Preparation method and application of novel molybdenum oxide photoelectrocatalyst

Abstract

The application belongs to the field of composite materials and relates to a novel cadmium hydroxide (Cd(OH)2) doped molybdenum oxide photoelectrocatalyst and a preparation method thereof. A cadmium hydroxide doped molybdenum oxide (MoO 3‑x ) film (Cd(OH)2@MoO 3‑x ) is prepared by using a wet chemical one-step electrochemical codeposition method. The introduction of cadmium hydroxide not only significantly improves the light absorption characteristics of the molybdenum oxide material, but also significantly improves the performance of the molybdenum oxide photoelectrocatalytic water splitting for hydrogen production. The preparation process disclosed by the application is simple, has a short time course, simple instruments and equipment, and low cost of non-noble metals, and the prepared Cd(OH)2@MoO 3‑x film has excellent photoelectrocatalytic performance and good application prospect.

Description

Technical Field

[0001] This invention relates to the field of composite materials, and in particular to the preparation method and application of photoelectrocatalysts. Background Technology

[0002] Molybdenum oxide (MoO) 3-x (x ≤ 0 ≤ x ≤ 1) is an inexpensive two-dimensional metal oxide semiconductor material widely used in steel, electrocatalysis, electrochromism, batteries, sensors, capacitors, and other fields. As a semiconductor electrocatalyst, it can induce valence band electrons to transition to the conduction band under illumination, generating electron-hole pairs, which can increase the rate of redox reactions. With the introduction of national energy conservation and emission reduction policies, the full utilization of green energy such as sunlight has received widespread attention. Utilizing sunlight to improve chemical reaction kinetics has become one of the important development directions in the chemical production industry.

[0003] Because molybdenum oxide (MoO) semiconductors do not respond strongly to light, illumination cannot effectively enhance its electrocatalytic performance. Furthermore, the surface energy, conductivity, and other physicochemical properties of MoO are not optimal. Therefore, it is necessary to improve the photoelectrocatalytic performance of MoO through appropriate methods. Doping impurities into two-dimensional layered semiconductor materials can modulate the interlayer spacing, surface energy, conductivity, and band structure, thereby reducing the band gap and improving light utilization. This is an effective means to improve the photoresponse performance of semiconductors and is of great significance for increasing the utilization rate of solar energy in photoelectrocatalysis. Summary of the Invention

[0004] In view of this, the present invention relates to a method for preparing a novel cadmium hydroxide (Cd(OH)2)-doped molybdenum oxide composite thin film material and its application in photoelectrocatalytic water splitting for hydrogen production.

[0005] It should be noted that in photoelectrocatalysis applications, molybdenum oxide itself has a certain light absorption property, and light irradiation can enhance the performance of electrocatalysis. However, its light absorption and utilization rate is low, and it cannot fully convert the energy of sunlight into chemical energy and store it in energy molecules such as hydrogen during electrocatalysis. Therefore, it is necessary to improve the absorption capacity of molybdenum oxide for sunlight (especially visible light) by controlling the band structure of the molybdenum oxide semiconductor material, thereby improving its photoelectrocatalytic performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A novel method for preparing Cd(OH)₂-doped molybdenum oxide photocatalysts utilizes a wet chemical one-step electrochemical co-deposition method to prepare two-dimensional layered molybdenum oxide (MoO₂) doped with Cd(OH)₂. 3-x Thin film, namely Cd(OH)2@MoO 3-x Thin film; specifically, the preparation method includes the following steps:

[0008] 1) Preparation of substrate electrode: A 3 mm disc gold electrode (Ni, Cu, C, etc. can also be used) is polished sequentially with 1.0, 0.3 and 0.05 μm alumina powder, then washed with deionized water and ethanol for 5 min under ultrasonic conditions, and then rinsed with flowing secondary water to obtain the substrate electrode.

[0009] 2) Electrochemical co-deposition preparation of Cd(OH)2@MoO 3-x Thin film: The disk gold electrode, Ag / AgCl reference electrode, and carbon rod counter electrode treated in step 1) are inserted into a film containing (NH4)6Mo7O 24 The Cd(OH)2@MoO was obtained by electrochemical co-deposition in a mixed solution of 4H2O and cadmium salt. 3-x film.

[0010] Optionally, in step 2), the mixed solution contains (NH4)6Mo7O 24 The concentration is 1-1000 mM; the cadmium salt concentration is 0.05-10 mM, and the cadmium salt is CdCl2, Cd(NO3)2 or CdSO4; (NH4)6Mo7O 24 The concentration ratio with cadmium salts is 100-20000;

[0011] Furthermore, the electrochemical co-deposition voltage is -0.6 to -1.1V, the temperature is 10℃ to 50℃, and the deposition time is 1ms to 100s.

[0012] This invention also requests the application of the novel cadmium hydroxide (Cd(OH)2)-doped molybdenum oxide photocatalyst in water electrolysis for hydrogen production.

[0013] As can be seen from the above technical solutions, compared with the prior art, the novel molybdenum oxide photocatalyst and its preparation method provided by the present invention have the following superior effects:

[0014] This invention utilizes a simple electrochemical co-deposition method to dope cadmium hydroxide into molybdenum oxide thin films, resulting in a wider absorption spectrum and greater absorption intensity in the composite film, thus improving light utilization. This significantly enhances its photoelectrocatalytic water splitting performance for hydrogen production. Furthermore, the equipment is simple, the preparation is rapid, and the cost is low, making it a promising candidate for future applications. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0016] Figure 1 Cd(OH)2, MoO 3-x Cd(OH)2@MoO 3-x Linear scan voltammetry comparison of hydrogen evolution through water electrolysis of thin-film catalysts under light irradiation.

[0017] Figure 2 100mM(NH4)6Mo7O 24 Linear scan voltammetry of 100 mM CdSO4 solution.

[0018] Figure 3 Cd(OH)2@MoO 3-x High-angle dark-field transmission electron microscopy (HAADF) images of the thin films and X-ray energy dispersive spectra of Mo, O, and Cd.

[0019] Figure 4 Cd(OH)2@MoO 3-x Optical scanning voltammetry of the thin film at a slow scan rate (0.1 mV / s) for hydrogen evolution in water electrolysis.

[0020] Figure 5 Cd(OH)2, MoO 3-x Cd(OH)2@MoO 3-x UV-Vis spectrum of thin-film catalyst.

[0021] Figure 6 For 10mA / cm 2 The overpotential change over a period of 36,000 s under the hydrogen evolution current of water electrolysis. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] This invention discloses a novel molybdenum oxide photocatalyst (Cd(OH)2@MoO) 3-x The preparation method of the thin film is disclosed in detail:

[0024] 1) Base electrode: A 3mm diameter disc gold electrode (or other conductive substrate, such as carbon, Ni, Cu, etc.) is polished sequentially with 1.0, 0.3 and 0.05μm alumina powder. After polishing, it is washed with deionized water and ethanol under ultrasonic conditions (5 minutes for each process). After ultrasonication, it is rinsed with running secondary water.

[0025] 2) Electrochemical co-deposition: Three electrodes (disk gold electrode, Ag / AgCl reference electrode, and carbon rod counter electrode) were inserted into a solution containing 100 mM (NH4)6Mo7O 24 Cd(OH)₂@MoO₂ with a thickness of approximately 3 μm can be obtained by electrochemical co-deposition for 2 s in a mixed solution of 4H₂O and 0.25 mM CdSO₄ at a potential of -0.8 V (Vs. Ag / AgCl reference electrode). 3-x film.

[0026] To better understand the present invention, the following embodiments are provided for further detailed description of the present invention, but they should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0027] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0028] Example 1

[0029] Using a 3mm diameter disc gold electrode as the base electrode, the electrode was polished sequentially with 1.0, 0.3 and 0.05μm alumina powder. After polishing, the electrode was washed with deionized water and ethanol under ultrasonic conditions (5 minutes for each process), and then rinsed with running secondary water after ultrasonication.

[0030] A Cd(OH)2 thin film can be prepared by inserting three electrodes (disk gold electrode, Ag / AgCl reference electrode, and carbon rod counter electrode) into a solution containing 0.2 mM CdSO4 and applying a potential of -0.8 V (Vs. Ag / AgCl reference electrode) for 2 s for electrochemical co-deposition.

[0031] The linear sweep voltammograms of its electrocatalysis and photoelectrocatalysis are shown below. Figure 1 (Solid triangle and hollow triangle).

[0032] Example 2

[0033] Using a 3mm diameter disc gold electrode as the base electrode, the electrode was polished sequentially with 1.0, 0.3 and 0.05μm alumina powder. After polishing, the electrode was washed with deionized water and ethanol under ultrasonic conditions (5 minutes for each process), and then rinsed with running secondary water after ultrasonication.

[0034] Three electrodes (disk gold electrode, Ag / AgCl reference electrode, and carbon rod counter electrode) were inserted into a solution containing 100 mM (NH4)6Mo7O. 24 MoO₂ can be prepared by electrochemical co-deposition for 2 seconds in a solution of ·4H₂O with a potential of -0.8V (Vs.Ag / AgCl reference electrode).3-x film.

[0035] The linear sweep voltammograms of its electrocatalysis and photoelectrocatalysis are shown below. Figure 1 (Solid square lines and hollow square lines).

[0036] Example 3

[0037] Using a 3mm diameter disc gold electrode as the base electrode, the electrode was polished sequentially with 1.0, 0.3 and 0.05μm alumina powder. After polishing, the electrode was washed with deionized water and ethanol under ultrasonic conditions (5 minutes for each process), and then rinsed with running secondary water after ultrasonication.

[0038] Three electrodes (disk gold electrode, Ag / AgCl reference electrode, and carbon rod counter electrode) were inserted into a solution containing 100 mM (NH4)6Mo7O. 24 Cd(OH)₂@MoO₂ can be prepared by electrochemical co-deposition for 2 s in a solution of 4H₂O and 0.25 mM CdSO₄ under a potential of -0.8 V (Vs. Ag / AgCl reference electrode). 3-x Thin film. The hydrogen evolution performance of the prepared catalyst was tested, and its electrocatalytic and photoelectrocatalytic linear scanning voltammetry is shown in [Figure number missing]. Figure 1 (Solid circle and hollow circle).

[0039] In addition, to further verify the superiority of the present invention over the prior art, the inventors also conducted the following experiments, as follows:

[0040] (1) Linear voltammetry scans were performed on the electrocatalytic water splitting to hydrogen production of the catalysts prepared in Examples 1, 2, and 3 in 0.1 M KOH electrolyte, comparing the results under dark conditions and simulated visible light irradiation (100 mW / cm²). 2 The performance of hydrogen evolution under the condition of )

[0041] from Figure 1 It can be seen that Cd(OH)2@MoO 3-x The composite catalyst exhibits the best electrocatalytic and photoelectrocatalytic performance, and its hydrogen evolution current is significantly higher than that of pure Cd(OH)2 and MoO2. 3-x Thin film, and visible light irradiation can increase the hydrogen evolution current of the composite catalyst by about 4 times (at -0.3V), Cd(OH)2@MoO 3-x Under light conditions, compared to MoO 3-x The hydrogen evolution current is 12 times higher in the dark (at -0.3V).

[0042] The principle of photoelectrocatalysis is that light with energy greater than the band gap of a semiconductor can excite electrons from the valence band to the conduction band, generating electrons and holes. The generated electrons can be used in reduction reactions, thus enhancing hydrogen evolution performance. Doping with Cd(OH)₂ and visible light irradiation both enhance the performance of MoO₂.3-x The catalytic hydrogen evolution performance is significantly improved, and it has good application prospects.

[0043] (2) Determination of the possibility of electrochemical co-deposition:

[0044] A three-electrode system (disc gold electrode, silver / silver chloride reference electrode, and carbon rod counter electrode) was used to test 0.1 mol / L ammonium molybdate ((NH4)6Mo7O) 24 Cathodic linear voltammetry scans were performed on the cadmium sulfate (CdSO4) and aqueous solution, respectively, to obtain... Figure 2 .

[0045] from Figure 2 It can be seen that the electrodeposition potential of cadmium sulfate is more negative than that of ammonium molybdate, and both can be electrodeposited simultaneously at potentials below -0.6V (more negative). When the applied potential cannot generate a large number of cadmium atoms, the molybdenum oxide generated first can catalyze the electrolysis of water to produce hydrogen gas and hydroxide ions. The hydroxide ions can precipitate cadmium into the molybdenum oxide in the form of cadmium hydroxide.

[0046] (3) Elemental content analysis

[0047] Because cadmium sulfate is more difficult to deposit than ammonium molybdate, at the same concentration, the co-deposited product contains a higher content of molybdenum oxide and a lower content of cadmium hydroxide. When using 100mM (NH4)6Mo7O... 24 A mixed solution of 4H₂O and 0.25 mM CdSO₄ was co-deposited at -0.8 V. The resulting composite film, analyzed by inductively coupled plasma atomic ratio (ICP-ARP) spectroscopy, showed an atomic mass ratio of 29.1 ppm (0.00291%) for cadmium. Elemental contents are shown in Table 1.

[0048] Table 1. Elemental content (ICP test results)

[0049]

[0050] (4) Elemental distribution analysis

[0051] The Cd(OH)2@MoO prepared in Example 3 3-x The elemental distribution of the composite film was measured by energy dispersive spectroscopy, and the results are as follows: Figure 3 The cadmium element is uniformly distributed in the composite film, indicating that the composite components are uniformly mixed.

[0052] (5) Dynamic switching light verification of light response

[0053] The Cd(OH)2@MoO prepared in Example 3 3-x The periodic on-off optical scanning voltammogram of the catalyst under slow cathode scan (0.1 mV / s) conditions is shown in [reference needed]. Figure 4 .

[0054] Cd(OH)2@MoO 3-x Under conditions where the light source is switched on and off, it can be observed that the hydrogen evolution current increases and decreases as the light source is switched on and off.

[0055] (6) Improved light absorption performance

[0056] The Cd(OH)2@MoO prepared in Example 3 3-x Catalyst and undoped Cd(OH)2 MoO 3-x The ultraviolet-visible absorption spectrum is illustrated in the figure. Figure 5 .

[0057] Cd(OH)2@MoO 3-x More than MoO 3-x The absorbance is enhanced, and Cd(OH)2@MoO 3-x The absorption wavelength shifted by 56 nm to longer wavelengths indicates that it can absorb a wider range of visible light.

[0058] (7) Variation in band gap width:

[0059] The band gap width of molybdenum oxide was measured to be 2.6 eV before doping (Example 2) and 2.3 eV after doping (Example 3) using the Tauc method. The reduction in band gap width allows for the absorption of more energy from visible light and the generation of more electron-hole pairs. Photogenerated electrons can increase the rate of chemical reduction reaction.

[0060] (8) Stability of the catalyst

[0061] The Cd(OH)2@MoO prepared in Example 3 3-x The catalyst was in 0.1M KOH electrolyte at a rate of 10 mA / cm². 2 The hydrogen evolution reaction is carried out by the current, and the change in overpotential is shown in... Figure 6 .

[0062] Within the range of 36,000 s, the hydrogen evolution overpotential remained basically stable, proving that the catalyst has high stability and practical value.

[0063] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a cadmium hydroxide (Cd(OH)₂)-doped molybdenum oxide photocatalyst, characterized in that, Two-dimensional layered molybdenum oxide (MoO) doped with cadmium hydroxide (Cd(OH)2) was prepared by a wet chemical one-step electrochemical co-deposition method. 3-x Thin film, namely Cd(OH)2@MoO 3-x Thin film; specifically, the preparation method includes the following steps: 1) Preparation of substrate electrode: A 3 mm disc gold electrode was polished sequentially with 1.0, 0.3 and 0.05 μm alumina powders, then washed with deionized water and ethanol for 5 min under ultrasonic conditions, and then rinsed with flowing secondary water to obtain the substrate electrode. 2) Electrochemical co-deposition preparation of Cd(OH)2@MoO 3-x Thin film: The disk gold electrode, Ag / AgCl reference electrode, and carbon rod counter electrode treated in step 1) are inserted into a film containing (NH4)6Mo7O 24 The Cd(OH)2@MoO was obtained by electrochemical co-deposition in a mixed solution of 4H2O and cadmium salt. 3-x Thin film; (NH4)6Mo7O 24 Concentrations range from 1 to 1000 mM; (NH4)6Mo7O 24 The concentration ratio with cadmium salts is 100-20000; The electrochemical co-deposition voltage is -0.6 to -1.1 V, and the deposition time is 1 ms to 100 s.

2. The method for preparing a cadmium hydroxide (Cd(OH)₂)-doped molybdenum oxide photocatalyst according to claim 1, characterized in that, In step 2), the concentration of cadmium salt in the mixed solution is 0.05-10 mM, and the cadmium salt is CdCl2, Cd(NO3)2 or CdSO4; Furthermore, the electrochemical co-deposition temperature is 10℃-50℃.

3. The application of a cadmium hydroxide (Cd(OH)2)-doped molybdenum oxide photocatalyst prepared by the method described in claim 1 in hydrogen production by water electrolysis.

Images