Vol 55, No 9 (2019)

In an electrochemical cell with electrolyte containing silver or copper salts, the metal deposition takes place on the surface of a transparent electrically conducting coating. Under certain conditions, the metal film becomes specular and the electrochemical cell periodically switches from transparent to mirror state in response to changes in the voltage. The data obtained on electrochemical cells switchable between transparent to mirror states are analyzed. It is noted that the electrolyte properties play the decisive role in characteristics of such devices. Their prototypes with three optical states: transparent‑transient semitransparent‑mirror are realized recently. The modes are achieved in which the mirror state is preserved for a long period (over 2 h) at switched-off voltage (deenergized state). These results allow us to expect that the development of electrochemically switchable glasses-mirrors for windows will soon reach its commercial stage.

Modified screen printed electrode (MSPE) with 2-[[4-(dimethyl amino) phenyl] diazenyl] benzoic acid (Methyl Red) was prepared for determination of aluminum ions in water and pharmaceutical (Maalox and Epicogel) samples. The MSPE reveals linear response over a wide concentration range of 5.0 × 10^–6–1.0 × 10^–2 mol L^–1 of aluminum at 25°C with a trivalent cationic slope of 20.4 ± 0.5 mV decade^–1 with detection limit 5.0 × 10^–6 mol L^–1 in pH range 3–5. Moreover, the mechanism of chemical reaction between Methyl Red and aluminum ions on the sensor surface was studied using IR spectra, energy dispersive X-ray analysis (EDX) and scanning electron microscope (SEM). The prepared sensor also showed reproducible and stable response over a period of 14 week with fast response time about 5 s. The proposed potentiometric method was validated according to the IUPAC recommendations. The results obtained from the proposed sensor were comparable with those obtained with inductively coupled plasma mass spectrometry (ICP–MS).

To perform the oxygen reduction reaction effectively, the active layer of the lithium–oxygen battery positive electrode must have developed surface possessing a complicated pore structure. During discharge (the oxygen reaction cathodic component), the electrode accumulates lithium peroxide, a final product of electrochemical and chemical reactions (resulting in the conjunction of lithium ions, oxygen molecules. and electrons); the latter undergoes oxidation (the oxygen reaction anodic component) during the lithium–oxygen battery charging. The lithium peroxide is a water-insoluble compound that has no electronic conduction; when depositing on the electrode surface it seals openings of narrow pores and prevents oxygen penetration therein. To obtain more lithium peroxide via oxygen reduction in the presence of lithium ions, a cluster of large pores, practically unsealed with the lithium peroxide, is produced in the active layer; the pores supply oxygen deep into the active layer. The Li₂O₂ accumulation occurs in a cluster of lesser pores with developed surface. In the creating of the lithium–oxygen battery positive electrode active layer optimal structure, the difficulty is that some key quantities are unknown in advance. They are the large-scale and lesser pore average size and their volume fractions in the active layer. To solve the problem, the regular biporous model of the pore structure can be used. In the model, the pore radii are strictly fixed. This opens a relatively easy way for the interconnecting, by calculations, of parameters and the lithium–oxygen battery dimensioning specifications during its discharge. This work aimed at the proposing of the positive electrode active layer regular biporous model and developing of a procedure for the calculating of the lithium–oxygen battery dimensioning specifications during the discharge. it is shown, in a specific context, how the varying of the positive electrode active layer structure and the oxygen consumption constant k can control the Li₂O₂ accumulation.

The necessity of the studying of carbonaceous materials differing in their surface area and structure is called for by the fact that these materials are used until now in the designing of positive electrodes for lithium-oxygen current sources. Under the model conditions, the effect of some factors on the effectiveness of oxygen reduction reaction at the positive electrode is studied. Among them are: properties of the dimethylsulfoxide- and acetonitrile-based electrolytes, the carbonaceous material (ХС 72, Super P, and carbon nanotubes) structure and its relevant transport processes depending on the electrode active layer mass (thickness) and the polarization current density, which determines the oxygen reaction effectiveness at the carbonaceous material. The electrochemically active surface area is shown to increase with the specific surface area, which is determined by the carbonaceous material porous structure, its mass at the electrode, the solvent properties, and the reaction rate. The active layer thickness and current density must be chosen for each carbonaceous material individually, depending upon its structure. At that, the active layer entire surface must be electrochemically accessible; it must make possible the lithium peroxide formation and subsequent decomposition. In the dimethylsulfoxide-based electrolyte (high donor number), the oxygen reduction reaction is highly reversible; the lithium peroxide formation here occurs via disproportionation in the solution bulk and results in the formation of Li₂O₂ particles with disordered (in all probability, toroidal) structure. This facilitates the back reaction (Li₂O₂ anodic decomposition), in good agreement with literature data [1]. In acetonitrile-based electrolyte (low donor number), the oxygen reduction reaction occurs in adsorbed state, producing LiО₂ that disproportionates at the electrode surface forming a lithium peroxide insulating film whose oxidation needs high overvoltage. On the strength of all the parameters, carbon nanotubes are most effective in the oxygen reduction reaction in the dimethylsulfoxide-based electrolyte, because the carbon nanotubes have large volume of mesopores for the reactant transport, high electrochemically active surface area for the Li₂O₂ accumulation, and thus provide high characteristics per electrode.

Activated carbons were successfully prepared from rice husk (RH) by chemical activation using KOH (RH-K4) or NaOH (RH-N3) as activating agents and characterized by means of SEM, EDX, FTIR, Raman, Boehm titration, and TGA methods. The as-prepared activated carbon samples are composed of spherical particles with lots of cracks and crevices as showed in SEM images. They have numerous surface functional groups which proofed by FTIR and Boehm titration. Raman result revealed that the crystalline size along basal plane (L_a) of RH-K4 and RH-N3 are 3.27 and 3.46 nm, respectively, which demonstrated the higher disorder degree of RH-K4 compared to RH-N3. Cyclic voltammetry and charge-discharge tests exhibit the electric double layer capacitor characteristic of the electrodes. RH-K4 shows a better performance at low scan rate and current density, whereas RH-N3 is superior at high scan rate and current density. At all experimental conditions studied, the as-prepared electrodes behave better in K₂SO₄ electrolyte than in Na₂SO₄ electrolyte.

Using the method of measuring ohmic resistance of steel AISI 304 specimens, the time dependence of steel corrosion rate in the 0.1–2 M HCl solutions is determined under the conditions of free air access. In the 0.5 M HCl solution, the effect of thiourea and polyethylene polyamine inhibitors on the steel AISI 304 corrosion rate is studied. It is shown that the inhibitory effect of thiourea on the corrosion rate of AISI 304 steel depends on the time of steel exposure to the solution.