Bismuth oxychloride nanoflake, preparation method and application thereof in preparation of formate by carbon dioxide electro-reduction

Abstract

The application discloses bismuth oxychloride nanosheet, a preparation method and application thereof in preparation of formate by carbon dioxide electro-reduction, and the preparation method comprises the following steps: dissolving bismuth nitrate pentahydrate in water, adding a surfactant and potassium chloride, stirring and reacting at room temperature after complete dissolution, obtaining a white solution after the reaction is completed, centrifuging, washing and drying to obtain the bismuth oxychloride nanosheet; wherein the mass of the surfactant is 25-65% of the mass of the bismuth nitrate pentahydrate. The preparation method of the bismuth oxychloride nanosheet is simple and practical, low in cost, capable of being enlarged, and beneficial to industrialized production, and the content of the surfactant is regulated, and one-step synthesis is realized at normal temperature and pressure. The obtained bismuth oxychloride nanosheet is excellent in electrochemical reduction of carbon dioxide, high in selectivity of formate, high in efficiency, low in toxicity and sustainable.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, specifically to a bismuth oxychloride nanosheet, its preparation method, and its application in the electroreduction of carbon dioxide to prepare formate. Background Technology

[0002] Energy production heavily relies on fossil fuels, leading to massive emissions of carbon dioxide into the atmosphere from human activities. Faced with the drastic depletion of non-renewable resources and the ever-increasing greenhouse gas emissions, the reduction of carbon dioxide into higher-energy compounds (such as methanol, formic acid, and methane) offers a solution to the greenhouse effect. Electrocatalytic carbon dioxide reduction has received considerable attention in the past decade due to its high efficiency, stability, and ease of control. The choice of electrolyte, pH, and reaction conditions in carbon dioxide electroreduction often affects the selectivity and efficiency of the reaction. For example, most carbon dioxide electroreduction processes use aqueous electrolytes, which readily synthesize products such as carbon monoxide. Formic acid, with its wide industrial and commercial applications in fine chemicals, batteries, agriculture, and dyes, is undoubtedly one of the preferred products for carbon dioxide reduction.

[0003] Electrocatalysis uses electricity to form chemical bonds. Choosing a suitable electrocatalyst can not only lower the activation energy barrier for CO2 electroreduction but also influence the selectivity, activity, and stability of the reaction through different active sites on the catalyst. Electroreduction reactions depend not only on reaction conditions but also, and more importantly, on the catalyst material. Therefore, designing various electrocatalytic materials to selectively convert CO, formic acid, methanol, ethanol, hydrocarbons, and oxalic acid has become a hot research topic. Among these, two-dimensional nanomaterials have seen rapid research progress in the past decade since the discovery of exfoliated graphene. Nanosheet materials possess unique electronic properties, flexibility, and mechanical strength, and also have extremely high surface areas. The large number of exposed surface atoms provides more possibilities for surface modification, functionalization, doping, and defect control, thus leading to their widespread use in photocatalysis, thermal catalysis, and electrocatalysis. Studies have shown that p-block metals such as tin (Sn), lead (Pb), and bismuth (Bi) are generally effective catalysts for the selective conversion of CO2 to formate / formic acid. Bismuth (Bi) is a stable, low-toxicity, and abundant metal that is more inexpensive than the precious metals platinum, gold, silver, and copper primarily used in electrocatalysis research. It also possesses the unique property of inhibiting the hydrogen evolution reaction (HER) at the same potential, making it a promising research subject. Currently, although bismuth and bismuth oxide have been proven to effectively convert carbon dioxide into formate, the limited number of active sites and weak intrinsic activity of bulk metallic bismuth or bismuth oxide result in unsatisfactory reaction results when used directly.

[0004] Existing literature discloses the preparation of bismuth oxychloride single-crystal nanosheets. These nanosheets, which exhibit good dispersibility and near-ultraviolet fluorescence, are prepared by a simple hydrolysis method. The thickness of these nanosheets is approximately 15-20 nm. However, the literature does not indicate that the nanosheets possess electrocatalytic properties ("Preparation and Optical Properties of Bismuth Oxide Single-Crystal Nanosheets", Jin Wang et al., Journal of Hebei Normal University, September 2017, Vol. 41, No. 5, pp. 424-429). Summary of the Invention

[0005] The technical problem to be solved by this invention is to propose a new method for preparing bismuth oxychloride nanosheets that is simple, practical, easy to scale up and produce at low cost, and to combine it with a mobile phase electrocatalysis method to achieve high selectivity and high efficiency in the electrocatalytic reduction of carbon dioxide at room temperature and pressure to prepare formate.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] A method for preparing bismuth oxychloride nanosheets includes the following steps: dissolving bismuth nitrate pentahydrate in water, adding a surfactant and potassium chloride, stirring the mixture at room temperature after complete dissolution, obtaining a white solution after the reaction is complete, centrifuging, washing, and drying to obtain the bismuth oxychloride nanosheets; wherein the mass of the surfactant is 25-65% of the mass of the bismuth nitrate pentahydrate.

[0008] Preferably, the surfactant is polyvinylpyrrolidone.

[0009] Preferably, the surfactant is polyvinylpyrrolidone K30.

[0010] Preferably, the mass of the surfactant is 41.2% of the mass of the bismuth nitrate pentahydrate.

[0011] Preferably, the molar ratio of bismuth nitrate pentahydrate to potassium chloride is 1:1.

[0012] Preferably, the molar volume ratio of bismuth nitrate pentahydrate to water is 0.04 mol: 1 L.

[0013] Preferably, the reaction time is 5 hours.

[0014] The present invention also proposes a bismuth oxychloride nanosheet, which is prepared by the aforementioned method for preparing bismuth oxychloride nanosheets.

[0015] Preferably, the bismuth oxychloride nanosheets have a crystal form of 85-0681.

[0016] The present invention also proposes an application of the aforementioned bismuth oxychloride nanosheets in the electroreduction of carbon dioxide to prepare formate.

[0017] Preferably, in specific applications, both the anolyte and the catholyte are 1M KHCO3 solutions, the inflow and outflow rates of the anolyte and the catholyte are 10mL / min, the CO2 gas flow rate is 35sccm, and the experimental current is 100-700mA.

[0018] The advantages of this invention are:

[0019] (1) The preparation method of bismuth oxychloride nanosheets described in this invention controls the content of surfactant, synthesizes it in one step at room temperature and pressure, is simple and practical, low in cost, can be scaled up, and is conducive to industrial production. The obtained bismuth oxychloride nanosheets have excellent electrochemical reduction performance of carbon dioxide, and the formate is highly selective, efficient, and has low toxicity, which is sustainable.

[0020] (2) The undoped and unmodified bismuth oxychloride nanosheets prepared in this invention are used in a flow cell and a gas diffusion electrode to electrocatalytically reduce carbon dioxide to formate in a potassium bicarbonate electrolyte solution, with a maximum current density reaching 700 mA / cm². -2 Its highest formate production Faraday efficiency is 82.5%, and its liquid phase selectivity reaches 100%. Compared with ordinary bulk bismuth-based catalysts, it has better performance in the electrochemical reduction of carbon dioxide to produce formate. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the white solution of bismuth oxychloride nanosheets prepared in Example 1 of the present invention;

[0022] Figure 2 The XRD pattern of the bismuth oxychloride nanosheets prepared in Example 1 of this invention is shown below.

[0023] Figure 3 The images shown are transmission electron microscope (TEM) and scanning electron microscope (SEM) images of bismuth oxychloride nanosheets prepared in Examples 1-2 and Comparative Examples 1-2 of this invention; wherein, A1, B1, C1, and D1 are the transmission electron microscope images corresponding to Example 1, Comparative Example 2, Example 2, and Comparative Example 1, respectively, and A2, B2, C2, and D2 are the scanning electron microscope (SEM) images corresponding to Example 1, Comparative Example 2, Example 2, and Comparative Example 1, respectively.

[0024] Figure 4 The linear scan voltammetry diagram of bismuth oxychloride nanosheets prepared in Example 1 in potassium bicarbonate electrolyte solution is shown in Example 3 of the present invention.

[0025] Figure 5 In Example 3 of this invention, the Faraday efficiency of formate formation using bismuth oxychloride nanosheets prepared in Example 1 in potassium bicarbonate electrolyte solution under different currents is shown.

[0026] Figure 6 In Example 3 of this invention, bismuth oxychloride nanosheets prepared in Example 1 were used at 300 mA cm⁻¹ -2 The proton NMR spectrum of the liquid phase products after the reaction at the current density. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all test materials and reagents used in the following examples are commercially available.

[0029] Unless otherwise specified in the embodiments, the techniques or conditions described in the literature in this field or in accordance with the product manual may be followed.

[0030] In the following examples and comparative examples, the polyvinylpyrrolidone used is polyvinylpyrrolidone K30.

[0031] Example 1

[0032] A method for preparing bismuth oxychloride nanosheets includes the following steps:

[0033] Dissolve 0.97 g (2 mmol) of bismuth nitrate pentahydrate in 50 ml of distilled water, then add 400 mg of polyvinylpyrrolidone (PVP) and 0.15 g (2 mmol) of potassium chloride. After complete dissolution, stir evenly at room temperature for 5 hours to obtain a white solution, as shown in the figure. Figure 1 As shown. Centrifugation yielded a white precipitate, which was washed with distilled water and then dried in a vacuum drying oven at 80°C for 12 hours to obtain a white powder, which is bismuth oxychloride nanosheets.

[0034] The structure of the product prepared in Example 1 was identified, and the results are shown in the figure. Figures 2-3 , Figure 2 The image shows the XRD pattern of the bismuth oxychloride nanosheets prepared in Example 1. Figure 2 It can be seen that the crystal form of the product prepared in this embodiment corresponds to JCPDS card No. 85-0681; Figure 3 In the image, A1 and A2 are transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the bismuth oxychloride nanosheets prepared in Example 1, respectively. Figure 3It can be seen that the obtained bismuth oxychloride is a uniform nanosheet with a width of 200nm-20nm.

[0035] Example 2

[0036] A method for preparing bismuth oxychloride nanosheets includes the following steps:

[0037] 0.97 g (2 mmol) of bismuth nitrate pentahydrate was dissolved in 50 ml of distilled water, and 600 mg of polyvinylpyrrolidone (PVP) and 0.15 g (2 mmol) of potassium chloride were added. After complete dissolution, the solution was stirred uniformly at room temperature for 5 h to obtain a white solution. The white precipitate was obtained by centrifugation, washed with distilled water, and dried in a vacuum drying oven at 80 °C for 12 h to obtain a white powder, which is bismuth oxychloride nanosheets.

[0038] The structure of the product prepared in this embodiment was identified, and the results are shown in the figure. Figure 3 , Figure 3 C1 and C2 are transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the bismuth oxychloride nanosheets prepared in this embodiment, respectively; Figure 3 It can be seen that the obtained bismuth oxychloride is also a uniform nanosheet, but it consumes more surfactant.

[0039] Comparative Example 1

[0040] Dissolve 0.97 g (2 mmol) of bismuth nitrate pentahydrate in 50 ml of distilled water, and add 0.15 g (2 mmol) of potassium chloride. After complete dissolution, stir uniformly at room temperature for 5 h to obtain a white solution. Centrifuge to obtain a white precipitate, wash with distilled water, and dry in a vacuum drying oven at 80 °C for 12 h to obtain a white powder.

[0041] The structure of the product prepared in this comparative example was identified, and the results are shown in the figure. Figure 3 , Figure 3 D1 and D2 are transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the product prepared in this comparative example; [The remaining text appears to be incomplete and requires further context.] Figure 3 It can be seen that the obtained bismuth oxychloride is a single block material, and there is no bismuth oxychloride sheet required.

[0042] Comparative Example 2

[0043] 0.97 g (2 mmol) of bismuth nitrate pentahydrate was dissolved in 50 ml of distilled water, and 200 mg of polyvinylpyrrolidone (PVP) and 0.15 g (2 mmol) of potassium chloride were added. After complete dissolution, the solution was stirred uniformly at room temperature for 5 h to obtain a white solution. The solution was centrifuged to obtain a white precipitate, washed with distilled water, and dried in a vacuum drying oven at 80 °C for 12 h to obtain a white powder.

[0044] The structure of the product prepared in this comparative example was identified, and the results are shown in the figure. Figure 3 B1 and B2 are transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of the prepared product, respectively; from Figure 3 It can be seen that the obtained bismuth oxychloride has a morphology that is a mixture of thin sheets and bulk materials.

[0045] Example 3

[0046] Examples of using bismuth oxychloride nanosheets as catalysts for the electrochemical reduction of carbon dioxide to prepare formate:

[0047] The electrocatalytic reduction of carbon dioxide was carried out in a three-electrode flow cell system. 25 mg of bismuth oxychloride nanosheets prepared in Example 1 were dispersed in a mixture of 1.25 mL water and 3.75 mL isopropanol. 50 μL of Nafion (5 wt%) solution was added, and the mixture was ultrasonically dispersed for 30 min to obtain a homogeneous electrode solution. The electrode solution was then uniformly sprayed onto a 25 cm² surface. 2 The working electrode was obtained by natural drying on a gas diffusion electrode (GDE); a silver-silver chloride electrode was used as the reference electrode. Electrochemical performance was tested using a flow cell on an electrochemical workstation (Shanghai Chenhua CHI 660e) equipped with a high-current amplifier (Shanghai Chenhua CHI 680c). The flow cell consisted of three chambers: an anolyte chamber containing the anode (nickel foam), a cathode chamber containing the cathode and the Ag / AgCl reference electrode, and a CO2 flow chamber. The anolyte and cathode electrolyte chambers were separated by an anion exchange membrane (FAA-PK-130). The effective size of the catalyst was 1 × 1 cm. 2 The resistance compensation was set to 85%. The solution resistance was measured by electrochemical impedance spectroscopy (EIS) and was found to be 4.5 Ω. Both the anolyte and cathode electrolyte were 1 M KHCO3, and the inflow and outflow of the electrolyte were controlled by a peristaltic pump (JIHPIMP, BT-50EA / 253Yx-PPS) at a flow rate of 10 mL / min. High-purity CO2 gas was introduced at a constant flow rate of 35 sccm using a mass flow controller (Qixing, CS-200A), which was also monitored by the mass flow controller. A linear scanning voltammetry diagram of the bismuth oxychloride nanosheets prepared in Example 1 was obtained by scanning the flowing potassium bicarbonate electrolyte solution using the above apparatus. Figure 4 As shown. The experimental current was controlled at 100mA for the reaction.

[0048] Figure 6 300mA cm -2 The 1H NMR spectrum of the liquid-phase products after the reaction at the specified current density, where DMSO is an internal standard, and formic acid in the figure represents formate. Figure 6It can be seen that the liquid products consist only of formate (water peak at 4.75). The gaseous products contain trace amounts of carbon monoxide, methane, and hydrogen, as determined by gas chromatography.

[0049] Following the method described above, the current was increased from 100mA to 700mA, and the corresponding Faraday efficiency was calculated. Figure 5 .Depend on Figure 4 and Figure 5 As can be seen, the results are similar to those of indium oxide, with the optimal Faraday efficiency of the reaction product at 400 mA cm⁻¹. -2 The reaction can be extended to 700 mA cm⁻¹ -2 Faraday efficiency is over 60%.

[0050] Following the above method, using the material prepared in Comparative Example 2 as a catalyst, 100 mA cm -2 The formate Faraday efficiency under current is 57%.

[0051] The product Faraday efficiency mentioned in this invention is only the product Faraday efficiency of formate, and when combined with the gas phase product, it can reach close to 100%.

[0052] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing bismuth oxychloride nanosheets, characterized in that: Includes the following steps: Bismuth nitrate pentahydrate was dissolved in water, and a surfactant and potassium chloride were added. After complete dissolution, the mixture was stirred and reacted at room temperature. After the reaction was completed, a white solution was obtained. The solution was centrifuged, washed, and dried to obtain the bismuth oxychloride nanosheets. The surfactant was 25-65% of the mass of bismuth nitrate pentahydrate. The surfactant was polyvinylpyrrolidone. The bismuth oxychloride nanosheets were uniform nanosheets with a crystal form of 85-0681.

2. The method for preparing bismuth oxychloride nanosheets according to claim 1, characterized in that: The mass of the surfactant is 41.2% of the mass of the bismuth nitrate pentahydrate.

3. The method for preparing bismuth oxychloride nanosheets according to claim 1, characterized in that: The molar ratio of bismuth nitrate pentahydrate to potassium chloride is 1:

1.

4. The method for preparing bismuth oxychloride nanosheets according to claim 1, characterized in that: The molar volume ratio of bismuth nitrate pentahydrate to water is 0.04 mol: 1 L.

5. The method for preparing bismuth oxychloride nanosheets according to any one of claims 1-4, characterized in that: The reaction time is 5 hours.

6. A bismuth oxychloride nanosheet, characterized in that: The nanosheets were prepared using the method described in any one of claims 1-5.

7. The application of bismuth oxychloride nanosheets as described in claim 6 in the electroreduction of carbon dioxide to prepare formate.

8. The application of bismuth oxychloride nanosheets according to claim 7 in the electroreduction of carbon dioxide to prepare formate, characterized in that: In practical applications, both the anolyte and the catholyte are 1 M KHCO3 solutions. The inflow and outflow rates of the anolyte and catholyte are 10 mL / min, the CO2 gas flow rate is 35 sccm, and the experimental current is 100-700 mA.

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