RU2843324C1 - Method for synthesis of electrolyte powder based on barium cerate-zirconate doped with scandium - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of materials for electrochemical devices and can be used to form an electrolyte in proton-ceramic fuel cells, electrolytic cells and electrochemical sensors. Electrolyte powder based on barium cerate-zirconates doped with scandium is obtained by controlled two-jet coprecipitation from barium, cerium, zirconyl and scandium nitrate solution using an aqueous solution of ammonia with concentration of 1 mol./dm³ and ammonium carbonate with concentration of 3 mol./dm³. Controlled two-jet coprecipitation of metal cations of synthesized powder is carried out by parallel dosing of nitric acid solution of metal salts, as well as an aqueous solution of ammonia and ammonium carbonate into a reaction medium – distilled water with continuous mixing and constant pH~9.0. Obtained hydroxo-carbonate precipitate is separated by filtration, dried at 150 °C for 24 hours, annealed in a muffle furnace at 1400 °C for 6 hours and milled in a ball mill with a rotation speed of 250 rpm for 1 hour.

EFFECT: obtained electrolyte material with perovskite structure has chemical composition BaCe_0.4Zr_0.5Sc_0.1O_3-δ and an average particle size of 40 mcm, which can be considerably reduced by grinding in a planetary mill.

1 cl, 1 dwg, 1 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

The invention relates to the production of materials for electrochemical devices, namely, to a method for producing a powder based on barium cerate zirconate doped with scandium (Ba(Ce,Zr,Sc) _O3 ), which can be used to form an electrolyte in proton-ceramic fuel cells (PCFC), electrolyzers and electrochemical sensors.

Solid oxide fuel cells (SOFC) are devices that allow efficient conversion of energy from the chemical reaction of fuel oxidation (hydrogen, methane, methanol, etc.) into electrical energy. The existing disadvantages of SOFC, in particular operation at high temperatures, as well as high production and maintenance costs, stimulate the search for new solutions in the design and construction of these devices.

The operating temperatures of SOFCs usually depend on the type of electrolyte used. Therefore, many studies are currently devoted to medium-temperature SOFCs, which are operated at 500-700 °C. These include, in particular, devices based on proton-conducting electrolytes. Among the known electrolyte materials, the greatest attention has been paid to complex oxides based on perovskite BaZrO ₃ -BaCeO ₃ , which are distinguished by a combination of high proton conductivity at low temperatures and acceptable stability.

LEVEL OF TECHNOLOGY

The main method for obtaining electrolyte materials is the solid-phase synthesis method, which is characterized by simplicity of implementation and the required equipment. For example, this method was used to obtain a proton-conducting electrolyte of the composition Sr _1-x Ba _x Ce _0.5 Zr _0.35 Y _0.1 Sm _0.05 O _3-δ (x = 0; 0.1; 0.3; 0.5; 0.7 and 0.9) [US10714779B2, published 14.07.2021]. According to the known method, weighed portions of SrO, BaCO ₃ , CeO ₂ , ZrO ₂ , Y ₂ O ₃ and Sm ₂ O ₃ powders, taken based on the stoichiometric ratio, were mixed in ethanol, ground in an agate mortar and fired at 950 °C for 8 hours. Then, the fired powders were pressed using a hydraulic press and sintered at 1400 and 1450 °C for 6 and 8 hours, respectively. The wide distribution of particle sizes and their low specific surface area are considered the main disadvantages of this method, preventing the production of gas-tight ceramics at the sintering temperatures used.

The solid-phase method for synthesizing the electrolyte material is described in the article [AK Azad, JTS Irvine, Synthesis, chemical stability and proton conductivity of perovskites Ba(Ce,Zr)1-xScxO3-δ (Solid State Ionics, 2007, v. 178, pp 635-640, see Abstract, 2. Experimental)]. The powder samples of BaCO ₃ , CeO ₂ , ZrO ₂ and Sc ₂ O ₃ , selected in a stoichiometric ratio, were mixed in an acetone medium using zirconium grinding media and fired at 950 °C. The powders were then pressed using a hydraulic press and sintered at temperatures of 1350 and 1450 °C with a final sintering temperature of 1600 °C. The wide particle size distribution and their low specific surface area are considered the main disadvantages of this method. This method is also characterized by high final firing temperatures.

The sol-gel method was used to obtain an electrolyte of the chemical composition: BaZr _0.1 Ce _0.6 Sm _0.1 Y _0.1 Yb _0.1 O ₃ [CN112531190A, published 19.03.2021]. The method involves preparing a solution by dissolving weighed portions of barium, cerium, zirconium, samarium, yttrium and ytterbium nitrates in deionized water with stirring. Citric and ethylenediaminetetraacetic (EDTA) acids are added to the resulting solution in a certain molar ratio to metal ions. An aqueous ammonia solution is used to bring the solution to pH ~ 7 to stabilize metal complexes with organic ligands. The resulting mixture is stirred until a viscous gel is formed. The gel is placed in a muffle furnace for drying for 5 hours at 300 ° C to obtain a precursor. Further calcination of the precursor is carried out at a temperature of 1100 °C for 5 hours to obtain electrolyte powder. Ceramic samples are obtained by pressing in a mold under a pressure of 10 MPa, followed by sintering at 1350 °C for 5 hours. The proposed method allows obtaining samples of dense ceramics at lower temperatures, but this method is characterized by low productivity, high pollution levels (CO, CO ₂ , NO _x are released during the reaction process) and difficulty in scaling.

The electrolyte material of the composition Ba(Zr _0.1 Ce _0.7 Y _0.2 )O _3-δ is obtained by the additional precipitation method [S. H Min, JG Lee, OS Jeon, MG Park, KH Ryu, JH Myung, and YG Shul, Characteristics of Ba(Zr _0.1 Ce _0.7 Y _0.2 )O _3-δ nano-powders synthesized by different wet-chemical methods for solid oxide fuel cells (Ceramics International, 2017, pp 433–437, https://doi.org/10.1016/j.ceramint.2017.09.195].

According to this method, a solution of nitrates of the corresponding metals is added dropwise to a solution of ammonium carbonate with vigorous stirring until complete precipitation. The resulting suspension is maintained with constant stirring for 2 hours and then settled for 6 hours. The resulting precipitate is washed several times with distilled water and ethanol and, after washing, dried at 100 °C for 24 hours, and then calcined at 1000 °C for 3 hours.

Methods for synthesizing electrolyte material based on Ba(Ce,Zr,Sc) _O3 using the coprecipitation method have not been found in the prior art.

DISCLOSURE OF THE ESSENCE OF THE INVENTION

The technical problem solved by the claimed invention consists in expanding the methods for producing electrolyte powders using the coprecipitation method.

For this purpose, a method for synthesizing an electrolyte powder based on barium cerate-zirconate doped with scandium is proposed, including the simultaneous precipitation of metal ions in a reaction medium, filtration of the resulting suspension to separate the hydroxy-carbonate precipitate, which is successively subjected to drying, high-temperature treatment and grinding.

The new method is characterized in that the electrolyte powder is obtained by controlled two-jet coprecipitation from a nitric acid solution of barium, cerium, zirconium and scandium using an aqueous solution of ammonia with a concentration of 1 mol/ ^dm3 and ammonium carbonate with a concentration of 3 mol/ ^dm3 , while the controlled two-jet coprecipitation of the metal cations of the synthesized powder is carried out by parallel dosing of a nitric acid solution of metal salts, as well as an aqueous solution of ammonia and ammonium carbonate into the reaction medium - distilled water with continuous stirring and a constant pH value of ~ 9.0, followed by filtration and separation of the hydroxy-carbonate precipitate, which is dried at a temperature of 150 °C for 24 hours, fired in a muffle furnace at a temperature of 1400 °C for 6 hours and ground in a ball mill at a rotation speed 250 rpm for 1 hour.

The essence of the claimed method is that during controlled two-jet coprecipitation, barium, zirconyl, cerium and scandium cations at a pH of the reaction medium of 9 are simultaneously quantitatively precipitated in the form of insoluble hydroxides and carbonates, which ensures maximum contact between the forms of precipitates. The resulting hydroxy-carbonate precipitate promotes the formation of a monophase complex oxide after high-temperature heat treatment. As a result, the resulting powder has an average particle size of 40 μm, with the possibility of significantly reducing it by grinding in a planetary mill.

The new technical result achieved by using the invention consists in obtaining a powder material based on barium cerate-zirconate doped with scandium, with a perovskite structure, an average particle size of 40 μm, with the possibility of significantly reducing it by grinding in a planetary mill, suitable for the manufacture of electrolytes for PCTE, electrolyzers and electrochemical sensors.

BRIEF DESCRIPTION OF DRAWINGS

The invention is illustrated by a diffraction pattern of a powder sample obtained according to the claimed method (Fig.).

IMPLEMENTATION OF THE INVENTION

To produce a powder material based on barium cerate-zirconate doped with scandium, a nitric acid aqueous solution of metal salts was prepared in laboratory conditions by mixing concentrated nitrate solutions of barium, cerium, zirconyl and scandium, followed by dilution with distilled water to obtain the required concentration of cations. Concentrated nitric acid solutions of metals were prepared by dissolving basic zirconium carbonate, barium carbonate, cerium carbonate and scandium oxide in nitric acid upon heating.

An aqueous solution of ammonia and ammonium carbonate was prepared by diluting ammonia to 1 mol/ ^dm3 , followed by dissolving ammonium carbonate powder with constant stirring and a temperature of 80 °C. The molar ratio of ammonia and ammonium carbonate in the solution should be 1:3.

Controlled two-jet coprecipitation was carried out by parallel dosing of an aqueous solution of metal salts, as well as an aqueous solution of ammonia and ammonium carbonate into the reaction medium - distilled water with constant stirring using an overhead stirrer and maintaining a constant pH value at 9 by controlling the dosing rate of the aqueous solution of ammonia and ammonium carbonate. The volume of the reaction medium should be minimal to carry out coprecipitation in the constant stirring mode.

The suspension obtained after coprecipitation was subjected to filtration to separate the precipitate, followed by drying of this precipitate at a temperature of 150 °C until a constant weight was achieved.

The dried precipitate was subjected to high-temperature treatment in an air atmosphere at a temperature of 1400 °C for 6 hours.

To reduce the average size of the resulting particles, it is necessary to grind the powder material.

Example

To prepare an aqueous nitric acid solution of metal salts, 200 ^cm3 of distilled water, 501 ^cm3 of a barium nitrate solution with a concentration of 0.274 mol/ ^dm3 , 26 ^cm3 of a cerium nitrate solution with a concentration of 2.152 mol/ ^dm3 , 24 cm3 ^{of a} zirconium nitrate solution with a concentration of 2.865 mol/ ^dm3 and 6 ^cm3 of a scandium nitrate solution with a concentration of 2.436 mol/ ^dm3 were successively dosed into a beaker. The concentrated solutions were poured together with constant stirring and then brought to 1000 ^cm3 with distilled water.

To prepare an aqueous solution of ammonia and ammonium carbonate, 450 ^{cm3 of} distilled water, 53 cm3 ^of a commercial aqueous solution of ammonia and 216 g of ammonium carbonate were successively placed in a beaker, followed by bringing the resulting solution to 750 ^cm3 with distilled water. Dissolution was carried out with constant stirring and at a temperature of 80 °C.

After preparing the nitric acid aqueous solution of metal salts, as well as the aqueous solution of ammonia and ammonium carbonate, controlled two-jet coprecipitation was carried out. It took place with constant stirring of the reaction medium at a speed of 300 rpm, which was 200 ^cm3 of distilled water, by dosing the nitric acid solution of metal salts, as well as the aqueous solution of ammonia and ammonium carbonate in a dropwise mode. The pH of the reaction medium was maintained at 9.0 by adjusting the feed rate of the aqueous solution of ammonia and ammonium carbonate. Coprecipitation was considered complete when all the nitric acid aqueous solution of metal salts was exhausted.

After coprecipitation, the resulting suspension was filtered, and the wet precipitate separated in this way was successively dried in a drying cabinet at a temperature of 150 °C for 24 hours, subjected to high-temperature treatment in a muffle furnace at a temperature of 1400 °C for 6 hours, and ground in a ball mill at a rotation speed of 250 rpm for 1 hour. All operations were carried out in an air atmosphere.

The proposed method was used to obtain a powder material based on barium cerate-zirconate doped with scandium, with a perovskite structure, an average particle size of 40 μm, with the possibility of significantly reducing it by grinding in a planetary mill, suitable for the manufacture of electrolytes for PCTE, electrolyzers and electrochemical sensors.

Claims (1)

A method for synthesizing an electrolyte powder based on barium cerato-zirconates doped with scandium, characterized in that the electrolyte powder is obtained by controlled two-jet coprecipitation from a nitric acid solution of barium, cerium, zirconyl and scandium using an aqueous solution of ammonia with a concentration of 1 mol/dm ³ and ammonium carbonate with a concentration of 3 mol/dm ³ , wherein the controlled two-jet coprecipitation of the metal cations of the synthesized powder is carried out by parallel dosing of a nitric acid solution of metal salts, as well as an aqueous solution of ammonia and ammonium carbonate into a reaction medium - distilled water with continuous stirring and a constant pH value of ~9.0, followed by filtration and separation of the hydroxy-carbonate precipitate, which is dried at a temperature of 150 °C for 24 hours, fired in a muffle furnace at temperature of 1400 °C for 6 hours and ground in a ball mill at a rotation speed of 250 rpm for 1 hour.