CN107570166B - A kind of composite carbon and transition element oxide nano-catalyst preparation method and application - Google Patents

Abstract

The invention discloses a preparation method of composite carbon and transition element oxide nano-catalyst and application based on the catalyst for water electrolysis and oxygen evolution, belonging to the technical field of nano-catalysis, nano-materials and metal organic framework materials.

Description

A kind of composite carbon and transition element oxide nano-catalyst preparation method and application

technical field

The invention relates to a preparation method of a composite carbon and transition element oxide nano-catalyst and the application of the catalyst for electrolysis of water for oxygen evolution, belonging to the technical fields of nano-catalysis, nano-materials and metal-organic framework materials.

Background technique

With the increasing level of people's material life and industrial development, environmental pollution and energy crisis continue to worsen. According to statistics in 2003, the recoverable reserves of natural gas in the world are 2.4 Gt, and crude oil is 138.3 Gt, totaling 140.7 Gt. Based on the annual production of 3.2 Gt, the recoverable reserves are 44 years. Aviation, aerospace, chemical industry, ships, and automobiles all use oil. The world's high dependence on oil leads to a shortage of oil, and the entire world will face a shutdown. In addition, fossil fuels contain carbon, dust, sulfur, etc., which inevitably pollute the environment after combustion. With the ever-increasing demand for energy and the gradual exhaustion of fossil fuels, it is urgent to find a clean energy alternative. Obtaining clean and efficient energy (hydrogen and oxygen) has become a hot topic of contemporary scientific research. Water is one of the most abundant resources containing hydrogen and oxygen elements on earth. Water is decomposed to generate hydrogen and oxygen, and the hydrogen is exothermic and burned into water. The process is regenerated, clean and green. The electrocatalytic water splitting reaction includes two half-reactions, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Among them, hydrogen evolution is faster, while oxygen evolution involves the cleavage of four OH covalent bonds, two Water molecules lose four electrons and consume energy to generate OO covalent bonds, which need to overcome higher energy barriers to achieve. To this end, scholars have made a lot of efforts to develop high-efficiency oxygen evolution catalysts. Of the many systems explored, iridium dioxide (IrO ₂ ) and ruthenium dioxide (RuO ₂ ) are believed to be the most effective. However, their scarcity and expensive price limit their wide practical applications. For this reason, it is an opportunity and a challenge to develop efficient, inexpensive and earth-abundant non-precious metal oxygen evolution catalysts to reduce the electricity consumption of oxygen evolution.

Metal-organic complexes have the advantages of high porosity, large specific surface area, regular pores, adjustable pore size, convenient synthesis, chemical modification according to the target, rich and diverse structures, and easy design. , sensing materials, optoelectronic materials, drug release and other aspects have been widely used. Currently, the research on functional materials derived from MOFs precursors or templates is increasing. For example, porous carbon, metal oxide, metal/carbon, and metal oxide/carbon nanomaterials have been reported. The constructed 3D metal oxides, using Excellent properties have been shown for high-efficiency supercapacitors, lithium-ion batteries, and oxygen reduction. In 2014, Chaikittisilp and his team first reported the preparation of electrocatalysts for water splitting using MOFs as precursors. They used zeolitic imidazolate framework-9 (ZIF-9) as the precursor to prepare nanoporous _CoxOy -C composites for electrocatalytic _OER . Because direct high-temperature pyrolysis of MOFs precursors often leads to framework collapse and agglomeration, an innovative strategy currently used is to utilize carbon nanomaterials such as graphene and multiwalled carbon nanotubes (CNTs). After loading MOFs, carbon-based composite electrocatalysts were prepared by high-temperature pyrolysis to prevent product agglomeration and increase its specific surface area. For example, in 2016, Aijaz and his team synthesized Co@Co3O4 nanoparticles embedded in carbon nanotube _- grafted nitrogen-doped carbon by high-temperature reduction and oxidative calcination of Co-MOF in _H2 atmosphere _. Polyhedral high activity oxygen evolution catalyst. Although there are many kinds of MOFs, the number of MOFs precursors for electrocatalysts that are easy to prepare and transform into controllable morphology is limited. At present, studies on the preparation of oxygen evolution catalysts using three-dimensional (3D) MOFs microcrystals or nanocrystals as precursors have been reported. To the best of our knowledge, the preparation of oxygen evolution catalysts based on one-dimensional MOFs nanofibers has not been reported.

SUMMARY OF THE INVENTION

One of the technical tasks of the present invention is to provide a method for preparing composite carbon and transition element oxide nano-catalysts in order to make up for the deficiencies of the prior art. The method has low cost of raw materials, simple preparation process, low reaction energy consumption and industrial application. prospect.

The second technical task of the present invention is to provide the use of the composite carbon and transition element oxide nanocatalysts, that is, the composite carbon and transition element oxide nanocatalysts are used to catalyze the electrolysis of water for oxygen evolution, and the catalyst has good oxygen evolution electricity. Catalytic activity and electrochemical stability.

For achieving the above object, the technical scheme adopted in the present invention is as follows:

1. A composite carbon and transition element oxide nano-catalyst preparation method, the steps are as follows:

Dissolve copper nitrate, manganese nitrate and cobalt nitrate in 15-18 mL of water to obtain a blue-clear copper nitrate-manganese nitrate-cobalt nitrate mixture; mix 0.40 mmol of L-aspartic acid with 0.50-0.58 mmol of hydrogen Sodium oxide is dissolved in 2.0-4.0 mL of water to obtain a clear aspartic acid base solution; the aspartic acid base solution is added to the copper nitrate-manganese nitrate-cobalt nitrate mixture, room temperature for 5min, to form a precipitate; after 1h pump Filtration, drying at 60 °C, to obtain Cu-MOF nanofibers loaded with Mn(II) and Co(II) ion nanofibers, namely CuMnCo-MOF nanofibers; the CuMnCo-MOF nanofibers were heated in a tube furnace to obtain composite carbon and transition element oxide nanocatalysts;

1) The copper nitrate, manganese nitrate and cobalt nitrate are in a ratio of 1:3:1, and the amount of copper nitrate is 1.5-2.6 mmol;

2) The Cu-MOF nanofiber has the chemical formula [CuL(H ₂ O)]n, and L is the L(II) ion of aspartic acid H ₂ L; a unit structure of the Cu-MOF nanofiber consists of a Cu(II) ion center, one L(II) ion and one H ₂ O molecule;

3) The CuMnCo-MOF nanofibers are composed of Cu-MOF nanofibers with a diameter of 90-160 nm and a length of 400-900 um loaded with Co(II) and Mn(II) ions;

4) The composite carbon and transition element oxide nano-catalyst is a fibrous composite material composed of semiconductor CuO, MnO ₂ and Co ₂ O ₃ nanoparticles supported on carbon crystallites, and the fiber diameter is 80-130 nm wide and long. 300-850 μm;

5) The CuMnCo-MOF nanofibers are heated in a tube furnace under an air atmosphere with a heating rate of 3-5 °C/min, heated to 250-300 °C, and kept for 1.5-2.5 h, and then heated for 2 ℃/min cooling rate to cool down to room temperature.

2. The above-mentioned composite carbon and transition element oxide nano-catalyst are used as the application of electrolysis water oxygen evolution catalyst, and the steps are as follows:

Disperse 6 mg of composite carbon and transition element oxide nanocatalyst in 250 μL isopropanol, 720 μL water and 30 μL, 5 wt% perfluorinated resin solution, and ultrasonically 120W at room temperature for 10-15 min to obtain a uniform mixture; add 6 μL dropwise The mixed solution is placed on a glassy carbon electrode and dried at room temperature to prepare a composite carbon and transition element oxide nano-catalyst working electrode;

Using a three-electrode electrochemical workstation, composite carbon and transition element oxide nanocatalyst working electrode, Pt sheet (5 mm × 5 mm × 0.1 mm) as the counter electrode, Ag/AgCl electrode as the reference electrode, and the electrolyte is 0.5 M The electrocatalytic water splitting performance was tested in KOH aqueous solution.

The above carbon-based copper-cobalt oxide nanosheets electrolyzed water for oxygen evolution. When the current density J=10mA/cm ² , the potential was 1.48V vs RHE; the Tafel slope was 65mV dec ^-1 , which all showed that the material was highly efficient in oxygen evolution. Catalytic activity; before and after 500 cycles, no obvious change was found in the polarization curve of this type of material, indicating that the catalyst has good stability.

Beneficial technical effects of the present invention:

1. The composite carbon and transition element oxide nanocatalysts obtained by the present invention are generated by one-dimensional metal-organic framework CuMnCo-MOF nanofibers, which are heated and pyrolyzed at 250-300 ° C in an air atmosphere, and the preparation process is simple and easy to control. The product has high preparation efficiency and is easy to be industrialized.

2. The present invention provides the application of a composite carbon and transition element oxide nanocatalyst as an oxygen evolution catalyst for electrolysis of water. Since the catalyst is a nanofiber composed of CuO, MnO ₂ and Co ₂ O ₃ semiconductor nanoparticles supported on carbon crystallites, the morphology is regular, monodisperse, high specific surface area, and more and different active sites are exposed. The synergistic effect of CuO, MnO ₂ and Co ₂ O ₃ semiconductor nanoparticles and carbon crystallites is exerted, so that the catalytic oxygen evolution based on the composite material has high catalytic efficiency and good stability.

Detailed ways

The present invention will be further described below in conjunction with the embodiments, but the protection scope of the present invention is not limited to the embodiments, and changes made by professionals in the field to the technical solutions of the present invention should all fall within the protection scope of the present invention.

Example 1

A kind of composite carbon and transition element oxide nano-catalyst preparation method

Dissolve 1.5 mmol copper nitrate, copper nitrate, manganese nitrate and cobalt nitrate in a ratio of 1:3:1 in 15-18 mL of water to obtain a blue and clear copper nitrate-manganese nitrate-cobalt nitrate mixture; mix 0.40 mmol of L-aspartic acid and 0.50 mmol of sodium hydroxide were dissolved in 2.0 mL of water to obtain a clear aspartic acid base solution; the aspartic acid base solution was added to the copper nitrate-manganese nitrate-cobalt nitrate mixture , at room temperature for 5 min, a precipitate was formed; after 1 h, suction filtration, and drying at 60 °C to obtain Cu-MOF nanofibers loaded with Mn(II) and Co(II) ion nanofibers, namely CuMnCo-MOF nanofibers; The composite carbon and transition element oxide nanoparticles were prepared by placing them in a tube furnace and heating in an air atmosphere with a heating rate of 3 °C/min, heating to 250 °C, holding for 1.5 h, and then cooling to room temperature at a cooling rate of 2 °C/min. catalyst.

Example 2

A kind of composite carbon and transition element oxide nano-catalyst preparation method

Dissolve 2.6 mmol copper nitrate, copper nitrate, manganese nitrate and cobalt nitrate in a ratio of 1:3:1 in 18 mL of water to obtain a blue clear copper nitrate-manganese nitrate-cobalt nitrate mixture; L-aspartic acid and 0.58 mmol sodium hydroxide were dissolved in 4.0 mL of water to obtain a clear aspartic acid alkali solution; the aspartic acid alkali solution was added to the copper nitrate-manganese nitrate-cobalt nitrate mixture, room temperature 5 min, a precipitate was formed; after 1 h, suction filtration, and drying at 60 °C to obtain Cu-MOF nanofibers loaded with Mn(II) and Co(II) ion nanofibers, namely CuMnCo-MOF nanofibers; the CuMnCo-MOF nanofibers were placed in The composite carbon and transition element oxide nanocatalysts were prepared by heating in a tube furnace in an air atmosphere with a heating rate of 5 °C/min, heating to 300 °C, holding for 2.5 h, and then cooling to room temperature at a cooling rate of 2 °C/min.

Example 3

A kind of composite carbon and transition element oxide nano-catalyst preparation method

Dissolve 2.0 mmol copper nitrate in 1:3:1 ratio of copper nitrate, manganese nitrate and cobalt nitrate in 16.5 mL of water to obtain a blue clear copper nitrate-manganese nitrate-cobalt nitrate mixture; L-aspartic acid and 0.54 mmol sodium hydroxide were dissolved in 3.0 mL of water to obtain a clear aspartic acid alkali solution; the aspartic acid alkali solution was added to the copper nitrate-manganese nitrate-cobalt nitrate mixture, room temperature 5 min, a precipitate was formed; after 1 h, suction filtration, and drying at 60 °C to obtain Cu-MOF nanofibers loaded with Mn(II) and Co(II) ion nanofibers, namely CuMnCo-MOF nanofibers; the CuMnCo-MOF nanofibers were placed in The composite carbon and transition element oxide nanocatalysts were prepared by heating in a tube furnace in an air atmosphere with a heating rate of 4 °C/min, heating to 275 °C, holding for 2.0 h, and then cooling to room temperature at a cooling rate of 2 °C/min.

Example 4

The Cu-MOF nanofibers described in Examples 1-3 have the chemical formula [CuL(H ₂ O)]n, and L is the L(II) ion of aspartic acid H ₂ L; a unit structure of the Cu-MOF nanofibers , consisting of one Cu(II) ion center, one L(II) ion and one H ₂ O molecule; the CuMnCo-MOF nanofibers are composed of Cu -MOF nanofibers support Co(II) and Mn(II) ions; the composite carbon and transition element oxide nanocatalyst is composed of semiconductor CuO, MnO ₂ and Co ₂ O ₃ nanoparticles supported on carbon crystallites The fiber-like composite material, the fiber diameter is 80-130nm wide and 300-850 μm long.

Example 5 Application of composite carbon and transition element oxide nanocatalysts as oxygen evolution catalysts for electrolysis of water

Disperse 6 mg of composite carbon and transition element oxide nanocatalysts prepared in Example 1 in 250 μL isopropanol, 720 μL water and 30 μL, 5 wt% perfluorinated resin solution, and sonicate at room temperature 120W for 10-15min to prepare Homogeneous mixed solution; drop 6 μL of the mixed solution onto the glassy carbon electrode, and dry at room temperature to prepare the composite carbon and transition element oxide nano-catalyst working electrode;

Using a three-electrode electrochemical workstation, composite carbon and transition element oxide nanocatalyst working electrode, Pt sheet (5 mm × 5 mm × 0.1 mm) as the counter electrode, Ag/AgCl electrode as the reference electrode, and the electrolyte is 0.5 M The electrocatalytic water splitting performance was tested in KOH aqueous solution.

Example 6 The steps and methods are the same as those of Example 5, except that the composite carbon and transition element oxide nanocatalyst prepared in Example 1 is replaced with the catalyst prepared in Example 2.

Example 7 The steps and methods are the same as those in Example 5, except that the composite carbon and transition element oxide nanocatalyst prepared in Example 1 was replaced with the catalyst prepared in Example 3.

Example 8 The composite carbon and transition element oxide nanocatalysts prepared in Examples 1-7 were electrolyzed for oxygen evolution from water. When the current density was J=10mA/cm ² , the potential was 1.48 V vs RHE; the Tafel slope was 65mV dec ^-1 , indicating that the material has high catalytic activity for oxygen evolution; before and after 500 cycles, no obvious change was found in the polarization curve of this type of material, indicating that the catalyst has good stability.

Claims (6)

1. a preparation method of composite carbon and transition element oxide nano-catalyst, is characterized in that, step is as follows: Dissolve copper nitrate, manganese nitrate and cobalt nitrate in 15-18mL of water to obtain a blue and clear copper nitrate-manganese nitrate-cobalt nitrate mixed solution; 0.40mmol of L-aspartic acid and 0.50-0.58mmol of hydrogen Sodium was dissolved in 2.0-4.0 mL of water to obtain a clear aspartic acid alkali solution; the aspartic acid alkali solution was added to the copper nitrate-manganese nitrate-cobalt nitrate mixture, room temperature for 5min, to form a precipitate; suction filtration after 1h , and dried at 60 °C to obtain Cu-MOF nanofibers loaded with Mn(II) and Co(II) ion nanofibers, namely CuMnCo-MOF nanofibers; the CuMnCo-MOF nanofibers were heated in a tube furnace to obtain composite carbon and Transition element oxide nanocatalysts; The copper nitrate, manganese nitrate and cobalt nitrate are in a ratio of 1:3:1, and the amount of copper nitrate is 1.5-2.6 mmol. 2 . The method for preparing a composite carbon and transition element oxide nanocatalyst according to claim 1 , wherein the Cu-MOF nanofibers have the chemical formula [CuL(H ₂ O)] _n , and L is L(II) ion of aspartate H ₂ L; a unit structure of Cu-MOF nanofibers consisting of one Cu(II) ion center, one L(II) ion and one H ₂ O molecule. 3. the preparation method of a kind of composite carbon and transition element oxide nano-catalyst as claimed in claim 1, is characterized in that, described CuMnCo-MOF nano-fiber, is 90-160nm by diameter width, length is 400-900um The Cu-MOF nanofibers loaded with Co(II) and Mn(II) ions are composed. 4. the preparation method of a kind of composite carbon and transition element oxide nano-catalyst as claimed in claim 1 is characterized in that, described composite carbon and transition element oxide nano-catalyst are made of semiconductor CuO, MnO ₂ and Co ₂ A fibrous composite material composed of _O3 nanoparticles supported on carbon crystallites, the fiber diameter is 80-130 nm wide and 300-850 μm long. 5. the preparation method of a kind of composite carbon and transition element oxide nano-catalyst as claimed in claim 1, is characterized in that, described CuMnCo-MOF nano-fiber is placed in tubular furnace heating, is to carry out under air atmosphere, and temperature rises The rate is 3-5°C/min, heated to 250-300°C, maintained for 1.5-2.5h, and then cooled to room temperature at a cooling rate of 2°C/min. 6. Application of the composite carbon and transition element oxide nanocatalyst prepared by the preparation method as claimed in claim 1 as an oxygen evolution catalyst for electrolysis of water.