Preparation method and application of a nickel-iron-based transition metal fluoride catalyst

Abstract

This invention relates to the field of hydrogen production, and discloses a method for preparing a nickel-iron-based transition metal fluoride catalyst and its application. The invention first uses nickel foam as a substrate, pretreats the nickel foam with dielectric barrier discharge plasma, then performs a one-step hydrothermal process to obtain an in-situ grown transition metal catalyst. Finally, through fluorination and activation, a nickel-iron-based transition metal fluoride is obtained. Direct in-situ growth of the catalyst on nickel foam and performance improvement through fluorination significantly enhance the catalyst's electrocatalytic water splitting performance, while also greatly improving its stability.

Description

Technical Field

[0001] This invention relates to the field of hydrogen production, and more particularly to a method for preparing a nickel-iron-based transition metal fluoride catalyst and its application. Background Technology

[0002] In recent years, energy and environmental issues have become increasingly serious and have attracted growing attention, necessitating the development of environmentally friendly, sustainable, and renewable new energy sources. Hydrogen energy, with its advantages including high energy density and zero pollution, is one of the most promising green energy sources and a most likely alternative to traditional fossil fuels. Due to abundant water resources, electrocatalytic water splitting is a relatively simple and ideal method for producing high-purity hydrogen. However, while precious metals such as platinum, iridium, and rhodium are the best catalysts for electrocatalytic water splitting, their scarcity and high cost hinder large-scale industrial hydrogen production and cost reduction. Transition metals (such as Y and Ni), on the other hand, are relatively inexpensive, and electrodes made from these transition metals can achieve performance comparable to those made from precious metals in electrocatalytic water splitting for hydrogen production.

[0003] Electrodes made from transition metals can achieve various redox states, and fluorination can further significantly improve their catalytic performance. However, there is currently no universal, rapid, and tunable pathway to construct fluorinated metal foam compounds to better regulate the reconstruction and growth of catalyst surface structures. Furthermore, catalyst durability is a crucial consideration for industrial production; therefore, process improvements are needed to continuously enhance catalyst activity and stability, achieving highly efficient electrocatalytic water splitting.

[0004] These challenges have greatly hampered the industrial development of electrocatalytic water splitting for hydrogen production. Therefore, developing electrocatalysts with low cost, high catalytic performance, long durability, and adjustable fluorination is of paramount importance. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a method for preparing a nickel-iron-based transition metal fluoride catalyst and its application. The invention first uses nickel foam as a substrate, pretreats the nickel foam with dielectric barrier discharge plasma, then performs a one-step hydrothermal process to obtain an in-situ grown transition metal catalyst. Finally, through fluorination and activation, a nickel-iron-based transition metal fluoride is obtained. Direct in-situ growth of the catalyst on nickel foam and performance improvement through fluorination significantly enhance the catalyst's electrocatalytic water splitting performance and greatly improve its stability.

[0006] The specific technical solution of this invention is: a method for preparing a nickel-iron-based transition metal fluoride catalyst, comprising the following steps:

[0007] Step 1): Nickel foam pretreatment: Cut the nickel foam into slices, ultrasonically rinse with acetone and hydrochloric acid respectively, rinse several times with anhydrous ethanol and deionized water respectively, dry and set aside.

[0008] First, the nickel foam is cut into slices to facilitate subsequent electrocatalytic testing and use. Ultrasonic treatment with acetone and hydrochloric acid solutions removes surface oil and oxide layers, obtaining a clean surface to facilitate in-situ catalyst growth. The surface is then rinsed several times with anhydrous ethanol and deionized water to remove excess acetone and hydrochloric acid, allowing for drying.

[0009] Step 2): Atmospheric pressure dielectric barrier discharge plasma treatment: The dried nickel alloy foam is treated on both sides with atmospheric pressure dielectric barrier discharge plasma to obtain plasma pretreated nickel foam.

[0010] Dielectric barrier discharge involves placing an insulating dielectric in a discharge space and inducing discharge through an electric field. Commonly used insulating dielectrics include breakdown-resistant materials such as quartz, glass, and ceramics, which ensure continuous and uniform discharge while preventing arc formation. The entire process can be described as the gas between two electrodes generating electrons under enhanced voltage stimulation, with surface charge gradually accumulating and frequently colliding to transfer energy, thereby forming highly reactive excited-state atoms, molecules, ions, and free radical species—a process of discharge-charge transport-excited particles. Therefore, numerous grooves are etched into the surface of the foam substrate, increasing the specific surface area, adding more active sites, and facilitating catalyst growth.

[0011] Step 3): Preparation of NiFe-Y2O3 metal foam: Pour 15-25 ml of deionized water into a container, weigh 0.2-0.3 mM Y(NO3)2·6H2O, 0.2-0.3 mM Fe(NO3)3·9H2O, 0.4-0.6 mM Ni(NO3)2, 4-6 mM urea and 2.5 mM NH4F and dissolve them in the deionized water, stirring. Transfer the resulting solution and plasma-pretreated nickel foam (0.01-0.03 g) to a reactor, and perform a hydrothermal reaction at 140-160℃ for 8-12 h. After naturally cooling to room temperature, rinse repeatedly with ethanol and deionized water, and finally dry to obtain NiFe-Y2O3 metal foam.

[0012] Yttrium nitrate and ferric nitrate are used as catalysts for growth on nickel foam, and nitric acid is easily removed, preventing the introduction of impurities. Nickel nitrate, urea, and ammonium fluoride create an alkaline environment that facilitates the reaction. Under alkaline conditions, yttrium nitrate and ferric nitrate react with hydroxyl groups on the surface of the nickel alloy foam, forming a heterogeneous interface on the foam. Furthermore, theoretical quantitative simulations (DFT) of atoms show that the synergistic effect of yttrium and iron in forming the heterogeneous interface lowers the energy barrier. This significantly reduces the Gibbs free energy of the heterogeneous interface formed between yttrium and iron on the nickel foam substrate, providing higher electron mobility and more efficient charge transfer kinetics.

[0013] Step 4): Fluorination of NiFe-Y2O3 metal foam: Heat NH4F to a molten state at 250-300℃ in a glass container, immerse the NiFe-Y2O3 metal foam in the molten NH4F, then remove and cool it, and wash it slowly with deionized water to obtain the nickel-iron-based transition metal fluorinated product.

[0014] The surface energy of the fluorinated catalyst was calculated using theoretical atom simulation (DFT). The results showed that the surface energy of NiFe-Y2O3 after fluorination was higher than that before fluorination. Higher surface energy indicates higher electrocatalytic activity, which demonstrates the improved performance of the catalyst after fluorination.

[0015] Step 5): Activation of metal foam: The nickel-iron-based transition metal fluoride product is electrochemically activated in a three-electrode cell in 0.8-1.2M potassium hydroxide solution by cyclic voltammetry to obtain the nickel-iron-based transition metal fluoride catalyst.

[0016] Electrochemical activation ensures that the active sites on the surface of the fluorinated catalyst are activated as much as possible, thereby maximizing the catalytic performance of the catalyst.

[0017] Preferably, in step 1), the size of the slice is (0.8-1.2)cm×(0.4-0.6)cm×(0.4-0.6)cm.

[0018] Preferably, in step 1), the sample is ultrasonically rinsed with acetone and hydrochloric acid for 5-15 minutes, rinsed several times with anhydrous ethanol and deionized water, and dried at 50-70°C for 0.5-1.5 hours for later use.

[0019] Preferably, in step 2), the voltage of the atmospheric pressure dielectric barrier discharge plasma is set to 45-55V, the current is 0.8-1.2A, and the treatment time is 10-20 minutes under air conditions.

[0020] Preferably, in step 3), the stirring time is 20-40 minutes.

[0021] Preferably, in step 3), the drying temperature is 50-70℃ and the time is 1-3h.

[0022] Preferably, in step 4), the mass ratio of NiFe-Y2O3 metal foam to NH4F is 1:50-1:100.

[0023] Preferably, in step 4), the immersion time is 0.5-1.5 minutes.

[0024] Preferably, in step 5), the concentration of potassium hydroxide solution is 0.8-1.2M; the electrochemical activation conditions are: using mercuric oxide as the reference electrode, a carbon rod as the counter electrode, and a catalyst as the working electrode, activation is performed for 400-600 cycles at a scan rate of 40-60mV / s at room temperature and atmospheric pressure.

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] (1) The present invention directly grows the metal active component from the nickel foam substrate, which makes the bonding between substances more reliable and the bonding between the metal active component and the nickel foam more solid. This is beneficial to improving the stability of the catalyst and will also reduce the damage to the environment to a certain extent. Nickel foam substrate is selected and no other metal elements are introduced.

[0027] (2) The present invention uses atmospheric pressure plasma to pretreat nickel metal foam, which etches a large number of grooves on the foam surface, increases the specific surface area, increases more active sites, and facilitates the growth of catalyst.

[0028] (3) By combining advanced testing methods and theoretical calculations (DFT), the present invention reduces the charge transfer resistance and achieves a fast electron transport rate by hydrothermal synthesis of Y and Fe elements, thereby effectively improving the performance of the catalyst.

[0029] (4) This invention proposes a fluorination method. The surface energy of NiFe-Y2O3 after fluorination is higher than that before fluorination, and higher surface energy indicates higher electrocatalytic activity, demonstrating the improved catalyst performance after fluorination. Surface wettability and bubble release behavior during electrolysis are also significantly improved, thereby reducing overpotential fluctuations at high current densities. This simple method can also be applied to achieve highly active and durable electrocatalysts. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments.

[0031] Example 1

[0032] Step 1): Nickel alloy foam pretreatment: Cut the nickel alloy foam into 1cm×0.5cm×0.5cm slices, then ultrasonically rinse with acetone and 10% hydrochloric acid for 10 minutes each, followed by rinsing several times with anhydrous ethanol and deionized water. Afterward, dry the washed nickel alloy foam in a 60℃ oven for 1 hour for later use.

[0033] Step 2): Atmospheric pressure dielectric barrier discharge plasma treatment: Using an atmospheric pressure dielectric barrier discharge plasma with a voltage of 50V and a current of 1A, treat both sides of the dried nickel alloy foam for about 15 minutes under air conditions. This yields plasma-treated nickel foam (0.032g).

[0034] Step 3): Preparation of NiFe-Y2O3 metal foam: Prepare the reaction solution by pouring 20 ml of deionized water into a clean beaker. Weigh out 0.25 mM Y(NO3)2·6H2O, 0.25 mM Fe(NO3)3·9H2O, 0.50 mM Ni(NO3)2, 5 mM urea, and 2.5 mM NH4F and dissolve them in the deionized water. Stir with a magnetic device for 30 minutes until the solution is completely homogeneous. Transfer the prepared solution and the nickel alloy foam to a 30 ml polytetrafluoroethylene reactor liner and perform a hydrothermal reaction at 150 °C for 10 h. After the reaction is complete, allow it to cool naturally to room temperature and rinse the sample repeatedly with ethanol and deionized water. Finally, dry it in a 60 °C oven for 2 h for later use.

[0035] Step 4): Fluorination of NiFe-Y₂O₃ metal foam: NH₄F was heated to a molten state at 250°C in a glass container. The NiFe-Y₂O₃ metal foam prepared above was immersed in molten ammonium fluoride for 1 minute. The mass ratio of NiFe-Y₂O₃ metal foam to NH₄F was 1:62. Then, it was removed and cooled in a cold water bath, and finally washed several times with deionized water under slow flow. The nickel-iron-based transition metal fluorinated product was obtained.

[0036] Step 5): Activation of the metal foam: The prepared nickel-iron-based transition metal fluoride product was activated by cyclic voltammetry in a three-electrode cell in 1.0 M potassium hydroxide. Mercuric oxide was used as the reference electrode, a carbon rod as the counter electrode, and the catalyst as the working electrode. Activation was performed for 500 cycles at room temperature and atmospheric pressure with a scan rate of 50 mV / s. The activated nickel-iron-based transition metal fluoride product was obtained.

[0037] The prepared nickel-iron-based transition metal fluoride catalyst exhibited excellent electrocatalytic activity and structural stability in a three-electrode cell in 1.0 M potassium hydroxide, with mercury oxide as the reference electrode, a carbon rod as the counter electrode, and the catalyst as the working electrode. At a current density of 10 mA / cm², the catalyst showed good electrocatalytic activity and structural stability. -2 and 100mAcm -2The catalyst requires overpotentials of only 132 mV and 214 mV in the HER process, respectively, while the overpotentials required in the OER process are 178 mV and 281 mV, respectively. This is achieved at a current density of 100 mA / cm². -2 and 200mAcm -2 After 100 hours of water electrolysis, the HER process decreased by only about 2.97% and 7.89%, respectively. The OER process decreased by about 2.78% and 8.48%, respectively. After 50 hours of 100 mA cm⁻¹... -2 After the double hydrolysis test, its stability decreased by only about 3.41%.

[0038] Example 2

[0039] Step 1): Nickel alloy foam pretreatment: Cut the nickel alloy foam into 1cm×0.5cm×0.5cm slices, then ultrasonically rinse with acetone and 10% hydrochloric acid for 10 minutes each, followed by rinsing several times with anhydrous ethanol and deionized water. Afterward, dry the washed nickel alloy foam in a 60℃ oven for 1 hour for later use.

[0040] Step 2): Atmospheric pressure dielectric barrier discharge plasma treatment: Using an atmospheric pressure dielectric barrier discharge plasma with a voltage of 50V and a current of 1.5A, treat both sides of the dried nickel alloy foam for about 15 minutes under air conditions. This yields plasma-treated nickel foam (0.027g).

[0041] Step 3): Preparation of NiFe-Y2O3 metal foam: Prepare the reaction solution by pouring 20 ml of deionized water into a clean beaker. Weigh out 0.33 mM Y(NO3)2·6H2O, 0.17 mM Fe(NO3)3·9H2O, 0.5 mM Ni(NO3)2, 5 mM urea, and 2.5 mM NH4F and dissolve them in the deionized water. Stir with a magnetic device for 30 minutes until the solution is completely homogeneous. Transfer the prepared solution and the nickel alloy foam to a 30 ml polytetrafluoroethylene reactor liner and perform a hydrothermal reaction at 150 °C for 10 h. After the reaction is complete, allow it to cool naturally to room temperature and rinse the sample repeatedly with ethanol and deionized water. Finally, dry it in a 60 °C oven for 2 h for later use.

[0042] Step 4): Fluorination of NiFe-Y₂O₃ metal foam: NH₄F was heated to a molten state at 250°C in a glass container. The NiFe-Y₂O₃ metal foam prepared above was immersed in molten ammonium fluoride for 1 minute. The mass ratio of NiFe-Y₂O₃ metal foam to NH₄F was 1:75. Then, it was removed and cooled in a cold water bath, and finally washed several times with deionized water under slow flow. The nickel-iron-based transition metal fluorinated product was obtained.

[0043] Step 5): Activation of the metal foam: The prepared nickel-iron-based transition metal fluoride product was activated by cyclic voltammetry in a three-electrode cell in 1.0 M potassium hydroxide. Mercuric oxide was used as the reference electrode, a carbon rod as the counter electrode, and the catalyst as the working electrode. Activation was performed for 500 cycles at room temperature and atmospheric pressure with a scan rate of 50 mV / s. The activated nickel-iron-based transition metal fluoride product was obtained.

[0044] The prepared nickel-iron-based transition metal fluoride catalyst exhibited excellent electrocatalytic activity and structural stability in a three-electrode cell in 1.0 M potassium hydroxide, with mercury oxide as the reference electrode, a carbon rod as the counter electrode, and the catalyst as the working electrode. At a current density of 10 mA / cm², the catalyst showed good electrocatalytic activity and structural stability. -2 and 100mAcm -2 The catalyst requires only 137 mV and 189 mV overpotentials in the HER process, respectively, while the overpotentials required in the OER process are 214 mV and 304 mV, respectively. This is achieved at a current density of 100 mA / cm². -2 and 200mAcm -2 After 100 hours of water electrolysis, the HER process decreased by only about 3.54% and 8.27%, respectively. The OER process decreased by about 3.96% and 8.97%, respectively. After 50 hours of 100 mA cm⁻¹... -2 After the double hydrolysis test, its stability decreased by only about 3.09%.

[0045] Example 3

[0046] Step 1): Nickel alloy foam pretreatment: Cut the nickel alloy foam into 1cm×0.5cm×0.5cm slices, then ultrasonically rinse with acetone and 10% hydrochloric acid for 10 minutes each, followed by rinsing several times with anhydrous ethanol and deionized water. Afterward, dry the washed nickel alloy foam in a 60℃ oven for 1 hour for later use.

[0047] Step 2): Atmospheric pressure dielectric barrier discharge plasma treatment: Using an atmospheric pressure dielectric barrier discharge plasma with a voltage of 50V and a current of 2A, treat both sides of the dried nickel alloy foam for about 10 minutes under air conditions. This yields plasma-treated nickel foam (0.025g).

[0048] Step 3): Preparation of NiFe-Y2O3 metal foam: Prepare the reaction solution by pouring 20 ml of deionized water into a clean beaker. Weigh out 0.3 mM Y(NO3)2·6H2O, 0.20 mM Fe(NO3)3·9H2O, 0.50 mM Ni(NO3)2, 5 mM urea, and 2.5 mM NH4F and dissolve them in the deionized water. Stir with a magnetic device for 30 minutes until the solution is completely homogeneous. Transfer the prepared solution and the nickel alloy foam to a 30 ml polytetrafluoroethylene reactor liner and perform a hydrothermal reaction at 150 °C for 10 h. After the reaction is complete, allow it to cool naturally to room temperature and rinse the sample repeatedly with ethanol and deionized water. Finally, dry it in a 60 °C oven for 2 h for later use.

[0049] Step 4): Fluorination of NiFe-Y₂O₃ metal foam: NH₄F was heated to a molten state at 250°C in a glass container. The NiFe-Y₂O₃ metal foam prepared above was immersed in molten ammonium fluoride for 1 minute. The mass ratio of NiFe-Y₂O₃ metal foam to NH₄F was 1:80. Then, it was removed and cooled in a cold water bath, and finally washed several times with deionized water under slow flow. The nickel-iron-based transition metal fluorinated product was obtained.

[0050] Step 5): Activation of the metal foam: The prepared nickel-iron-based transition metal fluoride product was activated by cyclic voltammetry in a three-electrode cell in 1.0 M potassium hydroxide. Mercuric oxide was used as the reference electrode, a carbon rod as the counter electrode, and the catalyst as the working electrode. Activation was performed for 500 cycles at room temperature and atmospheric pressure with a scan rate of 50 mV / s. The activated nickel-iron-based transition metal fluoride product was obtained.

[0051] The prepared nickel-iron-based transition metal fluoride catalyst exhibited excellent electrocatalytic activity and structural stability in a three-electrode cell in 1.0 M potassium hydroxide, with mercury oxide as the reference electrode, a carbon rod as the counter electrode, and the catalyst as the working electrode. At a current density of 10 mA / cm², the catalyst showed good electrocatalytic activity and structural stability. -2 and 100mAcm -2 The catalyst requires only 115 mV and 153 mV overpotentials in the HER process, respectively, while the overpotentials required in the OER process are 198 mV and 294 mV, respectively. This is achieved at a current density of 100 mA / cm². -2 and 200mAcm -2 After 100 hours of water electrolysis, the HER process decreased by only about 3.54% and 8.27%, respectively. The OER process decreased by about 3.96% and 8.97%, respectively. After 50 hours of 100 mA cm⁻¹... -2 After the double hydrolysis test, its stability decreased by only about 3.09%.

[0052] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A process for the preparation of a nickel-iron-based transition metal fluoride catalyst, characterized in that: Includes the following steps: Step 1): Nickel foam pretreatment: Cut the nickel foam into slices, ultrasonically rinse with acetone and hydrochloric acid respectively, rinse several times with anhydrous ethanol and deionized water respectively, dry and set aside; Step 2): Atmospheric pressure dielectric barrier discharge plasma treatment: The dried nickel alloy foam is treated on both sides with atmospheric pressure dielectric barrier discharge plasma to obtain plasma pretreated nickel foam. Step 3): Preparation of NiFe-Y2O3 metal foam: Pour 15-25 ml of deionized water into a container, weigh 0.2-0.3 mM Y(NO3)2·6H2O, 0.2-0.3 mM Fe(NO3)3·9H2O, 0.4-0.6 mM Ni(NO3)2, 4-6 mM urea and 2.5 mM NH4F and dissolve them in the deionized water, stirring; transfer the resulting solution and 0.01-0.03 g of plasma-pretreated nickel foam to a reaction vessel, and perform a hydrothermal reaction at 140-160℃ for 8-12 h, cool naturally to room temperature, rinse repeatedly with ethanol and deionized water, and finally dry to obtain NiFe-Y2O3 metal foam; Step 4): Fluorination of NiFe-Y2O3 metal foam: NH4F is heated to a molten state at 250-300℃ in a glass container, NiFe-Y2O3 metal foam is immersed in molten NH4F, then removed and cooled, and washed slowly with deionized water to obtain nickel-iron-based transition metal fluorination products. Step 5): Activation of metal foam: The nickel-iron-based transition metal fluoride product is electrochemically activated in a three-electrode cell in 0.8-1.2M potassium hydroxide solution by cyclic voltammetry to obtain the nickel-iron-based transition metal fluoride catalyst.

2. The production method according to claim 1, characterized by: In step 1), the size of the slice is (0.8-1.2)cm×(0.4-0.6)cm×(0.4-0.6)cm.

3. The production method according to claim 1 or 2, characterized by: In step 1), ultrasonically rinse with acetone and hydrochloric acid for 5-15 minutes respectively, rinse several times with anhydrous ethanol and deionized water respectively, and dry at 50-70℃ for 0.5-1.5 hours for later use.

4. The preparation method according to claim 1, characterized in that: In step 2), the voltage of the atmospheric pressure dielectric barrier discharge plasma is set to 45-55V and the current is 0.8-1.2A, and it is treated under air conditions for 10-20 minutes.

5. The preparation method according to claim 1, characterized in that: In step 3), the stirring time is 20-40 minutes.

6. The preparation method according to claim 1, characterized in that: In step 3), the drying temperature is 50-70℃ and the time is 1-3 hours.

7. The preparation method according to claim 1, characterized in that: In step 4), the mass ratio of NiFe-Y2O3 metal foam to NH4F is 1:50-1:

100.

8. The preparation method according to claim 1, characterized in that: In step 4), the immersion time is 0.5-1.5 minutes.

9. The preparation method according to claim 1, characterized in that: In step 5), The concentration of the potassium hydroxide solution is 0.8-1.2M; The electrochemical activation conditions were as follows: mercuric oxide was used as the reference electrode, a carbon rod as the counter electrode, and a catalyst as the working electrode. The activation was carried out at room temperature and atmospheric pressure for 400-600 cycles at a scan rate of 40-60 mV / s.

10. The application of the nickel-iron-based transition metal fluoride catalyst obtained by the preparation method according to any one of claims 1-9 in electrocatalytic water splitting for hydrogen production.