


Vol 53, No 4 (2017)
- Year: 2017
- Articles: 13
- URL: https://journal-vniispk.ru/1023-1935/issue/view/11817
Article
Effects of Mg, Al Co-doping into Mn site on electrochemical performance of LiNi0.5Co0.2Mn0.3O2
Abstract
In order to study the influence of multiple ions doping into single-site on the structure and electrochemical properties of Ni-rich layered-structure cathode material LiNi0.5Co0.2Mn0.3O2, the coprecipitation of hydroxides was applied to synthesize Mg, Al co-doped cathode material LiNi0.5Co0.2Mn0.3–xMg1/2xAl1/2xO2 (x = 0.00, 0.01, 0.02, 0.04) in this paper. Morphology and structure, kinetic parameter, impedance and electrochemical performance of the material were respectively characterized by SEM, XRD, CV, EIS and galvanostatic charge/discharge test. The results of comprehensive analysis showed that the properties of material were improved obviously when the amount of doping was 0.02. At this amount of doping, the corresponding material has smaller cation mixing, higher hexagonal ordering of layered-structure, larger Li+ ion diffusion coefficients which are 2.444 × 10–10 and 4.186 × 10–10 cm2 s–1 for Li+ intercalation and deintercalation respectively, smaller impedance which is 33.93 Ω, higher specific capacity of first-discharge which is 168.01 mA h g–1 and higher capacity retention rate which is up to 95.06% after 20 cycles at 0.5 C (100 mA g–1).



Impact of carbon coating thickness on the electrochemical properties of Li3V2(PO4)3/C composites
Abstract
A series of Li3V2(PO4)3/C composites with different amounts of carbon are synthesized by a combustion method. The physical and electrochemical properties of the Li3V2(PO4)3/C composites are investigated by X-ray diffraction, element analysis, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy and electrochemical measurements. The effects of carbon content of Li3V2(PO4)3/C composites on its electrochemical properties are conducted with cyclic voltammetry and electrochemical impedance. The experiment results clearly show that the optimal carbon content is 4.3 wt %, and more or less amount of carbon would be unfavorable to electrochemical properties of the Li3V2(PO4)3/C electrode materials. The results would provide some basis for further improvement on the Li3V2(PO4)3 electrode materials.



Crystal growth of thin [Zn2(H2N-BDC)2(4-bpdb)] · 3DMF metal–organic framework nanostructure on functionalized surfaces: study of structure effect on methyldopa adsorption affinity
Abstract
Thin films of a three-dimensional porous Zn(II)-based metal–organic framework, [Zn2(NH2-BDC)2(4-bpdb)] · 3DMF (TMU-17-NH2), containing azine-functionalized pores, were deposited on surfaces of silk fiber via a stepwise manner. The effect of sequential dipping steps in growth of TMU-17-NH2 has been studied. These systems depicted a decrease in the size accompanying a decrease in the sequential dipping steps. The TMU-17-NH2 has been used as matrices for the adsorption and in vitro guest delivery of methyldopa (MD).



Studies on Co-oxidation resistances of electrolytes based on sulfolane and lithium bis(oxalato)borate
Abstract
How to exert the high-voltage performance of LiNi0.5Mn1.5O4 and break through the bottleneck effect of corresponding electrolyte have become key points in advanced lithium-ion battery. Lithium bis(oxalato) borate (LiBOB) and sulfolane (SL) are chosen as additives to investigate their effects on the electrochemical performance of lithium-ion battery with LiNi0.5Mn1.5O4 cathode. The quantum chemistry calculation theory shows that oxidation potential of SL–BOB– is dramatically increased, consistent with the experimental result in CV measurement. Meanwhile, results of CV and charge–discharge cycling indicate that LiBOB and SL would be involved in the initial oxidation reaction to form an effective solid electrolyte interface film on surfaces of the cathode electrode thus enhance the cycling performance of LiNi0.5Mn1.5O4/Li cells. Electrochemical impedance spectroscopy data proves that SL is beneficial to resistance decrease. All these data will become important corroborations that the combined electrolyte LiBOB and SL have good oxidation resistances.



PPy doped with different metal sulphate as electrode materials for supercapacitors
Abstract
A facile approach has been established to prepare PPy via in situ polymerization with different metal sulfate as dopants. The morphology and structure of PPy and doped PPy were characterized by scanning electron microscopy (SEM) and fourier transform infrared (FT-IR). It was found that doped PPy has different morphology and a slight structure change. The electrochemical performance of the samples has been illustrated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and AC impedance measurements. Compared with the PPy, the specific capacitance of PPy/Cu2+ has been improved to 224 F g–1 at the current density of 0.6 A g–1. Also, the relationship between electrochemical properties of doped PPy and various parameters of metal ions has been investigated.



CuS–MWCNT based electrochemical sensor for sensitive detection of bisphenol A
Abstract
The rapid and simple detection of bisphenol A is very important for the safety and reproduction of organisms. Here, a sensitive and reliable electrochemical sensor was established for bisphenol A detection based on the high amplification effect of copper sulfide-multi-walled carbon nanotube (CuS–MWCNT) nanocomposites. The flower-like CuS–MWCNT were successfully synthesized by a simple hydrothermal method accompanied by polyvinylpyrrolidone (PVP). Compared with bare glassy carbon electrode (GCE), CuS–MWCNT modified GCE could amplify the electrochemical signals in about ten times, which was attributed to the synergistic effect of CuS and MWCNT. The MWCNT could increase the specific surface area of electrodes and improve the electrode activity. The integration of CuS could further enhance the electrode conductivity as well as accelerate the electron transfer rate. Raman spectra and transmission electron microscope (TEM) were used to characterize the successful fabrication of CuS–MWCNT nanocomposites and its uniform and monodispersed morphology. Under optimizing conditions, the oxidation currents of bisphenol A via the differential pulse voltammetric (DPV) showed a good linear relationship with its concentration in a wide range of 0.5–100 μM, with a detection limit of 50 nM. This electrochemical sensor of bisphenol A provided a convenient and economical platform with high sensitivity and reproducibility, which had great potential in environmental monitoring.



Determination of hydroxylamine using a carbon paste electrode modified with graphene oxide nano sheets
Abstract
A carbon paste electrode that was chemically modified with 3-(4'-amino-3'-hydroxy-biphenyl-4-yl)-acrylic acid (3,4-AA) was used as a selective electrochemical sensor for the detection of hydroxylamine. Cyclic voltammetry (CV), choronoamperometry (CHA) and square wave voltammetry (SWV) were used to investigate oxidation of hydroxylamine in aqueous solution. Under optimized concentration the electrocatalytic oxidation current peak for hydroxylamine increased linearly with concentration in the range of 0.025–10.0 μM. The detection limits for hydroxylamine was 0.012 μM. Finally, the modified electrode was applied to detection hydroxylamine in water samples.



Application of anodized edge-plane pyrolytic graphite electrode for analysis of clindamycin in pharmaceutical formulations and human urine samples
Abstract
Different graphitic carbon-based electrode materials were evaluated for direct electro-oxidation of clindamycin and electroanalytical parameters such as sensitivity, residual background current, and signal-tobackground current ratio were compared to select the best one for the clindamycin electroanalysis. Such electrode materials include glassy carbon, carbon paste, pyrolytic graphite (edge-plane and basal-plane), carbon nanotube, reduced graphene oxide, and carbon black. The edge-plane pyrolytic graphite electrode after a simple and fast electrochemical pretreatment showed superior performance compared with the other carbon electrodes. Raman and Fourier transform infrared spectroscopy were employed to analyze the surface microstructure and chemical bonding of the carbon materials and scanning electron microscopy was used to study their surface morphologic features. The applicability of the electrochemically activated edge-plane pyrolytic graphite electrode for the determination of clindamycin in pharmaceutical formulations and human urine samples was evaluated.



The effect of monoethanolamine on conductivity and efficiency of electrodialysis of acid and salt solutions
Abstract
Experimental studies of the specific conductivity (SC) are carried out for aqueous solutions of organic and inorganic acids and salts including those containing different amounts of monoethanolamine (MEA), which model the absorption solutions used in purification of gas mixtures from carbon dioxide and containing heatstable salts (HSS). It is shown that the addition of MEA to binary aqueous electrolyte solutions gives rise to changes in the SC: in the MEA concentration range from 0 to ∼1.5 M, the SC of the resulting ternary solutions increases but decreases again with the further increase in MEA concentration. This behavior of SC is typical also of aqueous binary amine solutions. It is shown that in the presence of MEA, the quantitative removal of dissolved acids and salts proceeds faster with the simultaneous increase in the specific energy consumption by a factor of 7–9 (up to 85.7–93.6 kJ/dm3). It is assumed that the reason for the decrease in SC and the enhancement of energy consumption at electrodialysis of mixed solutions is the probable existence of monoethanolamine both as free solvated ions and neutral molecules and as self-assembled associated structures (ion pairs and more complex particles) which involve also the ions of salts dissolved in amine-containing solutions.



Electroconvection in systems with heterogeneous ion-exchange membranes after thermal modification
Abstract
It is found that the variations in the structure (morphology and microrelief) and chemical composition of surface of heterogeneous ion-exchange membranes as a result of thermal modification have different effects on the current—voltage characteristics and conditions for the generation of electroconvective instability at the membrane/solution interface under intense current modes. After thermal treatment of strongly acidic sulfocation-exchange membrane, which is characterized by a low catalytic activity in the reaction of water dissociation and a high thermal stability of fixed groups, a fraction of conducting surface area increases and the membrane microrelief develops. As a result, the diffusion limiting current density increases and the length of plateau of the current—voltage curve decreases. Therewith, the thickness of the region of electroconvective instability of solution in the near-membrane region increases and the polarization of electromembrane system, at which the mode of unstable electroconvection is reached, decreases. The thermodestruction of strongly basic anion-exchange membranes, conversely, leads to suppression of electroconvection and an increase in the length of plateau of the current—voltage curve due to the formation of fixed weakly basic amino groups, which are catalytically active in the reaction of water dissociation. A linear correlation is found between the dimensions of the region of electroconvective instability and a fraction of weakly basic functional amino groups in the composition of strongly basic membranes.



Effects of peak current density on the structure and property of PbO2–CeO2 nanocomposite electrodes prepared by pulse electrodeposition
Abstract
PbO2–CeO2 nanocomposite electrodes were prepared by pulse electrodeposition method in the lead nitrate solution containing CeO2 nanoparticles with different peak current density. The content of CeO2 nanoparticles in the electrodes increase with the increase of peak current density. The effects of peak current density on the morphology and structure of PbO2–CeO2 nanocomposite electrodes were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The SEM and XRD results show that the increase of peak current density can make the morphology finer and more compact, and the crystal size decreases with the increase of peak current density. The oxygen evolution overpotential and stability of PbO2–CeO2 nanocomposite electrodes enhance with the increase of peak current density. The electrocatalytic property of PbO2–CeO2 nanocomposite electrodes was examined for the electrochemical oxidation of rhodamine B (RhB). The results show that the RhB removal efficiency on PbO2–CeO2 nanocomposite electrodes increase with the increase of peak current density, which can be attributed to the higher oxygen evolution overpotential and CeO2 content in the composite electrodes.



Short Communications
The effect of ligands on contact exchange in the NdFeB–Cu2+–P2O74-–NH4+ system
Abstract
Peculiarities of open-circuit interaction between the surface of electronegative NdFeB magnet and electrolytes containing pyrophosphate and ammonia complexes of copper are studied. It is shown that in the first minutes of the magnet immersion, the rate of open-circuit contact exchange in the pyrophosphate- ammonia electrolyte is close to its value in the pyrophosphate electrolyte (0.98 and 0.90 mA/cm2, respectively) being gradually halved. Although the contact-exchange rate in pyrophosphate-ammonia electrolyte is higher as compared with the ammonia electrolyte, the contact exchange does no become the reason for the loss of adhesion of the deposited copper-containing coatings to the substrate. This is associated with both the formation of a strongly adhered copper layer on cathodic domains of the magnet surface and the absence of poorly soluble products of magnet dissolution formed on the surface of anodic sites.



Electrochemical behavior of nickel–polyaniline electrode in 1 M LiClO4–propylene carbonate electrolyte
Abstract
Doping of emeraldine-base (EB) with lithium salts involves the addition of lithium cations to nitrogen in imine groups and intercalation of counter ions i.e., proceeds similarly to doping with protonic acids. The results of studies show that doping of polyaniline (PANI) with a lithium salt proceeds relatively difficultly as compared with protonic doping. For a polyaniline electrode, to attain faster the stationary mode by repeated cycling (“electrode training”) in an organic lithium electrolyte and to reach the higher capacitance, the method of preliminary lithiation of the NiO surface layer on the nickel substrate with Li+ cations through the EB film is proposed. The studies show that preliminary cycling of the Ni/PANI electrode (7 cycles at 10 mV s–1) in the region of negative potentials (from 0 to–2.99 V vs. Ag/AgCl) leads to substantial increase in the capacitance characteristics of the PANI film in the region of its intrinsic redox activity from–0.4 to +1.1 V at high charge–discharge currents (2–5 A/g).


