Vol 55, No 6 (2019)

The approaches to increasing the efficiency of lithium–oxygen battery (LOB), which are based on the use of PtCo/carbon nanotubes (CNT) catalyst and iodine-containing liquid-phase mediator, are compared. It is found that, when 1 M LiClO₄/DMSO electrolyte is used, the 20PtCo/CNT catalyst provides an increase of the capacity of a Swagelok LOB model in the complete discharge to a voltage of 2 V as compared to the CNT-based LOB. During the cycling of LOB with each of the materials, the charging voltage increases to 4.5 V. This leads not only to an increase in the rate of electrochemical oxidation of lithium peroxide, but also to an acceleration of corrosion of the electrolyte and active material. In the presence of iodine compounds in the electrolyte, Li₂O₂ is oxidized by the chemical mechanism, which reduces the charging voltage. In the 0.05 M LiI + 1 M LiClO₄/DMSO electrolyte, 85 successive cycles were obtained at a capacity of 500 mA h/g_С in the LOB discharging stage and a final charging voltage of not more than 3.8 V. When scaling the LOB to the size of the positive electrode (5 × 5 cm²), the complete discharge capacity close to this characteristic of Swagelok model (as calculated for the geometric electrode surface area) was reached. An introduction of iodine-containing additive into the electrolyte enabled us to obtain up to 100 cycles at a capacity of 300 mA h/g_C. The results of the work show that the use of iodine-based redox mediator is more effective from the viewpoint of stability of characteristics of LOB of this type as compared with the use of the platinum-containing catalyst.

The partial substitution of tantalum for cobalt in the SrCoO_{3 – δ} structure is shown to result in suppression of the hexagonal phase formation and stabilization of the high-temperature cubic perovskite phase. Using ex situ high-temperature diffraction method, it is shown that perovskite SrCo_0.9Ta_0.1O_{3 – δ} (SCT10) does not interact with the Ce_0.8Gd_0.2O_{2 – δ} electrolyte commonly used in medium-temperature solid-oxide fuel cells. The SrCo_0.9Ta_0.1O_{3 – δ} perovskite is found to exhibit transport characteristics necessary for being used as the cathodic material in medium-temperature solid-oxide fuel cells. A voltammetric characteristic of microtubular fuel cell with the SCT cathode is shown.

The mixed alkaline effect (MAE) is a well-known anomaly in glasses. It results in a non-linear response of various physical properties on mixing of alkali ions in the glass. In this paper, the MAE is studied in antimony oxides based glasses 60Sb₂O₃–20MoO₃–(20 – x)Li₂O–xNa₂O and 60Sb₂O₃–20MoO₃–(20 – x)Li₂O–xK₂O (in mol %). The influence of Na/Li and K/Li ratios on ionic AC and DC conductivities, and T_g is presented. Dependences of T_g on x, in both types of glasses, have typical minima at x ≅ 10, it means that the minima take place at approximately equal concentrations of both mixed alkali ions. The minimum for K₂O containing glasses is deeper, probably due to a larger difference between ionic radii of K⁺ and Li⁺ ions. In glasses with one type of alkali ion, T_g decreases in the sequence: K → Li → Na. Temperature dependences of the DC conductivity obey Arrhenius-like relation. The conductivity steeply decreases with increasing Na or K content due to the larger ionic radius of both ions comparing to that of Li ions. At the same time, the conduction activation energy goes through a flat maximum at x = 15 (1.21 eV) for Na₂O modifier and at x = 5 (1.16 eV), for K₂O modifier. In antimony oxide based glasses, Li⁺, Na⁺, and K⁺ ions are modifiers and dominant charge-carriers. Due to larger ionic radii of Na⁺, and K⁺, the decrease of the conductivity after their addition is reasonable.

An original method for the synthesis of silver vanadate was developed. It includes mechanical activation of the precursor in the course of plastic deformation on a high-pressure apparatus of the Bridgman anvil type, which is significantly time- and energy-saving. It was shown that the addition of silver vanadate to fluorocarbon improves the electrochemical characteristics of the electrodes, especially in pulsed discharge modes.

The methods of ¹H NMR and pulsed field gradient NMR are used to study the protic solid electrolyte of calix[4]arene-para-sulfonic acid in the temperature range of –15 to 24°C and water content λ of 1.6 to 5.7 H₂O molecules per SO₃H. Analysis of the ¹H signal intensity in NMR spectra showed that no ice phase is formed in the whole studied temperature and water content range. The hydration numbers of H⁺(H₂O)_h complexes are calculated on the basis of the temperature dependences of chemical shift values. The pulsed field gradient NMR technique is used to determine self-diffusion coefficients. Activation energies E_act are calculated on the basis of the temperature dependences of self-diffusion coefficients. Good agreement of the data on diffusion E_act and protic conductivity are shown. A corollary of the Nernst–Einstein equation is used to calculate the values of protic conductivity on the basis of self-diffusion data. The calculated values of protic conductivity in the water content λ range of 1.6 to 5.7 agree with the data obtained experimentally.

Polymer of intrinsic microporosity PIM-1 was used for electrospun polymer nanofiber producing. After pyrolysis, the obtained nanofibers, in a form of entire mat, were used as a support for cathode electrocatalyst for high-temperature polymer electrolyte membrane fuel cell on polymer polybenzimidazole membrane. The material was characterized by the methods of standard contact porosimetry, Raman spectroscopy and scanning electron microscopy. The I-V curves for membrane-electrode assembly suggest a possibility of using the carbon material for electrodes in a fuel cell on polymer membrane.

A technology for preparation of thin-film solid-state batteries based on the silver‑iodine electrochemical system by aerosol deposition in vacuum is developed. Functional layers of the battery are studied by optical and scanning electron microscopy. Voltammetric characteristics of the thus assembled battery show that its maximum discharge current exceeds 3 mA/cm², which is sufficient for supplying power to the majority of medical devices.

Some features of processes occurring during the polarization of smooth platinum electrode in 10.0 M methanesulfonic acid (CH₃SO₃H) solution at high anodic potentials are studied by the cyclic voltammetry method. On cyclic voltammograms of smooth platinum electrode in concentrated methanesulfonic acid solution, well-pronounced oxidation waves are observed at potentials E = 2.0–2.5 V and E = 2.9–3.7 V. The electrochemical processes occurring in 10 M CH₃SO₃H solution within the E = 2.0–2.5 V potential range are shown to be associated with discharge of water molecules; the broad oxidation wave within the potential range of E = 2.9–3.7 V is related to the formation of peroxide compounds. Based on the electrochemical measurements and analysis of products of preparative electrooxidative electrolysis, the formation of a complex organosulfur peroxide compound, bis(methanesulfonyl) peroxide CH₃S(O)₂OOS(O)₂CH₃ (other names: dimethyl disulfoperoxide, or dimethanesulfonyl peroxide, or dimesylate peroxide) is established. Anodic oxidation mechanism in concentrated CH₃SO₃H solutions is proposed. It is supposed that the formation of the peroxide compound is associated with the participation of mesylate-radicals that dimerize at the smooth platinum anode and then are desorbed into the solution bulk.