RU2807675C1 - Solid oxide electrolyte material with proton conductivity based on barium aluminum indate - Google Patents

Abstract

FIELD: electrochemical devices.

SUBSTANCE: production of materials for electrochemical devices, namely, solid oxide electrolyte materials with proton conductivity based on barium aluminum indate (Ba₇In₆Al₂O₁₉), which can be used as an electrolyte material in proton-conducting solid oxide fuel cells used to generate electricity. Increasing proton conductivity and chemical stability in a carbon dioxide atmosphere is a technical result, which is achieved by the fact that the material is barium aluminum indate, doped with yttrium, having the composition Ba₇In_6-xY_xAl₂O₁₉ (x = 0.05-0.25).

EFFECT: material is characterized by high values of proton conductivity at temperatures less than 800°C.

1 cl, 9 ill., 1 tbl

Description

The invention relates to the production of materials for electrochemical devices, namely, to solid oxide electrolyte materials with proton conductivity based on barium aluminum indate (Ba ₇ In ₆ Al ₂ O ₁₉ ), which can be used as an electrolyte material in proton-conducting solid oxide fuel cells, used to generate electricity.

Currently, the most promising proton conductor is doped barium cerate BaCeO ₃ , which has the highest proton conductivity among the known complex oxides with a perovskite structure of the general formula ABO ₃ . However, these materials have low chemical stability, in particular, ceramics are susceptible to degradation when interacting with carbon dioxide CO ₂ and water vapor in the air [Scholten MJ, Schoonman J., Miltenburg JC, Oonk HAJ Synthesis of strontium and barium cerate and their reaction with carbon dioxide // Solid State Ionics. - 1993. V. 61. P. 83-91]. They are trying to partially solve the problem by replacing cerium with zirconium (partially or completely), which makes it possible to slightly increase the stability time of compounds in a carbon dioxide atmosphere, but does not lead to a radical increase in chemical stability [Sažinas R., Bernuy-López C., Einarsrud M.- A., Grande T. Effect of CO ₂ Exposure on the Chemical Stability and Mechanical Properties of BaZrO ₃ -Ceramics // Journal of the American Ceramic Society. - 2016. V. 99. P. 3685-3695]. At the same time, zirconates are characterized by lower values of proton conductivity than cerates [Yamazaki Y., Hernandez-Sanchez R., Haile SM High total proton conductivity in large-grained yttrium-doped barium zirconate // Chem. Mater. - 2009. V.21. P. 2755-2762]. In addition, when zirconium is introduced into the B-sublattice, the sintering temperature of materials (1700°C) increases significantly to obtain high-density ceramics [Kreuer KD Proton-Conducting Oxides// Annu. Rev. Mater. Res. - 2003. V. 33. P. 333-359].

Based on the above, known materials are characterized by low efficiency when operating in fuel cells and the search for materials characterized by both chemical stability and high values of proton conductivity is relevant.

Chemical compounds with a new structure different from the perovskite structure, for example, a coherent intergrowth structure, can be considered as new promising proton conductors. Barium aluminum indate Ba ₇ In ₆ Al ₂ O ₁₉ is known as such. This material is a proton conductor at temperatures below 400°C and atmospheric humidity pH ₂ O = 2⋅10 ^-2 atm, however, the values of proton conductivity for it are relatively low and at 400°C are 2.6⋅10 ^-5 Ohm ^-1 ⋅cm ^-1 . No data have been found on the study of the chemical stability of this compound to carbon dioxide.

The objective of the present invention is to develop a material with increased proton conductivity and chemical stability in a carbon dioxide atmosphere, which can be used as an electrolyte in a solid oxide fuel cell.

For this purpose, a solid oxide electrolyte material with proton conductivity based on barium aluminum indate is proposed, which is barium aluminum indate doped with yttrium, having the composition Ba ₇ In _{6 - x} Y _x Al ₂ O ₁₉ (x = 0.05 - 0.25).

When yttrium is introduced into the indium sublattice, interatomic distances increase, which is confirmed by an increase in the crystal lattice parameters presented in the table; due to this, the values of oxygen-ion and proton conductivity increase.

The chemical resistance of the material to carbon dioxide is ensured by the structural features, namely, the coherent fusion of blocks of different structures, due to which they lose the ability to react with carbon dioxide.

The obtained samples of barium aluminum indate doped with yttrium are characterized by high values of proton conductivity with dominance of proton transport at T < 800°C and pH ₂ O = 2⋅10 ^-2 atm, phase stability, chemical resistance to carbon dioxide, which are necessary conditions for using the material as an electrolyte in a proton-conducting fuel cell.

The new technical result achieved by the claimed invention is the creation of a material based on barium aluminum indate, characterized by high values of proton conductivity at T < 800°C and pH ₂ O = 2⋅10 ^-2 atm and chemical resistance to carbon dioxide.

The invention is illustrated by a table containing the compositions of samples of the material under study and the parameters of the unit cells of complex oxides Ba ₇ In _{6- x} Y _x Al ₂ O ₁₉ corresponding to the samples, as well as by drawings showing:

- in fig. 1 - diffraction pattern of the sample x = 0.05;

- in fig. 2 - diffraction pattern of sample x = 0.10;

- in fig. 3 - diffraction pattern of sample x = 0.15;

- in fig. 4 - diffraction pattern of the sample x = 0.20;

- in fig. 5 - diffraction pattern of sample x = 0.25;

- in fig. 6 - diffraction patterns of the sample x = 0.10 after its heat treatment in a carbon dioxide atmosphere (10, 24, 48 hours, T = 600°C, pCO ₂ = 1 atm);

- in fig. 7 - temperature dependences of the electrical conductivity of samples of materials Ba ₇ In _{6- x} Y _x Al ₂ O ₁₉ (x = 0.05, 0.1, 0.15, 0.20, 0.25) in comparison with the material Ba ₇ In ₆ Al ₂ O ₁₉ in dry (pH ₂ O = 3.5⋅10 ^-5 atm, closed signs) and humid (pH ₂ O = 2⋅10 ^-2 atm, open signs) air;

- in fig. 8 - dependence of proton electrical conductivity on the dopant concentration (x) at different temperatures;

- in fig. 9 - dependence of conductivity on the partial pressure of oxygen pO ₂ using the example of the composition Ba ₇ In _5.9 Y _0.1 Al ₂ O ₁₉ at different temperatures.

The material Ba ₇ In _{6- x} Y _x Al ₂ O ₁₉ (x = 0.05, 0.1, 0.15, 0.20, 0.25) was obtained by solid-phase synthesis, known, for example, from [Andreev R. and Animitsa I. Transport Properties of Intergrowth Structures Ba ₅ In ₂ Al ₂ ZrO ₁₃ and Ba ₇ In ₆ Al ₂ O ₁₉ // Appl. Sci. 2023, 13, 3978. https://doi.org/10.3390/app13063978].

X-ray phase analysis of samples of materials Ba ₇ In _5.95 Y _0.05 Al ₂ O ₁₉ (Fig. 1), Ba ₇ In _5.90 Y _0.10 Al ₂ O ₁₉ (Fig. 2), Ba ₇ In _5.85 Y _0.15 Al ₂ O ₁₉ (Fig. 2) was carried out. 3), Ba ₇ In _5.80 Y _0.20 Al ₂ O ₁₉ (Fig. 4), Ba ₇ In _5.75 Y _0.25 Al ₂ O ₁₉ (Fig. 5) on a Bruker Advance D8 diffractometer in CuKα radiation at a tube voltage of 40 kV and current 40 mA. The shooting was carried out in the interval 2θ = 20°-90° with a step of 0.05°θ and an exposure of 1 second per point. The analysis showed that the materials Ba ₇ In _6-x Y _x Al ₂ O ₁₉ (x = 0.05, 0.10, 0.15, 0.20, 0.25) are single-phase and characterized by a hexagonal structure (space group P6 ₃ /mmc).

In fig. Figure 6 shows diffraction patterns using the example of a Ba ₇ In _5.90 Y _0.10 Al ₂ O ₁₉ sample after heat treatment in a carbon dioxide atmosphere (10, 24, 48 hours, T = 600°C, pCO ₂ = 1 atm). The analysis showed that the materials do not interact with CO ₂ at a temperature of 600°C. Before and after exposure to a CO ₂ flow, the samples remained single-phase. Consequently, ceramics based on Ba ₇ In ₆ Al ₂ O ₁₉ are not subject to carbonization, which guarantees its sufficient strength and long-term operation of electrolytes with stable performance characteristics.

Using the impedance spectroscopy method on an Impendancemeter Elins Z-1000P device, the electrical conductivity of the resulting materials Ba ₇ In _{6- x} Y _x Al ₂ O ₁₉ (x = 0.05, 0.10, 0.15, 0.20, 0.25) was determined in the temperature range from 300°C to 900°C , in the frequency range 1 Hz-1 MHz, in an air atmosphere pO ₂ = 0.21 atm. The measurement results are shown in Fig. 7 in dry pH ₂ O = 3.5⋅10 ^-5 atm (closed signs) and wet pH ₂ O = 2⋅10 ^-2 atm (open signs) atmospheres. The data demonstrate high values of electrical conductivity in the studied temperature range, which for the materials Ba ₇ In _{6- x} Y _x Al ₂ O ₁₉ (x = 0.05, 0.10, 0.15, 0.20, 0.25) are higher than for the material Ba ₇ In ₆ Al ₂ O ₁₉ . With increasing concentration of the dopant (x), an increase in the values of proton electrical conductivity is observed (Fig. 8). The increase effect reaches 0.75 orders of magnitude at 400 ^o C. The dependence of electrical conductivity on the partial pressure of oxygen of the Ba ₇ In _{6- x} Y _x Al ₂ O ₁₉ samples (x = 0.05, 0.10, 0.15, 0.20, 0.25) was studied by the electrochemical method, the data are presented using the sample x = 0.10 as an example (Fig. 9). The partial pressure of oxygen was set and measured by an oxygen pump and a sensor, respectively, made of Y-doped ZrO ₂ ceramic. The study was carried out in the range of 10 ^-18 - 0.21 atm. The constancy of the electrical conductivity values was confirmed by the ionic nature of the material’s conductivity in a wide range of oxygen partial pressures and temperatures.

Thus, a new proton-conducting material based on barium aluminum indate, chemically stable in a carbon dioxide atmosphere, has been obtained, which can potentially be used as an electrolyte material for a solid oxide fuel cell.

Table Sample a, Å s, Å Ba ₇ In ₆ Al ₂ O ₁₉ 5.920(5) 37.7177 Ba ₇ In _5.95 Y _0.05 Al ₂ O ₁₉ 5.946(2) 37.889(0) Ba ₇ In _5.90 Y _0.10 Al ₂ O ₁₉ 5.951(2) 37.951(9) Ba ₇ In _5.85 Y _0.15 Al ₂ O ₁₉ 5.958(7) 37.986(8) Ba ₇ In _5.80 Y _0.20 Al ₂ O ₁₉ 5.968(6) 38.016(1) Ba ₇ In _5.75 Y _0.25 Al ₂ O ₁₉ 5.978(4) 38.057(8)

Claims (1)

Solid oxide electrolyte material with proton conductivity based on barium aluminum indate, which is barium aluminum indate doped with yttrium, having the composition Ba ₇ In _{6 - x} Y _x Al ₂ O ₁₉ (x = 0.05 - 0.25).