An alkali metal ion-doped WO3 nanorod array photoelectrode and its preparation method

Abstract

This invention discloses a WO3 nanorod array photoelectrode doped with alkali metal ions and its preparation method. The method employs a one-step molten alkali etching oxidation process to grow a highly crystalline and highly oriented WO3 nanorod array photoelectrode in situ on a tungsten substrate. By introducing alkali metal hydroxides, this invention lowers the transition temperature from tungsten metal to tungsten oxide. Furthermore, by using a one-step molten alkali etching oxidation process to prepare an alkali metal-doped WO3 nanorod array on a tungsten substrate, the band structure of WO3 is modulated to expand its light absorption and improve carrier separation efficiency, thereby enhancing the activity and stability of the WO3 photoelectrode in the photoelectrocatalytic water oxidation reaction.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrochemical water splitting for hydrogen production technology, specifically relating to an alkali metal ion-doped WO3 nanorod array photoelectrode and its preparation method. Background Technology

[0002] The large-scale use of fossil fuels has not only led to the depletion of natural resources, but also caused serious damage to the Earth's climate and human environment. Therefore, it is necessary to develop new technologies for the conversion and storage of efficient and environmentally friendly renewable energy. Photoelectrocatalytic water splitting to produce hydrogen can convert and store widely available solar energy into clean and economical hydrogen energy, which is one of the ideal ways to solve the energy crisis and environmental pollution problems.

[0003] Commonly used photoanode materials for photoelectrocatalytic water splitting to produce hydrogen include TiO2, BiVO4, α-Fe2O3, and WO3. Among them, WO3 is an indirect bandgap n-type semiconductor with a bandgap of 2.5~2.9 eV. Furthermore, WO3 exhibits good resistance to photocorrosion, remaining stable in acidic and neutral solutions under illumination, and its relatively positive valence band position (+3.1 V) is also noteworthy. NHE ( ), corresponding to photogenerated holes, have a strong oxidizing ability, which can be used not only for water splitting to produce oxygen, but also for oxidizing and decomposing common organic pollutants.

[0004] However, the large band gap of WO3 means it can only absorb a small amount of visible light; its positive conduction band position requires a large overpotential for photoelectrocatalytic water splitting; and the space charge layer on its surface allows generated electrons and holes to separate only through different transfer rates, resulting in a high recombination rate of photogenerated carriers and severely affecting photoelectric conversion efficiency. To address these shortcomings of WO3, various methods can be employed, such as transition metal ion doping, heterojunctions, and defect engineering. Ion doping is an effective and simple method to improve the photoelectrode activity of WO3; however, the method of preparing WO3 using W-sheets generally requires very high temperatures, exceeding 1000℃, due to the high melting point of tungsten. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an alkali metal ion-doped WO3 nanoparticle. Rod array photoelectrode and its fabrication method. This application introduces alkali metal hydroxides to lower the transition temperature from tungsten metal to tungsten oxide, and fabricates an alkali metal-doped WO3 nanorod array on a W metal sheet using a one-step molten alkali etching oxidation method. By modulating the band structure of WO3, its light absorption is expanded, and the carrier separation efficiency is improved, thereby enhancing the photoelectric water splitting activity of the WO3 photoelectrode.

[0006] One objective of this invention is to provide a method for preparing an alkali metal ion-doped WO3 nanorod array photoelectrode, comprising the following steps: After cleaning the tungsten sheet, it is dried with inert gas. Alkali metal hydroxide and cleaned and dried tungsten sheets are calcined at high temperature in the same environment. During the calcination process, the alkali metal hydroxide volatilizes to the surface of the tungsten sheet, completing the etching and oxidation. After the calcination is completed, the product is naturally cooled and washed to obtain the alkali metal ion-doped WO3 nanorod array photoelectrode. The heating rate of the high-temperature calcination is 2~20℃ / min, the high-temperature calcination temperature is 600~750℃, and the high-temperature calcination time is 30~300min; The mass ratio of the alkali metal hydroxide to the tungsten sheet is 1:1 to 10:1.

[0007] Furthermore, the cleaning method for the tungsten sheet is as follows: the tungsten sheet is first ultrasonically cleaned with 1 mol / L HCl for 5-60 min, and then ultrasonically cleaned with acetone, ethanol, and deionized water for 5-60 min respectively.

[0008] Furthermore, the alkali metal hydroxide is one or more of LiOH, NaOH, KOH, and RbOH; preferably KOH.

[0009] Further, the alkali metal hydroxide is placed flat in container A, and the cleaned and dried tungsten sheet is placed obliquely into square container B, with the tungsten sheet at an angle of 5° to 80° to the horizontal. Containers A and B are simultaneously pushed into a tube furnace for high-temperature calcination. The distance between containers A and B is 1 to 20 cm, preferably 5 cm. An appropriate distance allows the alkali metal hydroxide vapor concentration to act uniformly on the tungsten sheet, resulting in a uniformly distributed tungsten oxide nanoarray. If the distance between containers A and B is too close (less than 1 cm), the alkali metal hydroxide concentration will be too high, causing the tungsten sheet to oxidize and separate; if the distance between containers A and B is too far (greater than 20 cm), the alkali metal hydroxide concentration will be too low, resulting in an uneven distribution of the tungsten oxide nanoarray.

[0010] Furthermore, the atmosphere for high-temperature roasting is air, oxygen, and a mixture of air and oxygen.

[0011] Furthermore, the product after high-temperature calcination is first ultrasonically cleaned with deionized water for 5-60 minutes, and then ultrasonically cleaned with ethanol for 5-60 minutes to remove excess alkali metal hydroxides from the photoelectrode surface.

[0012] The second objective of this invention is to provide an alkali metal ion-doped WO3 nanorod array photoelectrode prepared by the above-described preparation method.

[0013] Furthermore, the alkali metal ion-doped WO3 nanorod array photoelectrode includes a tungsten metal substrate and an alkali metal-doped WO3 semiconductor catalyst layer grown on the surface of the tungsten metal substrate. The tungsten metal substrate can serve as a precursor for WO3 growth and as a current collector for carrier migration. The valence state of W in WO3 is +4, +5, or +6, which correspond to WO3 with different oxygen vacancy concentrations.

[0014] Furthermore, the doping concentration of alkali metal ions in the alkali metal ion-doped WO3 nanorod array photoelectrode is 0.1~5%.

[0015] Compared with the prior art, the present invention has the following advantages: (1) The present invention involves calcining a cleaned and dried tungsten sheet with an alkali metal hydroxide in the same environment at high temperature (calcination heating rate of 2~20℃ / min, calcination temperature of 600~750℃, calcination time of 30~300min), utilizing the alkali metal hydroxide to volatilize to the surface of the tungsten sheet, and simultaneously completing the etching and oxidation processes at high temperature, thereby obtaining an alkali metal ion-doped WO3 nanorod array photoelectrode in one step. The mass ratio of alkali metal hydroxide to tungsten sheet is 1:1 to 10:1. This ratio range ensures that the alkali metal hydroxide can continuously and stably volatilize and deposit on the tungsten sheet surface during calcination. The calcination heating rate of 2 to 20 °C / min ensures the stable and uniform volatilization and deposition of the alkali metal hydroxide on the tungsten sheet surface, promoting uniform growth of the nanorod array and facilitating light absorption and electrolyte diffusion. Simultaneously, in-situ introduction of alkali metal ion doping and oxygen vacancies adjusts the conduction band position and band gap of WO3, expanding its absorption in the visible and infrared regions, thus solving the problem that WO3 can only absorb a small amount of visible light. The calcination temperature of 600 to 750 °C is sufficient... To ensure the effective volatilization and participation of alkali metal hydroxides in the reaction, while avoiding excessive sintering of tungsten sheets, the above-mentioned mass ratio allows WO3 conversion to be completed at temperatures far below the traditional 1000℃. At this temperature, in-situ doping enhances the carrier concentration and conductivity of WO3, reduces the overpotential required for photoelectrocatalytic water splitting, and overcomes the energy barrier problem caused by an overpositive conduction band position. A calcination time of 30–300 min ensures the reaction is fully completed, giving the nanorod array an appropriate aspect ratio and crystallinity. The enhanced conductivity promotes the effective separation of photogenerated electrons and holes, significantly reduces the carrier recombination rate, and thus greatly improves the photoelectric conversion efficiency of the WO3 nanorod array photoelectrode.

[0016] (2) By adjusting parameters such as the type of alkali metal hydroxide, the distance between the tungsten sheet and the alkali metal hydroxide, and the calcination temperature and time, the present invention can precisely control the band structure and carrier concentration of WO3, thereby achieving high efficiency. The efficient and stable WO3 photoelectrode provides a feasible path.

[0017] (3) The preparation method of the present invention adopts a one-step alkali etching oxidation process, which does not require a high temperature of more than 1000℃ (the calcination temperature is only 600~750℃), and has the advantages of simple preparation, low cost and green environmental protection. Attached Figure Description

[0018] Figure 1 In the image, (a) is a scanning electron microscope (SEM) image of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Example 1 of the present invention; (b) is a transmission electron microscope (TEM) image of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Example 1 of the present invention; (c) and (d) are both SEM images of the cross-section of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Example 1 of the present invention.

[0019] Figure 2 The XRD patterns of the alkali metal ion-doped WO3 nanorod array photoelectrodes prepared in Examples 1 and 10-12 of this invention and commercial WO3.

[0020] Figure 3 In the image, (a) shows the UV-Vis image of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Examples 1 and 10-12 of the present invention and commercial WO3; (b) shows the bandgap image of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Examples 1 and 10-12 of the present invention and commercial WO3.

[0021] Figure 4 XPS images of alkali metal ion-doped WO3 nanorod array photoelectrodes prepared in Examples 1 and 10-12 of this invention are shown below; (a) is the spectrum of W 4f; (b) is the spectrum of K 2p; (c) is the spectrum of O 1s; and (d) is the XPS valence band spectrum of the KOH-700 sample prepared in Example 1 and commercial WO3.

[0022] Figure 5 The following are the photoelectrochemical performance diagrams of the alkali metal ion-doped WO3 nanorod array photoelectrodes prepared in Examples 1 and 10-12 of this invention; wherein, (a) is the LSV curve; (b) is the IPCE curve; (c) is the electrochemical impedance spectroscopy; and (d) is the Mott-Schottky curve. Detailed Implementation

[0023] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0024] Unless otherwise specified, all reagents used in this invention are commercially available, and all methods used are conventional techniques in the art.

[0025] Example 1 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it out. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the metal tungsten sheet is at a 45-degree angle to the horizontal line. Place crucible A and crucible B in the same tube furnace for roasting. The horizontal distance between crucible A and crucible B is 5cm. The roasting heating rate of the tube furnace is 10℃ / min, the roasting temperature is 700℃, and the roasting holding time is 120min. After roasting, cool it with the furnace. The roasted W sheet is ultrasonically cleaned with deionized water and ethanol for 30min respectively to obtain an alkali metal ion doped WO3 nanorod array photoelectrode, which is named KOH-700.

[0026] pass Figure 1 The scanning electron microscope images (a), (c), and (d) show that the thickness of the formed WO3 film is approximately 40 micrometers, and the width of the WO3 nanowires is approximately 500 nm; Figure 1 The transmission electron microscope image (d) shows a clear WO3 semiconductor (020) crystal plane with a spacing of approximately [missing information]. The photoelectrode diameter is 0.375 nm. XRD and UV-Vis data analysis revealed that the formed crystal is monoclinic WO3 with numerous defects. XPS analysis showed that the WO3 surface is doped with potassium (K), and the K doping content decreases with increasing calcination temperature. Electrochemical performance testing showed that the optimal WO3 photoelectrode can achieve a photocurrent of 1.2 mA / cm². 2 (@1.23V vs RHE), and its electrochemical impedance is also the lowest.

[0027] Example 2 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the W sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of LiOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 5cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 10℃ / min, the heating and holding temperature is 700℃, and the heating and holding time is 120 min. After calcination, cool the crucible with the furnace. After calcination, clean the W sheet with deionized water and ethanol by ultrasonic cleaning for 30 min to obtain alkali metal ion-doped WO3 nanorod array photoelectrode.

[0028] Example 3 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of NaOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal line. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 10℃ / min, the heating and holding temperature is 700℃, and the heating and holding time is 120min. After calcination, cool the crucible with the furnace. After calcination, clean the WO3 nanorod array photoelectrode with deionized water and ethanol for 30min respectively.

[0029] Example 4 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of RbOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 5cm. Place crucible A and crucible B in the same tube furnace and heat them at a heating rate of 10℃ / min. The heating and holding temperature is 700℃ and the heating and holding time is 120min. After calcination, cool the crucible with the furnace. Clean the calcined W sheet with deionized water and ethanol by ultrasonic cleaning for 30min respectively to obtain an alkali metal ion-doped WO3 nanorod array photoelectrode.

[0030] Example 5 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 2cm. Place crucible A and crucible B in the same tube furnace and heat them at a heating rate of 10℃ / min, a holding temperature of 700℃, and a holding time of 120min. After calcination, cool the crucible with the furnace. Clean the calcined WO3 nanorod array photoelectrode with deionized water and ethanol for 30min respectively.

[0031] Example 6 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 10cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 10℃ / min, the heating and holding temperature is 700℃, and the heating and holding time is 120min. After calcination, cool the crucible with the furnace. After calcination, clean the W sheet with deionized water and ethanol by ultrasonic cleaning for 30min respectively to obtain alkali metal ion-doped WO3 nanorod array photoelectrode.

[0032] Example 7 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 20cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 10℃ / min, the heating and holding temperature is 700℃, and the heating and holding time is 120min. After calcination, cool the crucible with the furnace. After calcination, clean the W sheet with deionized water and ethanol by ultrasonic cleaning for 30min respectively to obtain alkali metal ion-doped WO3 nanorod array photoelectrode.

[0033] Example 8 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal line. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 5cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 2℃ / min, the heating and holding temperature is 700℃, and the heating and holding time is 120min. After calcination, cool the furnace. The calcined W sheet is ultrasonically cleaned with deionized water and ethanol for 30min respectively to obtain an alkali metal ion-doped WO3 nanorod array photoelectrode.

[0034] Example 9 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 5cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 20℃ / min, the heating and holding temperature is 700℃, and the heating and holding time is 120min. After calcination, cool the crucible with the furnace. After calcination, clean the W sheet with deionized water and ethanol by ultrasonic cleaning for 30min respectively to obtain alkali metal ion-doped WO3 nanorod array photoelectrode.

[0035] Example 10 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal line. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 5cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 5℃ / min, the heating and holding temperature is 600℃, and the heating and holding time is 120 min. After calcination, cool the furnace. The calcined W sheet is ultrasonically cleaned with deionized water and ethanol for 30 min respectively to obtain an alkali metal ion-doped WO3 nanorod array photoelectrode, which is named KOH-600.

[0036] Example 11 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 5cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 5℃ / min, the heating and holding temperature is 650℃, and the heating and holding time is 120min. After calcination, cool the crucible with the furnace. The calcined WO3 nanorod array photoelectrode is ultrasonically cleaned with deionized water and ethanol for 30min respectively to obtain an alkali metal ion-doped WO3 nanorod array photoelectrode, which is named KOH-650.

[0037] Example 12 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal line. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 5cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 5℃ / min, the heating and holding temperature is 750℃, and the heating and holding time is 120min. After calcination, cool the crucible with the furnace. The calcined WO3 nanorod array photoelectrode is ultrasonically cleaned with deionized water and ethanol for 30min respectively to obtain an alkali metal ion-doped WO3 nanorod array photoelectrode, which is named KOH-750.

[0038] Example 13 A method for fabricating an alkali metal ion-doped WO3 nanorod array photoelectrode includes the following steps: (1) Cut the tungsten (W) sheet into a rectangle of 2cm*3cm with a thickness of 0.27mm and a mass of 3.0g. First, use 1mol / L HCl to ultrasonically clean for 30min, then use acetone, ethanol and deionized water to ultrasonically clean for 30min each. After cleaning, use compressed nitrogen gas to blow dry the W sheet for later use. (2) Weigh 5g of KOH and place it in a quartz crucible A (i.e., container A) and spread it evenly. Then place the crucible in a tube furnace. Place the cleaned tungsten sheet obliquely into a square quartz crucible B (i.e., container B) so that the tungsten sheet is at a 45-degree angle to the horizontal. Push the crucible containing the tungsten sheet into the tube furnace. The horizontal distance between crucible A and crucible B is 5cm. Place crucible A and crucible B in the same tube furnace at the same time and heat them. The heating rate is 5℃ / min, the heating and holding temperature is 700℃, and the heating and holding time is 30min. After calcination, cool the crucible with the furnace. After calcination, ultrasonically clean the WO3 nanorod array photoelectrode with deionized water and ethanol for 30min respectively to obtain alkali metal ion doped WO3 nanorod array photoelectrode.

[0039] Results Analysis Figure 1 In the images, (a) is a scanning electron microscope (SEM) image of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Example 1 of the present invention; (b) is a transmission electron microscope (TEM) image of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Example 1 of the present invention; (c) and (d) are both SEM images of the cross-section of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Example 1 of the present invention. Figure 1 As can be seen from (a) to (d) in this embodiment, a nanorod array is grown on the W sheet. The array is 50 micrometers thick and the nanorods are about 100 nm in diameter. This vertical array forms an electron transport channel, which is beneficial for the separation of charge carriers.

[0040] Figure 2 The images show the XRD patterns of the alkali metal ion-doped WO3 nanorod array photoelectrodes prepared in Examples 1 and 10-12 of this invention, compared with commercial WO3. Figure 2 It can be seen that the WO3 photoelectrode treated at different temperatures exhibits monoclinic phase diffraction peaks. The three strongest peaks appear at 2θ = 23.1°, 23.6° and 24.4°, which correspond to the (002), (020) and (200) crystal planes of the monoclinic WO3 crystal, respectively. As the treatment temperature increases, the crystallinity of WO3 increases. In addition, as the oxidation temperature increases, the WO3 crystal exhibits preferential growth of the (002) crystal plane, and the diffraction peaks shift to smaller angles. This is because at higher temperatures, more K ions are incorporated into the WO3 crystal, resulting in increased interatomic spacing and improved conductivity of the WO3 photoelectrode.

[0041] Figure 3 In the image, (a) shows the UV-Vis images of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Examples 1 and 10-12 of this invention and commercial WO3; (b) shows the bandgap images of the alkali metal ion-doped WO3 nanorod array photoelectrode prepared in Examples 1 and 10-12 of this invention and commercial WO3. Figure 3 As shown in (a) and (b), the absorption band edge of commercial WO3 is located at approximately 440 nm, absorbing only a small amount of visible light. With increasing annealing temperature, the absorption band edge of the alkali-treated WO3 photoanode gradually shifts towards red light, especially for the KOH-700 and KOH-750 photoelectrodes, whose absorption band edges are located at approximately 470 nm and 480 nm, respectively, showing a more pronounced shift. Notably, the absorbance of the KOH-600 and KOH-65 photoelectrodes in the visible and near-infrared regions increases significantly, which is related to the KOH-700 photoanode. x WO 3-x The formation of oxygen vacancies is related to this. The two photoelectrodes, KOH-600 and KOH-650, contain a large number of oxygen vacancies, and these defect energy levels lead to light absorption in the visible and near-infrared regions. However, the energy of electrons and holes excited by these defect energy levels in the visible and near-infrared regions is too low to enable photocatalytic water splitting.

[0042] Figure 4 XPS spectra of the alkali metal ion-doped WO3 nanorod array photoelectrodes prepared in Examples 1 and 10-12 of this invention; wherein, (a) is the spectrum of W 4f; (b) is the spectrum of K 2p; (c) is the spectrum of O 1s; and (d) are the XPS valence band spectra of the KOH-700 photoelectrode prepared in Example 1 and commercial WO3. Figure 4Figure (a) shows the W 4f elemental spectrum of the alkali-treated WO3 photoanode. It can be seen that the intensity of the W 4f peak gradually weakens with increasing annealing temperature, indicating that the binding energy of W 4f in the alkali-treated WO3 photoelectrode gradually decreases. In addition, with increasing annealing temperature, the binding energy of the W 4f peak undergoes a slight red shift due to potassium (K) doping. Figure 4 Image (b) shows the K 2p elemental spectrum of the WO3 photoanode after alkali-thermal treatment. It can be seen that the K 2p peak intensity of the KOH-600 photoelectrode is stronger, indicating that the K 2p peak in the WO3 photoelectrode is higher. + Mainly K x WO 3-x The K 2p peak exists in the form of K, and its intensity gradually weakens with increasing annealing temperature, confirming that K 2p exists in the form of K. + It has been successfully doped into the WO3 lattice. Figure 4 As shown in (c), the two component peaks of the O 1s peak are located at 530.2 eV and 532 eV, respectively, corresponding to the lattice oxygen in the WOW bond and the adsorbed hydroxyl oxygen in the W-OH bond. For the KOH-700 photoelectrode, a slight shift in the O 1s peak was observed, with a decrease in peak intensity at 530.2 eV and an increase in peak intensity at 532 eV. This may be due to the chemical shift of the hydroxyl groups grafted onto the WO3 surface, leading to a change in the electron cloud density of the O 1s peak.

[0043] Figure 5 The figures show the photoelectrochemical performance of the alkali metal ion-doped WO3 nanorod array photoelectrodes prepared in Examples 1 and 10-12 of this invention; wherein, (a) is the LSV curve in 1M sodium sulfate (Na2SO4) electrolyte under simulated sunlight (AM1.5G) irradiation; (b) is the IPCE curve; (c) is the electrochemical impedance spectroscopy; and (d) is the Mott-Schottky curve. Figure 5 As shown in (a), the photocurrent density of the alkali-treated WO3 photoelectrode first increases and then decreases with increasing annealing temperature. The photocurrent density of the KOH-700 photoelectrode reaches 1.2 mA / cm². 2 This is almost four times that of the KOH-600 photoelectrode. The lower photocurrent density of the KOH-600 and KOH-650 photoelectrodes is likely due to insufficient light absorption and non-stoichiometric Kx. x WO 3-xThe generated oxygen vacancies readily become recombination centers for charge carriers. Increasing the annealing temperature can eliminate some of these oxygen vacancies; therefore, as the annealing temperature increases, the concentration of oxygen vacancies gradually decreases, and the photocurrent density of the WO3 photoelectrode continuously increases. Another possible explanation is that the hydroxyl graft layer generated by alkaline heat treatment accelerates the oxidation kinetics of water, thereby increasing the current density of the alkaline-treated WO3 photoelectrode. When the annealing temperature rises to 750℃, the photocurrent density decreases, possibly because the nanorod array breaks down into nanoparticles, hindering longitudinal electron transport.

[0044] like Figure 5 As shown in (b), the IPCE (photocurrent efficiency) performance of different WO3 photoelectrodes was tested under simulated sunlight irradiation in 1 M Na2SO4 electrolyte at 1.6 V vs. RHE. Photoelectric efficiency mainly consists of three parts: light absorption efficiency, carrier separation efficiency, and collection efficiency. The photoelectric conversion efficiency of the KOH-700 and KOH-750 photoelectrodes was significantly improved in the wavelength range of 420–500 nm. Considering the enhanced light absorption capabilities of the KOH-700 and KOH-750 photoelectrodes, it can be concluded that the improved IPCE of KOH-700 and KOH-750 is due to the enhanced light absorption capabilities.

[0045] Depend on Figure 5 (c) shows the electrochemical impedance spectroscopy (EIS) diagrams for different WO3 photoelectrodes. The radius of the arc in the Nyquist plot reflects the charge transfer in the photocatalytic system. A smaller radius indicates lower resistance, lower impedance of charge carriers during migration, and a lower recombination probability. After alkaline heat treatment, the semicircle of the sample first decreases and then increases with increasing annealing temperature, with the KOH-700 photoelectrode reaching its minimum impedance. This indicates that appropriate alkaline heat treatment can effectively improve the conductivity of the photoanode. The EIS trend is consistent with the photoelectrochemical photocurrent density, indicating that the increase in photoanode photocurrent density is partly due to the improved conductivity of the photoelectrode. As the concentration of photogenerated charge carriers increases, the photocurrent density increases, thereby leading to improved conductivity of the photoelectrode.

[0046] Depend on Figure 5 As shown in (d), the slope of the straight line segment of the Mott-Schottky curve is positive, indicating that the prepared WO3 photoelectrode is an n-type semiconductor. The intercept of the straight line segment on the horizontal axis can be used to deduce the flat band potential of the semiconductor. The flat band potentials of the four photoelectrodes, KOH-600, KOH-650, KOH-700, and KOH-750, are -0.05V, -0.10V, -0.18V, and -0.27V, respectively (relative to the standard hydrogen electrode, NHE). Ignoring the band bending of the semiconductor, the Fermi level of the semiconductor can be considered close to the flat band potential, thus allowing the determination of the Fermi level position.

[0047] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described in this invention to avoid redundancy. Although preferred embodiments of this invention have been described, those skilled in the art, once they understand the inventive concept of this invention, can make other changes and modifications to these embodiments, and all such changes and modifications fall within the scope of this invention.

[0048] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. If such modifications and variations fall within the scope of equivalents of this invention, then this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an alkali metal ion-doped WO3 nanorod array photoelectrode, characterized in that, Includes the following steps: After cleaning the tungsten sheet, it is dried with inert gas. Alkali metal hydroxide and cleaned and dried tungsten metal sheets are calcined at high temperature in the same environment to etch and oxidize the surface of the tungsten metal sheets. After calcination, the product is naturally cooled and washed to obtain the alkali metal ion-doped WO3 nanorod array photoelectrode. The heating rate of the high-temperature calcination is 2~20℃ / min, the high-temperature calcination temperature is 600~750℃, and the high-temperature calcination time is 30~300min; The mass ratio of the alkali metal hydroxide to the tungsten sheet is 1:1 to 10:

1.

2. The method for preparing the alkali metal ion-doped WO3 nanorod array photoelectrode according to claim 1, characterized in that, The alkali metal hydroxide is one or more of LiOH, NaOH, KOH, and RbOH.

3. The method for preparing the alkali metal ion-doped WO3 nanorod array photoelectrode according to claim 1, characterized in that, The alkali metal hydroxide is placed in container A and spread out. The cleaned and dried tungsten metal sheet is placed obliquely in container B, so that the tungsten metal sheet is at an angle of 5° to 80° with the horizontal line. Containers A and B are placed in the same environment for high-temperature roasting, and the horizontal distance between containers A and B is 1 to 20 cm.

4. The method for preparing the alkali metal ion-doped WO3 nanorod array photoelectrode according to claim 1, characterized in that, The atmosphere for high-temperature roasting is air, oxygen, or a mixture of air and oxygen.

5. The method for preparing the alkali metal ion-doped WO3 nanorod array photoelectrode according to claim 1, characterized in that, The cleaning method for the tungsten sheet is as follows: first, ultrasonically clean the tungsten sheet with 1 mol / L HCl for 5-60 min, and then ultrasonically clean it with acetone, ethanol, and deionized water for 5-60 min respectively.

6. The method for preparing the alkali metal ion-doped WO3 nanorod array photoelectrode according to claim 1, characterized in that, The product after high-temperature calcination is first ultrasonically cleaned with deionized water for 5-60 minutes, and then ultrasonically cleaned with ethanol for 5-60 minutes to remove excess alkali metal hydroxides from the photoelectrode surface.

7. An alkali metal ion-doped WO3 nanorod array photoelectrode prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The alkali metal ion-doped WO3 nanorod array photoelectrode includes a tungsten metal substrate and an alkali metal-doped WO3 semiconductor catalyst layer grown on the surface of the tungsten metal substrate.

8. The alkali metal ion-doped WO3 nanorod array photoelectrode according to claim 7, characterized in that, The doping concentration of alkali metal ions in the WO3 nanorod array photoelectrode doped with alkali metal ions is 0.1~5%.

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