Vol 55, No 10 (2019)

In this work, the electrodeposition of lead dioxide on a Pb electrode was realized by a potentiostatic method in 0.5 mol/L sulfuric acid solution at 1.3 V (ECS) during 30 min. The result of XRD showed that the crystal structure of PbO₂ in acid solution is pure β-PbO₂. The electrodegradation of tris (4-(dimethylamino) phenyl) methylium chloride (methyl violet 10B) dye in an aqueous solution of 0.1 mol/L sodium sulfate has been studied by potentiostatic method using β-PbO₂ as anode. The methyl violet 10B was successfully oxidized by hydroxyl radicals electrogenerated from oxidation of water on the Pb/β-PbO₂ electrode surface. The anodic oxidation of methyl violet 10B followed the pseudo-first order kinetics. The time and applied potential had significant effect on the electrochemical degradation of methyl violet 10B at the Pb/β-PbO₂ electrode with a degradation rate of 10.5 g/(m² day).

In this paper, the growth process of T2 brass passive film in generator cooling water was studied, the effect of CO₂’s leakage on the crystal structure and anti-corrosion performance of passive film was analyzed, and we were trying to repair the passive film by adjusting pH of solution. Electrochemical Impedance Spectroscopy (EIS), Potentiodynamic Polarization (PP), Potentiostatic Scan (PS), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS) were used in this paper. The test results showed that a thin and dense Cu₂O passive film was formed on the surface of T2 brass after immersed in the cooling water for 2 days. And then a loose CuO outside layer was formed gradually, during this period the Cu₂O was further oxidized to be CuO, the dense structure of the inner Cu₂O layer was thus damaged. Finally a double-layer passive film consisted by Cu₂O and CuO was formed at the 24th day of immersed. Corrosion pits and cracks appeared on the outside passive film after erosed by CO₂. The anti-corrosion performance of the passive film cannot be completely restored by self in alkaline solution.

We designed a hydrogen peroxide biosensor. The electrochemical detection of H₂O₂ was performed based on immobilization of cobalt nanoparticles–ferritin (CoNPs–Fer) onto multiwalled carbon nanotubes (MWCNTS) ensnared into chitosan (CS) matrices. Electrochemical techniques such as differential pulse voltammetry (DPV) and cyclic voltammetry (CV) was used to check the property of biosensor. Energy-dispersive X-ray spectroscopy (EDXS) and field emission scanning electron microscopy (FESEM) techniques showed the prosperous immobilization of CoNPs–Fer on the modified GC electrode surface. The hydrogen peroxide-designed biosensor displayed a linear range from 0.2 to 14 nM (R² = 0.99), a detection limit of 1.29 nM (S/N = 3) and sensitivity of –0.1105 μA/nM.The apparent heterogeneous electron transfer rate constant (K_s) and the charge transfer coefficient (α) were gained 4.19 s^–1 and 0.49, respectively. This biosensor can detect hydrogen peroxide with high sensitivity, selectivity, and low detection limit.

This work assesses the applicability of the EMF method for determination of the values of thermodynamic functions for the Li–S electrochemical system in lithium–sulfur cells with various states of charge. It is shown that the EMF method can be used for determination of the values of thermodynamic functions for the Li–S electrochemical systems in lithium–sulfur cells with various states of discharge only in the first charge–discharge cycle. The EMF method is inapplicable in the following charge–discharge cycles owing to disturbance of equilibrium in the electrochemical system due to the direct chemical interaction between sulfur and high-order polysulfides of lithium (Li₂S_n, n > 4) and the metallic lithium electrode. The thermodynamic functions of the Li–S system with different sulfur reduction degree are in the following ranges: ΔG = –480…–410 kJ/mol; ΔH = –490…–420 kJ/mol; ΔS = –120…–20 J/(mol K) at the temperature of 303 K. Quantum–chemical calculations of the values of thermodynamic functions are carried out for electrochemical reduction of sulfur and lithium polysulfides. The calculated values of thermodynamic functions agree reasonably with the measured values. The thermodynamic efficiency of energy conversion is estimated for discharge of lithium–sulfur cells at 30°C; it is 93–98%.

A scalable synthesis of unique pyrolysis carbons from phosphorus-doped epoxyphenolics (EPN) through a facile curing and pyrolysis process is reported. The obtained carbons with a high pyrolysis yield of ca. 48% are investigated by SEM, TEM, XRD, Raman and nitrogen adsorption, and evaluated as anode for LIBs. The results show that the nanocrystal structure, proportion of defect sites and porosity (nanovoids) of the obtained carbons are highly dependent on pyrolysis temperature, thus affecting their electrochemical properties. The EPN carbon pyrolyzed at 900°C (EPN900) delivers the largest reversible capacity of nearly 420 mA h g^–1 at 0.1 C, which is higher than the theoretical capacity of graphite, mainly resulting from lithium-ions insertion into the turbostratic nanosheets and absorption on defect sites. While the EPN carbon pyrolyzed at 2800°C (EPN2800) exhibits a balanced lithium storage performance with relatively large reversible capacity of 343 mA h g^–1, high initial coulombic efficiency (~86%), and superior cycling performance (299 mA h g^–1 after 100 cycles at 0.3 C). This work provides a feasible solution for the large-scale preparation of high performance anode material and deepens the high-value utilization of the staple epoxy product.

One of important problems associated with the use of Pt/C electrocatalysts in low-temperature fuel cells is their degradation due to oxidation of the carbon support. The use of noncarbon supports resistant to oxidation, for example, oxides of certain metals in the highest degree of oxidation is a promising direction. TiO₂ with the high specific surface area (104 m²/g) is synthesized and used in fabrication of supported platinum catalysts. For Pt/TiO₂ and carbon-containing composite Pt/TiO₂+C, the electrochemically active surface area of platinum and the their activity in oxygen electroreduction reaction are estimated. The assessed stability of synthesized materials far exceeds the stability of commercial Pt/C catalysts.

An attempt is made to resolve a long standing difference in the predicted distribution of the eddy diffusivity in the viscous sublayer, where the literature shows a dependence on either the cube or the fourth power of the distance from a solid wall. The resolution suggested is that a y³ dependence prevails very close to the wall while a y⁴ dependence may prevail in the outer part of the viscous sublayer near the border with the outer turbulent flow. However, at high values of the Schmidt number, the overall mass-transfer rate will show behavior corresponding to the y³ dependence, and any hints of the y⁴ dependence would be very hard to observe experimentally.