A surface fluorine-modified bismuth vanadate photoelectrode, a preparation method and application thereof

Abstract

The application provides a surface fluorine-modified bismuth vanadate photoelectrode and a preparation method and application thereof. Fluorine atoms are attached to the surface of the bismuth vanadate, and part of the fluorine atoms replace the two-coordinated oxygen atoms on the surface of the bismuth vanadate, namely the surface fluorine-modified bismuth vanadate photoelectrode. The surface fluorine-modified bismuth vanadate photoelectrode greatly improves the oxidation rate and molecular reaction efficiency of hydroxyl radicals generated by photoelectrolysis of water, effectively improves the glycerol oxidation efficiency, the selectivity of the product formic acid, and reduces the energy consumption of the reaction.

Description

Technical Field

[0001] This invention relates to the field of photoelectrocatalytic biomass conversion technology, and in particular to a surface-fluorinated bismuth vanadate photoelectrode, its preparation method, and its application. Background Technology

[0002] Glycerol is a widely available and inexpensive biomass feedstock. Through catalytic oxidation, it can be converted into various high-value-added chemicals, such as glyceraldehyde, glyceric acid, dihydroxyacetone, glycolic acid, and formic acid. Among these, the catalytic oxidation of glycerol to formic acid involves the activation of multiple chemical bonds, including CO, CH, OH, and CC. This oxidation process is highly challenging and has therefore attracted considerable attention.

[0003] Currently, the main method for the catalytic conversion of glycerol to formic acid is electrochemical oxidation. The principle involves the electrochemical oxidation of glycerol at the anode, with the oxidation products and product selectivity controlled by adjusting the electrode potential, electrolyte solution, glycerol concentration, and the structure and composition of the catalyst. Theoretically, the complete oxidation of a glycerol molecule to formic acid requires a theoretical oxidation potential of 0.69 V (relative to the standard hydrogen electrode, SHE). In reality, when glycerol is electrooxidized to formate in an alkaline environment, the oxidation potential is generally not less than 1.30 V (relative to the reversible hydrogen electrode, RHE). Therefore, this method of selectively oxidizing glycerol to formic acid is energy-intensive.

[0004] Another issue is that the selective oxidation of glycerol to formic acid involves a complex multi-step reaction pathway, including dehydrogenation, adsorption / desorption of reaction intermediates, and C / C bond cleavage. The correlation between the catalytic active site and reaction kinetics remains unclear. Simultaneously carrying out glycerol dehydrogenation and C / C bond cleavage in a single-active-site catalytic system is challenging. Furthermore, from an energy perspective, density functional analysis [J. Phys. Chem. C 2011, 115, 19702–19709] indicates that C / C bonds only break after glycerol dehydrogenation. For example, the C / C bonds in dihydroxypropane (DHA) are significantly smaller than those in alkanes (83-90 kcal / mol). α The bond is relatively weak (acetone has a concentration of 80 kcal / mol) [Nat. Commun., 2021, 12, 6840]. Meanwhile, the second most potent oxidizing agent is the hydroxyl radical (·OH)(E... 0(·OH / H₂O) = 2.80V vs. SHE) is usually generated by Fenton chemistry and has been proven to be a powerful tool for the oxidation and cleavage of organic compounds [Chem. Soc. Rev. 2019, 48, 2615–2656]. However, the amount of hydroxyl radicals introduced is difficult to control, which can easily lead to over-oxidation of the product. Insufficient cleavage of glycerol and over-oxidation are key factors that hinder the high-selectivity oxidation of glycerol to formic acid, resulting in low reaction efficiency and poor selectivity. Summary of the Invention

[0005] The purpose of this invention is to provide a surface-fluorinated bismuth vanadate photoelectrode, its preparation method, and its application, in order to solve the problems of high energy consumption, low reaction efficiency, and poor reaction selectivity in the existing method of selective oxidation of glycerol to formic acid.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0007] A surface-fluorinated bismuth vanadate photoelectrode is provided, wherein fluorine atoms are attached to the surface of bismuth vanadate, and some fluorine atoms replace the di-coordinated oxygen atoms on the surface of bismuth vanadate.

[0008] Preferably, fluorine atoms form F-Bi-O bonds with the Bi end positions on the surface of bismuth vanadate, allowing fluorine atoms to adhere to the surface of bismuth vanadate; some fluorine atoms replace the two-coordinated oxygen atoms on the surface of bismuth vanadate, forming an F-Bi-F double hydrogen bond structure, which is the surface fluorine-modified bismuth vanadate photoelectrode.

[0009] The surface structure of bismuth vanadate BiVO4 is shown in formula (Ⅰ):

[0010]

[0011] The structure of the F-Bi-O bond formed by fluorine atoms and the Bi terminal sites on the surface of bismuth vanadate BiVO4 is shown in formula (II):

[0012]

[0013] Some fluorine atoms replace the di-coordinated oxygen atoms on the surface of bismuth vanadate, forming an F-Bi-F double hydrogen bond structure as shown in formula (Ⅲ):

[0014]

[0015] Optionally, the mass fraction of the fluorine atoms is 0.2-2.2 wt%.

[0016] Preferably, the mass fraction of the fluorine atoms is 0.6 wt%.

[0017] Preferably, the surface fluorine modification occurs on the (112) crystal plane of the bismuth vanadate photoelectrode.

[0018] The present invention also provides a method for preparing the surface fluorine-modified bismuth vanadate photoelectrode, wherein bismuth vanadate is impregnated in an impregnation solution containing sodium fluoride.

[0019] Optionally, the pH value of the sodium fluoride impregnation solution is 5.74-7.04; preferably, the pH value of the sodium fluoride impregnation solution is 6.01.

[0020] Optionally, the soaking time is 1-3 hours; preferably, the soaking time is 2 hours.

[0021] Optionally, the impregnation temperature is 20-50°C. Preferably, the impregnation temperature is 20°C.

[0022] Preferably, the bismuth vanadate is BiVO4 grown or coated on one side of the conductive glass.

[0023] Preferably, the conductive glass is FTO conductive glass or ITO conductive glass.

[0024] This invention also provides an application of a surface-fluorinated bismuth vanadate photoelectrode in the field of photoelectric water splitting coupled with biomass oxidation reaction.

[0025] Preferably, the biomass is glycerol.

[0026] Preferably, the photoelectric water splitting coupled biomass oxidation reaction uses the surface-fluorinated bismuth vanadate photoelectrode as the anode.

[0027] Preferably, the photoelectric water splitting coupled biomass oxidation reaction uses the surface-fluorine-modified bismuth vanadate photoelectrode as the anode, Pt wire as the cathode, and Ag / AgCl as the reference electrode to form a three-electrode system.

[0028] Preferably, the photoelectric water splitting coupled biomass oxidation reaction uses sodium sulfate solution as the electrolyte.

[0029] Preferably, the reaction solution for the photoelectric water splitting coupled biomass oxidation reaction is a mixture of electrolyte and glycerol. Under nitrogen protection, the reaction is carried out under light irradiation at a bias voltage of 0.2-1.6V versus RHE for 1-4 hours, so that glycerol is selectively oxidized to formic acid on the anode.

[0030] Preferably, the anode and cathode reaction chambers of the photoelectric water splitting coupled biomass oxidation reaction are isolated by a proton exchange membrane.

[0031] Preferably, the amount of hydrogen produced is measured by the water displacement method at the cathode.

[0032] Preferably, in the photoreaction, the light direction is to irradiate the non-conductive surface of the anode, and the light intensity is 100 mW / cm². 2 .

[0033] The above-described solution of the present invention has at least the following beneficial effects:

[0034] (1) The surface-fluorinated bismuth vanadate photoelectrode of the present invention has fluorine atoms attached to the surface of bismuth vanadate, and some fluorine atoms replace the di-coordinated oxygen atoms on the surface of bismuth vanadate, thus forming a surface-fluorinated bismuth vanadate photoelectrode. The surface-fluorinated bismuth vanadate photoelectrode of the present invention utilizes sodium fluoride modification on the surface of the bismuth vanadate photoelectrode, and the surface fluorine modification causes the valence electrons of bismuth, vanadium, and oxygen in bismuth vanadate to transfer to fluorine. On the one hand, bismuth vanadate forms an O-Bi-F structure, which is beneficial for the adsorption of glycerol's CC bonds. On the other hand, the formed F-Bi-F double hydrogen bond structure can enhance the adsorption of H2O and also promote the transfer of charge carriers on the electrode surface. This leads to the oxidation of water to generate hydroxyl radicals as needed, thereby activating the glycerol CC bonds, catalyzing the breaking of the glycerol CC bonds, and oxidizing them to formic acid. This greatly improves the oxidation rate and molecular reaction efficiency of hydroxyl radicals generated by photoelectrolysis of water, effectively improving the oxidation efficiency of glycerol and the selectivity of the product formic acid. It does not require an alkaline environment to activate glycerol and promote the oxidation process, nor does it require an external oxidant. The conversion can be achieved at a bias voltage of 0.2-1.6V versus RHE. Especially when the conversion is carried out below 1.3V, the power consumption can be greatly reduced, and the rate of hydrogen generation at the cathode can reach 186.3 mmol / h.

[0035] (2) In the fluorine-modified bismuth vanadate photoelectrode of the present invention, the mass fraction of fluorine atoms is 0.2-2.2 wt%. When the mass fraction of fluorine is less than 0.6 wt%, fluorine is distributed at the bismuth end sites on the bismuth vanadate surface, forming O-Bi-F bonds. When the mass fraction of fluorine is equal to 0.6 wt%, in addition to the bismuth end sites, fluorine replaces some of the dicoordinated oxygen on the bismuth vanadate surface, forming F-Bi-F double hydrogen bonds and O-Bi-F bonds. This special structure alters the reaction pathway of bismuth vanadate, changing the product from dihydroxyacetone to formic acid. When the mass fraction of fluorine is greater than 0.6 wt%, it causes the bismuth vanadate surface structure to collapse, which is detrimental to the catalytic oxidation reaction of glycerol. Through precise atomic-level control of the bismuth vanadate photoelectrode surface, the O-Bi-F and F-Bi-F sites play a controlling role in the breaking and formation of the CH / CO / OH / CC bonds of glycerol.

[0036] (3) The surface-fluorinated bismuth vanadate photoelectrode of the present invention is used for the photoelectrochemical water splitting coupled with glycerol oxidation to produce formic acid. It has the advantages of simple operation, mildness and environmental friendliness, and provides a new way to produce formic acid with high selectivity by breaking the C-C bond of glycerol. Under acidic reaction conditions, glycerol can be directly oxidized to formic acid with high selectivity, avoiding the alkaline environment required for electrocatalysis to activate glycerol, thereby saving the post-treatment cost of product acidification. Attached Figure Description

[0037] Figure 1 This is a differential charge density diagram of the surface-fluorinated bismuth vanadate photoelectrode prepared in Example 1;

[0038] Figure 2 This is a graph showing the relationship between the absorption signal intensity and the magnetic field intensity of the surface fluorine-modified bismuth vanadate photoelectrode prepared in Example 1.

[0039] Figure 3 This is a graph showing the relationship between product selectivity and reaction time for the surface-fluorinated bismuth vanadate photoelectrode prepared in Example 1 used in the photoelectric water splitting coupled glycerol oxidation reaction. Detailed Implementation

[0040] Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0041] Example 1

[0042] In this embodiment, the surface-fluorinated bismuth vanadate photoelectrode forms F-Bi-O bonds with the Bi end positions on the bismuth vanadate surface, allowing fluorine atoms to adhere to the bismuth vanadate surface. Some fluorine atoms replace the di-coordinated oxygen atoms on the bismuth vanadate surface, forming an F-Bi-F double hydrogen bond structure, thus constituting the surface-fluorinated bismuth vanadate photoelectrode. The mass fraction of the fluorine atoms is 0.6 wt%. Surface fluorine modification occurs on the (112) crystal plane of the bismuth vanadate photoelectrode.

[0043] It should be noted that the surface structure of bismuth vanadate BiVO4 is shown in formula (Ⅰ):

[0044]

[0045] The structure of the F-Bi-O bond formed by fluorine atoms and the Bi terminal sites on the surface of bismuth vanadate BiVO4 is shown in formula (II):

[0046]

[0047] Some fluorine atoms replace the di-coordinated oxygen atoms on the surface of bismuth vanadate, forming an F-Bi-F double hydrogen bond structure as shown in formula (Ⅲ):

[0048]

[0049] The surface-fluorinated bismuth vanadate photoelectrode described in this embodiment is prepared by an impregnation method, in which bismuth vanadate is impregnated in an impregnation solution containing sodium fluoride.

[0050] The preparation method of the surface-fluorinated bismuth vanadate photoelectrode specifically includes the following steps:

[0051] A 0.1 mol / L NaF solution was used as the impregnation solution. FTO or ITO conductive glass with BiVO4 grown on it was completely immersed in the impregnation solution and impregnated at 20°C for 2 hours to obtain a surface-fluorinated bismuth vanadate photoelectrode.

[0052] The impregnation solution can be prepared as follows: Take 0.21g of NaF, add 50mL of deionized water, and sonicate and stir until a homogeneous solution is formed. The sonication power is 50W, the time is 15min, and the temperature is 20℃. The pH value of the impregnation solution is 6.01.

[0053] The FTO conductive glass with BiVO4 grown on it can be immersed in the impregnation solution with the side containing BiVO4 tilted upwards at a 45° angle. After impregnation, the surface-fluorine-modified bismuth vanadate photoelectrode is removed, rinsed with deionized water, and dried at 60°C for 1 hour. Ion chromatography determined that the mass fraction of fluorine atoms on the bismuth vanadate surface was 0.6 wt%.

[0054] The FTO conductive glass with BiVO4 grown thereon can be prepared by the following method:

[0055] (1) Take 0.971g of Bi(NO3)3·5H2O and 3.321g of KI, mix and dissolve in 50mL of deionized water, then add 68wt% nitric acid dropwise to adjust the pH value to 1.7 to obtain solution A;

[0056] (2) Dissolve 0.497 g of p-benzoquinone in 20 mL of anhydrous ethanol and stir until homogeneous to obtain solution B;

[0057] (3) Mix solution A from step (1) and solution B from step (2) thoroughly to obtain an electrodeposition solution;

[0058] (4) Electrodeposition was performed on the electrodeposition solution obtained in step (3) in a three-electrode system, with FTO conductive glass as the working electrode, saturated Ag / AgCl as the reference electrode, and platinum wire as the counter electrode; electrodeposition was performed at a bias voltage of -0.1V versus Ag / AgCl for 200s to obtain a red sheet-like BiOI film; then, the obtained BiOI film was rinsed with deionized water to remove the residual solution on the surface and dried at 60°C.

[0059] (5) Dissolve 0.139g of VO(acac)2 in 2mL of dimethyl sulfoxide, mix well, and then drop 0.2mL of the mixture onto the surface of the BiOI film in step (4) to distribute it evenly. Place it in a tube furnace and heat treat it for 2h under air conditions at 450℃, and control the heating rate to be 2℃ per minute to obtain the heat-treated film.

[0060] (6) Take out the heat-treated film from step (5), place it in a 1 mol / L NaOH solution, wash away excess V2O5 on the surface with stirring, rinse with deionized water and dry with nitrogen to obtain FTO conductive glass with BiVO4 grown on it.

[0061] like Figure 1 The figure shows the differential charge density diagram of the prepared surface-fluorinated bismuth vanadate photoelectrode.

[0062] The surface-fluorinated bismuth vanadate photoelectrode described in this embodiment can be applied to a photoelectrochemical water splitting coupled biomass oxidation reaction. The biomass can be glycerol. The photoelectrochemical water splitting coupled biomass oxidation reaction uses the surface-fluorinated bismuth vanadate photoelectrode as the anode, a Pt wire as the cathode, and Ag / AgCl as the reference electrode, forming a three-electrode system, with sodium sulfate solution as the electrolyte. The anode and cathode reaction chambers of the photoelectrochemical water splitting coupled biomass oxidation reaction are isolated by a proton exchange membrane, which can be a naphthol 117 proton exchange membrane. This proton exchange membrane isolates the cathode from other electrodes.

[0063] In this embodiment, the sodium sulfate solution has a pH of 2 and a concentration of 0.5 mol / L. 1 mmol of glycerol is added to 10 ml of the sodium sulfate solution, and the mixture is magnetically stirred at 300 rpm for 20 min to obtain a mixture.

[0064] The reaction conditions for the photoelectric water splitting coupled biomass oxidation reaction are as follows: A mixture of electrolyte and glycerol is subjected to nitrogen protection using an electrochemical workstation (CHI 660E) with voltage applied and current-time (it) mode applied at a bias voltage of 1.2V versus RHE for 4 hours (RHE represents a reversible hydrogen electrode), allowing glycerol to be selectively oxidized to formic acid at the anode. The amount of hydrogen produced at the cathode is measured using the water displacement method. During the photoluminescence reaction, a xenon lamp light source equipped with an AM1.5G filter (simulating sunlight) can be used to irradiate the anode, with the light direction pointing towards the non-conductive surface of the anode, and the light intensity at 100 mW / cm². 2 .

[0065] Example 2

[0066] In this embodiment, the surface-fluorinated bismuth vanadate photoelectrode forms F-Bi-O bonds with the Bi end positions on the bismuth vanadate surface, allowing fluorine atoms to adhere to the bismuth vanadate surface. Some fluorine atoms replace the di-coordinated oxygen atoms on the bismuth vanadate surface, forming an F-Bi-F double hydrogen bond structure, thus constituting the surface-fluorinated bismuth vanadate photoelectrode. The mass fraction of the fluorine atoms is 0.2 wt%. Surface fluorine modification occurs on the (112) crystal plane of the bismuth vanadate photoelectrode.

[0067] The surface-fluorinated bismuth vanadate photoelectrode described in this embodiment is prepared by an impregnation method, in which bismuth vanadate is impregnated in an impregnation solution containing sodium fluoride.

[0068] The preparation method of the surface-fluorinated bismuth vanadate photoelectrode specifically includes the following steps:

[0069] A 0.01 mol / L NaF solution was used as the impregnation solution. The ITO conductive glass with BiVO4 grown on it was completely immersed in the impregnation solution and impregnated at 50°C for 1 hour to obtain a surface-fluorinated bismuth vanadate photoelectrode.

[0070] The impregnation solution can be prepared as follows: Weigh 0.021g of NaF into a 100mL beaker, add 50mL of deionized water, and sonicate and stir until a homogeneous solution is formed. The sonication power is 50W, the time is 15min, and the temperature is 20℃. The pH value of the impregnation solution is 5.74.

[0071] The ITO conductive glass with BiVO4 grown on it can be immersed in the impregnation solution with the side containing BiVO4 tilted upwards at a 45° angle. After impregnation, the surface-fluorine-modified bismuth vanadate photoelectrode is removed, rinsed with deionized water, and dried at 60°C for 1 hour. Ion chromatography determined that the mass fraction of fluorine atoms on the bismuth vanadate surface was 0.2 wt%.

[0072] The surface-fluorinated bismuth vanadate photoelectrode described in this embodiment can be applied to a photoelectrochemical water splitting coupled biomass oxidation reaction. The biomass can be glycerol. The photoelectrochemical water splitting coupled biomass oxidation reaction uses the surface-fluorinated bismuth vanadate photoelectrode as the anode, a Pt wire as the cathode, and Ag / AgCl as the reference electrode, forming a three-electrode system, with sodium sulfate solution as the electrolyte. The anode and cathode reaction chambers of the photoelectrochemical water splitting coupled biomass oxidation reaction are isolated by a proton exchange membrane, which can be a naphthol 117 proton exchange membrane. This proton exchange membrane isolates the cathode from other electrodes.

[0073] In this embodiment, the sodium sulfate solution has a pH of 2 and a concentration of 0.5 mol / L. 1 mmol of glycerol is added to 10 ml of the sodium sulfate solution, and the mixture is magnetically stirred at 300 rpm for 20 min to obtain a mixture.

[0074] The reaction conditions for the photoelectric water splitting coupled biomass oxidation reaction are as follows: A mixture of electrolyte and glycerol is subjected to nitrogen protection using an electrochemical workstation (CHI 660E) with voltage applied and current-time (it) mode applied at a bias voltage of 0.2V versus RHE for 4 hours (RHE represents a reversible hydrogen electrode), allowing glycerol to be selectively oxidized to formic acid at the anode. The amount of hydrogen produced at the cathode is measured using the water displacement method. During the photoluminescence reaction, a xenon lamp light source (simulating sunlight) equipped with an AM1.5G filter is used to irradiate the anode, with the light direction pointing towards the non-conductive surface of the anode, and the light intensity at 100 mW / cm². 2 .

[0075] Example 3

[0076] In this embodiment, the surface-fluorinated bismuth vanadate photoelectrode forms F-Bi-O bonds with the Bi end positions on the bismuth vanadate surface, allowing fluorine atoms to adhere to the bismuth vanadate surface. Some fluorine atoms replace the di-coordinated oxygen atoms on the bismuth vanadate surface, forming an F-Bi-F double hydrogen bond structure, thus constituting the surface-fluorinated bismuth vanadate photoelectrode. The mass fraction of the fluorine atoms is 2.2 wt%. Surface fluorine modification occurs on the (112) crystal plane of the bismuth vanadate photoelectrode.

[0077] The surface-fluorinated bismuth vanadate photoelectrode described in this embodiment is prepared by an impregnation method, in which bismuth vanadate is impregnated in an impregnation solution containing sodium fluoride. Specifically, the method includes the following steps:

[0078] A 0.5 mol / L NaF solution was used as the impregnation solution. The FTO conductive glass with BiVO4 grown on it was completely immersed in the impregnation solution and impregnated at 20°C for 3 hours to obtain a surface-fluorinated bismuth vanadate photoelectrode.

[0079] The impregnation solution can be prepared as follows: Weigh 1.05g of NaF into a 100mL beaker, add 50mL of deionized water, and sonicate and stir until a homogeneous solution is formed. The sonication power is 50W, the time is 15min, and the temperature is 20℃. The pH value of the impregnation solution is 7.04.

[0080] The FTO conductive glass with BiVO4 grown on it can be immersed in the impregnation solution with the side containing BiVO4 tilted upwards at a 45° angle. After impregnation, the surface-fluorinated bismuth vanadate photoelectrode is removed, rinsed with deionized water, and dried at 60°C for 1 hour. Ion chromatography determined that the mass fraction of fluorine atoms on the bismuth vanadate surface was 2.2 wt%.

[0081] The surface-fluorinated bismuth vanadate photoelectrode described in this embodiment can be applied to a photoelectrochemical water splitting coupled biomass oxidation reaction. The biomass can be glycerol. The photoelectrochemical water splitting coupled biomass oxidation reaction uses the surface-fluorinated bismuth vanadate photoelectrode as the anode, a Pt wire as the cathode, and Ag / AgCl as the reference electrode, forming a three-electrode system, with sodium sulfate solution as the electrolyte. The anode and cathode reaction chambers of the photoelectrochemical water splitting coupled biomass oxidation reaction are isolated by a proton exchange membrane, which can be a naphthol 117 proton exchange membrane. This proton exchange membrane isolates the cathode from other electrodes.

[0082] In this embodiment, the sodium sulfate solution has a pH of 2 and a concentration of 0.5 mol / L. 1 mmol of glycerol is added to 10 ml of the sodium sulfate solution, and the mixture is magnetically stirred at 300 rpm for 20 min to obtain a mixture.

[0083] The reaction conditions for the photoelectric water splitting coupled biomass oxidation reaction are as follows: A mixture of electrolyte and glycerol is subjected to nitrogen protection using an electrochemical workstation (CHI 660E) with voltage applied and current-time (it) mode applied at a bias voltage of 1.6V versus RHE for 4 hours (RHE represents a reversible hydrogen electrode), allowing glycerol to be selectively oxidized to formic acid at the anode. The amount of hydrogen produced at the cathode is measured using the water displacement method. During the photoluminescence reaction, a xenon lamp light source equipped with an AM1.5G filter (simulating sunlight) can be used to irradiate the anode, with the light direction pointing towards the non-conductive surface of the anode, and the light intensity at 100 mW / cm². 2 .

[0084] Example 4

[0085] In this embodiment, the surface-fluorinated bismuth vanadate photoelectrode forms F-Bi-O bonds with the Bi end positions on the bismuth vanadate surface, allowing fluorine atoms to adhere to the bismuth vanadate surface. Some fluorine atoms replace the di-coordinated oxygen atoms on the bismuth vanadate surface, forming an F-Bi-F double hydrogen bond structure, thus constituting the surface-fluorinated bismuth vanadate photoelectrode. The mass fraction of the fluorine atoms is 1.2 wt%. Surface fluorine modification occurs on the (112) crystal plane of the bismuth vanadate photoelectrode.

[0086] The surface-fluorinated bismuth vanadate photoelectrode described in this embodiment is prepared by an impregnation method, in which bismuth vanadate is impregnated in an impregnation solution containing sodium fluoride. Specifically, the method includes the following steps:

[0087] A 0.1 mol / L NaF solution was used as the impregnation solution. The FTO conductive glass with BiVO4 grown on it was completely immersed in the impregnation solution and impregnated at 35°C for 2 hours to obtain a surface-fluorinated bismuth vanadate photoelectrode.

[0088] The impregnation solution can be prepared as follows: Weigh 0.21g of NaF into a 100mL beaker, add 50mL of deionized water, and sonicate and stir until a homogeneous solution is formed. The sonication power is 50W, the time is 15min, and the temperature is 20℃. The pH value of the impregnation solution is 6.01.

[0089] The FTO conductive glass with BiVO4 grown on it can be immersed in the impregnation solution with the side containing BiVO4 tilted upwards at a 45° angle. After impregnation, the surface-fluorinated bismuth vanadate photoelectrode is removed, rinsed with deionized water, and dried at 60°C for 1 hour. Ion chromatography determined that the mass fraction of fluorine atoms on the bismuth vanadate surface was 1.2 wt%.

[0090] The surface-fluorinated bismuth vanadate photoelectrode described in this embodiment can be applied to a photoelectrochemical water splitting coupled biomass oxidation reaction. The biomass can be glycerol. The photoelectrochemical water splitting coupled biomass oxidation reaction uses the surface-fluorinated bismuth vanadate photoelectrode as the anode, a Pt wire as the cathode, and Ag / AgCl as the reference electrode, forming a three-electrode system, with sodium sulfate solution as the electrolyte. The anode and cathode reaction chambers of the photoelectrochemical water splitting coupled biomass oxidation reaction are isolated by a proton exchange membrane, which can be a naphthol 117 proton exchange membrane. This proton exchange membrane isolates the cathode from other electrodes.

[0091] In this embodiment, the sodium sulfate solution has a pH of 2 and a concentration of 0.5 mol / L. 1 mmol of glycerol is added to 10 ml of the sodium sulfate solution, and the mixture is magnetically stirred at 300 rpm for 20 min to obtain a mixture.

[0092] The reaction conditions for the photoelectric water splitting coupled biomass oxidation reaction are as follows: A mixture of electrolyte and glycerol is subjected to nitrogen protection using an electrochemical workstation (CHI 660E) with voltage applied and current-time (it) mode applied at a bias voltage of 0.9V versus RHE (RHE stands for reversible hydrogen electrode) for 4 hours, allowing glycerol to be selectively oxidized to formic acid at the anode. The amount of hydrogen produced at the cathode is measured using the water displacement method. During the photoluminescence reaction, a xenon lamp light source equipped with an AM1.5G filter (simulating sunlight) is used to irradiate the anode, with the light direction pointing towards the non-conductive surface of the anode, and the light intensity at 100 mW / cm². 2 .

[0093] Example 5

[0094] The surface-fluorinated bismuth vanadate photoelectrode of this embodiment is the same as that of Example 1, except that the mass fraction of fluorine atoms is 0.7 wt%.

[0095] The surface-fluorine-modified bismuth vanadate photoelectrode of this embodiment was prepared by impregnation method. The mass fraction of fluorine atoms on the bismuth vanadate surface was determined to be 0.7 wt% by ion chromatography.

[0096] The surface-fluorinated bismuth vanadate photoelectrode of this embodiment undergoes photoelectric water splitting coupled with biomass oxidation reaction under the same conditions and steps as in Example 1.

[0097] Example 6

[0098] The surface-fluorinated bismuth vanadate photoelectrode of this embodiment is the same as that of Example 1, except that the mass fraction of fluorine atoms is 0.8 wt%.

[0099] The surface-fluorine-modified bismuth vanadate photoelectrode of this embodiment was prepared by impregnation method, and the mass fraction of fluorine atoms on the bismuth vanadate surface was determined to be 0.8 wt% by ion chromatography.

[0100] The surface-fluorinated bismuth vanadate photoelectrode of this embodiment undergoes photoelectric water splitting coupled with biomass oxidation reaction under the same conditions and steps as in Example 1.

[0101] Comparative Example 1

[0102] The bismuth vanadate photoelectrode in this comparative example is unmodified and is the FTO conductive glass with BiVO4 grown in Example 1. The photoelectric water splitting coupled biomass oxidation reaction is carried out in the same way as in Example 1.

[0103] Comparative Example 2

[0104] This comparative example uses the surface-fluorinated bismuth vanadate photoelectrode prepared in Example 1, and performs the photoelectric water splitting coupled biomass oxidation reaction under the same conditions and steps as in Example 1. The only difference is that when performing the photoelectric water splitting coupled biomass oxidation reaction, a three-electrode system is not used, but the surface-fluorinated bismuth vanadate photoelectrode is directly fixed on the anode clamp.

[0105] Comparative Example 3

[0106] This comparative example uses the surface-fluorinated bismuth vanadate photoelectrode prepared in Example 1, and performs the photoelectrochemical water splitting coupled biomass oxidation reaction under the same conditions and steps as in Example 1. The only difference is that no light is applied during the photoelectrochemical water splitting coupled biomass oxidation reaction, i.e., no light intensity of 100 mW / cm² is applied. 2 The light.

[0107] Effect Comparison

[0108] To verify the technical effect of the surface fluorine-modified bismuth vanadate photoelectrode described in this invention, the following experiments were conducted:

[0109] The photoelectrodes from Examples 1-6 and Comparative Examples 1-3 were used to perform photoelectrochemical water splitting coupled with biomass oxidation. The mixture of electrolyte and glycerol during and after the reaction was collected as the test sample. A small amount of dilute sulfuric acid was added to the test sample for dilution, and the sample was filtered through a nylon 66 filter membrane and placed in a sample vial for liquid chromatography (LC) analysis. LC analysis was performed on the contents of glycerol, dihydroxyacetone, glyceraldehyde, and formic acid using an external standard method. A Shimadzu LC-20AT LC system was used with an injection volume of 10 μL. Based on the LC results, the main products of glycerol selective oxidation, the selectivity of each product, and the formic acid yield were determined.

[0110] Among them, such as Figure 3 The image shows the surface-fluorinated bismuth vanadate photoelectrode of Example 1, under a bias voltage of 1.2V versus RHE illumination (AM 1.5G, 100mW / cm). 2 The relationship between the selectivity of photoelectrochemically coupled glycerol oxidation products and reaction time on a surface-fluorinated bismuth vanadate photoanode.

[0111] The results of the experiment are as follows:

[0112]

[0113] The surface-fluorinated bismuth vanadate photoelectrode from Example 1 was used. With 5,5-dimethyl-1-pyrrolline-N-oxide as a spin trap, electron spin resonance was observed after 2 minutes of illumination, and the in-situ generated free radicals were detected. The results showed that... Figure 2 The graph showing the relationship between absorbed signal intensity and magnetic field intensity is shown. According to... Figure 2 It can be seen that surface-fluorinated bismuth vanadate can increase the rate of water oxidation to generate hydroxyl radicals. The generated hydroxyl radicals can promote the breakage of the C-C bonds of glycerol to form hydroxymethyl radicals. These hydroxymethyl radicals can combine with hydroxyl radicals to eventually form formic acid.

[0114] As can be seen from the above results, the surface fluorine-modified bismuth vanadate photoelectrode of the present invention greatly improves the oxidation rate and molecular reaction efficiency of hydroxyl radicals generated by photoelectrolysis of water, and can effectively improve the oxidation efficiency of glycerol and the selectivity of the product formic acid.

[0115] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A surface-fluorinated bismuth vanadate photoelectrode for the production of formic acid from glycerol oxidation, characterized in that, Fluorine atoms are attached to the surface of bismuth vanadate, and some fluorine atoms replace the two-coordinated oxygen atoms on the surface of bismuth vanadate, which is the surface fluorine modified bismuth vanadate photoelectrode. Fluorine atoms form F-Bi-O bonds with the Bi end sites on the surface of bismuth vanadate, allowing fluorine atoms to attach to the surface of bismuth vanadate; some fluorine atoms replace the two-coordinated oxygen atoms on the surface of bismuth vanadate, forming an F-Bi-F double hydrogen bond structure, which is the surface fluorine-modified bismuth vanadate photoelectrode. The mass fraction of the fluorine atoms is 0.6 wt%. The structure of the F-Bi-O bond formed by fluorine atoms and the Bi terminal sites on the surface of bismuth vanadate BiVO4 is shown in the following equation: ； Some fluorine atoms replace the di-coordinated oxygen atoms on the surface of bismuth vanadate, forming an F-Bi-F double hydrogen bond structure as shown in the following formula: ； Surface fluorine modification occurs on the (112) crystal plane of the bismuth vanadate photoelectrode.

2. A method for preparing a surface-fluorinated bismuth vanadate photoelectrode according to claim 1, characterized in that, A 0.1 mol / L NaF solution was used as the impregnation solution. FTO or ITO conductive glass with BiVO4 grown on it was completely immersed in the impregnation solution and impregnated at 20°C for 2 hours to obtain a surface-fluorinated bismuth vanadate photoelectrode. The pH value of the impregnation solution was 6.

01.

3. The application of the surface-fluorinated bismuth vanadate photoelectrode of claim 1 in the field of photoelectric water splitting coupled with biomass oxidation reaction; The biomass is glycerol.

4. The application according to claim 3, characterized in that, The photoelectric water splitting coupled biomass oxidation reaction uses the surface-fluorinated bismuth vanadate photoelectrode as the anode.

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