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1.
The kinetics of the redox reaction between mandelic acid (MA) and ceric sulfate have been studied in aqueous sulfuric acid solutions and in H 2SO 4? MClO 4 (M + = H +, Li +, Na +) and H 2SO 4? MHSO 4 (M + = Li +, Na +, K +) mixtures under various experimental conditions of total electrolyte concentration (that is, ionic strength) and temperature. The oxidation reaction has been found to occur via two paths according to the following rate law: rate = k[MA] [Ce(IV)], where k = k1 + k2/(1 + a) 2[HSO 4?] 2 = k1 + k2/(1 + 1/a) 2[SO 42?] 2, a being a constant. The cations considered exhibit negative specific effects upon the overall oxidation rate following the order H + ? Li + < Na + < K +. The observed negative cation effects on the rate constant k1 are in the order Na + < Li + < H +, whereas the order is in reverse for k2, namely, H + ? Li + < Na +. Lithium and hydrogen ions exhibit similar medium effects only when relatively small amounts of electrolytes are replaced. The type of the cation used does not affect significantly the activation parameters. 相似文献
2.
Owing to the high lability of cations in the three-dimensional framework of K 1+x
Mo 12S 14 (0 ≤ x ≤ 1.6), first-principles calculations and electrochemical methods have been carried out to study the insertion of cations
in the empty channels of this compound. The cavity microelectrode that is a suitable electrode for powder material analysis
has been used in voltammetric experiments. Results obtained for Li +, Na +, Rb +, K +, Cs + and NH 4
+ cations are presented and discussed. 相似文献
3.
The enthalpy changes of salting process of hen-egg
white lysozyme in buffer acetate solutions (pH=4.25) as a function of concentration
of following electrolytes: LiCl, KCl, K 2SO 4,
Li 2 SO 4 and (NH 4) 2SO 4
are determined. Obtained data according to McMillan and Mayer’s approach,
has been analyzed in the terms of the enthalpic pairwise interaction coefficients:
lysozyme – lysozyme hxx,
and lysozyme – salt hxy.
The ability of cations to precipitate lysozyme solution in relation to the
concentration of cations can be seen from the series as follows: Li +>
Na +>K +>NH 4+ + 相似文献
4.
The electrochemical performances of the α-, γ-, and δ-MnO 2 with different crystallographic structures were systematically investigated in 0.5 mol/L Li 2SO 4, 0.5 mol/L Na 2SO 4, 1 mol/L Ca(NO 3) 2, and 1 mol/L?Mg(NO 3) 2 electrolytes. The results showed that the electrochemical performances of the manganese dioxides depended strongly on the crystallographic structures of MnO 2 as well as the cation in the electrolytes. Because the δ-MnO 2 consists with layers of structure and the interlayer separation is 7 Å, which is suitable for insertion/extraction of some alkaline and alkaline–earth cations, the δ-MnO 2 electrode showed the higher specific capacitance than that of α-MnO 2 and γ-MnO 2. We also found that the α-, γ-, and δ-MnO 2 electrodes in the Mg(NO 3) 2 electrolyte showed a higher specific capacitance, while all the α-, γ-, and δ-MnO 2 electrodes in the Li 2SO 4 electrolyte exhibited a better cycle life. The reason for the different behavior of Li + and Mg 2+ during the charge/discharge process can be ascribed to the charge effect of the cations in the electrolytes. The ex situ X-ray diffraction (XRD) and long-time cyclic voltammogram measurements were used to systematically study the energy storage mechanism of MnO 2-based electrodes. A progressive crystallinity loss of the materials is also observed upon potential cycling at the oxidized states. A reasonable charge/discharge mechanism is proposed in this work. 相似文献
5.
The ion-exchange equilibrium of protons in SO 3H groups of a sulfonic cation exchanger based on immobilized cis-tetraphenylcalix[4]resorcinolarene with cations of Li +, Na +, Ag +, Cu 2+, In 3+, and protonated 1,3,5,7-tetraazaadamantane in aqueous solutions of electrolytes at 293 K was studied. The corrected coefficients of the cation exchange selectivity were calculated. 相似文献
6.
Understanding cation (H +, Li +, Na +, Al 3+, etc.) intercalation/de‐intercalation chemistry in transition metal compounds is crucial for the design of cathode materials in aqueous electrochemical cells. Here we report that orthorhombic vanadium oxides (V 2O 5) supports highly reversible proton intercalation/de‐intercalation reactions in aqueous media, enabling aluminum electrochemical cells with extended cycle life. Empirical analyses using vibrational and x‐ray spectroscopy are complemented with theoretical analysis of the electrostatic potential to establish how and why protons intercalate in V 2O 5 in aqueous media. We show further that cathode coatings composed of cation selective membranes provide a straightforward method for enhancing cathode reversibility by preventing anion cross‐over in aqueous electrolytes. Our work sheds light on the design of cation transport requirements for high‐energy reversible cathodes in aqueous electrochemical cells. 相似文献
7.
The electrochemical performances of activated carbon (AC) in 0.5 mol/l Li 2SO 4, Na 2SO 4 and K 2SO 4 aqueous electrolytes were investigated. The cyclic voltammetric results at different scan rates show that the rate behaviors of AC in the three electrolytes improve in the order of Li 2SO 4 < Na 2SO 4 < K 2SO 4. This improvement can be mainly ascribed to the following two reasons: (1) the decreasing equivalent series resistance in the order of Li 2SO 4 > Na 2SO 4 > K 2SO 4, which is the main factor influencing the maximum output power, and (2) the increasing migration speed of hydrated ions in the bulk electrolyte and in the inner pores of AC electrode in the order of Li + < Na + < K +. Their cycling behaviors do not show any differences in capacitive fading. The above results provide valuable information to explore new hybrid supercapacitors. 相似文献
8.
Herein, the effect of the alkali cation (Li +, Na +, K +, and Cs +) in alkaline electrolytes with and without Fe impurities is investigated for enhancing the activity of nickel oxyhydroxide (NiOOH) for the oxygen evolution reaction (OER). Cyclic voltammograms show that Fe impurities have a significant catalytic effect on OER activity; however, both under purified and unpurified conditions, the trend in OER activity is Cs + > Na + > K + > Li +, suggesting an intrinsic cation effect of the OER activity on Fe‐free Ni oxyhydroxide. In situ surface enhanced Raman spectroscopy (SERS), shows this cation dependence is related to the formation of superoxo OER intermediate (NiOO ?). The electrochemically active surface area, evaluated by electrochemical impedance spectroscopy (EIS), is not influenced significantly by the cation. We postulate that the cations interact with the Ni?OO ? species leading to the formation of NiOO ??M + species that is stabilized better by bigger cations (Cs +). This species would then act as the precursor to O 2 evolution, explaining the higher activity. 相似文献
9.
Understanding cation (H +, Li +, Na +, Al 3+, etc.) intercalation/de-intercalation chemistry in transition metal compounds is crucial for the design of cathode materials in aqueous electrochemical cells. Here we report that orthorhombic vanadium oxides (V 2O 5) supports highly reversible proton intercalation/de-intercalation reactions in aqueous media, enabling aluminum electrochemical cells with extended cycle life. Empirical analyses using vibrational and x-ray spectroscopy are complemented with theoretical analysis of the electrostatic potential to establish how and why protons intercalate in V 2O 5 in aqueous media. We show further that cathode coatings composed of cation selective membranes provide a straightforward method for enhancing cathode reversibility by preventing anion cross-over in aqueous electrolytes. Our work sheds light on the design of cation transport requirements for high-energy reversible cathodes in aqueous electrochemical cells. 相似文献
10.
The influence of electrolyte pH, the presence of alkali metal cations (Na +, K +), and the presence of O 2 on the interfacial water structure of polycrystalline gold electrodes has been experimentally studied in detail. The potential of maximum entropy (PME) was determined by the laser-induced current transient (LICT) technique. Our results demonstrate that increasing the electrolyte pH and introducing O 2 shift the PME to more positive potentials. Interestingly, the PME exhibits a higher sensitivity to the pH change in the presence of K + than Na +. Altering the pH of the K 2SO 4 solution from 4 to 6 can cause a drastic shift in the PME. These findings reveal that, for example, K 2SO 4 and Na 2SO 4 cannot be considered as equal supporting electrolytes: it is not a viable assumption. This can likely be extrapolated to other common “inert” supporting electrolytes. Beyond this, knowledge about the near-ideal electrolyte composition can be used to optimize electrochemical devices such as electrolyzers, fuel cells, batteries, and supercapacitors. 相似文献
11.
Electrochemical intercalation of C 60 films from aqueous LiOH, KOH, NaOH, RbOH and CsOH solutions was studied by electrochemical methods and Raman spectroscopy. The intercalation of these alkali metals cations gives rise to reduction peaks at different applied potentials depending on the chemical nature of the cation used. Reduction of the C 60 films was observed to rather different extents depending on the composition of the working solution. Electrochemical and Raman experiments show that K + and Cs + ions form the most stables and active salts, while Li +, Na + and Rb + are not significantly intercalated. Furthermore, Raman characterization of the K + and Cs + doped films leads to the identification of the its main components, namely the K 2C 60 and CsC 60 species. 相似文献
12.
Performance of dye-sensitized nano-crystalline TiO2 thin film-based photo-electrochemical solar cells (PECSCs) containing gel polymer electrolytes is largely governed by the nature of the cation in the electrolyte. Dependence of the photovoltaic performance in these quasi-solid state PECSCs on the alkaline cation size has already been investigated for single cation iodide salt-based electrolytes. The present study reports the ionic conductivity dependence on the nature of alkaline cations (counterion) in a gel polymer electrolyte based on binary iodides. Polyacrylonitrile-based gel polymer electrolyte series containing binary iodide salts is prepared using one of the alkaline iodides (LiI, NaI, KI, RbI, and CsI) and tetrapropylammonium iodide (Pr4NI). All the electrolytes based on binary salts have shown conductivity enhancement compared to their single cation counterparts. When combined with Pr4NI, each of the Li+, Na+, K+, Rb+, and Cs+ cation containing iodide salts incorporated in the gel electrolytes has shown a room temperature conductivity enhancement of 85.59, 12.03, 12.71, 20.77, and 15.36%, respectively. The conductivities of gel electrolytes containing binary iodide systems with Pr4NI and KI/RbI/CsI are higher and have shown values of 3.28, 3.43, and 3.23 mS cm−1, respectively at room temperature. The influence of the nature of counterions on the performance of quasi-solid state dye-sensitized solar cells is investigated by assembling two series of cells. All the binary cationic solar cells have shown more or less enhancements of open circuit voltage, short circuit current density, fill factor, and efficiency compared to their single cation counterparts. This work highlights the importance of employing binary cations (a large and a small) in electrolytes intended for quasi-solid state solar cells. The percentage of energy conversion efficiency enhancement shown for the PECSCs made with electrolytes containing Pr4NI along with Li+, Na+, K+, Rb+, and Cs+ iodides is 260.27, 133.65, 65.27, 25.32, and 8.36%, respectively. The highest efficiency of 4.93% is shown by the solar cell containing KI and Pr4NI. However, the highest enhancements of ionic conductivity as well as the energy conversion efficiency were exhibited by the PECSC made with Li+-containing binary cationic electrolyte. 相似文献
13.
以FeCl 3-甲基橙(MO)为模板, 通过化学原位聚合法成功制备出氧化石墨烯/聚吡咯(GO/PPy)插层复合材料. 采用X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、扫描电镜(SEM)和透射电镜(TEM)等测试技术对复合材料进行物性表征. 此外, 利用循环伏安、恒电流充放电和交流阻抗测试方法对复合材料在两种不同水系电解液(1 mol·L -1 Na 2SO 4和1 mol·L -1 H 2SO 4)中的电化学性能进行了研究. 结果显示: 氧化石墨烯和聚吡咯表现出各自优势并发挥协同作用, 使得GO/PPy插层复合材料在中性和酸性电解液中都显示出可观的比电容. 电流密度为0.5 A·g -1时, GO/PPy 插层复合材料在Na 2SO 4和H 2SO 4电解液中的比电容分别为449.1 和619.0 F·g -1, 明显高于纯PPy的比电容. 经过800 次循环稳定性测试后, 两种不同电解液中, 复合材料初始容量的保持率分别为92%和62%. 其中酸性电解液体系中初始容量更大, 而中性溶液中具有更稳定的循环性能. 相似文献
14.
Silicon oxide-coated lithium aluminum layered double hydroxide (Li xAl 2-LDH@SiO 2) nanocrystals (NCs) are investigated to selectively separate lithium cations in aqueous lithium resources. We directly synthesized Li xAl 2-LDH NC arrays by oxidation of aluminum foil substrate under a urea and lithium solution. Various lithium salts, including Cl −, CO 32−, NO 3−, and SO 42−, were applied in aqueous solution to confirm the anion effect on the captured and released lithium quantity of the Li xAl 2-LDH NCs. In a 5% solution of sulfate ions mix with lithium chloride, the Li xAl 2-LDH NCs separated a larger quantity of lithium than in other anion conditions. To enhance regeneration stability and lithium selectivity, thin layers of SiO 2 were coated onto the Li xAl 2-LDH nanostructure arrays for inhibition of nanostructure destruction after desorption of lithium cations in hot water. The Li xAl 2-LDH@SiO 2 nanostructures showed enhanced properties for lithium adsorption, including increase of stable regeneration cycles from three to five cycles, and they showed high lithium selectivity in the Mg 2+, Na +, and K + cation mixed aqueous resource. Our nanostructured LDH lithium adsorbents would provide a facile and efficient application for cost-efficient and large-scale lithium production. 相似文献
15.
Cobalt hexacyanoferrate films are synthesized on a glassy carbon electrode with sodium, potassium, and ammonium salts in the
supporting electrolyte. The electrochemical behavior of the modified electrode is studied in individual solutions of the salts
and in their mixtures. The change in electrochemical properties of cobalt hexacyanoferrate agrees with an increase in the
interaction of cations with the film in the series Li +, Na +, K +, NH
4
+
, Cs +. The effect of the energy of interaction between the modify ing-substance crystal lattice and counter-ions on the electrochemical
processes is discussed 相似文献
16.
The rate of the cerium (IV) oxidation of p-chloromandelic acid has been studied in perchlorate media at an ionic strength of 1.50 mol/dm 3 by the stopped-flow technique and in H 2SO 4? MHSO 4 (M + = Li +, Na +, K +) and H 2SO 4? MClO 4 (M + = H +, Li +, Na +) mixtures at constant total electrolyte concentrations of 1.00 and 2.00 mol/dm 3 using the conventional spectrophotometric method. In perchlorate media the kinetic data indicate the formation of two intermediate complexes between cerium (IV) and the organic substrate, but only one is significantly involved in the intramolecular electron-transfer process. The oxidation rate is markedly lower in sulfate media, where two reaction paths have been found to contribute to the overall redox reaction. The univalent cations examined exhibit negative specific effects upon the overall oxidation rate increasing in the order H + < Li + < Na + < K +. Activation parameters have been also estimated. 相似文献
17.
An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH 4+, Li +, Na + and K +), anions (SO 42− and NO 3−) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry. 相似文献
18.
2D titanium carbide (Ti 3C 2T x MXene) showed good capacitance in both organic and neat ionic liquid electrolytes, but its charge storage mechanism is still not fully understood. Here, electrochemical characteristics of Ti 3C 2T x electrode were studied in neat EMI-TFSI electrolyte. A capacitive behavior was observed within a large electrochemical potential range (from − 1.5 to 1.5 V vs. Ag). Intercalation and de-intercalation of EMI + cations and/or TFSI − anions were investigated by in-situ X-ray diffraction. Interlayer spacing of Ti 3C 2T x flakes decreases during positive polarization, which can be ascribed to either electrostatic attraction effect between intercalated TFSI − anions and positively charged Ti 3C 2T x nanosheets or steric effect caused by de-intercalation of EMI + cations. The expansion of interlayer spacing when polarized to negative potentials is explained by steric effect of cation intercalation. 相似文献
19.
Polarographic and voltammetric methods were employed to study the influence of N-methylpyrrolidinone(2) (NMP) and N-methylthiopyrrolidinone(2) (NMTP) towards a series of cations. In NMP reversible electrode reactions were observed for Na +, K +, Tl +, Zn 2+, Cd 2+, Cu 2+, Ag + and irreversible reductions for Ba 2+, Mn 2+, Co 2+ and Ni 2+. 0.1 mol l ?1 tetraethylammoniumperchlorate solutions served as supporting electrolytes. Li + was not electroactive in the supporting electrolyte mentioned, but yielded an irreversible cathodic wave in tetra-n-butylammonium perchlorate. In NMTP, Li +, Na +, Tl +, Zn 2+, Cd 2+, Cu + and Ag + gave reversible cathodic waves on the DME, while Mn 2+, Co 2+ and Ni 2+ were reduced in an irreversible electrode process. Bisbiphenylchromium iodide serving as a reference system throughout this study showed reversible behaviour in both solvents. A comparison of E1/2 for given ions in both solvents showed a shift of about 0.5 V to more positive values in the case of a typically hard cation such as Na + whereas soft cations such as Ag + and Cu + shifted by more than 0.8 V to more negative values. The effects of these two solvents on the cations studied is discussed in terms of donor acceptor interactions between the cation and the solvent molecules with special respect to the changes caused by replacing the oxygen atom in NMP by a sulphur atom. 相似文献
20.
3‐Phenyl‐ and 3‐(p‐methoxyphenyl)‐7,8‐dihydroxy and ‐6,7‐dihydroxychromenones were prepared from ethyl 3‐oxo‐2‐phenylpropanoate, ethyl 3‐oxo‐2‐(4‐methoxyphenyl)‐propanoate and the trihydroxy benzenes in H 2SO 4. 3‐Aryl‐7,8‐ and 3‐aryl‐6,7‐dihydroxy‐2H‐chromenones reacted with the bis‐dihalides of poly‐glycols in DMF/MeCO 3 to afford 12‐Crown‐4, 15‐Crown‐4 and 18‐Crown‐6‐chromenones. The products were identified with IR, 1H NMR, low and high resolution mass spectroscopy and elemental analysis. Some 1:1 cation association constants, K b, of the 3‐phenyl chromenone crown ethers with Li +, Na +, K + and Rb + cations were studied by steady state emission fluorescence spectroscopy; K b chromenone‐crown complexes displayed crown ether‐cation binding selectivity rules properly in acetonitrile. 相似文献
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