Ag / Bi2WO6 catalyst for preparing formic acid by reducing CO2 through electro-catalysis in wide pH range, preparation method of Ag / Bi2WO6 catalyst and application of Ag / Bi2WO6 catalyst in electro-catalysis CO2 reduction electrode
By modifying the surface of Bi2WO6 with silver to form an Ag/Bi2WO6 composite material, the problems of slow reaction kinetics and pH influence of traditional Bi-based catalysts in a wide potential window are solved, and the effect of efficient electrocatalytic reduction of CO2 to formic acid in a wide pH range is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-06
- Publication Date
- 2026-04-14
AI Technical Summary
Traditional Bi-based catalysts exhibit slow reaction kinetics and low local current density over a wide potential window, and their catalytic performance is affected by the electrolyte pH, making it difficult to maintain high formic acid faradaic efficiency over a wide pH range.
Bi2WO6 catalyst was synthesized by solvothermal method, and silver was modified on its surface by liquid phase method to optimize the ratio of Ag to Bi2WO6, thereby increasing the specific surface area and CO2 adsorption capacity of the catalyst and forming Ag/Bi2WO6 composite material.
The catalyst significantly improved the activity and selectivity of electrocatalytic CO2 reduction to formic acid within alkaline, neutral, and acidic pH ranges, broadened the high formic acid selectivity current density window, and enhanced the industrial application potential of the catalyst.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of electrocatalytic CO2 reduction technology, specifically relating to an Ag / Bi2WO6 catalyst for electrocatalytic CO2 reduction to formic acid over a wide pH range, its preparation method, and its application in an electrocatalytic CO2 reduction electrode. Background Technology
[0002] With the continued growth of global energy demand and the increasing CO2 emissions, electrocatalytic CO2 reduction reaction (CO2RR) has attracted widespread attention as an effective way to convert CO2 into high-value-added chemicals or fuels. Among them, formic acid (HCOOH), as an important chemical raw material and a potential hydrogen energy carrier, has high economic value and promising energy utilization prospects.
[0003] Among numerous electrocatalytic materials, bismuth (Bi)-based catalysts have attracted considerable research attention due to their excellent selectivity and stability in the reduction of CO2 to formic acid. However, traditional Bi-based catalysts still have certain limitations in practical applications. Existing Bi-based materials exhibit slow reaction kinetics and low local current densities over a wide potential window, making it difficult to maintain a high Faradaic efficiency (FE) for formic acid at high current densities. Furthermore, the catalytic activity and formic acid selectivity of bismuth (Bi)-based catalysts are easily affected by the electrolyte pH, typically exhibiting superior performance only within a specific pH range, thus limiting their widespread application under actual industrial conditions. Therefore, developing a CO2 reduction electrocatalyst with high activity, high selectivity, and a wide current window over a wide pH range has become an important research direction. Summary of the Invention
[0004] To address the problems of low current density, narrow current window for high formic acid, and catalytic performance limitations imposed by electrolyte pH in traditional Bi-based materials for electrocatalytic CO2 reduction, this invention provides an Ag / Bi2WO6 catalyst for electrocatalytic CO2 reduction to formic acid over a wide pH range, its preparation method, and its application in an electrocatalytic CO2 reduction electrode.
[0005] The technical solution of the present invention is as follows: One objective of this invention is to provide a method for preparing an Ag / Bi2WO6 catalyst for the electrocatalytic reduction of CO2 to formic acid over a wide pH range. This method includes the following steps: (1) Dissolve the bismuth salt in ethylene glycol and stir to obtain solution 1; (2) Dissolve tungstate in isopropanol and stir to obtain solution 2; (3) Add solution 2 to solution 1 and heat in a hydrothermal reactor to react and obtain Bi2WO6; (4) Add Bi2WO6 and silver salt to water, stir and then add reducing agent to obtain solution 3. Continue stirring to carry out the reaction. Centrifuge, wash and freeze dry the obtained product to obtain Ag / Bi2WO6 catalyst.
[0006] Preferably, the bismuth salt in (1) is bismuth nitrate pentahydrate, bismuth acetate, bismuth chloride or bismuth sulfate, more preferably bismuth nitrate pentahydrate.
[0007] Preferably, the concentration of bismuth salt in solution 1 of (1) is 0.1-0.5 mol / L. -1 More preferably, it is 0.268 mol L. -1 .
[0008] Preferably, in (2), the tungstate is sodium tungstate dihydrate, ammonium metatungstate, ammonium paratungstate or ammonium tungstate, more preferably sodium tungstate dihydrate.
[0009] Preferably, the concentration of tungstate in solution 2 of (2) is 0.01-0.1 mol / L. -1 More preferably, it is 0.044 mol L. -1 .
[0010] Preferably, the stirring time in (1) and (2) is 5-60 min, more preferably 20 min. Preferably, the volume ratio of isopropanol in (2) to ethylene glycol in (1) is (1-4):1, more preferably 3:1.
[0011] Preferably, the reaction temperature in (3) is 80-180℃ and the time is 10-24h, more preferably 160℃ and 15h.
[0012] Preferably, the reducing agent in (4) is L-cysteine, ascorbic acid or β-mercaptoethylamine, more preferably L-cysteine.
[0013] Preferably, the silver salt in (4) is silver nitrate or silver acetate, more preferably silver nitrate.
[0014] Preferably, the concentration of Bi2WO6 in solution 3 of (4) is 0.01-0.05 mol / L. -1 More preferably, it is 0.014 mol L. -1 .
[0015] Preferably, the concentration of the reducing agent in solution 3 of (4) is 0.01-0.05 mol·L⁻¹. -1 More preferably, it is 0.012 mol L. -1 .
[0016] Preferably, the concentration of silver salt in solution 3 of (4) is 0.1-3 mmol / L. -1 More preferably 0.9 mmol L-1 .
[0017] Preferably, in (4), the stirring time is 1-12 h and the stirring time is 0.25-1 h, more preferably the stirring time is 4 h and the stirring time is 0.5 h.
[0018] Preferably, in (4), the freeze-drying temperature is -50 °C and the freeze-drying time is 6-24 h, more preferably 12 h.
[0019] The second objective of this invention is to provide an Ag / Bi2WO6 catalyst for the electrocatalytic reduction of CO2 to formic acid over a wide pH range, prepared by the method described above.
[0020] The third objective of this invention is to provide an electrocatalytic CO2 reduction electrode, which is prepared from the above-mentioned catalyst, anhydrous ethanol, a 5% solution of perfluorosulfonic acid polymer (Nafion), and hydrophobic carbon paper. The fourth objective of this invention is to provide a method for preparing an electrocatalytic CO2 reduction electrode. The method involves mixing the above-mentioned catalyst, anhydrous ethanol, and 5% Nafion solution, ultrasonically dispersing the mixture, uniformly coating it onto hydrophobic carbon paper, and drying it to obtain the electrocatalytic CO2 reduction electrode.
[0021] Preferably, the catalyst loading is 0.1-10 mg cm⁻¹ -2 More preferably 1 mg cm -2 .
[0022] Preferably, the ultrasound time is 10-60 min, more preferably 20 min.
[0023] Preferably, the mass-to-volume ratio of catalyst, anhydrous ethanol, and 5% Nafion solution is 5-10 mg:10 mL:0.02 mL, more preferably 8 mg:10 mL:0.02 mL.
[0024] The fifth objective of this invention is to provide an application of the above-mentioned electrocatalytic CO2 reduction electrode in the preparation of formic acid.
[0025] The sixth objective of this invention is to provide a method for preparing formic acid by electrocatalytic CO2 reduction. The method involves using a standard electrode system, with the aforementioned electrocatalytic CO2 reduction electrode as the working electrode, iridium oxide as the counter electrode, and a mercury / mercury oxide electrode or a silver / silver chloride electrode as the reference electrode, and using an electrolyte with a pH of 2-14 to carry out the electrocatalytic CO2 reduction reaction to prepare formic acid.
[0026] Preferably, the electrolyte is a potassium hydroxide solution or a potassium sulfate solution.
[0027] More preferably, the electrolyte concentration is 0.5-1.5 mol L. -1 .
[0028] Preferably, the CO2 flow rate is 10-40 sccm.
[0029] The beneficial effects of this invention are as follows: (1) In this invention, Ag / Bi2WO6 catalytic material was synthesized by solvothermal and liquid-phase synthesis methods. The preparation method is simple and efficient. The modification of Ag can increase the electrocatalytic CO2 reduction activity of Bi2WO6 and the selectivity of formic acid.
[0030] (2) This invention uses Bi2WO6 synthesized by a solvothermal method as a substrate, and then uses a liquid-phase synthesis method to modify the surface of Bi2WO6 with high formic acid selectivity with highly conductive Ag. The ratio of bismuth salt to silver salt is adjusted to optimize the ratio of Ag to Bi2WO6 in the catalyst, thereby increasing the specific surface area of Ag / Bi2WO6 and its adsorption capacity for CO2, thus promoting the electrocatalytic reduction of CO2 to formic acid. Compared with pure Bi2WO6, the Ag / Bi2WO6 composite electrocatalytic material provided by this invention can significantly improve the electrocatalytic CO2 reduction activity, formic acid selectivity and formic acid yield in a wide pH range (pH 2-14) of alkaline, neutral and acidic conditions, and broaden the high formic acid selectivity current density window, thereby greatly improving the ability of Ag / Bi2WO6 to electrocatalyze the reduction of CO2 to formic acid in a wide pH range and industrial-grade wide current density window, providing a new approach for the efficient industrial conversion of CO2.
[0031] (3) The Ag / Bi2WO6 catalyst of the present invention, in alkaline, neutral and acidic environments, respectively, introduces FE 甲酸 The maximum values were increased to 96.5%, 96.3%, and 96.6%, which are 1.037, 1.024, and 1.035 times that of Bi2WO6 under the same conditions; the highest local current density of formic acid was increased to -634.6, -801.8, and -907.5 mA cm⁻¹. -2 The efficiency of performic acid production was 1.257, 1.589, and 1.729 times that of Bi2WO6 under the same conditions, respectively; and the efficiency of performic acid production was increased to 9.6, 11.9, and 13.3 mmol / h. -1 cm -2 It is 1.371, 1.859, and 3.022 times that of Bi2WO6 under the same conditions; the high formic acid current window (FE) 甲酸 >90%) widened to -50~-650, -50~-850, -50~-950 mAcm -2 .
[0032] (4) The Ag / Bi2WO6 composite material provided by the present invention is used for electrocatalysis rather than photocatalysis for the reduction of CO2 to formic acid, which broadens the range of catalytic materials for electrocatalytic reduction of CO2 to formic acid. Attached Figure Description
[0033] Figure 1 X-ray diffraction patterns of the catalysts in Examples 1-3 and Comparative Example 1; Figure 2 (a) Nitrogen adsorption-desorption curves of the catalysts in Examples 1-3 and Comparative Example 1. Figure 2 (b) CO2 adsorption curves of Examples 1-3 and Comparative Example 1; Figure 3 (a)- Figure 3 (d) are the Faraday efficiency diagrams of the electrocatalytic CO2 reduction reaction products of Examples 7, Comparative Example 3, Example 10, and Example 13, respectively. Figure 3 (e) is a graph showing the formic acid Faraday efficiency of Examples 7, 10, 13 and Comparative Example 3 under different currents; Figure 4 The graph shows the voltage, local current density of formic acid, and formic acid production efficiency of the electrocatalytic CO2 reduction reaction in an alkaline environment under different current densities for Examples 7, 10, 13, and Comparative Example 3. Figure 5 (a) Figure 5 (b) Faraday efficiency graphs of the electrocatalytic CO2 reduction reaction products of Example 8 and Comparative Example 4, respectively. Figure 5 (c) is a Faraday efficiency graph of the electrocatalytic CO2 reduction reaction of formic acid in Example 8 and Comparative Example 4; Figure 6 The graph shows the voltage, local current density of formic acid, and formic acid production efficiency of the electrocatalytic CO2 reduction reaction in Example 8 and Comparative Example 4 under different current densities in a neutral environment. Figure 7 (a) Figure 7 (b) Faraday efficiency graphs of the electrocatalytic CO2 reduction reaction products of Example 9 and Comparative Example 5, respectively. Figure 7 (c) is a Faraday efficiency graph of the electrocatalytic CO2 reduction reaction of formic acid in Example 9 and Comparative Example 5; Figure 8 The graph shows the voltage, local current density of formic acid, and formic acid production efficiency of the electrocatalytic CO2 reduction reaction in Example 9 and Comparative Example 5 under different current densities in a neutral environment. Detailed Implementation
[0034] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.
[0035] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0036] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.
[0037] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.
[0038] Example 1 The preparation of Ag / Bi2WO6 catalyst is carried out through the following steps: (1) Dissolve 1.3 g (2.68 mmol) bismuth nitrate pentahydrate in 10 mL of ethylene glycol and stir for 30 min to obtain solution 1; (2) Dissolve 0.44 g (1.33 mmol) sodium tungstate dihydrate in 30 mL of isopropanol and stir for 30 min to obtain solution 2; (3) Slowly add solution 2 to solution 1, stir until evenly dispersed, transfer to a reaction vessel, react at 160 °C for 12 h, cool to room temperature, centrifuge the obtained product, wash three times with ultrapure water and anhydrous ethanol alternately, freeze dry at -50 °C for 12 h to obtain Bi2WO6. (4) Add 0.1 g (0.14 mmol) Bi2WO6 and 0.0015 g (0.009 mmol) silver nitrate to 10 mL of ultrapure water, stir for 4 h, then add 0.015 g (0.12 mmol) L-cysteine, stir for 30 min, collect the product by centrifugation, wash three times with ultrapure water and anhydrous ethanol, freeze dry to obtain Ag / Bi2WO6 catalyst, denoted as Ag / Bi2WO6-2.
[0039] Example 2 The difference between this embodiment and Example 1 is that: (4) the amount of silver nitrate is 0.001 g (0.006 mmol), the amount of L-cysteine is 0.01 g, and the rest of the process operation and parameter settings are the same as in Example 1, so that Ag / Bi2WO6 catalyst is obtained, which is denoted as Ag / Bi2WO6-1.
[0040] Example 3 The difference between this embodiment and Example 1 is that: (4) the amount of silver nitrate is 0.002 g (0.012 mmol), the amount of L-cysteine is 0.02 g, and the rest of the process operation and parameter settings are the same as in Example 1, so that Ag / Bi2WO6 catalyst is obtained, which is denoted as Ag / Bi2WO6-3.
[0041] Example 4 The specific steps for preparing the electrocatalytic CO2 reduction electrode are as follows: Eight mg of the Ag / Bi₂WO₆₆₂ catalyst obtained in Example 1 was mixed with 10 mL of ethanol and 0.02 mL of 5% Nafion solution and ultrasonically dispersed. The mixture was then uniformly coated onto hydrophobic carbon paper and dried to obtain an electrocatalytic CO₂ reduction electrode, denoted as the Ag / Bi₂WO₆₆₂ electrode. The catalyst loading was 1 mg·cm⁻¹. -2 .
[0042] Example 5 The difference between this embodiment and Example 4 is that the catalyst used is Ag / Bi2WO6-1 obtained in Example 2, and the remaining process operations and parameter settings are the same as in Example 4, resulting in an Ag / Bi2WO6-1 electrode.
[0043] Example 6 The difference between this embodiment and Example 4 is that the catalyst used is Ag / Bi2WO6-3 obtained in Example 3, and the remaining process operations and parameter settings are the same as in Example 4, resulting in an Ag / Bi2WO6-3 electrode.
[0044] Example 7 The specific steps for preparing formic acid by electrocatalytic CO2 reduction electrode in an alkaline environment (pH=14) are as follows: Using the electrocatalytic CO2 reduction electrode from Example 4 as the working electrode, iridium oxide as the counter electrode, and a mercury / mercury oxide electrode as the reference electrode, the electrocatalytic CO2 reduction reaction was carried out in an electrolytic cell at a concentration of 1 mol / L. -1 Potassium hydroxide solution (pH=14) was used as the electrolyte to test the electrocatalytic CO2 reduction performance in a flow cell electrolyzer. The electrolyte flow rate at both the anode and cathode was 5 mL / min. -1The CO2 flow rate was 30 sccm. In the electrocatalytic CO2 reduction test, different current densities (-50 to -750 mA cm⁻¹) were used. -2 The timing voltage test was performed, and the gas phase reaction products were detected by gas chromatography, while the liquid phase products were detected by nuclear magnetic resonance hydrogen spectroscopy.
[0045] Example 8 Formic acid preparation by electrocatalytic CO2 reduction electrode in neutral environment (pH=7) The difference between this embodiment and Example 7 is that: the reference electrode is a silver / silver chloride electrode, the cathode electrolyte is a 0.5 mol L⁻¹ potassium sulfate solution (pH=7), the anode electrolyte is still a potassium hydroxide solution, and the remaining process operations and parameter settings are the same as in Example 7.
[0046] Example 9 Formic acid preparation by electrocatalytic CO2 reduction electrode in an acidic environment (pH=2) The difference between this embodiment and Embodiment 8 is that the cathode electrolyte is 0.5 mol / L. -1 A potassium sulfate solution, and with 0.01 mol L... -1 The pH of the H2SO4 solution was adjusted to 2, and the anolyte remained a potassium hydroxide solution. The remaining process operations and parameter settings were the same as in Example 8.
[0047] Example 10 The difference between this embodiment and embodiment 7 is that the electrocatalytic CO2 reduction electrode of embodiment 5 is used as the working electrode, while the remaining process operations and parameter settings are the same as those of embodiment 7.
[0048] Example 11 The difference between this embodiment and embodiment 8 is that the electrocatalytic CO2 reduction electrode of embodiment 5 is used as the working electrode, while the remaining process operations and parameter settings are the same as those of embodiment 8.
[0049] Example 12 The difference between this embodiment and embodiment 9 is that the electrocatalytic CO2 reduction electrode of embodiment 5 is used as the working electrode, while the remaining process operations and parameter settings are the same as those of embodiment 9.
[0050] Example 13 The difference between this embodiment and embodiment 7 is that the electrocatalytic CO2 reduction electrode of embodiment 6 is used as the working electrode, while the remaining process operations and parameter settings are the same as those of embodiment 7.
[0051] Example 14 The difference between this embodiment and embodiment 8 is that the electrocatalytic CO2 reduction electrode of embodiment 6 is used as the working electrode, while the remaining process operations and parameter settings are the same as those of embodiment 8.
[0052] Example 15 The difference between this embodiment and embodiment 9 is that the electrocatalytic CO2 reduction electrode of embodiment 6 is used as the working electrode, while the remaining process operations and parameter settings are the same as those of embodiment 9.
[0053] Comparative Example 1 Preparation of Bi2WO6 catalytic materials The difference between this comparative example and Example 1 is that step (4) is excluded; the remaining process operations and parameter settings are the same as in Example 1. Bi2WO6 was obtained as the catalyst material. Comparative Example 2 The difference between this comparative example and Example 4 is that the catalyst used is Bi2WO6 from Comparative Example 1, while the remaining process operations and parameter settings are the same as in Example 4, resulting in a Bi2WO6 electrode.
[0054] Comparative Example 3 The difference between this comparative example and Example 7 is that the working electrode used is the Bi2WO6 electrode from Comparative Example 2, while the remaining process operations and parameter settings are the same as in Example 7.
[0055] Comparative Example 4 The difference between this comparative example and Example 8 is that the working electrode used is the Bi2WO6 electrode from Comparative Example 2, while the remaining process operations and parameter settings are the same as in Example 8.
[0056] Comparative Example 7 The difference between this comparative example and Example 9 is that the working electrode used is the Bi2WO6 electrode from Comparative Example 2, while the remaining process operations and parameter settings are the same as in Example 9.
[0057] Figure 1 X-ray diffraction patterns of the Ag / Bi2WO6-2 catalyst from Example 1, the Ag / Bi2WO6-1 catalyst from Example 2, the Ag / Bi2WO6-3 catalyst from Example 3, and the Bi2WO6 catalyst from Comparative Example 1 are shown. After the addition of Ag, a diffraction peak at 2θ = 35.9°, attributed to the (101) crystal plane of Ag, appeared. However, as the amount of silver added gradually increased, the intensity and width of the diffraction peaks in the catalysts of Examples 1-3 did not change. This indicates that the addition of Ag only modifies the surface of Bi2WO6 and does not change the crystal structure of Bi2WO6.
[0058] Figure 2(a) The nitrogen adsorption-desorption curves of the catalysts in Examples 1-3 and Comparative Example 1 are shown in the figure. The specific surface areas of Bi2WO6, Ag / Bi2WO6-1, Ag / Bi2WO6-2, and Ag / Bi2WO6-3 are 52.56, 43.17, 58.74, and 53.84 m², respectively. 2 g -1 Compared with the other three catalysts (Bi2WO6, Ag / Bi2WO6-1, Ag / Bi2WO6-3), Ag / Bi2WO6-2 has a larger specific surface area, which can expose more active sites in the electrocatalytic CO2 reduction reaction, thereby improving catalytic performance. Figure 2 (b) shows the CO2 adsorption curves of Examples 1-3 and Comparative Example 1. As shown in the figure, the CO2 absorption volume of the four catalysts increases with increasing pressure. Under the same pressure, Ag / Bi2WO6-2 has a better CO2 absorption capacity than the other three catalysts (Bi2WO6, Ag / Bi2WO6-1, Ag / Bi2WO6-3), which promotes CO2 to be more easily adsorbed onto the catalyst, thereby increasing the mass transfer rate on the electrode surface and ultimately promoting the CO2 reduction reaction.
[0059] Figure 3 (a)-(d) are Faraday efficiency graphs of the electrocatalytic CO2 reduction reaction products of Example 7, Comparative Example 3, Example 10 and Example 13. Figure 3 (e) shows the formic acid Faraday efficiency graphs of the catalysts in Examples 1-3 and Comparative Example 1 at different currents. Figure 3 As shown in (a), Ag / Bi2WO6-2 in the range of -50 to -750 mA cm⁻¹ -2 Within the current density range, the main product of electrocatalytic carbon dioxide reduction is formic acid, accompanied by small amounts of H2 and CO. As the applied current increases from -50 mA cm⁻¹, the product... -2 The change was -750 mA cm -2 Formic acid's Faraday efficiency (FE) 甲酸 First increase then decrease, at -250 mA cm -2 It reaches a maximum value of 96.5% and can operate within the range of -50 to -650 mA cm⁻¹. -2 This wider current density window allows FE 甲酸 It has remained stable at over 90%. For example... Figure 3 As shown in (b), the selectivity of Bi₂WO₆ for the electrocatalytic reduction of carbon dioxide to formic acid is lower than that of Ag / Bi₂WO₆₂ at -250 mA cm⁻¹. -2 At that time, FE 甲酸 Reaching a maximum value of 93.1%, FE 甲酸 The current density window, which is greater than 90%, is reduced to -50 to -450 mA cm⁻¹.-2 .like Figure 3 As shown in (c)-(e), introducing different amounts of Ag onto the surface of Bi2WO6 can improve its Fe. 甲酸 At -250mA cm -2 FE of Ag / Bi2WO6-1, Ag / Bi2WO6-2, and Ag / Bi2WO6-3 at current densities 甲酸 The formic acid selectivity rates were 96.1%, 96.5%, and 96.1%, respectively, which are 1.032, 1.036, and 1.032 times that of pure Bi₂WO₆. Among them, Ag / Bi₂WO₆-2 showed the highest formic acid selectivity and high formic acid selectivity (FE). 甲酸 The current window is widest (>90%).
[0060] Figure 4 The graph shows the voltage, local current density of formic acid, and formic acid production efficiency of the electrocatalytic CO2 reduction reaction in an alkaline environment under different current densities for Examples 7, 10, 13, and Comparative Example 3. Figure 4 As shown in (a), due to the modification of the Bi2WO6 surface with highly conductive Ag, the order of electrochemical activity of the four catalysts is Ag / Bi2WO6-2 > Ag / Bi2WO6-1 > Ag / Bi2WO6-3 > Bi2WO6, reaching -650 mA cm⁻¹. -2 At the specified current density, the voltage of Ag / Bi₂WO₆⁻⁂ is -1.02 V, much smaller than that of Ag / Bi₂WO₆⁻⁁ (-1.22 V), Ag / Bi₂WO₆⁻⁃ (-1.15 V), and Bi₂WO₆ (-1.17 V). For example... Figure 4 As shown in (b) and (c), introducing different amounts of Ag onto the surface of Bi₂WO₆ can improve its local formic acid current density and formic acid production efficiency. Among the catalysts in Examples 1-3 and Comparative Example 1, the Ag / Bi₂WO₆-2 exhibits the most significant enhancing effect. At -650 mA cm⁻¹ -2 At the total current density, the local current density of Ag / Bi₂WO₆₻ formic acid reaches a maximum of -634.6 mA cm⁻¹. -2 It is 1.257 times that of Bi2WO6 (-504.8 mA cm⁻¹). -2 ). At 550mA cm -2 At the given total current density, the formic acid production efficiency reaches its maximum of 9.6 mmol / h. -1 cm -2 It is 1.371 times that of Bi2WO6 (7 mmol h) -1 cm -2 ).
[0061] Figure 5(a) is a Faraday efficiency diagram of the electrocatalytic CO2 reduction reaction products in Example 8. Figure 5 (b) is a Faraday efficiency graph of the electrocatalytic CO2 reduction reaction products in Comparative Example 4. Figure 5 (c) is a Faraday efficiency graph for the electrocatalytic CO2 reduction reaction of formic acid in Example 8 and Comparative Example 4. Figure 5 As shown in (a), in the range of -50 to -950 mA cm -2 Within the specified current density range, the electrocatalytic carbon dioxide reduction product of Ag / Bi₂WO₆₂ is mainly formic acid, accompanied by a small amount of byproducts. With increasing current density, the FE of formic acid first increases and then decreases, reaching a minimum at -250 mA cm⁻¹. -2 It reaches a maximum value of 96.3% and can operate within the range of -50 to -850 mA cm⁻¹ -2 This wider current density window allows FE 甲酸 It has remained stable at over 90%. For example... Figure 5 As shown in (b), the main product of Bi₂WO₆ electrocatalytic carbon dioxide reduction is formic acid, but a large number of byproducts are generated at high current densities. The FE of formic acid first increases and then decreases with increasing current density, reaching a certain value at -250 mA cm⁻¹. -2 It reaches a maximum value of 94.0% at that time, with high formic acid selectivity (FE). 甲酸 (>90%) Current window is -50 to -650 mA cm⁻¹ -2 .like Figure 5 As shown in (c), compared to pure Bi2WO6, Ag / Bi2WO6-2 exhibits a higher formic acid FE (1.024 times that of Bi2WO6) and a wider formic acid selectivity (FE) in the catalytic carbon dioxide reduction process. 甲酸 >90% current window (Ag / Bi2WO6-2: -50~-850 mA cm⁻¹) -2 Bi2WO6: -50~-650 mA cm -2 ).
[0062] Figure 6 The graph shows the voltage, local current density of formic acid, and formic acid production efficiency of the electrocatalytic CO2 reduction reaction in Example 8 and Comparative Example 4 under different current densities in a neutral environment. Figure 6 As shown in (a), the electrochemical activity of the Ag / Bi2WO6-2 catalyst is much greater than that of the Bi2WO6 catalyst due to the modification of the Bi2WO6 surface with highly conductive Ag. It reaches -750 mA cm⁻¹. -2 At the specified current density, the voltage across Ag / Bi₂WO₆⁻ is -1.9 V, much lower than that of Bi₂WO₆ (-2.4 V). For example... Figure 6As shown in (b) and (c), introducing Ag onto the Bi2WO6 surface can improve its local formic acid current density and formic acid production efficiency at -950 mA cm⁻¹. -2 At the total current density, the local current density of Ag / Bi₂WO₆₻ formic acid reaches a maximum of -801.8 mA cm⁻¹. -2 It is 1.589 times that of Bi2WO6 (-504.5 mA cm⁻¹) -2 ). At -850 mA cm -2 At the given total current density, the formic acid production efficiency reaches a maximum of 11.9 mmol / h. -1 cm -2 It is 1.859 times that of Bi2WO6 (6.4 mmol h) -1 cm -2 ).
[0063] Figure 7 (a) is a Faraday efficiency diagram of the electrocatalytic CO2 reduction reaction products in Example 9. Figure 7 (b) is a Faraday efficiency graph of the electrocatalytic CO2 reduction reaction products in Comparative Example 5. Figure 7 (c) is a Faraday efficiency graph for the electrocatalytic CO2 reduction reaction of formic acid in Example 9 and Comparative Example 5. Figure 7 As shown in (a), in the range of -50 to -1050 mA cm -2 Within the specified current density range, the electrocatalytic carbon dioxide reduction product of Ag / Bi₂WO₆₂ is mainly formic acid, accompanied by a small amount of byproducts. With increasing current density, the FE of formic acid first increases and then decreases, reaching a minimum at -350 mA cm⁻¹. -2 It reaches a maximum value of 96.6% and can operate within the range of -50 to -950 mA cm⁻¹ -2 This wider current density window allows FE 甲酸 It has remained stable at over 90%. For example... Figure 7 As shown in (b), the main product of Bi₂WO₆ electrocatalytic carbon dioxide reduction is formic acid, but a large number of byproducts are generated at high current densities. The FE of formic acid first increases and then decreases with increasing current density, reaching a certain value at -350 mA cm⁻¹. -2 The efficiency reached 93.3%, with high formic acid selectivity (FE). 甲酸 >90%) Current window is -50~-650mA cm -2 .like Figure 7 (c) shows that Ag / Bi2WO6-2 has a higher FE value in the catalytic carbon dioxide reduction process compared to pure Bi2WO6. 甲酸 (1.053 times that of Bi2WO6), and a wider selectivity for performic acid (FE) 甲酸>90% current window (Ag / Bi2WO6-2: -50~-950 mA cm⁻¹) -2 Bi2WO6: -50~-650 mA cm -2 ).
[0064] Figure 8 The graph shows the voltage, local current density of formic acid, and formic acid production efficiency of the electrocatalytic CO2 reduction reaction in Example 9 and Comparative Example 5 under different current densities in a neutral environment. Figure 8 As shown in (a), the electrochemical activity of the Ag / Bi₂WO₆₂ catalyst is significantly greater than that of the Bi₂WO₆ catalyst. At -850 mA cm⁻¹, the electrochemical activity reaches a certain level. -2 At the specified current density, the voltage across Ag / Bi₂WO₆⁻ is -3.1V, much lower than that of Ag / Bi₂WO₆ (-3.4V). For example... Figure 8 As shown in (b) and (c), introducing Ag onto the Bi2WO6 surface can improve its local formic acid current density and formic acid production efficiency at -1050 mA cm⁻¹. -2 At the total current density, the local current density and formic acid production efficiency of Ag / Bi₂WO₆₂ formic acid reached their maximum values of -907.5 mA cm⁻¹. -2 13.3 mmol h -1 cm -2 It is 1.729 times that of Bi2WO6 (-524.8 mA cm⁻¹). -2 ) and 3.022 times (4.4 mmol h -1 cm -2 ).
[0065] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing an Ag / Bi₂WO₆ catalyst for the electrocatalytic reduction of CO₂ to formic acid over a wide pH range, characterized in that, The preparation method includes the following steps: (1) Dissolve the bismuth salt in ethylene glycol and stir to obtain solution 1; (2) Dissolve tungstate in isopropanol and stir to obtain solution 2; (3) Add solution 2 to solution 1 and heat in a hydrothermal reactor to react and obtain Bi2WO6; (4) Add Bi2WO6 and silver salt to water, stir and then add reducing agent to obtain solution 3. Continue stirring to carry out the reaction. Centrifuge, wash and freeze dry the obtained product to obtain Ag / Bi2WO6 catalyst.
2. The preparation method according to claim 1, characterized in that, (1) The bismuth salt in solution 1 is bismuth nitrate pentahydrate, bismuth acetate, bismuth chloride, or bismuth sulfate, and the concentration of the bismuth salt in solution 1 is 0.1-0.5 mol / L. -1 .
3. The preparation method according to claim 1, characterized in that, (2) The tungstate in solution 2 is sodium tungstate dihydrate, ammonium metatungstate, ammonium paratungstate, or ammonium tungstate, and the concentration of tungstate in solution 2 is 0.01-0.1 mol / L. -1 .
4. The preparation method according to claim 1, characterized in that, The volume ratio of isopropanol in (2) to ethylene glycol in (1) is (1-4):
1. The reaction temperature in (3) is 80-180 ℃ and the reaction time is 10-24 h.
5. The preparation method according to claim 1, characterized in that, (4) The reducing agent is L-cysteine, ascorbic acid, or β-mercaptoethylamine, and the silver salt is silver nitrate or silver acetate; the concentration of Bi2WO6 in solution 3 is 0.01-0.05 mol L. -1 The silver salt concentration is 0.1-3 mmol / L. -1 The reducing agent concentration is 0.01-0.05 mol / L. -1 (4) The stirring time is 1-12 h, the stirring time is 0.25-1 h, the freeze-drying temperature is -50 ℃, and the freeze-drying time is 6-24 h.
6. An Ag / Bi2WO6 catalyst prepared by the method of any one of claims 1-5 for the electrocatalytic reduction of CO2 to formic acid over a wide pH range.
7. An electrocatalytic CO2 reduction electrode, characterized in that, The reduction electrode is prepared from the Ag / Bi2WO6 catalyst as described in claim 6, anhydrous ethanol, 5% perfluorosulfonic acid polymer solution, and hydrophobic carbon paper.
8. A method for preparing the electrocatalytic CO2 reduction electrode according to claim 7, characterized in that, The Ag / Bi2WO6 catalyst described in claim 6, anhydrous ethanol, and 5% perfluorosulfonic acid polymer solution were mixed and ultrasonically dispersed, then uniformly coated onto hydrophobic carbon paper and dried to obtain an electrocatalytic CO2 reduction electrode.
9. The preparation method according to claim 8, characterized in that, The loading of the Ag / Bi2WO6 catalyst was 0.1-1 mg cm -2 The ultrasonic time is 10-60 min, and the mass-to-volume ratio of catalyst, anhydrous ethanol, and 5% perfluorosulfonic acid polymer solution is 5-10 mg: 10 mL: 0.02 mL.
10. A method for preparing formic acid by electrocatalytic reduction of CO2, characterized in that, The method is as follows: using the electrocatalytic CO2 reduction electrode described in claim 7 as the working electrode, iridium oxide as the counter electrode, and mercury / mercury oxide electrode or silver / silver chloride electrode as the reference electrode, an electrolyte with a pH of 2-14 is used to carry out the electrocatalytic CO2 reduction reaction to prepare formic acid.