An iridium manganese oxide catalyst, its preparation method and use

Abstract

This invention relates to the field of water electrolysis for hydrogen production, specifically to an iridium manganese oxide catalyst, its preparation method, and its application. Commercially available iridium dioxide exhibits poor electrocatalytic stability in the OER reaction. To address this problem, this invention provides an iridium manganese oxide catalyst, which is calcined at high temperature using a composite molten salt medium composed of sodium nitrate and potassium hydroxide in a 1:1 mass ratio. The resulting IrMnO catalyst material exhibits a stable potential response during long-term oxygen evolution reaction testing. Chronopotential curves show that the catalyst's potential does not significantly increase during continuous operation, and no obvious activity decay or material dissolution and deactivation occurs, demonstrating superior stability compared to traditional iridium dioxide catalysts.

Description

Technical Field

[0001] This invention relates to the field of water electrolysis for hydrogen production, specifically to an iridium manganese oxide catalyst, its preparation method, and its applications. Background Technology

[0002] Hydrogen energy, as a clean, efficient, and renewable secondary energy carrier, is gradually becoming a key pathway for reshaping the energy structure and achieving deep decarbonization in multiple fields. Among numerous hydrogen production technologies, proton exchange membrane electrolysis (PEMWE) is considered one of the core technologies for green hydrogen production due to its characteristics such as fast dynamic response, high purity of product hydrogen, high operating current density, and good matching with the volatility of renewable energy. It shows broad application prospects in transportation, industry, and power peak shaving.

[0003] The electrode processes in proton exchange membrane (PEMWE) water electrolysis mainly include the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. The anodic OER involves a four-electron transfer process, exhibiting relatively slow reaction kinetics and a high overpotential, making it the main bottleneck limiting the overall hydrogen production efficiency of water electrolysis. Simultaneously, the anode side of the PEMWE operates in a harsh environment of strong acidity and high potential, placing extremely stringent requirements on the corrosion resistance, catalytic activity, and long-term operational stability of the catalytic materials.

[0004] Currently, iridium (Ir) and its oxides have become the mainstream catalysts for the oxygen evolution reaction (OER) at the anode in PEMWE (Potentially Oriented Metal-Enhanced Chemical Reactions) due to their excellent stability and catalytic activity in acidic media. However, iridium reserves in the Earth's crust are very limited and its price is extremely high, resulting in high catalyst material costs and severely restricting the large-scale and commercial application of PEMWE technology. Furthermore, traditional iridium-based catalysts (such as commercially available iridium dioxide) generally suffer from insufficient exposure of active sites, low mass transport efficiency, and susceptibility to dissolution or agglomeration and deactivation at high current densities, further diminishing their value in practical industrial applications.

[0005] Manganese (Mn)-based oxides have attracted considerable attention from researchers in recent years due to their abundant resources and low cost. Combining manganese with iridium to form an iridium-manganese oxide catalyst holds promise for improving catalytic activity and stability by reducing the amount of the precious metal iridium required and leveraging the synergistic effect between the two. Therefore, this invention provides an iridium-manganese oxide catalyst and its preparation method. Through a reasonable raw material ratio and a molten salt-assisted calcination process, a composite material with excellent catalytic performance is obtained, suitable for the oxygen evolution reaction at the anolyte of water electrolysis for hydrogen production. Summary of the Invention

[0006] A problem with existing technologies is that commercially available iridium dioxide exhibits poor electrocatalytic stability in the OER reaction. To address this issue, this invention provides an iridium-manganese oxide catalyst, the preparation method of which includes the following steps: (1) At room temperature, IrCl3 aqueous solution and MnCl2·4H2O aqueous solution were added to the composite molten salt aqueous solution at the same time and mixed and stirred evenly at room temperature to obtain a light red mixed solution. (2) The light red mixed solution was successively dehydrated by rotary evaporation and vacuum dried to obtain the IrMnO precursor; (3) The IrMnO precursor was calcined at high temperature in air to obtain a black calcined product; (4) The black calcined product was successively subjected to dilute sulfuric acid, water and anhydrous ethanol until neutral, and then dried to obtain IrMnO catalyst material, i.e. target product; the composite molten salt in the composite molten salt aqueous solution is a complex formed by NaNO3 and KOH.

[0007] Preferably, in step (1), the mass ratio of IrCl3 to MnCl2·4H2O in the aqueous solution of IrCl3 and the aqueous solution of MnCl2·4H2O is 1:1.

[0008] Preferably, in step (1), the mass ratio of IrCl3 in the aqueous solution of IrCl3 to the mass ratio of the composite molten salt in the aqueous solution of the composite molten salt is 30:400.

[0009] Preferably, the composite molten salt is a compound formed by NaNO3 and KOH in a mass ratio of 1:1.

[0010] Preferably, the calcination temperature in step (3) is 550°C and the calcination time is 2 h.

[0011] Beneficial effects: (1) This invention combines iridium chloride and manganese chloride in a 1:1 mass ratio and uses a molten salt-assisted calcination process (550℃, 2h) to form a composite oxide structure with a small amount of iridium and abundant manganese. Compared with commercial iridium dioxide, this invention significantly reduces the amount of iridium used while maintaining similar catalytic activity, thereby effectively reducing the cost of catalyst materials and facilitating the large-scale promotion of proton exchange membrane water electrolysis technology.

[0012] (2) The present invention uses a composite molten salt medium composed of sodium nitrate and potassium hydroxide in a mass ratio of 1:1 for high-temperature calcination. The resulting IrMnO catalyst material exhibits a stable potential response during long-term oxygen evolution reaction tests. The chronopotential curve shows that the potential of the catalyst does not increase significantly during continuous operation, and there is no obvious activity decay or material dissolution and deactivation. Its stability is better than that of traditional iridium dioxide catalysts.

[0013] (3) The molten salt-assisted calcination method in this invention helps to form a loose and porous structure, promotes the electronic interaction and synergistic effect between iridium and manganese, and improves the dispersion of the active components. The resulting catalytic material exhibits a low overpotential and a high current density in the oxygen evolution reaction, which can meet the requirements of high catalytic efficiency for industrial water electrolysis. Attached Figure Description

[0014] Figure 1 These are TEM images of IrMnO-550, IrMnO-450, and IrMnO-650.

[0015] Figure 2 Comparison of OER electrochemical performance test results for IrMnO-550, IrMnO-450, IrMnO-650, MnO2, and commercial IrO2.

[0016] Figure 3 Comparison of OER electrochemical performance test results for IrMnO-550, IrMnO-NaNO3, and IrMnO-KOH.

[0017] Figure 4 Comparison of OER electrochemical performance test results for IrMnO-550, IrMnO-550 (0.8:1), and IrMnO-550 (1.3:1).

[0018] Figure 5 The IrMnO-550 obtained in Example 1 of this invention, the MnO2 obtained in Comparative Example 5, and commercial IrO2 were respectively tested at 10 mAcm⁻¹. -2 Cyclic stability test data of OER reaction under continuous current density for 500 h.

[0019] Figure 6 : Steady-state polarization curves of PEMWE single cells assembled with IrMnO-550 obtained in Example 1 and commercial IrO2, respectively, measured at 80°C.

[0020] Figure 7 After assembling PEMWE single cells with IrMnO-550 obtained in Example 1 of this invention and commercial IrO2 respectively, at 1.5 A cm⁻¹ -2 Graphs showing long-term stable operation under current density. Detailed Implementation

[0021] The present invention will be described in detail below with reference to embodiments. However, it should be understood that the following embodiments are merely illustrative examples of implementation of the present invention and are not intended to limit the scope of the present invention.

[0022] The Nafion solution used in this invention is Nafion TMPerfluorinated resin solution (D520CS).

[0023] Example 1 An iridium manganese oxide catalyst is prepared by the following method: (1) Weigh 30 mg IrCl3 as iridium source and 30 mg MnCl2·4H2O as manganese source, so that the mass ratio of iridium to manganese is 1:1. Place them in two 50 mL beakers, add 2 mL of deionized water to each, and stir with a magnetic stirrer at room temperature for 15 min until completely dissolved to obtain a uniform iridium precursor solution and manganese precursor solution. (2) Take another 100 mL beaker, weigh 200 mg NaNO3 and 200 mg KOH, add 5 mL deionized water, stir magnetically for 20 min until completely dissolved to obtain a composite molten salt solution; add the prepared iridium precursor solution and manganese precursor solution slowly dropwise to the composite molten salt solution, stir continuously with a magnetic stirrer for 30 min at room temperature to ensure that the components are fully mixed and homogeneous to obtain a light red mixed solution; (3) Transfer the light red mixed solution to a rotary evaporator, set the temperature to 80℃ and the rotation speed to 100 rpm, and evaporate for 30 min until the water is completely evaporated. Transfer it to a vacuum drying oven, set the temperature to 65℃, and dry for 12 h to obtain the IrMnO-550 precursor. (4) Place the IrMnO-550 precursor into a tube furnace and heat it in an air atmosphere at 5°C for 5 min. -1 The heating rate was increased to 550 °C, calcined for 2 h, and then naturally cooled to room temperature to obtain a black calcined product. (5) Transfer the black calcined product to a 50 mL centrifuge tube, add 0.5 M H2SO4, deionized water and anhydrous ethanol, set the speed to 8000 rpm, centrifuge for 5 min, wash alternately 3 times until the washing liquid is neutral, transfer the washed black powder to a drying oven, dry at 65℃ for 12 h, and finally obtain the iridium manganese oxide catalyst, denoted as IrMnO-550.

[0024] Comparative Example 1 is the same as Example 1, except that the calcination temperature in step (4) of Comparative Example 1 is 450°C. The obtained catalyst is denoted as IrMnO-450.

[0025] Comparative Example 2 is the same as Example 1, except that the calcination temperature in step (4) of Comparative Example 2 is 650°C. The obtained catalyst is denoted as IrMnO-650.

[0026] TEM images of IrMnO-550, IrMnO-450, and IrMnO-650 are attached as shown in the instruction manual. Figure 1 As shown.

[0027] Comparative Example 3 is the same as Example 1, except that the amount of MnCl2·4H2O used in Comparative Example 3 is 38 mg. The obtained catalyst is denoted as IrMnO-550 (0.8:1).

[0028] Comparative Example 4 is the same as Example 1, except that the amount of MnCl2·4H2O used in Comparative Example 4 is 23 mg. The obtained catalyst is denoted as IrMnO-550 (1.3:1).

[0029] Comparative Example 5 is the same as Example 1, except that IrCl3 was not added in Comparative Example 5. The obtained catalyst is designated as MnO2.

[0030] Comparative Example 6 is commercial IrO2.

[0031] Comparative Example 7 was the same as Example 1, except that KOH was not added in Comparative Example 7. Instead, 400 mg of NaNO3 was added to 5 mL of deionized water and magnetically stirred for 20 min until completely dissolved. The resulting molten salt solution replaced the composite molten salt solution in Example 1. The obtained catalyst was designated as IrMnO-NaNO3.

[0032] Comparative Example 8 is the same as Example 1, except that NaNO3 was not added in Comparative Example 8. Instead, 400 mg of KOH was added to 5 mL of deionized water and magnetically stirred for 20 min until completely dissolved. The resulting molten salt solution replaced the composite molten salt solution in Example 1. The obtained catalyst is denoted as IrMnO-KOH.

[0033] Performance testing The OER electrochemical performance was tested using a Pine rotating disk electrode apparatus with a three-electrode system. The catalysts obtained in the examples and comparative examples were dispersed in isopropanol to form a slurry droplet, which was then uniformly coated onto a 1cm × 1cm carbon paper to obtain the working electrode (the catalyst loading on the carbon paper was 0.5 mg / cm²). 2 Using an HgSO4 electrode as the reference electrode and a graphite rod electrode as the counter electrode, 0.5 M H2SO4 was used as the acidic electrolyte. The test temperature was 25℃, and the time was 5 mV / s. -1 A linear scan was performed at a specified scan rate. The Tafel slope was calculated using the LSV curve. The test results are shown in the attached manual. Figure 2 , 3 As shown in Figure 4, the image test results show that the initial potential of the working electrode obtained in Example 1 is 1.36 V, and the current density is 10 mA cm⁻¹. -2 The overpotential is only 229 mV, and the Tafel slope is 97 mV dec. -1 The initial potential of the working electrode obtained in Comparative Example 1 was 1.42 V, and the current density was 10 mA cm⁻¹.-2 The overpotential is only 284 mV, and the Tafel slope is 135 mV dec. -1 Instruction manual attached. Figure 5 The IrMnO-550 obtained in Example 1 of this invention, the MnO2 obtained in Comparative Example 5, and commercial IrO2 were respectively tested at 10 mA cm⁻¹. -2 Cyclic stability test data for OER reaction under continuous catalysis at current density for 500 h and 15 h. The image shows that the IrMnO-550 obtained in Example 1 exhibits stable performance at 10 mA cm⁻¹. -2 The IrMnO-550 obtained in Example 1 can operate stably for over 500 hours at a current density without significant potential decay, while the MnO2 and commercial IrO2 obtained in Comparative Example 5 show significant performance decay within 15 hours, indicating that the IrMnO-550 obtained in Example 1 has superior electrocatalytic oxygen evolution cycle stability.

[0034] The starting potential of the working electrode obtained in Comparative Example 2 was 1.4 V, and the current density was 10 mA cm⁻¹. -2 The overpotential is only 253 mV, and the Tafel slope is 129 mV dec. -1 .

[0035] The starting potential of the working electrode obtained in Comparative Example 3 was 1.46 V, and the current density was 10 mA cm⁻¹. -2 The overpotential is only 269 mV, and the Tafel slope is 100 mV dec. -1 .

[0036] The starting potential of the working electrode obtained in Comparative Example 4 was 1.45 V, and the current density was 10 mA cm⁻¹. -2 The overpotential is only 264 mV, and the Tafel slope is 109 mV dec. -1 .

[0037] The starting potential of the working electrode obtained in Comparative Example 5 was 1.49 V, and the current density was 10 mA cm⁻¹. -2 The overpotential is only 420mV, and the Tafel slope is 324mV dec. -1 .

[0038] The starting potential of the working electrode obtained in Comparative Example 6 was 1.41 V, and the current density was 10 mA cm⁻¹. -2 The overpotential is only 276mV, and the Tafel slope is 117mV dec. -1 .

[0039] The starting potential of the working electrode obtained in Comparative Example 7 was 1.43 V, and the current density was 10 mA cm⁻¹. -2 The overpotential is only 270mV, and the Tafel slope is 116mV dec. -1.

[0040] The starting potential of the working electrode obtained in Comparative Example 8 was 1.5 V, and the current density was 10 mA cm⁻¹. -2 The overpotential is only 380mV, and the Tafel slope is 177mV dec. -1 .

[0041] PEMWE test: Membrane electrode assemblies (MEAs) were prepared using the catalyst-coated membrane (CCM) method. IrMnO-550 obtained in Example 1 or commercial IrO2 were used as the anode catalyst, and 40 wt% Pt / C (10 mg Pt / C dissolved in 2 mL isopropanol and 50 μL Nafion solution; Pt / C is a chemical reagent from Sinopharm Group, model SPT-40) was used as the cathode catalyst. First, 8 mg of the anode catalyst was dispersed in a mixed solution of 1600 μL isopropanol and 80 μL Nafion solution, and then sonicated for 1 h to form a uniform dispersion.

[0042] The anodic and cathode catalyst inks were uniformly sprayed onto the Nafion 117 film using a spray gun and then naturally dried at 80°C for 2 hours.

[0043] Both the cathode and anode porous transport layers (PTLs) are made of platinum-plated titanium felt.

[0044] The N117 film coated with the catalyst and the porous transport layer were hot-pressed at 130 °C and 5 MPa for 3 minutes. The catalyst loading of element Ir in the anode was 0.5 mg. Ir cm -2 The catalyst loading of elemental Pt in the cathode is 1.2 mg cm⁻¹. -2 The active surface area of ​​the catalyst on the anode and cathode surfaces is 4 cm². 2 The electrolyzer assembly pressure was maintained at 4 N / m. Test conditions: The proton exchange membrane electrolyzer was operated at 80 °C with a water flow rate of 5 mL / min. -1 Stability was determined by chronopotential method at 1.5 A cm⁻¹ -2 The electrocatalytic performance of IrMnO-550 or commercial IrO2 was evaluated. Test results are shown in the attached instruction manual. Figure 7 As shown. The PEMWE single cell corresponding to IrMnO-550 obtained in Example 1 exhibited a potential decay rate of only 27 μV h after 1000 h of continuous operation. -1 This meets the requirements for long-term industrial operation. However, the performance of a PEMWE single cell corresponding to commercial IrO2 degrades after 142 hours of operation, with a potential decay rate of 1.33 mV / h.

[0045] Instruction manual attached Figure 6 The steady-state polarization curves of the PEMWE single cells corresponding to IrMnO-550 obtained in Example 1 and commercial IrO2 were measured at 80°C (test conditions: polarization curves were recorded in the range of 0~2.2 V, the proton exchange membrane electrolyzer was operated at 80°C, and the water flow rate was 5 mL / min). -1 (The scan rate is 5 mV / s). The figure shows that the PEMWE single cell corresponding to the IrMnO-550 obtained in Example 1 operates at 1 A cm⁻¹. -2 The battery voltage at current density is only 1.68 V, significantly better than commercial IrO2 (at 1 A cm⁻¹). -2 The battery voltage at the current density is 1.762 V.

[0046] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. An iridium manganese oxide catalyst characterized by, The preparation method includes the following steps: (1) At room temperature, IrCl3 aqueous solution and MnCl2·4H2O aqueous solution were added to the composite molten salt aqueous solution at the same time and mixed and stirred evenly at room temperature to obtain a light red mixed solution. (2) The light red mixed solution was successively dehydrated by rotary evaporation and vacuum dried to obtain the IrMnO precursor; (3) The IrMnO precursor was calcined at high temperature in air to obtain a black calcined product; (4) The black calcined product was subjected to dilute sulfuric acid, water and anhydrous ethanol in sequence until it was neutral, and then dried to obtain IrMnO catalyst material; the composite molten salt in the composite molten salt aqueous solution is a compound formed by NaNO3 and KOH.

2. The iridium manganese oxide catalyst of claim 1, wherein, In step (1), the mass ratio of IrCl3 to MnCl2·4H2O in the aqueous solution of IrCl3 and MnCl2·4H2O is 1:

1.

3. The iridium manganese oxide catalyst according to claim 1, characterized in that, In step (1), the mass ratio of IrCl3 in the aqueous solution to the composite molten salt in the aqueous solution is 30:

400.

4. The iridium manganese oxide catalyst according to claim 1, characterized in that, The composite molten salt is a compound formed by NaNO3 and KOH in a mass ratio of 1:

1.

5. The iridium manganese oxide catalyst according to claim 1, characterized in that, The calcination temperature in step (3) is 550℃ and the calcination time is 2 h.

6. A water electrolysis reaction for hydrogen production, characterized in that, The iridium manganese oxide catalyst according to any one of claims 1-5 is used as the electrocatalyst for the oxygen evolution reaction at the anode, and the electrolyte is dilute sulfuric acid.

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