A three-dimensional porous network structure nano-iridium / iridium oxide composite catalyst and its preparation method

Abstract

This invention relates to a three-dimensional porous network structure nano-iridium / iridium oxide composite catalyst and its preparation method, which is used as a catalytic material for proton exchange membrane electrolysis of water to produce hydrogen and oxygen evolution, belonging to the field of green energy. The composite catalyst of this invention exhibits a three-dimensional porous network structure, the framework of which is composed of nano-iridium and iridium oxide, with the iridium oxide containing amorphous iridium oxide. This invention employs a simultaneous dynamic redox liquid-state in-situ generation method, obtaining a nano-iridium / iridium oxide composite catalyst with a special structure without calcination. This invention significantly reduces the oxygen evolution overpotential through the design and optimization of the catalyst's spatial structure. The components of this invention are rationally designed, the preparation process is simple and controllable, and the resulting product has superior performance, facilitating industrial application.

Description

Technical Field

[0001] This invention relates to a three-dimensional porous network structure nano-iridium / iridium oxide composite catalyst and its preparation method, which is used as a catalytic material for hydrogen production and oxygen evolution through proton exchange membrane water electrolysis, belonging to the field of green energy development technology. Background Technology

[0002] Depending on the membrane material used in the electrolyzer, hydrogen production via water electrolysis is generally classified into alkaline water electrolysis (AE), proton exchange membrane (PEM) water electrolysis, and high-temperature solid oxide water electrolysis (SOEC). In PEM water electrolysis, iridium oxide is a commonly used oxygen evolution catalyst. Currently, methods for preparing iridium oxide include melt processing, chemical precipitation, and thermal oxidation. The melt processing method involves reacting an iridium precursor with excess sodium nitrate to form an iridium salt, which is then dried and oxidized at high temperature to obtain iridium oxide. The chemical precipitation method involves reacting an iridium precursor with an alkali (such as sodium hydroxide) to form iridium hydroxide, which is then dehydrated at high temperature to produce iridium oxide. Another commercially common method for preparing iridium oxide involves reducing the iridium precursor to elemental iridium and heating it to a high temperature in air or oxygen to produce iridium oxide. For example, patent application CN118957657A relates to a composite iridium oxide / iridium supported oxygen evolution electrocatalyst and its preparation method. The catalyst includes a nanoparticle support, a conductive metal nano-iridium layer coated on the surface of the support, and an iridium oxide layer further coated on the surface of the conductive metal nano-iridium layer, wherein the iridium loading is 20-80 wt.%. The preparation method involves the following steps: 1) Preparation of the first precursor of the electrocatalyst: hydrated iridium chloride and support powder are uniformly mixed in an organic solvent, heated to 150-200℃, stirred and reacted. After the reaction is completed, the mixture is cooled to room temperature, centrifuged to separate the precipitate, washed, and the first precursor of the electrocatalyst with a conductive metal nano-iridium layer coated on the support surface is obtained; 2) Preparation of the second precursor of the electrocatalyst: the first precursor of the electrocatalyst is dispersed in deionized water with hydrated iridium tetrachloride and sodium hydroxide or potassium hydroxide, stirred at room temperature for a period of time, and then the mixture is heated to 70-100℃ and stirred and reacted. After the reaction is completed, the mixture is cooled to room temperature, centrifuged to separate the precipitate, washed, and the second precursor of the electrocatalyst with a hydroxy iridium oxide-coated conductive metal nano-iridium layer support is obtained; 3) Preparation of the composite iridium oxide / iridium supported oxygen evolution electrocatalyst: the second precursor of the electrocatalyst is mixed with sodium nitrate powder, ground thoroughly, calcined at 350-550℃, then cooled to room temperature, the product is washed with deionized water, and dried to obtain the composite iridium oxide / iridium supported oxygen evolution electrocatalyst. This patent continues to use a support for the catalyst. Some attempts have been made to develop technologies that do not require a support, such as patent application CN116005185A, which involves a composite catalyst of iridium and iridium oxide and its preparation method. However, the XRD pattern of this catalyst shows characteristic peaks of elemental iridium but not characteristic peaks of iridium dioxide.The preparation method includes: S1, mixing an iridium source and a complexing agent in water to form a solution; the complexing agent is selected from one or more organic polybasic acids and their soluble salts; S2, adjusting the pH of the solution to 7-10 and reacting; S3, removing water to obtain a catalyst precursor; S4, calcining the catalyst precursor in an oxygen-containing atmosphere, and after washing, obtaining the product. This patent does not address the cell voltage or voltage decay rate when the product is used to prepare hydrogen. Therefore, it can be seen that existing mainstream technologies for preparing iridium / iridium oxide composite catalysts all require high-temperature calcination. Furthermore, a search revealed that existing technologies do not involve the design and optimization of the spatial structure of this type of catalyst, nor do they contain any records of reducing its decay rate through the design and optimization of the catalyst's spatial structure. Summary of the Invention

[0003] This invention addresses the shortcomings of existing technologies by proposing, for the first time, a three-dimensional porous network structure for nano-iridium / iridium oxide composite catalysts, and also developing a calcination-free preparation method. This invention can significantly reduce the degradation rate during use through the design and optimization of the catalyst's spatial structure.

[0004] The three-dimensional porous network structure nano-iridium / iridium oxide composite catalyst obtained in this invention exhibits extremely superior performance, with an oxygen evolution overpotential of 220–210 mV and a Tafel slope of 78–75. When composited with an N115 membrane (125 μm thick), it forms a membrane electrode, achieving a membrane electrode performance of 2 A / cm². 2 The cell voltage for hydrogen production by electrolysis at the current density is ≤1.795V, and the cell voltage decay rate after 2000 hours of continuous electrolysis is ≤4.8 μV / hour. After optimization, the cell voltage decay rate after 2000 hours of continuous electrolysis is ≤4.25 μV / hour.

[0005] The composite catalyst of this invention exhibits a three-dimensional porous network structure. The framework of this three-dimensional porous network structure is composed of nano-iridium and iridium oxide, wherein the iridium oxide contains amorphous iridium oxide. Compared with the crystalline state, amorphous iridium oxide has a richer surface area and more active sites, thus exhibiting better catalytic activity.

[0006] This invention discloses a method for preparing a three-dimensional porous network structured nano-iridium / iridium oxide composite catalyst, comprising the following steps:

[0007] Step 1: Raw material dissolution; dissolve the iridium source in a mixed solvent, add surfactant, dispersant, and additives, and stir until completely dissolved; obtain a raw material solution, wherein the additives include citrate; the concentration of iridium in the raw material solution is 2~5.4 g / L, the concentration of surfactant is 2~10 g / L, the concentration of dispersant is 0.5~1.5 g / L, and the concentration of citrate is 1~7 g / L; the mixed solvent is composed of mixed alcohol and water in a mass ratio of mixed alcohol:water = 85~95:5~15.

[0008] Step 2: Preparation of reducing agent; dissolve the reducing agent in a solvent to obtain a reducing agent solution; the solvent is composed of water and alcoholic organic compounds in a mass ratio of alcoholic organic compounds:water = 2~2.5:7.5~8.

[0009] Step 3: Reduction; Add the reducing agent solution to the raw material solution according to the mass ratio of reducing agent:iridium = 2~4:1, stir until the reaction is complete; set aside the mixture after reaction; control the reduction temperature at 20~50℃.

[0010] Step 4: Settling; allow the reaction mixture to stand, then perform solid-liquid separation. The solid is dried to obtain a three-dimensional porous network structure nano-iridium / iridium oxide catalyst.

[0011] In this invention, the concentrations of iridium in the raw material solution are controlled as follows: 2-5.4 g / L, surfactant concentration: 1-10 g / L, dispersant concentration: 0.5-1.5 g / L, and citrate concentration: 1-7 g / L. Citrate (especially sodium citrate and ammonium citrate) acts as a complexing agent to increase the reduction potential of iridium, thereby reducing small and uniform iridium particles. Sodium and ammonium salts are chosen for their ease of separation and removal. Small amounts result in incomplete complexation, while large amounts increase the difficulty of impurity removal. The surfactant CTAB has two functions: first, it forms a complex with iridium ions, increasing the reduction potential and promoting the formation of small and uniform iridium particles; second, it prevents the aggregation of newly formed iridium. Small amounts are ineffective in preventing aggregation, while large amounts increase the difficulty of washing during solid-liquid separation.

[0012] In this invention, the ratio of reducing agent to iridium is controlled to be 2 to 4:1 by mass because an excessive amount of reducing agent will cause the formation rate of elemental iridium to be too fast, leading to increased agglomeration, which in turn affects the structure and morphology of the product, and thus affects the electrochemical performance. It is also not conducive to the construction of the three-dimensional network structure. If the reducing agent is too little, in addition to affecting the product yield, it will also cause the constructed three-dimensional network structure to collapse.

[0013] In industrial production applications, a reducing agent solution is added to the raw material solution to carry out the reaction. The reducing agent is added slowly while stirring until the reaction is complete.

[0014] To further enhance the effect, this invention controls the concentration of the reducing agent to 40-65 g / L. Combined with the concentration control of each component in the reducing agent solution and the strategy of adding and stirring simultaneously, the reduction reaction can be controlled within a reasonable range. Furthermore, due to the use of an organic solvent + water solvent system, simultaneous stirring during the addition of the reducing agent solution allows iridium to automatically form a three-dimensional porous network structure.

[0015] The iridium source is a water-soluble iridium salt. Preferably, it is at least one of iridium trichloride, chloroiridic acid, and ammonium chloroiridate.

[0016] Preferably, in step one of this invention, the mixed alcohol is selected from at least two of ethanol, ethylene glycol, and isopropanol, and more preferably from ethanol and ethylene glycol. Even more preferably, the mixed alcohol is composed of ethanol and ethylene glycol in a volume ratio of 1:1.

[0017] As a further preferred embodiment, in the mixed solvent used in step one of this invention, the mass ratio of the mixed alcohol to water is 85-90:10-15. In this invention, the amount of alcohol in the solvent used in step one is much greater than the amount of water because a three-dimensional porous network structure needs to be formed. If the proportion of water in the solvent is too high, such as greater than 45%, the network structure formation will fail.

[0018] Preferably, in step one of the present invention, the surfactant is selected from hexadecyltrimethylammonium bromide (CTAB), and the dispersant is selected from polyvinylpyrrolidone (PVP).

[0019] Preferably, in step one of the present invention, the additive is selected from at least one of sodium citrate and ammonium citrate, and more preferably, sodium citrate and ammonium citrate are composed in a mass ratio of 0.8~1.2:0.8~1.2.

[0020] Preferably, in step two of the present invention, the alcohol organic compound used is selected from at least one of methanol, ethanol, and ethylene glycol. More preferably, the alcohol organic compound is composed of ethanol, methanol, and ethylene glycol in a mass ratio of 75~85:7.5~12.5:7.5~12.5.

[0021] As a further preferred embodiment, in the solvent used in step two of the present invention, the mass ratio of alcoholic organic compounds to water is 2:8.

[0022] In this invention, a small amount of alcohol is used when dissolving the reducing agent in order to better integrate with the iridium-containing organic phase. In particular, a ternary mixed alcohol mainly composed of ethanol is used to cooperate with the raw materials in step one to construct a stable and porous three-dimensional structure as much as possible during the reduction process.

[0023] In this invention, the solubility of the reducing agent solution is preferably 45~60 g / L, more preferably 48~52 g / L.

[0024] In step three of this invention, the reduction temperature is controlled at 20~50℃. Too high a temperature will cause agglomeration due to vigorous reaction, while too low a temperature will lead to the formation of nanoparticle catalysts, among other problems.

[0025] Preferably, in step three of this invention, the stirring speed is 400-700 rpm. Stirring not only ensures a uniform reaction but also forms partially amorphous iridium (see...). Figure 1It can also introduce oxygen from the air, which is adsorbed onto the surface of newly generated iridium atoms to form derived iridium oxides. It establishes a dynamic balance between reduction and oxidation, thereby selecting more active sites, which provides the necessary conditions for obtaining high-quality catalysis.

[0026] Preferably, in step four of this invention, the settling time is greater than or equal to 6 hours, and more preferably 10 to 14 hours.

[0027] Preferably, in step four of this invention, solid-liquid separation is performed by centrifugation at a speed of 4000-7000 rpm. This is because research has found that excessively high centrifugation speeds, such as exceeding 7500 rpm, significantly increase the probability of three-dimensional structure collapse.

[0028] Preferably, in step four of this invention, the vacuum drying process is carried out at a temperature of 40-100°C for 12-24 hours, while maintaining a controlled vacuum level (0.08-0.085 MPa). The controlled drying temperature in this invention is not only for dehydration but also to further convert the adsorbed oxygen of iridium atoms into iridium dioxide containing amorphous states (see...). Figure 1 ).

[0029] After optimization, the specific surface area of ​​the nano-iridium / iridium oxide catalyst obtained by this invention can reach 1870 m². 2 / g and the loose density is 0.16g / cm³ 3 .

[0030] Principle and Advantages: Fresh, highly active nano-iridium has a large number of coordinated unsaturated atoms on its surface, resulting in very high surface energy. When exposed to air or separated from an aqueous phase, these active sites strongly chemisorb oxygen molecules (O2). These oxygen atoms are firmly fixed to the atoms on the iridium metal surface, easily forming iridium oxide under certain temperature and time conditions. This iridium oxide coats the surface of the iridium bulk phase, forming Ir@IrO2. The iridium oxide in this material is mostly amorphous, and some of the surface iridium in the bulk phase is also amorphous. Therefore, as a catalyst for PEM water electrolysis to produce oxygen, it not only has higher conductivity than conventional iridium oxide catalysts but also exhibits very high catalytic activity; furthermore, because the bulk phase is iridium metal, its stability is also good.

[0031] The amount of iridium oxide on the surface can be controlled by the rotation speed during the reduction reaction, the water content in the mixed solvent, the water content in the reducing agent, and the vacuum degree and temperature during vacuum drying. Attached Figure Description

[0032] Appendix Figure 1 The image shows the XRD pattern of the product obtained in Example 1.

[0033] Appendix Figure 2 Here is a scanning electron microscope image of the product obtained in Example 1;

[0034] Appendix Figure 3 This is a scanning electron microscope image of the product obtained in Example 2;

[0035] Appendix Figure 4 The image shows the performance effect of the membrane electrode made from the product obtained in Example 1;

[0036] Appendix Figure 5 The image shows the performance effect of the membrane electrode made from the product obtained in Example 1;

[0037] Appendix Figure 6 The image shows the performance effect of the membrane electrode made from the product obtained in Example 1;

[0038] Appendix Figure 7 The graph shows the current density and voltage changes when the product obtained in Example 1 was used to fabricate a membrane electrode and a commercially available iridium oxide-supported membrane electrode for electrolysis of 0.5 mol / L sulfuric acid.

[0039] Appendix Figure 8 Voltage-time fluctuation curves of 0.5 mol / L sulfuric acid electrolyzed in constant current mode after the product obtained in Example 1 was fabricated into a membrane electrode and an existing commercial iridium oxide supported membrane electrode. Detailed Implementation

[0040] Example 1

[0041] Step 1: Raw material dissolution; Dissolve the iridium source (iridium trichloride) in a mixed solvent, add the surfactant cetyltrimethylammonium bromide (CTAB), the dispersant polyvinylpyrrolidone (PVP), and additives (trisodium citrate and triammonium citrate), and stir until completely dissolved; obtain the raw material solution; the concentration of iridium in the raw material solution is 5.4 g / L, the concentration of surfactant is 10 g / L, the concentration of polyvinylpyrrolidone is 1.5 g / L, the concentration of trisodium citrate is 3 g / L, and the concentration of triammonium citrate is 3 g / L. The mixed solvent is composed of organic matter (50 wt% ethanol + 50 wt% ethylene glycol) and water in a mass ratio of organic matter:water = 8.5:1.5.

[0042] Step 2: Preparation of reducing agent; Dissolve 22g of reducing agent (sodium borohydride) in a solvent to obtain a reducing agent solution; The solvent is composed of organic matter (80wt% ethanol + 10wt% methanol + 10wt% ethylene glycol) and water in a mass ratio of organic matter:water = 2:8; The concentration of reducing agent in the reducing agent solution is 50g / L.

[0043] Step 3: Reduction; according to the mass ratio of reducing agent:iridium = 4:1, at 50℃, add the reducing agent solution to the raw material solution, and stir at a stirring speed of 700 rpm while adding the reducing agent solution until the reaction is complete; the mixture after the reaction is ready for use.

[0044] Step 4: Settling; The reaction mixture was left to stand overnight at room temperature, and then centrifuged (centrifugation speed of 5000 rpm). The solid was dried (drying temperature of 100℃ for 12 h) to obtain a three-dimensional porous network structure nano-iridium / iridium oxide catalyst.

[0045] Performance testing: The intrinsic catalytic activity and stability of the catalyst can be tested using a glassy carbon electrode on an electrochemical workstation. Polarization curves are shown below. Figure 7 This indicates that the oxygen evolution overpotential (218 mV) of this invention is significantly lower than that of commercial iridium oxide (259 mV), suggesting better catalytic activity. The constant current curve is shown below. Figure 8 The constant current curve of the catalyst of this invention slowly declines, indicating that the resistance decreases slowly until it stabilizes during electrolysis; while the constant current curve of commercial catalysts slowly rises during electrolysis, indicating that the resistance increases slowly. If it is loaded into an electrolytic cell, it will cause the cell voltage to rise slowly, and the energy consumption will increase.

[0046] The polarization curves of the prepared N115 film electrode are shown in the figure. Figure 4 .

[0047] The preparation method of N115 membrane electrode is as follows: First, prepare catalyst ink and cathode platinum black catalyst ink. The catalyst ink formula is as follows:

[0048] .

[0049] The cathode platinum black catalyst ink formula is as follows:

[0050] .

[0051] Operating procedure: Take materials in equal proportions according to the above formula and place them in a jacketed double-layer beaker. Ensure that the cooling water path of the double-layer beaker is filled with ice water below 5°C during the ultrasonication process. After ultrasonication for 1 hour, the slurry dispersion is complete. Platinum black is produced by Hunan Qiwei Hydrogen Energy Technology Co., Ltd.

[0052] The double-walled beaker is a 300 ml jacketed double-walled beaker.

[0053] The ultrasound equipment used was Ningbo Xinzhi Biotechnology Co., Ltd.'s JY98-IIIDN, and the ultrasound frequency was 19.5~20.5KHz.

[0054] Spraying process: 20 coats for the cathode, 27 coats for the anode, spray head flow rate 2 ml / min. Anode catalyst loading of this invention: 0.63 mg / cm³. 2 Cathode platinum black catalyst loading: 0.54 mg / cm³ 2 Note: The spraying temperature is 80℃.

[0055] Hot pressing process: The hot pressing process parameters for combining the anode catalyst obtained in Example 1 with the N115 membrane are: hot pressing temperature 150℃, hot pressing pressure 4MPa, and hot pressing time 300s.

[0056] The mounting details are as follows: the single-layer gas diffusion layer should be 0.02mm thicker than the single-layer sealing ring. That is, when the thickness of the two sealing rings is 0.8mm, the thickness of the two gas diffusion layers should be 0.84mm. Under this condition, the conductive function of the gas diffusion layer can be fully utilized.

[0057] Activation and polarization curve testing details are as follows: at 0.25 A / cm 2 Activation was performed for 30 minutes at a current density of 0.50 A / cm. 2 Activation was performed at a current density of 1.00 A / cm for 30 min, and finally at 1.00 A / cm. 2 Activate at a current density for 180 minutes. After activation, turn off the power and wait for 5 minutes before turning the power back on to test the polarization curve (test the electrode plate part of the fuel cell stack).

[0058] from Figure 4 It can be seen from this that at 60 degrees Celsius, at 2.00 A / cm 2 At a current density of ≤1.791V, the cell voltage for hydrogen production is ≤1.791V.

[0059] from Figure 6 As can be seen from this, at 60 degrees Celsius, at 2.00 A / cm 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is only 4.25 µV / h.

[0060] The anode catalyst developed in Example 1 of this invention was combined with BriPEM ® A membrane electrode was fabricated using an -802 film (80 micrometers) composite, and its polarization curve is shown in [Figure 1]. Figure 5 .

[0061] In the composite process, other conditions and equipment are the same as those in Example 1 for the composite process of the anode catalyst and N115 membrane; the difference lies in the spraying process: 25 sprays for the cathode and 22 sprays for the anode, with a nozzle flow rate of 2 ml / min. The anode catalyst loading of this invention is 0.51 mg / cm³. 2 Cathode platinum black catalyst loading: 0.68 mg / cm³ 2 .

[0062] The hot pressing process parameters are: hot pressing temperature 135℃, hot pressing pressure 4MPa, and hot pressing time 180s.

[0063] The activation process is as follows: at 0.25 A / cm 2 After activation at a current density of 1 hour, the current density was increased to 1.0 A / cm². 2Reactivate for 1 hour; total activation time: 2 hours.

[0064] pass Figure 5 It can be seen that at 59.8 degrees Celsius, the electrolysis of pure water results in an efficiency of 2.00 A / cm². 2 At a current density of 3.00 A / cm², the cell voltage for hydrogen production is ≤1.72 V. 2 At current densities, the cell voltage for hydrogen production is ≤1.799V. The material developed in this invention is particularly suitable for electrolysis at high current densities.

[0065] Example 2

[0066] Step 1: Raw material dissolution; Dissolve the iridium source (iridium trichloride) in a mixed solvent, add the surfactant cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone, and additives (trisodium citrate, triammonium citrate), and stir until completely dissolved; obtain the raw material solution; The concentration of iridium in the raw material solution is 2 g / L, the concentration of the surfactant is 1 g / L, the concentration of polyvinylpyrrolidone is 0.5 g / L, the concentration of trisodium citrate is 1 g / L, and the concentration of triammonium citrate is 1 g / L. The mixed solvent is composed of organic matter (50 wt% ethanol + 50 wt% ethylene glycol) and water in a mass ratio of organic matter:water = 9.5:0.5.

[0067] Step 2: Preparation of reducing agent; Dissolve 4g of sodium borohydride in a solvent to obtain a reducing agent solution; The solvent is composed of organic matter (80wt% ethanol + 10wt% methanol + 10wt% ethylene glycol) and water in a mass ratio of organic matter:water = 2:8; The concentration of the reducing agent in the reducing agent solution is 50g / L.

[0068] Step 3: Reduction; by mass ratio, reducing agent: iridium = 2:1, add the reducing agent solution to the raw material solution at 20℃, and stir at a stirring speed of 400 rpm while adding the reducing agent solution until the reaction is complete; the mixture after the reaction is ready for use.

[0069] Step 4: Settling; The reaction mixture was left to stand overnight at room temperature, and then centrifuged (centrifugation speed 4000 rpm). The solid was dried (drying temperature 40℃, time 24h) to obtain a three-dimensional porous network structure nano-iridium / iridium oxide catalyst.

[0070] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were as follows: at 60 degrees Celsius, electrolysis of pure water, at 2.00 A / cm 2 At a current density of [value missing], the cell voltage for hydrogen production is approximately 1.820V. At 60 degrees Celsius, at 2.00 A / cm [value missing]... 2At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is 4.8 µV / h.

[0071] Example 3

[0072] Step 1: Raw material dissolution; Dissolve the iridium source (iridium trichloride) in a mixed solvent, add the surfactant cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone, and additives (trisodium citrate, trisodium ammonium citrate), and stir until completely dissolved; obtain the raw material solution; The concentration of iridium in the raw material solution is 3.5 g / L, the concentration of the surfactant is 5 g / L, the concentration of polyvinylpyrrolidone is 1.0 g / L, the concentration of trisodium citrate is 2 g / L, and the concentration of trisodium citrate is 2 g / L. The mixed solvent is composed of organic matter (50 wt% ethanol + 50 wt% ethylene glycol) and water in a mass ratio of organic matter:water = 9:1.

[0073] Step 2: Preparation of reducing agent; Dissolve 10g of sodium borohydride in a solvent to obtain a reducing agent solution; The solvent is composed of organic matter (80wt% ethanol + 10wt% methanol + 10wt% ethylene glycol) and water in a mass ratio of organic matter:water = 2:8; The concentration of the reducing agent in the reducing agent solution is 50g / L.

[0074] Step 3: Reduction; according to the mass ratio of reducing agent:iridium = 2:1, at 30℃, add the reducing agent solution to the raw material solution, and stir at a stirring speed of 550 rpm while adding the reducing agent solution until the reaction is complete; the mixture after the reaction is ready for use.

[0075] Step 4: Settling; The reaction mixture was left to stand overnight at room temperature, and then centrifuged (centrifugation speed of 5000 rpm). The solid was dried (drying temperature of 65℃ for 18 h) to obtain a three-dimensional porous network structure nano-iridium / iridium oxide catalyst.

[0076] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were: at 60 degrees Celsius, at 2.00 A / cm 2 At a current density of [value missing], the cell voltage for hydrogen production by electrolyzing pure water is approximately 1.810V. At 60 degrees Celsius, at 2.00 A / cm [value missing], [value missing]. 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is 4.5 µV / h.

[0077] Example 4

[0078] Step 1: Raw material dissolution; Dissolve the iridium source (iridium trichloride) in a mixed solvent, add the surfactant cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone, and additives (trisodium citrate, ammonium citrate), and stir until completely dissolved; obtain the raw material solution; The concentration of iridium in the raw material solution is 4.5 g / L, the concentration of the surfactant is 8 g / L, the concentration of polyvinylpyrrolidone is 1.0 g / L, the concentration of sodium is 2.5 g / L, and the concentration of ammonium is 2.5 g / L. The mixed solvent is composed of organic matter (50 wt% ethanol + 50 wt% ethylene glycol) and water in a mass ratio of organic matter:water = 9:1.

[0079] Step 2: Preparation of reducing agent; Dissolve 18g of sodium borohydride in a solvent to obtain a reducing agent solution; The solvent is composed of organic matter (80wt% ethanol + 10wt% methanol + 10wt% ethylene glycol) and water in a mass ratio of organic matter:water = 2:8; The concentration of the reducing agent in the reducing agent solution is 50g / L.

[0080] Step 3: Reduction; According to the mass ratio of reducing agent:iridium = 2:1, at 40℃, add the reducing agent solution to the raw material solution and stir at a stirring speed of 650 rpm while adding the reducing agent solution until the reaction is complete; the mixture after the reaction is ready for use.

[0081] Step 4: Settling; The reaction mixture was left to stand overnight at room temperature, and then centrifuged (centrifugation speed of 5000 rpm). The solid was dried (drying temperature of 80℃ for 20 h) to obtain a three-dimensional porous network structure nano-iridium / iridium oxide catalyst.

[0082] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were: at 60 degrees Celsius, at 2.00 A / cm 2 At a current density of [value missing], the cell voltage for hydrogen production by electrolyzing pure water is approximately 1.815V. At 60 degrees Celsius, at 2.00 A / cm [value missing], [value missing]. 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is 4.5 µV / h.

[0083] Comparative Example 1

[0084] The other conditions are the same as in Example 1, except that the mixed solvent is composed of organic matter (100wt% ethanol) and water in a mass ratio of organic matter:water = 1.5:8.5.

[0085] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were as follows: at 60 degrees Celsius, electrolysis of pure water, at 2.00 A / cm 2At a current density of [value missing], the cell voltage for hydrogen production is approximately 1.92V. At 60 degrees Celsius, at 2.00 A / cm [value missing]... 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is 6.3 µV / h.

[0086] Comparative Example 2

[0087] Other conditions are the same as in Example 1, except that: when preparing the reducing agent, 22g of the reducing agent (sodium borohydride) is dissolved in a solvent to obtain a reducing agent solution; the solvent is composed of organic matter (100wt% ethanol) and water in a mass ratio of organic matter:water = 5:5; the concentration of the reducing agent in the reducing agent solution is 50g / L.

[0088] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were: at 60 degrees Celsius, at 2.00 A / cm 2 At a current density of [value missing], the cell voltage for hydrogen production is approximately 1.90V. At 60 degrees Celsius, at 2.00 A / cm [value missing]... 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is 5.8 µV / h.

[0089] Comparative Example 3

[0090] Other conditions are the same as in Example 1, except that in step three, during reduction, the reducing agent and iridium are added to the raw material solution at a mass ratio of 1:1 at 20°C, and the mixture is stirred at a speed of 300 rpm while adding the reducing agent solution until the reaction is complete; the mixture after the reaction is ready for use.

[0091] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were: at 60 degrees Celsius, at 2.00 A / cm 2 At a current density of [value missing], the cell voltage for hydrogen production is approximately 1.91V. At 60 degrees Celsius, at 2.00 A / cm [value missing]... 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is approximately 5.9 µV / h.

[0092] Comparative Example 4

[0093] Other conditions are the same as in Example 1, except that: in step one, when dissolving the raw materials, the iridium source (iridium trichloride) is dissolved in a mixed solvent, and the surfactant cetyltrimethylammonium bromide (CTAB) and the dispersant polyvinylpyrrolidone (PVP) are added and stirred until completely dissolved; a raw material solution is obtained; the concentration of iridium in the raw material solution is 5.4 g / L, the concentration of the surfactant is 10 g / L, and the concentration of polyvinylpyrrolidone is 7.5 g / L. The mixed solvent is composed of organic matter (50 wt% ethanol + 50 wt% ethylene glycol) and water in a mass ratio of organic matter:water = 8.5:1.5.

[0094] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were: at 60 degrees Celsius, at 2.00 A / cm 2 At a current density of [value missing], the cell voltage for hydrogen production is approximately 1.95V. At 60 degrees Celsius, at 2.00 A / cm [value missing]... 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is 6.2 µV / h.

[0095] Comparative Example 5

[0096] Other conditions are the same as in Example 1, except that: in step one, when dissolving the raw materials, the iridium source (iridium trichloride) is dissolved in the mixed solvent, and the surfactant cetyltrimethylammonium bromide (CTAB) and the dispersant polyvinylpyrrolidone (PVP) are added and stirred until completely dissolved; a raw material solution is obtained; the concentration of iridium in the raw material solution is 5.4 g / L, the concentration of surfactant is 15 g / L, the concentration of polyvinylpyrrolidone is 5 g / L, and the concentration of trisodium citrate is 8 g / L. The mixed solvent is composed of organic matter (50 wt% ethanol + 50 wt% ethylene glycol) and water in a mass ratio of organic matter:water = 8.5:1.5.

[0097] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were: at 60 degrees Celsius, at 2.00 A / cm 2 At a current density of [value missing], the cell voltage for hydrogen production is approximately 1.89V. At 60 degrees Celsius, at 2.00 A / cm [value missing]... 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is 4.8 µV / h.

[0098] Under the same detection conditions as in Example 1, when the product obtained in Comparative Example 6 was electrolyzed with 0.5 mol / L sulfuric acid in constant current mode, the voltage was approximately 1.51~1.52V after 30 hours of electrolysis.

[0099] Comparative Example 6

[0100] Other conditions are the same as in Example 1, except that: in step one, when dissolving the raw materials, the iridium source (iridium trichloride) is dissolved in the mixed solvent, and the surfactant cetyltrimethylammonium bromide (CTAB) and the dispersant polyvinylpyrrolidone (PVP) are added and stirred until completely dissolved; a raw material solution is obtained; the concentration of iridium in the raw material solution is 10 g / L, the concentration of surfactant is 15 g / L, the concentration of polyvinylpyrrolidone is 5 g / L, and the concentration of trisodium citrate is 8 g / L. The mixed solvent is composed of organic matter (50 wt% ethanol + 50 wt% ethylene glycol) and water in a mass ratio of organic matter:water = 8.5:1.5.

[0101] The obtained catalyst was tested according to the performance testing method of Example 1 (composite with N115 membrane), and the results were: at 60 degrees Celsius, at 2.00 A / cm 2 At a current density of [value missing], the cell voltage for hydrogen production is approximately 1.90V. At 60 degrees Celsius, at 2.00 A / cm [value missing]... 2 At the given current density, the cell voltage decay rate for hydrogen production over 2000 hours is 4.8 µV / h.

[0102] Under the same detection conditions as in Example 1, when the product obtained in Comparative Example 6 was electrolyzed with 0.5 mol / L sulfuric acid in constant current mode, the voltage was approximately 1.50~1.51V after 30 hours of electrolysis.

Claims

1. A nano-iridium / iridium oxide composite catalyst of a three-dimensional porous network structure, characterized by: The composite catalyst has a three-dimensional porous network structure, a skeleton of the three-dimensional porous network structure is composed of nanometer iridium and iridium oxide, and the iridium oxide contains amorphous iridium oxide; and the catalyst is prepared by the following steps: Step one: dissolving raw materials An iridium source is dissolved in a mixed solvent, a surfactant, a dispersant and an additive are added, and stirring and dissolving are performed until completion to obtain a raw material solution; the additive includes a citrate; the concentration of the iridium in the raw material solution is 2-5.4 g / L, the concentration of the surfactant is 2-10 g / L, the concentration of the dispersant is 0.5-1.5 g / L, and the concentration of the citrate is 1-7 g / L; the mixed solvent is composed of a mixed alcohol and water in a mass ratio of mixed alcohol: water = 85-95: 5-15; The additive is composed of sodium citrate and ammonium citrate in a mass ratio of 0.8-1.2: 0.8-1.2; In step one, the surfactant is cetyltrimethylammonium bromide, and the dispersant is polyvinylpyrrolidone; Step two: preparation of a reducing agent A reducing agent is dissolved in a solvent to obtain a reducing agent solution; the solvent is composed of water and an alcohol organic matter in a mass ratio of alcohol organic matter: water = 2-2.5: 7.5-8; Step three: reduction The reducing agent solution is added to the raw material solution in a mass ratio of reducing agent: iridium = 2-4: 1, and stirring is performed, until the reaction is completed; the mixed solution after the reaction is used; the temperature of the reduction is controlled to be 20-50 DEG C; Step four: sedimentation The mixed solution after the reaction is left to stand, and then solid-liquid separation is performed; the solid is dried to obtain a three-dimensional porous network structure nanometer iridium / iridium oxide catalyst; In step four, the standing time is greater than or equal to 6 h; In step four, the solid-liquid separation is performed by centrifugation; when the centrifugal separation is performed, the rotation speed is 4000-7000 r / min; In step four, the drying temperature is 40-100 DEG C, and the drying time is 12-24 h.

2. The nano-iridium / iridium oxide composite catalyst of a three-dimensional porous network structure according to claim 1, characterized in that: After compounding with N115 membrane, it constitutes membrane electrode, and the cell voltage of the membrane electrode is ≤1.795V at 2A / cm 2 The cell voltage of the membrane electrode is ≤1.795V at 2A / cm 2 The cell voltage of the membrane electrode is ≤1.795V at 2A / cm 2 The cell voltage of the membrane electrode is ≤1.795V at 2A / cm 2 The cell voltage of the membrane electrode is ≤1.795V at 2A / cm 2 The cell voltage of the membrane electrode is ≤1.795V at 2A / cm 3. The nano Ir / IrOx composite catalyst with three-dimensional porous network structure according to claim 1, characterized in that: The concentration of the reducing agent in the reducing agent solution is 40-65 g / L.

4. The nano Ir / IrOx composite catalyst of three-dimensional porous network structure according to claim 1, characterized in that: The iridium source is a water-soluble iridium salt, and the water-soluble iridium salt is selected from at least one of iridium trichloride, chloroiridic acid and ammonium chloroiridate.

5. The nano Ir / IrOx composite catalyst of three-dimensional porous network structure according to claim 1, characterized in that: In step two, the alcohol organic matter used is composed of ethanol, methanol and ethylene glycol in a mass ratio of 75-85: 7.5-12.5: 7.5-12.5; in the solvent used in step two, the mass ratio of the alcohol organic matter to water is 2:

8.

6. The nano-iridium / iridium oxide composite catalyst of a three-dimensional porous network structure according to claim 1, characterized in that: In step three, the temperature of the reduction is controlled to be 20-50 DEG C; The stirring speed is 400-700 r / min.

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