Novel porous metal oxide

Abstract

To provide a novel porous metal oxide that has high oxygen generation catalytic ability but is easy to manufacture.SOLUTION: A porous metal oxide is formed by firing an ion crystal composed of a chloride complex ion of a platinum group metal and a protonated primary amine compound. The porous metal oxide is formed with the firing temperature being 360°C to 600°C. The porous metal oxide is provided in which the chloride complex ion of the platinum group metal is [IrCl6]3- and / or [RuCl6]3-. The porous metal oxide is provided in which the primary amine compound is an aromatic primary amine compound and / or an aliphatic primary amine compound. According to the present invention, it is possible to provide a novel porous metal oxide having high oxygen generation catalytic ability but is easy to manufacture. In addition, the catalyst can be produced even from low-grade raw materials because the ion crystal, which is a catalyst precursor, is obtained by the same principle as that of the process of selective recovery of platinum group metals.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a novel porous metal oxide having high catalytic activity for oxygen generation, and more particularly to a novel porous metal oxide having high catalytic activity for oxygen generation, which is obtained by calcining ionic crystals. [Background technology]

[0002] Hydrogen production by water electrolysis, which can convert electricity generated from renewable energy sources into hydrogen, has attracted attention as a technology that can contribute to the realization of a decarbonized society. Water electrolysis consists of a hydrogen evolution reaction at the cathode and an oxygen evolution reaction at the anode. However, the high overvoltage of the anode oxygen evolution reaction is a particular challenge. Platinum group metals such as iridium (Ir) and ruthenium (Ru) and their oxides are considered promising oxygen evolution catalysts with low overvoltage and high activity. Further enhancements to the activity of these catalysts have been achieved by microparticulating them (Non-Patent Documents 1 and 2), making them porous (Non-Patent Document 3), and alloying them (Non-Patent Document 4). It is also known that highly active oxygen evolution catalysts can be produced using synthesis methods similar to those used for Adams catalysts or methods based on these methods (Non-Patent Documents 5 and 6, Patent Document 1). However, both production methods require complex multi-step procedures and require strict control of production conditions, such as pH adjustment and the amount of reducing agent.

[0003] Meanwhile, the present inventors have proposed a method for recovering platinum group metals as precipitates from hydrochloric acid solutions using primary amine compounds as recovery agents. Among platinum group metals, rhodium (Rh), which is known to be extremely difficult to recover actively, has also been reported to be recoverable as a precipitate using primary amine compounds. The Rh recovered as a precipitate is a chloride complex ion of Rh(III) ([RhCl6] 3- It has been found that these compounds are ionic crystals consisting of amine compounds and protonated amine compounds (Non-Patent Documents 7 to 9, Patent Documents 2 and 3). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-132465 [Patent Document 2] WO2017 / 170444 [Patent Document 3] JP 2019-163502 A [Non-patent literature]

[0005] [Non-Patent Document 1] ACS Catal.,2017,7,5983-5986. [Non-patent document 2] Int.J.Hydrog.Energy,2020,45,33491-33499. [Non-patent document 3] Nanoscale,2017,9,9291-9298. [Non-patent document 4] ACS Nano,2019,13,13225-13234. [Non-Patent Document 5] Int.J.Hydrog.Energy,2018,43,19460-19467. [Non-patent document 6] Catalysis,2019,9,318. [Non-Patent Document 7] ACS Omega,2019,4,1868-1873. [Non-patent document 8] ACS Omega,2019,4,14613-14620. [Non-Patent Document 9] Metals,2020,10,324. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a novel porous metal oxide that has high oxygen generation catalytic activity and can be produced by a simple method. [Means for solving the problem]

[0007] In order to achieve the above object, the present inventors have conducted various studies and found that a porous metal oxide having high oxygen evolution catalytic activity can be easily produced by calcining an ionic crystal composed of a platinum group metal chloride complex ion and a protonated primary amine compound, and have arrived at the present invention. 1. A porous metal oxide formed by firing an ionic crystal consisting of a platinum group metal chloride complex ion and a protonated primary amine compound. 2. The porous metal oxide of 1 above, wherein the firing temperature is 360°C to 600°C. 3. Chloride complex ions of platinum group metals are [IrCl6] 3- and / or [RuCl6] 3- 3. The porous metal oxide according to 1 or 2, 4. The porous metal oxide according to any one of 1 to 3 above, wherein the primary amine compound is an aromatic primary amine compound and / or an aliphatic primary amine compound. 5. The electrochemically active surface area measured in 0.5 mol / L sulfuric acid solution is 90 to 700 m 2 5. The porous metal oxide according to any one of 1 to 4 above, wherein the porous metal oxide has a viscosity of 1000 MPa or less. 6. An oxygen generating catalyst which is any one of the porous metal oxides described above in 1 to 5. 7. An oxygen generating catalyst precursor, which is an ionic crystal consisting of a platinum group metal chloride complex ion and a protonated primary amine compound. 8.(1) A step of mixing a primary amine compound with a hydrochloric acid solution containing a platinum group metal; (2) A step of calcining the resulting precipitate A method for producing porous metal oxide, comprising: [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a novel porous metal oxide that has high oxygen generation catalytic activity and can be produced by a simple method. [Brief explanation of the drawings]

[0009] [Figure 1] The structure of an ionic crystal consisting of an iridium chloride complex ion ([IrCl6]3-) and protonated p-phenylenediamine (PPDA) is shown. This is the result of X-ray structural analysis. [Figure 2] The principle of producing porous iridium oxide by calcination is shown schematically. [Figure 3] An example of the flow of manufacturing porous iridium oxide is shown below. [Figure 4] The current density-potential curve when examining the oxygen evolution overvoltage is shown below. The oxygen evolution overvoltage is the value obtained by subtracting the theoretical potential for oxygen evolution, 1.23 V, from the voltage (horizontal axis) when the current density (vertical axis) reaches 10 mA / cm2. [Figure 5] The durability of electrodes made from each material is shown ((A) porous iridium oxide, (B) porous ruthenium oxide). If the change in potential over time is constant, the electrode is highly durable. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. 1. Chloride complex ions of platinum group metals There are six platinum group metals: ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt). The chloride complex ion of a platinum group metal used in the present invention may be any of these chloride complex ions, but chloride complex ions of iridium (III), ruthenium (III), or both are more preferred, and chloride complex ions of iridium (III) are particularly preferred. In terms of catalytic activity as a metal oxide, iridium oxide and ruthenium oxide are superior to other metal oxides. Furthermore, when comparing iridium oxide and ruthenium oxide, ruthenium oxide has a superior catalytic activity, but iridium oxide is significantly superior in terms of durability. From the viewpoint of the balance between catalytic activity and durability, it is particularly preferable to use an iridium (III) chloride complex ion.

[0011] 2. Primary amine compounds The primary amine compound used in the present invention is not particularly limited, but is preferably an aromatic primary amine compound and / or an aliphatic primary amine. The aromatic ring of the aromatic primary amine compound may be a heterocycle such as a nitrogen-containing heterocycle. The aliphatic primary amine is preferably a linear alkyl monoamine, and more preferably a linear alkyl monoamine having 6 to 18 carbon atoms. A linear alkyl monoamine having 6 to 18 carbon atoms allows selective recovery of platinum group metals (see Patent Document 2), making it possible to produce a catalyst from low-grade raw materials and facilitating the reuse of the catalyst. Also, different primary amine compounds may be used in combination. Examples of the aromatic primary amine compound include the following. (I) Aromatic primary monoamine compounds such as aniline, 4-butylaniline, and 4-phenoxyaniline (II) Aromatic primary diamine compounds such as p-phenylenediamine (PPDA), m-phenylenediamine, 2,6-diaminopyridine, and 4,4'-oxydianiline, (III) Aromatic primary triamine compounds such as 1,3,5-benzenetriamine, melamine, and 2,4,6-triaminopyrimidine; (IV) Benzylamine compounds with two or more amines bonded, such as m-xylylenediamine (MXDA) and p-xylylenediamine Examples of the aliphatic primary amine compound include the following. (V) Linear alkyl monoamines with 6 to 18 carbon atoms, such as n-nonylamine In protonated primary amine compounds, the amino group is often protonated, but if the heterocyclic ring contains a nitrogen atom, the nitrogen atom may also be protonated. For example, in the case of aniline, the amino group is protonated, and in the case of melamine, one or two of the nitrogen atoms in the heterocyclic ring are protonated.

[0012] 3. Ionic crystals The ionic crystal formed in the present invention can be used as a catalyst precursor, which becomes a porous metal oxide for an oxygen generating catalyst by calcination. The ionic crystals consist of platinum group metal chloride complex ions and protonated primary amine compounds, but since these two are the main components, they may also contain other mixtures as long as they do not affect the formation of the ionic crystals. Ionic crystals are formed by ionic bonding between negatively charged platinum group metal chloride complex ions and positively charged protonated primary amine compounds. For example, the iridium chloride complex ion ([IrCl6] 3- ) and protonated 4-butylaniline ionic crystals are [IrCl6] 3- The basic structure is an ion pair consisting of six protonated 4-butylanilines and three chloride anions surrounding the ion pair. Also, for example, [IrCl6] 3- The ionic crystals of [IrCl6] and protonated p-phenylenediamine (PPDA) 3- and protonated PPDA (PPDA-2H + ), chloride anion, water is "[IrCl6] 3- :PPDA-2H + :Cl - The crystals are constructed in a ratio of 1:2:1:2 (Figure 1). There is no particular limit to the particle size of the ionic crystals, and they may be a mixture of various particle sizes, but for ease of handling, crystals in the range of 1 μm to 5 mm are more preferable. The particle size is calculated from the pore size of the filter through which they pass. Furthermore, the ionic crystal may be either a single crystal or a polycrystal, and there is no limit to the size of the crystallite (or crystal if it is a single crystal). Larger crystals are not necessarily preferable.

[0013] 4.Porous metal oxide Porous metal oxides can be produced by calcining ionic crystals. For example, the chloride complex ion of iridium ([IrCl6] 3-When ionic crystals consisting of iridium oxide (II) and p-phenylenediamine (PPDA) are fired, pores are formed, enabling the production of porous iridium oxide (Figure 2, SEM image at the bottom right of Figure 3). Porous ruthenium oxide can be produced from ionic crystals containing ruthenium(III). Furthermore, porous alloy metal oxides (iridium oxide / ruthenium oxide) can be obtained from ionic crystals containing both iridium(III) and ruthenium(III). It is also possible to combine metals to form alloys. The main components of iridium oxide and ruthenium oxide in the present invention are IrO2 and RuO2, but they may also contain oxides with different oxidation numbers, such as Ir2O3 and Ru2O3. In the present invention, calcination removes the primary amine compound that forms ionic crystals, forming voids (pores), resulting in a porous metal oxide. Since the electrochemically active surface area (ECSA), which is the area of the portion that actually functions as a catalyst, is large as described below, it can be said to have a dense porous structure. There is no method that can unequivocally define this porous structure, and it is impossible and impractical to identify porous metal oxides from their structure. Although the BET specific surface area is a tentative index of porosity, it is of course not possible to unequivocally define the porous structure using the BET specific surface area.

[0014] 5. Production of porous metal oxide using ionic crystals Ionic crystals can be prepared by methods already reported (Non-Patent Documents 7-9, Patent Documents 2-4). Ir(III) and Ru(III) also form chloride complex ions ([IrCl6]) in hydrochloric acid solution, similar to Rh(III). 3- and [RuCl6] 3- ), it is thought to form ionic crystals with primary amine compounds, similar to Rh, and can be prepared by methods already reported. Specifically, for example, a platinum group metal (e.g., Ir(III))-containing ionic crystals can be produced by mixing a primary amine compound with a platinum group metal dissolved in hydrochloric acid, and then leaving the mixture to stand, shaking, or stirring. The resulting precipitate can be collected to obtain the ionic crystals. "3. Ionic Crystals" As described above, it is not necessary to grow crystals, so it is sufficient to mix the ingredients to precipitate ionic crystals, and the operation may be any method such as standing, shaking, stirring, or a combination of these. In this way, the ionic crystals of the present invention can be easily produced without complex conditions. Next, the recovered ionic crystals are fired. The firing temperature is more preferably 360 to 600°C, even more preferably 380 to 480°C, and particularly preferably 380 to 400°C. The firing is preferably carried out in an air atmosphere by heating to the target temperature at a temperature increase rate of more preferably 10 to 50°C / min, even more preferably 15 to 25°C / min, and then maintaining the target temperature for more preferably 10 to 60 minutes, even more preferably 10 to 20 minutes. As described above, according to the method for producing porous metal oxide of the present invention, porous metal oxide can be produced simply by using ionic crystals as a catalyst precursor and calcining it. Furthermore, while conventional methods could only use high-purity starting materials (such as chloroiridic acid or iridium complexes), the present invention obtains ionic crystals using the same principle as the platinum group metal selective recovery method (Non-Patent Documents 7-9, Patent Documents 2 and 3). Therefore, even if the raw iridium or ruthenium contains other metal elements, ionic crystals containing only iridium or ruthenium can be selectively obtained, making it possible to produce catalysts from low-grade raw materials. Furthermore, used catalysts can be regenerated by leaching them with hydrochloric acid. By using primary amine compounds such as 4-butylaniline, p-phenylenediamine, melamine, and 2,6-diaminopyridine, ionic crystals containing only iridium or ruthenium can be obtained, even if other platinum group metal elements are mixed in.

[0015] 6. Applications of porous metal oxide The porous metal oxide of the present invention has catalytic activity for oxygen generation and can be used, for example, together with a conductive support such as carbon fiber as an anode in a water electrolysis device.

[0016] 7. Catalytic activity of porous metal oxides When an oxygen generating catalyst is cast onto a glassy carbon electrode and further coated with Nafion (trade name) to prepare an electrode, the catalytic activity in a 0.5 M aqueous sulfuric acid solution is preferably as follows: The catalytic performance was evaluated by, for example, using the electrode prepared above as the working electrode and performing cyclic voltammetry at a potential range of 1.2 to 1.4 V, varying the sweep rate from 5 to 80 mV / s, and determining the specific capacitance of iridium oxide and ruthenium oxide as 35 μF / cm from the increase in the electric double layer relative to the sweep rate. 2 When the electrochemically active surface area (ECSA) is calculated as 2 / g is more preferable, and 200 to 700m 2 / g is even better, 500-700m 2 / g is particularly preferred. Furthermore, linear sweep voltammetry was performed from 1.1 V to 1.9 V at a sweep rate of 10 mV / s and a current density of 10 mA / cm. 2 When the difference between the potential reached at this point and 1.23 V, which is the theoretical potential for oxygen generation, is calculated as the oxygen generating overvoltage, the oxygen generating overvoltage is more preferably 240 to 350 mV, even more preferably 240 to 320 mV, and particularly preferably 240 to 285 mV. The working electrode was rotated at 1600 rpm and the current density was 10 mA / cm 2 When the potential is fixed at 1000 V and the change in potential over time is measured to evaluate the durability, it is more preferable that the durability is 12 hours or more for iridium oxide and 5 hours or more for ruthenium oxide. Surprisingly, despite the extremely simple manufacturing method of the present invention, the porous iridium oxide produced by this method exhibits excellent oxygen evolution catalytic activity with an oxygen evolution overpotential of 0.34 V or less (Table 1). Furthermore, "Ir(III)-PPDA 380°C" has an oxygen evolution overpotential of 270 mV (Table 1), demonstrating nearly the highest oxygen evolution catalytic activity of any iridium oxide catalyst. moreover 、 The durability is also surprisingly longer than that of commercially available products, but it is particularly surprising that the durability of ruthenium oxide, which has low stability, has improved to more than 5 hours. [Example]

[0017] Example 1: Preparation of porous iridium oxide 1. Preparation of porous iridium oxide p-Phenylenediamine (PPDA) hydrochloride was added to a 5M hydrochloric acid solution containing iridium (Ir) so that the ratio of Ir to PPDA was 1:8, and the solution was allowed to stand for one week. The resulting precipitate was collected by filtration. This precipitate (an ionic crystal of Ir(III) and p-phenylenediamine (PPDA) ionically bonded) was heated to 380°C at a rate of 20°C per minute in an air atmosphere and calcined for 15 minutes to obtain porous iridium oxide (Figure 3).

[0018] Example 2: Production of porous iridium oxide by varying the heating temperature during firing Porous iridium oxide was obtained in the same manner as in Example 1, except that the heating temperature was changed within the range of 360 to 580°C (see the firing temperature for "Ir(III)-PPDA" in Table 1).

[0019] Example 3 Preparation of porous iridium oxide using different aromatic primary amine compounds Porous iridium oxide was obtained in the same manner as in Example 1, except that the hydrochlorides of 4-butylaniline (BuA), melamine, or m-xylylenediamine (MXDA) were used (Table 1, "Ir(III)-BuA" to "Ir(III)-MXDA").

[0020] Example 4 Preparation of porous iridium oxide using an aliphatic primary amine compound Porous iridium oxide was obtained in the same manner as in Example 1 except that n-nonylamine (NoA) hydrochloride was used (Table 1 "Ir(III)-NoA").

[0021] Example 5 Preparation of porous ruthenium oxide Porous ruthenium oxide was obtained in the same manner as in Example 1, except that a 5M hydrochloric acid solution containing ruthenium (Ru) was used (Table 1 "Porous ruthenium oxide").

[0022] Example 6 Preparation of Porous Iridium Oxide / Ruthenium Oxide p-Phenylenediamine (PPDA) hydrochloride was added to a 5M hydrochloric acid solution containing iridium Ir and ruthenium Ru so that the ratio of Ir:Ru in the ionic crystal was 1:1. Except for this, porous iridium oxide / ruthenium oxide was obtained in the same manner as in Example 1 (Table 1 "Porous iridium oxide / ruthenium oxide").

[0023] Example 7 Catalyst Evaluation 1. Preparation of the Working Electrode The porous iridium oxide prepared in the above example was dispersed in a solvent made by mixing water and 2-propanol in a volume ratio of 1:2, and an electrode area of 0.196 cm was formed. 2 By casting on a glassy carbon electrode, 0.128 mg / cm 2 After drying, 5 μL of a 0.25 wt% Nafion ethanol solution was cast onto the electrode, coating it with Nafion. Glassy carbon electrodes with porous ruthenium oxide or porous iridium oxide / ruthenium oxide were also fabricated using a similar method. For comparison, electrodes were also prepared in the same manner using commercially available iridium oxide (Aldrich, product number 206237) and ruthenium oxide (Aldrich, product number 238058). 2. Electrochemical Measurements Electrochemical measurements were performed using the glassy carbon electrode prepared as described above as the working electrode, a platinum wire as the counter electrode, and a silver-silver chloride electrode as the reference electrode, with a 0.5 mol / L aqueous sulfuric acid solution (saturated with nitrogen gas) as the electrolyte. All potentials are shown converted to the reversible hydrogen electrode (RHE) standard. Commercially available iridium oxide and ruthenium oxide were used as controls. 2-1 Evaluation of electrochemically active surface area Cyclic voltammetry was performed at a potential range of 1.2 to 1.4 V, with the sweep rate varying from 5 to 80 mV / s. The specific capacitance of iridium oxide and ruthenium oxide was calculated to be 35 μF / cm from the increase in the electric double layer relative to the sweep rate. 2 The electrochemically active surface area (ECSA) was calculated as 2-2 Evaluation of oxygen evolution overpotential Linear sweep voltammetry was performed at a potential of 1.1 V to 1.9 V at a sweep rate of 10 mV / s and a current density of 10 mA / cm. 2 The difference between the potential reached at this point and the theoretical potential for oxygen evolution, 1.23 V, was taken as the oxygen evolution overpotential. 2-3 Durability evaluation The working electrode was rotated at 1600 rpm and the current density was 10 mA / cm 2 The potential was fixed at 100 kJ / s, and the change in potential over time was measured. 2-4.Measurement results Porous iridium oxide produced from ionic crystals consisting of Ir(III) and p-phenylenediamine (PPDA) (Table 1 "Porous iridium oxide Ir(III)-PPDA") had an ECSA of 536 m when the calcination temperature was 380°C. 2 / g, and the ECSA decreased with lower and higher calcination temperatures. Regardless of the calcination temperature, the porous iridium oxide prepared from ionic crystals consisting of Ir(III) and PPDA (Table 1, "Porous iridium oxide from Ir(III)-PPDA") exhibited a larger ECSA than commercially available iridium oxide ("Iridium oxide (commercially available)"). Porous iridium oxide produced from ionic crystals consisting of Ir(III) and PPDA (Table 1, "Porous iridium oxide Ir(III)-PPDA") showed the lowest oxygen evolving overvoltage of 270 mV when the calcination temperature was 380°C. The oxygen evolving overvoltage correlated with the magnitude of the ECSA, and the larger the ECSA, the lower the overvoltage tended to be. Regardless of the calcination temperature, porous iridium oxide produced from ionic crystals consisting of Ir(III) and PPDA (Table 1, "Porous iridium oxide Ir(III)-PPDA") showed a lower overvoltage (oxygen evolving overvoltage can be determined from Figure 4) than commercially available iridium oxide (Table 1, "Iridium oxide (commercial product)"), demonstrating its superiority as an oxygen evolving catalyst. Porous iridium oxides prepared from ionic crystals consisting of various amine compounds and Ir(III) (Table 1 "Ir(III)-BuA," "Ir(III)-Meramine," "Ir(III)-MXDA," and "Ir(III)-NoA") all exhibited larger ECSA and lower oxygen evolution overpotential than commercially available iridium oxide (Table 1 "Iridium oxide (commercial product)"). This indicates that performance as an oxygen evolution catalyst is not significantly affected by the type of amine compound. Porous ruthenium oxide prepared from ionic crystals consisting of Ru(III) and PPDA (Table 1, "Porous ruthenium oxide from Ru(III)-PPDA") exhibited a lower oxygen evolution overvoltage than porous iridium oxide prepared in the same way (Table 1, "Porous iridium oxide from Ir(III)-PPDA, 380°C") . Ru is known to exhibit higher oxygen evolution catalytic activity than Ir, and this result reflects this. Furthermore, porous ruthenium oxide exhibited a larger ECSA and lower oxygen evolution overvoltage than commercially available ruthenium oxide (Table 1, Ruthenium oxide (commercial product)), indicating that, like iridium oxide, the oxygen evolution catalytic activity was improved by increasing the porosity of the ionic crystals through calcination. The porous oxide (iridium oxide / ruthenium oxide) of an alloy containing Ir and Ru in a molar ratio of 1:1 (Table 1, "Porous iridium oxide / ruthenium oxide in Ir(III) / Ru(III)-PPDA") exhibited an oxygen evolution overpotential intermediate between that of porous iridium oxide (Table 1, "Porous iridium oxide in Ir(III)-PPDA, 380°C") and porous ruthenium oxide. It was shown that the oxygen evolution catalytic activity can be changed by controlling the molar ratio of Ir and Ru. The durability test results showed that the potential of commercially available iridium oxide rose significantly in about 1.5 hours, but the potential of porous iridium oxide did not change significantly even after a long measurement period of 12 hours (Figure 5(A)). Furthermore, the potential of the commercially available ruthenium oxide rose significantly immediately, but the potential of porous ruthenium oxide did not change significantly over a long measurement period of 5 hours (Figure 5(B)). This indicates that increasing porosity improves not only the oxygen evolution overpotential but also the durability of the catalyst.

[0024] [Table 1] [Industrial Applicability]

[0025] According to the present invention, it is possible to produce an oxygen generating catalyst with high catalytic activity by a simple method. This catalyst can be used as an electrode for water electrolysis, and is therefore useful in industries involved in the process of converting electricity produced from natural energy into hydrogen through water electrolysis and storing it, particularly in industries related to water electrolysis devices.

Claims

1. A porous metal oxide is formed by firing an ionic crystal consisting of a platinum group metal chloride complex ion and a protonated primary amine compound.

2. 2. The porous metal oxide according to claim 1, wherein the firing temperature is 360 to 600°C.

3. The chloride complex ions of platinum group metals are [IrCl ６ ] ３－ and / or [RuCl ６ ] ３－ 3. The porous metal oxide of claim 1 or 2, wherein:

4. 4. The porous metal oxide according to claim 1, wherein the primary amine compound is an aromatic primary amine compound and / or an aliphatic primary amine compound.

5. Electrochemically active surface area of 90 to 700 m when measured in 0.5 mol / L sulfuric acid solution ２ The porous metal oxide according to any one of claims 1 to 4, wherein the porous metal oxide has a surface area of 1 / g.

6. An oxygen generating catalyst, which is the porous metal oxide of any one of claims 1 to 5.

7. An oxygen generating catalyst precursor, which is an ionic crystal consisting of a platinum group metal chloride complex ion and a protonated primary amine compound.

8. (1) mixing a primary amine compound with a hydrochloric acid solution containing a platinum group metal; (2) A step of calcining the resulting precipitate A method for producing porous metal oxide, comprising:

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