Carbon nitride photoelectrode and preparation method and application thereof

Abstract

The application discloses a carbon nitride photoelectrode and a preparation method and application thereof, and belongs to the technical field of material preparation and photoelectrocatalysis. A metal film is uniformly deposited on a conductive substrate by a physical evaporation method to obtain a metal-conductive substrate, nitrogen-rich carbon organic matter is pyrolyzed and polymerized with the metal-conductive substrate under an inert gas atmosphere to obtain the carbon nitride photoelectrode. In the carbon nitride thermal polymerization process, the nitrogen-rich carbon organic matter is used as a precursor, chemical coordination is formed with a metal having a vacant track, photo-generated electrons and holes are effectively transmitted, the interface resistance is reduced, and the photoelectrocatalytic conversion reaction efficiency is improved. The carbon nitride-based photoelectrode has strong light absorption, high photo-generated charge separation / migration capacity, simple process, low cost, green environmental protection, and an easy-to-control structure, and has great application and promotion potential.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation and photoelectrocatalysis technology, specifically relating to a carbon nitride photoelectrode, its preparation method, and its application. Background Technology

[0002] Since the 1970s, when Japanese scientists Fujishima and Honda first discovered that titanium dioxide could be used for photoelectrocatalytic water splitting to produce hydrogen, the core of photocatalysis technology has been exploring inexpensive photocatalysts with high visible light utilization, high quantum efficiency, and high stability (J. Phys. Chem. Lett. 2010, 1, 2655). Since Wang et al. introduced highly chemically stable organic polymer semiconductor graphitic carbon nitride into the field of photocatalysis for photocatalytic water splitting to produce hydrogen and oxygen (Nat. Mater. 2009, 8, 76), carbon nitride has attracted widespread attention. As a novel polymer semiconductor, carbon nitride is inexpensive, environmentally friendly, has visible light response, good stability, and easily tunable structure. It has not only demonstrated excellent performance in the field of photocatalysis but also shows potential in photoelectrocatalytic water splitting. However, the preparation and application of carbon nitride photocatalysis are still in their early stages, facing several serious challenges: (1) lack of suitable in-situ preparation and modification methods; (2) small visible light absorption range; (3) poor conductivity; and (4) low crystallinity. Therefore, developing in-situ preparation and modification methods for carbon nitride photoanodes, utilizing precursors to directly polymerize on the surface of conductive substrates to form carbon nitride thin films, achieving close contact between the carbon nitride thin film and the conductive substrate, optimizing the quality of the film, and promoting the separation and migration of photogenerated carriers are of great significance to the development of carbon nitride photoanodes. Summary of the Invention

[0003] The purpose of this invention is to provide a carbon nitride photoelectrode, its preparation method, and its applications. Using inexpensive nitrogen-rich carbon organic materials as precursors, the carbon nitride undergoes thermal polymerization, forming chemical coordination with metals containing empty orbitals. This optimizes the interface between the conductive substrate and carbon nitride, effectively promoting the separation and transport of photogenerated charges and holes at the phase interface, thus achieving photoelectrocatalytic conversion. The process is simple, low-cost, and has significant application potential.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing a carbon nitride photoelectrode: A metal-conductive substrate is obtained by uniformly depositing a metal thin film on a conductive substrate through physical vapor deposition, and a nitrogen-rich carbon organic compound is subjected to high-temperature pyrolysis polymerization with the metal-conductive substrate in an inert gas atmosphere to obtain a carbon nitride photoelectrode.

[0006] Preferably, the metal thin film material is any one of platinum, palladium, gold, silver, molybdenum, and cobalt; the deposition rate is 0.02 nm / s, and the deposition thickness is 5-25 nm.

[0007] Using nitrogen-rich carbon organic matter as a precursor, it is ground into powder, evenly spread on a metal-conductive substrate, and subjected to pyrolysis polymerization at 400-550℃ for 2-4 hours in an inert gas atmosphere; after cooling, it is ultrasonicated in deionized water for 10 minutes and dried with nitrogen to obtain the carbon nitride photoelectrode.

[0008] The nitrogen-rich carbon organic compound is at least one of cyanamide, dicyandiamide, melamine, urea, and thiourea.

[0009] The inert gas is at least one of nitrogen, argon, and helium.

[0010] The carbon nitride photoelectrode prepared by the method described above is used as an anode material in the photoelectrocatalytic water splitting reaction to produce oxygen.

[0011] The beneficial effects of this invention are as follows: Using nitrogen-rich organic molecules as precursors, a carbon nitride thin film can be formed on the surface of a conductive substrate through melt copolymerization, thereby achieving close contact between the carbon nitride thin film and the conductive substrate. During the formation of the carbon nitride thin film, the coordination effect between the metal and carbon nitride molecules allows the carbon nitride molecules to grow in situ on the metal surface, which is key to achieving a tight connection between the carbon nitride thin film and the conductive substrate. The synthesized photoanode has a suitable band structure, strong light absorption and charge transport capabilities, and its catalytic performance in neutral and alkaline electrolytes is significantly improved compared to ordinary carbon nitride photoanodes. Attached Figure Description

[0012] Figure 1 This is a comparison of optical photographs of the carbon nitride photoelectrode obtained in Example 1 and Comparative Example 1.

[0013] Figure 2 The images show SEM images of the carbon nitride photoelectrodes obtained in Example 1 and Comparative Example 1.

[0014] Figure 3 The photocurrent density diagrams for the carbon nitride photoelectrodes obtained in Examples 1, 2 and Comparative Example 1 under AM 1.5G illumination and a bias voltage of 1.23V are shown.

[0015] Figure 4 The images show a comparison of the XRD patterns of the carbon nitride photoelectrodes obtained in Examples 1, 3, and 4 with those in Comparative Example 1.

[0016] Figure 5 The image shows a comparison of the infrared ATR values ​​of the carbon nitride photoelectrodes obtained in Examples 1, 3, and 4 with those in Comparative Example 1.

[0017] Figure 6The gas generation rate of the carbon nitride photoelectrode obtained in Example 1 under AM 1.5G illumination and a bias voltage of 1.23V is given. Detailed Implementation

[0018] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0019] Example 1

[0020] A 25nm silver-plated FTO conductive surface was placed at the bottom of an alumina boat. 3 g of melamine was weighed and poured into a mortar, then ground thoroughly into powder. The powder was then poured into the alumina boat, and the temperature was increased to 550℃ at a rate of 2℃ / min under a nitrogen atmosphere, with a nitrogen flow rate of 100 cm⁻¹. 3 The carbon nitride photoelectrode was prepared by sonicating in deionized water for 10 min to remove residual polymer on the surface and non-conductive surfaces, followed by drying under a nitrogen atmosphere.

[0021] Example 2

[0022] A 5nm silver-plated FTO conductive surface was placed at the bottom of an alumina boat. 3 g of dicyandiamide was weighed and poured into a mortar, then ground thoroughly into powder. The powder was then poured into the alumina boat, and the temperature was increased to 550°C at a rate of 2°C / min under a nitrogen atmosphere, with a nitrogen flow rate of 100 cm⁻¹. 3 The carbon nitride photoelectrode was prepared by sonicating in deionized water for 10 min to remove residual polymer on the surface and non-conductive surfaces, followed by drying under a nitrogen atmosphere.

[0023] Example 3

[0024] A 25nm gold-plated FTO conductive surface was placed at the bottom of an alumina boat. 3 g of melamine was weighed and poured into a mortar, then ground thoroughly into powder. The powder was then poured into the alumina boat, and the temperature was increased to 550°C at a rate of 2°C / min under a nitrogen atmosphere, with a nitrogen flow rate of 100 cm⁻¹. 3 The carbon nitride photoelectrode was prepared by sonicating in deionized water for 10 min to remove residual polymer on the surface and non-conductive surfaces, followed by drying under a nitrogen atmosphere.

[0025] Example 4

[0026] A 25nm molybdenum-plated FTO conductive surface was placed at the bottom of an alumina boat. 3g of melamine was weighed and poured into a mortar, then ground thoroughly into powder. The powder was then introduced into the alumina boat. Under a nitrogen atmosphere, the temperature was increased to 550℃ at a rate of 2℃ / min, with a nitrogen flow rate of 100 cm⁻¹. 3 The carbon nitride photoelectrode was prepared by sonicating in deionized water for 10 min to remove residual polymer on the surface and non-conductive surfaces, followed by drying under a nitrogen atmosphere.

[0027] Comparative Example 1

[0028] Place the cleaned FTO, conductive side up, at the bottom of the corundum boat. Weigh 3 g of melamine and pour it into a mortar, grinding it thoroughly into powder. Pour the ground powder into the corundum boat and heat it to 550°C at a rate of 2 °C / min under a nitrogen atmosphere, with a nitrogen flow rate of 100 cm⁻¹. 3 The carbon nitride photoelectrode was prepared by sonicating in deionized water for 10 min to remove residual polymer on the surface and non-conductive surfaces, followed by drying under a nitrogen atmosphere.

[0029] The carbon nitride photoelectrodes prepared in Example 1 and Comparative Example 1 were characterized, and the results are as follows: Figure 1-5 As shown.

[0030] Figure 1 The images show a comparison of optical photographs of the carbon nitride photoelectrode obtained in Example 1 and Comparative Example 1. It can be seen from the images that the uniformity of the carbon nitride grown on the silver-conductive glass substrate is significantly improved, and there are no obvious particle boundaries.

[0031] Figure 2 The images show SEM images of the carbon nitride photoelectrodes obtained in Example 1 and Comparative Example 1. The images show that a carbon nitride film was uniformly grown on the silver-conductive glass, while no carbon nitride film was formed on the surface of the conductive glass in Comparative Example 1.

[0032] Figure 3 The graph shows the photocurrent density of the carbon nitride photoelectrodes obtained in Examples 1 and 2 and Comparative Example 1 under AM 1.5G illumination and a bias voltage of 1.23V. It can be seen from the graph that the photoresponse current of the carbon nitride thin film electrode grown on silver-conductive glass is significantly improved compared to the original carbon nitride thin film electrode. The carbon nitride thin film electrode prepared using melamine in Example 1 shows the greatest improvement in photoresponse current, reaching 80 μA / cm². -2 It is about five times the original carbon nitride.

[0033] Figure 4The figures show a comparison of the XRD patterns of the carbon nitride photoelectrodes obtained in Examples 1, 3, and 4 with those in Comparative Example 1. As can be seen from the figures, the XRD patterns of Ag-PCN, Au-PCN, and Mo-PCN are basically similar, with sharp peaks at 27.86°, 35.04°, 39.04°, and 52.08° attributed to the diffraction peaks of the conductive substrate FTO. Furthermore, a new diffraction peak appears at 28.7°, which can be attributed to the layered stacking of heptaazine structures similar to graphite in carbon nitride.

[0034] Figure 5 This is a comparison of the infrared ATR images of the carbon nitride photoelectrodes obtained in Examples 1, 3, and 4 with Comparative Example 1. The image shows the photoelectrode located at 852 cm⁻¹. -1 The absorption peak is attributed to the heptaazine ring fingerprint vibration peak in the carbon nitride structure, located in the 1200-1700 cm⁻¹ range. -1 The relatively strong absorption peaks at 3100 cm⁻¹ are due to the stretching vibration of the heptaazine ring. Additionally, the peak at 3100 cm⁻¹ is also present in the figure. -1 There is a relatively weak absorption peak nearby, which is due to the amino vibration of carbon nitride.

[0035] Figure 6 The gas generation rate of the carbon nitride photoelectrode obtained in Example 1 was tested using an offline detection method under AM 1.5G illumination and a bias voltage of 1.23V. The oxygen generation rate was approximately 0.11 μmol / cm³. -2 h -1 The hydrogen production rate is approximately 0.52 μmol / cm³. -2 h -1 .

[0036] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for preparing a carbon nitride photoelectrode, characterized in that: A metal-conductive substrate is obtained by uniformly depositing a metal thin film on a conductive substrate through physical vapor deposition. A carbon nitride photoelectrode is then prepared by high-temperature pyrolysis polymerization of nitrogen-rich carbon organic matter and the metal-conductive substrate under an inert gas atmosphere. The metal thin film material can be either gold or silver; the deposition rate is 0.02 nm / s, and the deposition thickness is 5-25 nm. Using nitrogen-rich carbon organic matter as a precursor, it is ground into powder, evenly spread on a metal-conductive substrate, and thermally polymerized at 400-550℃ for 2-4 hours in an inert gas atmosphere; after cooling, it is ultrasonicated in deionized water for 10 minutes and dried with nitrogen to obtain the carbon nitride photoelectrode. The nitrogen-rich carbon organic compound is at least one of cyanamide, dicyandiamide, and melamine.

2. The method according to claim 1, characterized in that: The inert gas is at least one of nitrogen, argon, and helium.

3. A carbon nitride photoelectrode prepared by any one of claims 1-2.

4. An application of a carbon nitride photoelectrode prepared by the method according to any one of claims 1-2, characterized in that: The aforementioned carbon nitride photoelectrode is used as an anode material in the photoelectrocatalytic water splitting reaction to produce oxygen.

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