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1.
The MnIII/MnII redox couple with a standard potential of +1.51 V versus the standard hydrogen electrode (SHE) has attracted interest for the design of V/Mn redox flow batteries (RFBs). However, MnIII disproportionation leads to a loss of capacity, an increase in pressure drop, and electrode passivation caused by the formation of MnO2 particles during battery cycling. In this work, the influence of TiIV or/and VV on MnIII stability in acidic conditions is studied by formulating four different electrolytes in equimolar ratios (Mn, Mn/Ti, Mn/V, Mn/V/Ti). Voltammetry studies have revealed an ECi process for MnII oxidation responsible for the electrode passivation. SEM and XPS analysis demonstrate that the nature and morphology of the passivating oxides layer depend strongly on the electrolyte composition. Spectroelectrochemistry highlights the stabilization effect of TiIV and VV on MnIII. At a comparable pH, the amount of MnIII loss through disproportionation is decreased by a factor of 2.5 in the presence of TiIV or/and VV. Therefore, VV is an efficient substitute for TiIV to stabilize the MnIII electrolyte for RFB applications.  相似文献   

2.
The present study represents comparative analysis of voltammetric and microgravimetric behavior of active ruthenium (Ru), electrochemically passivated ruthenium (Ru/RuO2) and thermally formed RuO2 electrodes in the solutions of 0.5 M H2SO4 and 0.1 M KOH. It has been found that cycling the potential of active Ru electrode within E ranges 0 V–0.8 V and 0 V–1.2 V in 0.5 M H2SO4 and 0.1 M KOH solutions, respectively, leads to continuous electrode mass increase, while mass changes observed in alkaline medium are considerably smaller than those in acidic one. Microgravimetric response of active Ru electrode in 0.5 M H2SO4 within 0.2 V–0.8 V has revealed reversible character of anodic and cathodic processes. The experimentally found anodic mass gain and cathodic mass loss within 0.2–0.8 V make 2.2–2.7 g F?1, instead of 17 g F?1, which is the theoretically predicted value for Ru(OH)3 formation according to equation: Ru+3H2O?Ru(OH)3+3H++3e?. In the case of Ru/RuO2 electrode relatively small changes in mass have been found to accompany the anodic and cathodic processes within E range between 0.4 V and 1.2 V in the solution of 0.5 M H2SO4. Meanwhile cycling the potential of thermally formed RuO2 electrode under the same conditions has lead to continuous decrease in electrode mass, which has been attributed to irreversible dehydration of RuO2 layer. On the basis of microgravimetric and voltammetric study as well as the coulometric analysis of the results conclusions are presented regarding the nature of surface processes taking place on Ru and RuO2 electrodes.  相似文献   

3.
The electrochemical behavior of adsorbed NO molecules on a Pt(100) electrode has been studied in perchloric acid solutions by means of cyclic voltammetry. According to the literature data, a saturated NO adlayer with a coverage of ~0.5 monolayers (MLs) is formed under open circuit conditions in an acidic nitrite solution as a result of a disproportionation reaction. The saturated adlayer is stable in the potential range of 0.4–0.9 V vs. a reversible hydrogen electrode in 0.1 M HClO4. NO molecules are oxidized at 0.9–1.1 V with the formation of adsorbed nitrite anions, and they can be reduced to ammonia at potentials less than 0.4 V. In this paper it has been shown that the adlayer stability depends on the surface coverage and extent of ordering. An unsaturated NO adlayer demonstrates NO ? NH3 redox transformations at 0.5–0.8 V.  相似文献   

4.
冯谙  范利军  蔡陶  李文坡 《应用化学》2015,32(9):1081-1087
采用计时电流法沉积纳米MnO2电极材料,利用Scharifker-Hills成核理论模型分析时间-电流(i-t)曲线判断了MnO2成核机理。 对3种不同的成核方式制得的MnO2材料进行电化学超级电容性能测试、用SEM观察了其微观形貌。 比较了不同沉积方法对沉积材料结构、电容性能的影响。 计时电流测试发现,在0.1 mol/L Mn2+溶液中,电势阶跃至0.365 V,初始成核符合瞬时成核机理,在0.01 mol/L Mn2+溶液中,电势阶跃至0.418 V,初始成核存在瞬时成核和连续成核两种不同机理,在0.5 mmol/L Mn2+溶液中,电势阶跃至0.515 V,初始成核则符合连续成核机理。 超级电容性能测试发现,瞬时成核下制得的MnO2电极材料相对于另外两种成核方式得到的电极材料具有更好的电容性能,这是因为瞬时成核更易于形成多孔、纳米片(棒)状等高比表面积的沉积物,表明制备方法影响MnO2电极材料电容性能。  相似文献   

5.
《Electroanalysis》2005,17(19):1734-1739
In the present study anodic oxidation of iridium layer formed thermally on a gold‐sputtered quartz crystal electrode has been investigated by electrochemical quartz crystal microgravimetry (EQCM) in the solutions of 0.5 M H2SO4 and 0.1 M KOH. The emphasis here has been put on the microgravimetric behavior of iridium as a metal, because a few previous EQCM studies reported in literature have been devoted to iridium oxide films (IROFs). The objective pursued here has been to elucidate the nature of the main voltammetric peaks, which occur at different ranges of potential in the solutions investigated. It has been found that anodic oxidation of iridium electrode in 0.5 M H2SO4 and 0.1 M KOH solutions is accompanied by irregular fluctuations of the electrode mass at 0.4 V<E<0.8 V followed by regular increase in mass at 0.8 V<E<1.2 V. The cathodic process initially, at 1.2 V>E>0.9 V, proceeds without any or with slight increase in electrode mass, whereas at E<0.8 V a regular decrease in mass is observed. It has been found that mass to charge ratio characterizing the processes of interest is 2 to 3 g F?1in acidic medium, whereas in the case of alkaline one it is 4 to 6 g F?1. The main pair of peaks seen in the voltammograms of Ir electrode in alkaline medium at E<0.8 V is attributable to redox transition Ir(0)→Ir(III), whereas those observed in the case of acidic medium at E>0.8 V should be related to the redox process Ir(0)→Ir(IV) going via intermediate stage of Ir(III) formation. As a consequence of these redox transitions, the gel‐like surface layer consisting of Ir(III) or Ir(IV) hydrous oxides forms on the electrode surface.  相似文献   

6.
采用简单的一步水热法制备了空心海胆状二氧化锰,无需任何模板剂和表面活性剂。该材料具有3D的纳米结构,结构稳定,并由单个的二氧化锰空心管自组装而成。该纳米材料的特殊结构为其提供了高的比电容。在1mol·L-1硫酸钠电解液中,扫速为1mV·s-1的条件下,该材料的比电容值为254.6F·g-1。在电流密度为1.0A·g-1的条件下,充放电循环1000次后比电容值仍保持为初始值的97.5%。表明该材料具有良好的电容性能和稳定性,其具备用作高性能超级电容器的电极材料的潜能。  相似文献   

7.
采用简单的一步水热法制备了空心海胆状二氧化锰,无需任何模板剂和表面活性剂。该材料具有3D的纳米结构,结构稳定,并由单个的二氧化锰空心管自组装而成。该纳米材料的特殊结构为其提供了高的比电容。在1mol·L-1硫酸钠电解液中,扫速为1mV·s-1的条件下,该材料的比电容值为254.6F·g-1。在电流密度为1.0A·g-1的条件下,充放电循环1000次后比电容值仍保持为初始值的97.5%。表明该材料具有良好的电容性能和稳定性,其具备用作高性能超级电容器的电极材料的潜能。  相似文献   

8.
The polarography of uranium(Vl) in the lactate medium is studied at different pH values. At pH 1 the half-wave potential of the uranium(Vl) wave remains the same as that of the simple ion, but the limiting current increases with increasing concentration of lactate; disproportionation of uranium(V) at the electrode surface is suggested. The rate of disproportionation is calculated. Polarograms observed in the region of pH 5 and 6 are interpreted on the basis of complexation of UO22+.  相似文献   

9.
Potassium manganese oxides were prepared by cathodic deposition from aqueous KMnO4 solution on an indium tin oxide slide. The products were characterized by XRD, XPS and SEM techniques. The as-prepared products were potassium manganese oxides with different manganese valence states. The component, morphology and size of the products could be controlled through adjusting the preparation parameters such as deposition potential, deposition time and acidity of the electrolyte. The results show that the deposition of potassium manganese oxide from aqueous KMnO4 is a pH value dependent procedure. Due to the facilitating of intercalation and deintercalation of cations, the specific capacitance of the products deposited for 500 s is higher than that indicate that the reversibility and performance of these potassium manganese oxides are also changed with the deposition time.  相似文献   

10.
The electrochemical behavior of a film, which consists of intermediate products of the α,α,α′,α′-tetrabromo-para-xylol (TBX) reduction and is deposited on a glassy-carbon electrode from 5 × 10?2 M TBX solutions, is studied in 0.1 M Bu4NBF4 solution in DMFA by cycling the potential from 0 to ?1.4 V with respect to an aqueous saturated calomel electrode. When the potential is cycled from 0 to ?2.1 V in a cell filled with the supporting electrolyte, the film, which is assumed to have the (-BrHC-C6H4-CHBr-)n composition, can be reduced to form poly(para-phenylenevilylene) (PPV). This film exhibits redox activity in the cathodic range in solutions of Bu4NBF4 in DMFA and in both cathodic and anodic ranges in solutions of Bu4NBF4 in AN. It is observed for the first time that, if the cathodic limit of the potential cycling range is extended to ?2.5 V, the cathodic doping of PPV at potentials below ?2 V disappears and a new reversible redox process takes place at more negative potentials.  相似文献   

11.
The behaviour of homocysteine and cysteine at mercury electrodes is compared. The one-electron oxidation associated with thiols is shown to be the same for both compounds in acidic phosphate buffer, giving rise to an adsorbed thiol—mercury complex, (RS)2Hg, at the electrode surface. Formation of this complex is utilized in the cathodic stripping voltammetric determination of homocysteine; the detection limit is 10?9 M after a deposition time of 90 s at a hanging mercury drop electrode. The similar E12 values for homocysteine and cysteine mean that prior separation is needed for their individual determination. Amperometric detection with a mercury-coated goal electrode after separation by cation-exchange liquid chromatography provides a method for the simultaneous determination of both compounds. Reduction of homocystine at the mercury electrode is also compared to that of cystine. The more negative reduction potential, and the maximum observed for homocystine on d.c. polarograms, which is not seen for cystine, is attributable to different reaction kinetics at the mercury electrode; the products of both the 2-electron reductions are the corresponding thiol-containing amino acids.  相似文献   

12.
The Randles–Sev?ik relationship has been applied to evaluate atomic hydrogen diffusivity in massive LaNi5 intermetallic compound. The electrode was cathodically hydrogenated in 6 M KOH solution (22 °C), and then voltammetry measurements were carried out at various, very slow potential scan rates (υ?=?0.01–0.1 mV?·?s?1). At potentials more noble than the equilibrium potential of the H2O/H2 system, the anodic peaks were registered as a consequence of oxidation of hydrogen absorbed in cathodic range. The peak potentials linearly increase with the logarithm of the scan rate with a slope of 0.059 V. The slope testifies to a symmetric charge transfer process with symmetry factor α?=?½. The peak currents linearly increase with the square root of the potential scan rate, and the straight line runs through the origin of the coordinate system. The slope of the I a (peak) ?=?f(υ 1/2) straight line is a measure of the atomic hydrogen diffusion coefficient. Assuming the hydrogen concentration in the LaNi5 material after cathodic exposure to be C 0,H?=?0.071 mol?·?cm?3 (63 % of theoretical value), the hydrogen diffusion coefficient equals D H?=?2.0?·?10?9 cm2s?1. Extrapolation of rectilinear segments of potentiodynamic polarization curves with Tafel slopes of 0.12 V and linear polarization dependencies from voltammetry tests allowed the exchange current densities of the H2O/H2 system on the tested material to be determined. The exchange current densities on initially hydrogenated LaNi5 alloy are close to 1 mA?·?cm?2, irrespective of the electrode potential scan rate.  相似文献   

13.
A study of the mechanism by which bismuth is electrodissolved in an aqueous solution of thiourea on the background of H2SO4 demonstrated that, in the thiourea concentration range 0.001 M < c < 0.5 M, a current oscillation is observed in cyclic voltammograms at E ≈ 0.4–0.3 V when the potential is swept from the anodic to the cathodic region. This oscillation is due to the loosening of the passivating film formed in the anodic process. It is shown that thiourea is not oxidized to formamidine disulphide at the bismuth electrode. thiourea and formamidine disulphide have mutually opposite effects on the height of the cathodic peak: the peak current falls with increasing thiourea concentration and grows with increasing formamidine disulphide concentration. According to the results of an X-ray fl uorescence analysis, sulfur is formed on the bismuth electrode upon its prolonged polarization of in a 0.5 M solution of thiourea. An explanation is provided for the experimental facts observed in the study.  相似文献   

14.
The synthesis and X-ray structure of a new manganese(V) mesitylimido complex with a tetraamido macrocyclic ligand (TAML), [MnV(TAML)(N-Mes)] ( 1 ), are reported. Compound 1 is oxidized by [(p-BrC6H4)3N ]+.[SbCl6] and the resulting MnVI species readily undergoes H-atom transfer and nitrene transfer reactions.  相似文献   

15.
The apparent values of n for the reduction of NO, HNO2 and NO2 in acidic halide solutions of intermediate concentration have been determined coulometrically. The value of napp for HNO2 is 1.0 in HCl solutions for intermediate flow rates at potential values in the range of the first two cathodic waves observed in voltammetric data. The value of napp exceeds 1.0 at low flow rate. The values of napp for reductions of NO in 5 M HC1 and NO2 in 3.0 M HClO4 containing 0.1 M bromide are 0.5. These results are explained on the basis of chemical reactions coupled to the electrode processes.  相似文献   

16.
The electrochemical oxidation of the alkaloid laudanosine (Ia) to O-methylflavinantine (II) has been studied in acetonitrile solvent. Using cyclic voltammetry, rotating disc voltammetry and preparative electrolyses on several alkaloids, simple aliphatic amines and aromatic compounds, some aspects of the mechanism of this coupling reaction are elucidated. The first anodic wave for laudanosine at platinum has Ep=0.55 V vs. Ag/Ag+. The electrode rapidly becomes partially passivated at potentials above 0.5 V. This is due to a film which “dissolves” below 0.5 V, at a rate independent of the potential. It is shown that the reaction (Ia)→(II) proceeds at 0.5 V by initial oxidation of the amine moiety. If acids such as sodium bicarbonate are added to the anolyte the amine is protonated causing the first wave to disappear. Oxidation at 1.1 V under these acidic conditions produces the same product, but more rapidly and in significantly higher yield because electrode filming and side reactions resulting from the amine oxidation are abrogated.  相似文献   

17.
The preparation of a series of six and seven coordinate manganese(II) complexes [Mn(II)(L)X]+, and [Mn(II)(L)X2]2? (X = halide, water, triphenylphosphine oxide, imidazole, 1-methyl imidazole and pyridine) incorporating the pentadentate planar macrocylic ligand L is described. Cyclic voltammetry of these complexes in acetonitrile each shows a reversible one-electron reduction wave near - 1.4 V vs a Ag/AgNO3 reference electrode. Quantitative reduction of these complexes by controlled potential electrolysis at a platinum gauze at - 1.4 V yields the corresponding one-electron reduction products which have been shown by ESR spectroscopy to be manganese(II)-ligand radical species, the electron being thought to reside on the di-imino pyridine moiety of the macrocyclic ligand. No metal reduced species could be isolated even in the presence of π-acceptor ligands such as CO or phosphines.  相似文献   

18.
Standard rate constants of charge transfer (k s) on platinum and glassy carbon electrodes for Nb(V)/Nb(IV) redox pair in the NaCl-KCl-K2NbF7 melt are determined using the method of cyclic voltammetry in the temperature range of 973 to 1123 K. It is found that k s increases with increasing temperature and when we pass from glassy carbon to platinum electrode. The “apparent” activation energies of charge transfer are determined; it is shown that the charge transfer between the Nb(V) and Nb(IV) complexes is quasi-reversible and is controlled predominantly by the diffusion.  相似文献   

19.
Voltammetric responses of Ni, Cu, Ag, Pt and glassy carbon (GC) electrodes in triethylamine-tris(hydrogen fluoride) medium in the anodic as well cathodic potential region were investigated. AAS as well as SEM measurements were also made to ascertain the dissolution rate and surface transformation due to fluoride film formation on the electrode surfaces. On Ni, bulk NiF2 film growth occurs only around 4.0 V following a thin NiF2 monolayer formation around 0 V. The NiF2 film shows very little solubility in the medium. Monolayer and bulk CuF2 phases are formed quite close to each other on Cu during anodic polarization. The anodically formed CuF2 dissolves to the extent of 12% in this medium. AgF formation follows a different mechanism during the first and subsequent anodic sweeps. The effect of MeCN as well as water addition on the solubility and stability of these fluoride films are also reported. Glassy carbon and Pt electrodes are relatively inert in this medium. Anodic voltammetric responses for other reactive species could be observed only on Pt and GC electrodes. On the cathodic side, all the electrodes show inert behaviour. Electrochemical reduction of PhNO2, for example, could be observed on all the electrodes. Electronic Publication  相似文献   

20.
Manganese(V)–oxo–porphyrins are produced by the electron‐transfer oxidation of manganese–porphyrins with tris(2,2′‐bipyridine)ruthenium(III) ([Ru(bpy)3]3+; 2 equiv) in acetonitrile (CH3CN) containing water. The rate constants of the electron‐transfer oxidation of manganese–porphyrins have been determined and evaluated in light of the Marcus theory of electron transfer. Addition of [Ru(bpy)3]3+ to a solution of olefins (styrene and cyclohexene) in CH3CN containing water in the presence of a catalytic amount of manganese–porphyrins afforded epoxides, diols, and aldehydes efficiently. Epoxides were converted to the corresponding diols by hydrolysis, and were further oxidized to the corresponding aldehydes. The turnover numbers vary significantly depending on the type of manganese–porphyrin used owing to the difference in their oxidation potentials and the steric bulkiness of the ligand. Ethylbenzene was also oxidized to 1‐phenylethanol using manganese–porphyrins as electron‐transfer catalysts. The oxygen source in the substrate oxygenation was confirmed to be water by using 18O‐labeled water. The rate constant of the reaction of the manganese(V)–oxo species with cyclohexene was determined directly under single‐turnover conditions by monitoring the increase in absorbance attributable to the manganese(III) species produced in the reaction with cyclohexene. It has been shown that the rate‐determining step in the catalytic electron‐transfer oxygenation of cyclohexene is electron transfer from [Ru(bpy)3]3+ to the manganese–porphyrins.  相似文献   

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