Porous graphene, preparation method and application thereof in preparation of biocl nanosheet electrocatalyst

Abstract

This invention belongs to the field of electrocatalysis technology, disclosing a porous graphene, its preparation method, and its application in the preparation of BiOCl nanosheet electrocatalysts. The preparation method of the BiOCl nanosheet electrocatalyst includes the following steps: adding a Bi metal-soluble salt and porous graphene sequentially to ethylene glycol, mixing them uniformly with magnetic stirring, and then placing them in a reaction vessel for hydrothermal reaction. After centrifuging and drying the resulting reactants, a catalyst precursor is obtained. Finally, the precursor is placed in a tube furnace and calcined under a protective atmosphere to obtain a BiOCl nanosheet electrocatalyst with porous graphene as the support. The electrocatalyst synthesized by this invention allows BiOCl nanosheets to be uniformly loaded on a porous graphene substrate, exhibiting structural stability, small size, large specific surface area, and providing active sites. When applied to the electrocatalytic reduction of carbon dioxide, it demonstrates excellent performance in the electrocatalytic reduction of CO2 to formic acid.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalysis technology, specifically relating to a porous graphene, its preparation method, and its application in the preparation of BiOCl nanosheet electrocatalysts. Background Technology

[0002] Currently, excessive emissions of carbon dioxide, a greenhouse gas, are causing environmental problems such as global warming, extreme weather, ocean acidification, and increased land drought. Utilizing carbon dioxide reduction reactions to convert CO2 into other carbon-based energy substances is one of the most effective ways to alleviate the environmental problems caused by CO2. Electrochemical CO2 reduction reaction (CO2RR) offers a promising approach and aligns with sustainable development principles for carbon cycling and storing fuels or chemicals for intermittent renewable energy. Electrocatalytic CO2 reduction is a complex process involving various electron transfers. Depending on the number of electrons transferred, CO2RR can produce a variety of reduction products, including carbon monoxide (CO), formic acid (HCOOH), methane (CH4), ethylene (C2H4), and ethanol (C2H5OH). The competition among these numerous reactions poses a significant challenge to the high selectivity of the target product. Among the CO2 reduction products, formic acid, as a safe and convenient liquid fuel, has attracted widespread attention due to its extensive applications in hydrogen storage, fuel cells, and other energy and industrial fields. However, most CO2RR experiments use aqueous solutions as the reaction electrolyte, and the Faraday efficiency and selectivity of formic acid production are inevitably limited by the competing hydrogen evolution reaction (HER). Therefore, exploring efficient CO2 reduction electrocatalysts is of great significance for further promoting the application of formic acid.

[0003] Formic acid, as a two-electron reduction product, has been extensively studied in electroreduction reactions. Catalysts with formic acid selectivity are mainly p-block group metals, such as In, Sn, Sb, Pb, and Bi, as well as some transition metals and metal oxides. Among these metals, bismuth-based materials are more abundant on Earth and have lower toxicity compared to other metals. Furthermore, bismuth-based catalysts possess high specific surface area and high edge density, providing numerous active and defect sites to promote carbon dioxide adsorption and activation, thereby increasing the reaction rate and selectivity of carbon dioxide reduction. Bismuth-based catalysts also exhibit lower CO absorption energy, higher CO2*- absorption energy, and stronger OCHO stabilization ability. More importantly, they have relatively poor activity for the HER reaction. These significant advantages make bismuth-based materials strong candidates for the electroreduction of carbon dioxide to produce formate. Studies have found that bismuth-based catalysts of BiOCl exhibit high Faradaic efficiency and product selectivity in the electroreduction of carbon dioxide to formate during electrochemical reactions. However, due to drawbacks such as low electron transport efficiency, scarce surface active sites, small specific surface area, and poor catalytic and structural stability, these catalysts are easily deactivated during electrochemical reduction, significantly affecting their performance and lifespan, thus limiting the development of Bi-based catalysts in the field of electrocatalytic carbon dioxide reduction. Porous graphene, on the other hand, possesses advantages such as good stability, high specific surface area, super toughness, excellent electrical and thermal conductivity, and controllable pore size and distribution. Combining bismuth-based catalysts with porous graphene can not only extend the catalyst's lifespan but also expose more active sites, further enhancing catalytic activity. In summary, this invention provides a simple method for preparing stable, uniformly dispersed, and highly catalytically active BiOCl nanosheet electrocatalysts using porous graphene as a support, which is crucial for the field of electrocatalytic carbon dioxide reduction. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a porous graphene, a preparation method, and its application in the preparation of BiOCl nanosheet electrocatalysts.

[0005] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0006] A method for preparing porous graphene includes the following steps:

[0007] Magnesium hydroxide powder was loaded into an alumina boat and then placed in a clean quartz tube in a CVD system. The CVD system was gradually heated and then maintained at a certain temperature. Subsequently, the argon flow was stopped, and a mixed gas flow containing C2H4 and H2 was introduced into the system to promote the growth of graphene, thereby forming a magnesium oxide graphene composite material. The magnesium oxide graphene composite material was then dispersed in a hydrochloric acid aqueous solution and continuously stirred on a hot plate to remove the magnesium oxide template. The obtained porous graphene material was collected by filtration, thoroughly washed multiple times with deionized water, and then freeze-dried to obtain porous graphene.

[0008] Furthermore, the method for preparing the porous graphene includes the following steps:

[0009] Magnesium hydroxide powder was loaded into an alumina boat and then placed in a clean quartz tube in a CVD system. The CVD system was gradually heated to 1030°C over 1 hour and maintained at this temperature for another hour. Subsequently, the argon flow was stopped, and a mixed gas flow containing C2H4 and H2 was introduced into the system for 1.5 hours to promote graphene growth, thereby forming a magnesium oxide graphene composite material. The magnesium oxide graphene composite material was then dispersed in a 3M hydrochloric acid aqueous solution and continuously stirred on a hot plate at 80°C for 24 hours to remove the magnesium oxide template. The obtained porous graphene material was collected by filtration, thoroughly washed multiple times with deionized water, and then freeze-dried to obtain porous graphene.

[0010] This invention also provides a method for preparing BiOCl nanosheet electrocatalysts using porous graphene as a support, comprising the following steps:

[0011] Step 1: Add the soluble Bi metal salt to ethylene glycol to obtain mixed solution A;

[0012] Step 2: Mix the above mixed solution A and porous graphene in a certain proportion and mix them evenly using a magnetic stirrer to obtain mixed solution B;

[0013] Step 3: Chloride ion solution is added dropwise to the obtained mixed solution B in a certain proportion to obtain mixed solution C; then it is placed in a reaction vessel, and the reaction vessel is placed in an oven for hydrothermal reaction, centrifuged and dried to obtain the catalyst precursor;

[0014] Step four: The catalyst precursor is placed in a tube furnace and calcined in a protective atmosphere, and then cooled in the furnace to obtain the BiOCl nanosheet catalyst.

[0015] Furthermore, the Bi metal soluble salt mentioned in step one is any one of bismuth nitrate hydrate, bismuth sulfate hydrate, and bismuth trichloride hydrate.

[0016] Furthermore, the mass ratio of the Bi metal soluble salt to the porous graphene in step two is 242.5:30.

[0017] Furthermore, the chloride ion solution mentioned in step three can be either a sodium chloride solution or a potassium chloride solution; the ratio of the chloride ion solution to mixed solution B is 1:1.

[0018] Furthermore, the protective atmosphere described in step four is a mixture of nitrogen and ammonia; the flow rate ratio of nitrogen to ammonia is 1:2; the heating rate of calcination is 3℃ / min; the temperature is raised to 400℃ and held for 120min, 180min, or 240min.

[0019] The present invention also provides an application of a BiOCl nanosheet electrocatalyst supported on porous graphene, wherein the BiOCl nanosheet electrocatalyst is used to improve the activity and selectivity of electrocatalytic reduction of carbon dioxide to formic acid.

[0020] Compared with the prior art, the present invention has the following technical advantages:

[0021] 1. The BiOCl nanosheet electrocatalyst based on porous graphene has advantages such as controllable structure, high specific surface area, and excellent electrical and thermal conductivity. It can ensure that more active sites participate in the reaction, promote electron transfer, and facilitate the adsorption of CO2 molecules in the electrocatalytic reduction of CO2, thereby ensuring the excellent performance of electrocatalytic reduction of CO2 to formic acid. Specifically, the BiOCl nanosheet electrocatalyst based on porous graphene has a Faradaic efficiency of over 90% for formic acid in the potential range of -0.683 to -0.971 V vs. RHE.

[0022] 2. This invention provides a simple synthesis method for Bi-based nanoscale electrocatalysts. The synthesized BiOCl nanosheet electrocatalyst is uniformly supported on a porous graphene substrate, overcoming difficulties such as low electron transport efficiency, scarce surface active sites, and poor catalytic and structural stability. It has important guiding significance for the study of the application mechanism of electrocatalytic CO2 reduction. At the same time, the BiOCl nanosheet electrocatalyst with porous graphene as the support exhibits high selectivity for formic acid generation. In addition, its advantages such as environmental sustainability, controllable structure, renewability, and high-efficiency electrocatalytic performance make it promising for applications in electrochemical catalysis, energy conversion, environmental remediation, and biomedicine. Attached Figure Description

[0023] Figure 1 This is a SEM (scanning electron microscope) image of the BiOCl nanosheet electrocatalyst with porous graphene as a support provided in Example 1 of the present invention.

[0024] Figure 2 This is the XRD (X-ray diffraction) pattern of the BiOCl nanosheet electrocatalyst with porous graphene as a support provided in Example 1 of the present invention.

[0025] Figure 3 This is a graph showing the FE (Faraday efficiency) of formic acid at different potentials for the BiOCl nanosheet electrocatalyst with porous graphene as a support provided in Example 1 of this invention.

[0026] Figure 4 The BiOCl nanosheet electrocatalyst with porous graphene as a support provided in Example 1 of this invention was tested in a carbon dioxide-saturated 0.1M KHCO3 solution at a rate of 5 mV s. -1 LSV (Linear Scan Voltammetry) curve of scan rate;

[0027] Figure 5 This is a graph showing the Faraday efficiency (FE) of H2 at different potentials for the BiOCl nanosheet electrocatalyst with porous graphene as the support provided in Example 1 of this invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments.

[0029] Example 1

[0030] A method for preparing BiOCl nanosheet electrocatalysts using porous graphene as a support includes the following steps:

[0031] The porous graphene was prepared as follows: Porous graphene was synthesized via chemical vapor deposition (CVD). Magnesium hydroxide powder was loaded into an alumina boat, which was then placed in a clean quartz tube within the CVD system. The CVD system was gradually heated to 1030°C over 1 hour and maintained at this temperature for another hour. Subsequently, the argon flow was stopped, and a mixed gas stream containing C2H4 (50 sccm) and H2 (30 sccm) was introduced into the system for 1.5 hours to promote graphene growth, thereby forming a magnesium oxide-graphene composite material. The magnesium oxide-graphene composite material was then dispersed in a 3M hydrochloric acid aqueous solution and continuously stirred on a hot plate at 80°C for 24 hours to remove the magnesium oxide template. The obtained porous graphene material was collected by filtration, thoroughly washed multiple times with deionized water, and then freeze-dried to obtain porous graphene.

[0032] A BiOCl nanosheet electrocatalyst supported on porous graphene was synthesized. Specifically, 0.2425 g of bismuth nitrate and 30 mg of porous graphene were dissolved in ethylene glycol solution and mixed uniformly with magnetic stirring. 28.5 mg of NaCl was dissolved in 30 mL of deionized water and mixed uniformly with ultrasonication. Then, while the mixture of bismuth nitrate and ethylene glycol was magnetically stirred, an aqueous sodium chloride solution was slowly added dropwise to form a grayish-white precipitate, and magnetic stirring was continued for 10 min. Subsequently, the mixture was placed in a reaction vessel, which was then placed in an oven for hydrothermal reaction. After the reaction, the reactants were centrifuged and dried. The precursor synthesized in the above steps was placed in a tube furnace, and the entire reaction was carried out under a protective atmosphere of N2 and NH3 (N2:NH3 ratio 50:100). The temperature was increased to 400 °C at a rate of 3 °C / min, then held for 120 min, and cooled with the furnace to obtain the BiOCl nanosheet electrocatalyst supported on porous graphene.

[0033] The BiOCl nanosheet electrocatalyst with porous graphene as a support synthesized in Example 1 was characterized by SEM, as shown in the following figures. Figure 1 As shown in the image, the results clearly show that the BiOCl nanosheet electrocatalyst supported by porous graphene exhibits a porous surface morphology and uniform size in the SEM image. Subsequently, the synthesized BiOCl nanosheet electrocatalyst was characterized by XRD, as shown in the image. Figure 2 As shown, the peak corresponding to BiOCl can be clearly seen. Therefore, this embodiment successfully synthesized a BiOCl nanosheet electrocatalyst.

[0034] Example 2

[0035] This embodiment prepared a BiOCl nanosheet electrocatalyst with porous graphene as the support. The only difference between this embodiment and Example 1 is that "heating to 400℃ and holding for 120 min" was changed to "heating to 400℃ and holding for 180 min"; the rest of the steps are the same.

[0036] Example 3

[0037] This embodiment prepared a BiOCl nanosheet electrocatalyst with porous graphene as the support. The only difference between this embodiment and Example 1 is that "heating to 400℃ and holding for 120 min" was changed to "heating to 400℃ and holding for 240 min"; the rest of the steps were the same.

[0038] Electrochemical tests were performed using a Chenhua (CHI660) electrochemical workstation. 10 mg of the BiOCl nanosheet electrocatalyst synthesized in Example 1 was placed in a 2 mL centrifuge tube, and 1 mL of isopropanol and 50 μL of naphthol (Nafion) solution (5%, D520, DuPont) were added. The mixture was sonicated for 10 min to form a uniform catalyst ink. Then, 30 μL of the catalyst ink was dropped onto the surface of hydrophobic carbon paper (Toray TGP-H-060) and dried at 45 °C for 1 h to prepare the working electrode. In an H-type electrolytic cell, using 0.1 M KHCO3 as the electrolyte, a platinum sheet (1 cm × 1 cm) as the counter electrode, and an Ag / AgCl electrode as the reference electrode, carbon dioxide gas was introduced into the H-type electrolytic cell to perform electrocatalytic carbon dioxide reduction tests.

[0039] To evaluate the electrocatalytic reduction of carbon dioxide to formic acid by the BiOCl nanosheet electrocatalyst synthesized in Example 1 using porous graphene as a support, an online gas phase product was detected using a Shimadzu GC-2030 chromatograph with a dielectric barrier discharge plasma detector (BID), and the liquid phase product was detected using ion chromatography. The Faradaic efficiency of formic acid at different potentials was obtained as follows: Figure 3 As shown, the BiOCl nanosheet catalyst exhibits a Faradaic efficiency exceeding 90% for formic acid in the potential range of -0.683 to -0.971 V vs. RHE. In particular, the Faradaic efficiency for formic acid reaches 96.4% at -0.943 V and -0.933 V, demonstrating the excellent formic acid selectivity of the BiOCl nanosheet electrocatalyst.

[0040] Figure 4 The linear sweep voltammetry (LSV) curves of the porous graphene-supported BiOCl nanosheet electrocatalyst synthesized in Example 1 in a carbon dioxide-saturated 0.1 M KHCO3 solution are shown. The results indicate that the porous graphene-supported BiOCl nanosheet electrocatalyst exhibits a high current density and a low initial potential in a carbon dioxide atmosphere. This demonstrates that the synthesized BiOCl nanosheet electrocatalyst possesses excellent electrocatalytic performance for carbon dioxide reduction.

[0041] Figure 5 This paper presents the competitive hydrogen evolution reaction analysis of the BiOCl nanosheet electrocatalyst synthesized in Example 1, which catalyzes the reduction of carbon dioxide at different potentials. Hydrogen production was detected using a Shimadzu GC-2030 chromatograph. The results show that the Faradaic efficiency of hydrogen is less than 5% in the potential range of -0.683 to -0.971 V vs. RHE, indicating that the BiOCl nanosheet catalyst has excellent electrocatalytic performance in the reduction of carbon dioxide to formic acid, with a very weak hydrogen evolution reaction.

[0042] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing BiOCl nanosheet electrocatalysts using porous graphene as a support, characterized in that, This includes the preparation steps of porous graphene and the preparation steps of BiOCl nanosheet electrocatalysts. The method for preparing porous graphene includes the following steps: Magnesium hydroxide powder was loaded into an alumina boat and then placed in a clean quartz tube in a CVD system. The CVD system was gradually heated and then maintained at a certain temperature. Subsequently, the argon flow was stopped, and a mixed gas flow containing C2H4 and H2 was introduced into the system to promote the growth of graphene, thereby forming a magnesium oxide graphene composite material. The magnesium oxide graphene composite material was then dispersed in an aqueous hydrochloric acid solution and continuously stirred on a hot plate to remove the magnesium oxide template. The resulting porous graphene material was collected by filtration, thoroughly washed multiple times with deionized water, and then freeze-dried to obtain porous graphene. The preparation method of the BiOCl nanosheet electrocatalyst with porous graphene as the support includes the following steps: Step 1: Add the soluble Bi metal salt to ethylene glycol to obtain mixed solution A; Step 2: Mix the above mixed solution A and porous graphene in a certain proportion and mix them evenly using a magnetic stirrer to obtain mixed solution B; Step 3: Chloride ion solution is added dropwise to the obtained mixed solution B in a certain proportion to obtain mixed solution C; then it is placed in a reaction vessel, and the reaction vessel is placed in an oven for hydrothermal reaction, centrifuged and dried to obtain the catalyst precursor; Step four: The catalyst precursor is placed in a tube furnace and calcined in a protective atmosphere, and then cooled in the furnace to obtain the BiOCl nanosheet catalyst.

2. The method for preparing BiOCl nanosheet electrocatalysts with porous graphene as a support according to claim 1, characterized in that, The specific preparation method of the porous graphene is as follows: magnesium hydroxide powder is loaded into an alumina boat and then placed in a clean quartz tube in a CVD system; the CVD system is gradually heated to 1030°C over 1 hour and maintained at this temperature for another hour; subsequently, the argon flow is stopped and a mixed gas flow containing C2H4 and H2 is introduced into the system for 1.5 hours to promote the growth of graphene, thereby forming a magnesium oxide graphene composite material; then the magnesium oxide graphene composite material is dispersed in a 3 M hydrochloric acid aqueous solution and continuously stirred on a hot plate at 80°C for 24 hours to remove the magnesium oxide template; the porous graphene material obtained by filtration is thoroughly washed multiple times with deionized water and then freeze-dried to obtain porous graphene.

3. The method for preparing BiOCl nanosheet electrocatalysts with porous graphene as a support according to claim 1, characterized in that, The Bi metal soluble salt mentioned in step one is any one of bismuth nitrate hydrate, bismuth sulfate hydrate, and bismuth trichloride hydrate.

4. The method for preparing BiOCl nanosheet electrocatalysts with porous graphene as a support according to claim 1, characterized in that, The mass ratio of the Bi metal soluble salt to porous graphene mentioned in step two is 242.5:

30.

5. The method for preparing BiOCl nanosheet electrocatalysts with porous graphene as a support according to claim 1, characterized in that, The chloride ion solution mentioned in step three can be either a sodium chloride solution or a potassium chloride solution; the ratio of the chloride ion solution to mixed solution B is 1:

1.

6. The method for preparing BiOCl nanosheet electrocatalysts with porous graphene as a support according to claim 1, characterized in that, The protective atmosphere described in step four is a mixture of nitrogen and ammonia; the flow rate ratio of nitrogen to ammonia is 1:2; the heating rate of calcination is 3℃ / min; the temperature is raised to 400℃ and held for 120 min, 180 min or 240 min.

7. A BiOCl nanosheet electrocatalyst with porous graphene as a support, prepared by the method according to any one of claims 1 to 6.

8. An application of the BiOCl nanosheet electrocatalyst based on porous graphene as described in claim 7, characterized in that, The BiOCl nanosheet electrocatalyst is used to enhance the activity and selectivity of electrocatalytic carbon dioxide reduction to formic acid.

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