We investigated the morphology and phase composition of tantalum diboride (TaB2) oxidation products by oxygen in the air across a temperature range of 20 to 1000°C. At isothermal conditions of 450, 500, 550, and 600°C, we determined the oxidation rate constants for TaB2 nanoparticles with an average particle diameter of 70 nm (0.0006, 0.0027, 0.009, and 0.015 s–1, respectively). The apparent activation energy for the oxidation reaction of TaB2 nanoparticles, derived from the temperature dependence of the rate constants, was estimated to be 115 ± 6 kJ/mol.

Near-spherical niobium diboride nanoparticles with an average diameter of ~17 nm, crystallizing in the hexagonal system and belonging to the space group P6/mmm, were obtained by reacting NbCl5 with NaBH4 in ionic melts of alkali metal halides at 1073 K under an argon pressure of 4 MPa for 15 h in an autoclave.

In this paper, we study the electrocatalytic activity and stability of materials in the Pt/Ti 1 – x Ru x O 2 – δ system, in oxygen electroreduction reactions, including under operating conditions in a fuel cell (FC). All the obtained electrocatalytic materials are shown to be stable in the electrode potential range of operation of a hydrogen-air FC, while the electroreduction of oxygen proceeds mainly by a four-electron mechanism. The power characteristics of the FC with the obtained electrocatalyst are comparable to those of a FC with a commercial electrocatalyst, while the stability of the obtained electrocatalysts is 5–6 times higher than that of Pt/C catalysts.

In  this  paper,  we  study  the  electrocatalytic  activity  and stability of materials in the Pt/Ti1 – xRuxO2 – δ system, in oxygen electroreduction reactions, including under operating conditions in a fuel cell (FC). All the obtained electrocatalytic materials are shown to be stable in the electrode potential range of operation of a hydrogen-air FC, while the electroreduction of oxygen proceeds mainly by a four-electron mechanism. The power characteristics of the FC with the obtained electrocatalyst are comparable to those of a FC with a commercial electrocatalyst, while the stability of the obtained electrocatalysts is 5–6 times higher than that of Pt/C catalysts.

Titanium diboride nanoparticles with diameter of 5–7 nm have been synthesized via the reaction of TiCl 4 with NaBH 4 in a NaCl‒KCl ionic melt in an autoclave reactor.

— The products of reaction between TiCl 4 and NaBH 4 in NaCl/KCl or KBr ionic melts at 973 and 1023 K under an argon pressure of 5 MPa have been characterized by various physicochemical analysis techniques. The results demonstrate that these conditions lead to the formation of TiB 2 nanoparticles with hexagonal symmetry (sp. gr. P 6/ mmm , AlB 2 structure) and lattice parameters a = 0.3022–0.3025 nm and с = 0.3214–0.3221 nm. The average diameters of the TiB 2 nanoparticles evaluated from electron microscopy, specific surface area, and X-ray diffraction (crystallite size) data for the two synthesis temperatures are ~10 and ~15, ~12 and ~17, and ~5 and ~10 nm, respectively.

The products of oxidation of ZrB2 powders with average particle sizes of ~100 and ~30 nm by atmospheric oxygen under isothermal conditions and during heating have been characterized by thermal analysis, X-ray diffraction, scanning electron microscopy, IR frustrated total internal reflection spectroscopy, energy dispersive X-ray analysis, and elemental analysis. The oxidation onset has been observed at 594 and 396°C, respectively. Oxidation at temperatures of ≥800°C leads to the formation of boron oxide and monoclinic ZrO2, independent of the particle size of ZrB2. The reaction rate constants for the oxidation of ZrB2 nanoparticles ~100 and ~30 nm in size have been determined to be 0.03, 0.15, and 0.31 h–1 at 600, 650, and 700°C and 0.11, 0.35, and 0.81 h–1 at 500, 600, and 700°C, respectively. The apparent activation energies for the oxidation of the ZrB2 nanoparticles ~100 and ~30 nm in size are 161 ± 4 and 62 ± 3 kJ/mol, respectively, as evaluated from the temperature dependence of the rate constants at the above temperatures.

We have studied reaction between ZrCl 4 and NaBH 4 at temperatures between 300 and 725°C. The results demonstrate that single-phase zirconium diboride nanoparticles are formed starting at 575°C. According to electron microscopy data, the ZrB 2 powder obtained at 575 and 725°C consists of variously shaped particles, some of which are almost spherical, ranging in diameter from ~10 to 20 and from 25 to 35 nm, respectively. These values agree with the equivalent particle diameters evaluated from the measured specific surface area of ZrB 2 , ~14 and ~32 nm, respectively, and with the crystallite size extracted from X-ray diffraction data: D hkl ~ 13 and 28 nm.

Products of the zirconium powder reaction with amorphous boron in a Na2B4O7 ionic melt at 650–850°C and those of the ZrCl4 reaction with NaBH4 at 300–725°C have been studied by means of X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetry, and elemental analysis. At temperature ≥750°C, single-phase ZrB2 with the particle size of 60–80 nm is formed in a Na2B4O7 ionic melt, whereas the ZrB2 powder obtained via the reaction of ZrCl4 with NaBH4 at temperature ≥575°C consists of particles differing in the shape, some of which are close to spherical with diameter of 10–35 nm.

The effect of antimony doping of tin dioxide at Sb/Sn = 0.2–2.5 on the physical properties and structure of air-dry samples of hydrous tin dioxide, SnO 2 ∙ nH 2 O (HTD), was studied by IR and Raman spectroscopy, powder X-ray diffraction, impedance measurements, TGA, and electron microscopy. The doped materials retained the structure of undoped HTD materials if the Sb/Sn ratio did not exceed the threshold value of 1.0. When Sb/Sn > 1, crystalline antimony oxide admixture appeared. The data of IR spectroscopy attested to the presence of two types of water in HTD-Sb, namely, physisorbed and chemisorbed water. The major part of water of the former type can be removed by evacuation at room temperature. Chemisorption occurs upon coordination of water molecules by metal ions through the formation of metal–oxygen bonds. Water molecules of the latter type are retained in evacuated samples at room temperature and on heating above the boiling point of liquid water. By impedance spectroscopy, HTD-Sb samples were shown to possess fairly high proton conductivity at high humidity; however, the conductivity decreased by two orders of magnitude after partial removal of water molecules of the former type. This attests to the destruction of the loosely bound hydrogen bond network, across which proton transfer takes place. It was also found that under conditions of constant humidity, the proton conductivity successively decreases with increasing antimony concentration. This is attributable to the fact that Sb(III) ions polarize the local environment to a lesser extent than Sn(IV) ions.

Specimens of tin dioxide with modifying Sb and Pt additives are synthesized. Their physicochemical properties (specific surface area, porosity, and conductivity), chemisorption and catalytic activity in the model reaction of CO oxidation are studied. A considerable chemisorption of CO on SnO 2 and SnO 2 -SbO x is observed at 150–180°C. The oxidation of CO in the flow of gases starts in the same temperature range. An addition of platinum leads to a significant increase in the rate of CO oxidation, the reaction starts at 80°C. It is proposed that the process proceeds at the SnO 2 /Pt interface.

Single-phase samples of tungsten bronzes M x WO3 (M = K+, Rb+, Cs+) are prepared by solid-state synthesis. The reversibility of the M0.33WO3/M+-solid electrolyte interface is studied subject to the alkali metal nature and humidity over a wide temperature interval. The exchange current density at 24°C and 58%-relative humidity is 3.6 × 10−4 A/cm2 for the Rb0.33WO3/Rb+-solid electrolyte interface; 2.2 × 10−4 A/cm2 for the Cs0.33WO3/Cs+-solid electrolyte interface; and 1.3 × 10−4 A/cm2 for the K0.33WO3/K+-solid electrolyte interface. A correlation between the reversibility of the bronze|solid electrolyte interface, which is characterized by the exchange current density, and the rate of potential equilibration in sensor systems, where the bronze is a reference electrode, is revealed. Ionic component of the conductivity of the synthesized tungsten oxide bronzes is measured at a background of the predominant electronic conductivity. The ionic conductivity is three orders of magnitude lower than the electronic conductivity; it decreases in the series Rb0.33WO3 > Cs0.33WO3 > K0.33WO3, amounting to 2.3 × 10−2, 2.1 × 10−3, and 2 × 10−4 S cm−1, respectively. The working capacity of the M0.3WO3 bronzes as reference electrodes in sensor systems for carbon dioxide detection is evaluated. The plots of the cell potential vs. the CO2 concentration in the electrochemical cells are linear, their slopes (59 ± 1 mV/decade) are characteristic for one-electron process. The fastest response to changes in the CO2 concentration was obtained with the sensor system that used Rb0.33WO3 as reference electrode.

Получены однофазные образцы оксидных вольфрамовых бронз MxWO3 (M = K+, Rb+, Cs+) твердофазным синтезом. Исследована обратимость границы M0.33WO3/M+-твердый электролит (ТЭ) в широком температурном интервале в зависимости от природы щелочного металла и влажности. Ток обмена при 24°С и влажности 58 отн. % равен 3.6 ? 10-4 А/см2 для границы Rb0.33WO3/Rb+-ТЭ, 2.2 ? 10-4 A/см2 для границы Cs0.33WO3/Cs+-ТЭ и 1.3 ? 10-4 А/см2 для границы K0.33WO3/K+-ТЭ. Обнаружена корреляция между обратимостью границы бронза/ТЭ, характеризуемой величиной тока обмена, и скоростью установления потенциала в сенсорных системах, использующих бронзу в качестве опорного электрода. Измерена ионная составляющая проводимости синтезированных вольфрамовых оксидных бронз на фоне преимущественно электронной проводимости. Ионная проводимость на три порядка меньше электронной и уменьшается в ряду Rb0.33WO3 > Cs0.33WO3 > K0.33WO3, составляя 2.3 ? 10-2, 2.1 ? 10-3 и 2 ? 10-4 См см-1 соответственно. Исследована работоспособность бронзы состава M0.3WO3 в качестве электрода сравнения в сенсорной системе на углекислый газ. Зависимости потенциала электрохимических ячеек от концентрации CO2 линейны с наклоном прямых, характеризующим одноэлектронный процесс (59 ± 1 мВ/дек). Сенсорная система с Rb0.33WO3 в качестве электрода сравнения показала максимальную скорость отклика на изменение концентрации СО2.

Bi-ionic oxide bronzes of the AxBOy type (A=Na, Ca, Na–Ca, Sr, Na–Sr; B=V) were synthesized by solid state method. The values of partial electronic conductivity in the zNa0.33V2O5–(1−z)Ca(Sr)0.165V2O5 systems and ionic reversibility at the zNa0.33V2O5–(1−z)Sr0.165V2O5/Na3Zr2Si2PO12 interface were determined as functions of Na0.33V2O5 content. It has been found that the ion substitution process Sr2+⇔2Na+ occurs at the Sr0.165V2O5/Na+-SE interface.