Cerium-Gadolinium Complex Oxide

Abstract

The present invention relates to a composite oxide based on cerium and gadolinium with a proportion of Gd between 8 and 22 mol %, corresponding to the molar ratio Gd / (Ce+Gd) expressed in %, which exhibits an improved relative density.

Description

[Technical field]

[0001] The present invention relates to a cerium-gadolinium composite oxide, a process for its preparation and its use. The present invention also relates to a SOFC or SOEC comprising the composite oxide of the present invention.

[0002] A solid oxide fuel cell (or SOFC) is an electrochemical conversion device that produces electricity directly from the oxidation of a fuel. It is an electrochemical device that produces electrical energy by electrochemically oxidizing a fuel gas (usually hydrogen-based). The device is ceramic-based and uses an oxygen-ion conducting metal oxide-derived ceramic as the electrolyte. All SOFCs must operate at high temperatures, since the ceramic oxygen-ion conductors known in the art (most typically doped zirconium oxide or doped cerium oxide) only exhibit technically relevant ionic conductivity above 500°C (for cerium oxide-based electrolytes) or 600°C (for zirconium oxide-based ceramics).

[0003] The electrolyte is a crucial part of the battery and in SOFCs has the following main functions: · allowing the passage of electric current in the form of mobile oxygen ions between the cathode (positive air electrode) and the anode (negative fuel electrode); · To prevent the passage of electrical current between the electrodes in electronic form that could cause an internal short circuit in the battery; Preventing mixing of fuel and air, this requires that the electrolyte be at least 94% of theoretical density, meaning there is no interconnecting porosity and therefore the electrolyte layer is gas impermeable and virtually free of defects.

[0004] As disclosed in US Patent Application Publication No. 2016 / 233534, recent developments in the field of SOFCs have led to the development of zirconia-based materials with inherently higher oxygen ion conductivity, the formula Ce 0.9 Gd 0.1 O 1.95A cerium-gadolinium composite has been used as an oxygen-ion conducting electrolyte. [Background technology]

[0005] European Patent No. 1484282B1 discloses a cerium-gadolinium composite oxide that can obtain a high relative density at a high processing temperature, but does not disclose the same composite oxide as that of the present invention.

[0006] US Patent No. 6,709,628 discloses a method for producing sintered oxide ceramics based on cerium, a first doping element selected from the group consisting of Lu, Yb, Tm, Er, Y, Ho, Dy, Gd, Eu, Sm, and Nd, and a second doping element selected from the group consisting of Cu, Co, Fe, Ni, and Mn, which includes a sintering step at a temperature of 750°C to 1200°C to reach a density of at least about 98% of the theoretically possible density. Without the second dopant, the density is only 90% at 1450°C. Ce 0.8 Gd 0.2 Co z O 2-a Or Ce 0.8 Gd 0.2 Cu z O 2-a Specific compositions such as the following are disclosed.

[0007] In the specification of U.S. Patent Application Publication No. 2016 / 0233535, Ce 0.9 Gd 0.1 O 1.95 Or Ce 0.9 Sm 0.1 O 1.95 A method of forming an electrolyte for a metal-supported solid oxide fuel cell (SOFC) is disclosed that includes combining a doped ceria electrolyte such as CoO with a sintering aid. As can be seen in Figure 9, the relative density of the doped ceria electrolyte without the sintering aid (e.g., Co3O4 or CuO) is lower than 94% after firing at 1100°C, which means that it will be even lower at lower temperatures.

[0008] US Patent No. 7,947,212 B2 discloses the use of divalent or trivalent cations to densify ceria-based electrolytes, without which the relative density is less than 94% (Figure 2).

[0009] JP 2000 / 007435 A discloses a ceria-based composite oxide that can be used for the manufacture of SOFCs. This composite oxide is prepared by a method different from that of the present invention. Furthermore, high density is obtained, but only at temperatures higher than 1500° C.

[0010] Duran et al., "Sintering and microstructural development of ceria-gadolinia dispersed powders", J. Mat. Sci. 1994, 29(7), discloses a composite oxide ceria-gadolinia having a lower Gd content than that of claim 1 and a relative density at temperatures higher than 1300°C.

[0011] The paper Journal of Physics: Conference Series 339(2012)012006 (doi:10.1088 / 1742-6596 / 339 / 1 / 012006) discloses a relative density of 10 mol % gadolinium doped ceria, which is lower than the composition of the present invention. Summary of the Invention [Problem to be solved by the invention]

[0012] The densification process of the electrolyte requires sintering at high temperatures, and it is also advantageous to reach a high relative density to ensure the preparation of a gas-tight and robust electrolyte to avoid contact with the fuel and oxidizing gases (see Journal of The Electrochemical Society 2002, 149(7), A797-A803).

[0013] Naturally, it is more advantageous to reach a high relative density at the lowest possible temperature in order to save energy. It is also desirable to sinter at the lowest possible temperature in order to avoid degradation, such as oxidation and sintering, of the other components used in the manufacture of the SOFC.

[0014] Finally, the electrolyte is in contact with hot gases and must therefore be able to withstand the harsh conditions encountered.

[0015] It has been found that the complex oxide of the invention is capable of reaching high relative densities at high temperatures, such as 950° C., without the addition or incorporation of sintering agents, making it possible to avoid the introduction of additional elements that may affect the final physicochemical properties of the inorganic layers of fuel cells comprising the complex oxide.

[0016] Therefore, the present invention aims to prepare a ceria-based electrolyte suitable for the manufacture of SOFCs, which can be sintered at high temperatures, such as 950° C., with high relative density without the addition of sintering agents. [Means for solving the problem]

[0017] The present invention relates to a composite oxide based on cerium and gadolinium, in which the proportion of Gd is between 8.0 and 22.0 mol %, which corresponds to the molar ratio Gd / (Ce+Gd) expressed in %.

[0018] The composite oxide of the present invention is disclosed in claims 1 to 41. The present invention also relates to composition C disclosed in claims 42 to 46.

[0019] The present invention also relates to a method for preparing a complex oxide as disclosed in claims 49-50, to the use of a complex oxide or composition C as disclosed in any one of claims 47 or 48. The present invention also relates to an SOEC as disclosed in claim 51 or 52. The present invention also relates to an SOEC as disclosed in claim 53.

[0020] All these objectives are defined in more detail below. [Brief description of the drawings]

[0021] [Figure 1-2] 1 shows the size distribution of a complex oxide obtained by laser diffraction as disclosed in an example. [Diagram 3] 1 shows a porogram obtained by mercury intrusion porosimetry of the composite oxide of Example 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] It is noted that in the remainder of the specification, unless otherwise indicated, any range of values ​​given includes the upper and / or lower limits.

[0023] The composite oxide of the invention is based on cerium oxide and gadolinium oxide. It is characterized by a proportion of Gd between 8.0 mol % and 22.0 mol %, which corresponds to the molar ratio Gd / (Ce+Gd) expressed in %.

[0024] The proportion of Ce corresponds to the balance up to 100%. The proportion of Ce is 78.0 mol% to 92.0 mol%.

[0025] More specifically, the proportion of Gd may be 8.0 mol% to 15.0 mol%, in which case the proportion of Ce is 85.0 mol% to 92.0 mol%.

[0026] More specifically, the proportion of Gd may be 8.0 mol% to 12.0 mol%, in which case the proportion of Ce is 88.0 mol% to 92.0 mol%.

[0027] More specifically, the proportion of Gd may be 9.0 mol% to 11.0 mol%, in which case the proportion of Ce is 89.0 mol% to 91.0 mol%.

[0028] More specifically, the proportion of Gd may be 9.5 mol% to 10.5 mol%, in which case the proportion of Ce is 89.5 mol% to 90.5 mol%.

[0029] More specifically, the proportion of Gd may be 18.0 mol% to 22.0 mol%, in which case the proportion of Ce is 78.0 mol% to 82.0 mol%.

[0030] More specifically, the proportion of Gd may be 19.0 mol% to 21.0 mol%, in which case the proportion of Ce is 79.0 mol% to 81.0 mol%.

[0031] More specifically, the proportion of Gd may be 19.5 mol% to 20.5 mol%, in which case the proportion of Ce is 79.5 mol% to 80.5 mol%.

[0032] The invention also relates to a mixed oxide consisting of the two oxides CeO2 and Gd2O3, in particular according to the proportions indicated above.

[0033] According to one embodiment, the X-ray diffractogram (CuKα1, λ=1.5406 angstroms) of the composite oxide shows a solid solution pattern. According to another embodiment, the X-ray diffractogram of the composite oxide shows a peak P at 2θ between 27.0° and 30.0°. This peak P has the highest intensity on the diffractogram.

[0034] The composite material of the present invention contains the above-mentioned elements (Ce, Gd) in the above-mentioned proportions, but may also contain impurities. The impurities may originate from the raw materials or starting materials used in the preparation process of the composite oxide. The total proportion of impurities is less than 0.20% by weight, preferably less than 0.10% by weight, and more preferably less than 0.05% by weight, relative to the composite oxide. Everything disclosed in this specification applies to a composite oxide consisting of CeO2 and Gd2O3 in the proportions shown above and impurities, with the total proportion of impurities being less than 0.20% by weight, preferably less than 0.10% by weight, and more preferably less than 0.05% by weight.

[0035] The composite material of the present invention exhibits the following specific physicochemical properties: 1) Relative density RD The composite oxide has a relative density (RD) of at least 95.0% after calcination at 1000°C for 5 hours. 1000℃ / 5h RD 1000℃ / 5h is preferably at least 96.0%. 1000℃ / 5h may be up to 99.0% or up to 98.0%. 1000℃ / 5h may be 96.0% to 99.0%, more specifically, 96.0% to 98.0%.

[0036] The composite oxide has a relative density RD of at least 94.0% after calcination at 950°C for 5 hours. 950℃ / 5h RD 950℃ / 5h is preferably at least 95.0%. 950℃ / 5h may be up to 98.0% or up to 97.0%. 950℃ / 5h may be 94.0% to 98.0%, more specifically 95.0% to 97.0%.

[0037] The composite oxide has a relative density RD of at least 99.0%, preferably at least 99.5%, after calcination at 1100° C. for 5 hours. 1100℃ / 5h RD 1100℃ / 5h RD may be up to 99.0% or up to 99.5%. 1100℃ / 5h may be 99.0% to 100.0%, more specifically, 99.5% to 99.9%.

[0038] The composite oxide has a relative density (RD) of at least 99.5% after calcination in air at 1200°C for 5 hours. 1200℃ / 5h It can be shown that

[0039] The composite oxide is, for example, After sintering at 1000℃ for 5 hours, RD of at least 95.0% 1000℃ / 5h and After sintering at 950℃ for 5 hours, RD of at least 94.0% 950℃ / 5h ; It can be shown that

[0040] The relative densities shown for the composite oxides are determined on samples without the addition of other materials such as sintering aids.

[0041] The relative density RD is well known to those skilled in the ceramic art and corresponds to the density of the complex oxide expressed as a percentage of the absolute density of the complex oxide (%RD=density / absolute density×100).

[0042] In the context of the present invention, the density of the complex oxide is measured on a compressed sample of the complex oxide after calcining it in air for 5 hours at the test temperature (950°C, 1000°C, 1100°C or 1200°C). The compressed sample is obtained by applying pressure to the complex oxide in powder form placed in a mold. The die advantageously has a parallelepiped shape, since this allows easy measurement of the volume after calcination in air.

[0043] More specifically, the compressed sample can be prepared by the following method: i) weighing the composite oxide powder and placing it in a mold; ii) compressing the powder under pressure; iii) removing the compressed sample obtained at the end of step ii) from the mould; iv) The pressed samples are then calcined in air at the target temperature for 5 hours; v) measuring the density of the fired compacted samples; vi) The relative density is then calculated.

[0044] Density is measured according to laboratory techniques known to those skilled in the art.

[0045] In step v), more specifically, the following method can be used: v1) Weigh the calcined compressed sample (weight in g); v2) Measure the volume of the compressed sample (cm 3 (unit volume), the compressed sample is parallelepiped shaped, and the volume of the parallelepiped is given by: Volume = length (cm) x width (cm) x height (cm).

[0046] The length, width and height of the parallelepiped can be easily measured with a micrometer.

[0047] In step ii), the pressure applied to obtain a compressed sample is preferably at least 95 MPa, or even at least 98 MPa.

[0048] The test conditions given in the examples can conveniently be used.

[0049] The absolute density (or theoretical density) is determined by first calculating the lattice constants of the complex oxide structure from the XRD pattern, and then calculating the absolute density according to the following formula: Absolute density (g / cm 3 )=SA / (a×b×c×N)

[0050] SA represents the molar mass of all atoms in the unit cell, a, b, and c represent the lattice constants, and N represents the Avogadro constant.

[0051] The absolute densities used in the calculations are given in the table below.

[0052] [Table 1]

[0053] 2) Porosity and pore diameter Dp (Hg porosity) The method of the present invention can provide a composite oxide having a specific pore size distribution. The composite oxide can show a peak corresponding to a pore diameter Dp of 30 to 100 nm, the maximum of which is in the range of pores having a diameter of 200 nm or less. Dp may be 30 to 70 nm. The pore diameter is measured by mercury intrusion porosimetry.

[0054] The peak typically exhibits a peak half width of less than 80 nm, more specifically less than 70 nm, even more specifically less than 60 nm, even more specifically less than 50 nm, even more specifically less than 40 nm, even more specifically less than 30 nm, even more specifically less than 20 nm.

[0055] The pore volume (Vp <200nm ) is typically less than 0.40 mL / g, more specifically less than 0.35 mL / g, and even more specifically less than 0.30 mL / g. <200nm is usually at least 0.10 mL / g.

[0056] Typically, the porogram shows a single peak in the range of pores with diameters of 200 nm or less.

[0057] 3) BET specific surface area Complex oxides are usually 5 to 40 m 2 This BET specific surface area is 10 to 35 m / g. 2 / g, or 20-30m 2 / g, or 25-30m 2 / g. BET surface area is well known to those skilled in the art. It is measured by nitrogen adsorption using the well-known Brunauer-Emmett-Teller method. The BET method is specifically described in the journal "The Journal of the American Chemical Society, 60, 309 (1938)". The recommendations of the standard ASTM D3663-03 can be followed.

[0058] 4) Particle size (by laser diffraction) The complex oxides may also exhibit size specific characteristics as determined by laser diffraction analysis for size (volume) distribution.

[0059] D50 may be 0.1 to 15.0 μm. More specifically, D50 may be 0.2 μm to 15 μm, or further 1.0 μm to 15.0 μm, or 5.0 μm to 15.0 μm.

[0060] D16 may be 0.1 to 4.0 μm. More specifically, D16 may be 0.1 to 1.0 μm.

[0061] D84 may be 10.0 to 50.0 μm. More specifically, D84 may be 15.0 to 50.0 μm.

[0062] The parameters D16, D84 and D50 are obtained from a volume distribution measured by laser diffraction. D16 is the diameter determined from a distribution obtained by laser diffraction where 16% of the particles have a diameter smaller than D16. D84 is the diameter determined from a distribution obtained by laser diffraction where 84% of the particles have a diameter smaller than D84. D50 is the diameter determined from a distribution obtained by laser diffraction where 50% of the particles have a diameter smaller than D50. D50 is also called the median of the distribution.

[0063] The distribution may exhibit at least two populations. More specifically, the distribution may exhibit at least two populations P1 and P2 having the following characteristics: Group P1 with diameter D1 less than 3.0 μm as its center and / or · Population P2 centered on diameter D2 greater than 8.0 μm.

[0064] In particular, in the region less than 100 μm in diameter, the distribution may show two populations P1 and P2 with the following characteristics: Group P1 with diameter D1 less than 3.0 μm as its center and / or · Population P2 centered on diameter D2 greater than 8.0 μm.

[0065] The expression "population centred on diameter D" means that a peak is observed on the distribution curve with a maximum located at D.

[0066] D1 may be, more specifically, 0.1 μm to 3.0 μm, and even more specifically, 0.1 μm to 1.0 μm.

[0067] D2 may be, more specifically, 8.0 to 100 μm, more specifically, 10.0 to 100.0 μm, even more specifically, 10.0 to 70.0 μm, and particularly specifically, 10.0 to 50.0 μm.

[0068] The two populations P1 and P2 have a ratio H2 / H1 of the heights H1 and H2 of the two peaks of P1 and P2, respectively, of greater than 0.1, more specifically greater than 0.3, more specifically greater than 1.0, even more specifically greater than 1.5; or less than 7.0, more specifically less than 5.5, even more specifically less than 1.0, more specifically less than 0.8, even more specifically less than 0.5, It's okay to be like that.

[0069] The ratio H2 / H1 is usually 0.1 to 7.0, more specifically 0.1 to 5.5, and even more specifically 0.1 to 1.0. H2 / H1 may be 0.1 to 0.8, or even 0.1 to 0.5, or 0.4 to 0.5.

[0070] The ratio H2 / H1 depends on the process conditions, in particular the concentration of solution S and the conditions of step e). The more concentrated the solution S, the smaller the ratio. The longer the duration and / or the greater the intensity of the grinding step e), the smaller the ratio.

[0071] The composite oxide is usually in powder form.

[0072] Method for preparing composite oxides The method for preparing a composite oxide of the present invention comprises the steps of: a) Cerium nitrate (Ce III forming a precipitate by adding an aqueous solution S containing gadolinium nitrate and ammonium bicarbonate (NH4HCO3) to a basic aqueous solution of ammonium bicarbonate (NH4HCO3); b) heating the aqueous slurry containing the precipitate obtained at the end of step a) at a temperature between 50°C and 95°C; c) recovering the solid obtained at the end of step b) and washing it with water; d) calcining the solid recovered from step c) in air at a temperature between 600°C and 1000°C; e) grinding the calcined solid; Includes.

[0073] Process a) In step a), two aqueous solutions are mixed: a basic solution of NH4HCO3 and cerium nitrate (Ce III A solution S containing cerium nitrate and gadolinium nitrate with a target ratio of Gd is used. The concentration of cerium nitrate in solution S is usually 0.15 to 0.50 mol / L. A solution S contains Ce III , Gd III , NO3 - , and H + The concentration of cerium nitrate in solution S can be conveniently the one disclosed in Example 1 or Example 2.

[0074] Solution S is obtained by mixing two aqueous solutions of cerium nitrate and gadolinium nitrate, and diluting the resulting mixed nitrate solution with water. The amount of water used for dilution may be 5-10 times the amount of the mixed nitrate solution. The ratio of the volume of water / volume of the mixed nitrate solution may be as disclosed in Example 1 or 2.

[0075] Each of the two solutions (Ce nitrate and Gd nitrate) used to prepare the mixed nitrate solution may exhibit a residual acidity. The residual acidity can be easily measured by acid / base titration using methyl orange as an indicator. The aqueous cerium nitrate solution preferably exhibits a residual acidity of less than 0.1 mol / L, or even less than 0.07 mol / L. The aqueous cerium nitrate solution used in the examples can be conveniently used. The aqueous gadolinium nitrate solution preferably exhibits a residual acidity of less than 1.0 mol / L. The aqueous cerium nitrate solution used in the examples can be conveniently used.

[0076] The basic aqueous solution of NH4HCO3 is prepared by dissolving NH4HCO3 in solid form in water. The concentration of the basic aqueous solution of NH4HCO3 is preferably 30-100 g / L. The concentrations disclosed in Example 1 or Example 2 can be conveniently used.

[0077] Cerium nitrate (Ce IIIA precipitate is formed by adding an aqueous solution S containing ammonium bicarbonate (NH4HCO3) and gadolinium nitrate to a basic aqueous solution of ammonium bicarbonate (NH4HCO3) (this is usually disclosed as "reverse precipitation"). The addition flow rate of the aqueous solution S added to the basic aqueous solution is usually 50-200 L / h. Typically, the addition is carried out for 20-120 minutes, more specifically for 20-60 minutes. The flow rates and / or durations used in one of the examples can be used conveniently.

[0078] The temperature at which step a) is carried out is expediently between 10°C and 30°C.

[0079] The amount of hydrogen carbonate used in step a) is such that the molar ratio r=NH4HCO3 / (Ce+Gd) is between 3.00 and 3.48, more particularly between 3.10 and 3.45. The molar ratio r can conveniently be one of the molar ratios used in example 1 or 2.

[0080] Bicarbonate is only used in step a).

[0081] Process (b) In step b), the aqueous slurry containing the precipitate obtained at the end of step a) is heated at a temperature between 50°C and 95°C, more particularly between 70°C and 95°C. This temperature may be between 70°C and 85°C. The temperature disclosed in example 1 or 2 (80°C) can be conveniently used. The treatment time may be between 1 hour and 4 hours. The time disclosed in example 1 or 2 (3 hours) can be conveniently used.

[0082] The aqueous slurry heated during step b) can be obtained according to two embodiments. According to a first embodiment (preferred), the aqueous slurry is obtained directly at the end of step a). This means that steps a) and b) can be conveniently carried out in the same vessel.

[0083] According to a second embodiment, the aqueous slurry of step b) is obtained by diluting the aqueous slurry obtained at the end of step a) with water.

[0084] Process c) In step c), the solid obtained at the end of step b) is recovered and washed with water, for example deionized water. The conductivity of the filtrate can be measured. Usually, washing is carried out until the conductivity of the filtrate reaches less than 5 mS / cm.

[0085] Step d) In step d), the solid recovered from step c) is calcined in air at a temperature between 600°C and 1000°C. The calcination temperature is preferably between 750°C and 850°C. The duration of step d) may be between 1 and 25 hours, more specifically between 1 and 20 hours. Under certain conditions, the calcination temperature is 800°C and the calcination time at this temperature is 8 hours. The conditions of step d) of example 1 can be applied. The calcination step is aimed at converting cerium and gadolinium into oxides and increasing the crystallinity of the composition.

[0086] Process (e) The calcined solid obtained at the end of step d) is ground. A hammer mill may be used. The calcined solid can also be ground in a mortar.

[0087] For the preparation of the composite oxide according to the invention, in particular in the range of proportions indicated in claim 1, the experimental details given in examples 1 to 3 can be followed.

[0088] Use of mixed oxides The composite oxide of the present invention can be used to manufacture SOFCs. In SOFCs, electricity is produced by the reaction of a fuel with an oxygen source. The oxygen source, typically air, contacts the cathode to form oxygen ions by reduction with electrons at the cathode. When the SOFC operates with a hydrocarbon fuel and electrons, the oxygen ions contact the fuel at the anode to form water and carbon dioxide.

[0089] The SOFC comprises two porous electrodes (A) and (C) separated by at least one electrolyte layer (L). The complex oxide of the present invention can be used as an oxygen ion conducting material in the fabrication of one or more of these three components, i.e. the anode, the cathode or at least one layer. Each of these three components of the SOFC is described in detail below. The present invention therefore also relates to a SOFC comprising one porous anode (A) and one porous cathode (C) separated by at least one layer (L), where at least one of the components (A), (C) or (L) is made from or comprises the complex oxide of the present invention.

[0090] The function of layer (L) is to act as a barrier to prevent direct contact between the fuel and the oxygen source. Another function of the barrier is to allow the diffusion of oxygen ions through the layer.

[0091] In the context of the present invention, at least one of the components (A), (C) or (L) is made from or comprises a complex oxide of the invention.

[0092] Anode (A) The present invention also relates to an anode comprising or made from the complex oxide of the present invention and optionally at least one other inorganic material. The anode is where the oxidation of the fuel takes place. The inorganic material other than the complex oxide used in the anode can be selected from the group consisting of zirconia doped with at least one element selected from the group consisting of Y, Sc, Ce, and combinations of two or more of these three elements; mixed oxides of cerium and gadolinium; metals such as nickel; lanthanum titanate; and lanthanum chromite.

[0093] Examples of lanthanum titanate include those of the formula La 0.2 Sr 0.25 Ca 0.45 It is TiO3.

[0094] Cathode (C) The present invention also relates to a cathode comprising or made from the complex oxide of the present invention and optionally at least one other inorganic material. In the cathode, oxygen reduction occurs. The inorganic material other than the complex oxide used in the cathode can be selected from the group consisting of zirconia doped with at least one element selected from the group consisting of Y, Sc, Ce, and combinations of two or more of these three elements; mixed oxides of cerium and gadolinium; mixed oxides of cerium and samarium; perovskites containing La, Sr, Co, and Fe; and perovskites containing La, Sr, Mn.

[0095] Perovskites containing La, Sr, Co, and Fe are usually represented by the general formula La x Sr 1x Co y Fe 1-y O 3{プラス又はマイナス}δ In the formula, x and y are numbers between 0.5 and 0.9 and between 0.1 and 0.9, respectively. For example, х=0.8; y=0.8 or x=0.6 and у=0.2. Examples of such perovskites are disclosed in “Synthesis and Study of LSCF Perovskites for IT SOFC Cathode Application”, ECS Transactions, 2009, 25(2) (DOI:10.1149 / 1.3205796). Perovskites containing La, Sr, and Mn are usually represented by the general formula La 1-x Sr x It can be represented by MnO3, where x is a number between 0 and 1.0.

[0096] Electrolyte layer (L) The present invention also relates to a layer comprising or made from the complex oxide of the present invention and, optionally, at least one other inorganic material, which may be selected from the group consisting of zirconia doped with at least one element selected from the group of Y, Sc, Ce and combinations of two or more of these three elements, or mixed oxides of cerium and gadolinium.

[0097] The manufacture of SOFCs may include the complex oxides of the invention disclosed in full detail hereinabove, and may also include complex oxides of the invention modified by the addition of sintering aids (see below) and / or mechanical treatments such as a grinding step.

[0098] Examples of SOFCs are given below. SOFC example Ex1 is based on the following configuration: · Anode (A); a layer (L) comprising or made from the complex oxide of the invention, optionally further comprising at least one other inorganic material; Cathode (C).

[0099] The SOFC of Ex1 may also include an additional layer (L1) between (L) and (C), the function of which is to prevent short circuits. This additional layer (L1) typically includes zirconia doped with at least one element selected from the group of Y, Sc, and Ce, and a combination of two or more of these three elements. If the SOFC of Ex1 includes an additional layer (L1), it may also include an additional layer (L2) between (L1) and (C) that includes or is made of a complex oxide of the invention and / or a mixed oxide of cerium and gadolinium different from the complex oxide of the invention. This additional layer (L2) is useful to prevent elements such as strontium from diffusing from the cathode (C) to the additional layer (L1).

[0100] In Ex1, the anode (A) and / or the cathode (C) may comprise a mixed oxide of cerium and gadolinium different from the composite material of the invention and / or the composite oxide of the invention.

[0101] Another example of a SOFC, Ex2, is based on the following configuration: · Anode (A); ·Layer(L); an additional layer (L2) comprising or made from the complex oxide of the invention, optionally further comprising at least one other inorganic material; Cathode (C).

[0102] Layer (L) typically comprises zirconia doped with at least one element selected from the group of Y, Sc, Ce, and combinations of two or more of these three elements.

[0103] In Ex2, the anode (A) and / or the cathode (C) may comprise or be made of a mixed oxide of the invention and / or a mixed oxide of cerium and gadolinium different from the mixed oxide of the invention.

[0104] The composite oxide of the present invention can be used in the manufacture of batteries disclosed in one of the following documents by replacing the cerium-gadolinium disclosed therein with the composite oxide of the present invention: WO 02 / 35628; WO 03 / 075382; WO 2004 / 089848; WO 2005 / 078843; WO 2006 / 079800; WO 2006 / 106334; WO 2007 / 085863; WO 2007 / 110587; WO 2008 / 001119; WO 2008 / 003976; WO 2008 / 015 461;WO 2008 / 053213;WO 2008 / 104760;WO 2008 / 132493;U.S. Patent Application Publication No. 2013 / 0052562;WO 2021 / 151692;WO 2016 / 124929;WO 2015 / 03310 No. 4; WO 2017 / 153751; WO 2021 / 096828; U.S. Pat. No. 8,435,694 B2; U.S. Pat. No. 10,749,188 B2; U.S. Patent Application Publication No. 2008 / 254336; DE 102013007637; U.S. Patent Application Publication No. 2013 / 0095408. The composite oxide of the present invention is described in the doctoral thesis of Clement Nicollet ("Nouvelles electrodes a oxygene pour SOFC a base de nickelates Ln2NiO 4+δ The compound can also be used in the manufacture of batteries as disclosed in "(Ln=La,Pr)prepareesparinfiltration" (p. 133).

[0105] The SOFC and its layers are fabricated by known methods: · For thicknesses of the support layer (electrolyte or anode) from 100 μm to the mm scale (typically <800 μm and <300 μm), casting methods (e.g. tape or slip casting); For thin layers (typically <50 μm), printing methods (e.g. screen printing, inkjet printing), spraying, laminating, spin coating; For ultra-thin layers L1 and L2 (typically <5 μm), in addition to printing methods, sputtering methods (e.g. magnetron or gas flow), physical vapor deposition, atomic layer deposition, pulsed laser deposition; For tubular design batteries, dip coating or injection molding can be used.

[0106] Those skilled in the art can also find relevant fabrication teachings in the above mentioned articles.

[0107] It is also possible to use the method disclosed in one of the documents disclosed above.

[0108] The composite oxide of the present invention can also be used to manufacture solid oxide electrolysis cells (SOECs). SOECs allow the production of green hydrogen by high-temperature electrolysis (typically 700-800 ° C). Examples of SOECs are given in Renewable and Sustainable Energy Reviews Volume 149, October 2021, 111322 ("Alternative and innovative solid oxide electrolysis cell materials: A short review") or in the paper by Pysik et al. referenced by https: / / doi.org / 10.1002 / fuce.201900245 ("Long-Term Behavior of a Solid Oxide Electrolyzer (SOEC) Stack").

[0109] The structure of SOEC is very similar to that of SOFC. Therefore, SOEC: · Anode (A*); an additional layer (L) comprising or made from the mixed oxide of the invention and / or a mixed oxide of cerium and gadolinium different from the mixed oxide of the invention, optionally further comprising at least one other inorganic material; · Cathode (C*); may include.

[0110] However, since SOECs work in a reversed mode compared to SOFCs, the accuracies given above for the anode (A*) and cathode (C*) must be taken from the accuracies for the cathode (C) and anode (A), respectively. For clarity, all content disclosed above for SOFCs remains valid for SOECs with accuracies for anode (A) → cathode (C*) and cathode (C) → anode (A*). For instance, an example SOEC follows the following configuration: · Cathode (C*); ·Layer(L); an additional layer (L1) comprising the complex oxide of the invention and optionally further comprising at least one other inorganic material; Anode (A*).

[0111] The composite oxide of the present invention can be used in the manufacture of a battery disclosed in Korean Patent No. 102305294B1; Chinese Patent No. 113445061; European Patent No. 3793012 by replacing the cerium-gadolinium disclosed in one of these documents with the composite oxide of the present invention.

[0112] Composition C containing the composite oxide of the present invention In the present invention, the complex oxide already exhibits a high relative density at a "low" temperature of 950°C. However, sintering aids may be added to the complex oxide in order to further improve its sinterability. The present invention therefore also relates to a composition C comprising the complex oxide of the present invention and further comprising at least one sintering aid.

[0113] The sintering aid may be, for example, element E selected from the group of Zn, transition metal elements, rare earth elements, or alkali metals. E may be more specifically selected from the group of transition elements. E may be selected from the group consisting of Li, Zn, Cu, Co, Fe, Mn, Ni, and combinations thereof. Element E may be added in the form of a salt, such as an acetate or nitrate. Element E may be present in the composition in the form of an oxide.

[0114] The proportion of the sintering aid in the composition C may be 0.1 to 5.0% by weight. This proportion may be higher than 0.5% by weight. It may be less than 3.0% by weight.

[0115] Composition C can be prepared by a method comprising the steps of (i) contacting the composite oxide of the present invention with a salt of element E or a precursor of the oxide of element E, (ii) removing the solution, (iii) drying the solid, and (iv) optionally calcining in air. Step (i) can be carried out in a liquid medium such as water or alcohol. The salt of element (E) can be, for example, a nitrate or acetate. The precursor of the oxide of element (E) can be, for example, an acetylacetonate.

[0116] Composition C may be in the form of a powder. All the features disclosed in 1) to 4) are still applicable to composition C.

[0117] Composition C can be used to manufacture SOFCs or SOECs. Even if the composite oxide of the present invention is replaced with composition C containing the composite oxide of the present invention and a sintering aid, all of the above disclosure regarding SOFCs or SOECs is still valid. EXAMPLES

[0118] Those skilled in the art will practice the invention as disclosed above and in the claims with the aid of and in light of the examples provided below.

[0119] In the following examples, cerium(III) nitrate and gadolinium nitrate are used, both of which are obtained by direct attack of the corresponding oxides with nitric acid. The aqueous cerium nitrate solution used to prepare the mixed nitrate solution shows a residual acidity of 0.05 mol / L. The aqueous gadolinium nitrate solution used to prepare the mixed nitrate solution shows a residual acidity of 0.60 mol / L. The residual acidity was measured by acid-base titration.

[0120] The basic solution used was prepared before each example by dissolving NH4HCO3 (Nissan Chemical Co., Ltd.) in water. In the following examples 1 to 3, the reactor used is a 200 liter reactor equipped with a stirrer.

[0121] Measurements of D16, D50, and D84 Particle size distribution was obtained using a laser diffraction particle size distribution analyzer LA-920 from Horiba, Ltd. The particles were dispersed in water containing 0.2 wt. % hexametaphosphate. A refractive index of 1.20 was used.

[0122] BET specific surface area The BET specific surface area was measured using a Macsorb HM model-1220 from MOUNTECH Co., Ltd. after the adsorbed species were desorbed at 210° C. for 30 min.

[0123] Hg porosity Porosity was obtained using an autopore IV 9500 automated mercury porosimeter following the manufacturer's guidelines after pretreatment at 210°C for 30 min. The sample size was approximately 0.2 g, the mercury contact angle was 130°, and the mercury surface tension was 485 dyn / cm.

[0124] X-ray diffraction An X-ray diffractometer Ultima IV equipped with a copper source (CuKα1, λ = 1.5406 Å) was used.

[0125] Density and relative density measurements The following methods were used, which can be used in the context of the present invention: i) weighing out the composite oxide powder and introducing it into a mold; ii) compressing the powder under pressure; iii) removing the compressed sample obtained at the end of step ii) from the mould; iv) The pressed samples are then calcined in air at the target temperature for 5 hours; v) The density of the fired pressed samples is measured by the following steps: v1) Weigh the calcined compressed sample (weight in g); v2) Measure the volume of the compressed sample (cm 3 (unit volume), the compressed sample is parallelepiped shaped, and the volume of the parallelepiped is given by: Volume = length(cm) x width(cm) x height(cm); vi) The relative density is then calculated.

[0126] The specific conditions used were as follows: In step i), dimensions of the rectangle: 23 × 7 mm; ·Amount of powder used: about 1g; In step ii), the powder is compressed in a uniaxial press to obtain a compressed sample.

[0127] The applied strength during pressing is 15.8 kN, which corresponds to a pressure of 98 MPa.

[0128] Example 1: Preparation of a composite oxide containing 10% Gd-cerium nitrate 0.27 mol / L and gadolinium nitrate 0.03 mol / L; total concentration 0.3 mol / L Step a): Cerium (III) nitrate solution (approximately 3 mol / L) and gadolinium nitrate solution (approximately 2 mol / L) were mixed to prepare CeO2:GdO 1.5 A mixed nitrate solution was prepared by mixing them in a ratio equivalent to 90:10 (molar ratio). This mixed nitrate solution (equivalent to 2.6 kg of composite oxide) was diluted with ion-exchanged water to prepare starting solution S (cerium nitrate 0.27 mol / L, gadolinium nitrate 0.03 mol / L; total concentration 0.3 mol / L).

[0129] The starting solution S was added at a constant flow rate over 30 minutes to 80.0 L of an aqueous solution of ammonium hydrogen carbonate (48.8 g / L) stirred at 25° C. to obtain a precipitate containing cerium and gadolinium. The pH of the slurry was 6.9.

[0130] Step b): The slurry obtained at the end of step a) is heat treated at 80° C. for 3 hours in a reactor equipped with air flushing above the liquid level. The slurry is allowed to cool to room temperature. The pH of the slurry is 8.1.

[0131] Step c): The slurry obtained at the end of step b) was filtered and washed several times using deionized water until the conductivity of the filtrate was below 5 mS / cm.

[0132] Step d): The cake obtained at the end of step c) was heated in a furnace in air with a temperature ramp of 1.6° C. / min until 800° C. was reached and held at 800° C. for 8 hours. The solid was then allowed to cool in the oven.

[0133] Step e): The calcined solid is pulverized by a hammer mill, thereby obtaining a composite oxide Ce in the form of a powder having a diameter of D84<50 μm. 0.9 Gd 0.1 O 2-δ obtained.

[0134] Example 2: Preparation of a composite oxide containing 10% Gd-cerium nitrate 0.36 mol / L and gadolinium nitrate 0.04 mol / L; total concentration 0.4 mol / L Step a): Cerium (III) nitrate solution (approximately 3 mol / L) and gadolinium nitrate solution (approximately 2 mol / L) were mixed to prepare CeO2:GdO 1.5 = 90:10 (molar ratio) to prepare a mixed nitrate solution. This mixed solution (equivalent to 5.2 kg of composite oxide) was diluted with ion-exchanged water to prepare starting solution S (cerium nitrate 0.36 mol / L, gadolinium nitrate 0.04 mol / L; total concentration 0.4 mol / L).

[0135] Starting solution S was added at a constant flow rate over 45 minutes to 107.0 L of an aqueous ammonium bicarbonate solution (72.9 g / L) stirred at 25° C., thereby obtaining a precipitate slurry containing cerium and gadolinium. The pH reached was 6.6.

[0136] Step b): The slurry obtained at the end of step a) is heat treated at 80° C. for 3 hours in a reactor equipped with air flushing above the liquid level. The slurry is allowed to cool to room temperature. The pH reached is 7.9.

[0137] Step c): The slurry obtained at the end of step b) was filtered and washed several times using deionized water until the conductivity of the filtrate was below 5 mS / cm.

[0138] Step d): The resulting precipitate was heated in a furnace in air at a rate of 1.6° C. / min until it reached 800° C. and was held at 800° C. for 8 hours. The solid was then allowed to cool in the oven.

[0139] Step e): The calcined solid is pulverized by a hammer mill, thereby obtaining Ce in the form of powder with D84<50 μm. 0.9 Gd 0.1 O 2-δ obtained.

[0140] Example 3: Preparation of a composite oxide containing 20% ​​Gd A composite oxide containing 20% ​​Gd was prepared with a molar ratio r of 3.30 according to the same method as in Example 1. Mixed nitrate solution: CeO2:GdO 1.5 =80:20 (molar ratio).

[0141] Comparative Example 1: Preparation of a composite oxide containing 10% Gd according to the recipe disclosed in Example 1 of EP 1484282 B1 - cerium nitrate 0.27 mol / L, gadolinium nitrate 0.03 mol / L; total concentration 0.3 mol / L Cerium nitrate solution (approximately 3 mol / L) and gadolinium nitrate solution (approximately 2 mol / L) were mixed together to prepare CeO2:GdO 1.5A mixed solution was prepared by mixing them at a molar ratio of 90:10. This solution (corresponding to 20 g of the composite oxide) was diluted with ion-exchanged water to prepare a 0.3 mol / L starting solution.

[0142] 0.4 L of the prepared 75 g / L ammonium bicarbonate aqueous solution was added to the starting solution at 25° C. under stirring to prepare a precipitate. 20 mL of 100 g / L ammonium bicarbonate aqueous solution was further added to the slurry. The pH of the slurry was 7.9. The slurry was heat-treated at 100° C. for 3 hours at atmospheric pressure in a flask equipped with a reflux condenser. After that, filtration and washing were repeated 10 times using deionized water, and the conductivity of the filtrate was 0.67 mS / cm. The obtained precipitate was calcined in a furnace at 700° C. in air for 5 hours and crushed in a mortar to obtain Ce in powder form. 0.9 Gd 0.1 O 2-δ 20g was obtained.

[0143] The composition of the obtained powder was confirmed using an ICP optical emission spectrometer (Hitachi High-Tech Corporation, inductively coupled plasma optical emission spectrometer, PS-3500DD).

[0144] [Table 2]

Claims

1. A composite oxide based on cerium and gadolinium, in which the proportion of Gd is 8.0 to 22.0 mol %, and this proportion corresponds to a molar ratio Gd / (Ce+Gd) expressed as a percentage.

2. CeO with a Gd content of 8.0 to 22.0 mol% ２ and G-d ２ O ３ and the ratio of these elements corresponds to a molar ratio Gd / (Ce+Gd) expressed as a percentage.

3. 3. The composite oxide according to claim 1, wherein an X-ray diffractogram (CuKα1, λ=1.5406 Å) of the composite oxide shows a solid solution pattern, and / or an X-ray diffractogram (CuKα1, λ=1.5406 Å) of the composite oxide shows a peak P at 2θ of 27.0° to 30.0°, and preferably, peak P has the highest intensity on the diffractogram.

4. After the compressed sample is calcined in air at 1000°C for 5 hours, it has a relative density RD of at least 95.0%, preferably at least 96.0%. １０００℃／５ｈ and / or exhibits a relative density RD 1000°C / 5h of up to 99.0% or up to 98.0% after calcination of a pressed sample at 1000°C in air for 5 hours, preferably RD 1000°C / 5h of 96.0% to 99.0%. monster.

5. After the compressed sample is sintered in air at 950°C for 5 hours, it has a relative density RD of at least 94.0%, preferably at least 95.0%. ９５０℃／５ｈ and / or after calcining a compressed sample in air at 950 ° C. for 5 hours, exhibits a relative density RD 950 ° C. / 5h of up to 98.0% or up to 97.0%. The composite oxide according to any one of claims 1 to 4.

6. After the compressed sample is sintered in air at 1100°C for 5 hours, it has a relative density RD of at least 99.0%, preferably at least 99.5%. １１００℃／５ｈ and / or after calcining a compressed sample in air at 1100 ° C. for 5 hours, exhibits a relative density RD 1100 ° C. / 5h of up to 99.5% or up to 99.9%. The composite oxide according to any one of claims 1 to 5.

7. The compressed samples were sintered in air at 1200°C for 5 hours and then had a relative density RD of at least 99.5%. １２００℃／５ｈ The composite oxide according to any one of claims 1 to 6, wherein

8. The relative density is given by the formula: %RD=density / absolute density×100, where the density is measured on the compressed sample of the composite oxide after calcining the compressed sample in air at a test temperature (950° C., 1000° C., 1100° C., or 1200° C.) for 5 hours, and the absolute ... 【Table 1】 The composite oxide according to any one of claims 4 to 7, wherein

9. In the range of pores having a diameter of 200 nm or less, the maximum exhibits a peak corresponding to a pore diameter Dp of 30 to 100 nm, more particularly 30 to 70 nm, Dp being determined by mercury intrusion porosimetry, and preferably the peak having a maximum value at Dp is less than 80 nm; or less than 70 nm; or less than 60 nm; or less than 50 nm; or less than 40 nm; or less than 30 nm; or less than 20 nm; and / or a porogram obtained by Hg porosity shows a single peak within the range of pores having a diameter of 200 nm or less.

10. A pore volume (Vp) of pores having a diameter of 200 nm or less of less than 0.40 mL / g, more specifically less than 0.35 mL / g, and even more specifically less than 0.30 mL / g ＜２００ｎｍ ) and the pore volume is measured by mercury intrusion porosimetry, and / or the composite oxide according to any one of claims 1 to 9, exhibiting a pore volume of pores having a diameter of 200 nm or less (Vp < 200 nm ) that is greater than 0.10 mL / g and the pore volume is measured by mercury intrusion porosimetry.

11. 5 to 40 m ２ 11. The composite oxide according to claim 1, wherein the composite oxide exhibits a BET specific surface area of ​​10 to 35 m 2 / g, or 25 to 30 m 2 / g, or 25 to 30 m 2 / g.

12. The particle size volume distribution obtained by laser diffraction has the following characteristics: A group P1 centered on a size D1 of less than 3.0 μm and / or A group P2 centered on a size D2 exceeding 8.0 μm and P2, The expression "population centered on a diameter D" means that a peak is observed on the distribution curve with a maximum located at D, preferably in the region of a diameter of less than 100 μm, said distribution having the following characteristics: A group P1 centered on a diameter D1 of less than 3.0 μm and / or A group P2 centered on a diameter D2 exceeding 8.0 μm and / or the distribution comprises a shoulder close to the peak of population P1.

13. The ratio H2 / H1 of the heights H1 and H2 of the two peaks P1 and P2, respectively, is greater than 0.1; or greater than 0.3; or greater than 1.0; or greater than 1.5; and / or The ratio H2 / H1 of the heights H1 and H2 of the two peaks P1 and P2, respectively, is less than 7.0; or less than 5.5; or less than 1.0; or less than 0.8; or less than 0.5; and / or The ratio H2 / H1 of the heights H1 and H2 of the two peaks P1 and P2, respectively, is 0.1 to 7.0; or 0.1 to 5.5; or 0.1 to 1.0; or 0.1 to 0.8; or 0.1 to 0.5; or ・０．４～０．５； The composite oxide according to claim 12, wherein

14. D50 is between 0.1 and 15.0 μm, D50 corresponding to the median of the volume distribution of particle sizes obtained by laser diffraction, and / or D16 is between 0.1 and 4.0 μm, D16 being a diameter determined from the volume distribution of the size of said particles obtained by laser diffraction, in which 16% of the particles have a diameter smaller than D16, and / or The complex oxide according to any one of claims 1 to 13, wherein D84 is 10.0 to 50.0 µm, and D84 is a diameter determined from a volume distribution of sizes obtained by laser diffraction in which 84% of the particles have a diameter smaller than D84.

15. A composition C comprising the complex oxide according to any one of claims 1 to 14 and a sintering aid, preferably the sintering aid is an element E selected from the group consisting of Li, Zn, Cu, Co, Fe, Mn, Ni, and combinations thereof, and / or the sintering aid is an element E in the form of an oxide, and / or Composition C according to any one of claims 1 to 14, wherein the proportion of the sintering aid in the composition is 0.1 to 5.0% by weight.

16. Composition C according to claim 15, which exhibits a relative density as defined in any one of claims 4 to 8.

17. A method for producing a composite oxide according to any one of claims 1 to 14, a) Cerium nitrate (Ce ＩＩＩ ) and gadolinium nitrate, and the aqueous solution S containing ammonium bicarbonate (NH ４ HCO ３ to a basic aqueous solution of 2,4-dichloro-1,4-dichloro-2 ... b) heating the aqueous slurry containing the precipitate obtained at the end of step a) at a temperature of 50°C to 95°C; c) recovering the precipitate at the end of step b) and washing it with water; d) calcining the solid recovered from step c) in air at a temperature of 600°C to 1000°C; e) grinding the calcined solid; and preferably A process wherein said molar ratio r=NH 4 HCO 3 3 / Ce+Gd is between 3.00 and 3.48, more particularly between 3.10 and 3.

45.

18. 17. A SOFC comprising one porous anode (A) and one porous cathode (C) separated by at least one layer (L), wherein at least one of the components (A), (C) or (L) is made from or comprises a complex oxide according to any one of claims 1 to 14 or is made from or comprises a composition C according to claim 15 or 16, preferably anode (A); A layer (L) comprising the composite oxide according to any one of claims 1 to 14 and / or a mixed oxide of cerium and gadolinium different from said composite oxide, and optionally further comprising at least one other inorganic material; cathode (C); SOFCs, including:

19. 17. An SOEC comprising one porous anode (A*) and one porous cathode (C*) separated by at least one layer (L), wherein at least one of components (A*), (C*) or (L) is made from or comprises a complex oxide according to any one of claims 1 to 14, or is made from or comprises composition C according to claim 15 or 16.

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