Diamond-based photoanode, its preparation method and photoelectrocatalytic device

Abstract

The present invention relates to the field of photoelectrocatalytic technology, and specifically provides a diamond-based photoanode, a preparation method thereof, and a photoelectrocatalytic device. The diamond-based photoanode includes a substrate, a boron-doped diamond film layer, and an n-type semiconductor film layer that are sequentially stacked; in the boron-doped diamond film layer, the ratio of boron atoms to carbon atoms is between 200 ppm and 9000 ppm; the n-type semiconductor film layer has a porous structure so that a part of the surface of the boron-doped diamond film layer facing away from the substrate is exposed, and the band gap width of the n-type semiconductor film layer is less than 2.5 eV. The diamond-based photoanode provided by the present invention has relatively excellent photoelectrocatalytic properties.

Description

Technical Field

[0001] The present invention relates to the field of photoelectrocatalytic technology, and particularly to a diamond-based photoanode, a preparation method thereof, and a photoelectrocatalytic device.

Background Art

[0002] Boron-doped diamond (BDD) electrodes have advantages such as a wide potential window, low background current, high chemical and mechanical stability, low resistance, strong surface antioxidant ability, and controllable surface termination. These advantages make BDD electrodes have broad research and application value in the field of electrocatalysis. For example, BDD electrodes can directly decompose refractory organic pollutants into non-toxic CO2 or obtain renewable energy substances such as methanol and ethanol through electrocatalytic reduction. However, the bandgap width (Eg) of BDD is ~5.5 eV, and it only has a light response in the deep ultraviolet band (wavelength less than 300 nm), and it cannot directly achieve photoelectrocatalytic applications in the solar spectrum band (400 nm - 760 nm).

[0003] Research reports have pointed out that TiO2 / BDD and nitrogen-doped titanium dioxide / BDD (N-TiO2 / BDD) heterojunction photoanodes have photoelectrocatalytic performance and can achieve photoelectrocatalytic applications of BDD materials in the solar spectrum band. However, on the one hand, the bandgap width of TiO2 is greater than 3.0 eV, and it only has a response in the ultraviolet region (wavelength less than 400 nm), resulting in a low solar light utilization efficiency of TiO2 / BDD photoelectric materials; on the other hand, although N-TiO2 has a strong solar light utilization rate, it has a large overpotential and a low photocurrent density.

[0004] Therefore, it is necessary to provide a new technical solution to solve the above technical problems existing in the existing diamond-based photoanodes.

Summary of the Invention

[0005] The purpose of the present invention is to provide a diamond-based photoanode, a preparation method thereof, and a photoelectrocatalytic device to solve the problems that the existing diamond-based photoanodes have poor response in the solar spectrum band and cannot make full use of solar light for photoelectrocatalysis.

[0006] To achieve the above technical objectives, the technical solutions adopted by the present invention are as follows:

[0007] A diamond-based photoanode includes a substrate, a boron-doped diamond film layer, and an n-type semiconductor film layer; the boron-doped diamond film layer is laminated on the surface of the substrate, and the n-type semiconductor film layer is laminated on the boron-doped diamond film layer;

[0008] In the boron-doped diamond film layer, the ratio of boron atoms to carbon atoms is between 200 ppm and 9000 ppm;

[0009] The n-type semiconductor film layer has a porous structure to locally expose the surface of the boron-doped diamond film layer facing away from the substrate;

[0010] The band gap of the n-type semiconductor film layer is less than 2.5 eV.

[0011] In some embodiments, the n-type semiconductor film layer is selected from a bismuth vanadate film layer, and the bismuth vanadate film layer has at least a monoclinic crystal structure;

[0012] And / or, the thickness of the n-type semiconductor film layer is between 200 nm and 500 nm;

[0013] And / or, the pore diameter of the porous structure is nanoscale.

[0014] In some embodiments, the diamond-based photoanode further includes a protective layer, and the protective layer is laminated on the surface of the n-type semiconductor film layer.

[0015] In some embodiments, the protective layer is selected from a titanium dioxide layer;

[0016] And / or, the thickness of the protective layer is between 2 nm and 5 nm.

[0017] Compared with the prior art, the diamond-based photoanode provided by the embodiment of the present invention includes a substrate, a boron-doped diamond film layer laminated on the surface of the substrate, and an n-type semiconductor film layer laminated on the surface of the boron-doped diamond film layer. Since the ratio of boron atoms to carbon atoms in the boron-doped diamond film layer is between 200 ppm and 9000 ppm, and the n-type semiconductor film layer has a porous structure so that the surface of the boron-doped diamond film layer facing away from the substrate is in a locally exposed state, it exhibits the characteristics of having a large current density at a small polarization potential, and at the same time has excellent charge transfer efficiency and excellent photoelectrocatalytic performance.

[0018] Correspondingly, the preparation method of the diamond-based photoanode provided by the embodiment of the present invention includes the following steps:

[0019] Deposit and form a boron-doped diamond film layer on the substrate;

[0020] Deposit and form an n-type semiconductor precursor film on the surface of the boron-doped diamond film layer;

[0021] Successively perform annealing and alkali etching treatments on the n-type semiconductor precursor film to obtain an n-type semiconductor film layer with a porous structure;

[0022] Wherein, in the boron-doped diamond film layer, the ratio of boron atoms to carbon atoms is between 200 ppm and 9000 ppm.

[0023] In some embodiments, the n-type semiconductor precursor film is composed of a mixture of bismuth vanadate and vanadium.

[0024] In some embodiments, the n-type semiconductor precursor film is deposited on the surface of the boron-doped diamond film layer by the following method:

[0025] Under the conditions that the vacuum pressure is less than 1.0E-4 and the flow rate ratio of argon to oxygen is 10 - 30 sccm / 100 sccm, the working pressure is controlled not to be greater than 0.2 Pa, and at the same time, sputtering coating treatment of the bismuth vanadate target and the vanadium target is carried out, so that bismuth vanadate and vanadium are simultaneously deposited on the surface of the boron-doped diamond film layer to obtain the n-type semiconductor precursor film.

[0026] In some embodiments, the ratio of the sputtering power density of bismuth vanadate to that of vanadium is 1:0.5 to 1:1.5;

[0027] and / or, the sputtering power density of bismuth vanadate is 15 W / cm 2 ~25 W / cm 2 and the sputtering power density of vanadium is 10 W / cm 2 ~30 W / cm 2 ;

[0028] and / or, the molar ratio of bismuth to vanadium in the n-type semiconductor precursor film is 1:1.2 to 1:2.

[0029] In some embodiments, the annealing process is to coat the surface of the n-type semiconductor precursor film with vanadyl acetylacetonate solution and keep it at 400 °C - 550 °C in an air atmosphere for 1 h - 4 h, so that the n-type semiconductor precursor film is transformed into a film layer including bismuth vanadate and vanadium pentoxide;

[0030] The alkali etching treatment is to place the film layer obtained by annealing in an alkali solution at 35 °C - 50 °C for 10 min - 30 min to remove the vanadium pentoxide and obtain a nano-porous structure in the n-type semiconductor film layer;

[0031] and / or, it further includes depositing a protective layer on the surface of the n-type semiconductor film layer.

[0032] Compared with the prior art, the preparation method of the diamond-based photoanode provided by the embodiments of the present invention has a simple process and a stable process, can obtain a diamond-based photoanode with relatively high performance consistency, and the obtained diamond-based photoanode has high photoelectrocatalytic characteristics.

[0033] In addition, the photoelectrocatalytic device provided by the embodiments of the present invention includes the diamond-based photoanode described above or the diamond-based photoanode prepared by the preparation method of the diamond-based photoanode described above.

[0034] Compared with the prior art, the photoelectrocatalytic device provided by the embodiment of the present invention includes the above-mentioned diamond-based photoanode, so it can exhibit the characteristic of a large current density at a relatively small polarization potential, and has excellent photoelectrocatalytic properties, making the photoelectrocatalytic device have relatively excellent photoelectrocatalytic effect and photoelectrocatalytic efficiency.

Description of the Drawings

[0035] Figure 1 It is a simplified process schematic diagram of the preparation method of the diamond-based photoanode provided by the embodiment of the present invention;

[0036] Figure 2 It is a simplified structural schematic diagram of the diamond-based photoanode prepared by the preparation method of the diamond-based photoanode provided by the embodiment of the present invention;

[0037] Figure 3 It is a simplified structural schematic diagram of the diamond-based photoanode prepared by the preparation method of the diamond-based photoanode provided by another embodiment of the present invention;

[0038] Figure 4 It is the EDS spectrum of the diamond-based photoanode provided by the first embodiment of the present invention;

[0039] Figure 5 It is the XRD spectrum of the diamond-based photoanode provided by the first embodiment of the present invention;

[0040] Figure 6 It is the Raman spectrum of the diamond-based photoanode provided by the first embodiment of the present invention;

[0041] Figure 7 It is the Raman spectrum of the diamond-based photoanode provided by the first, second, and third embodiments of the present invention;

[0042] Figure 8 It is the SEM morphology diagram of the boron-doped diamond film layer obtained in the first embodiment;

[0043] Figure 9 It is the SEM morphology diagram of the diamond-based photoanode obtained in the first embodiment;

[0044] Figure 10 It is the cross-sectional view of the diamond-based photoanode obtained in the first embodiment;

[0045] Figure 11 It is the SEM morphology diagram of the boron-doped diamond film layer obtained in the second embodiment;

[0046] Figure 12 It is the SEM morphology diagram of the boron-doped diamond film layer obtained in the third embodiment;

[0047] Figure 13SEM morphology diagram of the diamond-based photoanode obtained in Example 2;

[0048] Figure 14 Bar graph of the surface resistance of the boron-doped diamond film layers obtained in Example 1, Example 2, and Example 3;

[0049] Figure 15 Photoelectrochemical performance curves of the diamond-based photoanodes obtained in Example 1 to Example 3;

[0050] Figure 16 Photoelectrochemical performance curves of the diamond-based photoanodes obtained in Example 5, Comparative Example 1, and Comparative Example 2;

[0051] Figure 17 Photoelectrochemical performance curves of the diamond-based photoanodes obtained in Example 6, Example 7, and Example 8;

[0052] Figure 18 Transient photocurrent density curve of the diamond-based photoanode obtained in Example 1;

[0053] Figure 19 Absorption spectrum diagram of the bismuth vanadate film layer obtained in Example 4;

[0054] Figure 20 Graph for solving the bandgap of the bismuth vanadate film layer obtained in Example 4.

[0055] Reference numerals:

[0056] 10. Diamond-based photoanode; 11. Substrate; 12. Boron-doped diamond film layer; 13. n-type semiconductor film layer; 14. Protective layer.

Detailed Description of the Invention

[0057] The present invention will be further described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts fall within the scope of protection of the present invention.

[0058] It should be noted that all directional indicators (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative positional relationship and movement conditions between components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0059] It should also be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or there may be an intermediate element present at the same time. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or there may be an intermediate element present at the same time.

[0060] In addition, the descriptions involving "first", "second", etc. in the present invention are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0061] Please refer to Figure 1 、 Figure 2 , a method for preparing the diamond-based photoanode 10 according to an embodiment of the present invention, comprising the following steps:

[0062] S01. Deposit and form a boron-doped diamond film layer 12 on the surface of the substrate 11.

[0063] In step S01, the substrate 11 includes any one of silicon, titanium, molybdenum, niobium, tantalum, etc. In order to obtain a relatively high deposition quality of the boron-doped diamond film layer 12, the surface of the substrate 11 is kept clean and dry, and the substrate 11 can be pretreated, such as including cleaning and forming a diamond seed layer on the surface of the substrate 11. Among them, the cleaning process can first use acid and then use deionized water, acetone, ethanol, etc. for multiple cleanings to remove impurities and stains on its surface, so as to improve the bonding force between the boron-doped diamond film layer 12 and the substrate 11. The cleaning process can be carried out under ultrasonic conditions, and after cleaning, it can be dried in a nitrogen atmosphere, such as by blowing with nitrogen.

[0064] And forming a layer of diamond seed layer on the surface of the substrate 11 can effectively improve the deposition rate of the doped diamond film layer. Specifically, the diamond seed layer can be obtained in the following manner:

[0065] The substrate 11 is immersed in a mixed dispersion system containing nanoscale diamond particles and mechanically agitated to nucleate the diamond particles on the surface of the substrate 11. Among them, in the mixed dispersion system containing nanoscale diamond particles, the particle size of the diamond particles is 5 nm to 50 nm. In the mixed dispersion system containing nanoscale diamond particles, the dispersion liquid can be ethanol or the like. In some embodiments, the concentration of diamond particles in the mixed dispersion system is 10 mg / 100 mL to 50 mg / mL. In some embodiments, ultrasonic treatment can be used to uniformly nucleate the diamond particles on the surface of the substrate 11. In some embodiments, after nucleation on the surface of the substrate 11, it also includes cleaning and drying the substrate 11 with ethanol or the like to ensure that the surface of the substrate 11 is clean and dry. By forming a layer of nanoscale diamond seed layer on the surface of the substrate 11, nucleation points can be provided for the growth of the boron-doped diamond film layer 12, so as to accelerate the growth rate of the boron-doped diamond film layer 12 and facilitate the obtaining of a high-quality boron-doped diamond film layer 12.

[0066] The boron-doped diamond film layer 12 is obtained according to the following deposition method:

[0067] (1) Place the substrate 11 on the substrate in the vacuum reaction chamber of a hot filament chemical vapor deposition system (HFCVD), adjust the distance between the filament and the substrate to 6 mm to 15 mm, and close the chamber.

[0068] (2) Turn on the cooling water circulation machine, and sequentially open the mechanical pump bypass valve to make the chamber vacuum reach below 0.5 Pa.

[0069] (3) Introduce hydrogen (H2), methane (CH4), and trimethylborane ((CH3)3B) into the reaction chamber.

[0070] Among them, the flow rate of H2 is 400 sccm to 500 sccm; the flow rate of CH4 is 10 sccm to 25 sccm; the flow rate of (CH3)3B is 5 sccm to 25 sccm; by controlling the feeding ratio of boron (B) and carbon (C), the doping amount of boron in the boron-doped diamond film layer is adjusted to control the structure and performance of the BDD. In some embodiments, the atomic ratio of [B] / [C] is controlled to be 200 ppm to 9000 ppm. As the content of boron increases, the surface resistance of the boron-doped diamond film layer becomes smaller and the conductivity increases, but when it exceeds 9000 ppm, the crystallinity of the boron-doped diamond film layer becomes poor and there are many crystal defects, resulting in a decrease in the transmission efficiency. And if the content of boron is too low, less than 200 ppm, the conductivity of the boron-doped diamond film layer decreases, which will also lead to a decrease in the transmission efficiency.

[0071] (4) Open the holding pump and the holding valve, and adjust the pressure in the reaction chamber to be between 3.5 kPa and 4.5 kPa.

[0072] (5), Start the hot wire power supply, set the initial hot wire current to 280A - 320A, the target current to 460A - 480A, the current ramp rate to 150A / h - 200A / h, start the power control mode, set the hot wire power to 18.5kW - 21kW, the growth temperature to 830 ± 20 °C, set the substrate rotation speed to 1 - 3 rmp, and the growth time to 9h - 14h.

[0073] (6), After the growth is completed, turn off the power control mode, start the hot wire cooling program, the current decrease rate is 200A / h, the target current is 250A, and turn off the hot wire power supply.

[0074] (7), Close the maintenance valve and the maintenance pump, close the flow controllers of H2, CH4, and (CH3)3B, open the mechanical pump and the bypass valve to make the chamber vacuum not greater than 0.1 Pa. After continuing to cool for 5h - 7h, open the inflation valve to take out the sample, and obtain the boron-doped diamond film layer 12. The boron-doped diamond film layer 12 is a p-type film layer, and the thickness of the boron-doped diamond film layer 12 is 5μm - 9μm.

[0075] In addition, the boron-doped diamond film layer 12 can also be obtained by DC plasma CVD method and microwave plasma CVD method.

[0076] S02, Deposit an n-type semiconductor precursor film on the surface of the boron-doped diamond film layer 12.

[0077] In step S02, a magnetron sputtering method is used to deposit an n-type semiconductor precursor film on the surface of the boron-doped diamond film layer 12. The n-type semiconductor precursor film includes vanadium, bismuth, and oxygen. That is, the n-type semiconductor precursor film is an amorphous film formed by mixing these three elements of vanadium, vanadium, and oxygen. In the amorphous film, the molar amount of vanadium is greater than the molar amount of bismuth vanadate, that is, Bi:V is less than 1. In some embodiments, the ratio of the molar amount of bismuth to the molar amount of vanadium is 1:1.2 - 1:2 to facilitate obtaining an n-type semiconductor film layer 13 with better photocatalytic performance.

[0078] In some embodiments, before depositing the n-type semiconductor precursor film, it further includes the steps of cleaning the boron-doped diamond film layer 12 with ethanol and deionized water and drying it with nitrogen.

[0079] In some embodiments, the deposition process of the n-type semiconductor precursor film is as follows:

[0080] Under the conditions that the vacuum pressure is less than 1.0E-4 and the flow rate ratio of argon to oxygen is 10 - 30 sccm / 100 sccm, control the working pressure not to be greater than 0.2 Pa, and simultaneously perform sputtering coating on the bismuth vanadate target and the vanadium target, so that bismuth vanadate and vanadium are simultaneously deposited on the surface of the boron-doped diamond film layer 12 to obtain an n-type semiconductor precursor film. By regulating the sputtering process with the vanadium target, it is beneficial to obtain an n-type semiconductor film layer 13 with good photoelectrocatalytic performance. In some embodiments, the n-type semiconductor precursor film is obtained by magnetron sputtering, and the temperature of the substrate table is controlled to be 100 °C to 300 °C. If the temperature of the substrate table is lower than 100 °C, the binding force between the obtained n-type semiconductor precursor film and the boron-doped diamond film layer 12 is poor; when the temperature of the substrate table exceeds 300 °C, vanadium will volatilize during the sputtering process, resulting in a decrease in the vanadium content in the n-type semiconductor precursor film, which is not conducive to the formation of the n-type semiconductor film layer 13 with a porous structure, and ultimately leads to a decrease in the photocurrent efficiency of the obtained photoanode.

[0081] In some embodiments, during magnetron sputtering, control the ratio of the sputtering power density of bismuth vanadate to that of vanadium to be 1:0.5 - 1:1.5, so as to facilitate obtaining a higher vanadium content in the obtained n-type semiconductor precursor film, which is conducive to increasing the number of porous structures in the obtained n-type semiconductor film layer 13, and is also conducive to obtaining a nanoscale porous structure. If the sputtering power density of vanadium is low, the vanadium content in the obtained n-type semiconductor precursor film is too low, and it is difficult to obtain a porous structure, which is not conducive to the diffusion of the electrolyte and charge transfer, resulting in poor photocurrent efficiency; if the sputtering power density of vanadium is too high, the proportion of vanadium atoms will be too high, and when alkali etching is performed finally, it is easy to generate micron-scale or even larger hole structures, which will lead to a decrease in the photoelectric efficiency. In some embodiments, control the sputtering power density of bismuth vanadate to be 15 W / cm 2 ~25 W / cm 2 ,while controlling the sputtering power density of vanadium to be 10 W / cm 2 ~30 W / cm 2 ,Controlling the sputtering power density of both within the aforementioned range can be beneficial to reducing the backsputtering phenomenon during sputtering, thereby improving the film formation uniformity and reducing the defects of the film structure. In some embodiments, the thickness of the deposited n-type semiconductor precursor film is 200 nm - 500 nm. When the n-type semiconductor precursor film is within this thickness range, it is beneficial to obtain an n-type semiconductor film layer 13 with a thickness of 200 nm to 500 nm.

[0082] S03. Anneal and alkali-etch the n-type semiconductor precursor film in sequence to obtain an n-type semiconductor film layer 13 with a porous structure.

[0083] In step S03, the annealing process is to coat a vanadyl acetylacetonate solution on the surface of the n-type semiconductor precursor film, and then keep it at a temperature of 400°C to 550°C for 1h to 4h in an air atmosphere, so that the n-type semiconductor precursor film can be transformed into a film layer including a bismuth vanadate and vanadium pentoxide (BiVO4:V2O5) phase structure. The bismuth vanadate phase and vanadium pentoxide are mixed with each other, which is beneficial to the etching of vanadium pentoxide during the subsequent alkali etching process to obtain a porous n-type semiconductor film layer 13. In some embodiments, the concentration of the vanadyl acetylacetonate solution is 0.1M to 0.3M, and the solvent of the vanadyl acetylacetonate solution is selected from dimethyl sulfoxide. When the annealing temperature is lower than 400°C, the crystallinity of the generated bismuth vanadate is poor, which is not conducive to the exertion of the photoelectrocatalytic performance. If the annealing temperature is too high, the boron-doped diamond film layer 12 will be oxidized, resulting in more defects, which is also not conducive to the exertion of the photoelectrocatalytic performance. In some embodiments, after annealing, it is cooled to room temperature in a natural cooling manner.

[0084] In some embodiments, the alkali etching includes immersing the film layer including bismuth vanadate and vanadium pentoxide obtained after the annealing treatment in an alkali solution with a concentration of 0.5M to 2.5M, and the temperature of the alkali solution during soaking is 35°C to 50°C, and it is kept warm for 15min to 30min. In some embodiments, the alkali solution includes any one of a sodium hydroxide solution, a potassium hydroxide solution, etc. Through alkali etching, vanadium pentoxide is removed, thereby obtaining a bismuth vanadate film with a porous structure, and the pore diameter of the porous structure is nanoscale, that is, the n-type semiconductor film layer 13. After alkali etching, the obtained porous structure is nanoscale, and a partial surface of the boron-doped diamond film layer 12 facing away from the substrate 11 is exposed. The nanoscale porous structure and the partially exposed boron-doped diamond film layer are beneficial to increasing the contact area between the diamond-based photoanode 10 and the electrolyte, facilitating the diffusion effect of the electrolyte, and improving the carrier transport efficiency. At the same time, the porous structure is beneficial to increasing the light scattering space, thereby improving the utilization rate of sunlight.

[0085] In some embodiments, after alkali etching, deionized water, ethanol, etc. are also used to clean the obtained n-type semiconductor film layer 13 to obtain the n-type semiconductor film layer 13. The thickness of the obtained n-type semiconductor film layer 13 is 200nm to 500nm. If the thickness of the n-type semiconductor film layer 13 exceeds 500nm, it will lead to an increase in the migration distance of photo-generated carriers, and the carriers will recombine inside the n-type semiconductor film layer 13, resulting in a low photocurrent efficiency; if the thickness of the n-type semiconductor film layer 13 is less than 200nm, it will lead to a decrease in the light absorption efficiency, and then lead to a decrease in the utilization rate of sunlight and a decrease in the photoelectric efficiency.

[0086] Please refer to Figure 1 and Figure 3, in some embodiments, after obtaining the n-type semiconductor film layer 13, a protective layer 14 is further deposited on the surface of the n-type semiconductor film layer 13. The protective layer 14 can be a titanium dioxide (TiO2) film layer, and the thickness of the titanium dioxide film layer can be 2 nm to 5 nm. When it is less than 2 nm, it cannot protect the n-type semiconductor film layer 13, while if it exceeds 5 nm, it will affect the carrier transport efficiency between the n-type semiconductor film layer 13 and the electrolyte, resulting in a decrease in the carrier transport efficiency. The specific process of the protective layer 14 can be obtained according to the conventional deposition process, and will not be elaborated here.

[0087] The preparation method of the diamond-based photoanode 10 provided by the embodiment of the present invention has a simple process, and the obtained electrode structure is stable, which can be industrially applied. Moreover, because it can catalyze organic pollutants that are difficult to degrade, its photoelectric effect, photoelectric efficiency, and current density in the solar light band are significantly better than those of the existing TiO2 / BDD or N-TiO2 / BDD diamond-based photoanode 10, and it has a wide application prospect in related fields. The obtained diamond-based photoanode 10 includes a substrate 11, a boron-doped diamond film layer 12 stacked on the surface of the substrate 11, and an n-type semiconductor film layer 13 stacked on the surface of the boron-doped diamond film layer 12. The band gap of the n-type semiconductor film layer 13 is lower than 2.5 eV.

[0088] Due to the stable electrode structure and good photoelectrocatalytic effect of the diamond-based photoanode 10 in the embodiment of the present invention, it can be assembled with other components of the photoelectrocatalytic device into a photoelectrocatalytic device. In some embodiments, the photoelectrocatalytic device includes an anode and a cathode. Among them, the anode uses the diamond-based photoanode 10 of the embodiment of the present invention, that is, it includes a substrate 11, a boron-doped diamond film layer 12 stacked on the surface of the substrate 11, and an n-type semiconductor film layer 13 stacked on the surface of the boron-doped diamond film layer 12, and the n-type semiconductor film layer 13 has a porous structure, while the cathode can be an electrode with a silicon substrate 11 and a diamond film layer deposited on its surface. In some embodiments, the size of the porous structure of the n-type semiconductor film layer 13 of the anode is nanoscale. In some embodiments, in the photoelectrocatalytic device, an anticorrosive layer made of an epoxy resin material is further formed on the surface of the substrate 11 of the anode. Similarly, an anticorrosive layer made of an epoxy resin material is also formed on the surface of the substrate 11 of the cathode, so as to effectively inhibit the corrosion of the anode and the cathode by the electrolyte.

[0089] To better illustrate the technical solution of the present invention, the following will be further explained through several embodiments.

[0090] Example 1

[0091] This embodiment provides a diamond-based photoanode 10 and its preparation method.

[0092] Please refer toFigure 1 and Figure 2 For the preparation method of the diamond-based photoanode 10, the following steps are included:

[0093] (1) Ultrasonically clean a batch (50 pieces) of n-type Si (resistivity lower than 0.005 Ω·cm) (20 mm × 20 mm × 0.5 mm) substrates 11 with acetone and ethanol in sequence for 10 min; obtain clean substrates 11;

[0094] (2) Immerse the clean substrates 11 obtained in step (1) into an ethanol suspension containing micro-nano diamond particles (concentration: 50 mg / 100 mL) respectively for ultrasonic nucleation for 60 min, and rinse with ethanol and dry for standby.

[0095] (3) Place the Si substrates 11 obtained in step (2) on the substrate in the vacuum reaction chamber of the HFCVD system, adjust the distance between the filament and the substrate to 10 mm, and close the chamber.

[0096] (4) Turn on the cooling water circulation machine, and open the mechanical pump bypass valve in sequence to make the chamber vacuum degree reach 0.5 Pa.

[0097] (5) Introduce 480 sccm of H2, 15 sccm of CH4 and 10 sccm of trimethylborane ((CH3)3B), where the atomic ratio of boron to carbon is 200 ppm. Open the maintenance pump and maintenance valve to maintain the pressure in the reaction chamber at 4 kPa ± 0.5 kPa.

[0098] (6) Start the hot wire power supply, and set the initial hot wire current and the target current to 300 A and 460 A respectively, the current rising rate to 180 A / h, set the power density of the hot wire substrate stage to 18.5 W / cm 2 , the growth temperature to 820 ± 30 °C, set the substrate rotation speed to 1 rmp, and the growth time to 10 h.

[0099] (7) After the growth is completed, turn off the power control mode, start the hot wire cooling program, and turn off the hot wire power supply.

[0100] (8) Close the flow controllers of H2, CH4, and (CH3)3B, open the mechanical pump and the bypass valve to make the chamber vacuum degree 1 Pa, continue to cool for 3 h, then open the inflation valve to take out the sample, and obtain a boron-doped diamond film layer 12 with a thickness of 6 μm.

[0101] (9) Ultrasonically clean the boron-doped diamond film layer 12 obtained in step (8) with ethanol and deionized water for 2 min respectively, then dry it with nitrogen, and transfer it to the substrate stage in the magnetron sputtering vacuum chamber.

[0102] (10) Turn on the circulating cooling water system, and sequentially turn on the mechanical pump and the molecular pump to make the air pressure in the vacuum chamber reach 1.0E-4 Pa. Set the temperature of the substrate table to 200 °C and the chamber temperature to 120 °C.

[0103] (11) Introduce argon (Ar) and oxygen (O2), control the flow ratio of argon to oxygen to be 30 sccm / 100 sccm, and control the working pressure to be 0.2 Pa through the regulating valve.

[0104] (12) Start the radio frequency power supply, and at the same time start the radio frequency power supply to sputter the BiVO4 ceramic target and start the direct current power supply to sputter the V metal target. The sputtering power density of bismuth vanadate is 15 W / cm 2 and the sputtering power density of vanadium is 15 W / cm 2 , and the deposition thickness is 300 nm to obtain V-BiVO4.

[0105] (13) Coat the surface of the n-type semiconductor precursor film (V-BiVO4) obtained in step (12) with a 0.2 M vanadyl acetylacetonate solution. Then place the n-type semiconductor precursor film in a tubular furnace and heat it to 500 °C at a heating rate of 5 °C / min in an air atmosphere, and anneal it at 500 °C for 2 h under constant temperature. Finally, cool it to room temperature with the furnace to obtain a film layer including bismuth vanadate and vanadium pentoxide (BiVO4:V2O5).

[0106] (14) Immerse the film layer including bismuth vanadate and vanadium pentoxide (BiVO4:V2O5) in a 1 M sodium hydroxide solution, keep it at 40 °C for 20 min, take it out, wash it with deionized water, and perform drying treatment to obtain the n-type semiconductor film layer 13, that is, the bismuth vanadate film layer, and the bismuth vanadate film layer is laminated on the surface of the boron-doped diamond film layer 12, which is the diamond-based photoanode 10.

[0107] Example Two

[0108] This example provides a diamond-based photoanode 10 and a preparation method thereof.

[0109] Please refer to Figure 1 and Figure 2 and Example One. The diamond-based photoanode 10 of this example refers to Example One, and the difference is that in step (5), the atomic ratio of boron to carbon is controlled to be 2000 ppm, and the rest is the same as in Example One.

[0110] Example Three

[0111] This example provides a diamond-based photoanode 10 and a preparation method thereof.

[0112] Please refer to Figure 1 and Figure 2And Example 1, a reference example 1 of the diamond-based photoanode 10 of this example. The difference is that in step (5), the atomic ratio of boron to carbon is controlled to be 9000 ppm, and the rest is the same as in Example 1.

[0113] Example 4

[0114] This example provides a bismuth vanadate film layer and a preparation method thereof.

[0115] Please refer to Figure 1 and Figure 2 And Example 1, a reference example 1 of the preparation method of the bismuth vanadate film layer of this example. The difference is that the bismuth vanadate film layer is directly prepared on a glass substrate with reference to steps (10) to (14), and the thickness of the prepared bismuth vanadate film layer is 300 nm.

[0116] Example 5

[0117] This example provides a diamond-based photoanode 10 and a preparation method thereof.

[0118] Please refer to Figure 1 and Figure 2 And Example 1, a reference example 1 of the diamond-based photoanode 10 of this example. The difference is that in step (5), the atomic ratio of boron to carbon is controlled to be 2000 ppm, and in step (12), the deposited thickness is 500 nm, and the rest is the same as in Example 1.

[0119] Example 6

[0120] Please refer to Figure 1 and Figure 2 And Example 1, a reference example 1 of the diamond-based photoanode 10 of this example. The difference is that in step (5), the atomic ratio of boron to carbon is controlled to be 300 ppm, and in step (12), the deposited thickness is 200 nm, and the rest is the same as in Example 1.

[0121] Example 7

[0122] Please refer to Figure 1 and Figure 2 And Example 1, a reference example 1 of the diamond-based photoanode 10 of this example. The difference is that in step (5), the atomic ratio of boron to carbon is controlled to be 300 ppm, and in step (12), the deposited thickness is 300 nm, and the rest is the same as in Example 1.

[0123] Example 8

[0124] Please refer to Figure 1 and Figure 2And Example 1, a reference example 1 of the diamond-based photoanode 10 of this example. The difference is that in step (5), the atomic ratio of boron to carbon is controlled to be 300 ppm, and in step (12), the deposited thickness is 500 nm, and the rest is the same as in Example 1. Comparative Example 1

[0125] This comparative example provides a diamond-based photoanode 10 and a preparation method thereof.

[0126] Please refer to Figure 1 and Figure 2 And Example 1, steps (1) to (9) of the reference example 1 of the diamond-based photoanode 10 of this comparative example. The difference is that after obtaining the boron-doped diamond film layer 12, a titanium dioxide (TiO2) film layer is deposited on the surface of the boron-doped diamond film layer 12. The deposition method of the titanium dioxide film layer can be carried out according to the magnetron sputtering method, so it will not be elaborated here, and the thickness of the titanium dioxide film layer is 500 nm (the rest is the same as in Example 1, and TiO2 / BDD is obtained.

[0127] Comparative Example 2

[0128] This comparative example provides a diamond-based photoanode 10 and a preparation method thereof.

[0129] Please refer to Figure 1 and Figure 2 And Example 1, steps (1) to (9) of the reference example 1 of the diamond-based photoanode 10 of this comparative example. The difference is that after obtaining the boron-doped diamond film layer 12, a nitrogen-doped titanium dioxide (N-TiO2) film layer is deposited on the surface of the boron-doped diamond film layer 12. The deposition method of the titanium dioxide film layer can be carried out according to the magnetron sputtering method, so it will not be elaborated here, and the thickness of the titanium dioxide film layer is 500 nm, and the rest is the same as in Example 1, and N-TiO2 / BDD is obtained.

[0130] Performance test:

[0131] 1. Elemental composition analysis

[0132] Elemental analysis was performed on the diamond-based photoanode 10 obtained in Example 1. Specifically, the EDS spectrum, XRD spectrum, and Raman spectrum were analyzed, and the results are shown in Figure 4 , Figure 5 and Figure 6 respectively.

[0133] It can be seen from Figure 4 that the main elements of the film layer deposited on the surface of the BDD film layer are Bi, V, and O.

[0134] It can be seen from Figure 5It can be seen that the diffraction peaks appearing around 44° and 75° are the characteristic peaks of diamond, and the remaining diffraction peaks are the characteristic peaks of BiVO4. There are no other impurity peaks in the film layer. In addition, BiVO4 has a monoclinic crystal structure and excellent photoelectrocatalytic properties.

[0135] From Figure 6 it can be seen that the Raman shifts at 1332 cm -1 and 1222 cm -1 are the characteristic peaks of diamond and boron-doped diamond, and the remaining Raman shifts are the characteristic peaks of BiVO4. There are no other impurity peaks in the film layer. In addition, BiVO4 has a monoclinic crystal phase structure and excellent photoelectrocatalytic properties, and the Raman spectroscopy detection results match the XRD results.

[0136] According to the above elemental composition analysis, it can be confirmed that the diamond-based photoanode 10 obtained in Example 1 includes a boron-doped diamond film layer 12 laminated on the surface of the substrate 11 and a bismuth vanadate film layer deposited on the surface of the boron-doped diamond film layer 12.

[0137] The boron-doped diamond film layers 12 prepared in Example 1, Example 2, and Example 3 were tested by Raman spectroscopy, and the results are as Figure 7 shown.

[0138] From Figure 7 it can be seen that the Raman shift at ~1332 cm -1 is the Raman characteristic peak of diamond, and the Raman shift at ~1222 cm -1 is the Raman characteristic peak of boron-doped diamond. The sharper the peak position and the higher the peak intensity value at 1332 cm -1 indicate the better the quality of the BDD film layer. It can be seen from the figure that when the doping concentration increases, the quality of the film layer has a downward trend. When it reaches 9000 ppm, the Raman characteristic peak of diamond basically no longer exists.

[0139] 2. Microscopic morphology characterization

[0140] The SEM surface morphology of the boron-doped diamond film layer obtained in step (8) of Example 1 was observed, and the results are as Figure 8 shown.

[0141] From Figure 8 it can be seen that the boron-doped diamond film layer 12 uniformly and densely covers the surface of the substrate, and there are no obvious holes and warps on the film layer surface. In addition, the surface morphology of the film layer fluctuates, and the rough surface morphology has a relatively high specific surface area, which is beneficial to the photoelectrocatalytic effect.

[0142] The SEM surface morphology and cross-section of the diamond-based photoanode 10 obtained in step (14) of Example 1 were observed, and the results are as Figure 9 and Figure 10 shown.

[0143] It can be seen from Figure 9 that BiVO4 has good crystallinity. The BiVO4 film layer covers the surface of the BDD film layer, and there are a certain amount of nanopore structures in the BiVO4 film layer, so that the surface of the BDD film layer facing away from the substrate 11 is partially exposed.

[0144] It can be seen from Figure 10 that the BiVO4 film layer adheres tightly to the BDD film layer.

[0145] The boron-doped diamond film layers 12 obtained in Example 2 and Example 3 were scanned by SEM, and the results are shown in Figure 11 and Figure 12 respectively. The diamond-based photoanode 10 obtained in Example 2 was scanned by SEM, and the result is shown in Figure 13 as shown.

[0146] Combined with Figure 8 , Figure 11 and Figure 12 it can be seen that with the increase of [B] / [C], within a certain concentration range, the crystallinity of the diamond film layer has no obvious difference. However, as [B] / [C] continues to increase and reaches 9000 ppm, the crystallinity of the diamond film layer becomes poor and the surface defects increase. It can be seen from Figure 13 that the BiVO4 film layer obtained in Example 2 has good crystallinity. The BiVO4 film layer covers the surface of the BDD film layer, and there are a certain amount of nanopore structures in the BiVO4 film layer, so that the surface of the BDD film layer facing away from the substrate 11 is partially exposed.

[0147] 3. Surface resistance test

[0148] The surface resistance of the boron-doped diamond film layers 12 prepared in Example 1, Example 2, and Example 3 was measured, and the results are shown in Figure 14 as shown.

[0149] It can be seen from Figure 14 that as the boron doping amount increases, the surface resistance of the diamond film layer decreases.

[0150] Combined with Figure 7 , Figure 8 , Figure 11 , Figure 12 , Figure 13 and Figure 14 it can be seen that in the boron-doped diamond film layer, it is more appropriate to select the ratio of boron atoms to carbon atoms between 200 ppm and 9000 ppm.

[0151] 4. Photoelectrochemical performance test

[0152] The diamond-based photoanodes 10 obtained in Example 1, Example 2, and Example 3 were respectively subjected to photoelectrochemical performance tests, and the results are as Figure 15 .

[0153] From Figure 15 it can be seen that, compared with Example 1 and Example 3, at the same polarization potential, the BiVO4 / BDD2 electrode material obtained in Example 2 has a larger photocurrent density, that is, more excellent photoelectrocatalytic performance. This is because when the boron content is too high, the conductivity of the BDD film increases, but the defects of the film layer increase and the crystallinity becomes poor, resulting in a decrease in quality; when the boron content is too low, the quality of the BDD film layer becomes better but the conductivity of the film layer decreases. Both the film layer quality and conductivity will affect the charge transfer efficiency in the BDD film layer, and thus affect the photoelectrocatalytic performance of the material. And the BDD film layer with high quality and high conductivity has the best charge transfer efficiency, and thus has more excellent photoelectrocatalytic performance.

[0154] The photoelectrochemical performance tests were respectively carried out on Comparative Example 1, Comparative Example 2, and Example 5, and the results are as Figure 16 shown.

[0155] It can be Figure 16 seen that at the same polarization potential, the photocurrent density of BiVO4 / BDD obtained in Example 5 is much larger than that of the TiO2 / BDD and N-TiO2 / BDD electrode materials in the prior art. And at the same current density, the polarization potential of the electrode material obtained in Example 5 is much smaller than that of the TiO2 / BDD and N-TiO2 / BDD electrode materials. A higher photocurrent density and a lower overpotential mean more excellent photoelectrocatalytic performance.

[0156] The diamond-based photoanodes 10 obtained in Example 6, Example 7, and Example 8 were respectively subjected to photoelectrochemical performance tests, and the results are as Figure 17 .

[0157] From Figure 17It can be seen that the photoelectrochemical properties of the electrodes corresponding to BiVO4 film layers with different thicknesses were tested: the results show that the thickness of the BiVO4 film layer has a great influence on the photocurrent density. Compared with Example 6 and Example 8, at the same polarization potential, when the thickness of the BiVO4 film layer in Example 7 is 300 nm, the photocurrent density of the BiVO4 / BDD photoanode is greater. And at the same current density, when the thickness of the BiVO4 film layer is 300 nm, the polarization potential of the BiVO4 / BDD photoanode is lower. This is because when the thickness is less than 300 nm, the film is too thin, and the light absorption efficiency decreases, so the utilization rate of sunlight decreases, resulting in a low photocurrent efficiency of the electrode material. Because when the thickness is greater than 500 nm, the hole mobility of the BiVO4 film layer is low, the film is too thick, the carrier migration distance increases, and the carriers recombine inside, so the photocurrent efficiency is low.

[0158] The transient photocurrent density of the diamond-based photoanode 10 obtained in Example 1 was detected, and the results are as Figure 18 shown.

[0159] It can be Figure 18 seen that when the light illumination is turned on, the current density increases rapidly; when the light illumination is turned off, the current density decreases rapidly. At the same time, as time increases, the photocurrent density does not show an obvious attenuation trend, indicating that the BiVO4 / BDD photoanode has a reliable photoelectric response ability.

[0160] 5. Absorption spectrum performance test

[0161] The absorption spectrum of the bismuth vanadate film layer in Example 4 was tested, and the results are as Figure 19 shown.

[0162] It can be Figure 19 seen that the bismuth vanadate film layer has excellent light absorption efficiency, the absorption cut-off wavelength is about 500 nm, and the absorption wavelength extends to the visible light range. Thus, it can be seen that the bismuth vanadate film layer has visible light response ability when applied to the surface of the boron-doped diamond film layer of the present invention.

[0163] 6. Band gap width test

[0164] The band gap width (E g ) of the bismuth vanadate film layer obtained in Example 4 was analyzed. Specifically, it was calculated and analyzed according to formula (1), and the results are as Figure 20 shown. It can be Figure 20 seen that the band gap width of the bismuth vanadate film layer is about 2.4 eV, which is less than 2.5 eV.

[0165] αhv = const(hv - Eg) 1 / 2 ……(1).

[0166] Based on the bismuth vanadate film layers of Examples 1 to 3, Examples 5 to 8, Comparative Example 1, Comparative Example 2, and Example 4, it can be found that when the ratio of boron atoms to carbon atoms in the boron-doped diamond film layer of the diamond-based photoanode provided by the embodiments of the present invention is 200 ppm to 9000 ppm and the n-type semiconductor film layer has a porous structure such that the surface of the boron-doped diamond film layer facing away from the substrate is partially exposed, there is a large current density at a relatively small polarization potential, showing relatively excellent photoelectrocatalytic effects and being suitable as an electrode for a photoelectrocatalytic device.

[0167] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A preparation method of a diamond-based photoanode, characterized in that, It includes the following steps: Deposit and form a boron-doped diamond film layer on a substrate; Deposit and form an n-type semiconductor precursor film on the surface of the boron-doped diamond film layer; Successively perform annealing and alkali etching treatments on the n-type semiconductor precursor film to obtain an n-type semiconductor film layer with a porous structure; Wherein, in the boron-doped diamond film layer, the ratio of boron atoms to carbon atoms is between 200 ppm and 9000 ppm; Wherein, the annealing process is to coat a vanadyl acetylacetonate solution on the surface of the n-type semiconductor precursor film, and keep it warm for 1 h to 4 h under an air atmosphere and at a temperature of 400 °C to 550 °C, so that the n-type semiconductor precursor film is transformed into a film layer including bismuth vanadate and vanadium pentoxide; The alkali etching treatment is to place the film layer obtained by annealing in an alkali solution at 35 °C to 50 °C and keep it warm for 10 min to 30 min to remove the vanadium pentoxide and obtain a nanoscale porous structure in the n-type semiconductor film layer; It further includes depositing and forming a protective layer on the surface of the n-type semiconductor film layer.

2. The preparation method of the diamond-based photoanode according to claim 1, characterized in that, The n-type semiconductor precursor film is composed of a combination of three elements: vanadium, bismuth, and oxygen.

3. The preparation method of the diamond-based photoanode according to claim 2, wherein Deposit and form the n-type semiconductor precursor film on the surface of the boron-doped diamond film layer according to the following method: Under the conditions that the vacuum pressure is less than 1.0E-4 and the flow rate ratio of argon to oxygen is 10 - 30 sccm / 100 sccm, control the working pressure not to be greater than 0.2 Pa, and simultaneously perform sputtering coating treatments on a bismuth vanadate target and a vanadium target, so that the bismuth vanadate target and the vanadium target are simultaneously deposited on the surface of the boron-doped diamond film layer to obtain the n-type semiconductor precursor film.

4. The preparation method of the diamond-based photoanode according to claim 3, wherein, The ratio of the sputtering power density of the bismuth vanadate target to that of the vanadium target is 1:0.5 to 1:1.5; and / or, the sputtering power density of the bismuth vanadate target is 15 W / cm 2 ~25 W / cm 2 , the sputtering power density of the vanadium target is 10 W / cm 2 ~30 W / cm 2 ; And / or, the molar ratio of bismuth to vanadium in the n-type semiconductor precursor film is 1:1.2 to 1:

2.

5. A diamond-based photoanode, characterized in that, Prepared by the preparation method of the diamond-based photoanode according to any one of claims 1 - 4, including a substrate, a boron-doped diamond film layer, and an n-type semiconductor film layer; The boron-doped diamond film layer is laminated on the surface of the substrate, and the n-type semiconductor film layer is laminated on the boron-doped diamond film layer; In the boron-doped diamond film layer, the ratio of boron atoms to carbon atoms is between 200 ppm and 9000 ppm; The n-type semiconductor film layer has a porous structure so that a part of the surface of the boron-doped diamond film layer facing away from the substrate is exposed; The band gap of the n-type semiconductor film layer is lower than 2.5 eV.

6. The diamond-based photoanode according to claim 5, wherein, The n-type semiconductor film layer is selected from a bismuth vanadate film layer, and the bismuth vanadate film layer has at least a monoclinic crystal structure; And / or, the thickness of the n-type semiconductor film layer is between 200 nm and 500 nm; And / or, the pore diameter of the porous structure is nanoscale.

7. The diamond-based photoanode according to any one of claims 5 to 6, characterized in that, The diamond-based photoanode further includes a protective layer, and the protective layer is laminated on the surface of the n-type semiconductor film layer.

8. The diamond-based photoanode according to claim 7, characterized in that, The protective layer is selected from a titanium dioxide layer; And / or, the thickness of the protective layer is between 2 nm and 5 nm.

9. A photoelectrocatalytic device, characterized in that, A diamond-based photoanode prepared by the diamond-based photoanode according to any one of claims 5 to 8 or the preparation method of the diamond-based photoanode according to any one of claims 1 to 4.

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