A heterojunction ZnO / Co3O4 photoelectrode film and its preparation method and application

Abstract

The present invention discloses a preparation method and application of a heterojunction ZnO / Co3O4 photoelectrode film. A clean conductive glass (FTO) is placed in an acetone solution of ZnO, and a ZnO film is obtained by an electrophoretic deposition method. ZnO is then placed in an acetone solution for ultrasonic dispersion, and the obtained ZnO film is placed in an ethanol solution of Co3O4 with polyethylene glycol, and a thin layer of Co3O4 film is superimposed on the ZnO film by an immersion method; the obtained product is annealed at high temperature to obtain a ZnO / Co3O4 heterojunction film. The ZnO / Co3O4 photoelectrode film prepared by the present invention is used to improve the photogenerated electron transmission capacity of the ZnO photoelectrode, thereby effectively improving the photoelectrochemical performance and enhancing the anti-photocorrosion ability of ZnO.

Description

Technical Field

[0001] The invention belongs to the technical field of photoelectrochemistry, and in particular relates to a high-performance heterojunction ZnO / Co3O4 photoelectrode film and a preparation method and application thereof. Background Art

[0002] Energy is the material basis for human survival and development. With the growth of population and rapid economic development, the consumption of fuel by human beings is accelerating, and the usable time of fossil fuels is becoming more and more limited. In recent decades, with the depletion of fossil energy such as coal, oil, and natural gas and the increasingly severe environmental pollution problems, the sustainable development of human society has been seriously threatened. The development of a long-term sustainable green energy is imminent. Solar energy is an inexhaustible natural energy source. The energy it irradiates to the earth every second is equivalent to the energy generated by the combustion of 5 million tons of coal. Hydrogen energy is a green and pollution-free energy source. The only product of its combustion is water. Hydrogen energy is considered to be one of the most ideal alternative energy sources to solve energy crises and environmental problems because of its high calorific value, high efficiency and environmental friendliness. However, the large-scale acquisition of hydrogen currently mainly comes from the reforming of coal, oil and natural gas. Although this hydrogen production method is mature, it is costly and pollutes the environment. Therefore, it is imperative to seek a green, economical and environmentally friendly hydrogen production method. Therefore, the use of solar energy to produce hydrogen by photoelectrochemical (PEC) water decomposition has attracted widespread attention. Finding and studying semiconductors with the potential to prepare high-performance PEC photoanodes is an important research direction in this field.

[0003] ZnO is an n-type visible light driven semiconductor with a band gap of about 3.8 eV, which is consistent with the band structure of hydrogen production. At present, reports on the application of ZnO in PEC are very common. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a high-performance heterojunction material ZnO / Co3O4 photoelectrode film and its application, which has the advantages of simple preparation method, convenience, low cost, mild conditions, and easy control of experimental conditions.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a heterojunction ZnO / Co3O4 photoelectrode film, the preparation method of which comprises the following steps:

[0006] 1) adding ZnO powder to an acetone solution, then adding I2, dispersing the ZnO suspension by ultrasound, and preparing the ZnO film by electrophoretic deposition;

[0007] 2) adding Co3O4 powder to a mixed solution of ethanol and polyethylene glycol, dispersing by ultrasonic to obtain a Co3O4 homogeneous sol nanoparticle solution, adding the ZnO film obtained in step 1), and superimposing a layer of Co3O4 film on the ZnO film by an immersion method;

[0008] 3) The product obtained in step 2) is calcined at high temperature under inert gas or air conditions to obtain a heterojunction ZnO / Co3O4 photoelectrode film.

[0009] Furthermore, the above-mentioned heterojunction ZnO / Co3O4 photoelectrode film, step 1) is specifically: adding ZnO powder to an acetone solution, adding I2 after ultrasonic dispersion, and continuing ultrasonic dispersion to obtain a ZnO deposition suspension; inserting two cleaned conductive glass FTOs of equal area into the ZnO deposition suspension, and immersing the conductive surfaces of the two conductive glass FTOs opposite to each other and parallel to each other in the ZnO deposition suspension, depositing for 1-5 minutes under a DC voltage of 15-25V to obtain a ZnO film on the conductive glass FTO.

[0010] Furthermore, in the above-mentioned heterojunction ZnO / Co3O4 photoelectrode film, in step 1), ZnO powder: acetone: I2 = 6g: 2500mL: 1.2g.

[0011] Furthermore, in the above-mentioned heterojunction ZnO / Co3O4 photoelectrode film, step 2) is specifically: adding Co3O4 powder to an ethanol solution, then adding polyethylene glycol to the above solution, and obtaining Co3O4 homogeneous sol nanoparticles after ultrasonic dispersion; inserting the conductive glass FTO coated with ZnO film obtained in step 1) into the Co3O4 homogeneous solution, immersing it for 8-12 minutes, and superimposing a layer of Co3O4 film on the ZnO film.

[0012] Furthermore, in the above-mentioned heterojunction ZnO / Co3O4 photoelectrode film, in step 2), Co3O4 powder: anhydrous ethanol: polyethylene glycol = 6g: 3000mL: 50mL.

[0013] Furthermore, in the above-mentioned heterojunction ZnO / Co3O4 photoelectrode film, in step 3), the high-temperature calcination is calcination at a temperature of 100-300°C for 20-40 minutes.

[0014] Furthermore, in the above-mentioned heterojunction ZnO / Co3O4 photoelectrode film, the preparation method of the ZnO powder comprises the following steps: adding a zinc salt to an aqueous solution containing PVP and DMF, mixing evenly, and then dripping a 0.25M NaOH aqueous solution until the pH reaches 10, stirring the resulting mixed solution for 10 minutes and then transferring it to a hydrothermal kettle, placing it in an oven, and heating it at 100-180°C for 0.5-2h, and washing the resulting product by centrifugation with acetone and ethanol, and drying it at 50-70°C to obtain ZnO powder; the zinc salt is zinc nitrate, zinc acetate, zinc acetate or zinc chloride.

[0015] Furthermore, in the above-mentioned heterojunction ZnO / Co3O4 photoelectrode film, the preparation method of the Co3O4 powder includes the following steps: placing an appropriate amount of cobalt salt in a crucible, annealing at 300-500°C for 2-4h to obtain Co3O4 powder; the cobalt salt is cobalt nitrate, cobalt sulfate or cobalt chloride.

[0016] The above-mentioned heterojunction ZnO / Co3O4 photoelectrode film is used as a photocathode semiconductor material in the photolysis of water to produce hydrogen.

[0017] The beneficial effects of the present invention are:

[0018] 1. The ZnO / Co3O4 photoelectrode film prepared by the present invention has a heterojunction structure, which makes it easier to effectively separate photogenerated electrons and holes, reduce the recombination rate, and effectively improve the photoelectrochemical performance.

[0019] 2. The ZnO / Co3O4 photoelectrode film prepared by the present invention can effectively improve the carrier transmission efficiency and the collection efficiency of the electrons by the conductive substrate as a cathode material, and can obtain high PEC performance.

[0020] 3. The preparation method provided by the present invention has cheap raw materials and simple operation, which greatly reduces the cost and is pollution-free to the environment, thus realizing green chemistry. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 XRD patterns of ZnO powder, Co3O4 powder, ZnO photoelectrode film and ZnO / Co3O4 photoelectrode film.

[0022] Figure 2 This is a comparison of the photocurrent of ZnO / Co3O4 photoelectrode film and ZnO film.

[0023] Figure 3 This is a comparison chart of the impedance spectra of ZnO / Co3O4 photoelectrode film and ZnO film. DETAILED DESCRIPTION

[0024] Example 1 A method for preparing a heterojunction ZnO / Co3O4 photoelectrode film

[0025] (I) The preparation method is as follows

[0026] 1) Preparation of ZnO powder by hydrothermal method

[0027] 0.24g Zn(C2H3O2)2 and 0.4g PVP were dissolved in 40mL DMF and 8mL distilled water, and magnetically stirred for 20min. After mixing evenly, 0.25M NaOH solution was slowly added until the pH reached 10. After continuing magnetic stirring for 10min, the obtained mixed solution was transferred to a high-pressure hydrothermal autoclave, and then placed in an oven and heated at 140°C for 90min. The obtained product was centrifuged three times with acetone and ethanol respectively, and dried at 60°C to obtain ZnO powder.

[0028] 2) Preparation of Co3O4 powder by calcination

[0029] 1 g of Co(NO3)2 was placed in a crucible and calcined in a muffle furnace at 420°C for 3 h in air to obtain Co3O4 powder.

[0030] 3) Preparation of ZnO thin film

[0031] 0.06g ZnO powder was added to 25mL acetone solution, and 0.012g I2 was added after ultrasonic dispersion for 0.5h, and ultrasonic dispersion was continued for 0.5h to obtain ZnO deposition suspension. Two cleaned conductive glass FTO with equal area were prepared, and the conductive surfaces of the two conductive glass FTO were made to face each other and parallel to each other and immersed in the ZnO deposition suspension, and deposited for 3min under 25V DC voltage to obtain ZnO film.

[0032] 4) Preparation of ZnO / Co3O4 thin film

[0033] 0.06g Co3O4 powder was added to 30mL anhydrous ethanol and then 0.5mL polyethylene glycol was added, and the mixture was ultrasonicated for 0.5h to obtain a uniformly mixed Co3O4 solution. The conductive glass FTO coated with ZnO film obtained in step 3) was taken, and then the ZnO photoanode was immersed in the above Co3O4 solution for 10min, and then calcined at 300℃ in a muffle furnace for 0.5h to obtain a Co3O4 film superimposed on the ZnO film.

[0034] 5) The product obtained in step 4) is subjected to high temperature annealing at 300° C. for 30 min to obtain a heterojunction ZnO / Co3O4 photoelectrode film.

[0035] (II) Testing

[0036] Figure 1The XRD comparison diagram of ZnO powder, Co3O4 powder, ZnO photoelectrode film and ZnO / Co3O4 photoelectrode film. Figure 1 It can be seen that ZnO powder has seven obvious diffraction peaks at 31.7°, 34.4°, 36.2°, 47.5°, 56.6°, 62.8°, and 67.9°, which are characteristic peaks of ZnO. The diffraction peaks of ZnO sample are completely consistent with the peak spectrum of zinc oxide standard card, indicating that ZnO material is prepared. Co3O4 powder has six obvious diffraction peaks at 31.2°, 36.8°, 38.5°, 44.8°, 59.3°, and 65.1°, which are characteristic peaks of Co3O4. The diffraction peaks of Co3O4 sample are completely consistent with the peak spectrum of cobalt oxide standard card, indicating that Co3O4 material is prepared. The characteristic peaks displayed by ZnO photoelectrode film are not only completely consistent with the peak spectrum of zinc oxide standard card, but also completely consistent with the peak spectrum of tin dioxide standard card, indicating that ZnO photoelectrode film is prepared. The characteristic peaks displayed by the ZnO / Co3O4 photoelectrode film are completely consistent not only with the peak spectra of the zinc oxide and cobalt tetroxide standard cards, but also with the peak spectra of the tin dioxide standard card, indicating that the ZnO / Co3O4 photoelectrode film is prepared.

[0037] Example 2 Performance test of heterojunction ZnO / Co3O4 photoelectrode film

[0038] The photoelectrochemical properties of the pure ZnO photoelectrode film and the ZnO / Co3O4 photoelectrode film of Example 1 were tested for photocurrent, impedance, etc.

[0039] All electrochemical experimental tests were conducted in a three-electrode electrochemical workstation (Princeton Applied Research 2273). The sample film was used as the working electrode, the platinum sheet was used as the counter electrode, the Ag / AgCl was used as the reference electrode, the electrolyte was 0.1 M NaSO4, and the sample light irradiation area was 1 cm 2 .

[0040] Photocurrent test: The light source is a 300W xenon lamp, the bias voltage is 1.23Vvs.VRHE, and the measured results are as follows Figure 2 The results show that the photocurrent density of the heterojunction ZnO / Co3O4 photoelectrode film is 0.12 mA cm -2 The photocurrent of ZnO photoelectrode film is about 0.05 mA cm -2 The results show that the photocurrent of the heterojunction ZnO / Co3O4 photoelectrode film is larger than that of the ZnO photoelectrode film, which is increased by about 2.4 times. This shows that the photoelectrochemical performance is improved after loading Co3O4 and the binding efficiency of the electron-hole pairs in the ZnO / Co3O4 heterojunction is increased.

[0041] Electrochemical impedance spectroscopy (EIS) test: fixed voltage is 0Vvs.Voc, frequency range is 0.1~10 5 Hz. The measured results are as follows Figure 3 As shown in the figure, the results show that a larger semicircle radius means a larger composite resistance. Therefore, the capacitive arc radius of the heterojunction ZnO / Co3O4 photoelectrode film is the smallest, indicating that the charge transfer resistance of the heterojunction ZnO / Co3O4 photoelectrode film is smaller than that of the ZnO film. The impedance is relatively small and the photocurrent is the largest, which is consistent with Figure 2 In line with.

[0042] In summary, Figure 2 and Figure 3 It can be observed that the photoelectrochemical performance of the heterojunction ZnO / Co3O4 thin film is more stable than that of the ZnO thin film.

Claims

1. A heterojunction ZnO / Co3O4 photoelectrode film, characterized in that: The preparation method comprises the following steps: 1) adding ZnO powder to an acetone solution, then adding I2, dispersing the ZnO deposition suspension by ultrasonication, and preparing the ZnO film by electrophoretic deposition; 2) adding Co3O4 powder to a mixed solution of ethanol and polyethylene glycol, dispersing by ultrasonic to obtain a Co3O4 homogeneous sol nanoparticle solution, adding the ZnO film obtained in step 1), and superimposing a layer of Co3O4 film on the ZnO film by an immersion method; 3) calcining the product obtained in step 2) at a high temperature under an inert gas or air condition to obtain a heterojunction ZnO / Co3O4 photoelectrode film; Step 1) is specifically as follows: adding ZnO powder to an acetone solution, adding I2 after ultrasonic dispersion, and continuing ultrasonic dispersion to obtain a ZnO deposition suspension; inserting two cleaned conductive glass FTOs of equal area into the ZnO deposition suspension, and immersing the conductive surfaces of the two conductive glass FTOs opposite to each other and parallel to each other in the ZnO deposition suspension, and depositing for 1-5 minutes under a DC voltage of 15-25V to obtain a ZnO film on the conductive glass FTO; ZnO powder: acetone: I2 = 6g: 2500mL: 1.2g; Step 2) is specifically as follows: adding Co3O4 powder to an ethanol solution, then adding polyethylene glycol to the above solution, and obtaining Co3O4 homogeneous sol nanoparticles after ultrasonic dispersion; inserting the conductive glass FTO coated with a ZnO film obtained in step 1) into the Co3O4 homogeneous solution, immersing it for 8-12 minutes, and stacking a layer of Co3O4 film on the ZnO film; Co3O4 powder: anhydrous ethanol: polyethylene glycol = 6g: 3000mL: 50mL.

2. A heterojunction ZnO / Co3O4 photoelectrode film as claimed in claim 1, characterized in that: In step 3), the high temperature calcination is calcining at a temperature of 100-300° C. for 20-40 min.

3. A heterojunction ZnO / Co3O4 photoelectrode film as claimed in claim 1, characterized in that: The preparation method of the ZnO powder comprises the following steps: adding zinc salt to an aqueous solution containing PVP and DMF, mixing evenly, then dripping a 0.25M NaOH aqueous solution until the pH reaches 10, stirring the obtained mixed solution for 10 minutes, transferring it to a hydrothermal kettle, placing it in an oven, heating it at 100-180° C. for 0.5-2 hours, washing the obtained product by centrifugation with acetone and ethanol, and drying it at 50-70° C. to obtain ZnO powder; the zinc salt is zinc nitrate, zinc acetate, zinc acetate or zinc chloride.

4. A heterojunction ZnO / Co3O4 photoelectrode film as claimed in claim 1, characterized in that: The preparation method of the Co3O4 powder comprises the following steps: placing an appropriate amount of cobalt salt in a crucible, annealing at 300-500° C. for 2-4 hours, and obtaining Co3O4 powder; the cobalt salt is cobalt nitrate, cobalt sulfate or cobalt chloride.

5. Use of the heterojunction ZnO / Co3O4 photoelectrode film as claimed in claim 1 as a photocathode semiconductor material in photolysis of water to produce hydrogen.

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