Properties of Interface between Platinum Sponge and Solid Electrolyte Na5TbSi4O12in an Oxygen Atmosphere at Moderate Temperatures: Effect of the Platinum Grain Size

The behavior of electrochemical cells Pt(sponge)/Na₅TbSi₄₁₂/Na_0.65Co₂(cell I) and Pt(sponge)/Na₅TbSi₄₁₂/Pt(sponge) (cell II) is studied by, respectively, potentiometric and impedance methods in oxygen and argon atmospheres at 50–300°C. Dependence of potential of cell I on the oxygen concentration is affected by the grain size of platinum sponge and the temperature. At 50–200°C the coarse-grained platinum electrode in contact with solid electrolyte Na₅TbSi₄₁₂ exhibits an oxygen function characterized by the potential-determining reaction ₂(g) + ₂ + 2 = ^– ₂ + ^–. An impedance method shows the triple-phase boundary ₂, Pt(sponge)/Na₅TbSi₄₁₂ to be reversible with respect to oxygen. The reversibility is realized by minority charge carriers in the solid electrolyte, i.e. by oxygen ions.     

Electrochemical sensors based on platinized Ti1 − x Ru x O2

Electrocatalysts based on platinized titania modified with ruthenia (0–9 mol %) were studied. The synthesized materials were investigated as working electrodes in potentiometric sensors sensitive to hydrogen and carbon monoxide. All electrocatalysts showed reproducible behavior at pure gas concentrations from 400 to 4000 ppm. In CO-H₂ mixtures with comparable concentrations of both gases, the sensors were selective toward hydrogen at ≥0.05 mol % Ru, but not selective to hydrogen or CO at less than 0.05 mol % Ru in the substrate.     

Electrocatalytic properties of the catalysts based on carbon nanofibers with various platinum contents

The catalysts on carbon nanofibers with various platinum contents were synthesized. The morphology, resistance to oxidation, and electrochemical behavior of the catalysts in the reactions that occur in fuel cells were studied. The dependence of the specific output of cathodes of hydrogen—air fuel cells on the sizes of the platinum clusters was established.     

Reference electrodes for low-temperature gas sensors

The behavior of sodium oxide bronzes in contact with sodium-conducting solid electrolytes in atmospheres of oxygen, carbon dioxide, hydrogen sulfide, and humid air was investigated. The exchange currents at the Na_xCoO_y/NASICON interface was determined. It is shown that among the sodium-cobalt oxide bronzes the β-phase of the composition Na_0.6CoO₂ is the most reversible one (exchange current 236 μA/cm²). Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1994     

Superionic transitions in NASICON-type solid electrolytes

Four different methods, temperature dependent X-ray diffraction, impedance measurements, calorimetry and dilatometry, were employed to investigate the superionic transitons of NASICON type materials. Two singularities are found at 160 – 170 °C and about 230 °C. The first one is related to a second order phase transition close to the temperature of structural phase transition; the second one coincides with the inflection in the temperature dependence of conductivity. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–15, 1995     

Percolation model of conductivity of calix[n]arene-p-sulfonic acids

Proton conductivity of special class of aromatic sulfonic acids is described, in particular, calixarene sulfonic acids that consist of flat anionic layers interlinked by labile two-dimensional hydrogen-bond network. High proton conductivity of their hydrates was observed earlier. The dependence of their transport characteristics (the proton conductivity, the activation energy of conductivity) was shown to have threshold character. The studied systems’ behavior is described on basis of percolation model that assumes changing of the proton transport mechanism at low water content in the structure.     

Oxide supported platinum electrocatalysts for hydrogen and alcohol fuel cells

Efficient oxide supported electrocatalysts for hydrogen and alcohol fuel cells are developed. They are characterized by a low content of platinum, exhibit high activity in the oxidation of low-molecular alcohols and tolerance to the CO poisoning. It is shown that the application of catalysts developed (Pt/SnO₂-SbO _x ) enables one to raise the power of fuel cells operating on ethanol approximately by two times as compared with similar fuel cells with commercial PtRu/C catalysts.     

Effect of the Nature of a Sodium-Conducting Solid Electrolyte on the Impedance of Its Interface with the SmCo0.8Ti0.2O3 Oxide Electrode in an Oxygen Atmosphere

Impedance spectroscopy is employed for studying the behavior of the interface of the SmCo_0.8Ti_0.2O₃ semiconducting oxide electrode with a sodium-conducting solid electrolyte (Na⁺–SE) in atmospheres of argon and oxygen. Compounds with the susceptibility to hydration decreasing in the row Na₅TbSi₄O₁₂ Na₃Zr₂Si₂PO₁₂ Na₃Sc₂(PO₄)₃ are used as the Na⁺–SE. Only the systems containing the Na₅TbSi₄O₁₂ solid electrolyte, the grain surfaces of which acquire boundary layers formed by hydration products, are sensitive to oxygen. The exchange current of the electrode reaction O₂ (g) + e O₂ ^– increases from 1.8 to 19 mA/cm² in the temperature interval 250–300°C. The systems with Na⁺–SE that are not prone to hydration remain inactive in the oxygen atmosphere probably due to quick blocking of the active centers by nonconducting products of the secondary chemical reaction Na⁺ + O₂ ^– NaO₂.