Photoelectrochemical urea degradation photo-anode based on bismuth vanadate semiconductor film and electrode system thereof

Abstract

The invention relates to a photoelectrochemical urea degradation photoanode based on a bismuth vanadate semiconductor film and an electrode system thereof. The photoanode comprises a BiVO4 light absorption layer arranged on a transparent conductive substrate, a hole transport layer arranged on the BiVO4 light absorption layer and a Co-Ci cocatalyst layer arranged on the hole transport layer, the BiVO4 light absorption layer is excited by light to generate electron hole pairs, holes enter electrolyte under the combined action of extraction of the NiOBix hole transport layer and external bias voltage to carry out urea degradation half reaction, and meanwhile, the Co-Ci cocatalyst plays a role in improving surface reaction kinetics and reducing overpotential of urea oxidation reaction, so that the degradation efficiency of urea is improved. The photoanode has stronger carrier separation and migration capability and higher working stability, and the efficiency and stability of urea degradation are improved.

Description

Technical Field

[0001] This invention relates to the field of photoelectrochemical degradation of urea, and more particularly to a photoanode and electrode system for photoelectrochemical degradation of urea based on bismuth vanadate semiconductor thin film. Background Technology

[0002] Urea is one of the most important reactive nitrogen species in the nitrogen cycle, playing an indispensable role in the water-energy-food relationship. However, untreated urea or urine wastewater can cause serious environmental pollution and threaten human health. Photoelectrocatalytic urea oxidation technology under mild conditions has become a promising method for energy recovery and environmental remediation. Its basic principle is to utilize the electron-hole pairs generated when a photosensitive semiconductor is irradiated by sunlight, and with the assistance of an applied bias voltage, the charge carriers are transferred into the electrolyte to catalyze the urea reaction. In conventional photoanode electrode systems, n-type semiconductors with a large bandgap are usually selected as the light-absorbing layer of the photoanode. Their poor internal carrier separation efficiency leads to low overall conversion efficiency of the electrode system. Therefore, enhancing the internal carrier separation efficiency of the n-type semiconductor photoanode through special structural design and functional layer modification is of great significance for improving the overall urea degradation efficiency of the electrode system. Summary of the Invention

[0003] To address the technical problems existing in the prior art, this invention provides a photoanode for photoelectrochemical degradation of urea based on bismuth vanadate semiconductor thin film. The photoanode uses BiVO4 material with a large bandgap and low cost as the light absorption layer. By setting a hole transport layer and a Co-Ci cocatalyst layer on the BiVO4 light absorption layer, a photoanode with a special structure is constructed, which has strong carrier migration ability and working stability, thereby improving the urea degradation efficiency.

[0004] This invention provides a photoelectrochemical urea degradation photoanode based on bismuth vanadate semiconductor thin film, comprising a transparent conductive substrate, a BiVO4 light-absorbing layer disposed on the transparent conductive substrate, a hole transport layer disposed on the BiVO4 light-absorbing layer, and a Co-Ci cocatalyst layer disposed on the hole transport layer.

[0005] Furthermore, the hole transport layer is NiOBi. x Hole transport layer, where 0 < x < 7.5. The NiOBi x The stable hole transport layer is a type of Ni-based hole transport layer that also functions as a catalyst. Ni-based catalysts are high-performance catalysts for urea degradation, improving the efficiency of urea oxidation. NiOBi x The hole transport layer is placed on the BiVO4 light-absorbing layer, which not only improves the hole transport efficiency but also protects the stability of the BiVO4 light-absorbing layer, thus helping to improve the efficiency of urea oxidation.

[0006] Furthermore, the Co-Ci cocatalyst layer is composed of Co-Ci nanoparticles. The Co-Ci cocatalyst layer is disposed on NiOBi. x On the hole transport layer, the surface reaction kinetics are improved, which helps to reduce the overpotential of the urea oxidation reaction.

[0007] Furthermore, the BiVO4 light-absorbing layer is an n-type monoclinic phase with a thickness of 75–100 nm.

[0008] Furthermore, the Co-Ci nanoparticles have a particle size of 4–10 nm.

[0009] Furthermore, the NiOBi x The thickness of the hole transport layer is 750–850 nm.

[0010] Furthermore, the transparent conductive substrate is preferably an FTO substrate.

[0011] Furthermore, the NiOBi x The hole transport layer was fabricated on the BiVO4 light-absorbing layer using a spin-coating process. This simple and easy-to-operate spin-coating process simplifies the fabrication of the photoanode.

[0012] The aforementioned photoanode structure incorporates a stable NiOBi layer on the BiVO4 light-absorbing layer. x Hole transport layer, NiOBi x The hole transport layer improves hole transport efficiency while protecting the stability of the BiVO4 light-absorbing layer. The Co-Ci cocatalyst layer is placed on NiOBi. x The hole transport layer improves surface reaction kinetics and reduces the overpotential of urea oxidation reaction. This photoanode has stronger carrier separation and migration capabilities, as well as higher operational stability.

[0013] This invention provides an electrode system for the photoelectrochemical degradation of urea, comprising a working electrode, a reference electrode, and a counter electrode, wherein the working electrode is the aforementioned photoanode. This photoanode serves as the working electrode in the three-electrode system, improving the overall electro-assisted urea degradation efficiency and stability of the electrode system.

[0014] Furthermore, the reference electrode is an Ag / AgCl reference electrode; the counter electrode is a Pt counter electrode.

[0015] Furthermore, it also includes an electrochemical workstation that provides a voltage source, and the working electrode, reference electrode, and counter electrode are connected to the electrochemical workstation.

[0016] When this electrode system is working, the BiVO4 light-absorbing layer is stimulated by light to generate electron-hole pairs, and the holes pass through NiOBi x While the hole transport layer is extracted and introduced into the electrolyte, the Co-Ci cocatalyst layer improves surface reaction kinetics and reduces the overpotential of the urea oxidation reaction. In one embodiment, holes are transported via NiOBi... x Under the combined effect of hole transport layer extraction and external bias voltage, the urea enters the electrolyte to carry out the urea degradation half-reaction, while electrons are transferred to the Pt plate electrode surface on the other side to participate in the hydrogen evolution half-reaction, thus improving the efficiency and stability of urea degradation.

[0017] The photoelectrochemical degradation photoanode and electrode system for urea based on bismuth vanadate semiconductor thin film provided by this invention utilizes a BiVO4 light-absorbing layer and a NiOBi layer formed on a transparent conductive substrate. x The hole transport layer and the Co-Ci cocatalyst layer constitute a photoanode with a special structure, exhibiting stronger carrier separation and migration capabilities and higher operational stability. This NiOBi... x The hole transport layer plays a role in stabilizing hole transport, improving hole extraction efficiency, preventing electron-hole pair recombination, balancing carrier transport between different layers, and reducing charge accumulation. Simultaneously, this NiOBi... x The hole transport layer acts as a catalyst, improving the efficiency of urea oxidation. The Co-Ci co-catalyst is positioned on NiOBi. x On the hole transport layer, surface reaction kinetics are improved, and the overpotential of the urea oxidation reaction is reduced; the BiVO4 light-absorbing layer generates electron-hole pairs when excited by light, and the holes pass through NiOBi x The urea degradation half-reaction is carried out in the electrolyte under the combined action of hole transport layer extraction and external bias voltage. At the same time, the Co-Ci co-catalyst reduces the overpotential of urea oxidation reaction and improves urea degradation efficiency, thereby improving the overall urea degradation efficiency and stability of the electrode system under electric assistance. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of each functional layer of the photoanode according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of an electrode system and its operation according to an embodiment of the present invention.

[0020] Figure 3 NiOBi prepared by spin coating in one embodiment of the present invention x Schematic diagram of the hole transport layer. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings. The described embodiments are merely some, not all, of the embodiments of the present invention. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from publicly available commercial channels.

[0022] This specification uses spatially relative terms such as “below,” “under,” “down,” “above,” “above,” and “upper” to explain the positioning of one element relative to a second element. These terms are intended to cover different orientations of the device, except for those different from those shown in the figures.

[0023] Furthermore, the use of terms such as "first" and "second" to describe various elements, layers, regions, and sections is not intended to be restrictive. The use of terms such as "having," "containing," "including," and "comprises" are open-ended terms, indicating the presence of the stated elements or features, but not excluding additional elements or features, unless the context explicitly states otherwise.

[0024] One embodiment of the present invention provides a photoanode for the photoelectrochemical degradation of urea based on a bismuth vanadate semiconductor thin film, such as... Figure 1 As shown, it includes a transparent conductive substrate, a BiVO4 light-absorbing layer, a hole transport layer and a Co-Ci cocatalyst layer located on the transparent conductive substrate.

[0025] In a preferred embodiment, the transparent conductive substrate is an FTO substrate. A BiVO4 light-absorbing layer is disposed on the transparent conductive substrate, and the BiVO4 light-absorbing layer is an n-type monoclinic BiVO4 layer with a thickness of 75–100 nm. A hole transport layer is disposed on the light-absorbing layer, and the hole transport layer is preferably NiOBi. x Hole transport layer, where 0 < x < 7.5, NiOBi x The hole transport layer has a thickness of 750–850 nm. (NiOBi) x The hole transport layer, positioned on top of the light-absorbing layer, simultaneously serves as a protective layer for the light-absorbing layer, enhancing its stability. Meanwhile, NiOBi... x The hole transport layer is a Ni-based hole transport layer that acts as a Ni-based catalyst. Ni-based catalysts are high-performance urea degradation catalysts that help improve the efficiency of urea oxidation.

[0026] The Co-Ci cocatalyst layer is disposed on the hole transport layer, which improves the surface reaction kinetics and reduces the overpotential of the urea oxidation reaction. In a preferred embodiment, the Co-Ci cocatalyst layer is composed of Co-Ci nanoparticles with a particle size of 4–10 nm.

[0027] like Figure 2 This invention provides an electrode system in one embodiment, which is a three-electrode system including a working electrode, a reference electrode, and a counter electrode. The working electrode is the aforementioned photoanode. In a preferred embodiment, the reference electrode is an Ag / AgCl reference electrode, and the counter electrode is a Pt counter electrode. The electrode system also includes an electrochemical workstation that provides an external bias voltage to the electrode system. The working electrode, reference electrode, and counter electrode are connected to the electrochemical workstation, which contains a mixed solution of 0.1 mol / L phosphate and 0.33 mol / L urea. The percentage of urea in this mixed solution is similar to the percentage of urea in human urine. When the working electrode, i.e., the aforementioned photoanode, is exposed to sunlight, it generates electron-hole pairs. Holes are extracted through the hole transport layer and enter the electrolyte under the combined action of the external bias voltage to participate in the urea degradation half-reaction, while electrons are transferred to the surface of the Pt counter electrode on the other side to participate in the hydrogen evolution half-reaction. During this process, the BiVO4 light-absorbing layer generates electron-hole pairs when stimulated by light, and NiOBi x The hole transport layer enhances hole transport efficiency, while the Co-Ci cocatalyst improves surface reaction kinetics and reduces the overpotential of urea oxidation. This BiVO4 / NiOBi... x The / Co-Ci photoanode structure achieves strong carrier separation and migration capabilities and high operational stability, thereby improving the degradation efficiency and stability of urea.

[0028] In conjunction with the above-described photoanode structure, this invention also provides a method for preparing the photoanode.

[0029] An FTO conductive substrate was selected, and a BiVO4 light-absorbing layer was grown on the FTO conductive substrate using photoelectrodeposition. The specific steps were as follows: First, the conductive substrate was cut to the required size and then ultrasonically cleaned in alcohol and acetone solvents for 30–45 minutes, followed by drying. Next, a photoelectrodeposition reaction solution was obtained by dissolving 0.03–0.04 mol / L C3H6O3, 68–98% concentrated nitric acid, 0.4 mol / L KI, 0.015 mol / L bismuth nitrate pentahydrate, 98% alcohol, and 0.046 mol / L p-benzoquinone in ultrapure water. The reaction solution was then stirred. The cleaned and dried FTO conductive substrate was then placed in the reaction solution, and stirring was started. The photoelectrodeposition time was 240–360 s. The deposited BiVO4 was then kept at 450–500 °C for 2–3 hours. The thickness of the obtained BiVO4 layer was 75–100 nm, resulting in an electrode sheet with an FTO / BiVO4 structure.

[0030] NiOBi x The layer is set on the light-absorbing layer, using, for example Figure 3 Spin coating method for preparing NiOBi x For the hole transport layer, the gel was first prepared before spin coating. 0.2–0.3 mol / L Bi(NO3)3·5H2O and an appropriate amount of Ni(NO3)2·6H2O were dissolved in ethylene glycol methyl ether and stirred for 1–2 hours to obtain a mixed solution. This mixed solution was then mixed with a monoethanolamine solution at a molar ratio of 1:1 and stirred to obtain a homogeneous solution, which was then aged for 24–48 hours. Subsequently, BiVO4 was fixed on a spin coater, and an appropriate amount of NiOBi was taken out using a pipette. x The gel was dropped onto BiVO4 and spin-coated for 60–120 s at a spin speed of 1500 rpm, followed by holding at 400–450 °C for 2–3 h to obtain NiOBi with a thickness of 750–850 nm. x The electrode sheet has a structure of FTO / BiVO4 / NiOBi. x .

[0031] The Co-Ci cocatalyst layer is disposed on the hole transport layer. The cocatalyst is preferably Co-Ci nanoparticles with a particle size of 4–10 nm. In a preferred embodiment, the Co-Ci nanoparticles are grown on NiOBi using a photoelectrodeposition process. x On the hole transport layer. First, prepare the photoelectrodeposition reaction solution. Dissolve 0.1–0.3 mmol / L Co(NO3)·6H2O and 0.09–0.1 mol / L KHCO3 in ultrapure water to prepare the photoelectrodeposition reaction solution. The structure is FTO / BiVO4 / NiOBi. xThe electrode sheet was used as the working electrode, the Pt sheet as the counter electrode, and Ag / AgCl as the reference electrode. Photoelectrode deposition was performed under simulated sunlight irradiation at a deposition potential of -0.25 to -0.35 V for 300 to 600 s. The prepared Co-Ci nanoparticles had a particle size of 4 to 10 nm, resulting in a structure of FTO / BiVO4 / NiOBi. x The structural diagram of the / Co-Ci photoanode is shown below. Figure 1 As shown.

[0032] The electrode system for photoelectrochemical degradation of urea provided by this invention includes a photoanode with the aforementioned special structure as the working electrode, an Ag / AgCl reference electrode, a Pt sheet electrode, and an electrochemical workstation providing bias voltage. The photoanode, acting as the working electrode, generates electron-hole pairs upon illumination. Holes, extracted through a hole transport layer and under the combined action of the external bias voltage, enter the electrolyte to participate in the urea degradation half-reaction. Simultaneously, the Co-Ci co-catalyst improves surface reaction kinetics and reduces the overpotential of the urea oxidation reaction. Electrons are transferred to the surface of the Pt sheet electrode on the other side to participate in the hydrogen evolution half-reaction. Through the special structural design of the photoanode, the electrode system of this invention significantly improves the urea degradation efficiency and operational stability of the electrode system.

[0033] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A photoelectrochemical urea degradation photoanode based on a bismuth vanadate semiconductor film, comprising a transparent conductive substrate, characterized in that: It also includes a BiVO4 light absorption layer arranged on the transparent conductive substrate, a hole transport layer arranged on the BiVO4 light absorption layer, and a Co-Ci catalyst promoter layer arranged on the hole transport layer.

2. The photoanode according to claim 1, characterized in that The hole transport layer is NiOBi x Hole transport layer, wherein 0<x<7.

5.

3. The photoanode according to claim 1 or 2, characterized in that: The Co-Ci catalyst promoter layer is Co-Ci nanoparticles.

4. The photoanode according to claim 3, characterized in that The BiVO4 light absorbing layer is an n-type monoclinic phase, and its thickness is 75 to 100 nm; Preferably, the particle size of the Co-Ci nanoparticles is 4-10 nm.

5. The photoanode according to claim 3, characterized in that The NiOBi x The thickness of the hole transport layer is 750 to 850 nm.

6. The photoanode according to claim 4 or 5, characterized in that: The transparent conductive substrate is preferably a FTO substrate.

7. The photoanode according to claim 6, characterized in that The NiOBi x The hole transport layer is disposed on the BiVO4 light absorbing layer by a spin coating process.

8. An electrode system for photoelectrochemical degradation of urea, characterized in that: It comprises a working electrode, a reference electrode and a counter electrode, wherein the working electrode is the photoanode according to any one of claims 1 to 7.

9. The electrode system according to claim 8, characterized in that The reference electrode is an Ag / AgCl reference electrode; the counter electrode is a Pt counter electrode.

10. The electrode system according to claim 8 or 9, characterized in that Also included is an electrochemical workstation, which provides a voltage source, and the working electrode, the reference electrode and the counter electrode are connected to the electrochemical workstation.

Images