A nickel-iron oxyhydroxide oxygen evolution electrode and a method of making the same

Abstract

The application discloses a nickel-iron oxyhydroxide oxygen evolution electrode and a preparation method thereof, and relates to the field of hydrogen production by water electrolysis. The electrode is composed of a conductive substrate and nickel-iron oxyhydroxide after removing high-valence metal. The method grows nickel-iron M composite oxide on the conductive substrate in situ through a hydrothermal reaction of nickel salt, iron salt and high-valence metal M salt (M=chromium, molybdenum and tungsten), and then removes the high-valence metal M element in the nickel-iron M composite oxide through an anodic oxidation process by applying a positive potential through an electrochemical method, thereby realizing the change of the nickel-iron composite oxide crystal phase and valence state, and forming the nickel-iron oxyhydroxide oxygen evolution electrode. In the application, the nickel-iron M composite oxide generated through hydrothermal reaction provides a nickel-iron element pool for forming the nickel-iron oxyhydroxide, and a large number of oxygen evolution active sites are exposed after removing the high-valence metal element, thereby forming a nickel-iron oxyhydroxide oxygen evolution electrode rich in defects and high in activity, which can be used in the field of hydrogen production by water electrolysis.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen production by water electrolysis, specifically relating to a nickel-iron hydroxyl oxide oxygen evolution electrode and its preparation method. Background Technology

[0002] In recent years, the large-scale use of fossil fuels has led to increasingly serious energy depletion and environmental pollution problems, making the demand for renewable and clean energy more urgent. Hydrogen energy, as a highly efficient and clean energy source, is widely known. Hydrogen energy is a zero-carbon emission green energy source with the highest specific heat capacity and is renewable. It can be used in hydrogen fuel cells to convert hydrogen energy into heat energy for utilization. Electrolysis of water to produce hydrogen is continuous and environmentally friendly, making it a rising star in the hydrogen energy industry with unlimited potential. It can produce high-purity hydrogen and oxygen to replace fossil fuels for energy. The water electrolysis reaction consists of two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). During the oxygen evolution reaction, the four-electron transfer process required for the breaking of the OH bond and the formation of the OO bond is relatively slow kinetically. Therefore, a catalyst is needed to lower the reaction energy barrier and reduce costs.

[0003] OER catalysts, represented by noble metal catalysts RuO2 and IrO2, have exhibited excellent electrocatalytic activity and stability. However, the high cost and low reserves of Ru and Ir limit their widespread application in the field of water electrolysis for hydrogen production. Therefore, many researchers have devoted themselves to the study of non-noble metals, especially nickel and nickel-based composite metals. Among nickel-based OER catalysts, nickel-iron composite hydroxide (NiFe-LDH) and nickel-molybdenum composite oxides have shown good OER activity. Invention patent CN202210500972.1 discloses a method for preparing a transition metal sulfide composite hydroxide electrode and its application. By doping NiFe-LDH with non-metallic sulfur, sulfides and hydroxides are formed, thereby regulating and improving the oxygen evolution activity. However, these sulfides are unstable during the OER reaction, and they easily cause deactivation of the cathode electrode catalyst, leading to a decline in water electrolysis performance. Patent CN201911249955.X discloses a method for preparing and applying a 3D nanosheet-nanoring hybrid structure nickel-molybdenum oxide. This method utilizes high-valence molybdenum to construct a hybrid structure, forming a nickel-molybdenum oxide that exhibits good performance. However, the catalytic performance of this nickel-molybdenum-based oxide is generally inferior to that of nickel-iron catalysts.

[0004] In summary, there are currently no reports of forming a nickel-iron hydroxyl oxide electrode with both high defect content and high activity after removing high-valence M metal elements from NiFeM composite oxides. Summary of the Invention

[0005] In order to overcome the shortcomings and defects mentioned in the background art, one of the objectives of the present invention is to provide a nickel-iron hydroxyl oxide oxygen evolution electrode.

[0006] To achieve the above objectives, the technical solution adopted in this invention is as follows: nickel-iron M composite oxide is grown in situ on a conductive substrate by hydrothermal method, and then high-valence metal elements are removed by electrochemical method to form a nickel-iron hydroxyl oxide oxygen evolution electrode.

[0007] The second objective of this invention is to provide a method for preparing a nickel-iron hydroxyl oxide oxygen evolution electrode, the specific operation method of which is as follows:

[0008] (1) The conductive substrate is pretreated by acid washing, water washing and ethanol washing, and then dried in an oven for later use.

[0009] (2) Prepare a nickel-iron M metal salt solution. The nickel salt includes at least one of nickel nitrate, nickel chloride, and nickel sulfate; the iron salt includes at least one of ferric nitrate, ferric chloride, and ferric sulfate; the high-valence metal salt includes at least one of sodium chromate, sodium molybdate, ammonium molybdate, and sodium tungstate; such that the molar concentration ratio of nickel, iron, and M is (1-20):(0.1-5):(0.2-50), and adjust the pH to below 3.5 using acid;

[0010] (3) Transfer the above solution to a polytetrafluoroethylene reactor, add a piece of the prepared conductive substrate, and perform hydrothermal reaction at 80-200℃ for 3-24 hours. After it cools naturally to room temperature, rinse it repeatedly with ultrapure water and dry it in a vacuum oven at 40-100℃ for 2-24 hours to obtain the nickel-iron M composite oxide electrode grown in situ on the conductive substrate.

[0011] (4) Using the nickel-iron M composite oxide electrode grown in situ on the obtained conductive substrate as the working electrode, and the Ni mesh and titanium-ruthenium commercial electrode that are stable in alkaline solution as the auxiliary electrode, the high-valence metal is removed by periodic double current step method in an alkaline solution containing chloride ions (0.1-10M KOH + 0.01-0.5M NaCl). After the electrochemical reaction for 0.1-2h, the electrode is repeatedly washed with ultrapure water and dried in a vacuum oven at 40-100℃ for 2-24 hours to obtain a nickel-iron hydroxyl oxide oxygen evolution electrode.

[0012] Preferably, the conductive substrate in step (1) is selected as nickel foam (area density 380-420 g m³). -2 (Porosity 98%).

[0013] Preferably, the nickel salt in step (2) is nickel nitrate, the iron salt is ferric chloride, the high-valence metal salt is sodium molybdate, and the acid used is nitric acid.

[0014] Preferably, the hydrothermal reaction in step (3) is carried out at a temperature of 150°C for 6 hours, the drying temperature is 70-80°C for 6-9 hours, and the drying time is 6-9 hours.

[0015] Preferably, the chloride-containing alkaline solution in step (4) is 6M KOH + 0.01M NaCl, the temperature is 60℃, and the current density of the first stage of the periodic double-current step method is 0.5A / cm². 2 The current density in the second stage is 0 A / cm². 2 Each phase lasts 1 minute, and the number of cycles is 10.

[0016] Preferably, the drying temperature in step (4) is 70-80°C and the drying time is 4-6 hours.

[0017] This invention provides a nickel-iron hydroxyl oxide oxygen evolution electrode, which can be applied to alkaline water electrolysis for hydrogen production. Compared with existing technologies, this invention has the following technical advantages:

[0018] (1) The reagents used in the nickel-iron hydroxyl oxide electrode of the present invention do not contain precious metal-based reagents, and the reagents are readily available and easy to purchase.

[0019] (2) The nickel-iron hydroxyl oxide electrode of the present invention has excellent durability, and can withstand 100 mA cm⁻¹ in a 6 mol / L KOH electrolyte at 50°C. -2 A 100-hour constant current test was conducted, which showed good long-term stability, indicating that it has great application potential in water electrolysis.

[0020] (3) The OER activity of the nickel-iron hydroxyl oxide electrode described in this invention is significantly better than that of currently reported noble metal and non-noble metal catalysts, and its activity is superior to that of commercial IrO2. At 1 M KOH, 27 °C, and 10 mA cm⁻¹ -2 Overpotential < 200mV;

[0021] (4) The preparation method of the nickel-iron hydroxyl oxide electrode of the present invention is simple, easy to operate, and convenient for large-scale production. Attached Figure Description

[0022] Figure 1 The X-ray diffraction (XRD) patterns of a nickel-iron hydroxyl oxide oxygen evolution electrode obtained in Example 1 before and after the removal of high-valence metals are shown.

[0023] Figure 2 The image shows the X-ray photoelectron spectroscopy (XPS) analysis of the Mo3d orbitals before and after the removal of high-valence metals from the nickel-iron hydroxyl oxide oxygen evolution electrode obtained in Example 1.

[0024] Figure 3 This is a scanning electron microscope (SEM) image of a nickel-iron hydroxyl oxide oxygen evolution electrode obtained in Example 1 after the removal of high-valence metals.

[0025] Figure 4 The linear sweep voltammetry of a nickel-iron hydroxyl oxide electrode obtained in Example 1 at 1M KOH and 27°C is shown. Detailed Implementation

[0026] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0027] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0028] Example 1:

[0029] The nickel foam substrate was cut into 3.8cm × 4cm pieces. The cut nickel foam substrate was placed in anhydrous ethanol and sonicated for 20 minutes. Then, it was placed in 1mol / L hydrochloric acid and sonicated for 10 minutes. Afterward, it was placed in ultrapure water and sonicated for 20 minutes. After each sonication stage, it was rinsed three times with ultrapure water. Finally, it was placed in anhydrous ethanol and sonicated for 5 minutes. Afterward, it was removed and dried at room temperature for later use.

[0030] A mixed solution of Ni(NO3)2·6H2O, FeCl3, and Na2MoO4 with a molar ratio of nickel, iron, and molybdenum of 1:0.33:3 was prepared, and the pH of the system was adjusted to below 3.5 using nitric acid. The solution was then transferred to a 100 mL polytetrafluoroethylene reactor, and a piece of pre-treated nickel foam was added. The reactor was subjected to hydrothermal reaction at 150 °C for 6 hours. After the solution was allowed to cool naturally to room temperature, it was repeatedly rinsed with ultrapure water and dried in an oven at 70 °C for 9 hours to obtain a nickel-iron-molybdenum oxide electrode grown in situ on the nickel foam, denoted as NiFeMoO4 / NF.

[0031] The obtained NiFeMoO4 / NF was subjected to a periodic double-current step removal process at 60℃ in 6M KOH + 0.01M NaCl to remove high-valence metals. NiFeMoO4 / NF was used as the working electrode, and a commercially available Ni mesh and titanium-ruthenium electrode, stable in alkaline solution, were used as auxiliary electrodes. The current density in the first stage was 0.5 A / cm². 2 The current density in the second stage is 0 A / cm². 2 Each stage lasts for 1 minute, and after 10 cycles, the electrode is repeatedly washed with ultrapure water and dried in a vacuum oven at 70°C for 6 hours to obtain a nickel-iron hydroxyl oxide oxygen evolution electrode, denoted as NiFeOOH / NF.

[0032] The NiFeOOH / NF prepared above was used for the electrocatalytic oxygen evolution reaction (OER). The specific steps were as follows: a three-electrode system was constructed, with the working electrode being the NiFeOOH / NF electrode, the reference electrode being a mercury / mercuric chloride electrode, and the counter electrode being a titanium-ruthenium electrode. OER performance was tested in an oxygen-saturated 1 mol / L potassium hydroxide solution at 10 mA cm⁻¹. -2 The overpotential was only 145mV (data without resistance compensation).

[0033] Structural Analysis

[0034] Figure 1 The image shown is the X-ray diffraction (XRD) pattern of a nickel-iron hydroxyl oxide oxygen evolution electrode obtained in Example 1 before and after the removal of high-valence metals. Figure 1 As shown, after electrochemical removal of high-valence metals, the characteristic peaks of NiMoO4 and Fe2(MoO4)3 basically disappeared, and new characteristic peaks of NiOOH and FeOOH appeared.

[0035] Figure 2 The image shows the X-ray photoelectron spectroscopy (XPS) analysis of the Mo3d orbitals before and after the removal of high-valence metals from a nickel-iron hydroxyl oxide oxygen evolution electrode obtained in Example 1. The characteristic peaks of the high-valence metal molybdenum have basically disappeared.

[0036] Figure 3 The image shown is a scanning electron microscope (SEM) image of a nickel-iron hydroxyl oxide oxygen evolution electrode obtained in Example 1. The NiFeOOH / NF electrode is composed of micron-sized pillars, and the surface of the pillars is roughened due to the removal of high-valence metals. This structure increases the electrochemically active specific surface area of ​​the catalyst and the number of active sites, effectively improving the electrocatalytic performance of the catalyst.

[0037] Figure 4 The image shown is a linear voltammetric image of the oxygen evolution reaction (OER) of a nickel-iron hydroxyl oxide electrode obtained in Example 1, acquired in 1M potassium hydroxide electrolyte at a scan rate of 5 mV / s. (10 mA cm⁻¹) -2 The overpotential was only 145mV (data without resistance compensation).

[0038] Example 2:

[0039] The nickel foam substrate was cut into 10cm × 10cm pieces. The cut nickel foam substrate was placed in anhydrous ethanol and sonicated for 20 minutes. Then, it was placed in 1mol / L hydrochloric acid and sonicated for 10 minutes. Afterward, it was placed in ultrapure water and sonicated for 20 minutes. After each sonication stage, it was rinsed three times with ultrapure water. Finally, it was placed in anhydrous ethanol and sonicated for 5 minutes. Afterward, it was removed and dried at room temperature for later use.

[0040] Prepare Ni(NO3)2·6H2O, FeCl3, and (NH4)6Mo7O with a molar concentration ratio of nickel, iron, and molybdenum of 1:0.33:0.5. 24 A mixed solution of 4H2O was prepared. The solution was transferred to a 500mL polytetrafluoroethylene reactor, and a piece of pre-treated nickel foam measuring 10cm×10cm was added. The reaction was carried out at 150℃ for 6 hours. After the solution was allowed to cool naturally to room temperature, it was rinsed repeatedly with ultrapure water and dried in an oven at 70℃ for 9 hours to obtain a nickel-iron-molybdenum oxide electrode grown in situ on the nickel foam, denoted as NiFeMoO4 / NF.

[0041] The obtained NiFeMoO4 / NF was subjected to periodic double-current step removal of high-valence metals at 60℃ in 6M KOH + 0.01M NaCl. NiFeMoO4 / NF was used as the working electrode, and a commercially available Ni mesh and titanium-ruthenium electrode, stable in alkaline solution, were used as auxiliary electrodes. The current density in the first stage was 0.1 A / cm². 2 The current density in the second stage is 0 A / cm². 2 Each stage lasts 0.5 minutes, and after 20 cycles, the electrode is repeatedly washed with ultrapure water and dried in a vacuum oven at 70°C for 6 hours to obtain a nickel-iron hydroxyl oxide oxygen evolution electrode, denoted as NiFeOOH / NF.

[0042] The NiFeOOH / NF prepared above was used for the electrocatalytic oxygen evolution reaction (OER). The specific steps were as follows: a three-electrode system was constructed, with the working electrode being the NiFeOOH / NF electrode, the reference electrode being a mercury / mercuric chloride electrode, and the counter electrode being a titanium-ruthenium electrode. OER performance was tested in an oxygen-saturated 1 mol / L potassium hydroxide solution at 10 mA cm⁻¹. -2 The overpotential is 180mV (data without resistance compensation).

[0043] Example 3:

[0044] The preparation method is basically the same as in Example 1, except that the hydrothermal treatment uses a mixed solution of Ni(NO3)2·6H2O, Fe(NO3)3, and Na2WO4 with a molar concentration ratio of 1:0.25:10. OER performance was tested in an oxygen-saturated 1 mol / L potassium hydroxide solution at 10 mA cm⁻¹. -2 The overpotential is 240mV (data without resistance compensation).

[0045] Example 4:

[0046] The preparation method is basically the same as in Example 1, except that the hydrothermal treatment uses a mixed solution of Ni(NO3)2·6H2O, Fe(NO3)3, and Na2CrO4 with a molar concentration ratio of 1:0.5:1.25. OER performance was tested in an oxygen-saturated 1 mol / L potassium hydroxide solution at 10 mA cm⁻¹. -2 The overpotential is 250mV (data without resistance compensation).

[0047] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. Various process solutions that are not substantially different from the concept of the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a nickel-iron hydroxyl oxide oxygen evolution electrode, characterized in that: a nickel-iron M composite oxide is grown in situ on a conductive substrate, wherein M is at least one of chromium, molybdenum, and tungsten, and then the high-valence metal M element is electrochemically removed, thereby forming a defect-rich, highly active nickel-iron hydroxyl oxide oxygen evolution electrode. The method for preparing the nickel-iron hydroxyl oxide oxygen evolution electrode specifically includes the following steps: (1) The conductive substrate is pretreated by acid washing, water washing and ethanol washing, and then dried in an oven for later use. (2) Prepare solutions of nickel salt, iron salt, and M metal salt with a molar concentration ratio of (1-20):(0.1-5):(0.2-50), and adjust the pH to below 3.5 using acid; (3) Transfer the above solution to a polytetrafluoroethylene reactor, add the treated conductive substrate, and perform a hydrothermal reaction at 80-200℃ for 3-24 hours in an oven. After natural cooling and cleaning, place it in a vacuum oven at 40-100℃ for 2-24 hours to obtain a nickel-iron M composite oxide electrode grown in situ on a metal substrate. (4) The obtained nickel-iron M composite oxide electrode is subjected to an electrochemical periodic double current step method to remove high-valence metals in an alkaline solution containing chloride ions. After 0.1-2 hours of electrochemical reaction, it is repeatedly washed with ultrapure water and dried in a vacuum oven at 40-100℃ for 2-24 hours to obtain a nickel-iron hydroxy oxide oxygen evolution electrode.

2. The method for preparing a nickel-iron hydroxyl oxide oxygen evolution electrode according to claim 1, characterized in that: The conductive substrate includes foam metal, braided metal, and carbon-based material; the nickel salt includes at least one of nickel nitrate, nickel chloride, and nickel sulfate; the iron salt includes at least one of ferric nitrate, ferric chloride, and ferric sulfate; and the M metal salt includes at least one of sodium chromate, ammonium molybdate, sodium molybdate, and sodium tungstate.

3. The method for preparing a nickel-iron hydroxyl oxide oxygen evolution electrode according to claim 1, characterized in that: In the electrochemical removal of high-valence metals, an in-situ grown nickel-iron M composite oxide electrode is used as the working electrode, and a Ni mesh and titanium-ruthenium commercial electrode, which are stable in alkaline solution, are used as auxiliary electrodes. Electrochemical removal of high-valence metals is carried out in an electrolyte at a temperature of 27-90℃ and a concentration of 0.1-10M KOH + 0.01-0.5M NaCl by a periodic double current step method.

4. The method for preparing a nickel-iron hydroxyl oxide oxygen evolution electrode according to claim 1, characterized in that: In the periodic double-current step method used for the electrochemical removal of element M, the current density in the first stage is 0.01-0.5 A / cm². 2 The current density in the second stage is 0 A / cm². 2 Each stage lasts 0.1-5 minutes, with 5-40 cycles.

5. A method for preparing a nickel-iron hydroxyl oxide oxygen evolution electrode as described in claim 1, characterized in that, The application of the nickel-iron hydroxyl oxide oxygen evolution electrode in the field of water electrolysis for hydrogen production.

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