Process for producing cerium-gadolinium oxide powder, in particular cerium-gadolinium oxide powder intended for the production of electrolytes - Patent Application 20070122999

Abstract

) The present invention relates to a method for producing a cobalt oxide-containing, gadolinium-doped cerium oxide powder, comprising the sequential steps of: 1) preparing a wet product comprising a mixture of gadolinium-doped cerium oxide particles and water containing a cobalt complex; d) optionally removing at least a portion of said water; e) calcining the product obtained in step d) or, in the absence of step d), the product obtained from step 1) in an oxygenated fluid to obtain said powder.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a powder based on gadolinium-doped cerium oxide. The present invention also relates to a method for producing a sintered product, in particular an electrolyte, and also to solid oxide fuel cells and solid oxide electrolyzers containing such an electrolyte. Finally, the present invention relates to the gadolinium-doped cerium oxide powder obtained or which may be obtained according to the method of the present invention. [Background technology]

[0002] In the field of solid oxide fuel cells (i.e., "SOFCs") and solid oxide electrolysis cells (i.e., "SOECs"), gadolinium-doped cerium oxide (i.e., "GCO") used as an electrolyte represents an advantageous alternative to yttrium-stabilized zirconia because it exhibits higher ionic conductivity at lower operating temperatures (500°C-700°C).

[0003] During the fabrication of the electrolyte, high sintering temperatures of over 1500° C. are required to obtain densification of the GCO, which typically results in a decrease in mechanical properties accompanied by an enlargement of the microstructure.

[0004] To obtain densification at lower temperatures, it is known to use nanometer-sized GCO powders and / or to use small amounts of transition metal oxides, such as cobalt, copper, nickel, manganese or iron, as sintering agents.

[0005] Cobalt oxide is conventionally added to GCO powder by suspending the GCO powder in ethanol, followed by the addition of cobalt dinitrate dissolved in ethanol, drying, and calcining, for example, at 400° C., which allows the cobalt dinitrate to be converted to cobalt oxide. Summary of the Invention [Problem to be solved by the invention]

[0006] There is a continuing need to improve methods for producing sintered electrolytes.

[0007] One object of the present invention is to at least partially fulfill this need. [Means for solving the problem]

[0008] The present invention provides a method for producing gadolinium-doped cerium oxide powder including a cobalt oxide, or "Co-GCO powder," comprising the steps of: 1) gadolinium-doped cerium oxide particles; Water containing a cobalt complex preparing a wet product comprising, preferably consisting of, a mixture of wherein the wet product preferably has a Q Co ' / Q GCO Q so that '≦0.15 Co ' / Q GCO 'having a ratio, Here, Q GCO ' denotes the sum of the molar amounts of cerium and gadolinium in the wet product, and Q Co ' denotes the molar amount of cobalt in the wet product; d) optionally removing at least a portion of the water; e) calcining the product obtained from step d) or, if step d) is not present, the product obtained from step 1) in an oxygenated fluid to obtain the Co-GCO powder. The above method is proposed, which comprises the following sequential steps:

[0009] Surprisingly, and for reasons unknown, the inventors have discovered that powders according to the invention exhibit improved sintering.

[0010] The Co-GCO particles have the morphology of gadolinium-doped cerium oxide particles coated with cobalt oxide particles, the coating being particularly uniform.

[0011] In a preferred embodiment, the method comprises step d), wherein step 1) comprises: a) suspending gadolinium-doped cerium oxide powder in water; b) adding at least one water-soluble cobalt compound (i.e., a first reagent) to the suspension to form cobalt cations, wherein the amount of the first reagent is preferably 0.005≦Q Co / Q GCO ≦0.15, where Q GCO represents the sum of the molar amounts of cerium and gadolinium provided in step a), and Q Co indicates the molar amount of cobalt provided by the first reagent; c) adding at least one water-soluble cobalt ligand and / or at least one precursor of such a ligand (i.e., a second reagent) to the suspension to form a cobalt complex. The process includes the steps of:

[0012] The method according to the invention may also include one or more of the following optional and preferred features: The Q Co ' / Q GCO 'the ratio is 0.01 or more, preferably 0.02 or more, and less than 0.10 or 0.10, preferably less than 0.05 or 0.05; and / or in step b), Q Co / Q GCO the ratio is 0.01 or greater, preferably 0.02 or greater, and less than 0.10 or 0.10, preferably less than 0.05 or 0.05; the molar content of gadolinium in the gadolinium-doped cerium oxide powder of the wet product and / or in the powder suspended in step a) is 10% or more than 10% and less than 20% or 20%, expressed as a percentage based on the sum of the molar amount of cerium and the molar amount of gadolinium; In step a), the median diameter of the gadolinium-doped cerium oxide powder is greater than 20 nm and less than 0.8 μm; The gadolinium-doped cerium oxide powder of the wet product and / or the gadolinium-doped cerium oxide powder of the powder suspended in step a) is obtained via a melting process; the first reagent has a solubility in water of greater than 300 g / l when measured at 20°C; the first reagent is selected from cobalt dinitrate, cobalt acetate, cobalt acetylacetonate, cobalt dichloride, cobalt difluoride, cobalt sulfate, cobalt tartrate, cobalt bromide, cobalt iodide, cobalt thiocyanate, cobalt phosphate, and combinations thereof, and / or the second ... dinitrate, cobalt dichloride, cobalt difluoride, cobalt tartrate, cobalt bromide, cobalt iodide, cobalt thiocyanate, cobalt phosphate, and combinations thereof, and / or - ) and / or molecules containing a thiol group (-SH); the first reagent is selected from cobalt dinitrate, cobalt acetate, and combinations thereof, and / or the second reagent is selected from urea and its derivatives, citric acid, oxalic acid, ethylenediamine, salen, ethylenediaminetetraacetic acid, and combinations thereof; the first reagent is cobalt dinitrate, and / or the second reagent is selected from urea and its derivatives; In step c), the amount of the second reagent is adapted so that more than 99% of the amount of cobalt cations in the suspension is complexed; In step c), the second reagent contains only carbon, hydrogen and oxygen atoms, and optionally nitrogen and / or chlorine atoms; In step d), more than 80% by weight of the water is removed; In step e), the calcination temperature is above 300° C. and below 800° C., and the holding time at said temperature is preferably more than 1 hour and less than 10 hours.

[0013] The present invention also provides a cobalt oxide-containing gadolinium-doped cerium oxide powder, the powder comprising, in weight percent based on oxide: greater than 9.60% and less than 20.79% Gd2O3, and CeO2 greater than 72.55% and less than 89.32%, and greater than 0.23% and less than 6.51% cobalt oxide (expressed as Co3O4), and Less than 2% of oxides other than Gd2O3, CeO2 and cobalt oxide (expressed as Co3O4) having a chemical analysis of wherein the powder of gadolinium-doped cerium oxide particles is at least partially coated with cobalt oxide particles, thus resulting in a difference N 90 -N 10 (i.e., E value) is greater than 110; N 10 and N 90 but, In cobalt mapping, It is made up of a plurality of pixels, each pixel having a shade of color, the shade ranging from 0 to 255; and Generated by energy spectroscopy of a pellet formed by compressing the powder at a pressure of 125 MPa, wherein the shades correspond to the percentages of the number of pixels at 10% and 90%, respectively, in a cumulative distribution curve of the pixels as a function of shade, not taking into account pixels with a concentration D, the shades being sorted in ascending order, the shades being proportionally higher for higher cobalt contents; Regarding the above cerium oxide powder.

[0014] Preferably, the E value is greater than 125 and / or the powder has an S value of less than 2.20, preferably less than 2.00, the S value being (N 90 -N 10 ) / N 50 is the ratio, where N 50 is the shade corresponding to the percentage by number of the pixel of 50% on the cumulative distribution curve.

[0015] The color may be, for example, green.

[0016] Preferably, the powder is produced by a method according to the present invention.

[0017] The present invention also relates to a process for producing a sintered part, comprising a step f) of producing a preform from a powder according to the invention, preferably produced or producible by the method for producing a powder according to the invention, and a step g) of subsequently sintering said preform to obtain a sintered part.

[0018] Sintering the preform is preferably carried out at a temperature below 1500°C, preferably below 1490°C.

[0019] The present invention also relates to a method for producing a device selected from a solid oxide fuel cell and a solid oxide electrolyzer, comprising producing a sintered part from a powder produced or capable of being produced by a powder production method according to the present invention, wherein the sintered part, after production, is placed between the electrodes of the fuel cell or electrolyzer to constitute the electrolyte.

[0020] The method preferably includes the production of a sintered part produced by a method according to the invention, wherein said sintered part, after production, is placed between the electrodes of said fuel cell or said electrolyzer to constitute the electrolyte.

[0021] The present invention also relates to a wet product comprising gadolinium-doped cerium oxide particles in water containing a cobalt complex. The present invention also relates to a Co-GCO powder obtained or obtainable according to the method of the present invention.

[0022] Finally, the invention relates to sintered parts, in particular electrolytes, and devices obtained according to the method of the invention.

[0023] Other features and advantages of the present invention will also become apparent by consideration of the following description and accompanying drawings. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 1 shows an image taken using a scanning electron microscope of particles of the powder of Example 1, which is not in accordance with the present invention. [Figure 2] FIG. 2 represents a cobalt mapping produced by energy dispersive spectroscopy (or "EDS") of the same particles present in FIG. [Figure 3] FIG. 3 represents a photograph taken with a scanning electron microscope of the particles of the powder of Example 2 according to the invention. [Figure 4] FIG. 4 shows a cobalt mapping produced by EDS of the same particle shown in FIG. [Figure 5] FIG. 5 shows the cumulative distribution of pixels as a function of shading for the mappings in Examples 1, 2, and 3: a continuous line for Example 1 (percentiles N10, N50, and N90 are marked), a dotted line for Example 2, and a mixed line for Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0025] Figures 1 to 4 were all created at the same magnification.

[0026] definition A "cobalt complex" is conventionally a compound formed by the combination of at least one cobalt cation with one or more molecules or ions capable of donating an electron doublet to the cobalt cation. These doublet donors are conventionally called "ligands." Powder percentile or "centile" 50 (D 50 ) and 90(D 90 ) are the particle sizes corresponding to 50% and 90% volume percentages, respectively, on the cumulative particle size distribution curve of the powder, where the particle sizes are sorted in ascending order. For example, 90% by volume of the powder particles are D 90 and 10% by volume of the particles have a size smaller than D 90 The percentile can be determined using a particle size distribution performed using a laser particle size analyzer. The 50th percentile of a powder is called the "median size" of that powder. The term "impurities" refers to unavoidable components that are unintentionally mixed with raw materials or that result from reactions with these components. Impurities are not necessary components, but merely tolerated components. Preferably, the mass percentage of impurities is less than 2%, less than 1%, less than 0.5%, or even substantially zero. The verbs "include", "include" and "have" are to be construed in an open-ended manner unless otherwise indicated.

[0027] Other features and advantages of the present invention will also become apparent from reading the following detailed description of the preferred embodiments, which is provided for purposes of illustration only and is not intended to be limiting in any way.

[0028] In particular, the step 1) described in detail includes steps a) to c), however, a person skilled in the art may consider other known techniques for producing a wet product.

[0029] All the preferred characteristics for the GCO powder used in step a), especially those relating to particle size distribution and gadolinium content, are also preferred characteristics for the GCO powder of step 1).

[0030] Similarly, Q Co ' / Q GCO 'The ratio is preferably 0.005≦Q Co ' / Q GCO '≦0.15, where Q GCO ' represents the sum of the molar amounts of cerium and gadolinium in the wet product, and Q Co Q' indicates the molar amount of cobalt in the wet product. Co ' / Q GCO The ratio is 0.01 or greater than 0.01, preferably 0.02 or greater than 0.02, and less than 0.10 or 0.10, preferably less than 0.05 or 0.05.

[0031] Method for producing a powder according to the invention

[0032] In step a), the GCO powder is suspended in water.

[0033] The GCO powder can be produced via any conventional method. In a preferred embodiment, the GCO powder is obtained via a melting process, preferably an arc furnace melting process.

[0034] The molar content of gadolinium in the GCO powder, expressed as a percentage based on the sum of the molar content of cerium and the molar content of gadolinium, is preferably 10% or more, more preferably 20% or less. In one embodiment, this content is equal to 10%. In one embodiment, this content is equal to 20%.

[0035] Preferably, the median diameter of the gadolinium-doped cerium oxide powder is greater than 20 nm, preferably greater than 30 nm, preferably greater than 50 nm, preferably greater than 0.1 μm, and preferably less than 0.8 μm, preferably less than 0.6 μm, preferably less than 0.4 μm.

[0036] Preferably, the gadolinium-doped cerium oxide powder D 90 is less than 2.5 μm, preferably less than 2 μm.

[0037] Water is preferred, although other equivalent solvents are possible.

[0038] Water preferably accounts for more than 30%, preferably more than 40%, preferably more than 45%, and / or less than 90%, preferably less than 80%, preferably less than 70%, preferably less than 60%, preferably less than 55% of the mass of the suspension.

[0039] The GCO powder and water together preferably make up more than 95%, more than 98%, preferably more than 99% of the mass of the suspension, the remainder up to 100% preferably consisting of impurities.

[0040] Preferably, the suspension contains only water and GCO powder.

[0041] The suspension is conventionally prepared by simple mixing.

[0042] In step b), a first reagent selected from water-soluble cobalt compounds and combinations thereof is added to the suspension. The purpose of step b) is to form cationic cobalt in the suspension.

[0043] The sum Q of the molar amounts of cerium and gadolinium provided in step a) GCO and the molar amount Q of cobalt introduced by the first reagent in step b). Co The sum of Q is 0.005≦Q Co / Q GCO ≦0.15.

[0044] Preferably, Q Co / Q GCO The ratio is at or above 0.01, preferably at or above 0.02, and less than 0.10 or 0.10, preferably less than 0.05 or 0.05.

[0045] Any water soluble cobalt compound is suitable for use, with highly soluble water soluble cobalt compounds being preferred.

[0046] Preferably, the first reagent has a solubility in water of more than 50 g / l, preferably more than 100 g / l, preferably more than 150 g / l, preferably more than 200 g / l, preferably more than 250 g / l, preferably more than 300 g / l, and / or less than 1000 g / l, measured at 20°C.

[0047] Preferably, the first reagent is selected from cobalt dinitrate, particularly hydrated cobalt dinitrate, cobalt acetate, cobalt acetylacetonate, cobalt dichloride, particularly hydrated cobalt dichloride, cobalt difluoride, cobalt sulfate, particularly hydrated cobalt sulfate, cobalt tartrate, cobalt bromide, cobalt iodide, cobalt thiocyanate, cobalt phosphate, and combinations thereof. Preferably, the first reagent is selected from cobalt dinitrate, particularly hydrated cobalt dinitrate, cobalt acetate, cobalt dichloride, particularly hydrated cobalt dichloride, cobalt sulfate, particularly hydrated cobalt sulfate, cobalt bromide, cobalt iodide, cobalt thiocyanate, and combinations thereof. Preferably, the first reagent is selected from cobalt dinitrate, particularly hydrated cobalt dinitrate, cobalt acetate, and combinations thereof. More preferably, the first reagent is cobalt dinitrate, especially hydrated cobalt dinitrate, preferably cobalt dinitrate hexahydrate.

[0048] Preferably, the first reagent is introduced with water in the form of an aqueous solution.

[0049] Preferably, step b) is carried out with stirring.

[0050] In step c), the second reagent is added to the suspension obtained from step b). Preferably, the second reagent consists of a water-soluble cobalt ligand. Alternatively or additionally, a precursor of such a ligand may be added, i.e., a compound that, after being added to the suspension, generates the ligand, e.g., a precursor that decomposes in water to release the cobalt ligand.

[0051] The ligand has a functional group that reacts with the cobalt cations that result from the addition of the first reagent to form a cobalt complex.

[0052] Preferably, the cobalt ligand is a cobalt chelating ligand.

[0053] Preferably, the ligand is a high field ligand.

[0054] The amount of the second reagent is preferably adapted to complex more than 99%, preferably all, of the cobalt cations of the suspension. Preferably, the second reagent contains only carbon, hydrogen and oxygen atoms, and optionally nitrogen and / or chlorine atoms.

[0055] Preferably, the second reagent contains an amino group (-NH2) and / or a carboxylate (-COO - ) and / or thiol groups (-SH). Preferably, the second reagent is selected from molecules containing amino groups (-NH2) and / or carboxylates (-COO - ) is selected from molecules containing

[0056] Preferably, the second reagent is selected from urea and its derivatives, citric acid, oxalic acid, ethylenediamine, salen, ethylenediaminetetraacetic acid (ie, "EDTA"), and combinations thereof.

[0057] Preferably, the second reagent is selected from urea and its derivatives, ethylenediamine, and combinations thereof.

[0058] More preferably, the second reagent is selected from urea and its derivatives.

[0059] Preferably, the second reagent is introduced in the form of an aqueous solution with water.

[0060] Preferably, step c) is carried out with stirring. In one embodiment, the suspension is preferably maintained at a temperature above 40°C, preferably above 50°C, and below 90°C, preferably below 80°C.

[0061] The order of steps a) to c) may be any one of the following: a)+b)+c), or a)+c)+b), or b)+a)+c), or b)+c)+a), or c)+b)+a), or c)+a)+b), or c)+a)+b). In one embodiment, these steps are simultaneous.

[0062] The solution obtained after these steps can be called a "complexed suspension."

[0063] The amount of water in the complexed solution is not particularly limited, other than to limit the duration and / or cost of step d).

[0064] In step d), all or part of the water is extracted from the complexed suspension, preferably until a product having the consistency of wet sand or powder is obtained. The extraction is preferably continued until more than 70% by weight of the water has been removed from the complexed suspension. Preferably, in step d), more than 80% by weight, preferably more than 85% by weight, preferably more than 90% by weight, preferably more than 95% by weight of the water is removed from the complexed suspension.

[0065] In one embodiment, substantially all of the water is removed from the complexed suspension.

[0066] Any technique known to those skilled in the art for at least partially removing water from the complexed suspension may be used, such as drying or freeze-drying.

[0067] If drying is carried out in step d), it is preferably accompanied by stirring of the complexed suspension. Preferably, the drying temperature is above 50° C. and below 90° C., and the drying is preferably carried out in air.

[0068] In step e), the product obtained from step d) is calcined.

[0069] Preferably, the calcination temperature is above 300° C., preferably above 400° C., and below 800° C. The holding time at this temperature is preferably above 1 hour, preferably above 2 hours, and preferably below 10 hours.

[0070] The calcination is carried out in an oxygenated fluid, in air.

[0071] In a non-preferred embodiment, steps d) and e) are carried out simultaneously.

[0072] The Co-GCO powder obtained according to the invention has been found to be particularly suitable for producing sintered products, in particular electrolytes.

[0073] The inventors have found that the surfaces of gadolinium-doped cerium oxide particles are coated with cobalt oxide particles, where the latter are spread remarkably uniformly, as shown in FIGS.

[0074] Figures 1 and 3 show particles of gadolinium-doped cerium oxide powders containing cobalt oxide from Examples 1 and 2, respectively. Figures 2 and 4 are superimposed on Figures 1 and 3, respectively, and show the concentration of cobalt. Cobalt appears gray, and the higher the concentration, the lighter the gray. Figure 2, produced with the powder from Example 1, outside the present invention, shows a non-uniform distribution of gray, with numerous light-colored zones. In contrast, in Figure 4, produced with the powder from Example 2, according to the present invention, the gray is more uniformly distributed, indicating a more uniform cobalt distribution on the surface of the GCO particles.

[0075] Cobalt oxide is cobalt(II,III) oxide, expressed as CO3O4.

[0076] In Co-GCO powders, not all of the cobalt oxide is necessarily on the surface of the GCO particles.

[0077] The present invention also relates to the above-mentioned Co-GCO powder which has been or may be produced according to the method for producing a powder of the present invention.

[0078] The word "percentile N" 10 , N 50 and N 90 " is generated by energy spectrometry (i.e., "EDS") of a pellet consisting of powder compressed at a pressure of 125 MPa in cobalt mapping, with 256 color shades, corresponding to the percentage of pixels at 10%, 50%, and 90%, respectively, in the cumulative distribution curve of the pixels as a function of shade, sorted in ascending order, with the shade being proportionally higher as the cobalt content increases.

[0079] In other words, 90% (percentage by number) of the pixels in the mapping are N 90 and 10% of the pixels have a shade lower than N 10 It has a lower density than

[0080] The more pixels the mapping includes, the more accurate the percentile estimation will be. To increase the number of pixels, multiple zones of the pellet are preferably mapped.

[0081] The color of the tint used can be chosen arbitrarily, for example, the tint in the example is a light green tint for cobalt.

[0082] The mapping can in particular be performed as described in the case of the example.

[0083] The E value is the difference N 90 -N 10 and the S value is defined as (N 90 -N 10) / N 50 Ratio=E / N 50 is defined as:

[0084] The inventors believe that production by the method according to the invention results in a homogeneous coating of the particles with cobalt, particularly in oxide form, in the Co-GCO powder. The inventors have also found that the E value is greater than 110.

[0085] Preferably, the E value is greater than 115, preferably greater than 120, preferably greater than 125, preferably greater than 130, preferably greater than 135.

[0086] More preferably, the powders according to the invention have an S value of less than 2.20, preferably less than 2.10, preferably less than 2.00, preferably less than 1.90, preferably less than 1.80, preferably less than 1.70, preferably less than 1.60.

[0087] The powder preferably comprises, in mass percent based on oxides: Gd2O3 greater than 9.60% and / or less than 20.79%; and / or CeO2 greater than 72.55% and / or less than 89.32%; and / or Cobalt oxide (expressed as Co3O4) greater than 0.23%, preferably greater than 0.50%, preferably greater than 1.00%, preferably greater than 1.50%, and / or less than 6.51%, preferably less than 5.50%, preferably less than 4.50%, preferably less than 3.50%, preferably less than 2.50%; and / or Less than 2%, preferably less than 1%, of oxides other than Gd2O3, CeO2 and cobalt oxide (expressed as Co3O4), preferably less than 0.5% Includes:

[0088] The oxides make up more than 95% by weight of the Co-GCO powder, preferably more than 98% by weight, preferably more than 99% by weight, preferably 100%.

[0089] Preferably, the median diameter of the Co-GCO powder is greater than 0.1 μm, preferably less than 0.8 μm.

[0090] Preferably, the D of the Co-GCO powder 90 is less than 2.5 μm, preferably less than 2 μm.

[0091] Method for manufacturing a sintered part according to the invention

[0092] In step f), the Co-GCO powder is formed into the shape of a "preform" using any conventional technique, and then in step g), the preform is sintered.

[0093] Cooling produces a sintered part.

[0094] If the sintered part is intended to constitute an electrolyte, the shaping can be carried out by tape casting or by screen printing of a slip generally comprising the Co-GCO powder, a solvent, often water, a binder, generally a polymer, and a dispersant.

[0095] It is worth noting that, regardless of the embodiment, the sintering temperature may be less than 1600°C, preferably less than 1500°C, and more preferably less than 1490°C.

[0096] In one embodiment, sintering of the preform can be performed simultaneously with sintering of other components of the solid oxide fuel cell or solid oxide electrolyzer, such as electrodes, which is referred to as co-sintering.

[0097] The resulting sintered body preferably constitutes the electrolyte.

[0098] Example

[0099] The present invention is not limited to the embodiments described below, which are provided as examples.

[0100] To determine the chemical composition of a powder, beads are produced by melting the powder, and the content of various elements is measured on the beads by X-ray fluorescence, where oxygen is taken as the mass contribution to 100%.

[0101] The median diameter of the powder is conventionally measured using a laser particle size analyzer, model LA950V2, available from Horiba, Ltd.

[0102] In the examples, the following starting materials were used: Gadolinium-doped cerium oxide powder, which is produced by melting in an electric arc furnace, has a gadolinium molar content of 20% relative to the sum of the cerium molar content and the gadolinium molar content, and has a median diameter of 0.6 μm; Cobalt dinitrate hexahydrate, having a purity of greater than 99% by mass; In the case of Example 1, ethanol, having a purity of greater than 99.9% by weight; In the case of Example 2, the urea has a purity of more than 99% by weight.

[0103] A method for producing gadolinium-doped cerium oxide powder produced by melting in an electric arc furnace will now be described in more detail.

[0104] The gadolinium-doped cerium oxide powder is produced by mixing starting feedstock consisting of cerium oxide powder and gadolinium oxide powder. The starting feedstock is then melted in a single-phase Yellow-type electric arc furnace with graphite electrodes, a furnace vessel with a diameter of 0.8 m, a voltage of 195 V, a current of 1300 A, and a specific electrical energy of 3 kWh per kg of input. The molten material is then cast into a trickle form and then dispersed as beads by blowing compressed air. After complete cooling, the beads are then heat-treated in air at 1200°C for 4 hours. After heat treatment, the beads are first crushed in a jar mill and then crushed in a ball micromill in a wet medium. After drying, the gadolinium-doped cerium oxide powder is obtained.

[0105] In the case of Example 1, the following prior art method was carried out.

[0106] Six grams of gadolinium-doped cerium oxide powder was suspended in 100 mL of ethanol in a beaker at room temperature. 0.491 g of cobalt nitrate hexahydrate suspended in ethanol was then added with stirring. The suspension was dried on a hot plate at 60°C with stirring for 1 hour, and then calcined in air using the following thermal cycle: Heat at a rate of 100°C / hour to 400°C; Maintain at 400°C for 3 hours; The temperature is lowered to 250°C at a rate of 100°C / hour, and then allowed to cool naturally to room temperature.

[0107] In the case of Example 2, the method according to the invention was carried out.

[0108] In step a), 150 g of gadolinium-doped cerium oxide powder is suspended in 400 mL of water in a beaker at room temperature. In step b), 12.3 g of cobalt nitrate hexahydrate is added to the suspension while stirring. In step c), 7.59 g of urea is added to the suspension, with stirring being continued for 1 minute after the introduction of the urea. In step d), the complexed suspension obtained at the end of step c) is dried on a hot plate at 80° C. with stirring for 6 hours, and then in step e), it is calcined in air with the following thermal cycle: Heat at a rate of 100°C / hour to 400°C; Maintain at 400°C for 3 hours; The temperature is lowered to 250°C at a rate of 100°C / hour, and then allowed to cool naturally to room temperature.

[0109] In the case of Example 3, the method according to the invention was carried out.

[0110] In step a), 150 g of gadolinium-doped cerium oxide powder is suspended in 400 mL of water in a beaker at room temperature. In step b), 10.5 g of cobalt dinitrate hexahydrate is added to the suspension while stirring. In step c), 6.5 g of urea is added to the suspension, and stirring is continued for 1 minute after the introduction of the urea. In step d), the complexed suspension obtained at the end of step c) is dried on a hot plate at 80° C. with stirring for 6 hours, and then in step e), it is calcined in air with the following thermal cycle: Heat at a rate of 100°C / hour to 400°C; Maintain at 400°C for 3 hours; The temperature is lowered to 250°C at a rate of 100°C / hour, and then allowed to cool naturally to room temperature.

[0111] A cumulative pixel distribution curve as a function of shade, with shades sorted in ascending order, was generated in the following way:

[0112] 2 g of powder from each example is pressed into a die with a diameter of 10 mm at a pressure of 125 MPa to obtain a pellet for each example. Each pellet is then metallized using a Sputter Coater 208HR metallizer sold by CRESSINGTON equipped with a platinum target, the pellet being placed at a distance of 10 cm from the target during the metallization operation, where the spray current intensity is equal to 40 mA.

[0113] Each pellet is then observed in secondary electron mode using a ZEISS GeminiSEM 560 scanning electron microscope (SEM) equipped with a Bruker X Flash 6 / 60 model energy dispersive spectroscopy (EDS) probe under the following conditions: Working distance (WD): 10mm, High voltage (HV): 20 keV, Gun Mode: Analytic, VP mode 30Pa, Diaphragm: 120 pm, Magnification: 10,000x.

[0114] Cobalt mapping was performed on the pellets by energy dispersive spectrometry (EDS) using an EDS probe and Esprit software (version 2.3.1.1019) developed by BRUKER. 2 Five zones are mapped, where the scan settings are defined using the following parameters: Image size [i.e., number of pixels]: 600, Image input: Signal A; None, map: Time / point [μs]: 2048, Line average:1.

[0115] The resulting image shows the location and local content of cobalt: the darker the color, the higher the local cobalt content, and the color used is light green.

[0116] The settings used, which can be seen in the Combined mapping section, are as follows: Image Filter: None Map Filter:Smoothing:Value:3 Composite image: raw signal Color control: The three parameters are unchanged, the cursors for each parameter are positioned in the middle of the range, and the Co-Kα value remains at 1.

[0117] The resulting image does not include a scale bar or other information of this type.

[0118] For each pellet, each of the five images was analyzed using ImageJ software available at https: / / imagej.net / ij / download.html to assign a shade of green to each pixel in the image, with the shade ranging from 0 (black, representing no cobalt or no material) to 255 (the most intense color detected on the image, i.e., the highest cobalt content).

[0119] Before analysis using ImageJ software, the images were not subjected to any processing, in particular to modify their contrast.

[0120] Each image is analyzed using ImageJ software according to the following method: Open the image in ImageJ; Select Analyze and then Histogram: ImageJ will display in the form of a graph the distribution of pixels in the analyzed image as a function of gray level; Select List to access the numerical data and copy them into a spreadsheet.

[0121] For each pellet, the sum of pixels with the above shades for all five images (ie, for cobalt mapping) is determined for each shade (except shade 0 is not considered).

[0122] A curve is then plotted representing the cumulative number of pixels as a percentage for each grey value, where the grey levels are sorted in ascending order from 1 to 255. Figure 5 shows the cumulative distribution curves of pixels as a function of grey level for Examples 1, 2 and 3, where the grey levels are sorted in ascending order.

[0123] The E value is the difference N 90 -N 10 where N 90 is the shade reached by 90% of the cumulative pixels, and N 10 is the shade reached by 10% of the cumulative pixels.

[0124] The S value is (N 90 -N 10 ) / N 50 Ratio=E / N 50 where N 50 is the shade reached by 50% of the cumulative pixels.

[0125] Table 1 below shows the characteristics of the obtained Co-GCO powder.

[0126] [Table 1]

[0127] The inventors have surprisingly found that the sintering behavior of the powder of Example 2 according to the invention is better than the sintering behavior of the powder of Example 1 outside the invention.

[0128] In particular, after thermal expansion tests were carried out on dry cylindrical sample specimens from Examples 1 and 2, each having a diameter and height of 10 mm, using a TMA SETSYS EVO 1750 differential dilatometer (sold by SETARAM KEP TECHNOLOGIES) fitted with a high-density alumina sensor (a ramp up to 1450°C at a rate of 1.6°C / min, a hold at 1450°C for 1 hour, and a ramp down at a rate of 5°C / min), the curve of the differential thermal expansion (units, % / min) as a function of temperature showed a minimum value equal to 1362°C for Example 1 outside the invention and a value equal to 1250°C for Example 2 according to the invention. Therefore, the powder of Example 2 according to the invention has a maximum shrinkage rate reached at a lower temperature (1250°C) than the powder of Example 1 outside the invention (1362°C).

[0129] The present invention therefore allows for an improved method for producing electrolytes.

[0130] Without being bound by this theory, the inventors explain this result by a significantly more homogeneous dispersion of the cobalt oxide particles on the surface of the gadolinium-doped cerium oxide particles for the powder according to Example 2 according to the invention compared to the powder of Example 1 outside the invention, as shown in Figures 2 and 4, where the value of E is equal to 147 for the powder of Example 2 according to the invention and is greater than the value of E equal to 105 for the powder of Example 1.

[0131] Of course, the invention is not limited to the described embodiments, which are provided as non-limiting examples.

[0132] In particular, the products according to the invention are not limited to any particular shape or size.

Claims

1. 1. A method for producing a cobalt oxide-containing gadolinium-doped cerium oxide powder, comprising the steps of: 1) gadolinium-doped cerium oxide particles; Water containing a cobalt complex preparing a wet product comprising a mixture of wherein the wet product preferably has a Q Co ' / Q GCO Q so that '≦0.15 Co ' / Q GCO ' has a ratio, where Q GCO ' represents the sum of the molar amounts of cerium and gadolinium in the wet product, and Q Co ' denotes the molar amount of cobalt in the wet product; d) optionally removing at least a portion of said water; e) calcining the product obtained from step d) or, if step d) is absent, the product obtained from step 1) in an oxygenated fluid to obtain said powder. The method comprises the following sequential steps:

2. The method comprises step d), and wherein step 1) comprises: a) suspending gadolinium-doped cerium oxide powder in water; b) adding at least one water-soluble cobalt compound (i.e., a first reagent) to the suspension to form cobalt cations; Here, the amount of the first reagent is preferably 0.005≦Q Co / Q GCO ≦0.15, where Q GCO represents the sum of the molar amounts of cerium and gadolinium provided in step a), and Q Co represents the molar amount of cobalt provided by the first reagent; c) adding at least one water-soluble cobalt ligand and / or at least one precursor of such a ligand (i.e., a second reagent) to the suspension to form a cobalt complex. The method of claim 1 , comprising the steps of:

3. Q Co ' / Q GCO ' ratio is 0.01 or more than 0.01 and less than 0.10 or 0.10, and / or in step b), Q Co / Q GCO 3. The method of claim 1 or 2, wherein the ratio is 0.01 or greater than 0.01 and less than 0.10 or 0.

10.

4. Q Co ' / Q GCO ' ratio is 0.02 or more than 0.02 and less than 0.05 or 0.05, and / or in step b), Q Co / Q GCO 4. The method of claim 3, wherein the ratio is 0.02 or greater than 0.02 and less than 0.05 or 0.

05.

5. 5. The method according to claim 1, wherein the molar content of gadolinium in the gadolinium-doped cerium oxide powder of the wet product and / or in the powder suspended in step a) is 10% or more than 10% and less than 20% or 20%, expressed as a percentage based on the sum of the molar amounts of cerium and gadolinium.

6. 6. The method according to claim 1, wherein the median diameter of the gadolinium-doped cerium oxide powder of the wet product and / or the median diameter of the powder suspended in step a) is greater than 20 nm and less than 0.8 μm.

7. 7. The method according to any one of claims 1 to 6, wherein the gadolinium-doped cerium oxide powder of the wet product and / or the gadolinium-doped cerium oxide powder of the powder suspended in step a) is obtained via a melting process.

8. 8. The method of claim 2, wherein the first reagent has a solubility in water of more than 300 g / l when measured at 20°C.

9. the first reagent is selected from cobalt dinitrate, cobalt acetate, cobalt acetylacetonate, cobalt dichloride, cobalt difluoride, cobalt sulfate, cobalt tartrate, cobalt bromide, cobalt iodide, cobalt thiocyanate, cobalt phosphate, and combinations thereof; and / or The second reagent is an amino group -NH 2 and / or carboxylate-COO - and / or molecules containing a thiol group -SH, The method according to any one of claims 2 to 7.

10. the first reagent is selected from cobalt dinitrate, cobalt acetate, and combinations thereof; and / or the second reagent is selected from urea and its derivatives, citric acid, oxalic acid, ethylenediamine, salen, ethylenediaminetetraacetic acid, and combinations thereof; 10. The method of claim 9.

11. 11. The method of claim 10, wherein the first reagent is cobalt dinitrate and / or the second reagent is selected from urea and its derivatives.

12. 12. The method according to claim 2, wherein in step c) the amount of the second reagent is adapted so that more than 99% of the amount of cobalt cations in the suspension is complexed.

13. 13. The method according to any one of claims 2 to 12, wherein in step c) the second reagent contains only carbon, hydrogen and oxygen atoms, and optionally nitrogen and / or chlorine atoms.

14. 14. The method according to any one of claims 1 to 13, wherein in step d) more than 80% by weight of the water is removed.

15. 15. The method according to any one of claims 1 to 14, wherein in step e) the calcination temperature is above 300°C and below 800°C, and the holding time at said temperature is above 1 hour and below 10 hours.

16. 1. A cobalt oxide-containing gadolinium-doped cerium oxide powder, the powder comprising, in mass percent based on oxide: More than 9.60% and less than 20.79% Gd 2 O 3 , and CeO: over 72.55% and less than 89.32% 2 , and More than 0.23% and less than 6.51% cobalt oxide (Co 3 O 4 ), and Gd 2 O 3 , CeO 2 and cobalt oxide (Co 3 O 4 Less than 2% of oxides other than having a chemical analysis of wherein said powder of gadolinium-doped cerium oxide particles is at least partially coated with cobalt oxide particles, thus resulting in a difference N 90 -N 10 (i.e., E value) is greater than 110; N 10 and N 90 but, In cobalt mapping, It is made up of a plurality of pixels, each pixel having a shade of color, the shade ranging from 0 to 255; and Generated by energy spectroscopy of a pellet formed by compressing the powder at a pressure of 125 MPa, wherein the shades correspond to the percentages of the number of pixels at 10% and 90%, respectively, in a cumulative distribution curve of the pixels as a function of shade, without taking into account pixels with a concentration D, the shades being sorted in ascending order, the shades being proportionally higher for higher cobalt contents; The gadolinium-doped cerium oxide powder.

17. 17. The powder of claim 16 having an E value of greater than 125.

18. The powder has an S value of less than 2.20, and the S value is (N 90 -N 10 ) / N 50 is the ratio, where N 50 18. The powder according to claim 16 or 17, wherein σ is a shade corresponding to the percentage by number of said pixels of 50% on said cumulative distribution curve.

19. 19. The powder of claim 18, wherein the S value is less than 2.

00.

20. 20. A method for producing a sintered part, comprising step f) producing a preform from the powder according to any one of claims 16 to 19 or from a powder produced according to the method according to any one of claims 1 to 15, and then step g) sintering the preform to obtain a sintered part.

21. 21. The method of claim 20, wherein the sintering temperature is less than 1500°C.

22. 22. A method for manufacturing a device selected from a solid oxide fuel cell and a solid oxide electrolyzer, said method comprising producing a sintered part manufactured by the method of claim 20 or 21, wherein said sintered part is found after manufacture between the electrodes of said fuel cell or between the electrodes of said electrolyzer so as to constitute an electrolyte.

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