Synthesis of cubic crystal indium oxide and application thereof in electrocatalytic nitrogen reduction
阅读说明：本技术 立方晶型氧化铟的合成及其在电催化氮还原中的应用 (Synthesis of cubic crystal indium oxide and application thereof in electrocatalytic nitrogen reduction ) 是由 宋鹏飞 曹雪梅 于丽 马芳芳 马菁菁 李永莉 袁小龙 于 2020-12-18 设计创作，主要内容包括：发明公开了一种立方晶型氧化铟的合成及其在电催化氮还原反应中的应用,将尿素的水溶液,通过一定的方式加入四水合氯化铟的乙醇和水溶液在一定温度下反应一定时间,冷却至室温后,离心收集产物,用乙醇洗涤去除未反应残留物,在一定条件下干燥除去杂质,在一定温度下空气中煅烧一定时间,形成三氧化二铟晶体,用作三电极体系下的电催化还原氮气的催化剂,该合成方法操作简便,可控制性强,产量高。合成的该材料成本较低,没有贵金属,对环境污染小,对于氮气还原反应有较高的催化活性和良好的选择性,是一种优异的催化剂。(The invention discloses a synthesis of cubic crystal indium oxide and its application in electrocatalytic nitrogen reduction reaction, adding ethanol of indium chloride tetrahydrate and aqueous solution into aqueous solution of urea by a certain mode, reacting for a certain time at a certain temperature, cooling to room temperature, centrifugally collecting the product, washing with ethanol to remove unreacted residue, drying under a certain condition to remove impurities, calcining in air at a certain temperature for a certain time to form indium sesquioxide crystal, and using the crystal as a catalyst for electrocatalytic reduction of nitrogen under a three-electrode system. The synthesized material has the advantages of low cost, no noble metal, small environmental pollution, high catalytic activity and good selectivity for nitrogen reduction reaction, and is an excellent catalyst.)
1. A synthesis method of cubic crystal indium oxide is characterized by comprising the following steps:
1) respectively taking InCl according to a molar ratio of 1: 1-203·4H2O and urea; dissolving urea in water to obtain a urea aqueous solution, wherein the molar ratio of urea to water in the urea aqueous solution is 1: 1-100;
adding water, ethanol and ethanol into water respectively according to a molar ratio of 1: 1-20, and uniformly stirring to obtain an ethanol water solution;
2) adding InCl3·4H2Dissolving O in an ethanol water solution to obtain a mixed solution, wherein the molar ratio of indium chloride tetrahydrate to ethanol in the mixed solution is 1: 1-50;
3) slowly dropwise adding a urea aqueous solution into the mixed solution under the stirring condition, then reacting for 6-48 h at the temperature of 30-80 ℃ in a magnetic stirring oil bath kettle, naturally cooling to room temperature, centrifuging, and collecting a product;
4) and washing the product with ethanol, drying and annealing to obtain the indium oxide nano material.
2. The method for synthesizing cubic indium oxide as claimed in claim 1, wherein in the step 4), the product is washed with ethanol and then dried at 40-60 ℃ for 10-48 hours.
3. The method for synthesizing cubic indium oxide as claimed in claim 1, wherein in the step 4), annealing is performed at 100 to 600 ℃ in air for 2 to 6 hours.
4. The application of the cubic indium oxide synthesized by the method for synthesizing cubic indium oxide according to claim 1 in electrocatalytic nitrogen reduction reaction.
Technical Field
The invention belongs to the technical field of nano material chemistry, relates to a synthesis method of indium oxide, in particular to a synthesis method of a cubic crystal indium oxide material, and also relates to an application of the material in an electrocatalytic nitrogen reduction reaction.
Background
The limited nature of fossil fuels makes it critical to find renewable energy sources to replace fossil fuels. Nitrogen is one of the most productive chemicals and can be produced not only as a nitrogen-rich fertilizer but also as a carbon-free energy carrier, and can be conveniently condensed into liquid for transportation. Currently, NH is industrially used3Mainly adopts a Haber-Bosch process, wherein NH3Is formed by N2And H2 (N2 + 3H2 → 2NH3) In the case of iron or ruthenium as catalyst, a chemical reaction occurs, and the kinetics of the reaction is slow, requiring high temperatures to accelerate the reaction. Annual production of NH3The consumed energy accounts for about 1-2% of the annual total amount of world energy, and the consumption of a large amount of primary energy and the emission of greenhouse gases are accompanied. However, high temperatures in the production process can lead to NH3Decomposition, therefore high pressure is introduced according to Le Chatelier principle to reduce decomposition. The Haber-Bosch process based on iron-based catalysts requires high temperature (300-500 ℃) and high pressure (200-300 atm). With the reduction of fossil fuels and the increase of greenhouse gas emission, a green, sustainable and low-cost NH is developed3The production mode is urgent. Electrocatalytic and photo (electro) catalytic processes are considered as energy-saving and environmentally friendly NH3Production processes, which can be carried out under ambient conditions using renewable energy sources. Will N2Photocatalytic reduction to NH3Is less efficient than the electrocatalytic reduction of N2Because carriers generated due to various wavelengths and light are rapidly recombined, andnot all photons are available for the photocatalytic process. For example, Nitrogen Reduction Reaction (NRR) by electrocatalysis may be driven by electric energy generated by solar cells and wind power generation, and photo- (electro-) catalysis NRR may directly drive the reaction to occur with sunlight. Thus, the two ways are to implement N2And H2Conversion of O to NH3The method is an extremely effective way in the aspects of cleanness, energy conservation and sustainable development.
Disclosure of Invention
The invention aims to provide a method for synthesizing cubic crystal indium oxide, which is simple to operate and can control the appearance.
The invention also aims to provide an application method of the cubic indium oxide synthesized by the synthesis method in the electrocatalytic nitrogen reduction reaction.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows: a method for synthesizing cubic indium oxide specifically comprises the following steps:
1) respectively taking InCl according to a molar ratio of 1: 1-203·4H2O and urea; dissolving urea in water to obtain a urea aqueous solution, wherein the molar ratio of urea to water in the urea aqueous solution is 1: 1-100;
adding water, ethanol and ethanol into water respectively according to a molar ratio of 1: 1-20, and uniformly stirring to obtain an ethanol water solution;
2) adding InCl3·4H2Dissolving O in an ethanol water solution to obtain a mixed solution, wherein the molar ratio of indium chloride tetrahydrate to ethanol in the mixed solution is 1: 1-50;
3) slowly dropwise adding a urea aqueous solution into the mixed solution under the stirring condition, then reacting for 6-48 h at the temperature of 30-80 ℃ in a magnetic stirring oil bath kettle, naturally cooling to room temperature, centrifuging, and collecting a product;
4) washing the product with ethanol to remove unreacted residue; drying at 40-60 deg.C for 10-48 h, placing into a muffle furnace, annealing at 100-600 deg.C in air for 2-6 h to make in (OH)3Reaction to form In2O3Obtaining indium oxide (In)2O3) And (3) nano materials.
The other technical scheme adopted by the invention is as follows: in with different morphologies synthesized by the synthesis method2O3Application of the nano material in electrocatalytic nitrogen reduction reaction. The method specifically comprises the following steps:
weighing the prepared indium oxide nano material, grinding the indium oxide nano material into powder by using an agate mortar, taking a 1mL sample tube, and taking a certain amount of In2O3Putting the powder into a sample tube, sucking a small amount of Nafion solution by using a pipette, injecting the Nafion solution into the sample tube, and performing ultrasonic treatment to In2O3The powder is evenly dispersed in Nafion solution to obtain the catalyst dispersion liquid.
A three-electrode system for electricity taking chemical catalysis experiments is characterized in that the three electrodes are respectively as follows: the glassy carbon electrode loaded with the catalyst is used as a working electrode; the platinum wire electrode is a counter electrode; an Ag/AgCl electrode is used as a reference electrode; the electrolytic cells are all single electrolytic cell systems. The electrolyte was 0.1M aqueous hydrochloric acid (pH = 1). A small amount of catalyst dispersion liquid is taken by a liquid-transfering gun and is spotted on a glassy carbon electrode (GC XR303, the effective diameter is 3 mm, Shanghai immortal kernel instruments and meters Co., Ltd.), and the glassy carbon electrode is naturally dried in the air to be used as a working electrode.
The reduction reaction is carried out by continuously introducing nitrogen (N)2) The electrolytic bath of (3) was 0.1M HCl solution. The applied voltage was controlled by an electrochemical workstation model CHI660E, which provides a constant potential, all potential measurements were measured with an Ag/AgCl electrode as reference electrode, and the conversion formula for all applied potentials to a scale of Reversible Hydrogen Electrode (RHE) potential was: e (a)vs. RHE) = E (vs. Ag/AgCl) + 0.197 V + 0.0591 × pH。
Indium oxide as catalyst realizes the reaction to NH under the environmental condition3The experimental results of (1). NH in an electrolytic bath containing an indium oxide catalyst3The production rate of (A) is 6.42 mgh at-0.2V-1mg-1The faraday efficiency is about 6.8%.
The synthesis method of the invention is to calcine and synthesize the In with the cubic crystal structure at different temperatures by mixing the indium chloride tetrahydrate and the urea according to the specific proportion2O3The synthesis method is simple and has high efficiency. Synthesized In of cubic crystal structure2O3The material has high nitrogen reduction selectivity and can effectively catalyze nitrogen reduction reaction.
Drawings
FIG. 1 shows cubic In crystals obtained In examples 1 to 42O3The microscopic electron microscope topography is shown.
FIG. 2 shows cubic In crystals obtained In examples 1 to 42O3XRD pattern of (a).
FIG. 3 shows cubic In crystals obtained In examples 1 to 42O3Thermogram of (c).
FIG. 4 shows cubic In crystals obtained In examples 1 to 42O3The nitrogen reduction reaction is carried out by ultraviolet absorption attached figure.
FIG. 5 shows cubic In crystals obtained In examples 1 to 42O3Ammonia yield and faraday efficiency for nitrogen reduction.
FIG. 6 shows cubic In obtained In example 32O3Stability of catalytic nitrogen reduction reaction.
FIG. 7 shows cubic In obtained In example 32O3XPS chart of (a).
FIG. 8 shows cubic In prepared by a synthesis method of the prior art2O3The microscopic electron microscope topography is shown.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Example 1
Respectively taking InCl according to a molar ratio of 1: 13·4H2O and urea; dissolving urea in water to obtain urea aqueous solution, wherein the molar ratio of urea to water in the urea aqueous solution is 1: 1; respectively taking water and ethanol according to a molar ratio of 1: 1, adding the ethanol into the water, and uniformly stirring to obtain an ethanol aqueous solution; adding InCl3·4H2Dissolving O in ethanol water solution to obtain mixed solution, wherein the molar ratio of indium chloride tetrahydrate to ethanol in the mixed solution is 1: 1; slowly dropwise adding the urea aqueous solution into the mixed solution under the stirring condition, then reacting for 24 hours at the temperature of 80 ℃ in a magnetic stirring oil bath kettle, naturally cooling to room temperature, centrifuging, and collecting the product;washing the product with ethanol to remove unreacted residue; drying at 60 deg.C for 48h, placing into a muffle furnace, and annealing at 150 deg.C in air for 6h to allow in (OH)3Reaction to form In2O3Obtaining cubic indium oxide (In)2O3) A material.
Example 2
Respectively taking InCl according to a molar ratio of 1: 203·4H2O and urea; dissolving urea in water to obtain urea aqueous solution, wherein the molar ratio of urea to water in the urea aqueous solution is 1: 100; adding water, ethanol and ethanol into water respectively according to a molar ratio of 1: 20, and stirring uniformly to obtain an ethanol water solution; adding InCl3·4H2Dissolving O in ethanol water solution to obtain mixed solution, wherein the molar ratio of indium chloride tetrahydrate to ethanol in the mixed solution is 1: 1; slowly dropwise adding the urea aqueous solution into the mixed solution under the stirring condition, then reacting for 24 hours at the temperature of 80 ℃ in a magnetic stirring oil bath kettle, naturally cooling to room temperature, centrifuging, and collecting the product; washing the product with ethanol to remove unreacted residue; drying at 60 deg.C for 48h, placing into a muffle furnace, and annealing at 200 deg.C in air for 6h to allow in (OH)3Reaction to form In2O3Obtaining cubic crystal indium oxide (In)2O3）。
Example 3
Respectively extracting InCl according to a molar ratio of 1: 1103·4H2O and urea; dissolving urea in water to obtain urea aqueous solution, wherein the molar ratio of urea to water in the urea aqueous solution is 1: 50; adding water, ethanol and ethanol into water respectively according to a molar ratio of 1: 10, and stirring uniformly to obtain an ethanol water solution; adding InCl3·4H2Dissolving O in ethanol water solution to obtain mixed solution, wherein the molar ratio of indium chloride tetrahydrate to ethanol in the mixed solution is 1: 1; slowly dropwise adding the urea aqueous solution into the mixed solution under the stirring condition, then reacting for 24 hours at the temperature of 80 ℃ in a magnetic stirring oil bath kettle, naturally cooling to room temperature, centrifuging, and collecting the product; washing the product with ethanol to remove unreacted residue; drying at 60 deg.C for 48 hr, and placing into muffleAnnealing in a furnace at 250 deg.C for 6h in air to bring in (OH)3Reaction to form In2O3Obtaining cubic crystal indium oxide (In)2O3) And (3) nano materials.
Example 4
Respectively extracting InCl according to a molar ratio of 1: 1103·4H2O and urea; dissolving urea in water to obtain urea aqueous solution, wherein the molar ratio of urea to water in the urea aqueous solution is 1: 50; adding water, ethanol and ethanol into water respectively according to a molar ratio of 1: 10, and stirring uniformly to obtain an ethanol water solution; adding InCl3·4H2Dissolving O in ethanol water solution to obtain mixed solution, wherein the molar ratio of indium chloride tetrahydrate to ethanol in the mixed solution is 1: 1; slowly dropwise adding the urea aqueous solution into the mixed solution under the stirring condition, then reacting for 24 hours at the temperature of 80 ℃ in a magnetic stirring oil bath kettle, naturally cooling to room temperature, centrifuging, and collecting the product; washing the product with ethanol to remove unreacted residue; drying at 60 deg.C for 48h, placing into a muffle furnace, and annealing at 300 deg.C in air for 6h to allow in (OH)3Reaction to form In2O3Obtaining cubic crystal indium oxide (In)2O3) And (3) nano materials.
Produced In2O3Structural morphology of
1. In prepared In examples2O3The micro-morphology of (2).
FIG. 1 is a microscopic electron microscope image of the indium oxide nanomaterials prepared in examples 1 to 4, in which FIG. 1 is a Scanning Electron Microscope (SEM) image of the indium oxide nanomaterials prepared in examples 1 to 4, and FIG. 1 is a Transmission Electron Microscope (TEM) image of the indium oxide nanomaterials prepared in examples 1 to 4. The graph shows that the indium oxide nano materials prepared in examples 1 to 4 have a relatively regular cubic crystal structure, and some stacking fault structures can be captured in the regular cubic crystal structure. These grain boundary and stacking fault surface structures increase In2O3Catalytically active sites of the catalystIts ratio is regular In2O3More easily combined with gas molecules, increasing the active sites for catalysis.
2. Examples the cubic crystal structure In2O3Peak of X-ray diffraction
FIG. 2 shows X-ray diffraction peaks of the cubic indium oxide nanomaterials prepared In examples 1 to 4, and clearly shows that all the diffraction peaks can be well matched with typical cubic crystal rod In2O3(JCPDS card No. 06-0416) intense diffraction peaks were observed at 2 theta angles of 21.5, 30.5, 35.4, 51.0, and 60.7 corresponding to (211), (222), (400), (440), and (622) crystallographic In cristobalite2O3. While example 1 and example 2 are in (OH) for temperature reasons3Is not completely converted into In2O3So that In is present2O3And in (OH)3Mixed crystal forms. Since the conductivity of the metal oxide is inherently superior, the deposited material may have a reduced specific surface area and a reduced ability to adsorb gas, so that the nitrogen reduction catalytic activity is reduced,
3. in prepared In examples2O3Thermogravimetric analysis of
When the annealing temperature reaches 250 ℃ or higher, in (OH)3Converted In2O3The quality of (2) is sharply reduced (FIG. 3), and in (OH) is converted into a hydroxyl radical by dehydroxylation of the hydroxyl radical3Is converted into In2O3-x(OH) y corresponds. Total weight loss 20.40% higher than In (OH)3Completely converting In2O3The mass loss was predicted to be 16.28%. Probably due to the presence of physically and chemically adsorbed water molecules, for example about 6% of the mass before 200 ℃ is also reduced. Another constant temperature peak exists around 305 deg.C, which may be In2O3-x (OH)yThe result of the crystal order transformation. Indicating that the material tends to stabilize at this temperature.
4. In prepared In examples2O3Ultraviolet absorption attached figure of nitrogen reduction reaction
In obtained In examples 1 to 42O3The potential of (2) is over 2h, the ammonia content is determinedIndophenol blue spectrophotometry. In prepared In different examples2O3The ultraviolet absorption spectrum (figure 4) of the ammonia content generated by the electro-reduction reaction is-0.2V vs.The UV absorption intensity at RHE potential of In prepared In example 3 was not difficult to find2O3The absorbance was the strongest, indicating that the potential was-0.2V at the same reaction time vs.In prepared In example 3 at RHE2O3The production of ammonia is the greatest.
FIG. 5 shows In produced In example2O3Ammonia yield and faraday efficiency for nitrogen reduction.
In obtained In examples 1 to 42O3at-0.2V vs.The electrocatalytic reduction activity at RHE can be determined from NH3Production rate and faraday efficiency (figure 5). Visually reflects the ammonia production over the same period of time for the same catalyst dosage, In, as described above, example 32O3The maximum production rate is 6.42 mg h at the optimal potential due to the regular crystal form and more surface active sites-1mg-1And a faraday efficiency of 6.8%.
FIG. 6 shows In obtained In example 32O3Stability of catalytic nitrogen reduction reaction.
Fig. 6 is a chronoamperometric graph at a corresponding potential. The timing current at different potentials does not fluctuate greatly, and the timing current curve (FIG. 6) measured for a long time also shows better stability, which indicates that In2O3The material has better electrochemical stability.
FIG. 7 shows In obtained In example 32O3X-ray photoelectron spectrum
FIG. 7 shows In obtained In example 32O3The X-ray photoelectron spectrum shows that the material contains three elements of C, In and O, and C may be impurity on the surface of the material and only contains two elements of indium and oxygen. The figure illustrates In2O3The preparation is successful.
Comparative example
In(OH)3And In2O3Combination of x (OH) y nanorodsIn a typical synthesis. The method disclosed in the ACS Nano 2016, 10, 5578-5586) is adopted: 25g of urea and 3g of InCl3Dissolved in 100mL of deionized water. The aqueous solution was then heated in an oil bath under magnetic stirring at 80 ℃ for a controlled period of time. After cooling to room temperature, the white product was collected by centrifugation and washed with water to remove unreacted residue. Drying at room temperature for 48 h. Drying in (OH)3Putting the precursor into an oven, and treating in air at 250 ℃ for different times to obtain in (OH)3x(OH)yAnd (3) sampling. In (OH) was chosen to study the length effect3Five initial reaction cycles of 2, 3, 5, 8 and 12 h for the precursor, followed by treatment at 250 ℃ for 6h, to give in (OH) of varying lengths3x (OH) y samples as shown in FIG. 8.
FIG. 1 is a microscopic electron microscope image of an indium oxide nanomaterial prepared by the synthesis method of the present invention. FIG. 8 is a microscopic electron microscope image of an indium oxide nanomaterial prepared by a synthesis method in the prior art. It can be seen from FIG. 8 that the indium oxide nanorod structure is formed by the synthesis method in the prior art. The regular cubic crystal structure shown in figure 1 is synthesized by the method of the invention. Indium oxide having a cubic structure is much stronger in nitrogen reducibility than indium oxide having a rod-like structure.
XPS peak data of high resolution O1s of the cubic indium oxide nanomaterial prepared in examples 1-4 are shown in Table 1.