A sulfur-iodine co-modified bismuth subcarbonate catalyst, a preparation method and application thereof

Abstract

This invention discloses a sulfur-iodine co-modified bismuth subcarbonate catalyst, its preparation method, and its application, belonging to the field of electrocatalytic reduction technology. The sulfur-iodine co-modified bismuth subcarbonate catalyst is a Bi₂O₂CO₃ phase, composed of Bi... 13 S 18 The I2 nanosheet precursor was reconstructed in situ into a sulfur- and iodine-modified bismuth subcarbonate nanosheet structure under near-neutral CO2 electroreduction conditions, while retaining S on its surface and / or between layers. 2‑ and I ‑ Thus retaining Bi 3+ Simultaneous oxidation of the bismuth subcarbonate catalyst enables synergistic regulation of surface anions, constructing an active interface with abundant nanoscale pits and a high specific surface area. This invention employs a simple and mild process, and the resulting sulfur-iodine co-modified bismuth subcarbonate catalyst exhibits excellent performance in the electrocatalytic reduction of carbon dioxide to formate, achieving up to 1000 mA cm⁻¹. ‑2 It maintains high formate Faraday efficiency over a wide current density range and achieves long-term stable operation in membrane electrode systems, demonstrating good prospects for practical applications.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic reduction of carbon dioxide, specifically relating to a sulfur-iodine co-modified bismuth subcarbonate catalyst and its in-situ preparation method, as well as its application in the field of carbon dioxide electroreduction. Background Technology

[0002] Electrocatalytic carbon dioxide reduction (CO2RR) is an important technology for efficiently utilizing renewable energy and producing high-value chemicals under mild conditions. However, current CO2RR technology still suffers from problems such as high overpotential, insufficient product selectivity at high current densities, and poor stability. Developing catalysts with a large number of active sites and excellent mass transfer properties can effectively improve the activity and current density of CO2RR, thereby effectively overcoming the above limitations.

[0003] The CO2RR process for producing formic acid (salts) has advantages such as low overpotential, high selectivity, and high product added value, making it a promising branch of electrochemical carbon dioxide reduction (ECR) technology for industrialization. Bismuth (Bi) and its compounds are abundant, non-toxic, and have low hydrogen evolution activity. Their p orbitals are advantageous for adsorbing and activating oxygen atoms in CO2 molecules, making them ideal catalysts for CO2RR for producing formic acid (salts).

[0004] Studies have shown that for Bi metal and Bi 3+ In Bi-based catalysts, the addition of sulfur can modulate the electronic structure of adjacent Bi sites to enhance *H adsorption, or alter the configuration of hydrated cations near the reaction interface to increase the local pH, thereby enhancing the hydrolysis ability of Bi-based catalysts and improving the performance of CO2RR formate production. While the structures of existing Bi-SX (X being halogens such as Cl, Br, and I) dianionic compounds have been structurally resolved, related studies often involve pre-reducing the material to a metallic state under non-operating conditions. This can easily lead to the inability to simultaneously retain sulfide and halide ions during the drastic valence state changes and lattice rearrangement, making it difficult to simultaneously leverage their synergistic effects in improving the reaction environment and enhancing intrinsic activity. Therefore, developing a Bi-based catalyst capable of in-situ reconstruction under actual CO2RR operating conditions while simultaneously retaining the modification characteristics of sulfide and iodide ions is of great significance for improving the overall performance of CO2RR formate (salt) production under near-neutral conditions. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the problems of slow water dissociation kinetics, insufficient intrinsic activity, and limited stability of existing Bi-based catalysts in the near-neutral CO2RR formate (salt) production process. This invention provides a simple method for preparing a bismuth subcarbonate catalyst that can be reconstructed in situ under operating conditions and achieve sulfur-iodine co-modification, and the application of this catalyst in the electrocatalytic reduction of carbon dioxide to formate (salt).

[0006] To solve the above problems, the present invention adopts the following technical solution:

[0007] A sulfur-iodine co-modified bismuth subcarbonate catalyst, wherein the catalyst is a Bi₂O₂CO₃ phase, consisting of Bi 13 S 18 The I2 nanosheet precursor was obtained through in-situ reconstruction under CO2RR conditions, exhibiting a Bi2O2CO3 layered nanostructure with nanoscale pits and / or multi-cavity structures on the surface, and simultaneously retaining a small amount of S on the catalyst surface and / or between layers. 2- and I - The catalyst contains Bi, which maintains a +3 oxidation state, and S... 2- and I - Located in [Bi2O2] 2+ It is on the surface or between layers, but does not penetrate into the layer.

[0008] Furthermore, the catalyst has a tetragonal Bi2O2CO3 crystal phase, and the interplanar spacing in the interlayer direction is increased relative to standard Bi2O2CO3.

[0009] This invention provides an in-situ preparation method for the above-mentioned sulfur-iodine co-modified bismuth subcarbonate catalyst, comprising the following steps:

[0010] 1) Bismuth source was added to an aqueous acetic acid solution, and suspension A was obtained under continuous stirring and heating.

[0011] 2) Dissolve the sulfur source and iodine source in water and obtain solution B under heating conditions;

[0012] 3) Quickly add the suspension A obtained in step 1) to the solution B obtained in step 2), and react under heating and stirring conditions. After the reaction is complete, wash and dry the product to obtain Bi. 13 S 18 I2 nanosheet precursor;

[0013] 4) The Bi 13 S 18 I2 nanosheet precursors are dispersed in a solvent containing a binder to form a catalyst slurry, and the slurry is loaded onto a gas diffusion layer to obtain an electrode.

[0014] 5) Assemble the electrode obtained in step 4) as the cathode in a flowing electrolytic cell, and perform electrolysis under the conditions of introducing carbon dioxide gas and bicarbonate electrolyte, so that the Bi 13 S 18 The I2 nanosheet precursor was reconstructed in situ into a sulfur-iodine co-modified bismuth subcarbonate catalyst.

[0015] Further, in step 1) above, the acetic acid aqueous solution is composed of deionized water and acetic acid, preferably with a volume percentage concentration of 1%~2%; the bismuth source is preferably a bismuth salt, preferably bismuth nitrate pentahydrate or bismuth chloride, and the concentration of Bi element in the bismuth source added to the acetic acid aqueous solution is preferably 40-60 mM; the heating temperature is 100-120 ℃, so that the system is kept at a slight boiling.

[0016] Further, the sulfur source in step 2) above is preferably thioacetamide or thiourea; the iodine source is preferably potassium iodide or sodium iodide. In some specific embodiments of the present invention, the sulfur source is thioacetamide, and the iodine source is potassium iodide. They are added to deionized water and heated to 100-120 °C. The concentration of thioacetamide in the resulting solution B is preferably 80-120 mM, and the concentration of potassium iodide is preferably 40-60 mM. The slow release of sulfur from thioacetamide under heating conditions is utilized. 2- This allows the precipitation reaction in step 3) to proceed at a milder and more controllable rate; simultaneously, by utilizing the fact that the solubility product of Bi sulfides is significantly lower than that of iodides, a framework based on Bi2S3 structural units can be preferentially formed, and further I-containing structures can be formed. - Intercalated Bi 13 S 18 I2 nanosheets.

[0017] Preferably, in step 3), after adding suspension A to solution B, the mixture is stirred rapidly at 100-120 °C for 1 hour; after the reaction is complete, it is cooled to room temperature, repeatedly dispersed with water and ethanol, and washed by centrifugation. Finally, it is vacuum dried at room temperature to obtain Bi. 13 S 18 I2 nanosheet precursor.

[0018] Furthermore, in step 4), the catalyst slurry can be composed of Bi... 13 S 18 The gas diffusion layer consists of an I2 nanosheet precursor, ethanol, and Nafion dispersion. The substrate for the gas diffusion layer can be hydrophobic carbon paper, carbon cloth, etc., and is coated with a hydrophobic microporous layer on one side. In some specific embodiments of the present invention, 5 mg of the Bi... 13 S 18 I₂ nanosheet precursors were dispersed in a mixed solution of 1 mL ethanol and 10 μL 5 wt% Nafion, and after ultrasonic dispersion, were drop-coated onto a carbon paper-based gas diffusion layer to prepare a catalytic electrode; Bi₂ nanosheets were then deposited onto the electrode. 13 S 18 The loading of I2 nanosheet precursors can be 0.5-1.5 mg cm⁻¹. -2 .

[0019] Further, step 5) makes Bi 13 S 18The I2 nanosheet precursor was reconstructed in situ into a sulfur- and iodine-modified bismuth subcarbonate nanosheet structure under near-neutral CO2 electroreduction conditions, thereby retaining the Bi... 3+ Simultaneous oxidation of the surface anions allows for synergistic regulation, constructing an active interface with abundant nanoscale pits and a high specific surface area. In some specific embodiments of this invention, the cathode electrolyte of the flowing electrolytic cell can be 0.5 M KHCO3, the cathode CO2 flow rate can be 10-50 sccm, and constant current, constant voltage, or pulsed voltage electrolysis can be used, thereby enabling Bi... 13 S 18 I2 nanosheets were reconstructed in situ into bismuth subcarbonate co-modified with sulfur and iodine under CO2RR conditions.

[0020] This invention further provides the application of the sulfur-iodine co-modified bismuth subcarbonate catalyst in the electroreduction of carbon dioxide, specifically as a catalyst for the electrocatalytic reduction of carbon dioxide to formate. Therefore, this invention provides a catalytic electrode for the electrocatalytic reduction of carbon dioxide, wherein the above-mentioned sulfur-iodine co-modified bismuth subcarbonate catalyst is supported on the catalytic electrode. This catalytic electrode can be used to electrocatalyze the reduction of carbon dioxide by loading the above-mentioned sulfur-iodine co-modified bismuth subcarbonate catalyst. 13 S 18 The catalyst slurry of the I2 nanosheet precursor was drop-coated onto the surface of the gas diffusion layer and dried, and then electrolyzed and reconstructed in situ.

[0021] This invention also provides a method for the electrocatalytic reduction of carbon dioxide, employing a flow electrolyzer or membrane electrode assembly (MEA) device. The catalytic electrode, with the bismuth subcarbonate catalyst supported on a sulfur-iodine co-modified substrate, serves as the cathode. One side of the cathode catalyst layer is in contact with the electrolyte, and the other side is in contact with flowing carbon dioxide gas, thereby achieving highly efficient electrocatalytic conversion of carbon dioxide to formic acid (salt). Test results show that the catalytic electrode of this invention exhibits excellent ECR performance.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This invention first prepares Bi using a simple one-step method. 13 S 18 The process involves using I2 nanosheet precursors and then reconstructing them in situ using CO2RR conditions. This method is simple and easy to implement. The resulting catalyst retains Bi... 3+ Oxidized state, while retaining a small amount of S. 2- and I - Surface modification can simultaneously improve water dissociation kinetics under near-neutral conditions and enhance the intrinsic activity of catalytic sites; the resulting catalyst possesses a layered structure and surface nanoscale pits, providing a high specific surface area and abundant active sites, thereby improving reaction kinetics; this catalyst can achieve high reaction kinetics in a flow cell at temperatures up to 1000 mA cm⁻¹. -2It maintains a formate faradaic efficiency of over 96.3% over a wide current density range, and performs well in a membrane electrode electrolyzer at 500 mA cm⁻¹. -2 Under certain conditions, it can operate stably for 500 hours with a formate Faraday efficiency of over 95%, demonstrating good application potential. Attached Figure Description

[0024] Figure 1 This is a transmission electron microscope (TEM) image of the sulfur-iodine co-modified bismuth subcarbonate catalyst prepared in the embodiments of the present invention.

[0025] Figure 2 This is the X-ray diffraction pattern of the sulfur-iodine co-modified bismuth subcarbonate catalyst prepared in the embodiments of the present invention.

[0026] Figure 3 The X-ray photoelectron spectroscopy (XPS) spectra of (a) sulfur and (b) iodine of the sulfur-iodine co-modified bismuth subcarbonate catalyst prepared in the embodiments of the present invention are shown.

[0027] Figure 4 This refers to the Faradaic efficiency of the sulfur-iodine co-modified bismuth subcarbonate catalytic electrode prepared in the embodiments of the present invention, catalyzing the formic acid (salt) product under different current densities in a flow cell.

[0028] Figure 5 This refers to the Faradaic efficiency of the sulfur-iodine co-modified bismuth subcarbonate catalytic electrode prepared in the embodiments of the present invention in a membrane electrode electrolyzer at different current densities for the catalytic product formic acid (salt).

[0029] Figure 6 The sulfur-iodine co-modified bismuth subcarbonate catalytic electrode prepared in this embodiment of the invention was tested in a membrane electrode electrolyzer at 500 mA cm⁻¹. -2 Stability under current density. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0031] In this embodiment, a bismuth subcarbonate catalyst co-modified with sulfur and iodine was synthesized and prepared in situ by electrochemical methods, and its electrocatalytic performance for carbon dioxide reduction was studied.

[0032] 1. The precursor for the synthesis of sulfur-iodine co-modified bismuth subcarbonate catalyst is as follows:

[0033] 0.728 g Bi(NO3)3·5H2O was added to a mixed solution containing 30 mL of deionized water and 345 μL of acetic acid. The mixture was stirred rapidly and heated in an oil bath to 120 °C to obtain suspension A. The sample vial was sealed but not airtight, maintaining a slight boil. Separately, 300 mg of thioacetamide and 255 mg of potassium iodide were added to a single-necked flask containing 30 mL of deionized water. After dissolution, the solution was heated in an oil bath to 120 °C to obtain solution B. Suspension A was then shaken well and quickly poured into solution B. The mixture was stirred rapidly and kept at a constant temperature of 120 °C. The single-necked flask was sealed but not airtight, maintaining a slight boil. After reacting for 1 h, the mixture was cooled to room temperature. It was then repeatedly dispersed with water and ethanol, followed by centrifugation and washing. The final product was dried under vacuum at room temperature to obtain Bi. 13 S 18 I2 nanosheet precursor.

[0034] 2. A sulfur-iodine co-modified bismuth subcarbonate precursor electrode was prepared using a drop-coating method, the specific method of which is as follows:

[0035] 5 mg of Bi obtained in Example 1 13 S 18 I₂ nanosheet precursors were dispersed in a mixed solution of 1 mL ethanol and 10 μL 5 wt% Nafion, and ultrasonically dispersed for 1 h to obtain a catalyst slurry. This slurry was then drop-coated onto a 1 cm × 1 cm carbon paper gas diffusion layer to fabricate an electrode, allowing Bi₂ nanosheets to... 13 S 18 The I2 nanosheet precursor loading was 1 mg cm⁻¹ -2 The effective electrode area, calculated based on the cathode window area of ​​the flow cell, is 0.25 cm². 2 .

[0036] 3. The electroreduction performance of the prepared electrode for carbon dioxide was tested in a flowing electrolytic cell, and the specific method is as follows:

[0037] A three-electrode flow electrolysis cell system was adopted, with the electrode obtained in step 2 as the cathode, the titanium felt coated with IrO2 as the anode, the Hg / HgO electrode as the reference electrode, and a Nafion 211 membrane as the diaphragm. The cathode electrolyte was 0.5 M KHCO3, and the cathode CO2 flow rate was 20 sccm. Initially, under flowing CO2 gas and electrolyte conditions, the flow rate was 200 mA cm⁻¹. -2 Constant current electrolysis for 20 minutes to achieve Bi 13 S 18 The in-situ reconstruction of the I2 nanosheet precursor yielded a catalyst denoted as sulfoiodine co-modified bismuth subcarbonate (SI-BOC).

[0038] Characterization results showed that the in-situ reconstructed catalyst retained its lamellar morphology and formed numerous nanoscale pits on its surface; high-resolution transmission electron microscopy and X-ray diffraction results indicated that the material had transformed into the Bi₂O₂CO₃ phase; XPS confirmed that a small amount of S remained on the catalyst surface. 2- and I - .

[0039] The electrocatalytic CO2 reduction performance of the obtained catalyst was further tested. The results showed that the catalyst exhibited excellent CO2RR activity and selectivity for formate production under near-neutral conditions of 0.5 MKHCO3, reaching up to 1000 mA cm⁻¹. -2 Within the current density range, the formate Faraday efficiency remains above 96.3%; at 1000 mA cm⁻¹ -2 At this time, the formate formation rate can reach 18.1 mmol / cm². -2 h -1 .

[0040] 4. The electroreduction performance of the prepared electrode for carbon dioxide was tested in the membrane electrode assembly. The specific method is as follows:

[0041] Bi 13 S 18 I2 nanosheets, carbon black, and 5 wt% Nafion were mixed and dispersed in ethanol to prepare a cathode slurry, which was then sprayed onto a gas diffusion layer to obtain a MEA cathode. 13 S 18 The I2 nanosheet loading was 1.25 mg cm⁻¹. -2 The effective area of ​​the cathode is 5 cm². 2 The anode is a titanium felt coated with a dispersion of IrO2 and PTFE, and the catalyst loading is 1 mg / cm³. -2 The anolyte was 20 mM Cs₂CO₃, and the CO₂ flow rate at the cathode was set to 35 sccm. The electrolysis process was controlled by a constant current DC power supply.

[0042] In the aforementioned MEA device, at 500 mA cm -2 Continuous electrolysis was performed at the specified current density for 500 h. The results showed that the membrane electrode assembly maintained an electrolytic cell voltage of approximately 3.3 V and a formate Faradaic efficiency of no less than 95% during the test, demonstrating excellent long-term stability. XRD, TEM, and XPS characterization of the cathode after the test revealed that the catalyst also maintained the Bi₂O₂CO₃ phase in the MEA, retaining small amounts of S and I elements, indicating that its morphology, valence state, and structure exhibit good stability during long-term operation.

[0043] Figure 1 Transmission electron microscopy (TEM) images of the sulfur-iodine co-modified bismuth subcarbonate catalyst prepared in the examples are shown. From Figure 1 As can be seen, after the precursor undergoes in-situ transformation under operating conditions, the catalyst retains its nanosheet morphology, and its surface contains a large number of recessed pores, several nanometers in size, that do not penetrate the entire nanosheet. This unique pore structure may be the gaps created by the detachment of intercalated anions after the topological transformation of the network lattice.

[0044] Figure 2 The X-ray diffraction pattern of the sulfur-iodine co-modified bismuth subcarbonate catalyst prepared in the example is compared with the standard bismuth subcarbonate spectrum. Figure 1 The results confirmed that the catalyst phase was bismuth subcarbonate, while a small amount of sulfur / iodine was mainly adsorbed on the catalyst surface.

[0045] Figure 3 The X-ray photoelectron spectra of the sulfur-iodine co-modified bismuth subcarbonate catalyst prepared in the examples are shown below. Figure 2 The X-ray diffraction results confirmed that the obtained catalyst was composed of bismuth subcarbonate co-modified with iodine and sulfur elements.

[0046] Figure 4 The Faradaic efficiency (HCOO) of the sulfur-iodine co-modified bismuth subcarbonate (SI-BOC) catalytic electrode prepared for this example, catalyzed the formic acid (salt) product at different current densities in a flow cell. - (FE), it can be seen that SI-BOC maintains over 95% HCOO within a wide current density range with an upper limit in the ampere level. - FE, and no significant decrease in FE with increasing current was found, meeting the activity and selectivity requirements for industrial applications.

[0047] Figure 5 The figure shows the Faradaic efficiency of the bismuth subcarbonate catalytic electrode prepared for the example under different current densities in a membrane electrode electrolyzer for the catalytic product formate (salt). It can be seen that even at ampere-level current densities, it can still maintain a formate Faradaic efficiency of over 95%.

[0048] Figure 6 A sulfur-iodine co-modified bismuth subcarbonate catalyst was tested in a membrane electrode electrolyzer at 500 mA cm⁻¹. -2 Stability tests at current density show that the catalyst maintained no less than 95% formate FE and approximately 3.3 V of full cell voltage over 500 hours, with no significant degradation throughout the process.

[0049] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are only illustrative of the principles of the present invention. Various changes and modifications can be made to the present invention without departing from the scope of the principles of the present invention, and all such changes and modifications fall within the protection scope of the present invention.

Claims

1. A sulfur-iodine co-modified bismuth subcarbonate catalyst, wherein the catalyst is a Bi₂O₂CO₃ phase, characterized in that, By Bi 13 S 18 I2 nanosheet precursors were obtained through in-situ reconstruction under electrocatalytic carbon dioxide reduction conditions. They exhibited a layered nanostructure with nanoscale pits and / or multi-cavity structures on the surface, and retained S on the catalyst surface and / or between layers. 2- and I - The Bi element retains a +3 valence.

2. The sulfur-iodine co-modified bismuth subcarbonate catalyst according to claim 1, characterized in that, The catalyst has a tetragonal Bi2O2CO3 crystal phase, and the interplanar spacing in the interlayer direction is increased relative to standard Bi2O2CO3.

3. A method for preparing the sulfur-iodine co-modified bismuth subcarbonate catalyst according to claim 1 or 2, comprising the following steps: 1) Add the bismuth source to an aqueous acetic acid solution to form a suspension A under heating and stirring conditions; 2) Dissolve the sulfur source and iodine source in water and obtain solution B under heating conditions; 3) Suspension A was added to solution B, and the reaction was carried out under heating and stirring conditions. After the reaction was completed, the solution was washed and dried to obtain Bi. 13 S 18 I2 nanosheet precursor; 4) Change Bi 13 S 18 I2 nanosheet precursors are dispersed in a solvent containing a binder to obtain a catalyst slurry, and the catalyst slurry is loaded onto a gas diffusion layer to obtain an electrode; 5) Assemble the electrode obtained in step 4) as the cathode in a flowing electrolytic cell, and perform electrolysis under a carbon dioxide atmosphere and bicarbonate electrolyte conditions, so that the Bi 13 S 18 The I2 nanosheet precursor was reconstructed in situ into a sulfur-iodine co-modified bismuth subcarbonate catalyst.

4. The preparation method according to claim 3, characterized in that, The bismuth source mentioned in step 1) is bismuth nitrate pentahydrate or bismuth chloride; the acetic acid aqueous solution is composed of acetic acid and deionized water, wherein the volume percentage concentration of acetic acid is 1%~2%; the heating temperature is 100-120 ℃.

5. The preparation method according to claim 3, characterized in that, The sulfur source in step 2) is thioacetamide or thiourea, and the iodine source is potassium iodide or sodium iodide; heat to 100-120 ℃.

6. The preparation method according to claim 3, characterized in that, In step 3), suspension A is rapidly added to solution B, and the mixture is stirred continuously at 100-120 °C for 1 h. After the reaction is complete, the mixture is cooled to room temperature, dispersed repeatedly with water and ethanol, and washed by centrifugation. Finally, it is dried under vacuum at room temperature to obtain Bi. 13 S 18 I2 nanosheet precursor.

7. The preparation method according to claim 3, characterized in that, In step 4), the binder is Nafion, and the solvent is ethanol; the gas diffusion layer is hydrophobic carbon paper or carbon cloth with a microporous layer coated on one side, and the resulting electrode has Bi... 13 S 18 The loading of I2 nanosheet precursors was 0.5-1.5 mg cm⁻¹. -2 .

8. The preparation method according to claim 3, characterized in that, In step 5), the cathode electrolyte of the flowing electrolytic cell is 0.5 M KHCO3, the cathode carbon dioxide flow rate is 10-50 sccm, and electrolysis is performed under constant current, constant voltage, or pulsed voltage conditions to make Bi 13 S 18 I2 nanosheets were reconstructed in situ into bismuth subcarbonate co-modified with sulfur and iodine.

9. A catalytic electrode, characterized in that, The catalytic electrode is loaded with the sulfur-iodine co-modified bismuth subcarbonate catalyst according to claim 1 or 2.

10. A method for the electrocatalytic reduction of carbon dioxide to formate, characterized in that, Using the catalytic electrode described in claim 9 as the cathode in the electrocatalytic carbon dioxide reduction reaction system, one side of the electrode is in contact with the electrolyte and the other side is in contact with the flowing carbon dioxide gas, so that carbon dioxide is electrocatalytically reduced to form formate.

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