A method for preparing a cerium-doped nickel ferrite gas diffusion electrode and applications thereof

Abstract

The application discloses a preparation method of a cerium-doped nickel ferrite gas diffusion electrode and application thereof. The method comprises the following steps: (1) a hydrothermal reaction: taking nickel inorganic salt, iron inorganic salt precursor and an alkali source, dissolving them in water to obtain a precursor solution; immersing the precursor solution into a porous metal substrate to perform a hydrothermal reaction, then cooling to room temperature, washing the electrode and drying the electrode for use; (2) impregnation calcination: taking a cerium salt precursor, dissolving the cerium salt precursor in water, stirring until a transparent solution is obtained to obtain an impregnation solution; sequentially performing first-stage calcination treatment and second-stage calcination treatment on the electrode obtained in the step (1) to obtain the electrode. The method combines hydrothermal synthesis and impregnation calcination, realizes effective doping of the Ce element on the surface of an ordered support electrode, improves the success rate of electrode preparation, and thus the electrode has better activity and stability.

Description

Technical Field

[0001] This invention belongs to the field of water electrolysis technology, specifically relating to a method for preparing a cerium-doped nickel-iron oxide gas diffusion electrode and its application. Background Technology

[0002] In recent years, global renewable energy consumption has continued to grow, and water electrolysis for hydrogen production technology has been mature enough for application 50 years ago. However, the proportion of hydrogen produced in this way in the world's total hydrogen production is still very small. Alkaline liquid electrolyzers are a relatively mature technology, with more than 400 units already in operation by 1902. Alkaline water electrolyzers have an operating life of up to 15 years, making them the longest-operating commercial water electrolysis hydrogen production technology in the world. The core of the electrolysis process is the electrocatalyst required for the electrochemical reaction, which directly affects electrolysis efficiency, energy consumption, cost, and cell lifespan. Recently, there has been a growing trend of research on non-precious metal oxygen evolution catalysts for use under alkaline conditions.

[0003] Patent CN104659357A discloses a method for preparing a carbon-supported nickel-iron hydroxide composite material. Although the catalyst prepared by this method exhibits good oxygen evolution electrocatalytic activity under alkaline conditions, a significant drawback is the severe corrosion of the supported catalyst in an alkaline full electrolyzer test at lower electrolysis voltages, affecting the long-term operational life of the full electrolyzer. Patent CN105618060A discloses a graphene / nickel-iron layered double hydroxide non-metallic bifunctional oxygen catalyst. However, in practical applications, the catalyst particles are difficult to arrange in an orderly manner, resulting in low dispersion and low catalyst utilization. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a cerium-doped nickel-iron oxide gas diffusion electrode and its application. The gas diffusion oxygen evolution electrode prepared by this method can enable the oxygen evolution reaction in the electrochemical process to proceed efficiently under a relatively small applied bias voltage.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for preparing a cerium-doped nickel-iron oxide gas diffusion electrode, comprising the following steps:

[0007] (1) Hydrothermal reaction: Take nickel inorganic salt, iron inorganic salt precursor and alkali source, dissolve in water, stir to obtain precursor solution; immerse the porous metal substrate in precursor solution and carry out hydrothermal reaction, then cool to room temperature, wash the electrode and dry it for later use.

[0008] (2) Impregnation and calcination: Dissolve the cerium salt precursor in water and stir to obtain an impregnation solution; perform a first-stage calcination treatment on the electrode obtained in step (1), then immerse the calcined electrode in the impregnation solution, take out the electrode, and perform a second-stage calcination treatment to obtain the cerium-doped nickel-iron oxide gas diffusion electrode.

[0009] In the above technical solution, further, in step (1), the hydrothermal reaction temperature is 100-180℃ and the hydrothermal reaction time is 5-15h;

[0010] The drying process is vacuum drying, with a drying temperature of 50–80°C and a drying time of 6–12 hours.

[0011] In the precursor salt solution, the total molar concentration of nickel inorganic salt and iron inorganic salt precursors is 0.1-3 mM, and the molar ratio of nickel to iron is 1:9-1:1.

[0012] The alkaline source is one or more of urea, potassium hydroxide, and sodium hydroxide, and the molar concentration of the alkaline source in the precursor solution is 10-50 mM.

[0013] In the above technical solution, further, in step (1), the stirring time until a transparent solution is obtained is more than 30 minutes.

[0014] In the above technical solution, further, in step (1), the porous metal substrate includes any one of nickel foam, nickel felt, nickel mesh, stainless steel felt, and stainless steel mesh.

[0015] In the above technical solution, further, in step (2), the molar concentration of the cerium salt precursor in the impregnation solution is 0.1-3 mM;

[0016] The first stage of roasting is carried out at a temperature of 400–450°C for 3–15 hours in an air atmosphere; the second stage of roasting is carried out at a temperature of 100–200°C for 3–15 hours in an air atmosphere.

[0017] In the above technical solution, further, in step (2), the stirring time until a transparent solution is obtained is more than 30 minutes.

[0018] In the above technical solution, further, in step (2), the obtained product is a cerium-doped nickel-iron oxide gas diffusion electrode, the electrode includes a porous metal substrate and a nickel-iron oxide adhesion layer covering the surface of the porous metal substrate, the final morphological characteristics of the nickel-iron oxide adhesion layer are: a nickel-iron oxide nanosheet array layer with a diameter of 2 to 3 μm and a thickness of 50 to 100 nm, and the surface of the nanosheets is rough.

[0019] Another aspect of the present invention provides an application of the above-mentioned cerium-doped nickel-iron oxide gas diffusion electrode, wherein the electrode is used as an oxygen evolution catalyst in RFC, photoelectrocatalysis, APE water electrolysis cell or alkaline water electrolysis hydrogen generator, and metal-air fuel cell oxygen evolution reaction.

[0020] The beneficial effects of this invention are as follows:

[0021] 1. Conventional impregnation methods struggle to prepare ordered, thin, and uniform electrode catalyst layers. Hydrothermal synthesis allows for precise control of the electrode structure, enabling the controllable preparation of ordered electrodes. However, the presence of Ce precursor in the precursor solution during hydrothermal reactions can cause pulverization of the electrode substrate, compromising electrode preparation success rates. This invention employs a staged calcination process. In the first stage of calcination, the electrode decomposes thermally to form oxides, transforming its smooth surface into a rough one, creating a cavity structure conducive to impregnation. After the first stage of calcination, the main microstructure of the gas diffusion electrode is formed. Therefore, in the second stage of calcination, by lowering the calcination temperature, the Ce precursor can be incorporated into the cavities formed by hydroxide decomposition while maintaining the substrate structure formed in the first stage. This results in a more stable cerium-doped nickel-iron oxide gas diffusion electrode compared to adding a Ce precursor solution to the reaction solution, thus exhibiting better activity and stability.

[0022] 2. Traditional impregnation and calcination methods do not take into account the substrate changes caused by repeated high-temperature calcination and only focus on the preparation optimization of the catalyst loaded on the electrode. This invention combines hydrothermal synthesis with impregnation and calcination, which can effectively dope Ce elements on the ordered support electrode surface and improve the electrode preparation success rate. Attached Figure Description

[0023] Figure 1 Electron microscope images of Ce-doped electrode powder particles before and after calcination in Example 1, a is before calcination, b is after calcination;

[0024] Figure 2 The polarization curves of the electrode oxygen evolution reaction obtained in Examples 1, 2, 1, and 2 are shown. Detailed Implementation

[0025] The following, with reference to the accompanying drawings, further explains the fabrication method, characteristics, and applications of cerium-doped nickel-iron oxide gas diffusion electrodes:

[0026] Example 1

[0027] The Ce element impregnation calcination is carried out in a two-stage calcination process, including the following steps:

[0028] (1) Hydrothermal reaction:

[0029] Nickel nitrate, ferric nitrate, and urea were dissolved in deionized water and stirred thoroughly for 30 minutes to obtain a clear and transparent precursor solution. The total amount of nickel nitrate and ferric nitrate in the precursor solution was 3 mM, with a nickel nitrate to ferric nitrate molar ratio of 1:3, and the urea concentration was 10 mM. The cleaned nickel foam was vertically immersed into the precursor solution, and a hydrothermal reaction was carried out at 140°C for 8 hours, followed by vacuum drying at 80°C for 12 hours. Figure 1 As shown in (a), the product obtained after drying is a smooth, approximately hexagonal nanosheet.

[0030] (2) Impregnation and roasting:

[0031] Cerium nitrate was dissolved in water and stirred for 30 minutes until a transparent solution was obtained. A 2 mM cerium nitrate solution was prepared as the impregnation solution. The electrode obtained after the hydrothermal reaction was calcined at 450°C for 5 hours for the first stage of calcination. The product was then immersed in the impregnation solution for 3 minutes, and the electrode was removed and calcined at 150°C for 5 hours for the second stage of calcination. The above two stages of calcination were repeated 5 times. The electrode was then washed, dried, and ready for use to obtain a cerium-doped nickel-iron oxide gas diffusion electrode. Figure 1 As shown in (b), the product obtained after drying is a rough-surfaced, approximately hexagonal nanosheet.

[0032] Example 2

[0033] The Ce element impregnation calcination is carried out in a two-stage calcination process, including the following steps:

[0034] (1) Hydrothermal reaction:

[0035] Nickel nitrate, ferric nitrate, and urea were dissolved in deionized water and stirred thoroughly for 30 minutes to obtain a clear and transparent precursor solution. The total amount of nickel nitrate and ferric nitrate in the precursor solution was 3 mM, with a molar ratio of nickel nitrate to ferric nitrate of 1:3, and urea was 10 mM. The cleaned nickel foam was vertically immersed into the precursor solution and hydrothermally reacted at 140°C for 8 hours, followed by vacuum drying at 80°C for 12 hours.

[0036] (2) Impregnation and roasting:

[0037] Cerium nitrate was dissolved in water and stirred for 30 minutes until a transparent solution was obtained. A 2 mM cerium nitrate solution was prepared as the impregnation solution. The electrode obtained after the hydrothermal reaction was calcined at 450°C for 5 hours for the first stage of calcination. The product was then immersed in the impregnation solution. After 3 minutes, the electrode was removed and calcined at 350°C for 5 hours for the second stage of calcination. The above two stages of calcination and calcination were repeated 5 times. The electrode was then washed, dried and stored for later use to obtain a cerium-doped nickel-iron oxide gas diffusion electrode.

[0038] Comparative Example 1

[0039] The Ce element impregnation and calcination is completed in a single firing process, including the following steps:

[0040] (1) Hydrothermal reaction process:

[0041] Nickel nitrate, ferric nitrate, and urea were dissolved in deionized water and stirred thoroughly for 30 minutes to obtain a clear and transparent precursor solution. The total amount of nickel nitrate and ferric nitrate in the precursor solution was 3 mM, with a ratio of nickel nitrate to ferric nitrate of 1:3 and urea of ​​10 mM. The cleaned nickel foam was vertically immersed into the precursor solution and hydrothermally reacted at 140°C for 8 hours, followed by vacuum drying at 80°C for 12 hours.

[0042] (2) Impregnation and roasting process:

[0043] Dissolve cerium nitrate in water and stir for 30 minutes until a transparent solution is obtained. Prepare a 2 mM cerium nitrate solution, which is the impregnation solution. Immerse the electrode obtained after the hydrothermal reaction in the impregnation solution. After 3 minutes, remove the electrode and calcine it at 300°C. Repeat the above impregnation and calcine treatment 5 times, calcine for 3 hours each time. Wash and dry the electrode for later use to obtain a cerium-doped nickel-iron oxide gas diffusion electrode.

[0044] Comparative Example 2

[0045] The same materials, steps and conditions as in the hydrothermal reaction process in Example 1 (1) were used to complete the preparation of the nickel foam electrode, but without the cerium impregnation and calcination process.

[0046] Hydrothermal reaction: Nickel nitrate, ferric nitrate, and urea were dissolved in deionized water and stirred thoroughly for 30 minutes to obtain a clear and transparent precursor solution. The total amount of nickel nitrate and ferric nitrate in the precursor solution was 3 mM, with a ratio of nickel nitrate to ferric nitrate of 1:3 and urea of ​​10 M. The cleaned foamed nickel was vertically immersed into the precursor solution and hydrothermally reacted at 140°C for 8 hours. The mixture was then vacuum dried at 80°C for 12 hours to obtain a nickel-iron oxide gas diffusion electrode.

[0047] Test results:

[0048] Examples 1, 2, Comparative Example 1, and Comparative Example 2 all underwent the following half-cell tests: The half-cell system used a 1M KOH solution saturated with oxygen as the electrolyte, and polarization curves were scanned using an integrated electrode. Figure 2 As shown.

[0049] The gas diffusion electrode prepared using the method in Example 1 achieved 2000 mA / cm² in a 1M KOH electrolyte solution. 2 The potential at the electrolytic current density is 2.07V (vs. RHE).

[0050] The gas diffusion electrode prepared using the method in Example 2 achieved 2000 mA / cm² in a 1M KOH electrolyte solution. 2 The potential at the electrolytic current density is 2.14V (vs. RHE).

[0051] The gas diffusion electrode prepared by the method in Comparative Example 1 achieved 2000 mA / cm² in a 1M KOH electrolyte solution. 2 The potential at the electrolytic current density is 2.25V (vs. RHE).

[0052] The gas diffusion electrode prepared by the method in Comparative Example 2 achieved 2000 mA / cm² in a 1M KOH electrolyte solution. 2 The potential at the electrolytic current density is 2.28V (vs. RHE).

[0053] Example 1 employs a lower second-stage calcination temperature for staged calcination to impregnate Ce, resulting in a lower electrolysis voltage under specified conditions. This demonstrates better catalytic activity compared to Examples 2, Comparative Example 1, and Comparative Example 2. Therefore, the gas diffusion electrode prepared by the present invention exhibits excellent oxygen evolution electrocatalytic performance under alkaline conditions.

Claims

1. A method for preparing a cerium-doped nickel-iron oxide gas diffusion electrode, characterized in that, Includes the following steps: (1) Hydrothermal reaction: Take nickel inorganic salt, iron inorganic salt precursor and alkali source, dissolve in water, stir to obtain precursor solution; immerse the porous metal substrate in the precursor solution and carry out hydrothermal reaction, then cool to room temperature, wash the electrode and dry it for later use; (2) Impregnation and calcination: Dissolve the cerium salt precursor in water and stir to obtain an impregnation solution; perform a first-stage calcination treatment on the electrode obtained in step (1), then immerse the calcined electrode in the impregnation solution, take out the electrode, and perform a second-stage calcination treatment to obtain the cerium-doped nickel-iron oxide gas diffusion electrode. In step (2), the first stage of roasting is carried out at a temperature of 400~450℃ for 3~15 hours in an air atmosphere; the second stage of roasting is carried out at a temperature of 100~200℃. o C, calcination in air atmosphere for 3~15 hours.

2. The preparation method according to claim 1, characterized in that: In step (1), the hydrothermal reaction temperature is 100~180℃ and the hydrothermal reaction time is 5~15h; The drying process is vacuum drying, with a drying temperature of 50-80°C. o C, drying time is 6~12h; In the precursor solution, the total molar concentration of nickel inorganic salt and iron inorganic salt precursors is 0.1~3mM, and the molar ratio of nickel to iron is 1:9~1:

1. The alkaline source is one or more of urea, potassium hydroxide, and sodium hydroxide, and the molar concentration of the alkaline source in the precursor solution is 10~50mM.

3. The preparation method according to claim 1, characterized in that: In step (1), the stirring time is more than 30 minutes.

4. The preparation method according to claim 1, characterized in that, In step (1), the porous metal substrate includes any one of nickel foam, nickel felt, nickel mesh, stainless steel felt, and stainless steel mesh.

5. The preparation method according to claim 1, characterized in that: In step (2), the molar concentration of the cerium salt precursor in the impregnation solution is 0.1~3mM.

6. The preparation method according to claim 1, characterized in that: In step (2), the stirring time is more than 30 minutes.

7. The preparation method according to claim 1, characterized in that: In step (2), the product obtained is a cerium-doped nickel-iron oxide gas diffusion electrode. The electrode includes a porous metal substrate and a nickel-iron oxide adhesion layer covering the surface of the porous metal substrate. The final morphological characteristics of the nickel-iron oxide adhesion layer are: a nickel-iron oxide nanosheet array layer with a diameter of 2~3μm and a thickness of 50~100nm, and the surface of the nanosheets is rough.

8. The application of a cerium-doped nickel-iron oxide gas diffusion electrode prepared by the method according to any one of claims 1-7, characterized in that: The electrode is used as an oxygen evolution catalyst in RFC, photoelectrocatalysis, APE water electrolysis cells or alkaline water electrolysis hydrogen generators, and metal-air fuel cells for oxygen evolution reactions.

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