High-efficiency Bi2MoO6Coated BiVO4Preparation method of heterojunction photoelectrode system
阅读说明：本技术 一种高效的Bi2MoO6包覆BiVO4异质结光电极体系的制备方法 (High-efficiency Bi2MoO6Coated BiVO4Preparation method of heterojunction photoelectrode system ) 是由 陈卓元 田景 冯昌 荆江平 孙萌萌 于 2020-11-19 设计创作，主要内容包括：本发明属于光催化技术领域,尤其涉及一种高效的Bi-2MoO-6包覆BiVO-4异质结光电极体系的制备方法。以FTO导电玻璃作为基底浸至BiOI的沉积液中,通过电化学沉积于基体形成BiOI薄膜,而后通过点涂及退火法使基体表面薄膜形成纯BiVO4膜；将上述基底浸泡至含硝酸铋,钼酸钠的沉积液中通过水热法制得Bi2MoO6包覆BiVO4异质结光电极体系。本发明BMO@BVO异质结光电极体系中Bi-2MoO-6包覆在BiVO-4上与BiVO-4接触良好并形成II异质结。BMO@BVO-2在AM 1.5G(100mW·cm～(-2))和λ>420nm(100mW·cm～(-2))的光照射下的光生电流密度分别为1.47mA·cm～(-2)和1.11mA·cm～(-2),分别为纯的BiVO-4的4.9倍和3.9倍；可见其高效且光电化学裂解水性能高。(The invention belongs to the technical field of photocatalysis, and particularly relates to high-efficiency Bi 2 MoO 6 Coated BiVO 4 A preparation method of a heterojunction photoelectrode system. Soaking FTO conductive glass as a substrate into the deposition solution of the BiOI, forming a BiOI film on the substrate through electrochemical deposition, and then spot-coatingForming a pure BiVO4 film on the surface film of the substrate by an annealing method; and soaking the substrate into a deposition solution containing bismuth nitrate and sodium molybdate to prepare a Bi2MoO 6-coated BiVO4 heterojunction photoelectrode system by a hydrothermal method. Bi in the BMO @ BVO heterojunction photoelectrode system 2 MoO 6 Coating on BiVO 4 Upper and BiVO 4 The contact is good and a II heterojunction is formed. BMO @ BVO-2 at AM1.5G (100 mW. cm) ‑2 ) And λ>420nm(100mW·cm ‑2 ) The photo-generated current densities under light irradiation of (1) were 1.47mA · cm ‑2 And 1.11mA · cm ‑2 Are respectively pure BiVO 4 4.9 times and 3.9 times; therefore, the high-efficiency photoelectrochemistry water splitting agent has high water splitting performance.)
1. High-efficiency Bi2MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: 1) soaking FTO conductive glass serving as a substrate into the deposition solution of the BiOI, forming a BiOI film on the substrate through electrochemical deposition, and forming a pure BiVO on the surface film of the substrate through a spot coating and annealing method4A film;
2) the substrate is soaked into a deposition solution containing bismuth nitrate and sodium molybdate to prepare Bi through a hydrothermal method2MoO6Coated BiVO4Heterojunction photoelectrode systems.
2. Highly potent Bi as claimed in claim 12MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: the deposition solution of the BiOI in the step 1) is Bi (NO)3)3·5H2Dissolving O in KI solution to obtain mixed solution A, wherein Bi (NO) in the mixed solution A3)3·5H2The final concentration of O is 0.02-0.06mol/L, the final concentration of KI is 0.02-0.06mol/L, and the pH value of the mixed solution A is adjusted to 1.7-2.0; dissolving p-benzoquinone in ethanol to obtain a mixed solution B with the final concentration of the p-benzoquinone of 0.1-0.3 mol/L; and mixing the mixed solution A and the mixed solution B according to the volume ratio of 5:1-5: 3.
3. Highly potent Bi as claimed in claim 12MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: after the substrate forms the BiOI film in the step 1), vanadium acetylacetonate passes throughPoint coating on the surface of BiOI, drying at 60-80 ℃, annealing at 400-450 ℃ for 2-5h, washing, and drying at room temperature, even if the film on the surface of the substrate forms pure BiVO4And (3) a membrane.
4. Highly potent Bi as claimed in claim 12MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: said step 2) adding Bi (NO)3)3·5H2O and Na2MoO4·2H2Adding O into ethylene glycol respectively, mixing the two solutions in a volume ratio of 1:1 to obtain a mixed solution A, and adding ethanol to obtain a deposition solution; wherein, Bi (NO) in the ethylene glycol3)3·5H2The final concentration of O is 2-8mol/L, Na2MoO4·2H2The final concentration of O is 1-4 mol/L; the volume ratio of the mixed solution A to the ethanol is 1:5-1: 3.
5. Bi of high efficiency according to any of claims 1 to 42MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps:
(1) preparation of BiVO4Substrate: cleaning FTO conductive glass as a substrate, soaking the cleaned FTO conductive glass in the FTO conductive glass, depositing a layer of BiOI film on the FTO in a deposition solution of BiOI by an electrochemical deposition method, then coating vanadium acetylacetonate on the surface of the BiOI film of a substrate by a point coating method, drying the BiOI film at 60-80 ℃, placing the substrate in a tube furnace after drying, raising the temperature to 400-450 ℃ at the heating rate of 5-10 ℃/min, annealing for 2-5h, washing the substrate by NaOH solution and deionized water after annealing, and drying the substrate at room temperature, namely forming pure BiVO on the surface of the substrate4A film;
(2) preparation of Bi2MoO6/BiVO4: adding Bi (NO)3)3·5H2O and Na2MoO4·2H2And respectively dissolving O in ethylene glycol, mixing the two solutions after the O is completely dissolved, adding the mixture into ethanol to obtain a clear solution, immersing the substrate obtained in the step 1) into the clear solution, reacting for 8 hours at 160 ℃ under a drying condition, and washing and drying to obtain the product.
6. Highly potent Bi as claimed in claim 52MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: the electrodeposition condition is a three-electrode system, 300s of deposition is carried out under the constant potential of-0.1V, and a BiOI film is formed on the surface of the substrate, wherein the electrode system is FTO 1 x 5cm2Is a working electrode, Ag/AgCl is a reference electrode, and Pt is a counter electrode.
7. Highly potent Bi as claimed in claim 52MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: pure BiVO is not formed on the substrate in the step 2)4The surface of the membrane is immersed downwards in the deposition solution for reaction.
8. Highly potent Bi as claimed in claim 52MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system is characterized by comprising the following steps: and cooling after the reaction, taking out, washing with water and ethanol for several times in sequence, and drying at 80 ℃ for 4 hours to obtain the product.
Technical Field
The invention belongs to the technical field of photocatalysis, and particularly relates to high-efficiency Bi2MoO6Coated BiVO4A preparation method of a heterojunction photoelectrode system.
Background
Since the discovery of TiO2Since solar energy can be utilized to crack water to generate hydrogen, the photoelectrochemical water cracking technology is increasingly considered as a potential technology for providing green energy and solving the problem of environmental pollution. Meanwhile, more and more photocatalysts are used in the fields of hydrogen production and oxygen production by photoelectrochemical decomposition of water, such as ZnO, WO3And BiVO4And the like. However, TiO2And the wider band gap of ZnO, results in its ability to absorb less than 5% of the ultraviolet light in the solar spectrum. And BiVO4Due to the fact that the material has a proper band gap width (2.4-2.6 eV), is non-toxic and high in stability, the material is considered to be one of the photoelectrode materials which have the most potential for realizing efficient photoelectrochemical water splitting performance. However BiVO4Also has the inherent disadvantages of slow carrier migration, low photon-generated carrier separation efficiency and the like, which greatly limits BiVO4The photoelectrode is applied to the field of photoelectrochemical water splitting. Thus, BiVO is improved by modification4The carrier migration rate of the photoelectrode and the separation efficiency of the photogenerated carriers and the final improvement of the photoelectrochemical water splitting performance of the photoelectrode are that BiVO is used4Push to the inevitable choice of practical application.
The heterojunction photoelectrode system is constructed, so that the separation efficiency of the photon-generated carriers can be improved, the migration rate of the photon-generated carriers is improved, and the purpose of improving the photoelectrochemistry cracking water performance is finally achieved. In recent years, Bi2MoO6Due to the proper forbidden band width (2.6-2.8eV) and the proper energy band position (E)CB-0.32eV) andthe shape is easy to control, and the like, so that the composite material is used for forming a heterojunction by being compounded with other semiconductors, and the photocatalytic or photoelectrochemical water splitting performance of a composite photoelectrode system is improved. However, at present for Bi2MoO6/BiVO4The system is less studied, in particular, for Bi2MoO6/BiVO4The system is less studied for photoelectrochemical water splitting. BiVO is prepared by spin-coating4Coating with Bi2MoO6Bi is prepared on the nanorod array2MoO6/BiVO4Heterojunction photoelectrode, Bi found2MoO6/BiVO4Has a ratio of Bi2MoO6And BiVO4All have excellent photoelectrochemical properties, but the defect that after the heterojunction is formed, the photoproduced electrons are formed by Bi2MoO6The conduction band is transferred to the coating layer BiVO4On the guide belt and coating a layer of BiVO4The contact area with the conductive substrate is small, the transfer of photogenerated electrons from the material to the conductive substrate is relatively slow, and the photogenerated carriers cannot be timely and effectively transmitted to the conductive substrate, so that Bi is enabled to be in2MoO6/BiVO4The photoelectrochemical properties of the photoelectrode are not outstanding.
Therefore, the design and preparation of simple and efficient energy band-matched Bi2MoO6/BiVO4Heterojunction photoelectrode systems still have great challenges to achieve fast transport of photogenerated carriers.
Disclosure of Invention
The main purpose of the present invention is to provide a high-efficiency Bi2MoO6Coated BiVO4A preparation method of a heterojunction photoelectrode system.
In order to achieve the purpose, the invention adopts the technical scheme that:
high-efficiency Bi2MoO6Coated BiVO4A preparation method of a heterojunction photoelectrode system,
1) soaking FTO conductive glass serving as a substrate into the deposition solution of the BiOI, forming a BiOI film on the substrate through electrochemical deposition, and forming a pure BiVO on the surface film of the substrate through a spot coating and annealing method4A film;
2) the substrate is soaked into a deposition solution containing bismuth nitrate and sodium molybdate to prepare Bi through a hydrothermal method2MoO6Coated BiVO4Heterojunction photoelectrode systems.
The deposition solution of the BiOI in the step 1) is Bi (NO)3)3·5H2Dissolving O in KI solution to obtain mixed solution A, wherein Bi (NO) in the mixed solution A3)3·5H2The final concentration of O is 0.02-0.06mol/L, the final concentration of KI is 0.02-0.06mol/L, and the pH value of the mixed solution A is adjusted to 1.7-2.0; dissolving p-benzoquinone in ethanol to obtain a mixed solution B with the final concentration of the p-benzoquinone of 0.1-0.3 mol/L; and mixing the mixed solution A and the mixed solution B according to the volume ratio of 5:1-5: 3.
After the BiOI thin film is formed on the substrate in the step 1), the vanadium acetylacetonate is coated on the surface of the BiOI by a point coating method, dried at the temperature of 60-80 ℃, annealed at the temperature of 400-450 ℃ for 2-5h, washed and dried at room temperature, even if the pure BiVO is formed on the thin film on the surface of the substrate4And (3) a membrane.
Said step 2) adding Bi (NO)3)3·5H2O and Na2MoO4·2H2Adding O into ethylene glycol respectively, mixing the two solutions in a volume ratio of 1:1 to obtain a mixed solution A, and adding ethanol to obtain a deposition solution; wherein, Bi (NO) in the ethylene glycol3)3·5H2The final concentration of O is 2-8mol/L, Na2MoO4·2H2The final concentration of O is 1-4 mol/L; the volume ratio of the mixed solution A to the ethanol is 1:5-1: 3.
It is further said that:
(1) preparation of BiVO4Substrate: cleaning FTO conductive glass as a substrate, soaking the cleaned FTO conductive glass in the FTO conductive glass, depositing a layer of BiOI film on the FTO in a deposition solution of BiOI by an electrochemical deposition method, then coating vanadium acetylacetonate on the surface of the BiOI film of a substrate by a point coating method, drying the BiOI film at 60-80 ℃, placing the substrate in a tube furnace after drying, raising the temperature to 400-450 ℃ at the heating rate of 5-10 ℃/min, annealing for 2-5h, washing the substrate by NaOH solution and deionized water after annealing, and drying the substrate at room temperature, namely forming pure BiVO on the surface of the substrate4A film;
(2) preparation of Bi2MoO6/BiVO4: adding Bi (NO)3)3·5H2O and Na2MoO4·2H2And respectively dissolving O in ethylene glycol, mixing the two solutions after the O is completely dissolved, adding the mixture into ethanol to obtain a clear solution, immersing the substrate obtained in the step 1) into the clear solution, reacting for 8 hours at 160 ℃ under a drying condition, and washing and drying to obtain the product.
The electrodeposition condition is a three-electrode system, 300s of deposition is carried out under the constant potential of-0.1V, and a BiOI film is formed on the surface of the substrate, wherein the electrode system is FTO 1 x 5cm2Is a working electrode, Ag/AgCl is a reference electrode, and Pt is a counter electrode.
Pure BiVO is not formed on the substrate in the step 2)4The surface of the membrane is immersed downwards in the deposition solution for reaction.
And cooling after the reaction, taking out, washing with water and ethanol for several times in sequence, and drying at 80 ℃ for 4 hours to obtain the product.
As can be seen from the above, Bi2MoO6Successfully coated on BiVO4Photoelectrode surface and BiVO (BiVO) unchanged4And Bi2MoO6@BiVO4The photoelectrochemical property of the photoelectrode is obviously improved, and the Bi with the best photoelectrochemical property is obtained under the irradiation of simulated sunlight2MoO6@BiVO4The photo-generated current density can reach 1.47mA cm-2Is pure BiVO44.9 times of photoelectrode, and Bi2MoO6@BiVO4The heterojunction photoelectrode also has excellent photoelectrochemical stability due to Bi2MoO6And BiVO4A good II type heterojunction system is formed, photogenerated carriers can escape from the surface of the electrode more easily, the recombination efficiency of photogenerated electrons and holes is remarkably inhibited under the action of the heterojunction system, the electron transfer rate is remarkably improved, and further Bi is enabled to be2MoO6@BiVO4The type II heterojunction photoelectrode has obvious high-efficiency stability.
The invention is high-efficiency Bi2MoO6Coated BiVO4The heterojunction photoelectrode system has the maximum light in the scanning voltage range when the precursor solution concentration is 2mM, namely BMO @ BVO-2The current density is generated. At AM1.5G 100mW cm-2Under the irradiation of light, the photoproduction current density of BMO @ BVO-2 can reach 1.47 mA-cm-2Is pure BiVO44.9 times of photoelectrode.
Compared with the prior art, the invention has the beneficial effects that:
(1) bi in the BMO @ BVO heterojunction photoelectrode system2MoO6Coating on BiVO4Upper and BiVO4The contact is good and a II heterojunction is formed. BMO @ BVO-2 at AM1.5G (100 mW. cm)-2) And λ>420nm(100mW·cm-2) The photo-generated current densities under light irradiation of (1) were 1.47mA · cm-2And 1.11mA · cm-2Are respectively pure BiVO44.9 times and 3.9 times; therefore, the high-efficiency photoelectrochemistry water splitting agent has high water splitting performance.
(2) The BMO @ BVO-2 heterojunction photoelectrode system has high photoelectric conversion efficiency, can convert more light energy into electric energy, and is beneficial to improvement of photoelectrochemical cracking water performance of the BMO @ BVO-2 heterojunction photoelectrode. In addition, the BMO @ BVO-2 heterojunction photoelectrode system has a smaller work function, so electrons of the photoelectrode system can escape more easily, and the BMO @ BVO-2 heterojunction photoelectrode has better photoelectrochemistry cracking water performance.
(3) The photoelectrochemical cracking aqueous performance improvement of the BMO @ BVO-2 heterojunction photoelectrode system is also attributed to the fact that the heterojunction is constructed, so that the separation efficiency of photon-generated carriers is improved, and the migration of the carriers is accelerated. Bi2MoO6@BiVO4The design and preparation of the II type heterojunction photoelectrode provide important theoretical basis for further developing the efficient and stable photoelectrode.
Drawings
FIG. 1 is a sample XRD pattern of a series of BMO @ BVO-2 heterojunction photoelectrode systems provided by an example of the present invention;
FIG. 2 is a Raman spectrum of a series of samples of a BMO @ BVO-2 heterojunction photoelectrode system provided by an embodiment of the invention;
FIG. 3 is SEM and HRTEM images of a series of BMO @ BVO-2 heterojunction photoelectrode systems provided by an embodiment of the invention; wherein FIG. 3a is the SEM topography of the BVO, FIG. 3b is the SEM topography of BMO @ BVO-1 of example 3, FIG. 3c is the SEM topography of BMO @ BVO-2 of example 2, FIG. 3d is the SEM topography of BMO @ BVO-3 of example 3, FIG. 3e is the SEM topography of BMO @ BVO-4 of example 4, FIG. 3f is the SEM topography of the BMO, FIGS. 3g and h are TEM images of BMO @ BVO-2 of example 2, and FIG. 3i is the STEM Mapping graph of BMO @ BVO-2 of example 2;
FIG. 4 is an EDS plot of BMO @ BVO-2 of example 2 of the present invention;
FIG. 5 is a XPS total measurement spectrum of BMO @ BVO-2 of example 2 of the present invention;
FIG. 6 is an XPS spectrum of BMO @ BVO-2 of example 2 of the present invention; wherein fig. 6a is a Bi 4f XPS core spectrum, fig. 6b is a V2 p XPS core spectrum, fig. 6c is a Mo3d XPS core spectrum, and fig. 6d is an O1s XPS core spectrum;
FIG. 7 is a chart of the UV-VIS absorption spectra of a series of samples of a BMO @ BVO-2 heterojunction photoelectrode system provided by an example of the present invention;
FIG. 8 is an i-t curve and an i-V curve at 1V bias (vs Ag/AgCl) for a series of BMO @ BVO-2 heterojunction photoelectrode systems provided by an example of the present invention, all at 0.1M Na2SO4The measurement in solution of (a); wherein, FIG. 8a is the i-t curve of the series of samples under AM1.5G, FIG. 8b is the i-t curve of the series of samples under visible light, FIG. 8c is the i-V curve of the series of samples under AM1.5G, FIG. 8d is the i-V curve of the series of samples under visible light, FIG. 8e is the long-time photo-induced current density change curve of BMO @ BVO-2 of example 2 under AM1.5G, and FIG. 8f is the IPCE spectrogram of the series of samples under 1V bias (vs Ag/AgCl);
FIG. 9 is a surface charge distribution plot for a series of samples measured by SKP techniques provided by an embodiment of the present invention;
FIG. 10 is a graph of surface work function, PL and EIS for a series of samples provided by an embodiment of the present invention; wherein FIG. 10a is the surface work function converted from the measurements of FIG. 9, FIG. 10b is the PL test results for BVO, BMO and BMO @ BVO-2 of example 2, and FIG. 10c is the EIS plot for BVO, BMO and BMO @ BVO-2 of example 2;
FIG. 11 is a Mott-Schottky curve and linear fit plot of BVO and BMO prepared according to examples of the present invention;
fig. 12 shows the forbidden bandwidths of BVO and BMO obtained by the Tauc formula according to an embodiment of the present invention;
FIG. 13 is a schematic diagram of the mechanism of enhancement of photoelectrochemical properties of BMO @ BVO-2 of example 2 of the present invention under AM1.5G light.
Detailed Description
The following examples are given to facilitate a better understanding of the invention, but do not limit the invention. The experimental procedures in the following examples are conventional unless otherwise specified.
The invention provides a high-efficiency BMO @ BVO heterojunction photoelectrode system and photoelectrochemistry cracking water performance thereof. Bi2MoO6Coating on BiVO4Upper and BiVO4The contact is good and a II heterojunction is formed. BMO @ BVO-2 at AM1.5G (100 mW. cm)-2) And λ>420nm(100mW·cm-2) The photo-generated current densities under light irradiation of (1) were 1.47mA · cm-2And 1.11mA · cm-2Are respectively pure BiVO44.9 times and 3.9 times. The BMO @ BVO-2 heterojunction photoelectrode body has high photoelectric conversion efficiency, can convert more light energy into electric energy, and is favorable for improving the photoelectrochemical cracking water performance of the BMO @ BVO-2 heterojunction photoelectrode. In addition, the BMO @ BVO-2 heterojunction photoelectrode system has a smaller work function, so electrons of the photoelectrode system can escape more easily, and the BMO @ BVO-2 heterojunction photoelectrode has better photoelectrochemistry cracking water performance. The photoelectrochemical cracking aqueous performance improvement of the BMO @ BVO-2 heterojunction photoelectrode is also attributed to that the separation efficiency of a photon-generated carrier is improved and the migration of the carrier is accelerated by the construction of the heterojunction. Bi2MoO6@BiVO4The design and preparation of the II type heterojunction photoelectrode provide important theoretical basis for further developing the efficient and stable photoelectrode.
Example 1
High efficiency of Bi2MoO6Coated BiVO4The preparation method of the heterojunction photoelectrode system comprises the following steps of:
(1) preparation of BiVO4Substrate: 1 x 5cm2The FTO conductive glass is used as BiVO4And (4) growing a substrate. Placing FTO in a volume ratio of 1: 1:1 mixture of ethanol, acetone and waterUltrasonically cleaning the FTO substrate in a solution for 15min, then ultrasonically cleaning the FTO substrate in deionized water for 15min, airing to obtain a clean FTO substrate, soaking the FTO substrate in a deposition solution of the BiOI by an electrochemical deposition method, wherein the deposition conditions are as follows: three-electrode system (FTO 1 x 5 cm)2Is a working electrode, Ag/AgCl is a reference electrode, Pt is a counter electrode), and the BiOI thin film is obtained on the surface of an FTO substrate by depositing for 300s under the constant potential of 0.1V; then, 0.6mL of 0.02M vanadium acetylacetonate is taken to be coated on the surface of the BiOI film by a spot coating method, dried at 80 ℃, annealed at 450 ℃ for 2h (the temperature rise speed is 5 ℃/min) in a tube furnace, and finally cleaned in 1mol/L NaOH solution for 30min to remove redundant V2O5Washing with deionized water, and air drying at room temperature to obtain pure BiVO4Sample, labeled BVO.
Wherein the deposition solution of the BiOI is 4mmol of Bi (NO)3)3·5H2O was dissolved in 100mL of a KI solution containing 4mmol, the pH was adjusted to 1.7 with dilute nitric acid, and then mixed with 40mL of ethanol containing 9mmol of p-benzoquinone.
(2) Preparation of Bi2MoO6/BiVO4: 2mM of Bi (NO)3)3·5H2O and 1mM Na2MoO4·2H2Dissolving O in 12.5mL of ethylene glycol under stirring (ultrasonic) respectively, mixing the two solutions after completely dissolving, continuously stirring for about 10min, slowly adding 75mL of ethanol, continuously stirring for 10min to obtain a clear solution, pouring the clear solution into a reaction kettle, and simultaneously adding 1 piece of sample 1 x 5cm obtained in the step (1)2(FTO, conductive side down, i.e., pure BiVO is not formed on the substrate4The surface of the film faces downwards), the mixture is placed in a drying box, the reaction is carried out for 8 hours at 160 ℃, the mixture is taken out after cooling, the mixture is washed by water and ethanol for a plurality of times and dried for 4 hours at 80 ℃, and the obtained sample is Bi2MoO6/BiVO4According to the addition of Bi (NO)3)3·5H2O and Na2MoO4·2H2The amount of O marks the sample as BMO @ BVO-1 (see FIGS. 1, 2 and 3).
Example 2
High efficiency of Bi2MoO6Coated BiVO4A preparation method of a heterojunction photoelectrode system, wherein the concentration of the precursor is 2 mM.
The method comprises the following specific steps:
(1) preparation of BiVO4Substrate: 1 x 5cm2The FTO conductive glass is used as BiVO4And (4) growing a substrate. Placing FTO in a volume ratio of 1: 1:1, ultrasonically cleaning for 15min in a mixed solution of ethanol, acetone and water, then ultrasonically cleaning for 15min in deionized water, drying to obtain a clean FTO substrate, soaking the FTO substrate in a deposition solution of the BiOI by an electrochemical deposition method, wherein the deposition conditions are as follows: three-electrode system (FTO 1 x 5 cm)2Is a working electrode, Ag/AgCl is a reference electrode, Pt is a counter electrode), depositing for 300s under the constant potential of 0.1V to obtain a BiOI film on the surface of an FTO substrate, then coating 0.6mL of 0.02M vanadium acetylacetonate on the surface of the BiOI film by a spot coating method, drying at 80 ℃, annealing for 2h at 450 ℃ in a tube furnace (the heating rate is 5 ℃/min), and finally cleaning for 30min in 1mol/L NaOH solution to remove the redundant V2O5Washing with deionized water, and air drying at room temperature to obtain pure BiVO4Sample, labeled BVO. Wherein the deposition solution of the BiOI is 4mmol of Bi (NO)3)3·5H2O was dissolved in 100mL of a KI solution containing 4mmol, the pH was adjusted to 1.7 with dilute nitric acid, and then mixed with 40mL of ethanol containing 9mmol of p-benzoquinone.
(2) Preparation of Bi2MoO6/BiVO4: adding 4mM Bi (NO)3)3·5H2O and 2mM Na2MoO4·2H2Respectively stirring (ultrasonically) O to dissolve in 12.5mL of ethylene glycol, mixing the two solutions after completely dissolving, continuously stirring for about 10min, slowly adding 75mL of ethanol, continuously stirring for 10min to obtain a clear solution, pouring the clear solution into a reaction kettle, and simultaneously adding 1 piece of the sample (FTO, BiVO) obtained in the step (1)4Face down), reacting for 8h at 160 ℃, cooling, taking out, washing with water and ethanol for several times, and drying for 4h at 80 ℃ to obtain a sample Bi2MoO6/BiVO4According to the addition of Bi (NO)3)3·5H2O and Na2MoO4·2H2The amount of O marks the sample as BMO @ BVO-2 (see FIG. 1, FIG. 2, FIG. 3, and FIG. 4).
Example 3
High efficiency of Bi2MoO6Coated BiVO4A preparation method of a heterojunction photoelectrode system, wherein the concentration of the precursor is 2 mM.
The method comprises the following specific steps:
(1) preparation of BiVO4Substrate: 1 x 5cm2The FTO conductive glass is used as BiVO4And (4) growing a substrate. Placing FTO in a volume ratio of 1: 1:1, ultrasonically cleaning for 15min in a mixed solution of ethanol, acetone and water, then ultrasonically cleaning for 15min in deionized water, drying to obtain a clean FTO substrate, soaking the FTO substrate in a deposition solution of the BiOI by an electrochemical deposition method, wherein the deposition conditions are as follows: three-electrode system (FTO 1 x 5 cm)2Is a working electrode, Ag/AgCl is a reference electrode, Pt is a counter electrode), depositing for 300s under the constant potential of 0.1V to obtain a BiOI film on the surface of an FTO substrate, then coating 0.6mL of 0.02M vanadium acetylacetonate on the surface of the BiOI film by a spot coating method, drying at 80 ℃, annealing for 2h at 450 ℃ in a tube furnace (the heating rate is 5 ℃/min), and finally cleaning for 30min in 1mol/L NaOH solution to remove the redundant V2O5Washing with deionized water, and air drying at room temperature to obtain pure BiVO4Sample, labeled BVO. Wherein the deposition solution of the BiOI is 4mmol of Bi (NO)3)3·5H2O was dissolved in 100mL of a KI solution containing 4mmol, the pH was adjusted to 1.7 with dilute nitric acid, and then mixed with 40mL of ethanol containing 9mmol of p-benzoquinone.
(2) Preparation of Bi2MoO6/BiVO4: adding 6mM Bi (NO)3)3·5H2O and 3mM Na2MoO4·2H2Respectively stirring (ultrasonically) O to dissolve in 12.5mL of ethylene glycol, mixing the two solutions after completely dissolving, continuously stirring for about 10min, slowly adding 75mL of ethanol, continuously stirring for 10min to obtain a clear solution, pouring the clear solution into a reaction kettle, and simultaneously adding 1 piece of the sample (FTO, BiVO) obtained in the step (1)4Face down), reacting for 8h at 160 ℃, cooling, taking out, washing with water and ethanol for several times, and drying for 4h at 80 ℃ to obtain a sample Bi2MoO6/BiVO4According to the addition of Bi (NO)3)3·5H2O and Na2MoO4·2H2The amount of O marks the sample as BMO @ BVO-3 (see FIG. 1, FIG. 2, FIG. 3, and FIG. 4).
Example 4
High efficiency of Bi2MoO6Coated BiVO4A preparation method of a heterojunction photoelectrode system, wherein the concentration of the precursor is 2 mM.
The method comprises the following specific steps:
(1) preparation of BiVO4Substrate: 1 x 5cm2The FTO conductive glass is used as BiVO4And (4) growing a substrate. Placing FTO in a volume ratio of 1: 1:1, ultrasonically cleaning for 15min in a mixed solution of ethanol, acetone and water, then ultrasonically cleaning for 15min in deionized water, drying to obtain a clean FTO substrate, soaking the FTO substrate in a deposition solution of the BiOI by an electrochemical deposition method, wherein the deposition conditions are as follows: three-electrode system (FTO 1 x 5 cm)2Is a working electrode, Ag/AgCl is a reference electrode, Pt is a counter electrode), depositing for 300s under the constant potential of 0.1V to obtain a BiOI film on the surface of an FTO substrate, then coating 0.6mL of 0.02M vanadium acetylacetonate on the surface of the BiOI film by a spot coating method, drying at 80 ℃, annealing for 2h at 450 ℃ in a tube furnace (the heating rate is 5 ℃/min), and finally cleaning for 30min in 1mol/L NaOH solution to remove the redundant V2O5Washing with deionized water, and air drying at room temperature to obtain pure BiVO4Sample, labeled BVO. Wherein the deposition solution of the BiOI is 4mmol of Bi (NO)3)3·5H2O was dissolved in 100mL of a KI solution containing 4mmol, the pH was adjusted to 1.7 with dilute nitric acid, and then mixed with 40mL of ethanol containing 9mmol of p-benzoquinone.
(2) Preparation of Bi2MoO6/BiVO4: adding 8mM Bi (NO)3)3·5H2O and 4mM Na2MoO4·2H2Respectively stirring (ultrasonically) O to dissolve in 12.5mL of ethylene glycol, mixing the two solutions after completely dissolving, continuously stirring for about 10min, slowly adding 75mL of ethanol, continuously stirring for 10min to obtain a clear solution, pouring the clear solution into a reaction kettle, and simultaneously adding 1 piece of the sample (FTO, BiVO) obtained in the step (1)4Face down), reacting at 160 deg.C for 8 hr, cooling, washing with water and ethanolDrying for 4 hours at 80 ℃ for several times to obtain a sample which is Bi2MoO6/BiVO4According to the addition of Bi (NO)3)3·5H2O and Na2MoO4·2H2The amount of O marks the sample as BMO @ BVO-4 (see FIG. 1, FIG. 2, FIG. 3, and FIG. 4).
The experimental results are as follows:
as can be seen from FIG. 1, the series of sample XRD patterns, in which the diffraction peaks at 26.58 °, 37.77 °, 51.76 ° and 65.74 ° for 2 θ correspond to the (110), (200), (211) and (301) crystal planes (PDF #46-1088) of FTO; diffraction peaks at 18.67 °, 28.95 °, 30.55 °, 35.22 ° and 47.30 ° 2 θ correspond to monoclinic phase BiVO4The (110), (121), (040), (002) and (042) planes (PDF # 14-0688); diffraction peaks at 28.31 °, 32.53 °, 46.74 °, 55.44 ° and 58.48 ° 2 θ correspond to orthorhombic Bi2MoO6The (131), (200), (202), (331) and (262) crystal planes (PDF # 21-0102). BiVO4Photoelectrode hydrothermal coating Bi in different precursors2MoO6Thereafter, only significant BiVO was observed in the XRD patterns of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrodes4Does not find Bi2MoO6May be due to Bi2MoO6Are relatively dispersed.
As can be seen from FIG. 2, the Raman spectrum of the series of samples, BiVO4815cm in Raman spectrum of photoelectrode-1The peak at corresponds to VO4Symmetrical stretching mode of 123cm-1And 208cm-1The peak at corresponds to VO4Bending mode [21 ]]This also further illustrates BiVO4The successful synthesis of the compound. Bi2MoO6715cm in Raman spectrum of photoelectrode-1、796cm-1And 844cm-1Corresponds to octahedral MoO6Stretching mode of Mo-O in [21 ]]This also further illustrates Bi2MoO6The successful preparation. In BiVO4Loaded with different amounts of Bi2MoO6Then, the Raman spectra of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode are 815cm-1Peak at (b) compared with pure BiVO4Slightly widened, which may be byIn Bi2MoO6And BiVO4The effect of heterojunction formation between them.
From FIG. 3, SEM and HRTEM images of series of samples, pure BiVO in FIG. 3a4The nano-worm has an average particle size of about 80nm, and gaps exist among the nano-worm structures, so that the photoelectrode material can be in full contact with a solution. FIG. 3f is pure Bi2MoO6From the SEM image, it can be found that pure Bi is present2MoO6Is nanosphere of about 200 nm. BiVO (bismuth oxide) is added4Are placed in different concentrations of Bi2MoO6After hydrothermal reaction in the precursor, the surface morphologies of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode are changed. The BMO @ BVO-1 nano-worm-like structure in FIG. 3b was not changed, but the nano-worms were significantly coarsened, which indicates that BiVO4The surface of the photoelectrode is successfully coated with Bi2MoO6. With Bi2MoO6The BMO @ BVO-2 (figure 3c) still presents a nano-worm-like structure due to the increase of the concentration of the precursor solution, and the nano-worms become thicker, indicating that BiVO4Bi coated on surface of photoelectrode2MoO6The amount of (a) increases. FIG. 3i is a STEM Mapping chart of a prepared BMO @ BVO-2 photoelectrode, and the uniform distribution of four elements of Bi, V, O and Mo can be found, which shows that Bi2MoO6In BiVO4Are uniformly distributed. With Bi2MoO6The concentration of the precursor solution is further increased, BiVO4Bi coated on surface of photoelectrode2MoO6The amount of (b) is further increased, the BMO @ BVO-3 (fig. 3d) is changed from a nano worm-like structure to irregular large particles, and the inter-particle voids are significantly reduced, which is not favorable for sufficient contact of the photoelectrode material with the electrolyte solution, and may cause deterioration of photoelectrochemical properties. Further increase of Bi2MoO6When the concentration of the precursor solution is high, BiVO4Bi coated on surface of photoelectrode2MoO6The amount of (B) is further increased, and Bi2MoO6In BiVO4A dense thin film is formed on the surface of the photoelectrode, and the gaps among the particles disappear, which may also result in the deterioration of the photoelectrochemical properties of the photoelectrode. Further prepared by HRTEM pairThe micro-topography of the BMO @ BVO-2 photoelectrode of (a) was characterized as shown in fig. 3g and fig. 3 h. FIG. 3g is an HRTEM image under a low power microscope, and the nano-worm-like BiVO can be clearly observed4And BiVO4The surface of the film is coated with a layer of irregular Bi2MoO6. FIG. 3h is an HRTEM image under a high power lens, in which BiVO can be seen4And Bi2MoO6A distinct heterojunction interface, a lattice spacing of 0.308nm corresponding to BiVO4The lattice spacings of 0.210nm and 0.326nm of (121) correspond to Bi2MoO6The (142) and (140) crystal planes of (1). The results of both SEM and HETEM indicate successful fabrication of BMO @ BVO heterojunction photoelectrodes.
As can be seen from the EDS chart of BMO @ BVO-2 in FIG. 4, the presence of Bi, V, O, Mo, etc. is observed, which is consistent with the elemental composition of BMO @ BVO.
As can be seen from the XPS summary plot of FIG. 5BMO @ BVO-2, the BMO @ BVO-2 photoelectrode prepared therefrom was found to have elements such as Bi, V, O, M and C, where the element C was from the background C of the XPS test, consistent with the elemental composition of BMO @ BVO-2.
It can be seen from the XPS spectrum of FIG. 6BMO @ BVO-2, where FIG. 6a is the XPS spectrum of Bi 4f, where the binding energies at 159.4eV and 164.6eV correspond to BiVO4And Bi2MoO6Middle Bi3+Bi 4f of7/2And Bi 4f5/2. FIG. 6b is an XPS spectrum of V2 p, in which the binding energy at 516.4eV corresponds to BiVO4Middle V5+. FIG. 6c is an XPS spectrum of Mo3d, in which the binding energies at 232.4eV and 235.6eV are attributed to Bi2MoO6Middle Mo6+Mo3d of5/2And Mo3d3/2. FIG. 6d is an XPS spectrum of O1s showing binding energies at 530.1eV and 531.6eV corresponding to BiVO4And Bi2MoO6And adsorbed oxygen on the surface of the photoelectrode. The XPS results further demonstrate the successful fabrication of the BMO @ BVO heterojunction.
FIG. 7 is the UV-VIS absorption spectrum of a series of samples from which pure BiVO can be seen4The light absorption threshold of the photoelectrode is about 500nm and is in BiVO4Coating Bi by a hydrothermal method2MoO6Thereafter, the light absorption thresholds of BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 were not substantially changed.
FIG. 8 is an i-t curve and an i-V curve for a series of samples at 1V bias (vs Ag/AgCl), all at 0.1M Na2SO4Is measured in the solution of (1). From FIG. 8a, it can be seen that pure BiVO4And Bi2MoO6Photoelectrode is AM1.5G 100mW cm-2The photo-generated current density under irradiation is 0.3mA cm-2And 0.16. mu.A. cm-2. BiVO (bismuth oxide) is added4Placing the precursor solution with different concentrations for hydrothermal coating of Bi2MoO6And then, the photo-generated current density of the BMO @ BVO series photoelectrode is improved to different degrees. And the photo-generated current density of the BMO @ BVO heterojunction photoelectrode is increased and then decreased along with the increase of the concentration of the precursor solution in the hydrothermal reaction, and the photo-generated current densities of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 are respectively 1.33 mA-cm-2，1.47mA·cm-2，1.35mA·cm-2And 1.23mA · cm-2. Wherein the BMO @ BVO-2 photoelectrode has the highest photo-generated current density and is pure BiVO44.9 times of that of pure Bi2MoO6Several thousand times higher, indicating that the precursor concentration is optimal at 2 mM. FIG. 8c is a graph of BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3, BMO @ BVO-4 and BMO at AM1.5G 100 mW. cm-2Photoinduced i-V curve under irradiation, tested at 0.1M Na2SO4In solution. As can be seen from FIG. 8c, Bi2MoO6The photo-generated current density is very small and the change of the photo-generated current density along with the voltage cannot be seen. And the photo-generated current density of other prepared series photoelectrodes is continuously increased along with the increase of the applied bias voltage. BiVO4Still has smaller photo-generated current density, and BiVO4Placing the precursor solution with different concentrations for hydrothermal coating of Bi2MoO6Then, the photo-generated current density of the BMO @ BVO photoelectrode is improved to different degrees, and the BMO @ BVO-2 has the maximum photo-generated current density in the scanning voltage range, which also indicates that the precursor solution concentration is 2mM which is the most suitable concentration. FIGS. 8b and 8d are prepared BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3, BMO @ BVO-4And BMO in visible light (lambda)>420nm,100mW cm-2) I-t and i-V curves under illumination. As can be seen in FIG. 8b, pure BiVO4The photo-generated current density under the irradiation of visible light is only 0.28mA cm-2Hydrothermal coating of Bi in precursor solutions of different concentrations2MoO6Then, the variation trend of the photo-generated current density of the BMO @ BVO photoelectrode is shown in FIG. 8a as AM1.5G 100mW cm-2The change in photo-generated current density under illumination is substantially uniform. The photoproduction current densities of BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 were 1.07mA cm-2，1.11mA·cm-2，0.93mA·cm-2And 0.85mA · cm-2. Wherein the BMO @ BVO-2 photoelectrode has the highest photo-generated current density and is pure BiVO43.9 times of the photoelectrode is Bi2MoO6Thousands of times as many photoelectrodes as possible. Visible light (λ) in FIG. 8d>420nm,100mW·cm-2) The trend of the photoinduced i-V curve under irradiation is compared with that at AM1.5G 100mW cm in FIG. 8c-2The variation under illumination is substantially uniform.
I-t and i-V curves under simulated sunlight and visible light are combined to find that the photoelectrochemical performance of the BMO @ BVO-2 photoelectrode is compared with BiVO4And Bi2MoO6Are greatly improved, which shows that the generation and separation efficiency of the photon-generated carriers are greatly improved. BiVO4And Bi2MoO6Has good energy band matching degree, and proper amount of Bi2MoO6Coating to BiVO4In the above process, a heterojunction electric field is formed at the contact interface of the two, and the photogenerated carriers are efficiently and orderly separated under the action of the heterojunction electric field; at the same time, a proper amount of Bi2MoO6Coating and reserving BiVO4The porous structure of the photoelectrode thin film (shown in figure 3c) is beneficial to the full contact of the photoelectrode material and the electrolyte solution, so that the photo-generated holes can be rapidly transferred out to be consumed by reacting with the electrolyte solution, and therefore, the BMO @ BVO-2 has the best photoelectrochemical property. For BMO @ BVO-1, Bi2MoO6Has a small coating amount of BiVO4And Bi2MoO6The heterojunction electric field formed between the two is not enough to effectively separate photon-generated carriers, so that the BMO @ BVO-1 is inferior to the BMO @ BVO-2 in terms of the BMO @ BVO-1 but superior to the BMO @ BVO-2BiVO4And Bi2MoO6Photoelectrochemical properties of (a). And for BMO @ BVO-3 and BMO @ BVO-4 photoelectrodes, the coated Bi2MoO6In a large amount, and can form a heterojunction to accelerate the separation of photogenerated carriers, but the excess Bi2MoO6Block BiVO4The porous structure of the photoelectrode film is not beneficial to the full contact of the photoelectrode material and the electrolyte solution, so that the photoproduction holes can not be timely and effectively reacted with the electrolyte solution to be consumed, and the BMO @ BVO-3 and BMO @ BVO-4 have the characteristics of being inferior to BMO @ BVO-2 but superior to BiVO4And Bi2MoO6Photoelectrochemical properties of (a).
Next, the AM1.5G (100 mW. cm) was passed for a long time-2) Testing of photoinduced i-t curves under illumination the stability of the prepared BMO @ BVO-2 heterojunction photoelectrode was investigated, as shown in FIG. 8e, tested at 0.1M Na2SO4In solution. FIG. 8e shows that after 1000s of intermittent on-off light testing, the photo-generated current density of the BMO @ BVO-2 photo-electrode remained at 1.35 mA-cm–2The above shows that it has good stability.
The photoelectric conversion efficiency of the prepared series photoelectrode is further analyzed by testing the photo-generated current density under the irradiation of monochromatic light. Generally, IPCE is calculated by equation (1):
wherein Isc is the photo-generated current density (mA-cm) generated by the photoelectrode-2) I is the wavelength (nm) and Pin is the intensity of monochromatic light (mW. cm)-2). Therefore, the value of IPCE can be obtained by calculation by measuring the intensity of light at a single wavelength and the density of the photo-generated current generated by the photoelectrode. FIG. 8f shows Na concentration at 0.1M2SO4And calculating the photoelectric conversion efficiency of the prepared BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode according to the measured photo-generated current density. FIG. 8f shows that BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 all have strong light absorption within 500nmThis is consistent with the results of the uv-vis diffuse reflectance spectrum in fig. 7. Pure BiVO4The IPCE value of the photoelectrode is small, being about 8.82% (380nm) at the maximum. Coated with Bi2MoO6The IPCE values of BMO @ BVO heterojunction photoelectrode series are improved to different degrees, the IPCE values of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode series are respectively 12.64-28.05%, 13.37-29.46%, 10.85-27.75% and 7.90-18.70% within 360-480 nm, and the IPCE values of the photoelectrode series are maximum at 380nm, and the result shows that the IPCE values of the Bi @ BVO heterojunction photoelectrode series are Bi @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @2MoO6The coating obviously enhances the photoelectric conversion efficiency of the BMO @ BVO photoelectrode. Meanwhile, BMO @ BVO-2 has the highest photoelectric conversion efficiency compared with pure BiVO4The improvement is 20.64% (at 380 nm).
FIG. 9 is a surface charge distribution plot of a series of samples measured by the SKP technique, from which BiVO can be seen4Has a surface potential of 0 +/-49 mV and is loaded with Bi2MoO6Then, the surface potentials of the BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 photoelectrode all become negative, and the surface potential values thereof are respectively-114.5 +/-61.5 mV, -364 +/-56 mV, -199 +/-50 mV and-100.5 +/-50.5 mV, wherein the surface potential of the BMO @ BVO-2 is most negative and is more negative than that of pure Bi2MoO6The lower the 364 mV. The surface WFs of the prepared electrode has the following relationship with the surface voltage measured by SKP:
where wf (sample) is the work function for preparing the photoelectrode, wf (tungsten) is the surface potential (4.55eV) relative to the tungsten reference electrode, and aw (photoelectrode) is the surface potential of the photoelectrode obtained according to the SKP test.
FIG. 10 is a graph of surface work function, PL and EIS for a series of samples, showing the magnitude of the work function of the photoelectrode calculated by equation (2) as shown in FIG. 10a, where BVO, BMO @ BVO-1, BMO @ BVO-2, BMO @ BVO-3 and BMO @ BVO-4 electrodes have work functions of 4.55eV, 4.39eV, 4.19eV, 4.35eV and 4.45eV, respectively, with the BMO @ BVO-2 photoelectrode having the lowest work function, indicating that it has the least energy required to escape electronsThat is, electrons of BMO @ BVO-2 flow out of the electrode material and participate in the reaction more easily, and thus it has more excellent photoelectrochemical properties. FIG. 10b shows the PL test results for BVO, BMO @ BVO-2 and BMO photoelectrodes with an excitation wavelength of 325 nm. For semiconductors, when excited by light, electrons in the valence band are excited to transition to the conduction band, leaving photogenerated holes in the valence band. A part of photo-generated electrons and photo-generated holes can be separated to generate photo-generated current or generate oxidation-reduction reaction with other substances; another portion of the photogenerated electrons and holes recombine secondarily releasing energy, which can be detected by PL spectroscopy. Generally, the stronger the peak intensity of the PL spectrum, the stronger the recombination capability of photogenerated carriers and the poorer the photoelectrochemical properties. In FIG. 10b, compared to pure BiVO4And pure Bi2MoO6The PL spectrum intensity of the photoelectrode, BMO @ BVO-2 photoelectrode, was greatly reduced, indicating that the separation capability of its photogenerated carriers was greatly improved, which was attributed to the construction of the heterojunction. Therefore, the BMO @ BVO-2 photoelectrode has better photoelectrochemical properties.
In addition to the separation capability of photogenerated carriers, the mobility of carriers is also one of the factors that affect the photoelectrochemical properties of the photoelectrode. The EIS test can be used for characterizing the migration capability of the current carrier of the photoelectrode material, and the smaller the impedance arc radius in the EIS is, the better the migration capability of the current carrier of the photoelectrode material is represented. FIG. 10c is an EIS plot of the prepared BVO, BMO @ BVO-2 and BMO electrodes, from which it can be seen that BMO @ BVO-2 has a greatly reduced arc radius of resistance compared to BVO and BMO, indicating better carrier mobility. The construction of the heterojunction reduces the charge transfer potential of the thin-film electrode, so that carriers can be transferred to the surface of the electrode material more quickly after being generated, thereby having better photoelectrochemical properties.
FIG. 11 is a Mott-Schottky curve and line fit plot of the prepared BVO and BMO from which BiVO can be found4And Bi2MoO6The slopes of (a) and (b) are both positive values, indicating that both are n-type semiconductors. Meanwhile, the Mott-Schottky linear part is extended to the horizontal axis to obtain BiVO4And Bi2MoO6Flatness of photoelectrodeThe charged sites were 0.64V (vs RHE) and 0.22V (vs RHE), respectively. The valence band potential, the forbidden band width and the conduction band potential of the semiconductor photoelectrode have the following relations:
Eg＝EVB-ECB (3)
wherein E isVBIs the value of the valence band potential of the semiconductor photoelectrode, EgIs the value of the forbidden band width of the semiconductor photoelectrode, ECBIs the value of the conduction band potential of the semiconductor photoelectrode.
Fig. 12 shows the forbidden bandwidths of BVO and BMO obtained from the Tauc formula, and the straight line part of the graph obtained in the graph is extrapolated to the abscissa axis, and the intersection point is the forbidden bandwidth value for preparing the photoelectrode. As can be seen from the figure, BiVO is prepared4And Bi2MoO6The band gaps of the photoelectrode are 2.48eV and 2.85eV respectively. Thus, BiVO is calculated by the formula (3)4And Bi2MoO6The valence band potentials of the photoelectrode were 3.12V and 3.07V, respectively. Bi2MoO6The potential of the conduction band is negative to BiVO4And BiVO4Valence band potential of (B) is greater than Bi2MoO6This also confirms BiVO4And Bi2MoO6The method has good energy band matching, is beneficial to the construction of II type heterojunction, accelerates the effective separation of photon-generated carriers, and improves the photoelectrochemical property.
FIG. 13 is a schematic diagram of the enhanced photoelectrochemical properties of the BMO @ BVO-2 of example 2 under AM1.5G light, the BMO @ BVO heterojunction photoelectrode system having a higher than pure BiVO4And Bi2MoO6The photogenerated current density is obviously enhanced, which shows that the two have better energy band matching and form a II type heterojunction system with better energy band matching. BiVO prepared according to FIG. 124And Bi2MoO6The forbidden band widths of the photoelectrode are respectively 2.48eV and 2.85eV, and BiVO can be obtained through Figure S94And Bi2MoO6Relation of conduction band potential of photoelectrode EBi2MoO6(0.22V(vs RHE))＜EBiVO4(0.64V (vs RHE)), and the relationship E between the valence band potentialsBiVO4(3.12V(vs RHE))＞EBi2MoO6(3.07V (vs RHE)). After being excited by illumination, Bi2MoO6The photo-generated electrons on the conduction band can be transferred to BiVO4Further transferred to an FTO conductive substrate and finally transferred to a Pt electrode to remove H+Reducing to hydrogen; at the same time, BiVO4Bi to which photogenerated holes in the valence band can be transferred2MoO6The valence band is eventually consumed by the oxidation reaction associated with the electrolyte solution. Therefore, a large amount of photo-generated electrons can be transferred to the Pt electrode, so that the BMO @ BVO heterojunction photoelectrode has better photoelectrochemistry water splitting performance.
And as can be seen from the above examples, the obtained high-efficiency Bi2MoO6Coated BiVO4The heterojunction photoelectrode system is prepared by experiments on 4 samples with different precursor concentrations, and when the precursor concentration is 2mM, BMO @ BVO-2 has the maximum photoproduction current density in a scanning voltage range. Due to BiVO4And Bi2MoO6Has good energy band matching degree, and proper amount of Bi2MoO6Coating to BiVO4In the above process, a heterojunction electric field is formed at the contact interface of the two, and the photogenerated carriers are efficiently and orderly separated under the action of the heterojunction electric field; at the same time, a proper amount of Bi2MoO6Coating and reserving BiVO4The porous structure of the photoelectrode film is beneficial to full contact between a photoelectrode material and an electrolyte solution, so that a photoproduction hole can be quickly transferred out to react with the electrolyte solution to be consumed, and therefore, the BMO @ BVO-2 has the best photoelectrochemical property. For BMO @ BVO-1, Bi2MoO6Has a small coating amount of BiVO4And Bi2MoO6The heterojunction electric field formed between the two is not enough to efficiently separate photon-generated carriers, so that the BMO @ BVO-1 is second to the BMO @ BVO-2 but is better than the BiVO4And Bi2MoO6Photoelectrochemical properties of (a). And for BMO @ BVO-3 and BMO @ BVO-4 photoelectrodes, the coated Bi2MoO6In a large amount, and can form a heterojunction to accelerate the separation of photogenerated carriers, but the excess Bi2MoO6Block BiVO4The porous structure of the photoelectrode film is not beneficial to the full contact of the photoelectrode material and the electrolyte solution, so as to cause photoproduction holesCan not be timely and effectively reacted with an electrolyte solution to be consumed, so that BMO @ BVO-3 and BMO @ BVO-4 have the same BMO @ BVO-2 but are better than BiVO4And Bi2MoO6Photoelectrochemical properties of (a).
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications can be made without departing from the principles of the invention and these modifications are to be considered within the scope of the invention.
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