CN111534833B

CN111534833B - Copper nano electrode with high-index crystal face and preparation method and application thereof

Info

Publication number: CN111534833B
Application number: CN202010270321.9A
Authority: CN
Inventors: 邝允; 韩璐; 孙晓明
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2020-04-08
Filing date: 2020-04-08
Publication date: 2021-08-17
Anticipated expiration: 2040-04-08
Also published as: CN111534833A

Abstract

The invention belongs to the technical field of electrode materials, and particularly relates to a copper nano electrode with a high-index crystal face, and a preparation method and application thereof. The electrode comprises a conductive substrate and a copper nanowire aggregate loaded on the surface of the conductive substrate; the length of the copper nanowire is 10-200 μm, the length-diameter ratio is more than 1000, the surface of the copper nanowire has a step-shaped appearance and has a high-index crystal face, and the high-index crystal face comprises but is not limited to <200>, <220>, <222>, <311>, <310>, <320>, <331>, <400>, <510>, <511>, <533>, <610>, <755> high-index crystal faces. The invention also discloses a preparation method and application of the electrode. The electrode material with the high-index crystal face is prepared for the first time, can well inhibit side reactions when used for electrochemically reducing carbon dioxide, and has good selectivity on high-carbon products such as ethylene, ethanol and isopropanol.

Description

Copper nano electrode with high-index crystal face and preparation method and application thereof

Technical Field

The invention belongs to the technical field of electrode materials, and particularly relates to a copper nano electrode with a high-index crystal face, and a preparation method and application thereof.

Background

In recent years, with the mass exploitation and use of fossil fuels, the content of carbon dioxide in the atmosphere is increased dramatically, and a series of serious environmental problems such as greenhouse effect, global warming and the like are caused. Meanwhile, the problem of energy crisis is increasingly highlighted, and the reduction of the carbon dioxide content in the atmosphere and the search of novel clean energy become important problems. The electrocatalytic carbon dioxide reduction technology converts excessive carbon dioxide in the atmosphere into renewable fuels or value-added chemicals without generating additional pollutants, is an effective means for realizing carbon cycle and solving energy and environmental problems, and thus becomes a hot spot of people.

With the research, the copper-based material has a great application prospect in the electrocatalytic carbon dioxide reduction technology, and can catalyze the carbon dioxide reduction to generate a high-order hydrocarbon product with high commercial value. However, the search for copper-based catalysts with high current density and high product selectivity for carbon dioxide reduction remains a great challenge due to low product selectivity, difficulty in suppressing side reactions (hydrogen evolution reactions), and the like.

The present invention has been made to solve the above problems.

Disclosure of Invention

The invention provides a copper nano electrode with a high-index crystal face, which comprises a conductive substrate and a copper nano wire aggregate loaded on the surface of the conductive substrate; the copper nanowire has a face centered cubic crystal structure and has high index crystal planes including, but not limited to <200>, <220>, <222>, <311>, <310>, <320>, <331>, <400>, <510>, <511>, <533>, <610>, and <755> crystal planes.

Preferably, the conductive substrate is selected from one or more of carbon paper, carbon cloth, copper foil, copper foam or titanium foam.

Preferably, the copper nanowire has a length of 10-200 μm and an aspect ratio of greater than 1000.

Preferably, the surface of the copper nanowire has a step-like morphology. The copper material is essentially face centered cubic.

The lattice plane index is one of constants of the crystal, a plane passing through any three nodes in the space lattice is called a lattice plane, and the lattice plane is characterized by adopting the lattice plane index. The plane index is the reciprocal ratio of the intercept coefficients of a plane on 3 crystal axes, and the 3 integers obtained after conversion to the simplest integer ratio are called the Miller index of the plane. When 4 crystal axes are selected for hexagonal and trigonal crystals, 4 intercept coefficients exist for one crystal plane, and 4 integers obtained from the reciprocal ratio of the two are called the Miller-Blawian index of the crystal plane. The two indices are generally known as the plane indices. The miller index is used herein to represent the plane index.

Whereas the high index crystal planes mean that the spacing of the crystal planes is relatively large with respect to the low index crystal planes.

The high index facets described herein are divided by the miller index, and high index facets provided that one number is greater than or equal to 2. For example, the three fundamental crystal planes <111>, <110>, <100> are low index crystal planes, and the crystal planes <220>, <211>, <311>, <310> are high index crystal planes.

The copper nanowire electrode is a plurality of disordered parallel copper nanowires loaded on the conductive substrate.

The second aspect of the present invention provides a method for preparing a copper nano-electrode according to the first aspect, comprising the following steps:

(1) adding a copper salt solution into an alkaline solution, uniformly mixing, adding ethylenediamine, then adding a hydrazine solution into the mixed solution, and reacting to obtain a copper nanowire dispersion solution;

(2) and (2) coating the copper nanowire dispersion liquid obtained in the step (1) on a conductive substrate, drying to obtain the conductive substrate coated with the copper nanowires, and treating the conductive substrate for a certain time by adopting a square wave potential method to obtain the copper nanowire electrode.

Preferably, the conductive substrate in step (2) is one or more selected from copper foil, copper foam, titanium foam, carbon paper, or carbon cloth.

Preferably, the square wave potential treatment method adopts a three-electrode system, the working electrode is the conductive substrate coated with the copper nanowires in the step (2), the reference electrode is a silver-silver chloride electrode, and the counter electrode is a carbon rod, carbon paper or carbon cloth; the processing time of the square wave potential is longer than 5 minutes, the switching frequency of the square wave potential is larger than 2 Hz, the absolute value of the current density of the working electrode at the high potential is lower than that of the current density at the low potential, the high potential of the working electrode is higher than 0.15 volt, and the low potential is lower than 0 volt relative to the standard hydrogen electrode and relative to the standard hydrogen electrode.

Preferably, the electrolyte in the square wave potentiometric treatment process is selected from potassium bicarbonate solution, sodium bicarbonate solution, potassium carbonate solution, sodium carbonate solution, potassium sulfate solution, sodium sulfate solution, potassium chloride solution, potassium bromide solution, sodium bromide solution or sodium chloride solution.

The invention provides a use of the copper nano-electrode of the first aspect for electrochemical reduction of carbon dioxide, which can improve selectivity of high carbon products. In particular, the yield of ethylene products can be improved, and meanwhile, the side reaction hydrogen evolution reaction is well inhibited.

Wherein the high carbon product/higher order hydrocarbon product is ethylene, ethanol and isopropanol.

The technical scheme can be freely combined on the premise of no contradiction.

The invention has the following beneficial effects:

1. the invention prepares the electrode material with high-index crystal face for the first time. The copper nanowire loaded on the conductive substrate has uniform size, the length is about 10-200 mu m, the diameter is about 50-100nm, the length-diameter ratio is more than 1000, the surface of the copper nanowire has a step-shaped appearance, and the copper nanowire is rich in a large number of high-index crystal faces and has a rough surface.

2. The copper nano-electrode material can well inhibit side reactions when used for electrochemically reducing carbon dioxide, and has good selectivity on high-carbon products such as ethylene, ethanol and isopropanol. The standard hydrogen electrode is used as a standard, the faradaic efficiency of the hydrogen is controlled within 30 percent in the range of minus 0.9 volt to minus 1.3 volt; the faradaic efficiency of the high carbon product reaches 60% at minus 1.1 volts, with the faradaic efficiency of the product ethylene reaching 40%.

3. The copper nano electrode material has good catalytic stability in the electrocatalytic carbon dioxide reduction reaction. The catalytic activity and stability of the catalyst can be kept for more than 6 hours continuously at minus 1.1 volts by taking a reversible hydrogen electrode as a standard. And the appearance of the electrode material is not changed greatly, so that the structure of the electrode material is proved to have good stability.

4. The preparation method is simple, the prepared high-index crystal face is relatively stable, the selectivity of the electrocatalytic carbon dioxide reduction reaction is relatively high, and the method is convenient for popularization and industrialization.

Drawings

Fig. 1 is a scanning electron microscope image of the copper nanowire electrode material prepared in example 1.

FIG. 2 is a scanning electron microscope image of the high-index lattice plane copper nanowire electrode material prepared in example 1.

Fig. 3 is an X-ray diffraction pattern of the copper nanowire electrode material before and after the square wave treatment of example 1, wherein fig. 3a is a conductive base material, and fig. 3b is a sample (containing a conductive base material).

Fig. 4a is an electron diffraction pattern of the copper nanowire electrode material obtained after square wave treatment in example 1.

Fig. 4b is an electron diffraction pattern of the copper nanowire electrode material without square wave treatment in example 1.

Fig. 5 is a graph of faraday efficiency and current density of electrochemical reduction of carbon dioxide in potassium chloride solution for the copper nanowire electrode in example 2, fig. 5a and 5b use copper nanowire electrode material after square wave treatment, and fig. 5c and 5d use copper nanowire electrode material before square wave treatment.

FIG. 6 is a graph showing the stability of the copper nanowire electrode in electrochemical reduction of carbon dioxide in a potassium chloride solution in example 2.

Fig. 7 is a scanning electron microscope image of the copper nanowire electrode of example 2 after stability test of electrochemical reduction of carbon dioxide in potassium chloride solution.

FIG. 8 is a scanning electron microscope image of the high-index lattice plane copper nanowire electrode material obtained after square wave treatment for 30 minutes.

FIG. 9 is a scanning electron microscope image of the high-index lattice copper nanowire electrode material obtained after square wave treatment for 60 minutes.

FIG. 10 is a scanning electron microscope image of the high-index lattice plane copper nanowire electrode material obtained after square wave treatment for 120 minutes.

Fig. 11 is a graph of faraday efficiency and current density of different reduction products obtained at different potentials when potassium chloride solution is used as electrolyte in electrochemical reduction of carbon dioxide for the high-index lattice copper nanowire electrode material obtained after square wave treatment for 30 minutes in example 3, 11a is a graph of faraday efficiency of different reduction products, and 11b is a graph of current density.

Fig. 12 is a graph of faraday efficiency and current density of different reduction products obtained at different potentials when potassium chloride solution is used as electrolyte in electrochemical reduction of carbon dioxide in the high-index lattice copper nanowire electrode material obtained after square wave treatment for 60 minutes in example 3, where 12a is a graph of faraday efficiency of different reduction products and 12b is a graph of current density.

Fig. 13 is a graph of faraday efficiency and current density of different reduction products obtained at different potentials when potassium chloride solution is used as electrolyte in electrochemical reduction of carbon dioxide for the high-index lattice copper nanowire electrode material obtained after 120 minutes of square wave treatment in example 3, 13a is a graph of faraday efficiency of different reduction products, and 13b is a graph of current density.

Detailed Description

The present invention will be further described with reference to the following embodiments.

Example 1

Preparing a copper nanowire electrode material with a high-index crystal face by the following steps:

A. preparing a reaction solution, and preparing 0.1mol/L copper sulfate solution, 15mol/L sodium hydroxide solution, 35% hydrazine hydrate solution by mass concentration and 1mol/L potassium chloride solution;

B. taking 120mL of 15mol/L sodium hydroxide solution into a three-neck flask, adding 6mL of 0.1mol/L copper sulfate solution under stirring, carrying out ultrasonic treatment for five minutes, adding 760 mu L of ethylenediamine under stirring, preheating by using an oil bath kettle, adding 60 mu L of 35% hydrazine solution under stirring when the temperature is raised to 70 ℃, continuously stirring for 3 minutes, closing the stirring, keeping the reaction temperature at 70 ℃, and reacting for 2 hours to obtain a copper nanowire dispersion solution;

C. uniformly dispersing the copper nanowire dispersion liquid obtained in the step B into absolute ethyl alcohol, adding 1mL of Nafion solution with the mass fraction of 5% into the mixed dispersion liquid, performing ultrasonic treatment for 10 minutes to uniformly disperse the Nafion solution, and uniformly coating the mixed solution on 1cm by using a 10 mu L liquid transfer gun^-2The gas diffusion conductive substrate (in this case, preferably gas diffusion carbon fiber paper is used as the conductive substrate of the electrode), and dried to obtain a conductive substrate coated with copper nanowires. Then, taking 1mol/L potassium chloride solution as electrolyte, and carrying out square wave potential treatment on the conductive substrate coated with the copper nanowires, wherein the square wave potential treatment method adopts a three-electrode system, a working electrode is an electrode loaded with the copper nanowires, a reference electrode is a silver-silver chloride electrode, and a counter electrode is a carbon rod electrode; the processing time of the square wave potential is 90 minutes, the switching frequency of the square wave potential is 10 Hz, the high potential of the square wave potential is set to be 0.2 volt (relative to a standard hydrogen electrode), and the low potential is set to be minus 0.5 volt (relative to the standard hydrogen electrode), namely, the absolute value of the current density of the working electrode under the high potential is lower than that of the current density under the low potential. And obtaining the copper nanowire electrode material with the high-index crystal face.

And (3) characterizing the copper nanowire electrode material. The results are as follows:

fig. 1 is a scanning electron microscope image of the copper nanowire electrode material (without square wave potential treatment) obtained in example 1. It can be seen from fig. 1 that the prepared copper nanowires have smooth surfaces and uniform sizes.

FIG. 2 is a scanning electron microscope image of the copper nanowire electrode material obtained after the square wave potential treatment in example 1. As can be seen from FIG. 2, the surface of the nanowire electrode material after the square wave potential treatment is in a step-like morphology and has a face-centered cubic crystal structure, the length of the copper nanowire is 40-200 μm, and the length-diameter ratio is greater than 1000.

FIG. 3 is an X-ray diffraction pattern of the copper nanowire electrode material before and after the square-wave potential treatment in example 1.

Wherein SW-CuNWs represents the copper nanowire electrode material after square wave potential treatment;

CuNWs represents a copper nanowire electrode material before square wave potential treatment;

it is obvious from fig. 3 that the diffraction peak of the prepared copper nanowire is in good correspondence with the standard card library, and after comparison, the crystal face of the prepared copper nanowire is obviously changed before and after treatment.

Table 1 shows the relative change values of the peak intensities of the crystal planes in the X-ray diffraction patterns of the copper nanowire electrode material before and after the square wave treatment in example 1. Assuming that the actual peak intensity value of the <111> crystal plane is 1, the relative intensity values of the other crystal planes are equal to the ratio of the actual peak intensity value to the actual peak intensity value of the <111> crystal plane.

Table 1 the following conclusions can be drawn:

1. compared with the nanowire electrode material before square wave processing, the nanowire electrode material after square wave processing has obviously increased numbers of the five high-index crystal faces of <200>, <220>, <222>, <311>, <310 >.

2. Compared with the nanowire electrode material before square wave processing, eight high-index crystal planes <320>, <331>, <400>, <510>, <511>, <533>, <610>, <755> are added to the nanowire electrode material after square wave processing.

TABLE 1

Sample (I)	<111>	<200>	<220>	<222>	<310>	<311>
							CuNWs	1	0.290	0.106	0.065	0.06	0.100
SW-CuNWs	1	0.300	0.112	0.076	0.076	0.111
							Sample (I)	<111>	<320>	<331>	<400>	<510>	<511>
CuNWs	1	0	0	0	0	0
							SW-CuNWs	1	0.035	0.029	0.036	0.017	0.012
Sample (I)	<111>	<533>	<610>	<755>
							CuNWs	1	0	0	0
SW-CuNWs	1	0.011	0.01	0.012

Local areas of the nanowire electrode material before and after square wave treatment in example 1 were selected for electron diffraction analysis.

Fig. 4a is an electron diffraction pattern of the nanowire electrode material obtained after square wave treatment. Fig. 4b is an electron diffraction pattern of the copper nanowire electrode material without square wave treatment.

From fig. 4a, 4b, the following conclusions can be drawn:

the diffraction light ring of the <111> crystal plane can be clearly seen in the electron diffraction pattern of the copper nanowire without square wave treatment, and the diffraction light rings of the high index crystal planes <200>, <220>, <222>, <311>, <310>, <320>, <331>, <400> can be clearly seen in the electron diffraction pattern light ring of the sample after square wave treatment. This can prove that the number of the upper crystal planes of the nanowire electrode material after square wave treatment is increased. Therefore, fig. 4a and 4b are consistent with the data in table 1, i.e., the diffraction pattern halo of the high index crystal planes <200>, <220>, <222>, <311>, <310>, <320>, <331>, <400> of the copper nanowire without square wave processing is not clearly shown.

Example 2

A test related to electrochemical reduction of carbon dioxide was performed using the copper nanowire electrode material prepared in example 1 with a potassium chloride solution as an electrolyte.

The test system employed a three-electrode test system, in which the working electrode was the copper nanowire electrode material prepared in example 1, the counter electrode was a carbon rod electrode, and the reference electrode was a silver-silver chloride electrode. The test conditions were: the method comprises the following steps of introducing carbon dioxide gas into an electrolyte solution which is 1mol/L potassium chloride solution at a rate of 20 ml/min for 30 minutes before the start of a test to achieve the aim of saturating the electrolyte solution, then testing the Faraday efficiency and the current density of an electrode under the conditions of normal temperature and normal pressure and stirring, measuring the Faraday efficiency of various products generated by the reduction of carbon dioxide of the electrode material by adopting a constant potential scanning test method under different potentials, and measuring the current density of the electrocatalytic carbon dioxide reaction by adopting a linear scanning voltammetry.

The test results were as follows:

fig. 5 is a faraday efficiency graph and a current density graph of different reduction products obtained by using a potassium chloride solution as an electrolyte at different potentials before and after the square wave treatment obtained in example 1 when the copper nanowire electrode material electrochemically reduces carbon dioxide. Fig. 5a and 5b use the copper nanowire electrode material after square wave processing. Fig. 5c and 5d use the copper nanowire electrode material before square wave processing.

As is evident from fig. 5a, 5 b:

1. the electrode material after square wave treatment generates high carbon products such as ethylene, ethanol, isopropanol and the like when the voltage is minus 0.7 volt to minus 1.3 volt.

2. The faradaic efficiency of the product ethylene at minus 1.1 volts is as high as 40%.

3. When the voltage is minus 1.3 volts, the Faraday efficiency of ethylene still reaches 36 percent, and the Faraday efficiency of high-carbon products (ethylene, ethanol and isopropanol) reaches 62 percent, which is nearly 4 times that of low-carbon products (carbon monoxide and formic acid), and the excellent selectivity of the electrode material to the high-carbon products is reflected.

4. At minus 0.7 volt to minus 1.3 volt, the faradaic efficiency of hydrogen evolution reaction is lower than 30 percent, namely, the selectivity of hydrogen evolution of side reaction is obviously inhibited.

As is evident from fig. 5c, 5 d:

1. the electrode material without square wave treatment has little high carbon product yield at minus 0.7 volts to minus 1.3 volts, and the products mainly comprise hydrogen, carbon monoxide and formic acid.

2. At minus 1.1 volts, the faradaic efficiency of the product ethylene is only 5%.

3. When the voltage is minus 1.3 volts, the electrode mainly generates hydrogen evolution reaction, and the Faraday efficiency of the product obtained by reducing carbon dioxide is 16 percent.

4. The faradaic efficiency of the hydrogen evolution reaction is above 60% at minus 0.7 volts to minus 1.3 volts.

Fig. 6 is a stability test chart of the copper nanowire electrode material prepared in example 1 for electrochemically catalyzing and reducing carbon dioxide in a potassium chloride solution.

Fig. 6 shows that: the prepared copper nanowire electrode material with the high-index crystal face has the advantages that the Faraday efficiency and the current density of a high-carbon product can be kept not to be attenuated for more than 6 hours continuously at a point position of minus 1.1 volt. Indicating its superior catalytic activity and stability.

Fig. 7 is a scanning electron microscope image of the copper nanowire electrode material with the high-index crystal plane prepared in example 1 after stability test of electrochemical reduction of carbon dioxide with potassium chloride solution as an electrolyte.

FIG. 7 illustrates: the copper nanowire having a high-index crystal plane prepared in example 1 undergoes little change in morphology after undergoing a stability test for more than 6 hours, that is, the structure thereof has good stability.

Example 3

The copper nanowire electrode material with the high-index crystal plane is prepared according to the method described in the example 1, and the difference with the example 1 is only that: the duration of the square wave potential treatment was 30 minutes, 60 minutes and 120 minutes, respectively. Finally obtaining three copper nanowire electrode materials with high-index crystal faces.

And (3) characterizing the three obtained copper nanowire electrode materials.

And FIGS. 8-10 are scanning electron microscope images of the high-index lattice plane copper nanowire electrode material obtained after square wave treatment for 30 minutes, 60 minutes and 120 minutes.

As can be seen in fig. 8-10: with the increase of the square wave processing time, the smooth surface of the copper nanowire becomes rough gradually from the beginning until the processing time is 90 minutes, the surface of the copper nanowire has a step-shaped appearance, and when the processing time is continuously increased to 120 minutes, the copper nanowire can not keep the linear structure and becomes nanoparticles.

Example 4

Electrochemical reduction carbon dioxide testing was performed using the three copper nanowire electrode materials obtained in example 3.

Fig. 11 to 13 are graphs of faraday efficiencies (fig. 11a to 13a) and current densities (fig. 11b to 13b) of different reduction products obtained at different potentials when potassium chloride solution is used as electrolyte in electrochemical reduction of carbon dioxide for the high-index lattice plane copper nanowire electrode material obtained after square wave treatment for 30 minutes, 60 minutes and 120 minutes in example 3, respectively.

Fig. 11 a-13 a illustrate: the increase in the high carbon product content is evident as the square wave treatment duration increases, reaching a maximum of 62% for a treatment duration of 90 minutes (see example 1 for details), and decreasing the high carbon product content and increasing the carbon monoxide and formic acid content for a treatment duration of 120 minutes.

The high carbon product refers to: ethylene, ethanol, isopropanol.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. The copper nano electrode with the high-index crystal face is characterized by comprising a conductive substrate and a copper nanowire aggregate loaded on the surface of the conductive substrate; the copper nanowire has a face centered cubic crystal structure and has a high index crystal plane including, but not limited to, a <200>, <220>, <222>, <311>, <310>, <320>, <331>, <400>, <510>, <511>, <533>, <610>, <755> crystal planes;

the surface of the copper nanowire has a step-shaped appearance.

2. The copper nano-electrode according to claim 1, wherein the conductive substrate is selected from one or more of carbon paper, carbon cloth, copper foil, copper foam or titanium foam.

3. The copper nanoelectrode according to claim 1, wherein the copper nanowire has a length of 10-200 μm and an aspect ratio of more than 1000.

4. A method for preparing the copper nanoelectrode according to claim 1, comprising the steps of:

5. The method according to claim 4, wherein the conductive substrate in step (2) is selected from one or more of copper foil, copper foam, titanium foam, carbon paper, and carbon cloth.

6. The preparation method according to claim 4, wherein the square wave potential treatment method adopts a three-electrode system, the working electrode is the conductive substrate coated with the copper nanowires in the step (2), the reference electrode is a silver-silver chloride electrode, and the counter electrode is a carbon rod, carbon paper or carbon cloth; the processing time of the square wave potential is longer than 5 minutes, the switching frequency of the square wave potential is larger than 2 Hz, the absolute value of the current density of the working electrode at the high potential is lower than that of the current density at the low potential, the high potential of the working electrode is higher than 0.15 volt, and the low potential is lower than 0 volt relative to the standard hydrogen electrode and relative to the standard hydrogen electrode.

7. The method according to claim 4, wherein the electrolyte in the square wave potentiometric treatment process is selected from potassium bicarbonate solution, sodium bicarbonate solution, potassium carbonate solution, sodium carbonate solution, potassium sulfate solution, sodium sulfate solution, potassium chloride solution, potassium bromide solution, sodium bromide solution, and sodium chloride solution.

8. Use of the copper nanoelectrode of claim 1 for electrochemical reduction of carbon dioxide, wherein the copper nanoelectrode can increase the selectivity of ethylene, ethanol and isopropanol.