Method for the regulation of defects in a photoelectrode device and conversion thereof

Abstract

The present application belongs to the field of photoelectrode devices, and particularly relates to a method for regulating and converting defects in a photoelectrode device. The present application relates to obtaining a material with better carrier transfer capability using a simple synthesis method, and regulating defects of the modified photoanode to reduce the influence of adverse defects on the device and improve the surface OER performance. The present application selects zinc indium sulfide (named as ZIS) as a photoanode, uses a simple low-temperature water bath method, and obtains a Mg-doped ZIS photoanode device (named as ZIS:Mg) by performing Mg doping treatment on the ZIS. Then, the O defects caused by Mg doping are converted into Mg-O bonds by a simple nitrogen annealing method, and a ZIS:MA photoanode device is obtained.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrode devices, and specifically relates to a method for controlling and converting defects in photoelectrode devices. Background Technology

[0002] Photoelectrochemical water splitting for hydrogen production is one of the main methods for generating clean energy using solar energy. However, because the oxygen evolution reaction (OER) requires four electrons, the current solar-to-hydrogen conversion efficiency (STH) is far below the 10% required for commercialization. Therefore, optimizing the photoanode is key to improving STH. Commonly used photoanodes generally suffer from low carrier separation efficiency, which can be effectively mitigated through doping, crystal plane manipulation, and defect engineering.

[0003] Doping can modulate the energy band structure of a photoanode, promoting the transfer of photogenerated holes in the bulk phase and reducing bulk recombination of photogenerated carriers through a built-in electric field. However, doping can also introduce some negative effects. For example, additional defects introduced during doping can reduce the surface OER rate, and the extra energy levels caused by doping can lead to unavoidable recombination. Although some literature has reported effective mitigation of these problems through secondary doping and surface passivation, the defects caused by doping have not been truly eliminated. On the other hand, how to reactivate and utilize the introduced unfavorable defects, turning them from disadvantageous to advantageous, is rarely reported. Therefore, designing a method to treat the redundant defects introduced after doping is beneficial for further improving the performance of photoelectrodes and deepening the understanding of defect design.

[0004] Generally, doping alters the photoanode's band structure to address insufficient carrier separation. However, this introduces additional defects into the photoanode material. These defects act as recombination sites, trapping holes and reducing overall photoanode performance. Some literature reports attempts to passivate defects caused by the first doping through secondary doping. Multiple doping not only increases experimental complexity but also makes precise control difficult. Alternatively, surface passivation layers can be applied to address doping-induced defects; however, this introduces new interfaces, leading to more severe interfacial recombination. Even when in-situ co-catalysts are used to passivate and optimize the interface, these methods only address surface defects. Summary of the Invention

[0005] The current technology has the following drawbacks:

[0006] 1. Using secondary doping to treat defects essentially introduces more defects and does not fundamentally solve or utilize the problem of defects.

[0007] 2. Using passivation layers to treat defects can only target surface defects. In addition, the passivation layer itself can also cause interfacial recombination, so the OER performance of the passivation layer is not necessarily excellent.

[0008] 3. While in-situ co-catalyst passivation can reduce interfacial defects, its strict requirements for electrolyte and substrate increase the cost of the experiment and it cannot be used for various photoanodes.

[0009] To address the aforementioned technical problems, this application provides the following technical solution:

[0010] This invention aims to obtain materials with good bulk hole transfer capabilities using a simple synthesis method, and to improve the surface OER performance of the doped photoanode by treating defects. This invention selects zinc indium sulfide (ZIS) as the photoanode, and uses a simple low-temperature water bath method to dope ZIS with Mg, obtaining a Mg-doped ZIS photoanode device (ZIS:Mg). Then, a simple nitrogen annealing process is used to transform the O defects caused by Mg doping into Mg-O bonds, resulting in a ZIS:MA photoanode device.

[0011] This invention provides a method for controlling and converting defects in a photoelectrode device, comprising the following steps:

[0012] S1: The pretreated FTO conductive glass and reaction solution A are mixed and subjected to hydrothermal reaction to obtain a ZIS sample; the reaction solution A is obtained by dissolving zinc salt, indium salt and thio compound in water; the zinc salt is selected from zinc chloride, zinc sulfate, zinc nitrate or zinc acetate, the indium salt is selected from indium chloride or indium nitrate, and the thio compound is selected from thiourea or thioacetamide;

[0013] S2: The ZIS sample and reaction solution B are mixed and heated to obtain a ZIS:Mg sample; the reaction solution B is obtained by dissolving magnesium salt and sodium sulfite in water; the magnesium salt is selected from magnesium sulfate, magnesium nitrate or magnesium chloride;

[0014] S3: Under an inert atmosphere, the ZIS:Mg sample is heated to 100-350℃ and kept at that temperature for 1-4 hours, then cooled to room temperature (25±5℃) to obtain the ZIS:MA photoelectrode device.

[0015] Preferably, in step S1, the hydrothermal reaction temperature is 90-180℃ and the time is 2-8h.

[0016] Preferably, the mass ratio of zinc chloride, indium chloride and thiourea is 2-3:8-9:6-7.

[0017] Preferably, in step S2, the heating reaction temperature is 60-80℃ and the time is 1-5h.

[0018] Preferably, in step S2, the product is dried after heating and reaction.

[0019] Furthermore, the drying temperature is 45-55℃, and the time is 10-14 hours.

[0020] Preferably, in step S2, the mass ratio of magnesium sulfate to sodium sulfite is 3-25:10-15.

[0021] Preferably, in step S3, the inert atmosphere is a nitrogen atmosphere.

[0022] Preferably, in step S3, the heating rate is 5°C / min.

[0023] Specifically, the method for controlling and converting defects in the photoelectrode device includes the following steps:

[0024] (1) Cleaning the conductive substrate fluorine-doped tin oxide conductive glass (FTO): Use an ultrasonic instrument to clean the FTO with acetone, ethanol and deionized water three times in sequence, each time for 10-30 minutes.

[0025] (2) Synthesis of ZIS film: Dissolve 0.2-0.3g zinc chloride, 0.8-0.9g indium chloride, and 0.6-0.7g thiourea in 200-300mL of ultrapure water and stir continuously until uniformly dissolved. Place the washed FTO face down in a polytetrafluoroethylene liner and take 10-15mL of the above solution to carry out a hydrothermal reaction to obtain a ZIS sample.

[0026] (3) Preparation of ZIS:Mg photoelectrode: Place ZIS face down in a 15mL glass bottle. Dissolve 0.3-2.5g magnesium sulfate and 1-1.5g sodium sulfite in 200-300mL of ultrapure water, and put 10-15mL of the above solution into the glass bottle. Heat in a 70℃ water bath for 1-5 hours, then remove the sample, rinse with deionized water, and dry the obtained ZIS:Mg sample in a 50℃ oven for 12 hours.

[0027] (4) Preparation of ZIS:MA photoelectrode: The ZIS:Mg sample obtained above was placed in a tube furnace and annealed in nitrogen to obtain the optimal sample. The annealing process is as follows: The ZIS:Mg sample was placed face up in a crucible, and nitrogen gas was first passed through it at room temperature for 30 min. Then, the temperature was increased to 100-350℃ at a rate of 5℃ / min and held for 1-4 h. Finally, the sample was cooled to room temperature in a nitrogen atmosphere and removed to obtain the ZIS:MA photoelectrode device.

[0028] This invention employs a simple one-step nitrogen heat treatment method to transform the O defects introduced during the water bath Mg doping process into highly catalytically active Mg-O chemical bonds, and has the following key technical points:

[0029] 1. Adverse defects were passivated and processed without introducing an additional interface layer, solving the interface problems that are common in traditional passivation layer designs.

[0030] 2. It transforms the original defects from unfavorable to favorable, which is superior to the simple passivation effect in the ordinary passivation defect treatment approach.

[0031] 3. The formation of Mg-O bonds promotes the transfer of photogenerated holes, lowers the surface OER kinetic barrier, increases catalytic active sites, reduces recombination, and improves the overall performance of the photoanode.

[0032] 4. Through one-step nitrogen heat treatment, precise control of O defects introduced by Mg doping was achieved, providing a simple and efficient method for directional defect modification.

[0033] The present invention also provides a method for controlling and converting defects in the above-mentioned photoelectrode device to prepare a photoelectrode device.

[0034] The technical solution of the present invention has the following advantages compared with the prior art:

[0035] 1) The preparation method of the present invention is simple, and the problem of insufficient carrier separation capability of ZIS bulk phase is solved by low temperature water bath.

[0036] 2) The transformation from O defects to Mg-O bonds enables the utilization of O defects introduced during the doping process. This not only solves the adverse effects caused by doping but also further reduces surface hole recombination by utilizing defects.

[0037] 3) The Mg-O bonds formed after nitrogen annealing provide abundant surface active sites, which is beneficial to improving the OER reaction rate.

[0038] 4) After Mg-O is formed, the active site changes from the original Zn to Zn and Mg working together, which lowers the original OER reaction barrier and is conducive to further improving the performance of the photoanode. Attached Figure Description

[0039] Figure 1 (ab) Scanning electron microscope (SEM) front view and (cd) transmission electron microscope (TEM) image of ZIS and ZIS:MA.

[0040] Figure 2 JV curves for ZIS and ZIS:MA.

[0041] Figure 3 JV curves for ZIS, ZIS:Mg, and ZIS:MA.

[0042] Figure 4 JV curves for different annealing temperatures. Detailed Implementation

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0044] Example 1

[0045] (1) Use an ultrasonic instrument to clean the conductive substrate fluorine-doped tin oxide conductive glass (FTO) three times in sequence with acetone, ethanol and deionized water, each time for 30 minutes.

[0046] (2) Dissolve 0.2727 g zinc chloride, 0.8795 g indium chloride, and 0.6087 g thiourea in 200 mL of ultrapure water and stir continuously until uniformly dissolved. Place the washed FTO face down in a polytetrafluoroethylene liner and take 10 mL of the above solution to carry out a hydrothermal reaction to obtain a ZIS sample.

[0047] (3) Place the ZIS sample face down in a 15 mL glass bottle. Dissolve 2.4647 g of magnesium sulfate and 1.42 g of sodium sulfite in 200 mL of ultrapure water, and put 10 mL of the solution into the glass bottle. After heating in a 70 °C water bath for 3 hours, remove the sample, rinse with deionized water, and dry the resulting ZIS:Mg sample in a 50 °C oven for 12 hours.

[0048] (4) The ZIS:Mg sample obtained above was placed in a tube furnace and annealed in nitrogen to obtain the optimal sample. The annealing process is as follows: The ZIS:Mg sample was placed face up in the crucible, nitrogen was passed through it at room temperature for 30 min, and then the temperature was increased to 250℃ at a rate of 5℃ / min and held for 2 hours. Finally, the sample was cooled to room temperature in a nitrogen atmosphere and removed to obtain the ZIS:MA photoelectrode device.

[0049] The morphology of the ZIS:MA photoelectrode is as follows: Figure 1 As shown. From Figure 1 It can be seen that the entire device fabrication process did not significantly affect the morphology and crystal structure of ZIS. Its two-dimensional nanosheet structure was preserved, which is beneficial to the transport of photogenerated carriers and the surface OER reaction.

[0050] The photoelectrodes prepared above were assembled into a photoelectrochemical cell, and then water was photo-splitting was performed at different voltages. As a control, ZIS-loaded FTO was used as the working electrode and a platinum mesh as the counter electrode, and water was photo-splitting was performed under the same conditions. The results are shown in [Figure 1]. Figure 2 .from Figure 2 It can be seen that at 1.23V RHEAt this voltage, the dark current (dashed line in the figure) is negligible, and the photoelectrode prepared by the method in this embodiment can achieve a photocurrent of 4.91 mA / cm². 2 V on Negative shift to -0.06V RHE The photocurrent of ZIS thin film is only 0.5 mA / cm. 2 .

[0051] Example 2

[0052] The photoanode device was prepared according to the method of steps (1)-(3) in Example 1, except that step (4) was not performed to anneal ZIS:Mg with nitrogen, so that Mg-O chemical bonds could not be generated on the surface of the prepared photoanode. O defects would lead to a decrease in the surface OER rate and increase the recombination of electrons and holes.

[0053] The photoelectrodes prepared above were assembled into a photoelectrochemical cell, and then water was split by light at different voltages. At 1.23V... RHE At the specified voltage, the photoelectrode prepared by the method in this embodiment only achieves a photocurrent of 3.03 mA / cm². 2 V on Negative shift to 0.08V RHE Its photoelectric properties are far lower than those of Example 1, as shown in the results. Figure 3 .

[0054] Example 3

[0055] ZIS:MA photoelectrodes were prepared according to steps (1)-(4) of Example 1, except that in step (4), ZIS:MA photoelectrodes with different O defect transformation degrees were obtained by changing the nitrogen annealing temperature.

[0056] The photoelectrodes prepared above were assembled into a photoelectrochemical cell, and then water was split by light at different voltages. At 1.23V... RHE Under the specified voltage, the photoelectrode prepared by the method in this embodiment can achieve a photocurrent of 4.91 mA / cm². 2 V on Negative shift to -0.06V RHE The photocurrent of ZIS thin film is only 0.5 mA / cm. 2 The results are shown Figure 4 .

[0057] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for controlling and converting defects in a photoelectrode device, characterized in that, The steps include the following: S1: The pretreated FTO conductive glass and reaction solution A are mixed and subjected to hydrothermal reaction to obtain a ZIS sample; the reaction solution A is obtained by dissolving zinc salt, indium salt and thio compound in water; the zinc salt is selected from zinc chloride, zinc sulfate, zinc nitrate or zinc acetate, the indium salt is selected from indium chloride or indium nitrate, and the thio compound is selected from thiourea or thioacetamide; S2: The ZIS sample and reaction solution B are mixed and heated to obtain a ZIS:Mg sample; the reaction solution B is obtained by dissolving magnesium salt and sodium sulfite in water; the magnesium salt is selected from magnesium sulfate, magnesium nitrate or magnesium chloride; S3: Under an inert atmosphere, the ZIS:Mg sample is heated to 100-350℃ and kept at that temperature for 1-4 hours, then cooled to room temperature to obtain a ZIS:MA photoelectrode device.

2. The method for controlling and converting defects in the photoelectrode device as described in claim 1, characterized in that, In step S1, the hydrothermal reaction temperature is 90-180℃ and the time is 2-8h.

3. The method for controlling and converting defects in the photoelectrode device as described in claim 1, characterized in that, The mass ratio of zinc chloride, indium chloride and thiourea is 2-3:8-9:6-7.

4. The method for controlling and converting defects in the photoelectrode device as described in claim 1, characterized in that, In step S2, the heating reaction temperature is 60-80℃ and the time is 1-5h.

5. The method for controlling and converting defects in the photoelectrode device as described in claim 1, characterized in that, In step S2, the product is dried after heating and reaction.

6. The method for controlling and converting defects in the photoelectrode device as described in claim 5, characterized in that, The drying temperature is 45-55℃, and the time is 10-14 hours.

7. The method for controlling and converting defects in the photoelectrode device as described in claim 1, characterized in that, In step S2, the mass ratio of magnesium sulfate to sodium sulfite is 3-25:10-15.

8. The method for controlling and converting defects in the photoelectrode device as described in claim 1, characterized in that, In step S3, the inert atmosphere is a nitrogen atmosphere.

9. The method for controlling and converting defects in the photoelectrode device as described in claim 1, characterized in that, In step S3, the heating rate is 5°C / min.

10. A photoelectrode device prepared by a method for controlling and converting defects in the photoelectrode device according to any one of claims 1-9.

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