CN116005192A - Ferronickel oxyhydroxide oxygen evolution electrode and preparation method thereof - Google Patents

Abstract

The invention discloses a nickel-iron oxyhydroxide oxygen evolution electrode and a preparation method thereof, and relates to the field of hydrogen production by electrolysis of water. The electrode consists of a conductive substrate and nickel-iron oxyhydroxide after removal of high-valent metals. In this method, nickel-iron-M composite oxides are grown in situ on conductive substrates through the hydrothermal reaction of nickel salts, iron salts, and high-valent metal M salts (M = chromium, molybdenum, tungsten), and then electrochemically applied. The high-valent metal M element in the nickel-iron M composite oxide is removed during the potential anodization process, and then the crystal phase and valence state of the nickel-iron composite oxide are changed to form a nickel-iron oxyhydroxide oxygen evolution electrode. In the present invention, the nickel-iron M composite oxide generated by hydrothermal provides a nickel-iron element library for the formation of nickel-iron oxyhydroxide, and after removing high-valent metal elements, a large number of oxygen evolution active sites are exposed, forming a rich defect , Highly active nickel-iron oxyhydroxide oxygen evolution electrode, which can be used in the field of hydrogen production by electrolysis of water.

Description

A nickel-iron oxyhydroxide oxygen evolution electrode and its preparation method

technical field

The invention belongs to the field of hydrogen production by electrolyzing water, and in particular relates to a nickel-iron oxyhydroxide oxygen evolution electrode and a preparation method thereof.

Background technique

In recent years, due to the increasingly serious problems of energy depletion and environmental pollution caused by the large-scale use of fossil energy, human needs for renewable and clean energy are more urgent. Hydrogen energy has been widely known as an efficient clean energy. Hydrogen energy is a green energy with zero carbon emissions. It has the characteristics of the largest specific heat capacity and is renewable. It can be used in hydrogen fuel cells to convert hydrogen energy into heat energy for utilization. Hydrogen production by electrolysis of water is continuous and environmentally friendly. It is a rising star in the hydrogen energy industry, but it has unlimited potential. High-purity hydrogen and oxygen can be produced to replace fossil fuels to provide energy. The water electrolysis reaction consists of two half-reactions, the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). The kinetics are relatively slow, so a catalyst for this reaction is needed to reduce the reaction energy barrier and reduce the cost.

OER reaction catalysts are represented by noble metal catalysts RuO ₂ and IrO ₂ , which exhibit excellent electrocatalytic activity and stability. However, the high cost and low reserves of Ru and Ir limit their wide application in the field of hydrogen production by electrolysis of water. For this reason, a large number of scientific researchers devote themselves to the research of non-precious metals, especially nickel and nickel-based composite metals. Among nickel-based OER catalysts, nickel-iron composite hydroxide (NiFe-LDH), nickel-molybdenum composite oxide, etc. have shown good OER activity. Invention patent CN202210500972.1 discloses a preparation method and application of a transition metal sulfide composite hydroxide electrode. By doping NiFe-LDH with non-metallic sulfur, sulfide and hydroxide are formed, and the oxygen evolution activity is regulated and improved. . However, this sulfide is unstable during the OER reaction, and the sulfide can easily cause the deactivation of the cathode electrode catalyst, resulting in the degradation of the electrolytic water performance. Patent CN201911249955.X discloses a preparation method and application of a 3D nanosheet-nanorod mixed structure nickel-molybdenum oxide, which uses high-valent metal molybdenum to construct a mixed structure to form nickel-molybdenum oxide, which shows good performance. However, the catalytic performance of this nickel-molybdenum-based oxide is average compared with nickel-iron catalysts.

To sum up, there is no report about the removal of high-valent M metal elements in NiFeM composite oxides to form a nickel-iron oxyhydroxide electrode with rich defects and high activity.

Contents of the invention

In order to overcome the deficiencies and defects mentioned in the background art above, one of the objects of the present invention is to provide a nickel-iron oxyhydroxide oxygen evolution electrode.

In order to achieve the above purpose, the technical solution adopted in the present invention is: in-situ growth of nickel-iron-M composite oxide on the conductive substrate by hydrothermal method, and then removal of high-valent metal elements by electrochemical method to form nickel-iron oxyhydroxide oxygen electrode.

Two of purpose of the present invention provides a kind of preparation method of nickel-iron oxyhydroxide oxygen evolution electrode exactly, and concrete operating method is as follows:

(1) Utilize pickling, water washing, ethanol washing to carry out pretreatment to conductive substrate, then put into oven and dry and set aside;

(2) Prepare nickel-iron M metal salt solution. Described nickel salt comprises at least one in nickel nitrate, nickel chloride and nickel sulfate; Described iron salt comprises at least one in ferric nitrate, ferric chloride, ferric sulfate; Described high-valent metal salt comprises sodium chromate, At least one of sodium molybdate, ammonium molybdate, and sodium tungstate; the molar concentration ratio of nickel, iron, and M is (1-20):(0.1-5):(0.2-50), and acid is used to adjust the pH to below 3.5;

(3) Transfer the above solution to a polytetrafluoroethylene reactor, add a piece of treated conductive substrate, 80-200 ℃ hydrothermal reaction for 3-24 hours, after it is naturally cooled to room temperature, rinse it with ultrapure water repeatedly and drying in a vacuum oven at 40-100° C. for 2-24 hours to obtain a nickel-iron-M composite oxide electrode grown in situ on a conductive substrate;

(4) With the in-situ growth nickel-iron-M composite oxide electrode on the obtained conductive substrate as the working electrode, with the Ni mesh stable in the alkaline solution, the titanium ruthenium commercial electrode as the auxiliary electrode, in the alkali with chloride ion In liquid (0.1-10M KOH+0.01-0.5M NaCl), remove high-valent metals by periodic double current step method, after electrochemical reaction for 0.1-2h, use ultrapure water to wash repeatedly, put in vacuum oven for 40 drying at -100°C for 2-24 hours to obtain a nickel-iron oxyhydroxide oxygen evolution electrode.

Preferably, the conductive substrate in step (1) is nickel foam (area density 380-420 g m ^-2 , porosity 98%).

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

Preferably, the reaction temperature of the hydrothermal reaction in step (3) is 150°C, the reaction time is 6h, the drying temperature is 70-80°C, and the drying time is 6-9h.

As a preference, the lye with chloride ions in step (4) is 6M KOH+0.01M NaCl, the temperature is 60°C, and the current density of the first stage of the periodic double current step method is 0.5A/ cm ² , the current density of the second stage is 0A/cm ² , each stage lasts for 1 min, and the number of cycles is 10.

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

The invention provides a nickel-iron oxyhydroxide oxygen evolution electrode, which can be applied to hydrogen production by alkaline electrolysis of water. Compared with the prior art, the present invention has the following technical advantages:

(1) The medicine used in the nickel-iron oxyhydroxide electrode of the present invention does not contain precious metal-based medicines, and the medicine reserves are large and easy to purchase;

(2) A kind of nickel-iron oxyhydroxide electrode of the present invention has excellent durability, at 50 ℃, in 6mol/LKOH electrolytic solution, carry out 100 hours galvanostatic test under 100mA cm ^-2 , have shown good long-term stability, indicating its great application potential in water electrolysis;

(3) The OER activity of a nickel-iron oxyhydroxide electrode described in the present invention is significantly better than the noble metal and non-noble metal catalysts reported in the current research, and the activity is better than the catalytic activity of commercial IrO ₂ . Under the condition of 1MKOH, 27℃, the overpotential is less than 200mV at 10mA cm ^-2 ;

(4) The preparation method of a nickel-iron oxyhydroxide electrode described in the present invention is simple, easy to operate, and convenient for large-scale production.

Description of drawings

Fig. 1 is the X-ray diffraction spectrum (XRD) of a kind of nickel-iron oxyhydroxide oxygen evolution electrode obtained in Example 1 before and after removing high-valent metals.

Fig. 2 is the X-ray photoelectron spectrum analysis diagram (XPS) of Mo3d track before and after a kind of nickel-iron oxyhydroxide oxygen evolution electrode obtained in embodiment 1 removes high-valent metal.

3 is a scanning electron microscope (SEM) image of a nickel-iron oxyhydroxide oxygen evolution electrode obtained in Example 1 after removal of high-valent metals.

Figure 4 is a linear sweep voltammogram of a nickel-iron oxyhydroxide electrode obtained in Example 1 at 1M KOH at 27°C.

Detailed ways

In order to facilitate the understanding of the present invention, the present invention will be described more fully and in detail below in conjunction with the accompanying drawings and preferred embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

The technical solution of the present invention will be further described below in combination with specific embodiments.

Example 1:

Cut the foamed nickel substrate into 3.8cm×4cm pieces, put the cut foamed nickel substrate in absolute ethanol, ultrasonicate for 20 minutes, then put it in 1mol/L hydrochloric acid for 10 minutes, and then put it in Sonicate in ultrapure water for 20 minutes, and rinse with ultrapure water three times after each stage of sonication. Then put it into absolute ethanol, ultrasonically treat it for 5 minutes, take it out and dry it at room temperature for later use;

Prepare a mixed solution of Ni(NO ₃ ) ₂ 6H ₂ O, FeCl ₃ and Na ₂ MoO ₄ with a molar concentration ratio of nickel, iron and molybdenum of 1:0.33:3, and use nitric acid to adjust the pH of the system to below 3.5; Transfer to a 100mL polytetrafluoroethylene reactor, add a piece of processed nickel foam, react with water heat at 150°C for 6 hours, wait for it to cool down to room temperature, rinse it with ultrapure water repeatedly, and put it in an oven at 70°C After drying for 9 hours, a nickel-iron-molybdenum oxide electrode grown in situ on the nickel foam was obtained, which was denoted as NiFeMoO ₄ /NF.

The obtained NiFeMoO ₄ /NF was subjected to periodic double current step method at 60°C in 6M KOH+0.01M NaCl to remove high-valent metals. Using NiFeMoO ₄ /NF as the working electrode, and Ni mesh stable in alkaline solution, titanium ruthenium commercial electrode as the auxiliary electrode, the current density of the first stage is 0.5A/cm ² , and the current density of the second stage is 0A/cm ^2. Each stage lasts for 1 min. After 10 cycles, it is washed repeatedly with ultrapure water and dried in a vacuum oven at 70°C for 6 hours to obtain a nickel-iron oxyhydroxide oxygen evolution electrode, which is designated as NiFeOOH/NF.

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

structural analysis

Figure 1 shows the X-ray diffraction spectrum (XRD) before and after removing high-valent metals from a nickel-iron oxyhydroxide oxygen evolution electrode obtained in Example 1. As shown in Figure 1, after the electrochemical removal of high-valent metals, the characteristic peaks of NiMoO ₄ and Fe ₂ (MoO ₄ ) ₃ basically disappeared, and then new characteristic peaks of NiOOH and FeOOH appeared.

What Fig. 2 shows is the X-ray photoelectron spectroscopy (XPS) of the Mo3d orbital of a kind of nickel-iron oxyhydroxide oxygen evolution electrode obtained in embodiment 1 before and after removing the high-valent metal, and the characteristic peak of the high-valent metal molybdenum disappears substantially.

What Fig. 3 shows is the scanning electron micrograph (SEM) of a kind of nickel-iron oxyhydroxide oxygen evolution electrode that embodiment 1 obtains, and NiFeOOH/NF electrode is made of micro-column, and due to the removal of high-valent metal, micro-column The surface becomes rough. This structure increases the electrochemically active specific surface area of the catalyst, increases the number of active sites, and effectively improves the electrocatalytic performance of the catalyst.

Figure 4 shows the OER scanning linear voltammetry image collected in 1M potassium hydroxide electrolyte at a scan speed of 5mV/s obtained by Example 1, 10mA cm ^-2 When the overpotential is only 145mV (data without resistance compensation).

Example 2:

Cut the foamed nickel substrate into 10cm×10cm pieces, put the cut foamed nickel substrate in absolute ethanol, ultrasonic treatment for 20 minutes, then put it in 1mol/L hydrochloric acid for ultrasonic treatment for 10 minutes, and then put it in ultra-sonic Sonicate in pure water for 20 minutes, and rinse with ultrapure water three times after each stage of sonication. Then put it into absolute ethanol, ultrasonically treat it for 5 minutes, take it out and dry it at room temperature for later use;

Prepare the mixed solution of Ni(NO ₃ ) ₂ 6H ₂ O, FeCl ₃ and (NH ₄ ) ₆ Mo ₇ O ₂₄ 4H ₂ O with the molar concentration ratio of nickel, iron and molybdenum being 1:0.33:0.5; Transfer the solution to a 500mL polytetrafluoroethylene reactor, add a piece of processed nickel foam with a specification of 10cm×10cm, and conduct a hydrothermal reaction at 150°C for 6 hours. Dry in an oven at 70° C. for 9 hours to obtain an in-situ grown nickel-iron-molybdenum oxide electrode on nickel foam, which is denoted as NiFeMoO ₄ /NF.

The obtained NiFeMoO ₄ /NF was subjected to periodic double current step method at 60°C in 6M KOH+0.01M NaCl to remove high-valent metals. Using NiFeMoO ₄ /NF as the working electrode, and Ni mesh stable in alkaline solution, titanium ruthenium commercial electrode as the auxiliary electrode, the current density of the first stage is 0.1A/cm ² , and the current density of the second stage is 0A/cm ^2. Each stage lasts 0.5min. After 20 cycles, it is washed repeatedly with ultra-pure water and dried in a vacuum oven at 70°C for 6 hours to obtain a nickel-iron oxyhydroxide oxygen evolution electrode, which is recorded as NiFeOOH/ NF.

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

Example 3:

The preparation method is basically the same as in Example 1, except that the hydrothermal uses Ni(NO ₃ ) ₂ ·6H ₂ O, Fe(NO ₃ ) ₃ and Na ₂ WO ₄ mixed solution. The OER performance was tested in an oxygen-saturated 1mol/L potassium hydroxide solution, and the overpotential was 240mV at 10mA cm ^-2 (data without resistance compensation).

Example 4:

The preparation method is basically the same as in Example 1, except that the hydrothermal uses Ni(NO ₃ ) ₂ ·6H ₂ O, Fe(NO ₃ ) ₃ and Na ₂ CrO ₄ mixed solution. The OER performance was tested in an oxygen-saturated 1mol/L potassium hydroxide solution, and the overpotential was 250mV at 10mA cm ^-2 (data without resistance compensation).

The above is only a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited to the above examples, and various technical solutions that have no substantial difference from the concept of the present invention are within the scope of protection of the present invention.

Claims (5)

1. The ferronickel oxyhydroxide oxygen-evolving electrode is characterized in that high-valence metal M elements in ferronickel M (M=chromium, molybdenum and tungsten) composite oxides grown in situ on a conductive substrate are removed, so that the ferronickel oxyhydroxide oxygen-evolving electrode with rich defects and high activity is formed. The preparation method of the ferronickel oxyhydroxide oxygen evolution electrode comprises the following steps:

(1) Pre-treating the conductive substrate by acid washing, water washing and ethanol washing, and then drying in an oven for later use;

(2) Preparing nickel, iron and M metal salt solution to a molar concentration ratio of (1-20) (0.1-5) (0.2-50), and regulating pH to below 3.5 with acid;

(3) Transferring the solution into a polytetrafluoroethylene reaction kettle, adding a treated conductive substrate, carrying out hydrothermal reaction in an oven at 80-200 ℃ for 3-24 hours, naturally cooling, cleaning, and then drying in a vacuum oven at 40-100 ℃ for 2-24 hours to obtain a nickel-iron M composite oxide electrode growing in situ on a metal substrate;

(4) And (3) removing high-valence metal from the obtained ferronickel M composite oxide electrode in alkali liquor with chloride ions by using an electrochemical method, repeatedly cleaning by using ultrapure water after electrochemical reaction for 0.1-2 hours, and drying for 2-24 hours at 40-100 ℃ in a vacuum oven to obtain the ferronickel oxyhydroxide oxygen evolution electrode.

2. The ferronickel oxyhydroxide oxygen evolution electrode of claim 1, wherein: the conductive substrate comprises foam metal, braided metal and carbon-based material; the nickel salt comprises at least one of nickel nitrate, nickel chloride and nickel sulfate; the ferric salt comprises at least one of ferric nitrate, ferric chloride and ferric sulfate; the M salt comprises at least one of sodium chromate, ammonium molybdate, sodium molybdate and sodium tungstate.

3. The ferronickel oxyhydroxide oxygen evolution electrode of claim 1, wherein: when the electrochemical removal of high-valence metals, the in-situ grown nickel-iron-M composite oxide electrode is used as a working electrode, a Ni net and titanium-ruthenium commercial electrode which are stable in alkaline solution are used as auxiliary electrodes, and the electrochemical removal of the high-valence metals is carried out by a periodic double-current step method in the electrolyte with the temperature of 27-90 ℃ and the concentration of 0.1-10M KOH+0.01-0.5M NaCl.

4. The ferronickel oxyhydroxide oxygen evolution electrode of claim 1, wherein: in the periodic double-current step method for electrochemically removing M element, the current density in the first stage is 0.01-0.5A/cm ² The current density in the second stage is 0A/cm ² Each stage lasts for 0.1-5min, and the period number is 5-40.

5. A ferronickel oxyhydroxide oxygen evolution electrode according to claim 1, characterized by the use of the ferronickel oxyhydroxide oxygen evolution electrode in the field of hydrogen production by electrolysis of water.

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