Preparation method and application of iridium oxide-manganese dioxide catalyst

Abstract

The invention relates to a preparation method of an iridium oxide-manganese dioxide catalyst, which comprises the following steps: S1, fully dissolving a manganese source and an ammonium salt in deionized water, transferring the obtained solution into an autoclave for heating reaction, and washing and drying to obtain a carrier MnO2; s2, dispersing the carrier MnO2 in an alkaline solution with a pH value of 10-14, adding an iridium source, and dissolving the iridium source to obtain a dispersion liquid; and S3, carrying out heating reaction on the dispersion liquid in a high-pressure kettle, washing and drying to obtain the iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst. Meanwhile, the invention also discloses application of the catalyst. The stability is not lost while the intrinsic catalytic activity and the metal utilization rate are improved, and the obtained catalyst can be used as an oxygen evolution reaction catalyst to be applied to an acidic electrolyzed water oxygen evolution reaction.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogen production by electrolysis of water, and in particular to a preparation method and application of an iridium oxide-manganese dioxide catalyst. Background Art

[0002] PEM electrolysis has the advantages of high operating current density, high hydrogen purity, environmental friendliness and no pollution, which is in line with the development trend of new energy. The development of highly active, cost-effective and highly stable oxygen evolution reaction (OER) catalysts in acidic media is crucial for the practical application of PEM water electrolysis. At present, the electrocatalysts suitable for PEM electrolyzers that have been screened through theoretical calculations and experiments are mainly precious metals such as Ir and Ru and their oxides. Among them, Ru-based materials are prone to peroxidation, resulting in soluble Ru x>4 The production of species (such as RuO4 derivatives) has seriously hindered the commercial application of Ru-based materials in PEM devices. Therefore, Ir-based and its oxides are still considered as commercial anode catalysts for proton exchange membrane water electrolysis. However, due to the scarcity of Ir-based metals and their oxides, the high cost has largely limited the large-scale application of PEM water electrolysis. On the basis of low dosage, the development of highly active and stable Ir-based catalysts is one of the main ways to achieve the commercial application of PEM water electrolysis.

[0003] By screening suitable Ir-based catalyst carriers, combining the catalyst with the carrier material can improve its stability in corrosive acidic media. The performance of the catalyst-carrier system depends largely on the properties of the carrier material, such as stability, conductivity, and interaction with the catalyst. An ideal support material is conducive to uniformly dispersing and strongly anchoring the catalyst, while promoting faster electron transfer, thereby adjusting the electronic structure and chemical properties of the active catalytic metal to achieve higher catalytic efficiency. At present, based on the research on carriers, the research goals of low precious metal loading, high activity and high stability have been preliminarily achieved in solution electrochemistry. However, the relevant research on the application of such catalytic materials in proton exchange membrane water electrolysis electrolyzers is still relatively limited. This is because the chemical environment of solution electrochemistry is different from the environment under actual water electrolysis conditions. Therefore, how to better apply such materials to actual electrolyzer hydrogen production devices is one of the urgent problems to be solved for supported catalysts. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing an iridium oxide-manganese dioxide catalyst which can improve the intrinsic catalytic activity and metal utilization rate without losing stability.

[0005] Another technical problem to be solved by the present invention is to provide application of the iridium oxide-manganese dioxide catalyst.

[0006] To solve the above problems, a method for preparing an iridium oxide-manganese dioxide catalyst according to the present invention comprises the following steps: S1. Fully dissolve a manganese source and an ammonium salt in deionized water, transfer the resulting solution to an autoclave for heating and reaction, and wash and dry to obtain a carrier MnO2; the mass ratio of the ammonium salt to the manganese source is 1:1 to 5:1; S2, dispersing the carrier MnO2 in an alkaline solution with a pH of 10-14, adding an iridium source and dissolving it to obtain a dispersion; the mass ratio of the iridium source to the carrier MnO2 is 1:1-1:5; the mass ratio of the carrier MnO2 to the alkaline solution is 1:20-1:50; the iridium source is Na2IrCl6·6H2O; S3, heating the dispersion in an autoclave for reaction, washing and drying to obtain an iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst.

[0007] In step S1, the manganese source is at least one of KMnO4 and MnSO4·H2O; and the ammonium salt is (NH4)2S2O8.

[0008] The heating reaction conditions in step S1 and step S3 are both 90-180° C. and 1-12 h.

[0009] In the step S1, the carrier MnO2 is one of α-MnO2, β-MnO2, γ-MnO2 or δ-MnO2.

[0010] In the step S3, the particle size of the iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst is 1-2 nm; the mass percentage of Ir is 1 wt%-20 wt%.

[0011] An iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst prepared by the method described above.

[0012] The application of the iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst as described above is characterized in that the iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst is used as an oxygen evolution catalyst in the oxygen evolution reaction of acidic water electrolysis.

[0013] A membrane electrode is prepared using the iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst as described above.

[0014] The application of a membrane electrode as described above is characterized in that the membrane electrode is applied to a proton exchange membrane water electrolysis catalytic reaction.

[0015] Compared with the prior art, the present invention has the following advantages: 1. The present invention loads IrO2 on MnO2, successfully regulates the electronic structure of IrO2, and obtains a uniformly dispersed IrO2 cluster nanoparticle catalyst loaded on MnO2, which is used as an oxygen evolution reaction catalyst in the acidic electrolysis of water oxygen evolution reaction, while reducing the quantitative use of IrO2, while enhancing its stability and improving its intrinsic reaction activity.

[0016] 2. The IrO2 / MnO2 catalyst prepared by the present invention maintains high activity and high stability on the membrane electrode, while the IrO2 loading is low.

[0017] 3. The present invention synthesizes different crystal forms of MnO2 by hydrothermal method and uses it as a substrate to construct IrO2 / MnO2. Among them, β-MnO2 as a carrier to load IrO2 shows the best activity and stability. IrO2 / β-MnO2 has the best activity and stability at 10 mA cm -2 The low overpotential of 310 mV can be achieved at a current density of 1.905 V @ 1 A cm in a water electrolysis hydrogen production electrolyzer. -2 In comparison, IrO2 / β-MnO2 can exhibit a battery voltage of 1.820 V at this current density and can operate stably for 200 h. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0019] Figure 1 This is the preparation process flow of the IrO2 / MnO2 catalyst of the present invention.

[0020] Figure 2 HRTEM images of the IrO2 / MnO2 catalysts prepared in Example 1 (a) and Example 2 (b) of the present invention. The box diagram in the figure is a particle size distribution diagram.

[0021] Figure 3 The XPS spectra of the IrO2 / MnO2 catalysts prepared in Examples 1 and 2 of the present invention are shown in Figure 1. In which: a is the O 2p spectrum, and b is the Ir 4f spectrum.

[0022] Figure 4 2 are XRD patterns of the IrO2 / MnO2 catalysts prepared in Example 1 (a) and Example 2 (b) of the present invention.

[0023] Figure 5 The linear sweep voltammetry (LSV) curves of the test electrodes made of the IrO2 / MnO2 catalysts prepared in Example 1 and Example 2 in Application Examples 1 and 2 of the present invention are shown respectively.

[0024] Figure 6 This is a polarization curve diagram when the membrane electrode in Application Example 3 of the present invention is applied to the proton exchange membrane water electrolysis catalytic reaction.

[0025] Figure 7 This is a stability test diagram of the membrane electrode in Application Example 3 of the present invention when it is used in the proton exchange membrane water electrolysis catalytic reaction. DETAILED DESCRIPTION

[0026] The present invention synthesizes MnO2 of different crystal forms by a hydrothermal method, and uses it as a substrate to construct IrO2 / MnO2, and finally obtains a uniformly dispersed IrO2 / MnO2 catalyst with a particle size of 1 nm to 2 nm (such as 1.0 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2.0 nm, etc.). The specific process is as follows: like Figure 1 As shown, a method for preparing an iridium oxide-manganese dioxide catalyst comprises the following steps: S1. Fully dissolve the manganese source and ammonium salt in deionized water, transfer the resulting solution to an autoclave and heat at 90-180°C for 1-12 h, wash and dry to constant weight to obtain carrier MnO2. The obtained carrier MnO2 is one of α-MnO2, β-MnO2, γ-MnO2 or δ-MnO2.

[0027] After the manganese source and ammonium salt are fully dissolved, the solution is transferred to an autoclave for heating reaction in order to generate MnO2. A black precipitate appears in the solution after the heating reaction, indicating that MnO2 is successfully generated.

[0028] Wherein: the mass ratio (g / g) of ammonium salt to manganese source is 1:1~5:1.

[0029] The manganese source is at least one of KMnO4 and MnSO4·H2O; and the ammonium salt is (NH4)2S2O8.

[0030] S2. Disperse the carrier MnO2 in an alkaline solution with a pH of 10-14, add an iridium source and dissolve it to obtain a dispersion.

[0031] The mass ratio (g / g) of the iridium source to the carrier MnO2 is 1:1~1:5; the mass ratio (g / g) of the carrier MnO2 to the alkaline solution is 1:20~1:50. The preferred concentration of the alkaline solution is 1 mol L -1 The iridium source is Na2IrCl6·6H2O.

[0032] S3. Heat the dispersion in an autoclave at 90-180°C for 1-12 h, wash and dry to constant weight to obtain iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst.

[0033] Since the heating temperature will affect the crystallinity of the prepared catalyst, the higher the heating temperature, the higher the crystallinity of the prepared catalyst. However, when the temperature is too high, the particle size of the prepared catalyst will become larger and the corresponding active area will become smaller. When the heating temperature is too low, the reaction will be incomplete. Therefore, based on many other influencing factors, after a large number of experiments, it is concluded that the heating rate in the present invention may include a value within any range of 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, etc., which can be adjusted according to actual conditions; the heating temperature in steps S1 and S3 may include a value within any range of 90°C, 120°C, 150°C, 180°C, etc., which can be adjusted according to actual conditions; the insulation time may include a value within any range of 1h, 4h, 8h, 12h, etc., which can be adjusted according to actual conditions.

[0034] The particle size of the obtained iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst is 1~2 nm; the mass percentage of Ir is 1 wt%~20 wt%.

[0035] In the obtained IrO2 / MnO2 catalyst, the mass percentage of Ir may include values ​​within any range such as 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, etc., which can be adjusted according to actual conditions. The particle size of the IrO2 / MnO2 catalyst may include values ​​within any range such as 1.0 nm, 1.2 nm, 1.4 nm, 1.6 nm, 1.8 nm, 2.0 nm, etc., which can be adjusted according to actual conditions.

[0036] Application of an iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst: The iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst is used as an oxygen evolution catalyst in the oxygen evolution reaction in acidic water electrolysis.

[0037] The specific application process is as follows: 4 mg IrO2 / MnO2 catalyst, 30 μL 5% perfluorosulfonic acid (Nafion) solution, 745 μL isopropanol and 235 μL ultrapure water were mixed and ultrasonically dispersed for 1 h to prepare the electrochemical test ink solution. A glassy carbon electrode with a diameter of 5 mm (GC, area of ​​0.196 cm) was selected. 2 ), add 10 μL of ink solution onto the pre-polished GC, dry it under an infrared lamp to make a test electrode, and then perform water electrolysis and oxygen evolution reaction on the test electrode.

[0038] A membrane electrode prepared by using the iridium oxide-manganese dioxide (IrO2 / MnO2) catalyst is applied to the proton exchange membrane water electrolysis catalytic reaction.

[0039] The specific preparation process of the membrane electrode is as follows: 30 mg IrO2 / MnO2 catalyst, 60 μL 5% perfluorosulfonic acid (Nafion) solution, 5 mL isopropanol and 5 mL ultrapure water are mixed, ultrasonically obtained anode catalyst ink, and the anode catalyst is sprayed on the surface of the proton exchange membrane (Nafion 115); then, 20 mg Pt / C catalyst 20 mg, 40 μL 5% perfluorosulfonic acid (Nafion) solution, and 10 mL N,N-dimethylacetamide are mixed, ultrasonically obtained cathode catalyst ink, and the cathode catalyst is sprayed on the other side of the proton exchange membrane (Nafion 115), and finally a water electrolysis membrane electrode with low precious metal loading is obtained.

[0040] Example 1 A method for preparing an IrO2 / MnO2 catalyst comprises the following steps: S1. Weigh 0.85 g MnSO4·H2O and 1.14 g (NH4)2S2O8, dissolve in 40 mL deionized water, and stir at room temperature for 20 min to fully dissolve the solid. Then, put the solution into a 50 mL polytetrafluoroethylene liner, seal it in a stainless steel autoclave, and react at 140 °C in an oven for 12 h. After the reaction is cooled, centrifuge, wash and dry to obtain the carrier β-MnO2.

[0041] S2. Weigh 50 mg of β-MnO2 and dissolve it in 30 mL of NaOH (1 mol L -1 ) solution and ultrasonically dissolved for 20 min to fully disperse the solid matter. Then, 2.9 mL Na2IrCl6·6H2O (5 mg mL -1 ), and continue ultrasonic dispersion for 10-20 minutes to obtain a dispersion.

[0042] S3. Place the dispersion into a 50 mL polytetrafluoroethylene liner and seal it in a stainless steel autoclave, and react in an oven at 150 °C for 12 h. After the reaction is cooled, centrifuge, wash and dry.

[0043] The method of loading IrO2 on other crystalline MnO2 is the same as this method. In this reaction, sodium hexachloroiridate is used as a precursor solution, and its hydrolysis is promoted by adding an appropriate amount of alkaline solution, and then the hydrolysis product is heat-treated to finally form the desired metal oxide on the substrate carrier.

[0044] Figure 2a is a HRTEM image of the IrO2 / MnO2 catalyst prepared in Example 1 of the present invention, and the frame diagram in the figure is a particle size distribution diagram. As can be seen from the figure, this example successfully prepared a uniformly distributed nanocluster IrO2 / MnO2 catalyst.

[0045] Figure 3 The XPS spectrum of the IrO2 / MnO2 catalyst prepared in Example 1 of the present invention is shown in Figure 1, where a is the O 2p spectrum and b is the Ir 4f spectrum. It can be seen from the figure that Ir exists in the form of IrO2.

[0046] Figure 4 This is the XRD pattern of the IrO2 / MnO2 catalyst prepared in Example 1 of the present invention. It can be seen from the figure that the loading of IrO2 does not change the crystal form of MnO2.

[0047] Example 2 A method for preparing an IrO2 / MnO2 catalyst: In step S1, 0.755 g of MnSO4·H2O and 1.14 g of (NH4)2S2O8 were weighed, and the reaction temperature was 90°C; the other steps and methods were the same as in Example 1.

[0048] Figure 2 b is a HRTEM image of the IrO2 / MnO2 catalyst prepared in Example 2 of the present invention, and the frame diagram in the figure is a particle size distribution diagram. It can be seen from the figure that this example successfully prepared a uniformly distributed nanocluster IrO2 / MnO2 catalyst.

[0049] Figure 3 This is the XPS spectrum of the IrO2 / MnO2 catalyst prepared in Example 2 of the present invention, where a is the O 2p spectrum and b is the Ir 4f spectrum. It can be seen from the figure that Ir exists in the form of IrO2.

[0050] Figure 4 This is the XRD pattern of the IrO2 / MnO2 catalyst prepared in Example 2 of the present invention. It can be seen from the figure that the loading of IrO2 does not change the crystal form of MnO2.

[0051] Application Example 1 An application of an IrO2 / MnO2 catalyst, the IrO2 / MnO2 catalyst prepared in Example 1 is used as an oxygen evolution reaction catalyst in an acidic water electrolysis oxygen evolution reaction, and the electrochemical performance is evaluated, and the specific method includes the following: A1. Mix 4 mg IrO2 / MnO2 catalyst, 30 μL 5% Nafion solution, 745 μL isopropanol and 235 μL ultrapure water, and disperse them ultrasonically for 1 h to prepare an electrochemical test ink solution. A2, select a glassy carbon electrode tip with a diameter of 5 mm (GC, area of ​​0.196 cm 2 ), drip 10 μL of ink solution onto the pre-polished GC, dry it under an infrared lamp to make a test electrode; A3. Perform oxygen evolution reaction on the test electrode by electrolysis of water: Place 0.5 M H2SO4 solution in a five-well electrolytic cell, introduce N2 for half an hour to saturate the solution, and perform a linear sweep voltammetry (LSV) test at a scan rate of 5 mV s -1 , scanning range 1.2~1.7 V / RHE.

[0052] Test results such as Figure 5 As shown in the figure, the test electrode made of IrO2 / MnO2 catalyst prepared in Example 1 has a high conductivity at 10 mA cm -2 The overpotential is 309 mV.

[0053] Application Example 2 An application of an IrO2 / MnO2 catalyst, wherein the IrO2 / MnO2 catalyst prepared in Example 2 is used as an oxygen evolution reaction catalyst in an acidic water electrolysis oxygen evolution reaction, and the electrochemical performance is evaluated. The specific method is the same as that of Application Example 1.

[0054] Test results such as Figure 5 As shown in the figure, the test electrode made of IrO2 / MnO2 catalyst prepared in Example 2 has a high conductivity at 10 mA cm -2 The overpotential is 323 mV.

[0055] Example 3 A membrane electrode is prepared using the IrO2 / MnO2 catalyst prepared in Example 1, and the specific steps include: 30 mg IrO2 / MnO2 catalyst, 60 μL 5% perfluorosulfonic acid (Nafion) solution, 5 mL isopropanol and 5 mL ultrapure water were mixed, ultrasonicated to obtain anode catalyst ink, and the anode catalyst was sprayed on the surface of proton exchange membrane (Nafion115).

[0056] 20 mg of Pt / C catalyst, 40 μL of 5% perfluorosulfonic acid (Nafion) solution, and 10 mL of N,N-dimethylacetamide were mixed and ultrasonicated to obtain cathode catalyst ink. The cathode catalyst was sprayed on the other side of the proton exchange membrane (Nafion 115) to finally obtain a water electrolysis membrane electrode with low precious metal loading.

[0057] Application Example 3 An application of a membrane electrode, wherein the membrane electrode in Example 3 is applied to a proton exchange membrane water electrolysis catalytic reaction, the membrane electrode is placed in a small water electrolysis fixture, 80°C ultrapure water is passed into the anode, the entire system is placed in an environment of 80°C, and the current density of the water electrolysis is set to 0-2 A cm -2 Tests were carried out to obtain the polarization curve of membrane electrode water electrolysis.

[0058] Figure 6 is the membrane electrode polarization curve. Figure 6 It can be seen that the IrO2 / MnO2 catalyst still maintains excellent activity at low iridium loading. The membrane electrode prepared in Example 3 has a high activity at 1 A cm -2 , the battery tank voltage at 80°C is only 1.820 V; it also shows that the membrane electrode prepared using the IrO2 / MnO2 catalyst prepared in Example 1 can effectively improve the utilization rate of the water electrolysis catalyst and improve the reaction performance, that is, the IrO2 / MnO2 catalyst prepared in Example 1 has high catalytic activity and high metal utilization.

[0059] The membrane electrode prepared in Example 3 was applied to the proton exchange membrane water electrolysis catalytic reaction. The membrane electrode was placed in a small water electrolysis fixture, and 80°C ultrapure water was passed into the anode. The whole system was placed in an environment of 80°C. The current density of the water electrolysis was set to 1 A cm -2 Conduct stability testing.

[0060] Figure 7 The stability test results of the membrane electrode are shown in Figure 2. Figure 7 It is known that the membrane electrode has a -2 , and can operate stably for at least 200 h at 80°C.

[0061] In summary, the present invention synthesizes different crystal forms of MnO2 by hydrothermal method and uses it as a substrate to construct IrO2 / MnO2. Among them, β-MnO2 as a carrier to load IrO2 shows the best activity and stability. IrO2 / β-MnO2 at 10 mAcm -2 The low overpotential of 310 mV can be achieved at a current density of 1.905 V @ 1 A cm in a water electrolysis hydrogen production electrolyzer. -2 In comparison, IrO2 / β-MnO2 can exhibit a battery voltage of 1.820 V at this current density and can operate stably for 200 h. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has high industrial utilization value.

Claims

1. A method for preparing an iridium oxide-manganese dioxide catalyst, comprising the following steps: S1. Fully dissolve a manganese source and an ammonium salt in deionized water, transfer the resulting solution to an autoclave for heating and reaction, and wash and dry to obtain a carrier MnO2; the mass ratio of the ammonium salt to the manganese source is 1:1 to 5:1; S2, dispersing the carrier MnO2 in an alkaline solution with a pH of 10-14, adding an iridium source and dissolving it to obtain a dispersion; the mass ratio of the iridium source to the carrier MnO2 is 1:1-1:5; the mass ratio of the carrier MnO2 to the alkaline solution is 1:20-1:50; the iridium source is Na2IrCl6·6H2O; S3, heating the dispersion in an autoclave for reaction, washing and drying to obtain an iridium oxide-manganese dioxide catalyst.

2. The method for preparing an iridium oxide-manganese dioxide catalyst according to claim 1, wherein: In step S1, the manganese source is at least one of KMnO4 and MnSO4·H2O; and the ammonium salt is (NH4)2S2O8.

3. The method for preparing an iridium oxide-manganese dioxide catalyst as claimed in claim 1, wherein: The heating reaction conditions in step S1 and step S3 are both 90-180° C. and 1-12 h.

4. The method for preparing an iridium oxide-manganese dioxide catalyst according to claim 1, wherein: In the step S1, the carrier MnO2 is one of α-MnO2, β-MnO2, γ-MnO2 or δ-MnO2.

5. The method for preparing an iridium oxide-manganese dioxide catalyst as claimed in claim 1, characterized in that: In step S3, the particle size of the iridium oxide-manganese dioxide catalyst is 1-2 nm; the mass percentage of Ir is 1 wt%-20 wt%.

6. An iridium oxide-manganese dioxide catalyst prepared by the method according to any one of claims 1 to 5.

7. The use of an iridium oxide-manganese dioxide catalyst as claimed in claim 6, characterized in that: The iridium oxide-manganese dioxide catalyst is used as an oxygen evolution catalyst in the oxygen evolution reaction of acidic water electrolysis.

8. A membrane electrode prepared using the iridium oxide-manganese dioxide catalyst as claimed in claim 7.

9. The use of a membrane electrode as claimed in claim 8, characterized in that the membrane electrode is used in a proton exchange membrane water electrolysis catalytic reaction.

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