Preparation method of amorphous IrOx / Ru catalyst for PEM water electrolysis to produce hydrogen

Abstract

The present invention relates to the technical field of electrochemical catalysts and aims to provide a method for preparing an amorphous IrOx / Ru catalyst for use in PEM water electrolysis to produce hydrogen. The method comprises the following steps: ultrasonically treating metal ruthenium powder, iridium salt, and isopropyl alcohol, stirring to form a solid suspension, adding sodium nitrate powder and mixing uniformly; heating and stirring in a water bath at a constant temperature until the liquid evaporates to dryness, obtaining a brownish-yellow powder; calcining at 350-450°C, naturally cooling, adding a perchloric acid solution, ultrasonically treating, and centrifuging to obtain a black solid; and centrifuging, washing, and drying to obtain an amorphous IrOx / Ru catalyst. x / Ru catalyst. The catalyst prepared by the present invention exhibits high OER activity and good stability under acidic conditions. The iridium content in the catalyst of the present invention is only 50% of that of commercial IrO2, resulting in a low cost. The catalyst also features a small particle size, uniform distribution of iridium and ruthenium, and low crystallinity. The iridium oxide in the catalyst has a disordered structure, resulting in high catalytic activity.

Description

Technical Field

[0001] The present invention relates to a preparation technology of an electrochemical catalyst, and in particular to a preparation method of an amorphous IrOx / Ru catalyst for producing hydrogen through PEM water electrolysis. Background Art

[0002] The development of renewable green clean energy has gradually become an important issue in the global energy technology revolution. Hydrogen energy is clean and efficient, and its only product is water, with no carbon dioxide emissions. It has the highest mass energy density (1.43x10 7 J / kg), hydrogen is widely considered one of the most ideal forms of energy for the future. Hydrogen is amenable to large-scale storage and has the potential to enable large-scale storage of discontinuous renewable energy sources such as wind and solar power. Water electrolysis is one of the most direct and effective hydrogen production technologies. Proton exchange membrane (PEM) water electrolysis offers advantages such as compact structure, high efficiency, pure water production, fast load response, and a wide regulation range. Compared to traditional alkaline electrolysis, it offers significant advantages, making it one of the most popular mainstream hydrogen production technologies.

[0003] The efficiency of PEM water electrolysis hydrogen production technology relies on two half-reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Currently, under acidic conditions, the HER and OER catalysts rely on traditional platinum- and iridium-based catalysts, respectively. The acidic environment provided by the proton exchange membrane creates a harsh environment for the anode catalyst. Furthermore, the anode reaction kinetics are slow and the oxygen redox equilibrium potential is high. In the complex four-step electron reaction, the energy relationship from OHads to OOHads results in a high activation energy for the oxygen evolution reaction. Since the speed of the anode reaction is largely dependent on the choice of anode catalyst, a suitable anode catalyst can reduce the energy consumption of the anode half-reaction to a certain extent.

[0004] Current research has found that RuO2 has the highest activity among various precious metal catalysts, but RuO2 suffers from poor stability in the complex anode environment of PEM water electrolysis. Other researchers have found that IrO2, while slightly less active, offers greater stability. Currently, IrO2 is the primary catalyst used on the anode side of commercial applications. However, iridium is one of the rarest elements in the Earth's crust, with an average mass fraction of 0.001% in crustal rocks, representing only 1 / 40th and 1 / 10th the reserves of gold and platinum, respectively. If electrolysis technology achieves high market penetration and scale, it will become highly dependent on the demand for iridium, leading to soaring catalyst manufacturing costs.

[0005] Therefore, reducing the iridium content in the anode catalyst of the PEM water electrolysis hydrogen production system is a key issue that needs to be urgently addressed. Summary of the Invention

[0006] The problem to be solved by the present invention is to overcome the deficiencies in the prior art and propose a method for preparing an amorphous IrOx / Ru catalyst for hydrogen production by PEM water electrolysis.

[0007] To solve the technical problem, the solution of the present invention is:

[0008] Provide an amorphous IrO for PEM water electrolysis to produce hydrogen x The preparation method of the Ru catalyst is characterized by comprising the following steps:

[0009] (1) Adding ruthenium powder and iridium salt to a crucible, adding a sufficient amount of isopropyl alcohol, and then ultrasonically treating and magnetically stirring at room temperature to form a solid suspension; adding sodium nitrate (NaNO3) powder to the solid suspension, and magnetically stirring at room temperature to mix uniformly; placing the crucible containing the mixed solution in a water bath and heating at a constant temperature, stirring until the liquid evaporates to obtain a brown-yellow powder;

[0010] The molar ratio of ruthenium metal powder to iridium salt is 2:1, and the mass ratio of iridium salt to sodium nitrate is 1:10.

[0011] (2) The powder obtained by evaporation was calcined at 350-450°C for 30-90 min, cooled naturally to room temperature and then taken out; 10 wt% perchloric acid solution was added and ultrasonicated for 30 min, and then centrifuged to obtain a black solid; after centrifugal washing and drying, amorphous IrO was obtained. x / Ru catalyst.

[0012] As a preferred embodiment of the present invention, in step (1), the iridium salt is any one of the following: iridium trichloride, iridium tetrachloride, and chloroiridic acid.

[0013] As a preferred embodiment of the present invention, in step (1), the sodium nitrate (NaNO3) powder is ground in advance and passed through a 300-mesh sieve.

[0014] As a preferred embodiment of the present invention, in step (1), the ultrasonic treatment and magnetic stirring time are both 60 minutes.

[0015] As a preferred embodiment of the present invention, in step (1), the temperature of the constant temperature water bath is 60-80°C.

[0016] As a preferred embodiment of the present invention, in step (2), the heating rate during calcination is 2 to 8°C / min.

[0017] As a preferred embodiment of the present invention, the centrifugal washing refers to washing with deionized water and ethanol at least four times to remove impurities; the drying treatment refers to placing the washed black solid in a drying oven at 70°C and drying it at a constant temperature for 12 hours.

[0018] The present invention further provides the aforementioned amorphous IrO x The invention discloses a method for applying a Ru / Ru catalyst in PEM water electrolysis hydrogen production, which is to use the catalyst as an anode catalyst to prepare a membrane electrode of a PEM water electrolysis hydrogen production system.

[0019] As a preferred embodiment of the present invention, the method specifically comprises the following steps:

[0020] (1) Proton exchange membrane pretreatment

[0021] First, the proton exchange membrane N117 was cut into appropriate sizes, placed in a 3% hydrogen peroxide solution at 80°C for 1 hour, and then rinsed with deionized water for 5 minutes; then placed in a 0.5M dilute sulfuric acid solution at 80°C for 1 hour, and then rinsed with deionized water for 5 minutes; finally, placed in deionized water at 80°C for 1 hour, and then placed in deionized water at room temperature for storage;

[0022] (2) Catalyst ink configuration

[0023] The catalyst powder: 5%wt Nafion solution: deionized water: isopropanol were placed in a suitable centrifuge tube at a mass ratio of 1:10:25:270 and ultrasonicated for 60 minutes to ensure uniform mixing of the catalyst ink. The anode catalyst was amorphous IrO x / Ru catalyst, and the cathode catalyst was 20%wt Pt / C catalyst;

[0024] (3) Spraying

[0025] The pretreated proton exchange membrane is placed in a drying oven for drying, and then laid flat on a heating table with the temperature set to 80°C; one-third of the total amount of anode catalyst ink is loaded into a spray pen and sprayed on one side of the proton exchange membrane; the gas volume and spraying speed are controlled to ensure uniform thickness of the catalyst layer; after spraying, the filling and spraying operations are repeated until all the anode catalyst ink is used up; then the cathode catalyst is sprayed on the other side of the proton exchange membrane, and the operation method is the same as that on the anode side, and finally a membrane electrode for building a PEM water electrolysis hydrogen production system is obtained.

[0026] Description of the invention principle:

[0027] In order to reduce the amount of precious metal iridium in the catalyst for oxygen evolution reaction at the anode of PEM water electrolysis, it is usually considered to mix other transition metal oxides with iridium oxide to achieve this, but this approach will lead to a decrease in catalyst activity.

[0028] The present invention breaks through the conventional thinking of technicians and instead reduces the amount of precious metal iridium in the catalyst by incorporating metallic ruthenium powder; more importantly, it can utilize the synergistic effect of metallic ruthenium to cause strain in the iridium oxide structure, thereby increasing the active surface area of ​​the catalyst and improving the intrinsic activity of the catalyst's active sites.

[0029] Considering the poor stability of ruthenium oxide in the acidic oxygen evolution reaction, the present invention innovatively proposes: controlling the calcination temperature to no more than 500°C during the catalyst preparation process to avoid the conversion of metallic ruthenium into ruthenium oxide and improve the stability of the catalyst.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. Amorphous IrO prepared by the present invention x The Ru catalyst exhibits high OER activity under acidic conditions, reaching 10 mA / cm 2 The lowest overpotential at the geometric area normalized working current density is only 190mV, which is 50mV lower than that of commercial IrO2; the amorphous IrO prepared by the present invention x The membrane electrode prepared with Ru / Ru catalyst showed good stability in PEM electrolyzer tests.

[0032] 2. Amorphous IrO prepared by the present invention x The iridium content in the / Ru catalyst is only 50% of that in commercial IrO2, which is low in cost and has great potential for application in PEM water electrolysis hydrogen production systems.

[0033] 3. Amorphous IrO provided by the present invention x Transmission electron microscopy (TEM) scanning electron microscopy (TEM) of the iridium / Ru catalyst revealed small particle size, uniform distribution of iridium and ruthenium, and low crystallinity. The absence of distinct rutile diffraction peaks in the X-ray diffraction spectrum also confirmed the disordered structure of the iridium oxide in the catalyst, leading to high catalytic activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Amorphous IrO x / Ru catalyst micromorphology and selected area electron diffraction pattern.

[0035] Among them, (a) and (d) are high-resolution transmission electron microscopy (HRTEM) images of amorphous IrO prepared at 350 °C. x (b) and (e) are morphology and FTF images of amorphous IrO prepared at 400 °C, taken by high-resolution transmission electron microscopy (HRTEM). x(c) and (f) are morphology and FTF images of amorphous IrO prepared at 450 °C, taken by high-resolution transmission electron microscopy (HRTEM). x Morphology and FTF diagram of the Ru / Ru catalyst; the scale in the figure indicates the magnification of the transmission electron microscope;

[0036] Figure 2 Amorphous IrO was obtained by calcining at 350℃, 400℃ and 450℃ for 30min respectively. x / Ru catalyst and commercial IrO2 catalyst obtained by TEM-EDS scanning elemental composition analysis results.

[0037] Figure 3 Amorphous IrO was obtained by calcining at 350℃, 400℃ and 450℃ for 30min respectively. x X-ray diffraction patterns of the Ru / Ru catalyst and the commercial IrO2 catalyst.

[0038] Figure 4 Amorphous IrO was obtained by calcining at 350℃, 400℃ and 450℃ for 30min respectively. x Polarization curve activity test diagram of oxygen evolution reaction of / Ru catalyst and commercial IrO2 catalyst in 0.5M dilute sulfuric acid solution.

[0039] Figure 5 Amorphous IrO was prepared by calcining at 350℃, 400℃ and 450℃ for 30min respectively. x Chronovoltage stability test diagram of membrane electrode prepared with / Ru catalyst and commercial IrO2 catalyst in hydrogen production test in PEM electrolyzer. DETAILED DESCRIPTION

[0040] The present invention will be described in further detail below with reference to the accompanying drawings. It should be noted that the embodiments described below are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0041] The isopropyl alcohol and other reagents in each example were directly purchased from Sinopharm Chemical Reagent Co., Ltd.

[0042] Example 1:

[0043] (1) Weigh 30.32 mg of ruthenium powder and 52.95 mg of iridium trichloride hydrate (chemical formula: IrCl3·3H2O, molecular weight: 353) into a crucible. Then add 15 ml of isopropyl alcohol and ultrasonicate for 60 min. Then stir magnetically in a magnetic stirrer at room temperature for 60 min to form a solid suspension. Grind sodium nitrate (NaNO3) powder and pass it through a 300-mesh sieve. Then add 530 mg of white sodium nitrate (NaNO3) powder to the solid suspension and stir magnetically at room temperature for 60 min to mix thoroughly. Place the crucible containing the mixed solution in a water bath at 60°C, heat it constantly, and stir magnetically until the liquid evaporates to dryness, obtaining a brown powder.

[0044] (2) The brown-yellow powder obtained after evaporating the solution was placed in a high-temperature box furnace, heated to 350°C at a heating rate of 5°C / min, and calcined at a constant temperature for 30 minutes. The powder was then naturally cooled to room temperature and taken out. A 10 wt% perchloric acid solution was added for ultrasonic treatment for 30 minutes, and then a black solid was separated by centrifugation in a high-speed centrifuge. The black solid was then centrifuged four times with deionized water and ethanol to remove impurities. The washed black solid was placed in a drying oven at a constant temperature of 70°C for 12 hours and ground to obtain amorphous IrO x / Ru catalyst, bottled.

[0045] Example 2:

[0046] The constant temperature calcination temperature in Example 1 was changed to 400 °C, and other operations were carried out in accordance with Example 1 to obtain amorphous IrO x / Ru catalyst.

[0047] Example 3:

[0048] The constant temperature calcination temperature in Example 1 was changed to 450 °C, and other operations were referred to Example 1 to obtain amorphous IrO x / Ru catalyst.

[0049] Embodiment 4:

[0050] The iridium salt in Example 1 was replaced with 50.1 mg of iridium tetrachloride (molecular formula IrCl4, molecular weight 334), the mass of sodium nitrate powder was changed to 501 mg, and the other operations were carried out in accordance with Example 1 to obtain amorphous IrO x / Ru catalyst.

[0051] Example 5:

[0052] The iridium salt in Example 1 was replaced with 77.25 mg of chloroiridic acid (molecular formula Cl6H 14 IrO6, molecular weight is 515), the mass of sodium nitrate powder is changed to 773 mg, and other operations are referred to Example 1 to prepare amorphous IrO x / Ru catalyst.

[0053] Example 6:

[0054] A brown powder was obtained according to step (1) of Example 1, placed in a high-temperature box furnace, heated to 350°C at a heating rate of 2°C / min, and calcined at 350°C for 30 min. Other operations were carried out in accordance with Example 1 to obtain amorphous IrO x / Ru catalyst.

[0055] Example 7:

[0056] A brown powder was obtained according to step (1) of Example 1, placed in a high-temperature box furnace, heated to 350°C at a heating rate of 8°C / min, and calcined at 350°C for 30 min. Other operations were carried out in accordance with Example 1 to obtain amorphous IrO x / Ru catalyst.

[0057] Example 8:

[0058] A brown powder was obtained according to step (1) of Example 1, placed in a high-temperature box furnace, heated to 350°C at a heating rate of 5°C / min, and calcined at 350°C for 60 min. Other operations were carried out in accordance with Example 1 to obtain amorphous IrO x / Ru catalyst.

[0059] Example 9:

[0060] A brown powder was obtained according to step (1) of Example 1, placed in a high-temperature box furnace, heated to 350°C at a heating rate of 5°C / min, and calcined at 350°C for 90 min. Other operations were carried out in accordance with Example 1 to obtain amorphous IrO x / Ru catalyst.

[0061] Embodiment 10:

[0062] The water bath constant temperature in Example 1 was changed from 60°C to 70°C, and other operations were performed in accordance with Example 1 to obtain amorphous IrO x / Ru catalyst.

[0063] Example 11:

[0064] The water bath constant temperature in Example 1 was changed from 60°C to 80°C, and other operations were performed in accordance with Example 1 to obtain amorphous IrO x / Ru catalyst.

[0065] Preparation of membrane electrode:

[0066] According to the following steps, amorphous IrO x / Ru catalyst to prepare membrane electrode for PEM electrolyzer:

[0067] (1) Proton exchange membrane pretreatment

[0068] First, the proton exchange membrane N117 was cut into appropriate sizes, placed in a 3% hydrogen peroxide solution at 80°C for 1 hour, and then rinsed with deionized water for 5 minutes; then placed in a 0.5M dilute sulfuric acid solution at 80°C for 1 hour, and then rinsed with deionized water for 5 minutes; finally, placed in deionized water at 80°C for 1 hour, and then placed in deionized water at room temperature for storage;

[0069] (2) Catalyst ink configuration

[0070] The catalyst powder: 5%wt Nafion solution: deionized water: isopropanol were placed in a suitable centrifuge tube at a mass ratio of 1:10:25:270 and ultrasonicated for 60 minutes to ensure uniform mixing of the catalyst ink. The anode catalyst was amorphous IrO x / Ru catalyst, and the cathode catalyst was 20%wt Pt / C catalyst;

[0071] (3) Spraying

[0072] After drying the pretreated proton exchange membrane in a drying oven, lay it flat on a heating platform set to 80°C. One-third of the total anode catalyst ink is loaded into a spray gun and sprayed on one side of the proton exchange membrane. The air volume and spraying speed are controlled to ensure a uniform catalyst layer thickness. After spraying, the loading and spraying operations are repeated until all the anode catalyst ink is used up. The cathode catalyst is then sprayed on the other side of the proton exchange membrane, following the same procedures as for the anode side. This membrane electrode is then used to construct a PEM water electrolysis hydrogen production system.

[0073] Performance testing method:

[0074] Take the amorphous IrO prepared in Example 1-3 x / Ru catalyst, and prepare a membrane electrode according to the aforementioned exemplary steps.

[0075] Then, referring to the records in the public document "Synthesis and characterization of electrocatalysts for the oxygen evolution in PEM water electrolysis", a three-electrode test system was built to conduct polarization curve activity tests, and a catalyst constant current timing voltage stability test was carried out in the PEM electrolyzer test platform.

[0076] Specific test conditions:

[0077] Polarization curve activity test: the electrolyte solution is 0.5M dilute sulfuric acid solution, and the catalyst loading is 0.3mg / cm 2 , the reaction temperature was 25 °C, and the polarization curve scan rate was 5 mV / s;

[0078] Constant current and time voltage stability test: the electrolyte is deionized water, and the membrane electrode anode catalyst loading is 2 mg / cm 2 , cathode catalyst 20%wtPt / C catalyst, loading amount is 1mg / cm 2 , operating temperature is 80℃, current density is 2A / cm 2 , timing time is 3600s.

[0079] The polarization curve test results of Examples 1-3 of the present invention are as follows: Figure 4 As shown, corresponding to curves b, c, and d, respectively, the constant current timing voltage curves of Examples 1-3 are as follows Figure 5 As shown, they correspond to curves b, c, and d respectively.

[0080] Comparative Example:

[0081] Commercial IrO2 (Ir≥84.5%) with a purity of 99.99% was purchased from McLean Company as the control group of this application. Performance tests were carried out according to the aforementioned membrane electrode preparation, three-electrode test system construction, and activity and stability evaluation methods, and polarization curves and constant current voltage timing curves were plotted, which are respectively Figure 4 a and Figure 5 a.

[0082] Comparative test and results:

[0083] The technical effects of the present invention will be further described below with reference to the accompanying drawings.

[0084] According to the test results, it can be found that the amorphous IrO prepared according to Examples 1-3 x / Ru catalyst has higher OER activity and stability than commercial IrO2 with a purity of 99.99%. In the same polarization curve activity test, amorphous IrO x / Ru catalyst reaches 10mA / cm 2 The lowest overpotential is only 190mV when the geometric area normalized current density is used, while the overpotential required for commercial IrO2 is 240mV, and the overpotential decreases by 50mV. Moreover, as the voltage increases, the amorphous IrO x / Ru catalyst increases the current density faster. In the constant current and time voltage test of PEM electrolyzer, amorphous IrO x The membrane electrode prepared with / Ru catalyst requires a lower operating voltage and the voltage rise is smaller after 1 hour.

[0085] From the EDS element scanning composition analysis results, it can be seen that amorphous IrO x The iridium content in the / Ru catalyst is only 42.63% to 44.45%, which is only about 50% of that in commercial IrO2. The rest is metallic ruthenium, which is much more expensive than metallic iridium, and the catalyst cost is greatly reduced.

[0086] The embodiments described above illustrate the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Amorphous IrO for PEM water electrolysis to produce hydrogen x A method for preparing a Ru catalyst, characterized in that: The following steps are involved: (1) Add ruthenium powder and iridium salt to a crucible, then add sufficient isopropyl alcohol, and after ultrasonic treatment, magnetic stirring is performed at room temperature to form a solid suspension; sodium nitrate powder is added to the solid suspension, and magnetic stirring is performed at room temperature to mix uniformly; the crucible containing the mixed solution is placed in a water bath and heated at a constant temperature, stirring until the liquid evaporates to obtain a brown-yellow powder; The molar ratio of ruthenium metal powder to iridium salt is 2:1, and the mass ratio of iridium salt to sodium nitrate is 1:

10. (2) The powder obtained by evaporation was calcined for 30-90 min, and the calcination temperature was controlled at 350-450 °C to avoid the conversion of metallic ruthenium into ruthenium oxide; after cooling naturally to room temperature, it was taken out, added with 10 wt% perchloric acid solution and ultrasonically treated for 30 min, and centrifuged to obtain a black solid; after centrifugal washing and drying, amorphous IrO was obtained. x / Ru catalyst.

2. The method according to claim 1, characterized in that In the step (1), the iridium salt is any one of the following: iridium trichloride, iridium tetrachloride, and chloroiridic acid.

3. The method according to claim 1, characterized in that In the step (1), the sodium nitrate powder is ground in advance and passed through a 300-mesh sieve.

4. The method according to claim 1, wherein In the step (1), the ultrasonic treatment and magnetic stirring time are both 60 minutes.

5. The method according to claim 1, wherein In the step (1), the temperature of the constant temperature water bath is 60-80°C.

6. The method according to claim 1, characterized in that In the step (2), the heating rate during calcination is 2-8°C / min.

7. The method according to claim 1, characterized in that The centrifugal washing refers to washing with deionized water and ethanol at least four times in succession to remove impurities; the drying treatment refers to placing the washed black solid in a drying oven at a constant temperature of 70° C. and drying for 12 hours.

8. The amorphous IrO according to claim 1 x The method for using a Ru catalyst in PEM water electrolysis to produce hydrogen is characterized in that: The catalyst is used as an anode catalyst to prepare a membrane electrode of a PEM water electrolysis hydrogen production system.

9. The method according to claim 8, characterized in that The method specifically comprises the following steps: (1) Proton exchange membrane pretreatment First, the proton exchange membrane N117 was cut into appropriate sizes, placed in a 3% hydrogen peroxide solution at 80°C for 1 hour, and then rinsed with deionized water for 5 minutes; then placed in a 0.5M dilute sulfuric acid solution at 80°C for 1 hour, and then rinsed with deionized water for 5 minutes; finally, placed in deionized water at 80°C for 1 hour, and then placed in deionized water at room temperature for storage; (2) Catalyst ink configuration The catalyst powder: 5%wt Nafion solution: deionized water: isopropanol were placed in a suitable centrifuge tube at a mass ratio of 1:10:25:270 and ultrasonicated for 60 minutes to ensure uniform mixing of the catalyst ink. The anode catalyst was amorphous IrO x / Ru catalyst, and the cathode catalyst was 20%wt Pt / C catalyst; (3) Spraying The pretreated proton exchange membrane is placed in a drying oven for drying, and then laid flat on a heating table with the temperature set to 80°C; one-third of the total amount of anode catalyst ink is loaded into a spray pen and sprayed on one side of the proton exchange membrane; the gas volume and spraying speed are controlled to ensure uniform thickness of the catalyst layer; after spraying, the filling and spraying operations are repeated until all the anode catalyst ink is used up; then the cathode catalyst is sprayed on the other side of the proton exchange membrane, and the operation method is the same as that on the anode side, and finally a membrane electrode for building a PEM water electrolysis hydrogen production system is obtained.

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