查看更多>>摘要：The electrical double layer (EDL) structure of mechanically renewed electrodes of Sn, Pb, and Sn-Pb alloy (1 at. % Pb) is studied in acetonictrile (AN) solutions of LiClO4 by the impedance method and cyclic voltammetry. The potential regions are found in which these electrodes can be considered in good approximation as ideal polarizable. In these solutions, the potentials of zero charge (E sigma 1/40) on Sn and Pb electrodes are found to be -0.37 +/- 0.02 and -0.59 +/- 0.02 V (vs. aqueous SCE), respectively. The experimental dependences of the capacitance on the potential are shown to be in good agreement with the classical EDL model of Gouy-Chapman-Stern-Grahame. Based on the results of capacitance measurements carried out on renewed Sn-Pb electrodes, it is found that as the time of exposure of the renewed alloy surface to electrolyte increases, the C vs. E curves indicate that the concentration of lead atoms in the surface layer of alloy also increases, i.e., Pb is the surface-active component of these alloys. By analyzing the observed time effects, the surface coverage of Sn-Pb electrode by lead atoms (0) is calculated in different time (t) after the renewal. It is shown that the 0 vs. t dependences well agree with the model proposed earlier that describes the process of surface segregation of atoms of the surface-active component of eutectic alloys by the mechanism of surface diffusion. The kinetics of process of surface segregation of lead atoms on the mechanically renewed Sn-Pb electrode is compared for AN and aqueous solutions. The increase in 0 is found to proceed slower in AN solutions than in aqueous solutions of the similar composition. The main reason for the differences observed is proposed.
查看更多>>摘要：Gold nanoparticles (AuNPs) have been deposited on titania nanotubular layers (TNT) via photocatalytic deposition, and the activity of the obtained AuNPs-TNT systems toward oxygen electroreduction reaction (ORR) in an alkaline medium has been studied and compared with the activity of AuNPs-TNT composites prepared from Au colloidal solutions. Two photodeposition methods were utilized for anchoring of AuNPs: direct UV-irradiation of a TNT electrode immersed into a HAuCl4 containing solution (TNT-Au1 composites) and initial adsorption of AuCl4-ions on TNT followed by UV-irradiation (TNT-Au2 composites). The size, spatial distribution, structure and surface of AuNPs deposited on TNT layers were studied via scanning and transmission electron microscopy, optical spectroscopy and underpotential deposition of lead ad-atoms on gold. It was found that these parameters depend on the photodeposition method. The TNT-Au2 composites have smaller size, higher surface concentration and more uniform distribution of AuNPs in the TNT layers as compared with the TNTAu1 systems. The electrocatalytic efficiency of Au-TNT electrodes in ORR was found to depend on various factors such as doping level of TNT support (governed by annealing temperature), AuNPs size and their loading amount. The electroreduction of oxygen was observed at less negative potentials when Au nanoparticles were grown on the TNT surface by photoreduction in comparison with the TNT electrodes modified with AuNPs from sols. The enhanced activity of the photocatalytically prepared AuNPs-TNT composites can be explained by the consolidation of the interface between gold nanoparticles and TiO2 support and the absence of ligands on the AuNPs surface.
Resendiz, R.Rodriguez, A.Larios, E. R.Torres, J....
13页
查看更多>>摘要：New analytical correlations between impedance magnitude and phase are developed and presented. These correlations are used for the assessment of impedance spectroscopy data. As correlations are obtained, they can be calculated point to point at each frequency of the spectra with no need to establish explicit premises related to stability, linearity or finite limits for their derivation. Their use is simpler than that based on the direct evaluation of the Kramers-Kroning transforms or alternative methods. An example of their derivation from basic equations involving complex numbers is described. They were obtained by looking for an explanation of the empirical fact that the slope of the Bode-Magnitude diagram vs frequency resembles the shape of the corresponding Bode-Phase diagram. Unlike the Kramers-Kronig transform, these new correlations can also be directly applied to test spectra with highly predominant capacitive or inductive responses or even incomplete loops. Their analytical expressions are exact for simple ideal elements and circuits, including the Warburg diffusion element. These correlations were tested with simulated spectra altered with known random error distributions, and they were able to detect the random distribution and the error level for simple spectra when the errors were > 0.5%. For more sophisticated spectra, the minimum error that can be detected without interference of the deviations due to the proper algorithm are around 2.5%. No exact correlation was found for a constant phase element (CPE), but a close empirical approximation was obtained for a single CPE. It is necessary to improve this approximation when a CPE is combined with some other elements because of detected deviations. In addition, it was found that in a first approach the algorithm does not detect non-linear behavior on a simple experimental circuit, but the test gave insights of how to detect it. On the contrary, it is well suited for detection of system stability issues. Examples of their application to actual experimental spectra, high capacitive or with several loops, are presented and the limitations discussed. More work and exhaustive tests are necessary to improve the method and stablish its real limitations, but its use for assessment of simple spectra at certain error level can already be done. Given that the derivation of the new correlations is only based on its complex number nature, this study concludes that the magnitude and phase of any complex number or 2D vector are not independent, and it is expected that similar correlations can be applied to any frequency-dependent complex variable, vector or transfer function, such as those used in optics or rheology.
查看更多>>摘要：The zeolitic imidazolate framework ZIF-67 can be used as a favorable catalyst carrier owing to its unique structure. Although the catalytic activity of ZIF-67 can be considerably improved by doping with transition metals such as manganese, manganese-doped ZIF-67 has rarely been applied in electrocatalysis. In this study, manganese-doped ZIF-67 was carbonized to form CoC@Mn and to prepare an electrochemical sensor for detecting o-nitrophenol (o-NP). The results showed that CoC@Mn exhibits a good electrocatalytic performance. The constructed sensor possessed a linear range of 0.5-100 uM for the detection of o-NP, with a detection limit of 0.16 uM. In addition, it was found to accurately detect o-NP in real lake and tap water samples. CoC@Mn is therefore expected to be an efficient electrocatalyst for detecting o-NP as an industrial pollutant.
查看更多>>摘要：In order to obtain a TiO2 nanocomposite film with enhanced photoelectrochemical properties for corrosion protection of metals, a TiO2 nanotube film was fabricated on a Ti substrate via anodization, then ZnIn2S4 nanosheets and CdSe nanoparticles were sequentially deposited on the TiO2 film by hydrothermal treatment and electrodeposition, respectively. The CdSe/ZnIn2S4 co-modified TiO2 heterostructured nanocomposite film showed remarkably enhanced visible light absorption and photoelectrochemical properties. Under white light irradiation, the photocurrent density of the nanocomposite film in the mixed solution with 0.1 M Na2S and 0.1 M Na2SO3 was 33 times higher than that of the TiO2 film. The nanocomposite could negatively shift the potential of the coupled 403 stainless steel immersed in a 0.5 M NaCl solution by 440 mV, showing efficient photoelectrochemical cathodic protection.
NSTL
Elsevier