Vol 55, No 5 (2019)

Porous LiMn₂O₄ spheres was easily fabricated with MnCO₃ spheres and MnO₂ as precursors and characterized in terms of structure and performance as the cathode of a lithium ion battery. The presence of pores with the average size of about 50 nm throughout the whole LiMn₂O₄ microspheres was confirmed by scanning electron microscope (SEM) and N₂ adsorption-desorption measurements. The electrochemical tests show that the synthesized product has smaller electrochemical polarization, faster Li-ion intercalation kinetics and higher electrochemical stability. It exhibits excellent rate capability and cyclic stability: delivering a reversible discharge capacity of 71 mA h g⁻¹ at a 5 C rate and yielding a capacity retention of over 92% at a rate of 0.5 C after 100 cycles. The superior performance of the synthesized product is attributed to its special structure: porous secondary spheres particles consisting of primary single-crystalline nanoparticles. The nanoparticle reduces the path of Li-ion diffusion and increases the reaction sites for lithium insertion/extraction, the pores provide room to buffer the volume changes during charge-discharge and the single crystalline nanoparticle endows the spinel with the best stability. Taking the excellent electrochemical performance and facile synthesis into consideration, the presented porous LiMn₂O₄ spheres could be a competitive candidate cathode material for high-performance lithium-ion batteries.

The influence of manganese ions on the electrodeposition process of lead dioxide on the glassy carbon electrode (GCE) in the lead nitrate solution was investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The results show that the electrodeposition process of lead dioxide was inhibited by the addition of manganese ions. However, the nucleation model is not influenced by the addition of manganese ions and the electrodeposition process still fits the instantaneous nucleation model with three-dimensional growth according to Scharifker—Hills’ model.

The preparation of Ni-functionalized graphene oxide/poly orthoaminophenol composites (Ni–FGO–POAP) is presented and the composites were used as graphite electrode modifier for methanol electrooxidation in NaOH. Nickel was accumulated by complex formation between Ni(II), in solution and amines sites in the polymer backbone to obtain Ni–FGO–POAP/G electrode. The electrochemical performance of Ni–FGO–POAP composite electrodes was investigated by common electrochemical techniques. The peak on the potentiodynamic curve for Ni–FGO–POAP electrode in alkaline solutions of methanol is observed which is ascribed to the methanol oxidation in alkaline medium. Under the CA regimes the reaction followed a Cottrellian behavior. The results obtained are discussed from the point of view of employment of the Ni–FGO–POAP composites for the catalytic electrodes of fuel cells. In addition, the atoms-in-molecule (AIM) theory is used to study atomic-scale charge/energy transfer in grapheme-like molecular system.

In this work, p-type CuSCN nanorod thin films were successfully prepared on the fluorine-doped tin oxide (FTO) conductive substrate by a simple electrochemical deposition at different deposition potentials (i.e., −0.1, −0.2, −0.3, −0.4 V), and the influence of deposition potential on the microstructural and photoelectrochemical properties of the prepared CuSCN thin films was then explored. The prepared CuSCN films were nanorod arrays with a rhombohedral β-CuSCN structure, and the better CuSCN crystal structure was achieved when deposited at −0.4 V. The p-type characteristic of the electrodeposited CuSCN thin films were verified by Mott–Schottky measurements. The CuSCN nanorods thin films deposited at −0.2, −0.3, and −0.4 V produced ten times higher photocurrent intensities than the CuSCN thin film deposited at −0.1 V, and the CuSCN thin film deposited at −0.4 V exhibited the best photoelectrochemical performance. The enhanced photoelectrochemical performance of the CuSCN thin film deposited at −0.4 V could be attributed to the better crystal structure, the more charge carrier concentration as well as the more efficient charge separation and migration. This work offers a facile approach to prepare the p-type CuSCN nanorod thin films through electrochemical deposition, and regulate their photoelectrochemical performance by controlling the deposition potential.

In the present work, the Schiff bases were synthesized by reacting sulfamethizole (SMTZ) with two different hydroxy benzaldehydes (2,3-dihydroxy benzaldehyde (DHBA) and 2,4,6-trihydroxy benzaldehyde (THBA)) and characterized by elemental analysis, ¹H-NMR and IR spectroscopies. From the obtained data, it was suggested that 4,6-dihydroxy salicylaldehyde reacted with both primary and secondary amine groups of SMTZ. The binding properties between the synthesized Schiff bases and calf thymus DNA (CT-DNA) at the physiological pH (7.4) was investigated by using cyclic voltammetry and UV-Vis spectroscopy techniques. The experimental results verify that the Schiff bases can bind to CT-DNA by electrostatic mode in 1 : 1 stoichiometry. Antifungal activities of the synthesized Schiff bases against Candida albicans ATCC 10231 were studied and their minimum inhibitory concentrations (MIC) were also determined. The MIC value of the Schiff base 1 synthesized from DHBA is smaller than that of the Schiff base 2 obtained from THBA. Although Schiff base 2 binds to CT-DNA with a higher affinity than Schiff base 1, it is less effective than Schiff base 1 against Candida albicans.

Materials containing from 3.1 to 7.7 wt % of cobalt were obtained by electrodeposition of cobalt on Vulcan XC72 carbon powder in suspension. The composition and average diameter of CoO crystallites formed as result of cobalt oxidation in the process of filtering and drying materials, depending on the electrolysis conditions and electrolyte composition, were studied using thermogravimetry and XRD. It is shown that the maximum amount of cobalt can be deposited from electrolytes containing, along with cobalt sulfate, additives of copper and nickel sulfates. Calculations by the Scherrer equation showed that an increase in the CoO content leads to a decrease in the diameter of crystallites, the size of which is in the nano-range. The analysis of X-ray and electrochemical studies indicates the formation, in the course of the borohydride’s synthesis, of combined catalysts containing nanoparticles of the Pt₃Co solid solution. The best PtCo/C material demonstrated significant improvement in ORR activity and superior stability compared to commercial Pt/C catalyst of the same platinum loading.

The article contains results of numerical analysis of convective-diffusion transport equations for the components of the bromate anion electrochemical reduction process at rotating disk electrode via the redox-mediator autocatalysis (EC″) mechanism. The problem is solved taking into account the difference in the diffusion coefficients of the components. It is assumed that the concentration of protons inside the solution is constant, including the diffusion layer, due to its high value compared to the concentration of bromate-anions. Comparison of the obtained results with the predictions of an approximate analytical study of the same system (Vorotyntsev, M.A., Antipov, A.E., Electrochim. Acta, 2017, vol. 246, p. 1217) confirms the adequacy of the developed analytical approach to the calculating of both the concentration profiles of the system’s components (with the exception of the case of very thick diffusion layer) and the current density for a wide range of external parameters: the solution composition, rate of the comproportionation reaction, the convection intensity (the electrode rotation velocity) and the passing current.

A new interpretation of critical nucleus, which is based on the kinetic analysis of nucleation, is proposed. By critical size of nucleus is meant the size that corresponds to the smallest flux of transition to the next size class. The relationship between the critical size and overpotential and equilibrium surface coverage with adatoms or between the critical size and the specific surface energy and adhesion energy is determined.