Preparation method of bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst

Abstract

The invention provides a preparation method of a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst, and belongs to the field of carbon dioxide electrocatalytic reduction. Urea and cobalt chloride hexahydrate are used as raw materials, a bismuth oxyiodide nanosheet is formed on a cobalt sulfide hollow nanotube through a two-step hydrothermal method in combination with a reaction of halide and bismuth nitrate, and the in-situ heterojunction electrode which has good selectivity on methanol and is used for electrocatalytic reduction of carbon dioxide is prepared. According to the method, a one-dimensional hollow nanotube structure is prepared by adopting a two-step thermal solvent method, and then bismuth oxyiodide nanosheets grow on the one-dimensional hollow nanotube structure in situ. The method is easy and convenient to operate, meanwhile, a compact heterojunction interface can be formed between the bismuth oxyiodide hollow nanotube and the cobalt sulfide hollow nanotube through in-situ growth, transfer of electrons of the composite material is promoted, the hollow nanotube structure is also beneficial to gas adsorption of the catalyst, and therefore the electro-catalytic performance is greatly improved. The preparation method provides a new thought and method for improving the selectivity and stability of electrocatalytic carbon dioxide reduction.

Description

Technical Field

[0001] The present invention relates to the technical field of catalyst preparation, and in particular to a method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst. Background Art

[0002] Since the Industrial Revolution, rapid socioeconomic development has consumed vast quantities of fossil fuels, and excessive carbon dioxide (CO2) emissions have led to severe energy crises and climate change. According to the latest data released by the National Oceanic and Atmospheric Administration (NOAA), the global average annual concentration of atmospheric CO2 reached 417.1 ppm in 2022, 50% higher than pre-industrial levels and 2.4 ppm higher than the 2021 level. This sharp rise in atmospheric CO2 levels will lead to a series of major environmental and safety issues, including global warming, sea level rise, ocean acidification, and climate anomalies. While CO2 production can be reduced through sequestration and storage, this is not the optimal solution. Therefore, converting CO2 into high-value-added chemicals has become a major challenge in clean energy research.

[0003] Synthesizing methanol from carbon dioxide is one of the best technologies for utilizing CO2. Compared with other products of CO2 reduction (such as carbon monoxide, methane or formic acid), methanol has a higher energy density, is more convenient to store and transport, and can be directly used in existing energy infrastructure. As a liquid fuel, methanol has higher energy conversion and utilization efficiency, and can effectively replace traditional fossil fuels and reduce greenhouse gas emissions. So far, different types of metal-based catalysts, molecular catalysts, porous crystal materials and single-atom catalysts have been reported as electrocatalysts for catalyzing the reduction of carbon dioxide to methanol. Although traditional electrocatalysts such as precious metals (Pt, Au, etc.) have been widely studied, their high cost, slow kinetic response and limited intrinsic activity have severely restricted their practical applications.

[0004] Cobalt sulfide, a cobalt-based sulfide, is widely used in various fields due to its excellent electrochemical properties. Its unique properties stem from the strong interatomic bonding between the intermediate sulfur atoms and the interfacial metal atoms, which effectively promotes charge transfer. However, the electrocatalytic reduction performance of pristine cobalt sulfide remains unsatisfactory due to its low catalytic activity, rapid degradation or loss of activity under reduction reaction conditions, and poor single product selectivity.

[0005] In summary, it is of great significance to study an electrocatalyst that is simple to prepare, low in cost, has excellent selectivity for methanol and strong stability. Summary of the Invention

[0006] In view of this, the present invention proposes a method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst to solve the above problems.

[0007] The technical solution of the present invention is achieved as follows:

[0008] A method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst comprises the following steps:

[0009] Step 1: Urea and cobalt chloride hexahydrate are completely dissolved in an organic solvent to form a mixed solution, and the mixed solution is then transferred to a high-pressure reactor for reaction; after the reaction, the solid is filtered out and washed by centrifugation with anhydrous ethanol, and then dried in a vacuum drying oven to obtain a cobalt sulfide nanorod precursor;

[0010] Step 2: Add the prepared cobalt sulfide nanorod precursor to the Na2S solution and mix evenly, then heat and react in a reactor to obtain Co9S8 nanotubes; after the reaction, cool the Co9S8 nanotubes naturally to room temperature, filter out the solids, wash them with anhydrous ethanol, and dry them in a vacuum drying oven to obtain Co9S8 with a hollow nanotube structure;

[0011] Step 3: Completely dissolve the iodide in an organic solvent to form a halide solution, and dissolve bismuth nitrate pentahydrate in an organic solvent to form a bismuth solution; mix the halide solution and the bismuth solution and stir to form a precursor solution; then add Co9S8 with a hollow nanotube structure to the precursor solution and transfer it to a high-pressure reactor for reaction; after the reaction is completed, naturally cool to room temperature, filter out the solids and then wash them with pure water, and then place them in a vacuum drying oven to dry, thereby obtaining a bismuth iodide-cobalt sulfide in-situ heterojunction electrocatalyst.

[0012] Furthermore, in step 1, the molar volume ratio of urea, cobalt chloride hexahydrate, and organic solvent is (0.7-1.0):(2.3-4.0):50.

[0013] Furthermore, in step 1, the reaction temperature is controlled at 100-120° C., the reaction time is 10-12 h, the product is washed with anhydrous ethanol 2-4 times, and dried for 8-12 h.

[0014] Furthermore, in step 2, the molar ratio of the cobalt sulfide nanorod precursor to Na2S is 1:2, and the mass concentration of the Na2S solution is 0.5-1.0 wt%.

[0015] Furthermore, in step 2, the heating temperature in the reactor is 150-180° C., the reaction is carried out for 12-18 hours, the mixture is washed with anhydrous ethanol 3-5 times, and dried for 8-12 hours.

[0016] Furthermore, in step three, the iodide is potassium iodide, and the organic solvent in steps one and three is one of anhydrous ethanol and ethylene glycol.

[0017] Furthermore, in step three, the molar volume ratio of iodide to organic solvent is 1-2:20, the molar volume ratio of bismuth nitrate pentahydrate to organic solvent is 1-2:20, and the mass proportion of bismuth iodide in the bismuth iodide-cobalt sulfide in-situ heterojunction electrocatalyst is 10-40%, preferably 30%.

[0018] Furthermore, in step three, the reaction temperature is 120-140° C., the reaction time is 10-12 h, the product is washed with pure water 2-4 times, and the vacuum drying temperature is 60-80° C. and the drying time is 22-26 h.

[0019] Furthermore, a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst was prepared by the above preparation method.

[0020] Furthermore, the above-mentioned bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst is used in an electrochemical workstation, and the working voltage applied in the electrochemical workstation is 0 to -1.8V, and the reduction time is 2h.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1) The catalyst is low in cost and has certain economic value;

[0023] 2) The bismuth oxyiodide-cobalt sulfide heterojunction is grown in situ, resulting in closer contact and better electrocatalytic effect;

[0024] 3) The catalyst has a hollow structure, exposing more active sites and significantly enhancing electrochemical performance;

[0025] 4) It not only has better selectivity for methanol, but also has greatly improved stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the linear sweep voltammetry curve of the electrocatalyst obtained in Example 1 in 0.5 M KHCO saturated with CO 2 ;

[0027] Figure 2 This is a graph of the methanol Faraday efficiency of the electrocatalyst obtained in Example 1 in 0.5 M KHCO saturated with CO 2 ;

[0028] Figure 3 This is the linear sweep voltammetry curve of the electrocatalyst obtained in Example 2 in CO2-saturated 0.5M KHCO3;

[0029] Figure 4This is a graph of the methanol Faraday efficiency of the electrocatalyst obtained in Example 2 in 0.5 M KHCO saturated with CO 2 ;

[0030] Figure 5 The linear sweep voltammetry curve of the electrocatalyst obtained in Comparative Example 1 in 0.5 M KHCO saturated with CO 2 ;

[0031] Figure 6 This is the methanol Faraday efficiency diagram of the electrocatalyst obtained in Comparative Example 1 in 0.5M KHCO3 saturated with CO2. DETAILED DESCRIPTION

[0032] In order to better understand the technical content of the present invention, specific examples are provided below to further illustrate the present invention.

[0033] Unless otherwise specified, the experimental methods used in the examples of the present invention are all conventional methods.

[0034] Unless otherwise specified, the materials, reagents, etc. used in the examples of the present invention can be obtained from commercial sources.

[0035] Example 1

[0036] A method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst comprises the following steps:

[0037] Step 1: Completely dissolve urea and cobalt chloride hexahydrate in an organic solvent to form a mixed solution. The mixed solution is then transferred to an autoclave for reaction at 110°C for 11 hours. After the reaction, the solids are filtered, washed three times with anhydrous ethanol by centrifugation, and then dried in a vacuum oven for 10 hours to obtain a cobalt sulfide nanorod precursor. The molar volume ratio of urea, cobalt chloride hexahydrate, and organic solvent is 0.85:2.65:50 mmoL / mL.

[0038] Step 2: The prepared cobalt sulfide nanorod precursor was added to a Na2S solution and mixed thoroughly. The mixture was then heated to 165°C in a reactor for 15 hours to produce Co9S8 nanotubes. After the reaction, the Co9S8 nanotubes were naturally cooled to room temperature. The solids were filtered, washed four times with anhydrous ethanol, and dried in a vacuum drying oven for 10 hours to obtain Co9S8 with a hollow nanotube structure. The molar ratio of the cobalt sulfide nanorod precursor to the Na2S solution was 1:2, and the Na2S solution concentration was 0.8 wt%.

[0039] Step 3: Completely dissolve the iodide in an organic solvent to form a halide solution, and dissolve bismuth nitrate pentahydrate in an organic solvent to form a bismuth solution; mix the halide solution and bismuth solution and stir to form a precursor solution; then add Co9S8 with a hollow nanotube structure to the precursor solution and transfer it to a high-pressure reactor to react at 130°C for 11 hours; after the reaction is completed, naturally cool to room temperature, filter out the solids, and then wash them with pure water three times, and then place them in a vacuum drying oven at 70°C for 24 hours to obtain a bismuth iodide-cobalt sulfide in-situ heterojunction electrocatalyst. Wherein, the iodide is potassium iodide, the organic solvent is anhydrous ethanol, the molar volume ratio of iodide to organic solvent is 1.5:20 in mmoL / mL, the molar volume ratio of bismuth nitrate pentahydrate to organic solvent is 1.5:20 in mmoL / mL, and the mass proportion of bismuth iodide in the bismuth iodide-cobalt sulfide in-situ heterojunction electrocatalyst is 10%.

[0040] Example 2

[0041] Compared with Example 1, the present embodiment differs in that the mass proportion of bismuth oxyiodide in the bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalyst in step 3 is 30%.

[0042] Comparative Example 1

[0043] Compared with Example 1, this comparative example differs in that a method for preparing an electrocatalytic carbon dioxide reduction catalyst comprises the following steps:

[0044] Step 1: Completely dissolve urea and cobalt chloride hexahydrate in an organic solvent to form a mixed solution. The mixed solution is then transferred to an autoclave for reaction at 110°C for 11 hours. After the reaction, the solids are filtered, washed three times with anhydrous ethanol by centrifugation, and then dried in a vacuum oven for 10 hours to obtain a cobalt sulfide nanorod precursor. The molar volume ratio of urea, cobalt chloride hexahydrate, and organic solvent is 0.85:2.65:50 mmoL / mL.

[0045] Step 2: Add the prepared cobalt sulfide nanorod precursor to the Na2S solution and mix evenly. Heat the mixture to 165°C in a reactor and react for 15 hours to obtain Co9S8 nanotubes. After the reaction, cool the Co9S8 nanotubes naturally to room temperature, filter out the solids, wash them four times with anhydrous ethanol, and dry them in a vacuum drying oven for 10 hours to obtain Co9S8 with a hollow nanotube structure as an electrocatalytic carbon dioxide reduction catalyst. The molar ratio of the cobalt sulfide nanorod precursor to Na2S is 1:2, and the mass concentration of the Na2S solution is 0.8wt%.

[0046] Performance Testing

[0047] The carbon dioxide reduction performance of the catalysts prepared in Examples 1-2 and Comparative Example 1 was tested using an electrochemical workstation. The test settings were as follows: linear sweep voltammetry (LSV) was used for testing. The electrolyte was 0.5M KHCO3 solution (CO2 saturated, pH ≈ 7.2). CO2 gas was continuously introduced for 30 minutes before the test to eliminate dissolved oxygen. The voltage range was 0-1.2V vs. RHE, the scan rate was 10mV / s, and the current density-potential curve was recorded. The test results of Example 1 are shown in FIG. Figure 1 , the test results of Example 2 are shown in Figure 3 , and the test results of comparative example 1 are shown in Figure 5 The constant potential method (IT) was used, with a potential range of -0.7 to -1.2 V vs. RHE. Each potential was tested independently for 2 h, with a gradient interval of 0.1 V. The generated gaseous and liquid products were tested and analyzed, and a methanol Faraday efficiency graph was output. The test results of Example 1 are shown in Figure 2 , Example 2 test results see Figure 4 , the test results of comparative example 1 are shown in Figure 6 .

[0048] from Figure 1 、 Figure 3 and Figure 5 The comparison shows that the bismuth iodide-cobalt sulfide in-situ heterojunction catalyst has stronger electrochemical performance than the cobalt sulfide catalyst. Figure 1 and Figure 3 By comparison, it can be seen that the bismuth iodide-cobalt sulfide in-situ heterojunction catalyst with a bismuth iodide mass ratio of 30% has better effect.

[0049] from Figure 2 、 Figure 4 Respectively Figure 6 By comparison, it can be seen that the bismuth iodide-cobalt sulfide in-situ heterojunction catalyst has a higher selectivity for methanol than the cobalt sulfide catalyst. Figure 2 and Figure 4 In comparison, it can be seen that the bismuth iodide-cobalt sulfide in-situ heterojunction catalyst with a bismuth iodide mass ratio of 30% has a higher selectivity for methanol.

[0050] The in situ grown BiOI in this application is anchored on the surface of Co9S8, exposing more active crystal faces and significantly increasing the density of active sites. The difference in the energy band structure between BiOI and Co9S8 leads to the formation of a built-in electric field at the interface. This electric field can accelerate the transfer of electrons from Co9S8 to BiOI, optimize the charge distribution on the catalyst surface, and reduce the activation energy of the CO2 reduction reaction. The introduction of BiOI can adjust the d-band center position of Co9S8, weaken the excessive adsorption of COOH intermediates by Co sites, and enhance the adsorption of OCHO intermediates by Bi sites, thereby promoting the breakage of CO bonds and the formation of CH bonds, thereby directionally guiding the methanol production path. In addition, Bi3+ The lone pair electrons of BiOI can stabilize CO2 molecules, and the Bi-O bonds exposed on the crystal surface can selectively adsorb CO2 and activate C=O bonds. The moderate adsorption energy of Bi sites on OCHO intermediates is beneficial to the stability of methanol precursors. In addition, the oxidation reaction of BiOI at the heterojunction interface (BiOI+H + +e - →Bi+1 / 2I2+H2O) can consume protons, forming a local alkaline microenvironment and promoting the conversion of CO2 into CO2 - (CO2+H2O+2e - →CO2 - +2OH - ), inhibiting the competitive hydrogen evolution reaction (HER). In addition, CO adsorbed on the Co9S8 surface can diffuse to the BiOI interface and combine with OCHO at the Bi site to form a CH3O intermediate, which generates methanol (CH3O+H + +e - →CH3OH). Therefore, the bismuth iodide-cobalt sulfide in-situ heterojunction of the present application achieves precise control of the CO2 reduction path through electronic structure regulation, interface synergistic catalysis, microenvironment optimization and structural mass transfer enhancement. The selective adsorption of key intermediates by Bi sites and the efficient electron transport of Co9S8 synergistically improve the methanol selectivity and reaction rate, while inhibiting the competitive hydrogen evolution reaction, showing electrocatalytic performance superior to that of single Co9S8. Therefore, the bismuth iodide-cobalt sulfide in-situ heterojunction catalyst prepared by the present invention can greatly improve the reduction performance of carbon dioxide.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst, characterized in that: The following steps are involved: Step 1: Urea and cobalt chloride hexahydrate are completely dissolved in an organic solvent to form a mixed solution, and the mixed solution is then transferred to a high-pressure reactor for reaction; after the reaction, the solid is filtered out and washed by centrifugation with anhydrous ethanol, and then dried in a vacuum drying oven to obtain a cobalt sulfide nanorod precursor; Step 2: Add the prepared cobalt sulfide nanorod precursor to the Na2S solution and mix evenly, then heat and react in a reactor to obtain Co9S8 nanotubes; after the reaction, cool the Co9S8 nanotubes naturally to room temperature, filter out the solids, wash them with anhydrous ethanol, and dry them in a vacuum drying oven to obtain Co9S8 with a hollow nanotube structure; Step 3: completely dissolving the iodide in an organic solvent to form a halide solution, and dissolving bismuth nitrate pentahydrate in an organic solvent to form a bismuth solution; The halide solution and the bismuth solution are mixed and stirred to form a precursor solution; Subsequently, Co9S8 with a hollow nanotube structure was added to the precursor solution and transferred to a high-pressure reactor for reaction. After the reaction was completed, it was naturally cooled to room temperature, the solid was filtered out and then washed with pure water, and then placed in a vacuum drying oven for drying to obtain iodine oxybismuth-cobalt sulfide in situ heterojunction electrocatalyst.

2. The method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst according to claim 1, characterized in that: In the step 1, the molar volume ratio of urea, cobalt chloride hexahydrate, and organic solvent is (0.7-1.0):(2.3-4.0):

50.

3. The method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst according to claim 1, characterized in that: In the step 1, the reaction temperature is controlled at 100-120° C., the reaction time is 10-12 h, the product is washed with anhydrous ethanol 2-4 times, and dried for 8-12 h.

4. The method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst according to claim 1, characterized in that: In the step 2, the molar ratio of the cobalt sulfide nanorod precursor to Na2S is 1:2, and the mass concentration of the Na2S solution is 0.5-1.0 wt%.

5. The method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst according to claim 1, characterized in that: In the step 2, the heating temperature in the reactor is 150-180° C., the reaction is carried out for 12-18 hours, the mixture is washed with anhydrous ethanol 3-5 times, and dried for 8-12 hours.

6. The method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst according to claim 1, characterized in that: The iodide in step 3 is potassium iodide, and the organic solvent in steps 1 and 3 is one of anhydrous ethanol and ethylene glycol.

7. The method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst according to claim 1, characterized in that: In the step three, the molar volume ratio of iodide to organic solvent is 1-2:20 in mmoL / mL, the molar volume ratio of bismuth nitrate pentahydrate to organic solvent is 1-2:20 in mmoL / mL, and the mass proportion of bismuth iodide in the bismuth iodide-cobalt sulfide in-situ heterojunction electrocatalyst is 10-40%.

8. The method for preparing a bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst according to claim 1, characterized in that: In the step 3, the reaction temperature is 120-140° C., the reaction time is 10-12 h, the product is washed with pure water 2-4 times, and the vacuum drying temperature is 60-80° C. and the drying time is 22-26 h.

9. A bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. The bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst according to claim 9, characterized in that: The bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst is used in an electrochemical workstation. The operating voltage applied to the bismuth oxyiodide-cobalt sulfide in-situ heterojunction electrocatalytic carbon dioxide reduction catalyst in the electrochemical workstation is 0 to -1.8V, and the reduction time is 2h.

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