Highly Conductive Fe-Doped (La,Sr)(Ga,Mg)O3-δ Solid-State Membranes for Electrochemical Application.

Membranes based on complex solid oxides with oxygen-ionic conductivity are widely used in high-temperature electrochemical devices such as fuel cells, electrolyzers, sensors, gas purifiers, etc. The performance of these devices depends on the oxygen-ionic conductivity value of the membrane. Highly conductive complex oxides with the overall composition of (La,Sr)(Ga,Mg)O3 have regained the attention of researchers in recent years due to the progress in the development of electrochemical devices with symmetrical electrodes. In this research, we studied how the introduction of iron cations into the gallium sublattice in (La,Sr)(Ga,Mg)O3 affects the fundamental properties of the oxides and the electrochemical performance of cells based on (La,Sr)(Ga,Fe,Mg)O3. It was found that the introduction of iron leads to an increase in the electrical conductivity and thermal expansion in an oxidizing atmosphere, while no such behavior was observed in a wet hydrogen atmosphere. The introduction of iron into a (La,Sr)(Ga,Mg)O3 electrolyte leads to an increase in the electrochemical activity of Sr2Fe1.5Mo0.5O6-δ electrodes in contact with the electrolyte. Fuel cell studies have shown that, in the case of a 550 µm-thick Fe-doped (La,Sr)(Ga,Mg)O3 supporting electrolyte (Fe content 10 mol.%) and symmetrical Sr2Fe1.5Mo0.5O6-δ electrodes, the cell exhibits a power density of more than 600 mW/cm2 at 800 °C.

Solid Electrolyte Membranes Based on Li2O-Al2O3-GeO2-SiO2-P2O5 Glasses for All-Solid State Batteries.

Rechargeable Li-metal/Li-ion all-solid-state batteries due to their high safety levels and high energy densities are in great demand for different applications ranging from portable electronic devices to energy storage systems, especially for the production of electric vehicles. The Li1.5Al0.5Ge1.5(PO4)3 (LAGP) solid electrolyte remains highly attractive because of its high ionic conductivity at room temperature, and thermal stability and chemical compatibility with electrode materials. The possibility of LAGP production by the glass-ceramic method makes it possible to achieve higher total lithium-ion conductivity and a compact microstructure of the electrolyte membrane compared to the ceramic one. Therefore, the crystallization kinetics investigations of the initial glass are of great practical importance. The present study is devoted to the parent glasses for the production of Li1.5+xAl0.5Ge1.5SixP3-xO12 glass-ceramics. The glass transition temperature Tg is determined by DSC and dilatometry. It is found that Tg decreases from 523.4 (x = 0) to 460 °C (x = 0.5). The thermal stability of glasses increases from 111.1 (x = 0) to 188.9 °C (x = 0.3). The crystallization activation energy of Si-doped glasses calculated by the Kissinger model is lower compared to that of Si-free glasses, so glass-ceramics can be produced at lower temperatures. The conductivity of the glasses increases with the growth of x content.

Densification and Proton Conductivity of La1-xBaxScO3-δ Electrolyte Membranes.

Bain La1-xBaxScO3-δ impairs sintering and leads to a decrease in its ceramic density. Two approaches have been studied for obtaining dense ceramics: using a high processing temperature and the introduction of a Co3O4 sintering additive. An addition of only 0.5 wt% of Co3O4 sintering additive, despite the positive sintering effect, causes a noticeable violation of stoichiometry, with partial decomposition of the material. This can lead to the formation of cationic vacancies, which form associates with oxygen vacancies and significantly reduce the oxygen ion and proton conductivity of the materials. There is also a partial substitution of Co for Sc in La1-xBaxScO3-δ, which reduces the stability of protons: it reduces the enthalpy of the hydration reaction, but increases the mobility of protons. Thus, the Co3O4 sintering additive causes a complex of negative effects on the conductivity of La1-xBaxScO3-δ materials. Only high-temperature (1800 °C) processing with protection against Ba loss contributes to the production of dense La1-xBaxScO3-δ ceramics. The chemical composition of such ceramics corresponds well to the specified one, which ensures high water uptake and, consequently, high proton conductivity.

Water Uptake and Transport Properties of La1-xCaxScO3-α Proton-Conducting Oxides.

In this study, oxide materials La1-xCaxScO3-α (x = 0.03, 0.05 and 0.10) were synthesized by the citric-nitrate combustion method. Single-phase solid solutions were obtained in the case of calcium content x = 0.03 and 0.05, whereas a calcium-enriched impurity phase was found at x = 0.10. Water uptake and release were studied by means of thermogravimetric analysis, thermodesorption spectroscopy and dilatometry. It was shown that lower calcium content in the main phase leads to a decrease in the water uptake. Conductivity was measured by four-probe direct current (DC) and two-probe ascension current (AC) methods at different temperatures, pO2 and pH2O. The effects of phase composition, microstructure and defect structure on electrical conductivity, as well as correlation between conductivity and water uptake experiments, were discussed. The contribution of ionic conductivity of La1-xCaxScO3-α rises with decreasing temperature and increasing humidity. The domination of proton conductivity at temperatures below 500 °C under oxidizing and reducing atmospheres is exhibited. Water uptake and release as well as transport properties of La1-xCaxScO3-α are compared with the properties of similar proton electrolytes, La1-xSrxScO3-α, and the possible reasons for their differences were discussed.