Preparation method of a self-supporting alkaline overall water-splitting electrode material

Abstract

This invention discloses a method for preparing a self-supporting alkaline water-splitting electrode material, belonging to the technical field of water electrolysis catalytic materials. Using high-porosity nickel foam as a self-supporting substrate, after surface pretreatment to remove impurities and oxide layers, a nickel-iron binary metal precursor nanosheet array is grown in situ on the substrate via a hydrothermal method. Then, a low-temperature phosphating modification combined with annealing crystallization process is used to prepare a nickel-iron-phosphorus oxide composite self-supporting water-splitting electrode material. This invention abandons the traditional binder molding process, ensuring a strong bond between the active components and the substrate, effectively reducing electrode interfacial impedance and enriching catalytic active sites. The synergistic effect of the nickel-iron bimetallic material and phosphating modification optimizes the electrode's electronic structure, giving the electrode excellent dual-function catalytic performance for hydrogen and oxygen evolution. It exhibits strong corrosion resistance and good cycle stability in strongly alkaline electrolytes. The preparation process of this invention is mild, simple to operate, highly reproducible, and low in production cost, enabling large-scale industrial production. The resulting electrode can effectively reduce energy consumption in alkaline water splitting and is suitable for various applications such as industrial green hydrogen preparation and water electrolysis energy storage, possessing broad market application prospects.

Description

Technical Field

[0001] This invention belongs to the field of preparation technology of catalytic electrode materials for water electrolysis, specifically relating to a method for preparing a self-supporting alkaline water electrolysis electrode material, which is suitable for industrial catalytic scenarios of overall water splitting to produce hydrogen and oxygen under alkaline conditions. Background Technology

[0002] Hydrogen energy, as a clean and efficient secondary energy source, is a core energy carrier for replacing traditional fossil fuels. Electrolysis of water to produce hydrogen is a mature technology with high-purity, pollution-free products, making it a core technology for large-scale green hydrogen production. Among these technologies, alkaline water electrolysis has become the mainstream process due to its low equipment cost, stable operation, and suitability for industrial mass production. Electrode materials, as the core component of alkaline water electrolysis devices, directly determine the energy consumption, efficiency, and lifespan of the electrolysis process. An ideal water electrolysis electrode must simultaneously possess excellent dual catalytic activity for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), good conductivity, strong alkalinity and corrosion resistance, and long-term cycle stability.

[0003] Currently, commercial alkaline water electrolysis electrodes mostly use precious metal-based materials such as platinum, iridium, and ruthenium. Although these materials exhibit excellent catalytic performance, their scarcity and high price significantly increase the production cost of hydrogen production through water electrolysis, making them unsuitable for large-scale industrial applications. Existing non-precious metal-based electrode materials are mostly powdered catalysts, requiring the addition of binders to coat them onto the substrate surface during use. This approach has several drawbacks: First, the binder can cover the catalyst's active sites, increase the electrode interfacial impedance, and reduce electron transport efficiency and catalytic reaction rate. Second, the bonding force between the powdered catalyst and the substrate is weak, making it prone to detachment and pulverization during long-term electrolysis, leading to electrode performance degradation and shortened lifespan. Third, most non-precious metal catalysts only possess single hydrogen evolution or oxygen evolution activity, failing to achieve dual-function catalysis for complete water electrolysis. This necessitates the use of two different electrodes, resulting in complex equipment structures and high assembly costs.

[0004] Existing self-supporting electrode fabrication technologies often suffer from cumbersome processes, poor parameter controllability, and uneven active structures. Some methods require stringent conditions such as high temperature, high pressure, and vacuum, making mass production difficult and reproducibility challenging. Furthermore, the prepared electrodes exhibit insufficient catalytic stability at high current densities, high polarization overpotentials, and high energy consumption, failing to meet the requirements for efficient, low-consumption, and long-term operation in industrial alkaline water splitting. Therefore, developing a simple, low-cost, bifunctional catalytically superior, and highly stable self-supporting alkaline water splitting electrode fabrication method has significant engineering application value and market potential. Summary of the Invention

[0005] Purpose of the invention

[0006] The purpose of this invention is to overcome the defects of the prior art and provide a method for preparing a self-supporting alkaline water-splitting electrode material. This method solves the problems of existing electrodes, such as dependence on binders, few active sites, weak bifunctional catalysis, poor stability, high preparation cost, and difficulty in industrial mass production. The invention produces a self-supporting bifunctional electrode material that does not require binders, has high electron transport efficiency, is alkaline and corrosion resistant, and has excellent water-splitting catalytic performance.

[0007] Technical solution

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a self-supporting alkaline water-splitting electrode material includes four core steps: substrate pretreatment, precursor solution preparation, in-situ hydrothermal growth, and low-temperature phosphating modification. The specific preparation process is as described in claims 1-7 above.

[0010] The core technical principle of this invention is as follows: High-porosity, high-conductivity, and strong alkali resistance foamed nickel is selected as a self-supporting substrate, eliminating the need for additional binders. The substrate's three-dimensional porous structure provides ample growth space and conductive pathways. A nickel-iron binary metal precursor nanosheet array is grown in situ on the surface of the foamed nickel using a hydrothermal method. The synergistic effect of the nickel-iron bimetallic material initially enhances the dual-catalytic activity of the electrode. Low-temperature phosphating modification transforms the metal precursor into a nickel-iron-phosphorus oxide composite active component. Phosphating optimizes the material's electronic structure, enriches surface defects and active sites, significantly improving the material's dual-function catalytic ability for hydrogen evolution and oxygen evolution, while simultaneously strengthening the bond between the active component and the substrate. A low-temperature annealing process further regulates the material's crystal form, enhancing the electrode's conductivity and structural stability, ultimately yielding a self-supporting dual-function electrode material that can be directly used for alkaline water splitting.

[0011] Beneficial effects

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] 1. Binder-free self-supporting structure with excellent stability: This invention adopts an in-situ growth process, which allows the active components to grow directly and firmly on the surface of the nickel foam substrate, completely eliminating the traditional binder system and avoiding the problems of active sites being covered and interface impedance increasing. At the same time, it effectively prevents catalyst shedding and pulverization. The electrode can operate stably for a long time under strong alkaline and high current density conditions, and its service life is greatly improved.

[0014] 2. Outstanding bifunctional catalytic performance and low energy consumption: By combining nickel-iron bimetallic synergistic modification with low-temperature phosphating process, the electronic structure and microstructure of the material are controlled to construct rich active sites for hydrogen evolution and oxygen evolution. The resulting electrode has excellent HER and OER catalytic performance, low polarization overpotential for total water splitting and fast current response rate. Under the same working conditions, the electrolysis energy consumption is reduced by 15% to 25% compared with traditional non-precious metal electrodes.

[0015] 3. The preparation process is simple and controllable, and suitable for mass production: The entire process adopts hydrothermal synthesis + low-temperature phosphating process. The reaction conditions are mild, the parameters are adjustable, and the repeatability is good. It does not require harsh equipment such as high temperature, vacuum, and high pressure. The process is simple, the production cycle is short, and the raw material cost is low, which can realize large-scale industrial production.

[0016] 4. Structure and performance adapted to industrial scenarios: The three-dimensional porous foam nickel substrate structure has good air permeability and fast electrolyte permeation rate, which can effectively accelerate gas-liquid mass transfer, avoid bubble accumulation and block active sites, and is suitable for industrial high current density continuous water electrolysis. It also has excellent resistance to strong alkali corrosion and strong industrial adaptability. Detailed Implementation

[0017] Example 1

[0018] A method for preparing a self-supporting alkaline water-splitting electrode material, comprising the following specific steps:

[0019] S1. Substrate pretreatment: Select 1.0 mm thick nickel foam with 92% porosity as the substrate. Clean it with acetone, anhydrous ethanol and deionized water at 180W power for 15 min each to remove surface oil and oxide impurities. Dry it in a 70℃ oven for 5 min for later use.

[0020] S2. Preparation of precursor solution: Weigh 0.03 mol nickel nitrate hexahydrate, 0.01 mol ferric nitrate hexahydrate, and 0.1 mol urea according to the nickel-iron-urea molar ratio of 3:1:10, dissolve them in 100 mL of deionized water, and stir for 25 min at 25 °C and 400 r / min to obtain a uniform and transparent precursor mixed solution with a total metal ion concentration of 0.12 mol / L.

[0021] S3. In-situ hydrothermal growth: The pretreated nickel foam is completely immersed in the precursor solution and placed in a hydrothermal reactor (70% filling). The reaction is carried out at 140℃ for 8 hours. After natural cooling to room temperature, the nickel foam is removed, rinsed repeatedly with deionized water 3 times, and dried at 65℃ for 5 hours to obtain nickel-iron precursor modified nickel foam intermediate.

[0022] S4. Low-temperature phosphating modification: The intermediate and sodium hypophosphite were placed in ceramic boats at a mass ratio of 1:4 in the upper and lower reaches of a tube furnace, respectively. Nitrogen gas (flow rate 100 sccm) was introduced to purge the air in the furnace. The temperature was increased to 320°C at a rate of 3°C / min and held for 3 hours. The temperature was then naturally cooled to room temperature. Subsequently, the temperature was increased to 420°C for annealing and held for 1.5 hours to finally obtain a self-supporting alkaline water-splitting electrode material.

[0023] The electrode material prepared in this embodiment was applied to the complete water electrolysis test in 1.0 mol / L KOH alkaline electrolyte. Under room temperature conditions and a current density of 10 mA / cm², the complete water electrolysis voltage was only 1.52 V. After 100 hours of continuous cycling test, the catalytic performance decay rate was less than 3%, showing excellent stability.

[0024] Example 2

[0025] A method for preparing a self-supporting alkaline water-splitting electrode material, comprising the following specific steps:

[0026] S1. Substrate pretreatment: Select nickel foam with a thickness of 0.8 mm and a porosity of 90%, and clean it with acetone, anhydrous ethanol and deionized water in sequence for 10 min. The cleaning power is 150W. Dry it at 60℃ for later use.

[0027] S2. Preparation of precursor solution: Nickel-iron-urea molar ratio 2:1:8. Weigh 0.02 mol nickel chloride hexahydrate, 0.01 mol ferric chloride hexahydrate, and 0.08 mol urea, dissolve them in 100 mL deionized water, stir at 30℃ and 300 r / min for 20 min to prepare a precursor solution with a total metal ion concentration of 0.10 mol / L.

[0028] S3. In-situ hydrothermal growth: Nickel foam is immersed in the precursor solution, the hydrothermal reactor is filled to 65%, and the reaction is carried out at 120°C for 10 hours. After cooling, it is taken out and rinsed, and then dried at 60°C for 6 hours to obtain the intermediate.

[0029] S4. Low-temperature phosphating modification: The mass ratio of intermediate to sodium hypophosphite is 1:3. Nitrogen flow rate is 80 sccm. The temperature is raised to 280℃ at 2℃ / min and held for 4 hours. Then, it is annealed at 400℃ for 2 hours to obtain the target electrode material.

[0030] In this embodiment, the electrode prepared in 1.0 mol / L KOH electrolyte has a total water splitting voltage of 1.55 V at a current density of 10 mA / cm², and the performance degradation rate after 100 h of cycling is less than 4%.

[0031] Example 3

[0032] A method for preparing a self-supporting alkaline water-splitting electrode material, comprising the following specific steps:

[0033] S1. Substrate pretreatment: Select nickel foam with a thickness of 1.2mm and a porosity of 95%, and ultrasonically clean it with acetone, anhydrous ethanol and deionized water for 20 minutes each at 200W power, and then dry it at 80℃ for later use.

[0034] S2. Preparation of precursor solution: Nickel-iron-urea molar ratio 4:1:12. Weigh 0.04 mol nickel nitrate hexahydrate, 0.01 mol ferric nitrate hexahydrate, and 0.12 mol urea, dissolve in 100 mL deionized water, stir at 25 °C and 500 r / min for 30 min, and the total metal ion concentration is 0.15 mol / L.

[0035] S3. In-situ hydrothermal growth: The hydrothermal reactor was filled to 75% and reacted at 160℃ for 6 hours. After cooling and rinsing, it was dried at 70℃ for 4 hours to prepare the intermediate.

[0036] S4. Low-temperature phosphating modification: The mass ratio of intermediate to sodium hypophosphite is 1:5. The nitrogen flow rate is 120 sccm. The temperature is increased to 350℃ at 5℃ / min and held for 2 hours. The temperature is then annealed at 450℃ for 1 hour to obtain the target electrode material.

[0037] In this embodiment, the electrode prepared in 1.0 mol / L KOH electrolyte exhibits a total water splitting voltage of 1.50 V at a current density of 10 mA / cm², and a cycle performance decay rate of less than 2.5% after 100 h, demonstrating optimal catalytic performance.

[0038] Comparative Example 1 (Traditional Powder-Bonded Electrode)

[0039] A common nickel-iron-phosphorus oxide powder catalyst was mixed with a PVDF binder at a mass ratio of 9:1, NMP solvent was added, and the mixture was ground into a slurry. This slurry was then coated onto a nickel foam substrate, dried, and pressed into a sheet to prepare a bonded electrode. Under the same testing conditions, the total water splitting voltage at a current density of 10 mA / cm² was 1.68 V, and the performance degradation rate after 100 h of cycling was as high as 12%. The catalytic performance and stability were far lower than those of the self-supporting electrode prepared in this invention.

[0040] Implementation effect verification

[0041] Based on the test results of the above embodiments and comparative examples, it can be seen that the self-supporting alkaline water-splitting electrode prepared by the present invention through in-situ hydrothermal + low-temperature phosphating process does not require a binder, has excellent bifunctional catalytic activity and structural stability, and its overpotential for water splitting is significantly lower than that of traditional bonded electrodes, with extremely low performance degradation over long-term operation. At the same time, the preparation process is simple, the raw material cost is low, and the controllability is strong, making it suitable for industrial-scale mass production and continuous water electrolysis for hydrogen production. Compared with the existing technology, it has significant technical advantages and application value.

Claims

1. A method for preparing a self-supporting alkaline water-splitting electrode material, characterized in that, Includes the following steps: S1. Substrate pretreatment: Select nickel foam as a self-supporting substrate, and ultrasonically clean it with acetone, anhydrous ethanol and deionized water for 10-20 minutes in sequence to remove oil, oxide layer and impurities from the substrate surface. Then place it in an oven at 60-80℃ to dry for later use. S2. Preparation of precursor solution: Dissolve nickel salt, iron salt and urea in deionized water at a molar ratio of 2-4:1:8-12, stir at room temperature for 20-30 minutes until completely dissolved, and obtain a uniform and transparent nickel-iron precursor mixed solution. S3. In-situ hydrothermal growth: The pretreated nickel foam substrate from step S1 is completely immersed in the precursor solution prepared in step S2, transferred to a hydrothermal reactor, and hydrothermally reacted at 120-160℃ for 6-10 hours. After the reaction is completed, it is naturally cooled to room temperature, the substrate is removed, the surface residual solution is rinsed with deionized water, and dried to obtain nickel-iron precursor modified nickel foam intermediate. S4. Low-temperature phosphating modification: The intermediate prepared in step S3 and sodium hypophosphite are placed in upstream and downstream ceramic boats of a tube furnace, respectively. Under nitrogen atmosphere protection, the temperature is raised to 280-350℃ at a heating rate of 2-5℃ / min and held for 2-4 hours for phosphating modification. After cooling to room temperature, a self-supporting alkaline water-splitting electrode material is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the porosity of the nickel foam is 90-95%, the thickness is 0.8-1.2 mm, and the ultrasonic cleaning power is 150-200 W.

3. The preparation method according to claim 1, characterized in that, In step S2, the nickel salt is either nickel nitrate hexahydrate or nickel chloride hexahydrate, the iron salt is either ferric nitrate hexahydrate or ferric chloride hexahydrate, and the total metal ion concentration of the precursor mixed solution is 0.08–0.15 mol / L.

4. The preparation method according to claim 1, characterized in that, In step S2, the stirring speed is 300-500 r / min, and the solution temperature is kept constant at 25-30℃ during the stirring process.

5. The preparation method according to claim 1, characterized in that, In step S3, the filling degree of the hydrothermal reactor is 60-75%, the drying temperature is 60-70℃, and the drying time is 4-6 hours.

6. The preparation method according to claim 1, characterized in that, In step S4, the mass ratio of sodium hypophosphite to the intermediate is 3 to 5:1, and the nitrogen flow rate of the tubular furnace is 80 to 120 sccm.

7. The preparation method according to claim 1, characterized in that, In step S4, after phosphating modification, annealing is also performed at a temperature of 400-450℃ for 1-2 hours to further optimize the crystal structure of the material.

8. The application of a self-supporting alkaline water electrolysis electrode material prepared by the method according to any one of claims 1-7 in industrial alkaline water electrolysis for hydrogen production and large-scale water electrolysis for hydrogen production and energy storage.