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Enn Lust Gunnar Nurk Silvar Kallip Indrek Kivi Priit Möller 《Journal of Solid State Electrochemistry》2005,9(10):674-683
The analysis of the medium temperature half-cell Ce0.8Gd0.2O1.9|70 wt% La0.6Sr0.4CoO3- (LSCO) + 30 wt % Ce0.8Gd0.2O1.9 (CGO) has been made by electrochemical impedance, cyclic voltammetry and chronoamperometry. The shape of complex impedance plots depends on temperature and cathodic polarisation of the electrode. Nyquist (Z, Z-) plots were fitted by equivalent circuit taking into account the electrolyte properties (at very high frequencies), charge transfer process at grain boundaries (at high frequencies), and medium and low frequency O2 reduction process at the cathode surface and inside the porous cathode material. Two different time constants have been obtained for the cathode process, i.e. for electroreduction of oxygen. It was found that the addition of CGO into the cathode material (LSCO) only somewhat decreases the surface catalytic activity but the noticeably higher low-frequency resistance (i.e. mainly diffusion-like mass transfer resistance RD) values at lower temperatures have been calculated. It was found that the mainly bulk diffusion-limited process at T773 K deviates toward the kinetically mixed process (diffusion + charge transfer) with increasing temperature. 相似文献
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Physicochemical properties and compositions of KxH(3-x)PW12O40 salts, where 2 < or = x < or = 3, have been investigated. It has been found that freshly prepared K2HPW12O40 salt (drying at 313 K) contains particles of heteropolyacid and particles of the neutral potassium salt, the sample being in 78.6% amorphous. On aging at room temperature, the heteropolyacid spreads to form a surface layer covering the neutral potassium salt particles K3PW12O40. Heat treatment of KxH(3-x)PW12O40 salts, where 2 < or = x < 3, from 313 K to higher temperatures induces the transformation of the heteropolyacid-covering K(3) core into a well-dispersed, amorphous surface layer. On further heating of the acidic potassium salts, the surface layer decomposes between 855 and 915 K with the formation of a PW8O26-type bronze as a new phase, the K3PW12O40 salt remaining unchanged. The latter starts to decompose at 1093 K, and in the case of all samples, the process is completed at about 1183 K. Rietveld structure refinement, XPS, and 31P NMR measurements of acidic potassium salts indicate that the core of these salts is always formed by the K3PW12O40 salt, which is covered by a heteropolyacid. Comparison of lattice parameters of the K3 salt and HPW leads to the conclusion that the layer is composed of partially or completely dehydrated heteropolyacid molecules. The coverage of the core by HPW in the K2 sample was estimated to be equal to one monolayer. 相似文献
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Enn?LustEmail author Alar?J?nes Tanel?P?rn Priit?Nigu 《Journal of Solid State Electrochemistry》2004,8(4):224-237
Electrochemical characteristics for the nanoporous carbon|Et4NBF4+acetonitrile interface have been studied by cyclic voltammetry and impedance spectroscopy methods. The influence of the electrolyte concentration and thickness of the nanoporous electrode material on the shape of the cyclic voltammetry and impedance curves has been established and the reasons for these phenomena are discussed. A value of zero charge potential, depending slightly on the structure and concentration of the electrolyte, the region of ideal polarizability and other characteristics have been established. The nanoporous nature of the carbon electrodes introduces a distribution of resistive and capacitive elements, giving rise to complicated electrochemical behaviour. Analysis of the complex plane plots shows that the nanoporous carbon|Et4NBF4+acetonitrile electrolyte interface can be simulated by an equivalent circuit, in which two parallel conduction paths in the solid and liquid phases are interconnected by the double-layer capacitance in parallel with the complex admittance of the hindered reaction of the charge transfer or of the partial charge transfer (i.e. adsorption stage limited) process. The values of the characteristic frequency depend on the electrolyte concentration and electrode potential, i.e. on the nature of the ions adsorbed at the surface of the nanoporous carbon electrode. The value of the solid state phase resistance established is independent of the thickness of the electrode material. 相似文献
4.
Indrek Koppel Tamara Aid-Pavlidis Kaur Jaanson Mari Sepp Priit Pruunsild Kaia Palm T?nis Timmusk 《BMC neuroscience》2009,10(1):68
Background
Brain-derived neurotrophic factor (BDNF) is a small secreted protein that has important roles in the developing and adult nervous system. Altered expression or changes in the regulation of the BDNF gene have been implicated in a variety of human nervous system disorders. Although regulation of the rodent BDNF gene has been extensively investigated, in vivo studies regarding the human BDNF gene are largely limited to postmortem analysis. Bacterial artificial chromosome (BAC) transgenic mice harboring the human BDNF gene and its regulatory flanking sequences constitute a useful tool for studying human BDNF gene regulation and for identification of therapeutic compounds modulating BDNF expression. 相似文献5.
Cellobiohydrolases (CBH-s) attack primarily from the cellulose chain ends. It is known that CBH-s can differ in their chain
end preference. Here the cellulose reducing end-specific fluorescence labeling was studied with the aim to find the most suitable
labeled cellulose for easy determination of CBH-s chain end preference. Anthranilic acid (AA) was used as fluorescence label.
Bacterial cellulose, amorphous Avicel and filter paper were subjected to the labeling. Suitability of modified bicincoic acid
method for determination of reducing groups on cellulose was also confirmed. AA labeled celluloses were hydrolysed with family
7 and 6 CBH-s from Trichoderma reesei and Phanerochaete chrysosporium. Hydrolysis data were plotted as released label (%) versus total degradation (%) (progress curves). Most characteristic progress curves were obtained with AA labeled regenerated amorphous
Avicel where the family 6 CBH-s produced clearly upward curved progress curves confirming their preference for non-reducing
ends. 相似文献
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In this study, we introduced a simple and sensitive method of capillary electrophoresis with ultraviolet light-emitting diode-induced native fluorescence (UV-LEDIF) detection for the determination of isoquinoline alkaloids in extracts of Chelidonium majus L. Samples were extracted with acidic methanol and the extracts were directly analysed by CE. Simultaneous determination of protopine, chelidonine, coptisine, sanguinarine, allocryptopine, chelerythrine and stylopine was performed in 20mM phosphate buffer (pH 3.1). The baseline separation of these alkaloids was finished within 20 min. As these alkaloids have native fluorescence, they were directly detected using the commercially available UV light emitting diode without troublesome fluorescent derivatisation. Satisfactory LOD values were obtained for the studied compounds considering their appearance in natural extracts. Lower limits of detection were 0.05 μg/mL for protopine, 0.06 μg/mL for stylopine and allocryptopine, 0.07 μg/mL for chelidonine, 0.22 μg/mL for sanguinarine, 1.7 μg/mL for chelerythrine and 5.5 μg/mL for coptisine. The developed method was successfully applied to determine the contents of seven alkaloids in the aerial parts of Chelidonium majus L, which varied from 0.025 to 0.763% (w/w). Also, to demonstrate the potential of the proposed CE method, an estimation of the cytotoxic properties of selected Celandine alkaloids in a natural extract was carried out. 相似文献
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Enn Lust Gunnar Nurk Alar Jänes Mati Arulepp Priit Nigu Priit Möller Silvar Kallip Väino Sammelselg 《Journal of Solid State Electrochemistry》2003,7(2):91-105
Electrical double layer and electrochemical characteristics at the nanoporous carbon|acetonitrile interface with additions
of Et4NBF4, Et3MeNBF4, EtMe3NBF4, LiClO4, and LiBF4 have been studied by cyclic voltammetry and impedance spectroscopy methods. A value of zero charge potential, dependent on
the structure of the cations as well as on the composition of the anions, the region of ideal polarizability, and other characteristics
has been established. Analysis of the complex plane plots shows that the nanoporous carbon|acetonitrile+0.1 M electrolyte
(Et4NBF4, Et3MeNBF4, or EtMe3NBF4) interface can be simulated by the equivalent circuit, in which the two parallel conduction parts in the solid and liquid
phases are interconnected by the double layer capacitance in parallel with the complex admittance of the hindered reaction
of the charge transfer process or of the partial charge transfer (i.e. adsorption stage limited) process. The values of the
characteristic frequency depend on the electrolyte composition and on the electrode potential, i.e. on the nature of the ions
adsorbed at the surface of the nanoporous carbon electrode. In the region of moderate a.c. frequencies, the modified Randles-like
equivalent circuit has been used for simulation of the complex plane plots. In the region of negative surface charge densities,
the intercalation process of Li+ ions from LiClO4 and LiBF4 solutions into the surface film is possible and these data can be simulated using the modified Ho et al. model or Meyer et
al. model.
Electronic Publication 相似文献
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Enn Lust Priit Möller Indrek Kivi Gunnar Nurk Silvar Kallip 《Journal of Solid State Electrochemistry》2005,9(12):882-889
Cyclic voltammetry, chronoamperometry and electro-chemical impedance have been used for the analysis of the following medium
temperature half-cells: Ce0.85Sm0.15O1.925| La0.6Sr0.4CoO3-δ, Ce0.85Sm0.15O1.925| Pr0.6Sr0.4CoO3-δ and Ce0.85Sm0.15O1.925| Gd0.6Sr0.4CoO3-δ. The influence of the atomic mass of the A–site cation in the perovskite cathode on the oxygen reduction kinetics has been
discussed. The total polarisation resistance, obtained from the Z′′, Z′-plots, increases with the rise of atomic mass of the cation in the A-site position. Two different time constants have been
obtained for the oxygen electroreduction process, and the replacement of La3+ by Gd3+ in the cathode material decreases somewhat the surface catalytic activity, but the noticeably higher low-frequency series
resistance, i.e. mainly diffusion-like mass transfer resistance, values have been obtained. However, the mainly diffusion-limited
process at T≤773 K for Gd0.6Sr0.4CoO3-δ and the kinetically mixed process (diffusion + charge transfer) for Pr0.6Sr0.4CoO3-δ and La0.6Sr0.4CoO3-δ have been established. At higher temperature (T≥993 K) and more negative potentials, the O2 reduction process is limited mainly by the heterogeneous charge transfer step.
Presented at the fourth Baltic Conference on Electrochemistry, Greifswald, March 13–16, 2005. 相似文献
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Pikma Piret Ers Heigo Siinor Liis Zhao Jinfeng Oll Ove Romann Tavo Grozovski Vitali Siimenson Carolin Väärtnõu Mart Paalo Maarja Härmas Riinu Lust Karmen Thomberg Thomas Jänes Alar Nerut Jaak Jäger Rutha Valk Peeter Kivi Indrek Maide Martin Möller Priit Kanarbik Rait Nurk Gunnar Lust Enn 《Journal of Solid State Electrochemistry》2023,27(7):1547-1591
The electrochemistry nowadays has many faces and challenges. Although the focus has shifted from fundamental electrochemistry to applied electrochemistry, one needs to acknowledge that it is impossible to develop and design novel green energy transition devices without a comprehensive understanding of the electrochemical processes at the electrode and electrolyte interface that define the performance mechanisms. The review gives an overview of the systematic research in the field of electrochemistry in Estonia which reflects on the excellent collaboration between fundamental and applied electrochemistry.
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