A cobalt-manganese ion co-doped BiVO4 photoanode, a preparation method and application thereof

Abstract

The application belongs to the field of photoelectrocatalytic hydrogen production, and particularly relates to a cobalt-manganese ion co-doped BiVO4 photoanode as well as a preparation method and application thereof. The preparation method of the cobalt-manganese ion co-doped BiVO4 photoanode comprises the following steps: dipping a BiVO4 photoanode in a solution containing a cobalt salt and a manganese salt at 30-70 DEG C for 0.5-5 h, and obtaining the cobalt-manganese ion co-doped BiVO4 photoanode after drying. The application constructs the cobalt-manganese ion co-doped BiVO4 photoanode by dipping cobalt and manganese ions on the surface of BiVO4 for surface modification, and the cobalt and manganese ions exist in the form of divalent or trivalent on the surface of the BiVO4 photoanode, which is conducive to being converted into hydroxyl oxide in the process of photoelectrocatalysis, so as to improve the performance of photoelectrochemical water splitting for hydrogen production of BiVO4.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrocatalytic hydrogen production, specifically relating to a cobalt-manganese ion co-doped BiVO4 photoanode, its preparation method, and its application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] The massive consumption of fossil fuels has already caused immense damage to the environment, and developing clean and environmentally friendly renewable energy sources is considered a crucial way to solve the environmental and energy crisis. Hydrogen energy has attracted widespread attention worldwide due to its high energy density and zero pollutant emissions. Among various hydrogen production technologies, photoelectrochemical (PEC) water splitting technology has been extensively studied because it can convert abundant and sustainable solar energy into efficient hydrogen energy, effectively addressing the energy crisis. Simultaneously, developing high-performance, high-abundance, and stable photoanodes is also essential.

[0004] In recent years, BiVO4 has been actively explored for use in PEC water splitting due to its suitable band gap, favorable valence band position, and relatively low cost. However, pure BiVO4 suffers from severe charge recombination, poor water oxidation kinetics, and low stability, resulting in its water splitting performance failing to meet expectations. Existing technologies combine BiVO4 with transition metal oxides to form heterostructures, thereby enhancing carrier mobility and suppressing electron-hole recombination. However, the photoanodic catalytic oxidation of water to oxygen relies on intermediates with high valence states to enhance catalytic activity. Transition metal oxides, with their stable crystal structures, are difficult to further oxidize and convert into high-valence intermediates, thus limiting their photoelectric performance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a cobalt-manganese ion co-doped BiVO4 photoanode, its preparation method, and its application. The present invention modifies the surface of BiVO4 by impregnating it with cobalt and manganese ions, thereby constructing a cobalt-manganese ion co-doped BiVO4 photoanode. The cobalt and manganese ions exist in divalent or trivalent forms on the surface of the BiVO4 photoanode, which is beneficial for their conversion into hydroxyl oxides during photoelectrocatalysis, thus improving the photoelectrochemical water splitting hydrogen production performance of BiVO4.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] In a first aspect, a method for preparing a cobalt-manganese ion co-doped BiVO4 photoanode includes the following steps:

[0008] BiVO4 photoanodes are immersed in a solution containing cobalt and manganese salts at 30-70℃ for 0.5-5 hours and then dried to obtain cobalt-manganese ion co-doped BiVO4 photoanodes.

[0009] By immersing the BiVO4 photoanode in a mixed solution of cobalt and manganese salts at a lower temperature, cobalt and manganese can be loaded onto the BiVO4 photoanode in ionic form, rather than as oxides obtained by hydrothermal methods in the prior art.

[0010] Preferably, the concentration of the cobalt salt is 0.01–0.06 mol / L, and the concentration of the manganese salt is 0.01–0.06 mol / L.

[0011] Preferably, the cobalt salt includes at least one of cobalt nitrate and cobalt acetate, and the manganese salt includes at least one of manganese nitrate and manganese acetate.

[0012] Preferably, the method for preparing the BiVO4 photoanode includes the following steps:

[0013] Bismuth nitrate was added to an aqueous solution of potassium iodide and nitric acid at pH 1.7 to obtain a mixed solution. The mixed solution was then slowly poured into an ethanol solution of p-benzoquinone and stirred to obtain an electroplating solution. BiIO was obtained by electrodeposition on a fluorine-doped tin oxide substrate using a three-electrode system with the electroplating solution as the electrolyte. A dimethyl sulfoxide solution containing vanadium acetylacetonate was added dropwise to the BiIO, and after high-temperature calcination and soaking in NaOH, BiVO4 photoanode was obtained.

[0014] More preferably, the molar ratio of bismuth nitrate, potassium iodide and benzoquinone is 1:(9-11):(0.9-1), and the volume ratio of the mixture to the ethanol solution of p-benzoquinone is (2-3):1.

[0015] More preferably, in the three-electrode system, fluorine-doped tin oxide is used as the working electrode, a platinum sheet is used as the counter electrode, Ag / AgCl is used as the reference electrode, the electrodeposition voltage is -0.1V vs. Ag / AgCl, and the electrodeposition time is 180–240s.

[0016] More preferably, the molar ratio of bismuth nitrate to vanadium acetylacetonate is 1:(0.05-0.1).

[0017] More preferably, the high-temperature calcination temperature is 400-500℃, the time is 1-3h, and the heating rate is 1-3℃ / min.

[0018] In a second aspect, the present invention provides a cobalt-manganese ion co-doped BiVO4 photoanode, which is obtained by the preparation method described in the first aspect.

[0019] Thirdly, the present invention provides the application of cobalt-manganese ion co-doped BiVO4 photoanode as described in the second aspect in photoelectrocatalytic water splitting for hydrogen production.

[0020] The beneficial effects achieved by one or more technical solutions of the present invention are as follows:

[0021] This invention successfully incorporates Co and Mn ions into the surface of a BiVO4 photoanode using a simple impregnation method, without the formation of Co and Mn oxides. The incorporation of Co and Mn ions in divalent and trivalent forms on the BiVO4 photoanode surface facilitates their conversion to hydroxyl oxides during the photoelectrocatalytic process, significantly enhancing both photoelectrochemical activity and stability. This results in a photocurrent density of 3.2 mA / cm² at 1.23 V vs. RHE for the composite photoanode. 2 . Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0023] Figure 1 The XRD patterns of BiVO4 in Comparative Example 1 and CoMn:BiVO4 in Example 1 are shown.

[0024] Figure 2 The XPS spectra of CoMn:BiVO4 in Example 1 are shown, where (a) is the full XPS spectrum, (b) is the Co 2p spectrum, and (c) is the Mn 2p spectrum.

[0025] Figure 3 Contact angle test diagrams for (a) BiVO4 in Comparative Example 1 and (b) CoMn:BiVO4 in Example 1;

[0026] Figure 4 The UV-Vis absorption spectra of BiVO4 in Comparative Example 1 and CoMn:BiVO4 in Example 1 are shown.

[0027] Figure 5 Photocurrent density and potential diagrams of BiVO4 in Comparative Example 1 and its photocurrent density under dark conditions, Co:BiVO4 in Comparative Example 2, Mn:BiVO4 in Comparative Example 3 and CoMn:BiVO4 in Example 1.

[0028] Figure 6 Electrochemical impedance spectroscopy (EIS) of BiVO4 in Comparative Example 1 and its properties under dark conditions, Co:BiVO4 in Comparative Example 2, Mn:BiVO4 in Comparative Example 3 and CoMn:BiVO4 in Example 1.

[0029] Figure 7 Stability test curves for BiVO4 in Comparative Example 1 and CoMn:BiVO4 in Example 1;

[0030] Figure 8 The photocurrent density of CoMn:BiVO4 before and after stability testing is compared in Example 1. Detailed Implementation

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments and comparative examples.

[0032] Example 1

[0033] First, 3.32 g of KI was added to 50 mL of ultrapure water. Then, HNO3 was slowly added dropwise to the KI solution until the pH of the mixed solution dropped to 1.7. Next, 0.97 g of Bi(NO3)3·5H2O was added to the KI solution. Then, an ethanol solution containing 0.49 g of p-benzoquinone was slowly poured into the above mixed solution to form a BiOI plating solution. A typical three-electrode system (1 cm × 1 cm) was used for BiOI electrodeposition. Pt foil was used as the counter electrode, fluorinated tin oxide (FTO) as the working electrode, and Ag / AgCl (saturated KCl solution) as the reference electrode. Electrodeposition was performed at -0.1 V Ag / AgCl for 300 s. An 80 μL LDMSO solution containing 0.2 M VO(acac)2 was then dropped onto the BiOI electrode surface, followed by calcination at 450 °C (heating rate 2 °C / min) for 2 h in a muffle furnace to convert BiOI to BiVO4. The obtained BiVO4 photoanode was immersed in 1M NaOH solution for 30 min to remove excess V2O5 from the photoanode surface. Finally, the surface of the BiVO4 photoanode was treated with ultrapure water and dried at room temperature.

[0034] Cobalt nitrate and manganese nitrate were added sequentially to 50 mL of ultrapure water and stirred thoroughly at room temperature for 30 min to obtain a solution containing 0.01 mol / L cobalt ions and 0.05 mol / L manganese ions. The BiVO4 photoanode was then placed in the solution with the conductive side facing up. Finally, it was placed in a water bath and the mixture was gradually heated to 50 °C for 2 h. After that, it was taken out and carefully rinsed with ethanol and ultrapure water. After drying at room temperature, the cobalt and manganese ion co-doped BiVO4 photoanode was obtained, denoted as Co,Mn:BiVO4.

[0035] Comparative Example 1

[0036] First, 3.32 g of KI was added to 50 mL of ultrapure water. Then, HNO3 was slowly added dropwise to the KI solution until the pH of the mixed solution dropped to 1.7. Next, 0.97 g of Bi(NO3)3·5H2O was added to the KI solution. Then, an ethanol solution containing 0.49 g of p-benzoquinone was slowly poured into the above mixed solution to form a BiOI plating solution. A typical three-electrode system (1 cm × 1 cm) was used for BiOI electrodeposition. Pt foil was used as the counter electrode, fluorinated tin oxide (FTO) as the working electrode, and Ag / AgCl (saturated KCl solution) as the reference electrode. Electrodeposition was performed at -0.1 V Ag / AgCl for 300 s. An 80 μL LDMSO solution containing 0.2 M VO(acac)2 was then dropped onto the BiOI electrode surface, followed by calcination at 450 °C (heating rate 2 °C / min) for 2 h in a muffle furnace to convert BiOI to BiVO4. The obtained BiVO4 photoanode was immersed in 1M NaOH solution for 30 min to remove excess V2O5 from the surface of the BiVO4 photoanode. Finally, the surface of the BiVO4 photoanode was treated with ultrapure water and dried at room temperature. The obtained BiVO4 photoanode is denoted as BiVO4.

[0037] like Figure 1 As shown, the diffraction peaks of Co,Mn:BiVO4 in Example 1 and BiVO4 in Comparative Example 1 all correspond to the BiVO4 standard card JCPDS14-0688. No new diffraction peaks appeared in the Co,Mn:BiVO4 obtained after doping, indicating that no oxide structure was formed when cobalt and manganese were incorporated.

[0038] like Figure 2 As shown in Figure a, the XPS full spectrum reveals corresponding peaks for Co and Mn elements, confirming the incorporation of cobalt and manganese ions. Further analysis of the valence states of the incorporated cobalt and manganese ions is conducted, as shown in... Figure 2 As shown in b, the Co 2p spectrum shows Co 2+ and Co 3+ The characteristic peaks indicate that cobalt ions can be incorporated in a higher trivalent state; such as Figure 2 As shown in c, Mn also appears in the Mn 2p spectrum. 2+ and Mn 3+ The peak. The incorporation of cobalt and manganese ions into BiVO4 at higher valence states may cause Co,Mn:BiVO4 to exhibit higher PEC activity.

[0039] Contact angle tests were performed on BiVO4 and CoMn:BiVO4. The results are as follows: Figure 3 As shown, the contact angle of BiVO4 is approximately 134°, indicating hydrophobicity; while the contact angle of Co,Mn:BiVO4 is approximately 19°, indicating hydrophilicity. This suggests that Co,Mn:BiVO4 can better contact the electrolyte solution, thereby improving its PEC performance.

[0040] The UV-Vis absorption spectra of BiVO4 and CoMn:BiVO4 were measured. The results are as follows: Figure 4 As shown, the absorption edge of BiVO4 is at 507 nm, while CoMn:BiVO4 has a significant redshift with an absorption edge of 518 nm, indicating that the photoresponse range of Co and Mn:BiVO4 is enhanced.

[0041] Comparative Example 2

[0042] The preparation of the BiVO4 photoanode was the same as in Example 1. Cobalt nitrate was added to 50 mL of ultrapure water and stirred thoroughly at room temperature for 30 min to obtain a solution containing 0.01 mol / L cobalt ions. The BiVO4 photoanode was then placed in the solution with the conductive side facing up. Finally, it was placed in a water bath and the mixture was gradually heated to 50 °C for 2 h. After that, it was taken out and carefully rinsed with ethanol and ultrapure water. After drying at room temperature, the cobalt ion-doped BiVO4 photoanode was obtained, denoted as Co:BiVO4.

[0043] Comparative Example 3

[0044] The preparation of the BiVO4 photoanode was the same as in Example 1. Manganese nitrate was added to 50 mL of ultrapure water and stirred thoroughly at room temperature for 30 min to obtain a solution containing 0.05 mol / L manganese ions. The BiVO4 photoanode was then placed in the solution with the conductive side facing up. Finally, it was placed in a water bath and the mixture was gradually heated to 50 °C for 2 h. After that, it was taken out and carefully rinsed with ethanol and ultrapure water. After drying at room temperature, the manganese ion-doped BiVO4 photoanode was obtained, denoted as Mo:BiVO4.

[0045] Example 2

[0046] The electrochemical workstation used for photoelectrocatalytic hydrogen production was a CHI660E. The three-electrode system consisted of: a platinum wire as the counter electrode, Ag / AgCl (3.5M KCl) as the reference electrode, and BiVO4 from Comparative Example 1 and its reaction under dark conditions, Co:BiVO4 from Comparative Example 2, Mn:BiVO4 from Comparative Example 3, and CoMn:BiVO4 from Example 1 as the working electrodes. The electrolyte solution used during the tests was a 1.0M potassium borate solution with pH 9.0, and the xenon lamp intensity was 100 mW / cm². 2 The scan rate was 10 mV·s. -1 According to the Nernst equation, all potentials must be converted to potentials relative to the reversible hydrogen electrode (RHE): E RHE =E Ag / AgCl +0.059×pH+0.197V.

[0047] like Figure 5 As shown, at 1.23V RHEAt this level, BiVO4 exhibits the lowest photocurrent density, at 1.0 mA cm⁻¹. -2 The photocurrent density of Co:BiVO4 increased to 2.15 mA / cm². -2 The photocurrent density of Mn:BiVO4 increased to 2.52 mA cm⁻¹. -2 Co-doping with Co and Mn ions significantly improved the performance of BiVO4, with the photocurrent density of CoMn:BiVO4 increasing to 3.21 mA cm⁻¹. -2 Furthermore, the onset potential also showed a significant improvement. These results indicate that co-doping with CoMn ions has an excellent synergistic effect in enhancing the PEC performance of BiVO4.

[0048] The electrochemical impedance spectroscopy (EIS) of the photoanode was tested under illumination, and the recorded EIS spectra are as follows: Figure 6 The Nyquist plots are shown. The order of decreasing semicircle radius is: BiVO4 > Co:BiVO4 > Mn:BiVO4 > CoMn:BiVO4. The results indicate that CoMn:BiVO4 has the smallest radius, meaning its charge transfer kinetics during water oxidation are faster. Furthermore, a smaller semicircle radius indicates a smaller charge transfer resistance (Rct), suggesting that CoMn:BiVO4 significantly reduces the interfacial Rct. These results demonstrate that CoMn co-doping significantly enhances the charge separation and transfer capabilities of BiVO4.

[0049] Figure 7 For BiVO4 and CoMn: BiVO4 at 1.23V RHE Stability testing was conducted after 2 hours of irradiation. The photocurrent density of pure BiVO4 decreased sharply after 2 hours, retaining 43.5% of the initial photocurrent. The photocurrent density of the CoMn:BiVO4 photoanode decreased less, retaining 82.2% of the initial photocurrent, demonstrating its good stability. Following the stability test, the photocurrent density of CoMn:BiVO4 was tested again, as shown... Figure 8 As shown, the curve exhibits a slight downward trend, further demonstrating the excellent stability of the CoMn:BiVO4 photoanode. These results indicate that co-doping with CoMn ions significantly improves the stability of the photoelectrode. This improved stability may be due to the fact that co-doping with CoMn ions facilitates the formation of catalytic intermediates and makes the catalyst structure more stable, thereby enhancing the stability of the photoelectrode.

[0050] Example 3

[0051] Unlike Example 1, the mixture was gradually heated to 70°C and then timed for 0.5 hours.

[0052] Example 4

[0053] Unlike Example 1, the mixture was gradually heated to 30°C and then timed for 5 hours.

[0054] Example 5

[0055] Unlike Example 1, cobalt nitrate and manganese nitrate were added sequentially to 50 mL of ultrapure water and stirred thoroughly at room temperature for 30 min to obtain a solution containing 0.06 mol / L cobalt ions and 0.01 mol / L manganese ions. Then, the BiVO4 photoanode was placed in the solution with the conductive side facing up.

[0056] Example 6

[0057] Unlike Example 1, cobalt nitrate and manganese nitrate were added sequentially to 50 mL of ultrapure water and stirred thoroughly at room temperature for 30 min to obtain a solution containing 0.01 mol / L cobalt ions and 0.06 mol / L manganese ions. Then, the BiVO4 photoanode was placed in the solution with the conductive side facing up.

[0058] Example 7

[0059] Unlike Example 1, cobalt nitrate and manganese nitrate were added sequentially to 50 mL of ultrapure water and stirred thoroughly at room temperature for 30 min to obtain a solution containing 0.01 mol / L cobalt ions and 0.01 mol / L manganese ions. Then, the BiVO4 photoanode was placed in the solution with the conductive side facing up.

[0060] Example 8

[0061] Unlike Example 1, cobalt nitrate and manganese nitrate were added sequentially to 50 mL of ultrapure water and stirred thoroughly at room temperature for 30 min to obtain a solution containing 0.06 mol / L cobalt ions and 0.06 mol / L manganese ions. Then, the BiVO4 photoanode was placed in the solution with the conductive side facing up.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-manganese ion co-doped BiVO4 photoanode, characterized in that, Includes the following steps: BiVO4 photoanodes are immersed in a solution containing cobalt and manganese salts at 30-70 °C for 0.5-5 h, and then dried to obtain cobalt-manganese ion co-doped BiVO4 photoanodes. The preparation method of the BiVO4 photoanode includes the following steps: Bismuth nitrate was added to an aqueous solution of potassium iodide and nitric acid at pH 1.7 to obtain a mixed solution. The mixed solution was then slowly poured into an ethanol solution of p-benzoquinone and stirred to obtain an electroplating solution. BiIO was obtained by electrodeposition on a fluorine-doped tin oxide substrate using a three-electrode system with the electroplating solution as the electrolyte. A dimethyl sulfoxide solution containing vanadium acetylacetonate was added dropwise to the BiIO, and after high-temperature calcination and soaking in NaOH, BiVO4 photoanode was obtained. Co and Mn ions are incorporated into the surface of the BiVO4 photoanode in divalent and trivalent forms.

2. The preparation method according to claim 1, characterized in that, The concentration of the cobalt salt is 0.01~0.06 mol / L, and the concentration of the manganese salt is 0.01~0.06 mol / L.

3. The preparation method according to claim 1, characterized in that, The cobalt salt includes at least one of cobalt nitrate and cobalt acetate, and the manganese salt includes at least one of manganese nitrate and manganese acetate.

4. The preparation method according to claim 1, characterized in that, The molar ratio of bismuth nitrate, potassium iodide and benzoquinone is 1:(9~11):(0.9~1), and the volume ratio of the mixed solution to the ethanol solution of p-benzoquinone is (2~3):

1.

5. The preparation method according to claim 1, characterized in that, In the three-electrode system, fluorine-doped tin oxide is the working electrode, a platinum sheet is the counter electrode, and Ag / AgCl is the reference electrode. The electrodeposition voltage is -0.1 V vs. Ag / AgCl, and the electrodeposition time is 180~240 s.

6. The preparation method according to claim 1, characterized in that, The molar ratio of bismuth nitrate to vanadium acetylacetonate is 1:(0.05~0.1).

7. The preparation method according to claim 1, characterized in that, The high-temperature calcination temperature is 400~500 ℃, the time is 1~3 h, and the heating rate is 1~3 ℃ / min.

8. A cobalt-manganese ion co-doped BiVO4 photoanode, characterized in that, Obtained by the preparation method described in any one of claims 1 to 7.

9. The application of the cobalt-manganese ion co-doped BiVO4 photoanode as described in claim 8 in photoelectrocatalytic water splitting for hydrogen production.

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