Anion exchange membrane oxygen evolution reaction catalyst and preparation method thereof

Abstract

The application discloses an anion exchange membrane oxygen evolution reaction catalyst and a preparation method thereof. The method comprises the following steps: preparing a water / isopropyl alcohol binary mixed solution containing a nickel salt, an iron salt and ammonium fluoride as solution A; preparing a water / isopropyl alcohol binary mixed solution containing potassium hydroxide and potassium carbonate as solution B; under normal pressure, 25 DEG C and stirring, solution B is added into solution A at a constant speed, and after aging, solid-liquid separation, washing and drying, a NiFe-based layered double hydroxide oxygen evolution catalyst is obtained. Through the synergistic effect of the water / isopropyl alcohol binary solvent, NH4F regulation and KOH / K2CO3 compound alkali source, controllable co-precipitation under normal pressure and low temperature is realized, the obtained catalyst has loose morphology, rich active sites and excellent charge transport performance. The method has simple process, easy-to-control parameters and clear amplification path, and the prepared catalyst is used for anion exchange membrane water electrolysis anode oxygen evolution reaction, and has low overpotential and high stability.

Description

Technical Field

[0001] This invention belongs to the field of oxygen evolution reaction catalyst technology, and particularly relates to an anion exchange membrane oxygen evolution reaction catalyst and its preparation method. Background Technology

[0002] Anion exchange membrane electrolysis for hydrogen production (AEMWE) uses anion exchange membranes as the electrolyte separator to achieve ion conduction and gas isolation in alkaline / weakly alkaline environments. It is considered to combine the potential advantages of traditional alkaline electrolysis and proton exchange membrane electrolysis (PEMWE): compared to liquid alkaline systems, it is expected to reduce the engineering complexity caused by electrolyte management and corrosion; compared to PEMWE, it has the potential to reduce dependence on precious metal catalysts and titanium-based materials, thereby promoting a low-cost, high-power-density, and scalable green hydrogen production route. However, in actual operation, AEMWE still faces challenges in the chemical stability and mechanical durability of the membrane and ionomers under strongly alkaline / high-current conditions, as well as the limitations of electrode structure and mass transfer management on high current efficiency. These factors collectively affect the electrolyzer's efficiency, lifespan, and consistency.

[0003] In AEMWE, the oxygen evolution reaction (OER) at the anolyte is a slow-kinetic process involving multi-electron coupling and transfer, often resulting in voltage loss and energy consumption in the main electrolytic cell. Therefore, highly active and long-life oxygen evolution catalysts and electrode configurations are crucial. Systems represented by non-noble metal catalysts such as NiFe-LDH (layered double hydroxide) have advantages such as tunable composition, low cost, and easy formation of active (oxygen) hydroxyl phases under alkaline conditions, making them an important direction for replacing Ir / Ru. However, existing systems also have prominent problems: insufficient intrinsic conductivity of the materials leads to limited charge transport at high current densities; insufficient three-phase interface construction of powder catalysts in MEAs; and ionomer coating and pore blockage can easily lead to hindered mass transfer and bubble desorption. Long-term operation may also lead to failure modes such as excessive structural reconstruction, metal dissolution / migration, catalyst layer detachment, and membrane / ionomer interface degradation, making it difficult to directly translate "high activity of laboratory three electrodes" into "high performance and long life at the device level". Summary of the Invention

[0004] In view of the above-mentioned defects of the prior art, the purpose of this invention is to provide a method for synthesizing NiFe-based basal double hydroxide catalysts suitable for the preparation of electrode materials for the oxygen evolution reaction of anion exchange membrane water electrolysis. This method should achieve controllable co-precipitation under normal pressure and low temperature conditions, taking into account the tunability of material structure, batch consistency and feasibility of scale-up preparation, thereby overcoming the problems of difficult morphology control, severe agglomeration, difficulty in scale-up and "difficulty in converting powder activity to device-level performance" in the preparation of existing LDH materials.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a catalyst, comprising the following steps: (1) Prepare metal salt solution A, wherein solution A contains nickel salt, iron salt, ammonium fluoride and water / isopropanol binary mixed solvent; (2) Prepare compound alkaline source solution B, wherein solution B contains potassium hydroxide, potassium carbonate and water / isopropanol binary mixed solvent; (3) Under normal pressure, 25°C and stirring conditions, solution B is added dropwise to solution A at a constant rate. After the addition is completed, stirring is continued to obtain a reaction slurry. (4) The slurry obtained from the reaction is subjected to solid-liquid separation, washing and drying to obtain NiFe base layer double hydroxide oxygen evolution catalyst.

[0006] In some embodiments, the volume ratio of deionized water to isopropanol in the water / isopropanol binary mixed solvent is 1:4 to 4:1, preferably 4:1.

[0007] In some embodiments, the molar ratio of Ni:Fe in the nickel salt and iron salt is 1:1 to 4:1, preferably 3:1.

[0008] In some embodiments, the amount of ammonium fluoride added to solution A is 1.25 to 4 times, preferably 1.25 times, relative to the total molar amount of nickel salt and iron salt.

[0009] In a preferred embodiment, the volume ratio of deionized water to isopropanol in the water / isopropanol binary mixed solvent is 4:1, the molar ratio of Ni:Fe in the nickel salt and iron salt is 3:1, and the amount of ammonium fluoride added in solution A is 1.25 times the total molar amount of nickel salt and iron salt.

[0010] In some embodiments, the molar ratio of potassium hydroxide to potassium carbonate is 24:16.

[0011] In some embodiments, solution B is added to solution A at a rate of 0.5 r / min, the stirring speed is 1000 r / min, and the stirring time after the addition is completed is 30 min.

[0012] In a second aspect, the present invention provides a catalyst obtained by the above-described preparation method.

[0013] In some embodiments, the catalyst is a NiFe-based basal double hydroxide having at least one of the following characteristics: (a) The XRD pattern shows characteristic diffraction peaks at 11.5°, 23.2°, and 34.5°; (b) SEM images show a loose, thin, layered structure with a layer thickness of 10-30 nm; (c) In 1 M KOH electrolyte, 100 mA / cm 2 The overpotential at current density is not higher than 300 mV.

[0014] In a third aspect, the present invention provides the application of the catalyst in the preparation of anion exchange membrane electrolysis anode materials or membrane electrode assemblies for hydrogen production.

[0015] Technical effect

[0016] This invention provides a method for preparing NiFe-based layered double hydroxide (LDH) materials. The method employs a water / isopropanol mixed solvent system, where a metal salt solution (solution A) and a compounded alkali source solution (solution B) are prepared separately. Solution B is then added dropwise to solution A at a constant rate using a metering pump, achieving controlled co-precipitation under ambient temperature and pressure. Compared to the hexane / isopropanol / water microemulsion soft template system, this invention does not rely on the microemulsion phase structure and a large amount of organic phase, but instead uses a water / isopropanol binary system that is more conducive to scale-up and process control. It exhibits significant differences in raw material system, reaction environment, process control method, and end application.

[0017] This invention successfully prepared NiFe-based layered double hydroxide (LDH) materials through the synergistic effect of a combined process involving a Ni / Fe metal system, a water / isopropanol binary solvent, NH4F regulation, a KOH / K2CO3 compound alkali source, and unidirectional low-speed drop-addition-ripening. Firstly, NiFe-LDH, as an OER precursor / catalyst material, differs from MgAl or MgAlSn adsorbents in terms of metal chemical environment, nucleation-growth behavior, and final application requirements. Furthermore, the Ni / Fe system is more prone to rapid hydrolysis, localized supersaturated precipitation, and non-uniform reconstruction under alkaline conditions. Using existing adsorbent preparation routes easily leads to uneven Ni / Fe distribution, particle agglomeration, lamellar stacking, and insufficient exposure of electrocatalytic active sites. Secondly, the water / isopropanol binary mixed solvent can improve wettability, dispersibility, and mass transfer environment while ensuring the operability of the inorganic salt system. Compared with the pure water system, it is more conducive to suppressing local transient nucleation and hard particle aggregation. Compared with the n-hexane / isopropanol / water microemulsion system, it does not rely on microemulsion droplet size, phase window, and a large amount of organic solvent to maintain the template structure, making the process simpler and reducing the engineering requirements for stirring, heat transfer, phase stability, and solvent recovery during scale-up. Thirdly, the OH- in the compound alkali source is used to provide the alkalinity required for the precipitation reaction, and CO3... 2- It helps to regulate the interlayer environment and the stability of the precipitation process, while NH4F can further affect crystal growth and lamellar morphology, thus making the obtained material more suitable for subsequent construction of AEMWE anode catalyst layer.

[0018] The equipment required for this invention is conventional laboratory and industrial-grade equipment, including a stirred reactor, a metering pump dripping system, a solid-liquid separation device (centrifuge or filtration), a washing unit, and a vacuum drying device. The equipment is highly versatile and easily implemented in existing powder material or catalyst production lines. Compared to routes using n-hexane / isopropanol / water reverse-phase surfactant-free microemulsions combined with high-speed centrifugation, this invention avoids scale-up obstacles such as large-volume organic phase involvement, microemulsion phase window control, flammable solvent recycling, and high-speed centrifugation. It is more suitable for transferring small-scale systems to jacketed stirred tanks and further using semi-continuous or continuous dripping reaction modes to achieve increased production capacity. Compared to constant pH dual-dropping control, this invention uses a combination of unidirectional metering dripping and a preset formulation, which simplifies control logic and reduces the difficulty of online adjustment during scale-up while ensuring critical process windows. The raw materials are all common chemical products with a stable supply chain, facilitating large-scale procurement and cost accounting.

[0019] This invention addresses the application requirements of AEMWE anode OER by constructing a NiFe-based catalytic material synthesis route that differs from existing methods for preparing LDH materials for pollutant adsorption. This route offers advantages such as atmospheric pressure operation, low energy consumption, simple process, easy parameter control, and a clear scale-up path. Attached Figure Description

[0020] Figure 1 XRD analysis chromatograms of LDH synthesized in Example 2 with different water:isopropanol volume ratios; Figure 2 SEM images of LDH synthesized in Example 2 at water:isopropanol ratios of (a) 1:4, (b) 2:3, (c) 3:2, and (d) 4:1. Figure 3 The following are the LSV analysis chromatograms (a) and (b) 100 mA / cm² of the samples synthesized in Example 2 at different water:isopropanol ratios. 2 Overpotential, (c) Tafel slope, (d) EIS analysis plot; Figure 4 The image shows the XRD analysis results of LDH synthesized under different nickel-iron atomic ratios in Example 3. Figure 5 SEM images of LDH synthesized under different nickel-iron atomic ratios in Example 3: (a) pure Ni, (b) Ni:Fe=1:1, (c) Ni:Fe=2:1, (d) Ni:Fe=3:1, and (e) Ni:Fe=4:1. Figure 6 (a) LSV analysis chromatogram and (b) 100 mA / cm² of the synthesized samples under different nickel-iron atomic ratios in Example 3. 2 Overpotential, (c) Tafel slope, (d) EIS analysis plot; Figure 7 The image shows the XRD analysis of LDH synthesized under different proportions of ammonium fluoride used in Example 4. Figure 8 SEM images of LDH synthesized in Example 4 with ammonium fluoride usage of (a) 10 mmol, (b) 15 mmol, (c) 20 mmol, and (d) 25 mmol. Figure 9 (a) LSV analysis chromatogram and (b) 100 mA / cm² of the synthesized samples with different amounts of ammonium fluoride used in Example 4. 2 Overpotential, (c) Tafel slope, (d) EIS analysis plot; Figure 10 The images show the XRD patterns of the LDH samples synthesized in Examples 1 and 5 on an equal scale. Figure 11 SEM images of LDH samples synthesized in Example 1 (a) and Example 5 (b) at an equal scale. Figure 12 (a) LSV analysis diagram, (b) Tafel slope diagram, (c) double layer capacitance diagram, and (d) EIS analysis diagram of the LDH samples obtained by equivalent scale-up synthesis in Examples 1 and 5; Figure 13 The graph shows the performance of the electrolytic cell constant potential test in Example 6. Detailed Implementation

[0021] The embodiments of the present invention are described below with reference to the accompanying drawings to make the technical content clearer and easier to understand. The present invention can be embodied in many different forms, and the scope of protection of the present invention is not limited to the embodiments mentioned herein.

[0022] Example 1

[0023] This embodiment provides a method for preparing NiFe-based oxygen evolution catalyst powder, including the following steps: (1) Preparation of solution A: Measure 36 mL of deionized water and 24 mL of isopropanol using a 50 mL graduated cylinder, pour them into a 100 mL beaker, add a magnetic stir bar, and mix thoroughly by magnetic stirring for 5 min. Weigh 6 mmol Ni(NO3)2·6H2O, 2 mmol Fe(NO3)3·9H2O, and 10 mmol NH4F and add them to the above mixed solvent. Mix under magnetic stirring for 10 min to prepare solution A.

[0024] (2) Preparation of solution B: Measure 24 mL of deionized water and 16 mL of isopropanol using a 50 mL graduated cylinder, pour them into a 50 mL beaker, add a magnetic stir bar, and stir magnetically for 5 min to mix evenly. Weigh 24 mmol KOH and 16 mmol K2CO3 and add them to the above mixed solvent. Continue stirring under magnetic stirring for 10 min until homogeneous to obtain solution B.

[0025] (3) Drop reaction: Pour solution A into a 100 mL flask, add a magnetic stir bar, place it on a hydrothermal stirring table, and stir at 25 ℃ and 1000 r / min; slowly add solution B to solution A at a rate of 0.5 r / min using a peristaltic pump until solution B is completely added, and continue stirring for 30 min until the reaction is complete to obtain a reaction slurry (the whole process takes about 7 hours).

[0026] (4) Washing and drying: After the reaction is completed, the solid product is separated and washed three times with deionized water and three times with ethanol. The washed solid is placed in a vacuum drying oven and dried for 24 h to obtain NiFe-based oxygen evolution reaction catalyst powder.

[0027] Example 2

[0028] NiFe-based oxygen evolution reaction catalyst powder (LDH) was prepared using the same method as in Example 1, except that in step (1), the volume ratios of deionized water and isopropanol were 1:4, 2:3, 3:2, and 4:1, respectively, while keeping the total volume of deionized water and isopropanol constant. The XRD and SEM images of the synthesized LDH are shown below. Figure 1 and 2 As shown.

[0029] The electrochemical performance of the synthesized LDH catalyst was tested using the Shanghai Chenhua electrochemical workstation. The test was conducted in a three-electrode system, with the catalyst-supported electrode as the working electrode, the Hg / HgO electrode as the reference electrode, and the Pt sheet as the counter electrode. The electrolyte was a 1.0 mol / L KOH solution. High-purity nitrogen was purged before the test to remove oxygen. All potentials were converted to RHE.

[0030] Polarization curves were obtained using linear sweep voltammetry (LSV) at a scan rate of 5 mV / s. Figure 3 a), and iR compensation is performed; the current density of 100 mA / cm² is extracted from the polarization curve. 2 The corresponding potential and overpotential are calculated. Figure 3 b); The Tafel slope is obtained by fitting the Tafel curve (η = b log j + a) based on the LSV data. Figure 3c), used to evaluate reaction kinetics; simultaneously, electrochemical impedance spectroscopy (EIS) was used for testing in the frequency range of 100 kHz–0.01 Hz under 5 mV AC perturbation conditions. Figure 3 d) The charge transfer resistance and interface charge transport performance are analyzed using Nyquist plots.

[0031] Example 3

[0032] NiFe-based oxygen evolution reaction catalyst powder was prepared using the same method as in Example 1, except that in step (1), while keeping the total molar amount of metal ions constant, the atomic ratios of Ni:Fe were pure Ni, Ni:Fe=1:1, Ni:Fe=2:1, Ni:Fe=3:1, and Ni:Fe=4:1. The XRD and SEM images of the synthesized LDH are shown below. Figure 4 and 5 As shown; the LSV analysis chromatogram of the synthesized LDH was obtained by testing using the same method as in Example 2. Figure 6 a) 100mA / cm 2 Overpotential ( Figure 6 b) Tafel slope ( Figure 6 c) EIS analysis Figure 6 d) such as Figure 6 As shown.

[0033] Example 4

[0034] NiFe-based oxygen evolution reaction catalyst powder was prepared using the same method as in Example 1, except that the amount of NH4F added in step (1) was 10 mmol, 15 mmol, 20 mmol, and 25 mmol, respectively. The XRD and SEM images of the synthesized LDH are shown below. Figure 7 and 8 As shown; the LSV analysis chromatogram of the synthesized LDH was obtained by testing using the same method as in Example 2. Figure 9 a) 100mA / cm 2 Overpotential ( Figure 9 b) Tafel slope ( Figure 9 c) EIS analysis Figure 9 d) such as Figure 9 As shown.

[0035] Depend on Figures 1-9It is evident that NiFe-LDH exhibits optimal electrochemical performance under the conditions of water:isopropanol = 4:1, NH4F = 20 mmol, and Ni:Fe = 3:1. This is because the three components achieve synergistic optimization: an appropriate amount of isopropanol regulates the reaction rate and forms a loose, thin-layer structure, increasing the specific surface area and ion transport efficiency; 20 mmol of NH4F effectively regulates crystal growth and introduces appropriate defects, increasing active sites while maintaining structural stability; and the Ni:Fe = 3:1 ratio ensures that Ni is the main active center while promoting charge transfer and reaction kinetics through Fe regulation of the electronic structure. The combined effect of these three factors achieves an optimal balance between structural openness, active site density, and electrical conductivity, resulting in superior electrochemical performance.

[0036] When the three factors deviate from the optimal ratio, the performance of NiFe-LDH will decline due to the imbalance of structure and electronic properties: Too low a concentration of isopropanol in the water:isopropanol ratio leads to excessively fast reaction, dense structure, and limited specific surface area and ion transport, while too high a concentration results in insufficient nucleation, loose structure, and decreased stability; Too low a concentration of NH4F results in insufficient defects and active sites, while too high a concentration leads to excessive etching, damage to structural stability, and potential reduction in conductivity; Too low a concentration of Ni in the Ni:Fe ratio reduces the main active sites and decreases catalytic activity, while too high a concentration lacks Fe's regulation of the electronic structure, leading to poorer charge transfer and reaction kinetics. Therefore, only when the three factors are in a moderate ratio can the optimal balance be achieved between structural openness, active site density, and electrical conductivity.

[0037] Example 5

[0038] The raw material dosage and solvent volume of Example 1 were scaled up threefold. The reaction, washing, and drying were carried out while maintaining key process conditions such as 25 °C, 1000 r / min stirring, and slow dripping using a peristaltic pump. This scale-up was used to verify the process stability and product consistency of the method under increased feed scale conditions.

[0039] The XRD and SEM images of the LDH synthesized in Examples 1 and 5 are shown below. Figure 10 and Figure 11 As shown. The same method as in Example 2 was used for testing, and the LSV analysis chromatogram of the synthesized LDH was obtained ( Figure 12 a) 100mA / cm 2 Overpotential ( Figure 12 b) Tafel slope ( Figure 12 c) EIS analysis Figure 12 d) such as Figure 12 As shown.

[0040] The combined structural characterization and electrochemical performance results show that after scaling up the reaction ratio (three-fold increase), the crystal structure of the material remains stable, with no new impurity phases or significant structural damage. Although the morphology shows some degree of loosening, it still maintains typical layered characteristics. The electrocatalytic performance (polarization curve, Tafel slope, capacitance, and impedance) changes little, and the performance differences are not significant. This indicates that the scale-up process has good process stability and product consistency, and no significant performance defects were introduced during the scaling-up process, demonstrating feasibility for further scale-up and practical application.

[0041] Example 6 (Electrolyzer Test)

[0042] The catalyst sample synthesized in Example 1 was used to prepare a membrane electrode assembly (MEA) using the CCM (Catalyst Coated Membrane) method. Specifically, the catalyst was uniformly coated onto the surface of an ion exchange membrane to form a catalytic layer structure. Subsequently, a hot-pressing treatment was performed at 80 °C and 5 MPa for 30 min to enhance the interfacial bonding strength between the catalytic layer and the membrane, resulting in a structurally stable MEA assembly. During the assembly of the electrolyzer, nickel was selected as the anode plate, titanium as the cathode plate, and nickel foam was used as the gas diffusion layer to improve gas transport efficiency and the effective utilization rate of the reaction interface.

[0043] In the electrochemical performance test, the assembled electrolytic cell was placed at an operating temperature of 80 °C and subjected to 1 mol·L⁻¹ hydrochloric acid. -1 KOH solution was used as the electrolyte for alkaline water electrolysis tests. -2 The system was subjected to constant current testing using the initial current density as the basis, and the results are as follows: Figure 13 As shown.

[0044] according to Figure 13 The test results shown indicate that after 100 hours of continuous operation, the performance retention rate of the electrolyzer is approximately 82%, demonstrating that the prepared membrane electrode has good stability and durability, and can maintain high water electrolysis performance even under long-term operating conditions.

Claims

1. A method for preparing a catalyst, comprising the following steps: (1) Prepare metal salt solution A, wherein solution A contains nickel salt, iron salt, ammonium fluoride and water / isopropanol binary mixed solvent; (2) Prepare compound alkaline source solution B, wherein solution B contains potassium hydroxide, potassium carbonate and water / isopropanol binary mixed solvent; (3) Under normal pressure, 25°C and stirring conditions, solution B is added dropwise to solution A at a constant rate. After the addition is completed, stirring is continued to obtain a reaction slurry. (4) The slurry obtained from the reaction is subjected to solid-liquid separation, washing and drying to obtain NiFe base layer double hydroxide oxygen evolution catalyst.

2. The preparation method according to claim 1, wherein, The volume ratio of deionized water to isopropanol in the water / isopropanol binary mixed solvent is 1:4 to 4:

1.

3. The preparation method according to claim 1, wherein, The volume ratio of deionized water to isopropanol in the water / isopropanol binary mixed solvent is 4:

1.

4. The preparation method according to claim 1, wherein, The molar ratio of Ni:Fe in the nickel salt and iron salt is 1:1 to 4:

1.

5. The preparation method according to claim 1, wherein, Compared to the total molar amount of nickel and iron salts, the amount of ammonium fluoride added to solution A is 1.25 to 4 times.

6. The preparation method according to claim 1, wherein, The volume ratio of deionized water to isopropanol in the water / isopropanol binary mixed solvent is 4:1, the molar ratio of Ni:Fe in the nickel salt and iron salt is 3:1, and the amount of ammonium fluoride added in solution A is 1.25 times the total molar amount of nickel salt and iron salt.

7. The preparation method according to claim 1, wherein, The molar ratio of potassium hydroxide to potassium carbonate is 24:

16.

8. The preparation method according to claim 1, wherein, The rate at which solution B is added to solution A is 0.5 r / min, the stirring speed is 1000 r / min, and the stirring time after the addition is completed is 30 min.

9. The catalyst obtained by the preparation method according to any one of claims 1-8.

10. The application of the catalyst according to claim 9 in the preparation of anion exchange membrane electrolysis anode material or membrane electrode assembly for hydrogen production.

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