce light emission. ECL-5 at ?0.43 V seems to be due to the reaction of luminol with ClO? electrogenerated at higher positive potential and HO2? electrogenerated at negative potential. ECL-6 was attributed to the reaction of luminol radical anions and ClO? electrogenerated at higher positive potential. The results indicated that luminol ECL can be readily initiated by various oxygen-containing species electrogenerated at different potentials, leading to multi-channel light emissions. Furthermore, the present work also reveals that ECL-2 is a predominant ECL reaction route at a gold electrode with higher potential scan rates under CV conditions. 相似文献
16.
Shen-Ming Chen Chia-Ching Tseng 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2005,575(1):147-160
The electrocatalytic properties of two related proteins, myoglobin (Mb) and hemoglobin (Hb), immobilized in a surfactant film (didodecyldimethylammonium bromide, DDAB) on an electrode were investigated. The direct electrochemistry of the myoglobin/DDAB and hemoglobin/DDAB films was compared and showed one redox couple, two redox couples, and three redox couples, when transferred to strong acidic, weak acidic and basic, and pH 13 aqueous solutions, respectively. The redox couples and their formal potentials are pH dependent. An electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry were used to study the in situ growth of both DDAB deposition on gold disk electrodes and myoglobin deposition on DDAB film-modified electrodes. The electrocatalytic properties were investigated and showed that the myoglobin/DDAB and hemoglobin/DDAB film modified electrodes are both electrocatalytically active for oxygen reduction, and more H2O2 was produced during electrocatalytic reduction using a myoglobin/DDAB film than when using a hemoglobin/DDAB film. The electrocatalysis that was active for l-cystine, N2O, and 2,2′-dithiosalicylic acid reductions showed an electrocatalytic current developed from the cathodic peak of the redox couple at about ?0.9 V (Fe(II)/Fe(I) redox couple) in neutral and weak basic aqueous solutions. The electrocatalysis that was active for l-cysteine oxidation, showed an electrocatalytic current developed from the cathodic peak of the redox couple at about +0.2 V (Fe(III)/Fe(IV) redox couple). Mb/DDAB and Hb/DDAB film modified electrodes are electrocatalytically active for trichloroacetic acid reduction in weak acidic and basic buffered aqueous solutions through the Fe(II)/Fe(I) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about ?0.1 V (from the Fe(III)/Fe(II) redox couple) in strong acidic aqueous solutions occurs only with higher concentrations of reactant. 相似文献
17.
Ivan Roche Keith Scott 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2010,638(2):280-286
Manganese oxides nanoparticles were chemically deposited on a high area (ca. 300 m2 g−1) carbon black substrate to act as electrocatalysts for oxygen reduction. The morphology and chemistry of the carbon-supported MnOx nanoparticles was characterised by Transmission Electron Microscopy), X-ray Diffraction, and chemical analysis. The oxygen reduction reaction (ORR) catalytic activity was studied in the 7–10 pH range using a rotating disk electrode (RDE). High activity towards oxygen reduction and very good stability in neutral and slightly basic solution were obtained. At low current densities, at 25 °C, MnOx/C displayed a reaction order with respect to OH− ions of −0.5 and Tafel slopes of −0.153 and −0.167 V dec−1 at pH 7 and 10 respectively; showing that the ORR mechanism on MnOx/C is unchanged in the 7–10 pH range. From the data, we propose that the first electrochemical step of the 4-electron ORR mechanism, in the 7–10 pH range, is the quasi equilibrium proton insertion process in MnO2 yielding MnOOH (insoluble in neutral or slightly basic solution). The ORR activity of the MnOx/C materials increased with increasing temperatures from 5 to 40 °C. The 2-electron pathway of oxygen reduction, yielding hydrogen peroxides as intermediates, may however be favoured over the 4-electron O2 reduction at higher temperatures. 相似文献
18.
M.T de Groot M.T.M Koper 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2004,562(1):81-94
A study was performed to determine the influence of nitrate concentration and acidity on the reaction rate and selectivity of the electrocatalytic nitrate reduction on platinum. There are two different nitrate reduction mechanisms on platinum: a direct mechanism (0.4–0.1 V vs. SHE) and an indirect mechanism (0.9–0.5 V vs. SHE). In the direct mechanism the dependence of the reaction rate on the nitrate concentration changes with increasing nitrate concentration. Whereas at low concentrations (<0.1 M) the reaction order in nitrate is positive, at high concentrations (>0.1 M) the reaction order is negative. This suggests that at high concentrations the amount of free surface sites determines the reaction rate. These free surface sites are needed either for the adsorption of a second species necessary for the reaction (water or hydrogen) or for the dissociation of nitrate to nitrite. Both at low and high nitrate concentrations the direct reduction is mainly selective towards ammonia, although small amounts of N2O and N2 were observed using differential electrochemical mass spectrometry (DEMS) at potentials between 0.4 and 0.2 V at high concentrations of nitrate. This N2 and N2O formation seems to be related to the NOads coverage on the electrode. The indirect reduction mechanism is autocatalytic as is illustrated by its unusual stirring behavior. Large amounts of NO were observed using DEMS. This suggests that not nitrate but NO+ (? HNO2) is involved in the actual electron transfer. NO+ is reduced to NO, which then reacts with HNO3 to reproduce NO+, resulting in an overall reaction of nitrate to nitrite. Both nitrite and a high acidity are needed for this mechanism to develop, but addition of nitrite is not necessary since nitrite is present in small amounts in HNO3 solutions of concentrations over 4 M. The autocatalytic reduction mechanism slows down and eventually terminates when NO starts to react to N2O, as was observed using DEMS. 相似文献
19.
A. Wróblewska O.V. Reshetnyak E.P. Koval’chuk R.I. Pasichnyuk J. Błażejowski 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2005,580(1):41-49
The electrochemiluminescence accompanying the oxidation of luminol on platinum or graphite anodes was investigated under potentiostatic and potentiodynamic conditions in order to find out how it varies in time and with electrode potential, pH of the medium, and substrate concentration. The single-stage process observed in the range between 0 and 1 V can be attributed to the oxidation of the anion occurring as a result of H+ abstraction by OH? from one of the NH sites of luminol. The radical species thus formed undergo either disproportionation or, more probably, electrochemical oxidation (preceded by the abstraction of H+ by OH? from the remaining NH sites) to yield 5-aminophthalazine-1,4-dione. Electrochemical oxidation of the addition products of OH? to one of the carbonyl carbon atoms of this molecule, accompanied by N2 elimination, leads to radical intermediates which, after the addition of successive OH? ions, are converted to the radical anion of 3-aminophthalic acid. Electrochemical oxidation of the radical anion thereby formed – accompanied by the abstraction of H+ by OH? from one of carboxylic groups – generates electronically excited mono-anions of 3-aminophthalic acid capable of emitting light. The proposed reaction scheme is confirmed by thermodynamic data obtained at the PM3, PM3(COSMO), DFT and DFT(PCM) levels of theory. The prospective analytical applications of the direct electrochemical oxidation of luminol are mentioned. 相似文献
20.
A. Restovic E. Rı́os S. Barbato J. Ortiz J.L. Gautier 《Journal of electroanalytical chemistry (Lausanne, Switzerland)》2002,522(2):141-151
We have studied the relationships between the cation distributions in bulk and on the surface and the electrocatalytical reactivity towards the oxygen reduction reaction (orr) on thin film electrodes of cobalt and manganese spinel type oxides MnxCo3?xO4 (0≤x≤1). The cationic distributions were computed from XRD, XPS, magnetism and oxidation power measurements showing the presence of the Co3+/Co2+ and Mn4+/Mn3+ solid state redox couples and also vacancies in octahedral sites. The electrocatalytic activity and kinetic parameters for the orr were determined using the RRDE technique in 1 M KOH solution at 25 °C. Two Tafel zones of slopes bc1 and bc2 around ?60 and ?120 mV dec?1 were observed. The disk current/ring current ratio, (ID/IR), increases with x and decreases with the applied overpotential. At constant overpotential η the real electrocatalytical current densities j increase when x increases. The orr can be characterized by an intrinsic kinetic parameter J′ obtained from this current ratio at various electrode rotational frequencies. This J′ increases with the redox couple Co2+/Co3+ ratio, increasing more in the bulk than at the surface of the electrode. 相似文献