A method of producing metal compounds for coating applications

Abstract

The invention relates to a method of producing metal compounds for coating applications (12), said method comprising providing a compound (10) of formula M (A)4 as a starting material, wherein M represents a metal, and wherein A represents a beta-dicarbonylate, and partially hydrolysing said compound (10) of formula M (A)4 to obtain a metal compound for coating applications (12) of formula M (A) XO(2-x / 2)∙y H2O, wherein x is at most 3.5 and at least 0.5. The invention also relates to a metal compound (10) of formula M (A) XO(2-x / 2)∙y H2O, to a coating solution (16) and to a method of coating a work piece ( 18 ).

Description

[0001] Title : A method of producing metal compounds for coating applications

[0002] Specification

[0003] The invention relates to methods of producing metal compounds for coating applications , to metal compounds for coating applications produced by way of such methods , to coating solutions comprising such metal compounds for coating applications , and to methods of coating a work piece with such coating solutions .

[0004] Specifically, the invention relates to metal compounds for use in electrochemical cells , in particular fuel cells and electrolyser cells . Fuel cells are energy conversion devices that allow for conversion of electrochemical fuel to electricity . Electrolyser cells may be considered as fuel cells running in reverse mode , i . e . using electricity to decompose a compound into its constituent parts , for example water into hydrogen and oxygen . Reversible cells are capable of operating in both modes .

[0005] Such electrochemical cells typically comprise cell chemistry layers that may be applied as thin coatings . The cell chemistry layers commonly include an electrolyte layer that is sandwiched between two electrode layers . In addition, the cell chemistry layers may comprise an electron barrier layer, e . g . between a cathode layer and the electrolyte layer . For such electron barrier layers , metal oxide coatings have proven advantageous . Metal beta-dicarbonylates are interesting candidates as metal source for the production of such metal oxide coatings. This is particularly due to the high solubility of metal beta- dicarbonylates in organic solvents, which facilitates the use of metal beta-dicarbonylates in coating applications. However, metal beta-dicarbonylates have limited storage stability in organic solutions.

[0006] It is an object of the invention to improve the stability of coating solutions for the production of metal oxide coatings.

[0007] According to the invention there is provided a method of producing metal compounds for coating solutions according to claim 1. The method comprises providing a compound of formula M(A)4as a starting material, wherein M represents a metal, and wherein A represents a beta-dicarbonylate . Accordingly, the stoichiometry of metal to beta-dicarbonylate in the starting material is 1:4. The method further comprises partially hydrolysing said compound of formula M(A)4to obtain a metal compound for coating applications of formula M (A)x0(2-x / 2) • y H2O, wherein x is at most 3.5 and at least 0.5. Thus, the resulting metal compound for coating applications is the product of the partial hydrolysis of the compound of formula M(A)4.

[0008] The resulting metal compound of formula M (A)XO(2-x / 2) • y H2O, wherein x is at most 3.5 and at least 0.5, is highly suitable for use in coating applications. Particularly, the metal compound exhibits high solubility in organic solvents such as alcohols. Moreover, the resulting organic solutions of the metal compound has proven to be highly storage stable. A hydrolysis is a chemical reaction in which a molecule of water, a hydroxide ion or an oxide ion breaks down one or more chemical bonds. In connection with the proposed method, hydrolysing the compound of formula M(A)4 means that betadicarbonylate ligands are replaced by hydroxide ions or oxide ions. According to the invention, the compound of formula M(A)4 is partially hydrolysed. Thus, not all of the beta-dicarbonylate ligands are replaced by hydroxide ions or oxide ions, but only a fraction of the beta-dicarbonylate ligands . This does not exclude that for some of the individual M(A)4 units all beta- dicarbonylate ligands are replaced and / or that for some of the individual M(A)4 units none of the beta-dicarbonylate ligands is replaced .

[0009] The coefficient "y" in the formula M (A)x0(2-x / 2) • y H2O can have different values. In some examples, y is at least 0 and at most 10.

[0010] In some preferred embodiments, no additional source of metal M is provided. Therefore, the compound of formula M(A)4 is the only starting material comprising the metal M. The metal compound for coating applications of formula M ( A)XO(2-x / 2) • y H2O is thus exclusively formed by partial hydrolysis of the compound of formula M(A)4, and not by a reaction of the compound of formula M(A)4with another compound comprising the metal M.

[0011] In some preferred embodiments, M represents a metal of the fourth group in the periodic table, i.e. the titanium group in the periodic table. Those metals are particularly suitable for coating applications in the field of electrochemical cells. In some preferred embodiments, M represents zirconium.

[0012] Alternatively, said metal of the fourth group in the periodic table may be hafnium (i.e. , M may represent hafnium) .

[0013] In some preferred embodiments, A represents a beta-diketonate . Thus, both carbonyl groups of the beta-dicarbonylate may be ketones. Alternatively, one or both of the carbonyl groups of said beta-dicarbonylate may be another carbonyl group than a ketone. Particularly, one or both of the carbonyl groups of said beta-dicarbonylate may be an aldehyde, the carbonyl group of a carboxylic acid or the carbonyl group of an ester.

[0014] In some preferred embodiments, A represents acetylacetonate . Metal acetylacetonates are typically comparably inexpensive metal beta-dicarbonylates . Moreover, metal acetylacetonates proved to reliably undergo partial hydrolysis .

[0015] In some preferred embodiments, M(A)4 represents zirconium acetylacetonate .

[0016] In some preferred embodiments, x is at most 3.0. Thus, in average at least one beta-dicarbonylate ligand is replaced from the individual starting material units. Where x is at most 3.0, precipitation of the metal compound for coating applications in a coating solution is reliably prevented. Preferably, x is at most 3.0 and at least 1.5. Where x is at least 1.5, the solubility of the metal compound for coating applications in organic solvents is typically high. Preferably, x is at most

[0017] 2.5, preferably x is at most 2.5 and at least 1.5, preferably x is at most 2.0, most preferably x is at most 2.0 and at least

[0018] 1.5. In some preferred embodiments, partially hydrolysing comprises heating said compound of formula M(A)4 at a heating temperature of at least 60 °C. By heating the compound of formula M(A)4 at such a heating temperature, the reaction kinetics may be increased, thus reducing the reaction time. Preferably, partially hydrolysing comprises heating the compound of formula M(A)4at a heating temperature of at least 80 °C, most preferably at a heating temperature of at least 100 °C. Even though heating the compound of formula M(A)4 at a heating temperature of at least 60 °C is preferred, partial hydrolysis may also be achieved at a lower heating temperature or even at room temperature. The extent of the partial hydrolysis may be influenced by the heating temperature, by the reaction time and / or by the amount of water, hydroxide ions and / or oxide ions that is available for partial hydrolysis.

[0019] In some preferred embodiments, the compound of formula M(A)4 is provided as a solid and partially hydrolysed as a solid in a water-containing atmosphere. This variant of the method is technically easy to perform, particularly on a large-scale. Moreover, the variant is cost-effective, particularly because the use of a solvent is avoided during partial hydrolysis . Preferably, the solid is a powder. The absolute humidity in said water-containing atmosphere preferably is at least 0.1%, more preferably at least 0.5%.

[0020] In some preferred embodiments, said water-containing atmosphere is saturated water vapour. Saturated water vapour provides a high concentration of water molecules for hydrolysis. In consequence, the reaction time may be reduced. In some preferred embodiments , said water containing atmosphere is an oxygen-reduced atmosphere or an oxygen-free atmosphere . An oxygen-reduced or oxygen-free atmosphere may result in the reduction of side reactions . As used herein, an "oxygen-reduced atmosphere" is an atmosphere having an oxygen content that is less than the oxygen content of air . Preferably, the oxygen- reduced atmosphere has an oxygen content of at most 10% . As used herein, an "oxygen-free atmosphere" is an atmosphere having an oxygen content of at most 1000 ppm .

[0021] In some preferred embodiments , partial hydrolysis is performed in a recirculated air furnace or in a rotary kiln . In order to increase the reaction kinetics , it is advantageous to recirculate the water-containing atmosphere . Thus , the use of a recirculated air furnace or a rotary kiln is preferred .

[0022] In some preferred embodiments , the compound of formula M (A) 4 is provided and partially hydrolysed as a part of a liquid composition comprising the compound of formula M (A) 4 and at least one solvent . This has the advantage that the partial hydrolysis can be achieved in a particularly homogenous way . Firstly, it can be avoided that units of the metal compound of formula M (A) 4 that are present within solid particles of the metal compound of formula M (A) 4 are isolated from water , hydroxide ions and / or oxide ions and in turn do not undergo partial hydrolysis . Furthermore , a homogeneous temperature distribution within the liquid composition can easily be achieved and maintained, e . g . by stirring the liquid composition .

[0023] Where the compound of formula M (A) 4 is partially hydrolysed as a part of a liquid composition, partial hydrolysis may be effected by residual water contained in the at least one solvent of the liquid composition. However, it is preferred to add additional water to the liquid composition, particularly in order to reduce the reaction time.

[0024] In some preferred embodiments, said liquid composition is a solution of said compound of formula M(A)4- In this case, partial hydrolysis is particularly homogeneous.

[0025] In some preferred embodiments, a concentration of the compound of formula M(A)4 in said liquid composition is between 5 wt . -% and 65 wt . -%.

[0026] In some preferred embodiments, the at least one solvent has a boiling temperature between 80 °C and 320 °C. Preferably, the at least one solvent has a boiling temperature between 110 °C and 250 °C. Such solvents allow heating the liquid composition at a high heating temperature. This may reduce the reaction time.

[0027] In some preferred embodiments, the at least one solvent is selected from the group consisting of: alcohols, preferably octanol or cyclohexanol, ethers, preferably diethylene glycol diethyl ether, l-Methoxy-2-propanol or diethylene glycol monobutyl ether, and esters, preferably Methoxy-2 -propyl acetate or texanol .

[0028] The liquid composition may also comprise more than one solvent (i.e. at least a first solvent and a second solvent that is different from the first solvent) . Where the liquid composition comprises more than one solvent, preferably the solvents are selected from the solvent group defined above. In some preferred embodiments, the at least one solvent is completely or partially removed from said liquid composition. The at least one solvent may be removed during partial hydrolysis or after completion of partial hydrolysis. Complete removal of the at least one solvent yields the metal compound for coating applications of formula M (A)x0(2-x / 2) • y H2O as a solid. In the solid form, the metal compound for coating applications is particularly storage stable. Removal of the at least one solvent may comprise evaporating the at least one solvent at an increased temperature (i.e. , a temperature that is higher than room temperature) and / or at reduced pressure (i.e., at a pressure that is lower than atmospheric pressure) . Removal of the at least one solvent may also comprise precipitating the metal compound for coating applications of formula M(A)x0(2-x / 2) -y H2O and removing the at least one solvent by filtration. Partial removal of the at least one solvent yields the metal compound for coating applications of formula M ( )x0(2-x / 2) • y H2O as a concentrated liquid composition, particularly as a concentrated solution.

[0029] The invention also relates to a metal compound for coating applications of formula M ( A)x0(2-x / 2) • y H2O, wherein x is at most 3.5 and at least 0.5, according to claim 20. The metal compound for coating applications is produced by way of a method as described above.

[0030] The metal compound for coating applications may be a solid or a part of a solid composition. Alternatively, the metal compound for coating applications may be a part of a liquid composition. Specifically, the metal compound for coating applications may be dissolved or suspended in said liquid composition. The invention also relates to a coating solution according to claim 21 . The coating solution comprises a metal compound for coating applications as described above . The coating solution further comprises at least one solvent . The metal compound for coating applications is dissolved in said at least one solvent .

[0031] Where the above-described method of producing metal compounds for coating applications yields the metal compound for coating applications of formula M ( )x0(2-x / 2) • y H2O as a solution ( i . e . , dissolved in a solvent or a solvent mixture ) , said solution may already constitute the coating solution .

[0032] Preferably, the coating solution is an alcoholic coating solution, i . e . the coating solution comprises at least one alcohol as a solvent .

[0033] In some preferred embodiments , the concentration of said metal compound for coating applications , calculated as metal oxide , in the coating solution is between 5 wt . -% and 40 wt . -% . A coating solution comprising the metal compound for coating applications in this concentration range has the advantage that a layer with a comparatively high layer thickness can be obtained with each coating step . In consequence , the number of coating steps may be reduced compared with the use of a less concentrated coating solution . Preferably, the concentration of said metal compound for coating applications , calculated as metal oxide , in the coating solution is between 10 wt . -% and 20 wt . -% , most preferably between 12 wt . -% and 17 wt . -% .

[0034] Preferably, the coating solution comprises at least one solvent selected from the group consisting of : alcohols , particularly ethanol , propanol , iso-propanol , octanol or cyclohexanol , ethers, particularly diethylene glycol diethyl ether, diethylene glycol monobutyl ether or l-methoxy-2-propanol , carboxylic acids, organic amines, amides, particularly dimethylformamide or N-methylpyrrolidone, and esters, particularly ethyl acetate. The coating solution may also comprise a mixture of at least two solvents of the solvents listed above.

[0035] Preferably, the coating solution comprises, in addition to the metal compound for coating applications, at least one metal salt. The metal of said metal salt is preferably scandium, yttrium, lanthanum or a rare earth metal. The anion of said metal salt is preferably a halide, a nitrate, a sulphate, a carboxylate or an alcoxide. The molar ratio of the metal of said metal compound for coating applications and the metal of said metal salt is preferably between 100:1 and 1:1, most preferably between 50:1 and 2:1.

[0036] Preferably, the coating solution comprises water. Where water is present in the coating solution, the concentration of water is preferably between 0.1 wt . -% and 35 wt . -% .

[0037] Preferably, the coating solution comprises at least one dispersant such as an organic polymer, particularly polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone or corresponding copolymers, or a carboxylic acid, particularly trioxadecanoic acid. The mass ratio of said dispersant to the metal compound for coating applications, calculated as metal oxide, in the coating solution is preferably between 2% and 150%, most preferably between 5% and 50%.

[0038] The invention also relates to a method of coating a work piece according to claim 23. The method comprises providing a work piece to be coated and coating the work piece with a coating solution as described above . Coating the work piece may comprise a number of subsequent coating steps . Thus , the coating may be obtained by subsequently forming a number of stacked layers on the work piece .

[0039] In some preferred embodiments , an electrode for an electrochemical cell , preferably a solid oxide fuel cell or a solid oxide electrolyser cell , is provided as the work piece and coated with the coating solution .

[0040] In some embodiments , an electrolyte layer for an electrochemical cell , preferably a solid oxide fuel cell or a solid oxide electrolyser cell , is provided as the work piece and coated with the coating solution . The electrolyte layer may be one of a plurality of sub layers .

[0041] Further embodiments are derivable from the following description and the drawings .

[0042] In the drawings :

[0043] Figure 1 shows a flow chart of a method of producing metal compounds for coating applications according to a first embodiment ;

[0044] Figure 2 shows a flow chart of a method of producing metal compounds for coating applications according to a second embodiment ; and

[0045] Figure 3 shows a flow chart of a method of coating a work piece . Figure 1 shows a flow chart of a method of producing metal compounds for coating applications 12.

[0046] In a first step 101, a compound 10 of formula M(A)4 is provided as a starting material, wherein M represents a metal, and wherein A represents a beta-dicarbonylate . The compound 10 is provided as a solid, preferably as a powder. In this example, the compound 10 of formula M(A)4 is zirconium acetylacetonate (Zr(Acac)4> . However, the compound 10 may also be hafnium acetylacetonate (Hf (Acac)4) , for example.

[0047] In a second step 103, the compound 10 of formula M(A)4 is partially hydrolysed. For this purpose, the compound 10 of formula M(A)4 is heated as a solid in a water-containing atmosphere. Partial hydrolysis of said compound 10 of formula M(A)4is performed to an extent that a metal compound for coating applications 12 of formula M (A)XO(2-x / 2) • y H2O is obtained, wherein x is at most 3.5 and at least 0.5.

[0048] The second step 103 is preferably performed in a recirculated- air furnace or in a rotary kiln. In such devices, extensive mixing of the starting material, i.e. the compound 10, and the water-containing atmosphere can be realised. This may increase the reaction kinetics of the partial hydrolysis. Furthermore, a homogenous partial hydrolysis may be achieved. Thus, the particles of the solid starting material may be partially hydrolysed to a similar extent.

[0049] Preferably, the water content of said water-containing atmosphere is at least 0.1%, more preferably at least 0.5%. The heating time of step 103 may be adjusted depending on the heating temperature. Particularly preferred combinations of heating temperature and heating time are as follows :

[0050] Figure 2 shows a flow chart of another method of producing metal compounds for coating applications 12.

[0051] In a first step 201, a liquid composition 14 comprising a compound 10 of formula M(A)4 is provided, wherein M represents a metal, and wherein A represents a beta-dicarbonylate . In addition to said compound 10 of formula M(A)4, the liquid composition 14 comprises at least one solvent. Preferably, the liquid composition 14 is a solution of said compound 10 of formula M(A)4 in said at least one solvent. In this example, the compound 10 of formula M(A)4 is zirconium acetylacetonate (Zr(Acac)4> . However, the compound 10 may also be hafnium acetylacetonate (Hf (Acac)4) , for example.

[0052] The at least one solvent is preferably selected from the group consisting of: alcohols, preferably octanol or cyclohexanol, ethers, preferably diethylene glycol diethyl ether, l-Methoxy-2- propanol or diethylene glycol monobutyl ether, and esters, preferably Methoxy-2 -propyl acetate or texanol.

[0053] The liquid composition 14 further comprises water. This water can be residual water contained in the at least one solvent. Moreover, additional water may be added to said liquid composition 14 (in addition to the residual water contained in the at least one solvent) .

[0054] In a second step 203, the compound 10 of formula M(A)4 is partially hydrolysed. For this purpose, the liquid composition 14 comprising said compound 10 of formula M(A)4 is heated. This results in the compound 10 of formula M(A)4 being partially hydrolysed by the water contained in the liquid composition 14. Hydrolysis of said compound 10 of formula M(A)4 is performed to an extent that a metal compound for coating applications 12 of formula M (A)XO(2-x / 2) • y H2O is obtained, wherein x is at most 3.5 and at least 0.5.

[0055] Preferably, said liquid composition 14 is heated at a heating temperature of at least 60 °C and at most 220 °C in the second step 203. The heating time may be between 3 min and 30 h. In order to avoid a loss of water during the second step 203, it is preferred that the second step 203 is performed at least temporarily in an air-tight vessel.

[0056] In a third step 205, the liquids (i.e. , the at least one solvent and excess water) may be removed from the reaction mixture. In this example, the liquids are completely removed in the third step 205. Thus, the metal compound for coating applications 12 of formula M (A)XO(2-x / 2) • y H2O is obtained as a solid. The liquids may be removed by heating the liquid composition in a convection oven, for example.

[0057] As an alternative, the liquids may be removed only partially from the reaction mixture. Partial removal of the liquids may yield a concentrated solution of the metal compound for coating applications 12 of formula M (A)XO(2-x / 2) • y H2O . Furthermore, the third step 205 may also be omitted.

[0058] Figure 3 shows a flow chart of a method of coating a work piece

[0059] 18.

[0060] In a first step 301, a coating solution 16 comprising the metal compound for coating applications 12 of formula M(A)XO(2-x / 2) -y H2O, wherein x is at most 3.5 and at least 0.5, is provided. In this example, the metal compound for coating applications 12 is provided as a solid. Providing the coating solution 16 comprises dissolving the metal compound for coating applications 12 in at least one solvent. Preferably, ethanol is used as the at least one solvent. The concentration of said metal compound for coating applications 12, calculated as metal oxide, in the coating solution 16 is preferably at least 10 wt . -% and at most 20 wt . -% .

[0061] The metal compound for coating applications 12 may also be provided as a part of a liquid composition, particularly as a part of a solution. In this case, this liquid composition may directly be used as the coating solution 16 without addition of further substances. However, it is preferred to add additional substances such as at least one solvent, a metal salt or a dispersant to the liquid composition.

[0062] In a second step 303, a work piece 18 to be coated is provided. In this example, the work piece 18 is an electrode 20 for an electrochemical cell, particularly a solid oxide fuel cell or a solid oxide electrolyser cell. In a third step 305 , the work piece 18 is coated with the coating solution 16 . Thus , the work piece 18 is provided with a coating 22 . In this example , only one side of the work piece 18 is coated with the coating solution 16 . Alternatively, several sides of the work piece 18 may be coated .

[0063] Conventional coating techniques may be used for providing work piece 18 with coating 22 . Preferably, coating 22 is provided on work piece 18 by spray coating , drop coating or doctor blade coating .

[0064] Coating the work piece 18 with the coating solution 16 may comprise several subsequent coating steps . Thus , the coating 22 may be build up by several layers that are stacked upon one another . As a result of the comparatively high concentration of the metal compound for coating applications 12 of formula M (A)XO (2-x / 2) • y H2O in the coating solution 16 , layers with a comparatively high layer thickness can be obtained in each coating step . In consequence , the number of coating steps may be reduced compared with the use of less concentrated coating solutions .

[0065] Examples

[0066] Example 1 : Production of a metal compound for coating applications

[0067] 12 g of zirconium acetylacetonate ( Zr (Acac ) 4 ) were added as a starting material to a recirculated-air furnace and heated at a heating temperature of 125 ° C in a water-containing atmosphere for 6 h . Partial hydrolysis of zirconium acetylacetonate yielded 8 . 5 g of a metal compound for coating applications of formula Zr (Acac) • y H2O. The molecular weight of said metal compound for coating applications was approximately 345 g / mol.

[0068] Example 2 : Production of a coating solution

[0069] The metal compound for coating applications obtained in example 1 and 1.8 g of Y(NO3) -6 H2O were mixed with 100 mL of ethanol.

[0070] The resulting liquid composition was stirred at a heating temperature of 60 °C for 2 h, resulting in a clear and storage stable alcoholic coating solution.

[0071] Example 3: Production of a metal compound for coating applications

[0072] 12 g of zirconium acetylacetonate (Zr(Acac)4) were dissolved in 25 mL of diethylene glycol monobutyl ether under heating. The resulting solution was first heated in an airtightly closed crystallisation dish at a heating temperature of 130 °C for 20 min. This was followed by stirring the solution in the now opened crystallisation dish for another 40 min. The zirconium acetylacetonate was partially hydrolysed yielding a metal compound for coating applications of formula Zr (Acac)XO(2- x / 2) - y H2O. In this example, hydrolysis was effected by residual water contained in the solvent. Alternatively, additional water may be added. This may accelerate the reaction kinetics. Preferably, between 0.5 and 5 wt . -% of water, more preferably 2 wt . -% of water, based on the total mass of the solvent, is added to the reaction mixture or to the solvent prior to addition of the solid. The opened crystallisation dish was then transferred to a recirculated-air furnace and heated at a heating temperature of 110 °C for 90 min which led to the removal of the liquid components from the reaction mixture. Thus, 6.9 g of said metal compound for coating applications were obtained as a solid. The molecular weight of said metal compound for coating applications was approximately 280 g / mol. Example 4 : Production of a coating solution

[0073] The metal compound for coating applications obtained in example 3 and 1.8 g of Y(NO3) -6 H2O were mixed with 100 mL of ethanol. The resulting liquid composition was stirred at a heating temperature of 78 °C for 2 h, resulting in a clear and storage stable alcoholic coating solution.

Claims

Claims1. A method of producing metal compounds for coating applications (12) , said method comprising: a. providing a compound (10) of formula M(A)4as a starting material, wherein M represents a metal, and wherein A represents a beta-dicarbonylate, b. partially hydrolysing said compound (10) of formula M(A)4to obtain a metal compound for coating applications (12) of formula M (A)XO(2-x / 2) • y H2O, wherein x is at most 3.5 and at least 0.5.

2. The method according to claim 1, wherein no additional source of metal M is provided.

3. The method according to any of the preceding claims, wherein M represents a metal of the fourth group in the periodic table.

4. The method according to any of the preceding claims, wherein M represents zirconium.

5. The method according to any of the preceding claims, wherein A represents a beta-diketonate .

6. The method according to any of the preceding claims, wherein A represents acetylacetonate .

7. The method according any of the preceding claims, wherein M(A)4represents zirconium acetylacetonate.

8. The method according to any of the preceding claims, wherein x is at most 3.0, preferably at most 3.0 and at least 1.5, preferably at most 2.5, preferably at most 2.5 and at least 1.5, preferably at most 2.0, most preferably at most 2.0 and at least 1.5.

9. The method according to any of the preceding claims, wherein partially hydrolysing comprises heating said compound (10) of formula M(A)4 at a heating temperature of at least 60 °C, preferably of at least 80 °C, most preferably of at least 100 °C.

10. The method according to any of the preceding claims, wherein the compound (10) of formula M(A)4 is provided as a solid and partially hydrolysed as a solid in a watercontaining atmosphere.

11. The method according to claim 10, wherein said watercontaining atmosphere is saturated water vapour.

12. The method according to any of claims 10 and 11, wherein said water containing atmosphere is an oxygen-reduced atmosphere or an oxygen-free atmosphere.

13. The method according to any of claims 10 to 12, wherein the partial hydrolysis is performed in a recirculated-air furnace or in a rotary kiln.

14. The method according to any of claims 1 to 9, wherein the compound (10) of formula M(A)4 is provided and partially hydrolysed as a part of a liquid composition (14) comprising at least one solvent.

15. The method according to claim 14, wherein said liquid composition (14) is a solution of said compound (10) of formula M (A) 4 •16. The method according to any of claims 14 and 15, wherein a concentration of the compound (10) of formula M(A)4 in said liquid composition (14) is between 5 wt . -% and 65 wt . -% .

17. The method according to any of claims 14 to 16, wherein the at least one solvent has a boiling temperature between 80°C and 320°C, preferably a boiling temperature between 110°C and 250°C.

18. The method according to any of claims 14 to 17, wherein the at least one solvent is selected from the group consisting of: alcohols, preferably octanol or cyclohexanol, ethers, preferably diethylene glycol diethyl ether, 1- Methoxy-2-propanol or diethylene glycol monobutyl ether, and esters, preferably Methoxy-2 -propyl acetate or texanol.

19. The method according to any of claims 14 to 18, wherein the at least one solvent is completely or partially removed .

20. A metal compound for coating applications (12) of formula M (A)XO (2-X / 2) • y H2O, wherein x ist at most 3.5 and at least 0.5, produced by way of a method according to any of the preceding claims .

21. A coating solution (16) comprising a metal compound for coating applications (12) according to claim 20.

22. The coating solution (16) according to claim 21, wherein the concentration of said metal compound for coating applications (12) , calculated as metal oxide, in the coating solution (16) is between 5 wt . -% and 40 wt . -%, preferably between 10 wt . -% and 20 wt . -%, most preferably between 12 wt . -% and 17 wt . -%.

23. A method of coating a work piece (18) , said method comprising : a. providing a work piece (18) to be coated, b. coating the work piece (18) with a coating solution (16) according to any of claims 21 and 22.

24. The method according to claim 23, wherein an electrode or electrolyte layer (20) for an electrochemical cell, preferably a solid oxide fuel cell or a solid oxide electrolyser cell, is provided as the work piece (18) .

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