A bulk-sulfur-doped zinc ferrite photoanode, a preparation method and application thereof

Abstract

The application relates to the technical field of photoelectrochemical water decomposition, in particular to a bulk-phase sulfur-doped zinc ferrite photoanode, a preparation method and application thereof. The preparation method of the bulk-phase sulfur-doped zinc ferrite photoanode comprises the following steps: S1) placing a conductive substrate in a mixed solution containing an iron compound and urea, and performing a hydrothermal reaction to obtain a beta-FeOOH nanorod array template; S2) under a heating condition, an excessive zinc nitrate solution is added dropwise to the surface of the beta-FeOOH nanorod array template, then a solid-phase reaction is performed at high temperature, and after cooling, zinc ferrite with zinc oxide covering on the surface is obtained, the zinc ferrite photoanode is obtained after removing the zinc oxide covering on the surface; S3) the zinc ferrite photoanode is immersed in a solution containing a sulfur compound, and an anion exchange reaction is performed to obtain a sulfur-doped zinc ferrite photoanode; and S4) the sulfur-doped zinc ferrite photoanode is subjected to electrochemical treatment under light to obtain the bulk-phase sulfur-doped zinc ferrite photoanode.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photoelectrochemical water splitting, in particular to a bulk sulfur-doped zinc ferrite photoanode, a preparation method and application thereof. BACKGROUND

[0002] To solve the problems of environmental pollution and energy exhaustion caused by the continuous exploitation and utilization of fossil fuels, it is increasingly urgent to find alternative green clean energy. Hydrogen energy, as an ideal clean energy, can replace fossil fuels to a certain extent due to its wide application, thereby alleviating the above-mentioned problems. Photoelectrochemical water splitting can convert solar energy into clean energy-hydrogen energy by using photoelectrocatalytic materials, which is one of the effective ways to alleviate energy crisis and environmental pollution.

[0003] In recent years, spinel ferrite (MFe2O4, M=Zn, Mg, Cu, Ca, Co, Ni, etc.) has attracted more and more attention from researchers in the field of photoelectrocatalysis due to its relatively narrow band gap (E g =1.90~2.40 eV), abundant reserves of constituent elements, and photochemical stability. It is one of the photoelectrocatalytic materials with great development prospects. In particular, zinc ferrite (ZnFe2O4) with n-type semiconductor properties is often used as a photoanode material due to its relatively narrow band gap (about 2.10 eV), suitable energy band structure, and excellent photochemical stability. However, its low electron mobility and slow water oxidation kinetics make its photoelectrochemical performance much lower than the theoretical expectation, which greatly limits its practical application in photoelectric conversion devices. Therefore, it is very important to develop effective ways to improve the photoelectrochemical performance of ZnFe2O4 to promote the large-scale application of photoelectrochemical water splitting for hydrogen production. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to provide a bulk sulfur-doped zinc ferrite photoanode, a preparation method and application thereof. The prepared photoanode material has high photoelectrochemical water oxidation performance.

[0005] To achieve the above-mentioned purpose, the present application provides a preparation method of a bulk sulfur-doped zinc ferrite photoanode, comprising the following steps:

[0006] S1) placing a conductive substrate in a mixed solution containing an iron compound and urea, and performing a hydrothermal reaction to obtain a β-FeOOH nanorod array template;

[0007] S2) under heating conditions, adding an excess of zinc nitrate solution to the surface of the above-mentioned β-FeOOH nanorod array template, then performing a solid-phase reaction at high temperature, and obtaining zinc ferrite with zinc oxide covering the surface after cooling, and removing the surface covering zinc oxide to obtain a zinc ferrite photoanode ZnFe2O4;

[0008] S3) soaking the above zinc ferrite photo-anode in a solution containing sulfur compounds to perform anion exchange reaction to obtain a sulfur-doped zinc ferrite photo-anode;

[0009] S4) performing electrochemical treatment under light irradiation on the above sulfur-doped zinc ferrite photo-anode to remove part of the sulfur on the surface and retain the sulfur in the bulk phase to obtain a bulk sulfur-doped zinc ferrite photo-anode ZnFe2O4 4-x S x .

[0010] The bulk phase refers to the interior of the material.

[0011] In the step S1), the iron-containing compound is preferably ferric chloride hexahydrate or ferric nitrate nonahydrate.

[0012] The molar ratio of the iron-containing compound to urea is preferably 0.1-1:1, and more preferably 1:1.

[0013] The temperature of the hydrothermal reaction is preferably 80-120 ℃, and more preferably 100 ℃.

[0014] The time of the hydrothermal reaction is 4-8 h, and more preferably 6 h.

[0015] The conductive substrate is not particularly limited in the present application, and can be any suitable conductive substrate known to those skilled in the art. Preferably, the conductive substrate is FTO conductive glass.

[0016] Preferably, the conductive substrate is cleaned with solvents such as acetone and anhydrous ethanol before the hydrothermal reaction.

[0017] Preferably, the non-conductive surface of the conductive substrate is placed against the wall of the reaction bottle during the hydrothermal reaction, so that the hydrothermal reaction is better performed on the conductive surface.

[0018] In the step S2), the temperature of the heating is preferably 80-120 ℃.

[0019] The concentration of the zinc nitrate solution is preferably 0.010-0.10 mol / L, and more preferably 0.10 mol / L.

[0020] The temperature of the solid-phase reaction is preferably 450-700 ℃, and more preferably 600 ℃.

[0021] The time of the solid-phase reaction is preferably 20-40 min, and more preferably 20 min.

[0022] The solid-phase reaction is preferably performed in a tube furnace.

[0023] The solid phase reaction is preferably carried out in an air atmosphere.

[0024] In the step S2), the method for removing the surface covered zinc oxide is preferably that the zinc ferrite with surface covered zinc oxide is soaked in an alkaline solution.

[0025] The alkaline compound in the alkaline solution preferably comprises one or more of sodium hydroxide and potassium hydroxide.

[0026] The concentration of the alkaline solution is preferably 4-7 mol / L, and more preferably 5 mol / L.

[0027] The soaking time is preferably 2-5 h, and specifically can be 2 h, 3 h or 4 h, and more preferably 3 h.

[0028] In the step S3), the sulfur-containing compound is preferably sodium sulfide nine hydrate.

[0029] The concentration of the solution of the sulfur-containing compound is preferably 0.1-1.0 mol / L, and more preferably 0.1 mol / L.

[0030] The temperature of the anion exchange reaction is preferably 80-120 ℃, and more preferably 100 ℃.

[0031] The time of the anion exchange reaction is preferably 4-8 h, and specifically can be 4 h, 6 h or 8 h, and more preferably 6 h.

[0032] In the step S4), the electrochemical treatment under light is a cyclic voltammetry test under light.

[0033] Preferably, the electrolyte used in the cyclic voltammetry test is a 0.5-3 mol / L NaOH solution, and more preferably a 1 mol / L NaOH solution; preferably, the voltage range of the cyclic voltammetry test is-0.4-0.8 V, and more preferably-0.5-0.6 V; preferably, the number of cycles is 5-20, and more preferably 20; the light condition is preferably provided by a simulated light source, and the simulated light source used is preferably a 300 W xenon lamp used in combination with an AM 1.5G filter; preferably, the light source intensity is 50-300 mW / cm 2 , and more preferably 100 mW / cm 2 .

[0034] The method can prepare a bulk sulfur-doped zinc ferrite photoanode with greatly improved photoelectrochemical water oxidation performance by a simple and unique synthesis method, the obtained photoanode material has good stability, the photocurrent density at a water decomposition potential of 1.23 V RHE is increased by 81 times, from 5.4 μA·cm -2boosted to 0.44 mA·cm -2 The synthetic method is simple, the obtained photoanode material is easy to apply, and the application in industrial production is facilitated.

[0035] The application provides a bulk-phase sulfur-doped zinc ferrite photoanode material prepared by the preparation method.

[0036] The morphology of the bulk-phase sulfur-doped zinc ferrite photoanode material is a nanorod array, the length of the nanorod is 400-500 nm, and the diameter is 30-50 nm.

[0037] The photoelectrochemical water oxidation performance of the bulk-phase sulfur-doped zinc ferrite photoanode material is significantly improved.

[0038] Based on this, the application provides a preparation method of the bulk-phase sulfur-doped zinc ferrite photoanode material, the bulk-phase sulfur-doped zinc ferrite photoanode material and application of the bulk-phase sulfur-doped zinc ferrite photoanode material in a photoelectrochemical water splitting reaction.

[0039] Preferably, the temperature of the photoelectrochemical water splitting reaction is room temperature, the electrolyte used in the reaction is a NaOH solution, the simulated light source used in the reaction is a 300 W xenon lamp used in cooperation with an AM 1.5G filter, and the intensity of the light source is preferably 50-300 mW / cm 2 , and more preferably 100 mW / cm 2 . The concentration of the NaOH solution is preferably 0.5-3 mol / L, and more preferably 1 mol / L.

[0040] In some specific embodiments of the application, the method is as follows: a three-electrode system is used, the counter electrode is a platinum electrode, the reference electrode is a silver / silver chloride electrode, the working electrode is the bulk-phase sulfur-doped zinc ferrite photoanode material, and the electrolyte is a 1 mol / L sodium hydroxide solution. Photoelectrochemical related tests are carried out in a quartz reaction cell under irradiation.

[0041] Specifically, the bulk-phase sulfur-doped zinc ferrite photoanode is first placed on an electrode clamp as a working electrode, and then a silver / silver chloride electrode and a platinum electrode are sequentially inserted and connected to three electrode clamps of an electrochemical workstation. Then, an appropriate amount of 1 mol / L sodium hydroxide solution is added to the quartz reaction cell. A xenon lamp light source is vertically irradiated on the working electrode area, and the light intensity is one solar light intensity (100 mW / cm 2 ). After preparation, related photoelectrochemical tests are carried out.

[0042] The application provides a preparation method of the above-mentioned bulk phase sulfur-doped zinc ferrite photoanode and application of the above-mentioned bulk phase sulfur-doped zinc ferrite photoanode material in photoelectrochemical water decomposition.

[0043] Compared with the prior art, the application provides a preparation method of a bulk phase sulfur-doped zinc ferrite photoanode, which comprises the following steps: S1) placing a conductive substrate in a mixed solution containing an iron compound and urea to perform a hydrothermal reaction, so as to obtain a β-FeOOH nanorod array template; S2) under a heating condition, dropping an excessive zinc nitrate solution onto a surface of the above-mentioned β-FeOOH nanorod array template, then performing a solid phase reaction at a high temperature, and after cooling, obtaining zinc ferrite with zinc oxide covering on the surface, and after removing the zinc oxide covering on the surface, obtaining a zinc ferrite photoanode; S3) immersing the above-mentioned zinc ferrite photoanode in a solution containing a sulfur compound to perform an anion exchange reaction, so as to obtain a bulk phase sulfur-doped zinc ferrite photoanode; and S4) performing an electrochemical treatment on the above-mentioned sulfur-doped zinc ferrite photoanode under light irradiation, removing part of the sulfur on the surface, retaining the sulfur in the bulk phase, and obtaining the bulk phase sulfur-doped zinc ferrite photoanode. The bulk phase sulfur-doped zinc ferrite photoanode with greatly improved photoelectrochemical water oxidation performance can be prepared through the simple and unique synthesis method, the photoanode obtained has good stability, the photocurrent density at the water decomposition potential 1.23 V is improved by 81 times, and is increased from 5.4 μA·cm RHE -2 to 0.44 mA·cm -2 -2. -2 . BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 Scanning electron microscope (SEM) photos of a zinc ferrite (ZnFe2O4) photoanode prepared in Example 1 and a bulk phase sulfur-doped zinc ferrite (ZnFe2O 4-x S x ) photoanode prepared in Example 2;

[0045] Figure 2 X-ray diffraction patterns of the zinc ferrite (ZnFe2O4) photoanode prepared in Example 1 and the ZnFe2O 4-x S x ) photoanode prepared in Example 2;

[0046] Figure 3 Performance graph of photoelectrochemical water decomposition of the ZnFe2O 4-x S x ) photoanode and a comparative sample ZnFe2O4 photoanode. DETAILED DESCRIPTION

[0047] In order to further illustrate the application, the following will be described in detail in combination with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the application, and are not limitations on the claims of the application.

[0048] All raw materials of the present application are not particularly limited in origin, and can be purchased on the market or prepared according to conventional methods well known to those skilled in the art.

[0049] The instruments used in the following Examples 1-2 are as follows:

[0050] Scanning electron microscope (FEI, Sirion 200 Schottky field emission scanning electron microscope)

[0051] X-ray diffractometer (Rigaku, SmartLab multifunctional rotating target X-ray diffractometer)

[0052] Electrochemical workstation (CHI, CHI650E electrochemical analyzer)

[0053] Xenon lamp light source (CEL-HXF300-T3 photocatalytic xenon lamp light source)

[0054] Example 1

[0055] Step 1, preparation of zinc ferrite (ZnFe2O4) photoanode

[0056] β-FeOOH deposited on the surface of conductive glass was prepared by a hydrothermal method. 20.27 g of ferric chloride hexahydrate and 4.50 g of urea were dissolved in 50 mL of deionized water, and after uniform stirring, the solution was transferred into a 500 mL volumetric flask. 30 mL of the solution was taken in a reagent bottle, and a clean conductive glass FTO was placed in it with the back against the bottle wall. After sealing, it was placed in a homogeneous reactor and heated to 100 ℃ for 6 h. After the reaction was completed, the product was washed with deionized water, and after natural air drying, a β-FeOOH nanorod array template was obtained. The β-FeOOH nanorod array template was placed on a preheated 100 ℃ heating table, and an excess of 0.10 mol / L zinc nitrate solution was added dropwise. After drying, it was placed in a preheated 600 ℃ tube furnace and calcined for 20 min. After cooling to room temperature, it was taken out and immersed in a 5 mol / L sodium hydroxide solution for 3 h to remove the surface zinc oxide. After washing with deionized water and drying, a zinc ferrite (ZnFe2O4) photoanode was obtained.

[0057] Figure 1 Figure a is a scanning electron microscope (SEM) photograph of the prepared zinc ferrite (ZnFe2O4) photoanode. It can be seen that the prepared sample is in the form of nanorods, with a length of about 400-500 nm and a diameter of about 30-50 nm, and the distribution is uniform.

[0058] The X-ray diffraction pattern (XRD) of the prepared zinc ferrite (ZnFe2O4) photoanode sample is shown in Figure 2The prepared sample was compared with the standard XRD card (JCPDS NO. 22-1012), and it was found that the sample was a spinel ZnFe2O4.

[0059] Step two, evaluation of the activity of the ZnFe2O4 photoanode in photoelectrochemical water splitting

[0060] The obtained ZnFe2O4 was placed on an electrode holder as a working electrode, and then a silver / silver chloride electrode and a platinum electrode were sequentially inserted and connected to the three electrode holders of an electrochemical workstation. Then, an appropriate amount of 1 mol / L sodium hydroxide solution was added to the quartz reaction cell. The xenon lamp light source was vertically irradiated on the working electrode area, and the light intensity was ensured to be one solar light intensity (100 mW / cm 2 ). Subsequently, photoelectrochemical tests were performed. In the case of light, linear voltammetry tests were performed. The parameter settings were as follows: scan rate: 25 mV / s; scan range: -0.50~0.60 V; sensitivity: 10 -3 .

[0061] The results are listed in Figure 3 . Figure 3 The ZnFe2O4 photoanode was prepared 4-x S x The J-V curve of the photoanode and the comparative sample ZnFe2O4 photoanode. It can be seen that the photocurrent density of the ZnFe2O4 photoanode at the water splitting potential 1.23 V RHE is 5.4 μA·cm -2 .

[0062] Example 2

[0063] Step one, preparation of the ZnFe2O4 photoanode

[0064] β-FeOOH deposited on the surface of conductive glass was prepared by a hydrothermal method. 20.27 g of iron chloride hexahydrate and 4.50 g of urea were dissolved in 50 mL of deionized water, and after uniform stirring, the solution was transferred into a 500 mL volumetric flask. 30 mL of the solution was taken in a reagent bottle, and a clean conductive glass FTO was placed in the bottle with the back against the wall. After sealing, the mixture was placed in a homogeneous reactor and heated to 100 ℃ for 6 h. After the reaction, the product was washed with deionized water, and after natural air drying, a β-FeOOH nanorod array template was obtained. The β-FeOOH nanorod array template was placed on a preheated 100 ℃ heating table, and an excess of 0.10 mol / L zinc nitrate solution was added dropwise. After drying, it was placed in a preheated 600 ℃ tube furnace and calcined for 20 min. After cooling to room temperature, it was taken out and immersed in a 5 mol / L sodium hydroxide solution for 3 h to remove the surface zinc oxide. After washing with deionized water and drying, a ZnFe2O4 photoanode was obtained.

[0065] Step two, preparation of bulk sulfur-doped zinc ferrite photoanode (ZnFe2O 4-x S x )

[0066] Sodium sulfide (12.00 g) was dissolved in 50 mL of deionized water, and after uniform stirring, it was transferred into a 500 mL volumetric flask. 30 mL of the solution was taken in a reagent bottle, and the ZnFe2O4 photoanode prepared in step one was placed in the bottle with the back against the bottle wall. After sealing, it was placed in a homogeneous reactor and heated to 100 °C for 6 h. After the reaction, the product was washed with deionized water, dried, and then subjected to cyclic voltammetry under light. After the treatment was completed, it was taken out, washed, and dried to obtain the bulk sulfur-doped zinc ferrite photoanode (ZnFe2O 4-x S x ).

[0067] Figure 1 Figure b in the middle is a scanning electron microscope (SEM) image of the prepared bulk sulfur-doped zinc ferrite (ZnFe2O 4-x S x ) photoanode. It can be seen that the prepared ZnFe2O 4-x S x sample still has the morphology of a nanorod array, and the surface morphology of the nanorods has not changed significantly.

[0068] The X-ray diffraction pattern (XRD) of the prepared ZnFe2O 4-x S x photoanode is shown in Figure 2 . Compared with the standard XRD card (JCPDS NO. 22-1012), the prepared sample is a spinel-type ZnFe2O4, and the treatment of S does not produce new diffraction peaks, indicating that the crystal phase has not changed.

[0069] Step three, evaluation of the photoelectrochemical water splitting activity of the bulk sulfur-doped zinc ferrite photoanode (ZnFe2O 4-x S x )

[0070] Similar to step two in Example 1, the obtained ZnFe2O 4-x S x photoanode was placed on an electrode holder as the working electrode, and then a silver / silver chloride electrode and a platinum electrode were sequentially inserted and connected to the three electrode holders of an electrochemical workstation. Then, an appropriate amount of 1 mol / L sodium hydroxide solution was added to the quartz reaction cell. The xenon light source was vertically irradiated on the working electrode area, and the light intensity was ensured to be one solar light intensity (100 mW / cm 2). Then photoelectrochemical test was carried out. Linear voltammetry test was carried out under light. Parameter setting: scan rate: 25 mV / s; scan range: -0.50~0.60 V; sensitivity: 10 -3 .

[0071] The results are listed in Figure 3 . Figure 3 ZnFe2O 4-x S x J-V curves of photoanode and comparative sample ZnFe2O4 photoanode. It can be seen that, after the treatment of anion exchange and light cycle voltammetry, the photocurrent density of ZnFe2O4 photoanode at water splitting potential 1.23 V 4-x S x 1.23 V RHE 0.44 mA·cm -2 . It shows that, after the treatment of anion exchange and light cycle voltammetry, the photocurrent density of ZnFe2O4 photoanode at water splitting potential 1.23 V RHE 1.23 V -2 0.44 mA·cm -2 .

[0072] The above description of the embodiments is only used to help understand the method of the present application and its core idea. It should be noted that, for those skilled in the art, without departing from the principles of the present application, the present application can be improved and modified in several ways, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for preparing a bulk sulfur-doped zinc ferrite photoanode, comprising the following steps: S1) placing a conductive substrate in a mixed solution containing an iron compound and urea, and performing a hydrothermal reaction to obtain a β-FeOOH nanorod array template; S2) under heating, adding an excess of a zinc nitrate solution to the surface of the β-FeOOH nanorod array template, and then performing a solid-phase reaction at high temperature, and after cooling, obtaining zinc ferrite with zinc oxide covering the surface, and removing the zinc oxide covering the surface to obtain a zinc ferrite photoanode ZnFe 2O 4; S3) immersing the zinc ferrite photoanode in a solution containing a sulfur compound, and performing an anion exchange reaction to obtain a sulfur-doped zinc ferrite photoanode; the sulfur compound is selected from sodium sulfide nine hydrates; the iron compound is ferric chloride six hydrates or ferric nitrate nine hydrates; the molar ratio of the iron compound to urea is 0.1-1:1; the temperature of the hydrothermal reaction is 80-120 ℃, and the time of the hydrothermal reaction is 4-8 h; the conductive substrate is FTO conductive glass; in the step S2), the temperature of the heating is 80-120 ℃; the concentration of the zinc nitrate solution is 0.010-0.10 mol / L; the temperature of the solid-phase reaction is 450-700 ℃; and the time of the solid-phase reaction is 20-40 min; in the step S2), the method for removing the zinc oxide covering the surface is immersing the zinc ferrite with zinc oxide covering the surface in an alkaline solution; the alkaline compound in the alkaline solution includes one or more of sodium hydroxide and potassium hydroxide; the concentration of the alkaline solution is 4-7 mol / L; and the time of the immersing is 2-5 h; in the step S3), the concentration of the solution containing the sulfur compound is 0.1-1.0 mol / L; the temperature of the anion exchange reaction is 80-120 ℃; and the time of the anion exchange reaction is 4-8 h; the cyclic voltammetry test voltage range is-0.4-0.8 V; and the cyclic voltammetry test cycle number is 5-20. 7.A bulk sulfur-doped zinc ferrite photoanode material prepared by the method of any one of claims 1-6, comprising a main body of zinc ferrite and sulfur elements for modification. The morphology of the bulk sulfur-doped zinc ferrite photoanode material is a nanorod array, the length of the nanorod is 400-500 nm, and the diameter is 30-50 nm. 9.Use of the bulk sulfur-doped zinc ferrite photoanode material prepared by the method of any one of claims 1-6 or the bulk sulfur-doped zinc ferrite photoanode material of any one of claims 7-8 in a photoelectrochemical water splitting reaction. S4) electrochemically treating the above-mentioned sulfur-doped zinc ferrite photoanode under light to remove the sulfur on the surface and retain the sulfur in the bulk phase, to obtain a bulk sulfur-doped zinc ferrite photoanode ZnFe2O4-S 4-x S x ; the electrochemical treatment under light is a cyclic voltammetry test under light.

2. The production method according to claim 1, characterized by, ​ ​ ​ ​ 3. The preparation method according to claim 1, characterized in that, ​ ​ ​ ​ 4. The production method according to claim 1, characterized by, ​ ​ ​ ​ 5. The preparation method according to claim 1, characterized in that, ​ ​ ​ 6. The production method according to claim 1, characterized by, In the step S4), the light condition is provided by a simulated light source, which is a 300 W xenon lamp used with an AM 1.5G filter; the intensity of the light source is 50-300 mW / cm 2 ; the electrolyte for the cyclic voltammetry test is a 0.5-3 mol / L NaOH solution; ​ ​ ​ 8. The bulk sulfur-doped zinc iron oxide photoanode material of claim 7, wherein, ​ ​ 10. Use according to claim 9, characterized in that, The temperature of the photoelectrochemical water decomposition reaction is room temperature; the electrolyte used in the reaction is a NaOH solution; the simulated light source used in the reaction is a 300 W xenon lamp used in combination with an AM 1.5G filter; and the intensity of the light source is 50-300 mW / cm 2 .

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