Method for producing iridium oxide

Abstract

The present invention provides a method for producing iridium oxide, the method including the steps of preparing iridium chloride, mixing the iridium chloride with a solvent and a pore control agent to produce a dispersion, mixing an ion exchange agent with the dispersion to perform ion exchange, removing the solvent from the dispersion to produce a powder, and heat treating the powder.

Description

[Technical Field]

[0001] This invention relates to a method for easily and commercially producing iridium oxide having a high pore volume and a high specific surface area as a catalyst for the oxygen evolution reaction that can be used in fuel cells and water electrolysis reactions. [Background technology]

[0002] Fuel cells and water electrolysis technologies have been attracting attention as a way to achieve carbon neutrality, but commercialization has been delayed due to difficulties in overcoming the issue of catalyst durability.

[0003] When a fuel cell and a water electrolysis system operate to generate electricity, the water produced as a by-product covers the surface of the catalyst. This causes a reversal voltage at the cathode due to a lack of hydrogen supply, and the carbon that supports the catalyst reacts with the water and becomes oxidized due to the high voltage, causing corrosion of the cathode catalyst.

[0004] This leads to a decrease in catalyst efficiency and problems with stability and durability.

[0005] One known method to solve the problem of reduced durability of electrodes in fuel cells and water electrolysis systems is to introduce an iridium (Ir)-based oxygen evolution reaction (OER) catalyst into the cathode.

[0006] This decomposes the by-product water before it corrodes the carbon that supports the electrode catalyst, stabilizing the electrode catalyst and improving its durability against reverse voltage phenomena.

[0007] The operating principle of a fuel cell can be expressed by the following reaction formula 1.

[0008] The operating principle of the oxygen generating reaction catalyst, which generates oxygen by decomposing the water (H2O) generated here, can be expressed by reaction formula 2.

[0009] [Reaction Scheme 1]

[0010] Anode: H 2 →2H + +2e -

[0011] Cathode: 1 / 2O2 + 2H + +2e - →H2O

[0012] Overall: H2+1 / 2O2→H2O+Heat

[0013] [Reaction Scheme 2]

[0014] 2H2O → 2H2 + O2

[0015] On the other hand, the iridium oxide (IrO2) catalyst used in the oxygen evolution reaction must have nano-sized particles and a high specific surface area to have high performance.

[0016] However, although it is possible to convert iridium metal into oxide by simple thermal oxidation at 1300°C or higher, sintering generates gigantic particles in the micron range, with a specific surface area of 30m 2 / g or less, it is difficult to exhibit catalytic performance.

[0017] Therefore, there is a need for a method that can easily produce iridium oxide having a high pore volume and a high specific surface area commercially. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] Korean Patent Publication No. 10-2019-0018836 [Patent Document 2] U.S. Patent No. 8,263,290 [Non-patent literature]

[0019] [Non-Patent Document 1] international journal of hydrogen energy 43(2018), 19460-19467 Summary of the Invention [Problem to be solved by the invention]

[0020] One embodiment of the present invention provides a method for producing iridium oxide, which can easily and commercially produce iridium oxide having a high pore volume and a high specific surface area from iridium metal. [Means for solving the problem]

[0021] According to one embodiment of the present invention, there is provided a method for producing iridium oxide, including the steps of preparing iridium chloride, mixing the iridium chloride with a solvent and a pore-controlling agent to prepare a dispersion, mixing an ion exchange agent with the dispersion to perform ion exchange, removing the solvent from the dispersion to prepare a powder, and heat-treating the powder.

[0022] The step of preparing iridium chloride may include a mixing step of preparing a mixture of iridium metal powder and an alkali metal compound, a calcination step of calcining the mixture to produce alkali-containing iridium oxide, a hydrochloric acid aqueous solution washing step of washing the alkali-containing iridium oxide with a hydrochloric acid aqueous solution to obtain iridium oxide, and a hydrochloric acid dissolution reaction step of dissolving the iridium oxide in hydrochloric acid under pressure and then reacting.

[0023] The alkali metal compound can include an alkali metal hydroxide, an alkali metal peroxide, or a mixture thereof.

[0024] The alkali metal hydroxide may include sodium hydroxide, potassium hydroxide, lithium hydroxide, or mixtures thereof.

[0025] The alkali metal peroxide may include sodium peroxide, potassium peroxide, lithium peroxide, or mixtures thereof.

[0026] The alkali-containing iridium oxide may include a compound represented by the following Chemical Formula 1:

[0027] [Chemical formula 1]

[0028] Na x Ir y O z

[0029] In Chemical Formula 1, x is an integer of 2 to 4, y is an integer of 1 to 3, and z is an integer of 3 to 8.

[0030] In the hydrochloric acid aqueous solution washing step, the concentration of the hydrochloric acid aqueous solution is 5% to 10%.

[0031] The hydrochloric acid dissolution reaction step is carried out under pressure of 5 to 10 pressures at 130 to 170°C for 2 to 6 hours.

[0032] In the step of preparing the dispersion, the solvent is an alcohol-based mixed solvent.

[0033] The alcohol-based mixed solvent may include ethanol and isopropanol.

[0034] The weight ratio of isopropanol to ethanol is 4:6 to 6:4.

[0035] In the step of preparing the dispersion, the solvent is mixed in an amount of 10 to 20 parts by weight per 1 part by weight of iridium chloride.

[0036] The pore control agent is a compound containing a benzene ring or a hydrocarbon compound having 6 to 10 carbon atoms.

[0037] The pore control agent can include 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, triethylbenzene, hexanol, xylene, toluene, butyl acetate, octanol, or mixtures thereof.

[0038] The molar ratio of iridium chloride to pore control agent is 1:1 to 1:3.

[0039] The ion exchange agent is an alkali metal nitrate.

[0040] The molar ratio of iridium chloride to the ion exchange agent is 1:5 to 1:10.

[0041] The ion exchange is carried out at 70°C to 90°C.

[0042] The powder preparation step is carried out by drying at 150 to 180°C for 12 hours or more.

[0043] The heat treatment step is carried out at 300°C to 600°C for 1 hour to 1.5 hours.

[0044] The iridium oxide produced had an average pore size of 2 nm to 5 nm and an average pore volume of 0.21 cm. 3 / g~0.25cm 3 / g, and the specific surface area is 100m 2 / g~420m 2 / g. [Effects of the Invention]

[0045] The method for producing iridium oxide according to one embodiment of the present invention makes it possible to easily and commercially produce iridium oxide having a high pore volume and a high specific surface area from iridium metal. [Brief explanation of the drawings]

[0046] [Figure 1] 1 is a process flow chart showing steps for manufacturing iridium oxide according to an embodiment of the present invention.

[0047] [Figure 2] FIG. 1 is a process flow chart showing the iridium chloride preparation step.

[0048] [Figure 3] 3 is a photograph showing the products at each stage of producing iridium oxide in Example 1.

[0049] [Figure 4] 1 is a graph showing the results of X-ray diffraction analysis (XRD) of the iridium oxides produced in Examples 1 to 4. DETAILED DESCRIPTION OF THE INVENTION

[0050] The advantages and features of the techniques described below, and the manner in which they are achieved, will become apparent from the following detailed examples taken in conjunction with the accompanying drawings. However, the embodied forms are not limited to the embodiments disclosed below. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the meaning commonly understood by one of ordinary skill in the art. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless specifically defined otherwise. Throughout the specification, when a part is said to "comprise" a certain element, this means that it may further include other elements, but not to the exclusion of other elements, unless otherwise specified.

[0051] Also, the singular includes the plural unless the phrase specifically states otherwise.

[0052] FIG. 1 is a process flow chart showing steps for producing iridium oxide according to one embodiment of the present invention.

[0053] The method for producing iridium oxide will now be described in detail with reference to FIG.

[0054] The method for producing iridium oxide includes an iridium chloride preparation step (S1), a dispersion preparation step (S2), an ion exchange step (S3), a powder preparation step (S4), and a heat treatment step (S5).

[0055] As an example, in the iridium chloride preparation step (S1), iridium chloride can be produced from iridium metal powder.

[0056] FIG. 2 is a process flow chart showing steps for producing iridium chloride.

[0057] With reference to FIG. 2, the method for producing iridium chloride will be described in detail.

[0058] The method for producing iridium chloride includes an alkali metal compound mixing step (S1-1), a calcination step (S1-2), a hydrochloric acid aqueous solution washing step (S1-4), and a hydrochloric acid dissolution reaction step (S1-5).

[0059] In the alkali metal compound mixing step (S1-1), a mixture of iridium metal powder and an alkali metal compound is mixed.

[0060] The alkali metal compound can include an alkali metal hydroxide, an alkali metal peroxide, or a mixture thereof, for example, a solid mixture of an alkali metal hydroxide and an alkali metal peroxide.

[0061] The alkali metal hydroxide can include sodium hydroxide, potassium hydroxide, lithium hydroxide, or mixtures thereof, for example, the alkali metal hydroxide is sodium hydroxide (NaOH).

[0062] The alkali metal peroxide can include sodium peroxide, potassium peroxide, lithium peroxide, or mixtures thereof, for example, the alkali metal peroxide is sodium peroxide (Na2O2).

[0063] As an example, the alkali metal hydroxide may include a mixture of sodium hydroxide and sodium peroxide.

[0064] The mixture may contain 0.5 to 1 part by weight, for example 0.6 to 0.7 parts by weight, of the alkali metal compound per 1 part by weight of the iridium metal powder. If the content of the alkali metal compound is less than 0.5 parts by weight per 1 part by weight of iridium metal powder, the amount of alkali component adsorbed on the surface of the iridium metal may be insufficient, resulting in uneven oxidation during the firing process. If the content exceeds 1 part by weight, the excess alkali metal compound may cover the surface of the iridium metal, preventing the oxidizing agent from coming into contact with the iridium metal.

[0065] Alternatively, the mixture may contain 1 to 3 parts by weight, for example 1.75 to 2.25 parts by weight, of the alkali metal peroxide in the alkali metal compound per part by weight of the iridium metal powder. If the content of alkali metal peroxide is less than 1 part by weight per part by weight of iridium metal powder, the iridium metal may remain even after calcination due to a lack of oxidizing agent, and if it exceeds 3 parts by weight, the iridium metal may be peroxidized to form iridium nanoparticles, which may make it difficult to pass through the filter paper in the subsequent filtration process to obtain the product.

[0066] In this case, when the alkali metal compound contains a mixture of an alkali metal hydroxide and an alkali metal peroxide, the weight ratio of the alkali metal hydroxide to the alkali metal peroxide is 1:2 to 1:4, for example, 1:2.5 to 1:3.5. If the weight ratio of alkali metal peroxide is less than 2, iridium metal may remain even after calcination due to a lack of oxidizing agent, and if it exceeds 4, iridium metal may be overoxidized to form iridium nanoparticles, making it difficult to pass through the filter paper in the subsequent filtration process to obtain the product.

[0067] In the calcination step (S1-2), the mixture is calcined to produce alkali-containing iridium oxide.

[0068] The firing is carried out at 750°C or higher. If the calcination temperature is less than 750°C, unreacted iridium metal may remain, but if the temperature is 750°C or higher, the iridium metal is completely converted into alkali-containing iridium oxide. For example, the firing is carried out by raising the temperature to 750° C. or higher over a period of 5 to 10 hours and maintaining the temperature at 750° C. or higher for 2 to 4 hours.

[0069] The alkali-containing iridium oxide produced by calcination may include a compound represented by the following Chemical Formula 1:

[0070] [Chemical formula 1]

[0071] Na x Ir y O z

[0072] In Chemical Formula 1, x is an integer of 2 to 4, y is an integer of 1 to 3, and z is an integer of 3 to 8.

[0073] For example, the alkali-containing iridium oxide represented by Chemical Formula 1 can include Na2IrO3, Na4IrO4, Na4Ir3O8, or a mixture thereof.

[0074] Optionally, the alkali-containing iridium oxide obtained in the calcination step may be washed with water before the hydrochloric acid aqueous solution washing step (S1-3).

[0075] The water may be deionized water, distilled water, or ultrapure water, and for example, deionized water may be used.

[0076] For example, the water washing step is carried out by washing the iridium oxide containing alkali with water at 60°C to 70°C for 2 to 4 hours. If the temperature in the water washing step is below 60°C, the washing will not be complete and residual alkaline ions may remain after washing. If the temperature exceeds 70°C, the washing water may evaporate and become concentrated. If the water washing step is done for less than two hours, the washing may not be complete, and if it is done for more than four hours, the working time may be unnecessarily long.

[0077] Optionally, a further filtration step can be included after the water washing step. For example, filtration can be performed hot using a paper filter on a water-washed solution.

[0078] Optionally, after the filtration step, a water washing step may be further performed, for example, washing with pre-prepared hot water at 60°C to 70°C may be performed after filtration.

[0079] The water washing step can remove some of the alkali metal ions from the alkali-containing iridium oxide, thereby obtaining some iridium oxide. However, even after the water washing step, about 400 ppm or more of alkali metal components may remain.

[0080] Therefore, in the hydrochloric acid aqueous solution washing step (S1-4), the iridium oxide containing alkali is washed with a hydrochloric acid aqueous solution to reduce the content of the remaining alkali metal component to 10 ppm or less, thereby producing iridium oxide.

[0081] The concentration of the aqueous hydrochloric acid solution may be 5% to 10%. If the concentration of the hydrochloric acid solution is less than 5%, the cleaning effect will not be good and alkali metals may still remain, while if it exceeds 10%, some iridium metal may also be dissolved in addition to alkali metals.

[0082] Optionally, a filtration step can be further included after the aqueous hydrochloric acid washing step. For example, filtration is performed by using a paper filter at a high temperature to remove the solution washed with an aqueous hydrochloric acid solution.

[0083] Alternatively, the iridium oxide that has been washed with the aqueous hydrochloric acid solution can be dried to produce a cake.

[0084] Drying is carried out at 100°C or higher for 12 to 24 hours. If the drying temperature is less than 100°C, not only will the drying time be longer, but residual moisture may remain even after drying.

[0085] The content of residual alkali metal components can be reduced through the step of washing with an aqueous hydrochloric acid solution. As a result, the iridium oxide cake has an alkali metal content of 10 ppm or less, for example, 0 ppm to 5 ppm.

[0086] If the content of alkali metal exceeds 10 ppm, the purity of the final product iridium chloride will decrease, which may have a negative effect on the catalytic reaction when producing a catalyst using this.

[0087] In the hydrochloric acid dissolution reaction step (S1-5), iridium oxide is dissolved in hydrochloric acid under pressure and then reacted to produce iridium chloride hydrate.

[0088] The content of hydrochloric acid relative to 1 part by weight of iridium oxide is 5 parts by weight to 15 parts by weight, for example, 8 parts by weight to 10 parts by weight. If the content of hydrochloric acid per 1 part by weight of iridium oxide is less than 5 parts by weight, the content of chloride ions necessary for the reaction may be insufficient, and 100% conversion of iridium oxide to iridium chloride may not be achieved. If the content exceeds 15 parts by weight, excessive energy costs may be required to evaporate the hydrochloric acid aqueous solution in the subsequent concentration process.

[0089] The hydrochloric acid dissolution reaction step may be carried out under pressure, for example in a pressurized vessel. The pressure during pressurization is 5 to 10 pressures, for example, 6 to 8 pressures. Since the pressure increases in proportion to the reaction temperature, there is no need to separately adjust the pressure within the following temperature range.

[0090] The hydrochloric acid dissolution reaction step is carried out under pressure at 130°C to 170°C for 2 to 6 hours, for example, at 150°C to 170°C for 2 to 4 hours. If the temperature in the hydrochloric acid dissolution reaction step is below 130°C, it may be difficult to convert iridium oxide to iridium chloride 100%. If it exceeds 170°C, the conversion to iridium chloride is easy, but the pressure vessel may corrode or deform, making commercial application difficult. If the time is less than 2 hours, the conversion reaction rate of iridium chloride may decrease, and if it exceeds 6 hours, excessive energy costs may be incurred.

[0091] Optionally, a filtration step may be further included after the hydrochloric acid dissolution reaction step.

[0092] Through the filtration step, the iridium chloride hydrate produced in the hydrochloric acid dissolution reaction step can be obtained. For example, filtration is carried out by using a paper filter to filter the solution that has undergone the hydrochloric acid dissolution reaction at a high temperature. At this time, a minimum amount of rinse solution, such as deionized water, is used to recover the remaining solution.

[0093] The iridium chloride hydrate produced is, for example, a compound represented by H2IrCl6·xH2O. The iridium chloride hydrate obtained in the hydrochloric acid dissolution reaction step is substantially completely dissolved, for example, 99.9% or more dissolved, and has an alkali metal content of 10 ppm or less.

[0094] This method for producing iridium chloride hydrate can increase production yield by inducing complete oxidation of iridium metal in the calcination step (S1-2), by using a single solvent of hydrochloric acid solution in the hydrochloric acid aqueous solution washing step (S1-4) to prevent the generation of nitrogen oxides, by using hydrochloric acid to remove alkali metal components used as an oxidant before the pressure reaction, the alkali metal content in the obtained iridium chloride is 10 ppm or less, and by the pressure reaction in the hydrochloric acid dissolution reaction step (S1-5), the solubility is 99.9% or more, and there is no unreacted iridium, so the purity of the product is very high.

[0095] Alternatively, the produced iridium chloride hydrate can be concentrated to produce iridium chloride (S1-6).

[0096] For example, the concentration can be performed by vacuum distillation.

[0097] The iridium chloride produced is, for example, a compound represented by IrCl4·xH2O.

[0098] In the dispersion preparation step (S2), the prepared iridium chloride is mixed with a solvent and a pore control agent to prepare a dispersion.

[0099] The solvent may be an alcoholic solvent such as ethanol, isopropanol, or a mixture thereof, for example, a mixed solvent of ethanol and isopropanol. When a mixed solvent of ethanol and isopropanol is used as the solvent, the particle size of the final product, iridium oxide (IrO2), can be made smaller than when using individual solvents. At this time, the weight ratio of isopropanol to ethanol is 4:6 to 6:4, and the molar ratio of isopropanol to ethanol is 1:1 to 1:1.5, for example, 1:1.2 to 1:1.4.

[0100] The solvent is mixed in an amount of 10 to 20 parts by weight per 1 part by weight of iridium chloride. If the content of the solvent is less than 10 parts by weight, the solubility of iridium chloride (IrCl4) may decrease, and if it exceeds 20 parts by weight, it may take a long time to remove the solvent thereafter.

[0101] The pore control agent increases the spacing between iridium atoms during the process of removing the solvent from the mixture of iridium chloride and solvent, thereby increasing the specific surface area and pore volume of the iridium oxide produced after the final heat treatment.

[0102] The pore control agent may be a compound containing a benzene ring or a hydrocarbon compound having 6 to 10 carbon atoms, such as 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, triethylbenzene, hexanol, xylene, toluene, butyl acetate, octanol, or a mixture thereof.

[0103] When the pore control agent is a hydrocarbon compound having 6 to 10 carbon atoms, if the carbon number exceeds 10, the viscosity of the dispersion increases and the pore control agent may not be completely removed during the heat treatment process, and if the carbon number of the pore control agent is less than 6, the effect of the pore control agent may not be clearly apparent.

[0104] The molar ratio of iridium chloride to pore control agent can be 1:1 to 1:3. If the molar ratio of the pore-controlling agent exceeds 3, the particle size of the iridium oxide may increase due to sudden heat generation during the subsequent heat treatment process, resulting in a decrease in the specific surface area. If the molar ratio is less than 1, the effect may not be clearly apparent.

[0105] The solvent and the pore control agent may be mixed with iridium chloride simultaneously or separately. For example, after iridium chloride and the solvent are mixed and stirred, the pore control agent may be added and stirred. At this time, the stirring time is not particularly limited, but if each stirring time is maintained for 1 hour or more, the iridium chloride can be completely dispersed.

[0106] In the ion exchange step (S3), an ion exchange agent is mixed with the dispersion liquid to carry out ion exchange.

[0107] The ion exchange agent exchanges chloride ions in iridium chloride with other ions in the solvent, widening the spacing between iridium atoms during the solvent removal process, thereby reducing the size of the iridium oxide produced after the final heat treatment and increasing the specific surface area and pore volume.

[0108] The ion exchange agent can be any material capable of exchanging chloride ions of iridium chloride, and can include, for example, easily cleaned alkali metal nitrates such as KNO3, NaNO3, or mixtures thereof.

[0109] The molar ratio of iridium chloride to ion exchanger can be 1:5 to 1:10, for example, 1:6 to 1:8. If the molar ratio of the ion exchange agent is more than 10, residual ion exchange agent remains during the ion exchange reaction, and even after the solvent is removed, the water-producing reaction continues, which may result in liquefaction before the subsequent heat treatment process. If the molar ratio of the ion exchange agent is less than 5, the chloride ion exchange may not be completed completely.

[0110] The ion exchange can be carried out at 70°C to 90°C. If the ion exchange temperature is below 70°C, the ion exchange efficiency may decrease, and if it exceeds 90°C, the solvent may evaporate first, causing powdering before the ion exchange reaction, which may also decrease the ion exchange rate.

[0111] The ion exchange is carried out at the above temperature with stirring for 5 hours or more. The stirring time is not particularly limited, but if the stirring is continued for 5 hours or more, the iridium chloride can be completely ion-exchanged.

[0112] In the powder production step (S4), the solvent is removed to produce a powder.

[0113] The solvent must be removed by drying at 200°C or higher in an atmospheric pressure atmosphere. However, at this time, the iridium nitrate compound may be reduced by the alcohol-based solvent and transformed back into iridium metal. Therefore, the solvent can be removed by vacuum drying at a relatively low temperature of 150°C to 180°C, for example, 160°C to 170°C, for 12 hours or more. When removing the solvent, if the drying temperature is less than 150°C, it may be difficult to completely remove the solvent, and if it exceeds 180°C, the solvent can be completely removed, but there is no clear advantage compared to increasing the temperature.

[0114] The drying time for removing the solvent is not particularly limited, but if the drying time is maintained for 12 hours or more, the solvent can be completely removed.

[0115] In the heat treatment step (S5), nitrate ions and hydrocarbon pore control agents present in the powder after solvent removal are removed.

[0116] The heat treatment temperature can be appropriately adjusted depending on the pore volume and specific surface area of the iridium oxide to be produced. For example, the heat treatment step is carried out at a temperature of 300° C. to 600° C., for example, 350° C. to 450° C., for 1 hour to 1.5 hours. If the heat treatment temperature is less than 300°C, it may be difficult to completely remove nitrate ions, and if it exceeds 600°C, aggregation of iridium oxide may occur, reducing the pore volume and the high specific surface area.

[0117] The temperature increase and maintenance time during the heat treatment may vary depending on the condition of the heat treatment furnace, but for example, the temperature may be increased at a rate of 2°C to 3°C per minute and maintained for 1 hour to 1.5 hours. If the temperature is maintained for a long time after heating, crystallization of iridium oxide may occur, increasing the pore size and reducing the specific surface area, while if the temperature is maintained for a short time, the conversion to iridium oxide may not be complete.

[0118] Optionally, after the heat treatment step, washing and filtering steps may be further carried out (S6).

[0119] The washing may be performed using deionized water, distilled water, or ultrapure water, for example, deionized water, and the solution washed with water may be filtered using a paper filter. The washing and filtering are repeated several times until the alkali ion content in the produced iridium oxide is reduced to 5 ppm or less.

[0120] Optionally, after washing and filtering, a drying step can be further carried out.

[0121] The drying temperature and drying time are not particularly limited, and as an example, drying is carried out until the moisture content of the iridium oxide after drying is less than 1% by weight, for example, at 100° C. or higher for 12 to 24 hours. If the drying temperature is less than 100°C, not only will the drying time be longer, but residual moisture may remain even after drying.

[0122] The iridium oxide produced is in the hydroxide form of iridium oxide (IrO2·xH2O).

[0123] Iridium oxide is manufactured using a pore control agent and an ion exchange agent, resulting in an average pore size of 2 nm to 5 nm and an average pore volume of 0.21 cm. 3 / g~0.25cm 3 / g, and the specific surface area is 100m 2 / g~420m 2 / g. [Example]

[0124] Specific examples of the invention will be presented below. However, the examples described below are merely for the purpose of specifically illustrating and explaining the invention, and should not be construed as limiting the scope of the invention.

[0125] [Production Example 1: Production of iridium chloride]

[0126] 13.5 g of NaOH powder and 40 g of Na2O2 powder are added to 20 g of Ir metal powder and then physically mixed.

[0127] The mixed powder is placed in a crucible and fired at 750°C, then allowed to cool slowly. The firing is carried out in stages, with the temperature raised to 750°C for 6 hours and maintained at that temperature for 2.5 hours. During firing, the lid of the crucible is left open.

[0128] The calcined powder is washed in 500 ml of deionized water and then filtered to remove potassium and sodium.

[0129] Next, it is washed with 200 g of HCl solution diluted to 5% in deionized water, and then transferred to a dryer and dried at 100° C. for 12 hours to obtain a powder.

[0130] The powder is placed in a pressure vessel and an additional 250 g of HCl is added and mixed.

[0131] The prepared pressure vessel is placed in a heat treatment furnace, and subjected to a high-temperature pressure reaction at 150°C for 4 hours, followed by cooling. When the pressure vessel is then opened, the powder is completely dissolved and present in solution.

[0132] The solution is distilled under reduced pressure at 80°C until it becomes a powder, and finally an iridium chloride precursor is produced.

[0133] [Production Example 2: Production of iridium oxide]

[0134] Example 1

[0135] FIG. 3 is a photograph showing the products at each stage of producing iridium oxide in Example 1. The process for producing iridium oxide in Example 1 will be described with reference to FIG.

[0136] 10 g of the iridium chloride powder produced in Production Example 1 and 75 g each of ethanol and isopropanol as solvents were added, followed by 7 g of trimethylbenzene as a pore control agent, which was placed in a water bath capable of stirring, and the mixture was then stirred for 1 hour to disperse.

[0137] After sufficient stirring, 20 g of potassium nitrate, an ion exchange agent, is added to the mixture, and the mixture is heated to 80° C. and stirred for 5 hours to carry out the ion exchange process.

[0138] After the ion exchange is completed, the mixture is transferred to a vacuum dryer, heated to 170°C, and dried for 12 hours to produce a powder from which the solvent has been completely removed.

[0139] The powder is then transferred to a heat treatment furnace and maintained at 350° C. for 1 hour to remove any remaining organic compounds.

[0140] Finally, the heat-treated powder is washed and filtered repeatedly using deionized water to remove residual potassium ions, and then dried in a dryer at 100°C for 24 hours.

[0141] X-ray diffraction analysis (XRD) of the produced iridium oxide confirmed that it had a composition of IrO2·xH2O with an amorphous crystalline structure, and BET analysis revealed a specific surface area of 412m 2 / g, pore volume 0.24 cm 3 / g and pore size of 2.5 nm.

[0142] (Examples 2 to 4 and Comparative Examples 1 to 4)

[0143] Iridium oxide was produced in the same manner as in Example 1, except that the reaction conditions were changed as shown in Table 1 below.

[0144] [Table 1]

[0145] For reference, Examples 2 to 4 are cases where the heat treatment temperature was changed, Comparative Example 1 is a case where no pore control agent was added, Comparative Examples 2 and 3 are cases where a single solvent was used, and Comparative Example 4 is a case where the iridium chloride precursor was directly heat treated without undergoing a process of forming pores therein.

[0146] [Experimental example: Characterization of iridium oxide]

[0147] The iridium oxides produced in the examples and comparative examples were subjected to X-ray diffraction analysis (XRD) and BET analysis, and the results are summarized in Table 2 and FIG.

[0148] [Table 2]

[0149] Referring to Table 2 and FIG. 4, the results of performing a crystallinity analysis (XRD analysis) on the products of Examples 1 to 4 show that as the heat treatment temperature increases, the iridium oxide gradually transforms into a crystalline substance, and as a result, the specific surface area and pore volume decrease, and the particle size increases due to the aggregation phenomenon of the iridium oxide.

[0150] Based on the above results, it can be seen that the intermediate product (powder before heat treatment), which has an enlarged pore volume due to the introduction of a pore control agent, loses its particle skeleton as the heat treatment temperature increases, ultimately transforming into a material with a low specific surface area and pore volume.

[0151] Moreover, Example 1 and Comparative Example 1 are results of comparing the pore distribution depending on whether or not a pore control agent is used. It can be seen that Comparative Example 1, which does not use a pore control agent, has a very low specific surface area and pore volume compared to Example 1. This indicates that the pore control agent provides a fine skeleton when forming an iridium oxide intermediate, thereby generating and maintaining a porous morphology.

[0152] Example 1 and Comparative Examples 2 and 3 show the results of comparing the method of using the solvent when mixing the solvent and iridium chloride powder. Unlike Example 1, when using only ethanol or isopropanol as a solvent, the pore control agent was not effective and was found to be unfavorable for pore formation, even though other manufacturing conditions such as ion exchange and heat treatment were the same. This is presumably due to the difference in solubility or binding strength between the solvent and the pore control agent.

[0153] Example 1 and Comparative Example 4 are the results of comparing products obtained by simple heat treatment without using a pore control agent or an ion exchange agent. Unlike Example 1, it can be seen that when no pore-forming agent is added, very low pore characteristics are exhibited despite the low heat treatment temperature.

[0154] Therefore, in order to produce iridium oxide with a high pore volume and a high specific surface area, a step of forming micropores must be carried out first, and an appropriate heat treatment temperature is required to maintain the pore shape.

[0155] Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements made by those skilled in the art using the basic concept of the present invention defined in the claims also fall within the scope of the present invention. [Industrial Applicability]

[0156] The present invention provides a method for easily and commercially producing iridium oxide having a large pore volume and a large specific surface area, which can be used as a catalyst for the oxygen generation reaction in fuel cells and water electrolysis reactions.

Claims

1. providing iridium chloride; mixing the iridium chloride with a solvent and a pore-controlling agent to prepare a dispersion; mixing an ion exchange agent with the dispersion to perform ion exchange; removing the solvent from the dispersion to produce a powder; and heat treating the powder Including, The pore control agent is a compound containing a benzene ring or a hydrocarbon compound having 6 to 10 carbon atoms.

2. The step of preparing iridium chloride comprises: a mixing step of preparing a mixture of iridium metal powder and an alkali metal compound; a calcination step of calcining the mixture to produce alkali-containing iridium oxide; a hydrochloric acid washing step of washing the alkali-containing iridium oxide with a hydrochloric acid aqueous solution to obtain iridium oxide; and a hydrochloric acid dissolution reaction step of dissolving the iridium oxide in hydrochloric acid under pressure and then reacting the iridium oxide; The method for producing iridium oxide according to claim 1 , comprising:

3. The method for producing iridium oxide according to claim 2 , wherein the alkali metal compound comprises an alkali metal hydroxide, an alkali metal peroxide, or a mixture thereof.

4. the alkali metal hydroxide comprises sodium hydroxide, potassium hydroxide, lithium hydroxide, or a mixture thereof; The method for producing iridium oxide according to claim 3 , wherein the alkali metal peroxide comprises sodium peroxide, potassium peroxide, lithium peroxide, or a mixture thereof.

5. The method for producing iridium oxide according to claim 2 , wherein the alkali-containing iridium oxide comprises a compound represented by the following Chemical Formula 1: [Chemical formula 1] Na ｘ Ir ｙ O ｚ (In the above Chemical Formula 1, x is an integer of 2 to 4, y is an integer of 1 to 3, and z is an integer of 3 to 8.)

6. 3. The method of claim 2, wherein the concentration of the hydrochloric acid solution in the hydrochloric acid washing step is 5% to 10%.

7. 3. The method for producing iridium oxide according to claim 2, wherein the hydrochloric acid dissolution reaction step is carried out under pressure of 5 to 10 pressures at 130 to 170° C. for 2 to 6 hours.

8. The method of claim 1 , wherein the solvent used in preparing the dispersion is an alcohol-based mixed solvent.

9. The method for producing iridium oxide according to claim 8 , wherein the alcohol-based mixed solvent contains ethanol and isopropanol.

10. 10. The method for producing iridium oxide according to claim 9, wherein the weight ratio of the isopropanol to the ethanol is 4:6 to 6:

4.

11. 2. The method of claim 1, wherein in the step of preparing the dispersion, the solvent is mixed in an amount of 10 to 20 parts by weight with respect to 1 part by weight of the iridium chloride.

12. 2. The method for producing iridium oxide according to claim 1, wherein the pore control agent comprises 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, triethylbenzene, hexanol, xylene, toluene, butyl acetate, octanol, or a mixture thereof.

13. 2. The method for producing iridium oxide according to claim 1, wherein the molar ratio of the iridium chloride to the pore control agent is 1:1 to 1:

3.

14. 2. The method for producing iridium oxide according to claim 1, wherein the ion exchange agent is an alkali metal nitrate.

15. 2. The method for producing iridium oxide according to claim 1, wherein the molar ratio of the iridium chloride to the ion exchange agent is 1:5 to 1:

10.

16. The method for producing iridium oxide according to claim 1, wherein the ion exchange is carried out at 70°C to 90°C.

17. 2. The method of claim 1, wherein the powder is dried at 150 to 180° C. for 12 hours or more.

18. 2. The method of claim 1, wherein the heat treatment is performed at 300 to 600° C. for 1 to 1.5 hours.

19. The iridium oxide produced is The average pore size is 2 nm to 5 nm, Average pore volume is 0.21 cm ３ / g to 0.25 cm ３ / g, Specific surface area is 100m ２ / g~420m ２ The method for producing iridium oxide according to claim 1, wherein the iridium content is 1 / g.

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