BISMUTH-COPPER BIMETALLIC COMPOSITE CATALYST FOR CARBON DIOXIDE ELECTROREDUCTION, AND PREPARATION METHOD THEREFOR AND USE THEREOF

Description

TECHNICAL FIELD

The present disclosure relates to the technical field of electrocatalyst preparation, in particular to a bismuth-copper bimetallic composite catalyst, and a preparation method therefor and a use thereof.

BACKGROUND ART

Massive emission of carbon dioxide, a greenhouse gas, has caused a series of energy shortage and climate change problems. Electrocatalytic carbon dioxide reduction process utilizes clean electric energy produced by renewable energy such as solar energy and wind energy to convert carbon dioxide into fuels and chemicals, which is considered one of the most promising methods that can effectively realize carbon neutrality.

Among many electrocatalytic reduction products, formic acid/formate is believed to be an ideal hydrogen carrier for fuel cells since its unique characteristics, including high mass/volume hydrogen capacity (53 g H₂ L⁻¹), low toxicity, flammability, and ease of transport. Formic acid/formate salt is also an important chemical raw material or intermediate in many industrial processes and is widely used in agricultural, food, textile and pharmaceutical industries. However, due to the competition of the hydrogen evolution reaction, the acquisition of high formate selectivity is generally at the expense of low current density and deteriorates rapidly as increasing cathode potential. Therefore, designing and synthesizing a catalyst having both high selectivity and ultra-high activity on formic acid/formate is one of the research hotspots at present.

Bismuth-based catalysts are inert to the hydrogen evolution reaction, and are therefore widely used in studies of carbon dioxide electroreduction to formic acid. By designing and synthesizing bismuth nanosheets, it can not only increase the active specific surface area of the catalyst and increase the number of exposed active sites, but also can enhance the charge conductivity of the catalyst. Although some progress has been made in the study of bismuth-based catalysts, the current density of most bismuth-based materials for electrochemical reduction of carbon dioxide to formic acid or formate is not higher than 1 A/cm² at present, and it is difficult to have both high selectivity and high activity at the same time. It remains a current research goal to develop new materials to achieve both high selectivity and high activity at the same time.

Bimetallic composite catalysts have been widely developed due to their potential synergistic effects, electronic modulation effects or metal-carrier strong interactions and the like. These effects often contribute to better catalytic performance. Therefore, the development of novel carbon dioxide reduction catalysts using the unique effects of bimetallic materials is increasingly concerned.

Based on the above research status, it is of great theoretical significance and industrial application value to prepare bimetallic composite catalysts with a relatively simple method and use the catalysts for electrocatalytic reduction of carbon dioxide to prepare formate with high selectivity and high activity.

SUMMARY

In order to solve the above technical problems, the present disclosure provides a bismuth-copper bimetallic composite catalyst, and a preparation method therefor and an application thereof. The bismuth-copper bimetallic composite catalyst is used in electrocatalytic carbon dioxide reduction reaction, which can achieve highly selective and highly active electrochemically reduction of carbon dioxide to formate.

To achieve the above objective, the present disclosure uses the following technical solutions:

• • An aspect of the present disclosure is to provide a bismuth-copper bimetallic composite catalyst, including ultra-small copper nanoclusters and bismuth nanosheets. The bismuth nanosheets are of a polycrystalline structure. The copper nanoclusters are dispersed on the bismuth nanosheets in a highly dispersed form, and a number of copper atoms of each the copper nanoclusters is less than 10.

In the above technical solution, further, the copper nanoclusters account for 20-33% of a total atomic mass of the bimetallic composite.

In the above technical solution, further, a thickness of each the bismuth nanosheets is 5-20 nm.

Another aspect of the present disclosure is to provide a method for preparing the bismuth-copper bimetallic composite catalyst mentioned above. The said method includes the following steps of:

• • (1) Mixing a soluble copper salt with water to obtain a mixed solution I, adding thiourea into the mixed solution I for reaction to obtain a reaction product I, and washing, centrifuging and drying the reaction product I to obtain a precursor A;
  • (2) Mixing a soluble bismuth salt with water to obtain a mixed solution II, adding sodium diethyldithiocarbamate into the mixed solution II for reaction to obtain a reaction product II, and washing, centrifuging and drying a reaction product II to obtain a precursor B;
  • (3) Ultrasonically dispersing the precursor A and the precursor B in an alcohol solvent to obtain a mixed solution III;
  • (4) Heating the mixed solution III obtained in step (3) to reflux to obtain a reaction product III, and washing, centrifuging and drying the reaction product III to obtain a copper sulfide and bismuth sulfide composite precursor C;
  • (5) Applying the copper sulfide and bismuth sulfide composite precursor C obtained in step (4) to a carbon material and using it as an electrode to obtain the bismuth-copper bimetallic composite catalyst after electrochemical reduction.

In the above technical solution, further, the soluble copper salt includes one of copper dichloride and copper dichloride hydrate.

A molar ratio of the soluble copper salt to the thiourea is 1:(0.5-2), preferably 1:1, and a reaction time is not shorter than 10 s.

In the above technical solution, further, the soluble bismuth salt is bismuth nitrate.

A molar ratio of the soluble bismuth salt to the sodium diethyldithiocarbamate is 1:(1-4), preferably 1:3, and a reaction time is not shorter than 1 min.

In the above technical solution, further, a mass ratio of the precursor A to the precursor B is (3.5-7):50.

The alcohol solvent includes ethylene glycol. A mass ratio of the glycol solvent to the precursor B is (33-55):50.

In the above technical solution, further, a temperature of the heating to reflux is 130° C.-140°°C., and a time is 1 h-4 h.

In the above technical solution, further, the copper sulfide and bismuth sulfide composite precursor is applied to the carbon material by means of drop-casting or spray-coating.

The carbon material includes any one of glassy carbon electrode, carbon paper, and carbon cloth.

The electrode is working electrode or cathode.

An electrolyte for the electrochemical reduction is potassium bicarbonate or potassium hydroxide, a concentration of the electrolyte is 0.1 M-1 M, an electroreduction potential ranges from −0.8 V vs. RHE to −1.1 V vs. RHE, and an electroreduction reaction time is 10 min-30 min.

Another aspect of the present disclosure is to provide a use of the bismuth-copper bimetallic composite catalyst mentioned above for electrochemical carbon dioxide reduction reaction, or a use of the bismuth-copper bimetallic composite catalyst prepared by means of the preparation method mentioned above for electrochemical carbon dioxide reduction reaction.

Compared with the prior art, the present disclosure has the following beneficial effects:

• • 1. Compared with the prior art, the bismuth-copper bimetallic composite catalyst according to the present disclosure has a specific structure that ultra-small copper nanoclusters are distributed on the surface of bismuth nanosheets in a highly dispersed form, where the copper nanoclusters adjust the electronic state of bismuth on the bismuth nanosheets, such that the ability of the bismuth-copper bimetallic composite to activate carbon dioxide is improved, thereby obtaining high selectivity and high activity for electrocatalytic reduction of carbon dioxide to formate, providing a new approach for efficient conversion of carbon dioxide.
  • 2. According to the preparation method of the present disclosure, a specific catalyst structure is obtained by electrochemically reducing the precursors of copper and bismuth, which is simple to operate, and the content of the copper clusters can be adjusted by changing reaction conditions, thereby adjusting the catalytic performance.
  • 3. The bismuth-copper bimetallic composite catalyst according to the present disclosure can be used for electrocatalytic reduction of carbon dioxide to prepare formate. Specifically, the bismuth-copper bimetallic composite catalyst prepared according to the present disclosure achieves both high formate selectivity (>90%) and extremely high activity (1.2 A cm⁻²).

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the technical solution in the embodiment of the present disclosure or the prior art, the following is a brief introduction of the accompanying drawings required to be used in the description of the embodiment or the prior art. Obviously, the accompanying drawings in the description below are some embodiments of the present disclosure. For those ordinary in the art, other accompanying drawings can also be obtained from these accompanying drawings without creative labor.

FIG. 1 shows a transmission electron microscopy image of a bismuth-copper bimetallic composite catalyst prepared in Example 2 of the present disclosure;

FIG. 2 shows an atomic force microscopy image of the bismuth-copper bimetallic composite catalyst prepared in Example 2 of the present disclosure;

FIG. 3 shows an X-ray diffraction pattern of the bismuth-copper bimetallic composite catalyst prepared in Example 2 of the present disclosure;

FIG. 4 shows a Fourier transformed Cu K-edge X-ray absorption fine structure spectra of a bismuth-copper bimetallic composite prepared in Example 2 of the present disclosure;

FIG. 5 shows a high-resolution transmission electron microscopy image of the bismuth-copper bimetallic composite prepared in Example 2 of the present disclosure and corresponding energy dispersive X-ray (EDX) element mapping images;

FIG. 6 shows a Faradaic efficiency-current density curve of electroreduction reaction of carbon dioxide to prepare formate in a flow cell electrolytic cell catalyzed by the bismuth-copper bimetallic composite catalyst prepared in Example 2 of the present disclosure;

FIG. 7 shows Faradaic efficiency-potential curves of electroreduction reaction of carbon dioxide to prepare formate in H-type electrolytic cell catalyzed by bismuth-copper bimetallic composite catalysts prepared in Examples 1-3 and a bimetallic composite with a higher copper content (50 at %) prepared in Comparative Example 1 of the present disclosure.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following non-limiting examples are provided to enable those of ordinary skill in the art to understand the present disclosure fully, but do not limit the present disclosure in any way.

Sources of all raw materials of the present disclosure are not particularly limited. The raw materials both obtained commercially and prepared according to conventional methods familiar to those skilled in the art meet the requirements of the present disclosure.

Purity of all the raw materials of the present disclosure is not particularly limited. The analytically pure raw materials are preferably used in the present disclosure.

To make the objectives, technical solutions, and advantages of the present disclosure clearer, the following clearly and completely describes the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings in the embodiments of the present disclosure. Apparently, the described embodiments are merely some rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative, and is in no way serves as any limitation on the present disclosure and its application or use. Based on the embodiments of the present disclosure, all the other embodiments obtained by those of ordinary skill in the art without inventive effort are within the protection scope of the present disclosure.

It should be noted that the terms used herein are only intended to describe specific embodiments and are not intended to limit the exemplary embodiments of the present disclosure. In addition, for the numerical ranges in the present disclosure, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated values or intermediate values within a stated range, as well as smaller ranges between any other stated values or the intermediate values within the stated values, is also included in the present disclosure. The upper and lower limits of these smaller ranges can be included or excluded independently from the range. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as generally understood by those skilled in the art described in the present disclosure. Although the present disclosure only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present disclosure. In addition, it should also be understood that the terms “include”, “comprise”, “have”, “contain”, and the like used herein are all open-ended terms, meaning including but not limited to.

Example 1

Bismuth-copper bimetallic composite catalyst was prepared as follows:

• • (1) Copper chloride and thiourea were separately dissolved in 50 ml of water to obtain a thiourea aqueous solution and a copper chloride aqueous solution with a concentration of 0.1 M, respectively. The thiourea aqueous solution was added into the copper chloride aqueous solution to react for one minute, and a precursor A was obtained by means of centrifuging, washing, and drying a reaction product.
  • (2) Bismuth nitrate and sodium diethyldithiocarbamate were separately dissolved in 50 mL of water to obtain a bismuth nitrate solution and a sodium diethyldithiocarbamate solution with a concentration of 0.1 M, respectively. The bismuth nitrate solution was added into the sodium diethyldithiocarbamate solution to react for one hour, and a precursor B was obtained by means of centrifuging, washing, and drying a reaction product.
  • (3) 3.5 mg of precursor A and 50 mg of precursor B were taken and ultrasonically dispersed in 40 mL of ethylene glycol to obtain a dispersion liquid. The dispersion liquid was placed in an oil bath and subjected to refluxing at 130° C. for 3 hours, and then was naturally cooled to a room temperature to obtain a product. The product was centrifuged and was washed repeatedly with ethanol and water, and then was centrifugally dried to obtain a copper sulfide and bismuth sulfide composite precursor.
  • (4) 2 mg of the copper sulfide and bismuth sulfide composite precursor was taken and ultrasonically dispersed in 0.5 mL of ethanol to obtain a dispersion liquid, and 5 μL of alcohol solution of perfluorosulfonic acid resin was added into the dispersion liquid to obtain a mixed solution. After uniform mixing, 5 μL of the mixed solution was dropped on a surface of a glassy carbon electrode as a working electrode which was subjected to in-situ electroreduction in a 0.1 M potassium bicarbonate solution for 10 min with a platinum electrode as an anode, a silver/silver chloride electrode as a reference electrode, and a potential of −0.9 V (relative to RHE), and a bismuth-copper bimetallic composite catalyst was obtained.
  • (5) An atomic percentage content of the copper atoms in the bismuth-copper bimetallic composite catalyst obtained in this example was 20% by testing.

Example 2

Bismuth-copper bimetallic composite catalyst was prepared as follows:

• • (1) Precursors A and B were prepared according to the method of Example 1.
  • (2) A copper sulfide and bismuth sulfide composite precursor was prepared according to the method of Example 1, except that an amount of the precursor A in step (3) of Example 1 was 4.7 mg.
  • (3) A bismuth-copper bimetallic composite catalyst was prepared according to the method of Example 1.
  • (4) An atomic percentage content of the copper atoms in the bismuth-copper bimetallic composite catalyst obtained in this example was 25% by testing.

As shown in FIG. 1, the transmission electron microscopy image proves that the obtained sample is of a nanosheet structure.

As shown in FIG. 2, the atomic force microscopy image shows that a thickness of the bismuth nanosheet is about 9.5 nm.

As shown in FIG. 3, the X-ray diffraction pattern indicates that the bismuth nanosheests are of a polycrystalline structure, and element copper does not form copper nanoparticles.

As shown in FIG. 4, the Fourier transformed Cu K-edge X-ray absorption fine structure spectra proves that a copper cluster is composed of 5 copper atoms, and the peak intensity of Cu—Cu bond of the cluster in the spectra is significantly lower than the peak intensity of Cu—Cu bond in the copper foil standard sample, indicating that the number of copper atom coordinates in the cluster is significantly less than that of the copper foil sample. Through fitting, it can be obtained that the number of copper coordinates in the cluster is 4, indicating that the copper cluster is composed of 5 copper atoms.

As shown in FIG. 5, elements copper and bismuth are uniformly dispersed without aggregation, indicating that the copper clusters are highly dispersed on the bismuth nanosheets.

Example 3

Bismuth-copper bimetallic composite catalyst was prepared as follows:

• • (1) Precursors A and B were prepared according to the method of Example 1.
  • (2) A copper sulfide and bismuth sulfide composite precursor was prepared according to the method of Example 1, except that an amount of the precursor A in step (3) of Example 1 was 7 mg.
  • (3) A bismuth-copper bimetallic composite catalyst was prepared according to the method of Example 1.
  • (4) An atomic percentage content of the copper atoms in the bismuth-copper bimetallic composite catalyst obtained in this example was 33% by testing.

Comparative Example 1

A bismuth-copper bimetallic composite catalyst was prepared according to the method of Example 1, except that an amount of the precursor A in step (3) was 14.1 mg, and an atomic percentage content of copper atoms in the prepared bismuth-copper bimetallic composite catalyst was 50%.

Example 4

Carbon dioxide electrocatalytic reduction performance test of bismuth-copper bimetallic composite catalysts.

Catalytic performance of the bismuth-copper bimetallic composite catalysts prepared in Examples 1-3 and Comparative example 1 of the present disclosure in carbon dioxide electrocatalytic reduction reaction was tested.

A carbon paper loaded with the bismuth-copper bimetallic composite catalyst obtained in Example 2 of the present disclosure was taken as a working electrode, a foamed nickel electrode as a counter electrode and a silver/silver chloride electrode as a reference electrode, to test the carbon dioxide electroreduction performance in a flow electrolytic cell using 0.1 M potassium bicarbonate solution as an electrolyte. In the testing process, a flow rate of the carbon dioxide was maintained at 20 sccm, and a flow rate of the anode and cathode electrolytes was maintained at 2 mL min⁻¹. A galvanostatic method was used for the test, with an applied current density ranging from −100 mA cm⁻² to −1200 mA cm⁻². A gaseous product of the reaction was detected with gas chromatography, and a liquid product was detected with hydrogen nuclear magnetic resonance spectroscopy.

A glassy carbon electrode loaded with the bismuth-copper bimetallic composite catalysts obtained in Examples 1-3 or Comparative example 1 of the present disclosure was taken as a working electrode, a platinum electrode as a counter electrode, and a silver/silver chloride electrode as a reference electrode, to test the carbon dioxide electroreduction performance in an H-type electrolytic cell using 0.1 M potassium bicarbonate solution as an electrolyte. In the testing process, a flow rate of the carbon dioxide was maintained at 10 sccm. A potentiostatic method was used for the test, with an applied potential ranging from −0.95 V vs. RHE to −1.25 V vs. RHE. A gaseous product of the reaction was detected with gas chromatography, and a liquid product was detected with hydrogen nuclear magnetic resonance spectroscopy.

As shown in FIG. 6, the selectivity of the bismuth-copper bimetallic composite catalyst prepared in Example 2 for preparing formate by electrocatalytic reduction of carbon dioxide at an ultra-high current density of −1200 mA cm⁻² is still higher than 90%.

As shown in FIG. 7, each the bismuth-copper bimetallic composite catalysts prepared in Examples 1-3 maintains a high formate Faradaic efficiency (>90%) over a wide potential range, while the material with a high content (50 at %) of copper atoms prepared in Comparative Example 1 only achieves high formate Faradaic efficiency in a narrow range.

Finally, it should be noted that the above various embodiments are merely intended to illustrate the technical solution of the present disclosure and not to limit the same; although the present disclosure has been described in detail with reference to the foregoing embodiments, it should be understood by those ordinary skilled in the art that the technical solutions described in the foregoing embodiments can be modified or equivalents can be substituted for some or all of the technical features thereof; and the modification or substitution does not make the essence of the corresponding technical solution deviate from the scope of the technical solution of each embodiment of the present disclosure.

For those skilled in the art, without departing from the scope of the technical solution of the present disclosure, many possible changes and modifications can be made to the technical solution of the present disclosure by using the technical contents disclosed above, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present disclosure without departing from the technical solution of the present disclosure shall still belong to the protection scope of the technical solution of the present disclosure.