A g-C3N4 modified GaN nanopillar photoelectrode material, photocathode, photoelectrochemical cell, its preparation method and application

Abstract

This application proposes a g-C3N4-modified GaN nanopillar photoelectrode material, a photocathode, a photoelectrochemical cell, and their preparation methods and applications. Modifying the GaN nanopillar surface with g-C3N4 not only broadens the absorption spectrum range of the photoelectrode material, but also forms a Z-shaped heterostructure with the GaN nanopillar, effectively passivating the surface states of the nanopillar and effectively transferring electrons from the conduction band of the GaN nanopillar to the valence band of the two-dimensional nanosheet g-C3N4, thereby increasing the photocurrent density and significantly improving the photoelectric conversion efficiency. This provides an effective solution to the efficiency loss caused by surface charge recombination of GaN nanopillars. Furthermore, when used in photoelectrochemical cells for hydrogen production through water splitting, g-C3N4-modified GaN nanopillars can prevent photoelectrochemical corrosion of the GaN nanopillars in the electrolyte. Additionally, g-C3N4, as a metal-free electrocatalyst, is suitable for sustainable water splitting systems, further enhancing the stability of the photoelectrode and improving the overall photoelectric performance of the device.

Description

Technical Field

[0001] This application belongs to the technical field of photoelectrodes, and particularly relates to a g-C3N4 modified GaN nanopillar photoelectrode material, a photocathode, a photoelectrochemical cell, and their preparation methods and applications. Background Technology

[0002] Photoelectrochemical (PEC) technology is considered an alternative technology to meet future energy demands, as it can convert solar energy into sustainable renewable hydrogen energy. However, the low efficiency of solar hydrogen production severely limits its practical application in water splitting. Many semiconductor materials have been used as photoelectrode materials for PEC water splitting, but due to their susceptibility to photocorrosion, most materials have not yet met the requirements of PEC systems. Gallium nitride (GaN) has become an ideal PEC photoelectrode material due to its high resistance to optical / chemical corrosion and suitable bandgap positions. Among them, the nanostructure of GaN nanopillars (NRs) provides a large number of reaction sites due to their large specific surface area; however, the poor absorbance caused by their large band gap leads to low photogenerated carrier transfer efficiency, which greatly affects its PEC performance. Therefore, how to solve the efficiency loss caused by surface charge recombination of GaN nanopillars is a problem that needs to be addressed.

[0003] Therefore, developing catalysts for surface modification of GaN nanopillar photoelectrodes is of great research significance for achieving high-performance PEC water splitting. Summary of the Invention

[0004] This application provides a g-C3N4 modified GaN nanopillar photoelectrode material, a photocathode, a photoelectrochemical cell, and their preparation methods and applications, to solve the problems existing in related technologies. The technical solution is as follows:

[0005] In a first aspect, embodiments of this application provide a g-C3N4 modified GaN nanopillar photoelectrode material, characterized in that it includes a Si substrate, on which a GaN nanopillar layer is grown, and the surface of the GaN nanopillar is modified with a g-C3N4 layer.

[0006] In one embodiment, the GaN nanopillar layer is grown on the Si substrate using molecular beam epitaxy. The GaN nanopillars have a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rods / m³. -2 .

[0007] In one embodiment, the process conditions for growing the GaN nanopillar layer on the Si substrate using molecular beam epitaxy are as follows:

[0008] The temperature of the Si substrate was controlled at 430–970℃, the rotation speed of the Si substrate was 5–10 r / min, and the equivalent pressure of the Ga beam was 1.2 × 10⁻⁶. -7 ~1.4×10 -7 GaN nanopillars were grown on Si substrates using a nitrogen flow rate of 1–5 sccm, a plasma source power of 200–400 W, and a growth time of 2–4 h.

[0009] In one embodiment, the g-C3N4 layer is prepared by spin-coating a g-C3N4 suspension onto the surface of GaN nanopillars.

[0010] The spin coating conditions were as follows: rotation speed of 500–2500 r / min; concentration of g-C3N4 suspension of 0.5–2.5 mg / mL; and volume of g-C3N4 suspension of 10–50 μL.

[0011] Secondly, embodiments of this application provide a method for preparing g-C3N4 modified GaN nanopillar photoelectrode material, comprising the following steps:

[0012] GaN nanopillars were grown on a Si substrate using molecular beam epitaxy.

[0013] g-C3N4 was loaded onto GaN nanopillars using a spin-coating method, followed by annealing, to prepare the g-C3N4-modified GaN nanopillar photoelectrode material.

[0014] In one embodiment, the annealing conditions are: annealing temperature of 50–150°C and annealing time of 5–20 min.

[0015] Thirdly, embodiments of this application provide a photocathode comprising any of the g-C3N4 modified GaN nanopillar photoelectrode materials described above.

[0016] In one embodiment, a Ti-Au alloy is used to connect a wire to the back side of a Si substrate of a g-C3N4 modified GaN nanopillar photoelectrode material to obtain the photocathode.

[0017] Fourthly, embodiments of this application provide a photoelectrochemical cell, including a photoanode, a photocathode as described above, and an electrolyte; the electrolyte is a 0.08–0.12 mol / L Na₂SO₄ solution, and the pH of the electrolyte is 8–10.

[0018] Fifthly, embodiments of this application provide the application of the aforementioned photoelectrochemical cell in photoelectrochemical water splitting for hydrogen production, wherein the photoelectrochemical cell produces hydrogen under sunlight irradiation.

[0019] The advantages or beneficial effects of the above technical solutions include at least the following:

[0020] The g-C3N4-modified GaN nanopillar photoelectrode material of this application not only broadens the absorption spectrum range of the photoelectrode material by modifying the surface of GaN nanopillars with g-C3N4, but also forms a Z-shaped heterostructure with the GaN nanopillars, effectively passivating the surface states of the nanopillars and effectively transferring electrons from the conduction band of the GaN nanopillars to the valence band of the two-dimensional nanosheet g-C3N4, thereby increasing the photocurrent density and greatly improving the photoelectric conversion efficiency; it provides an effective solution to the efficiency loss caused by surface charge recombination of GaN nanopillars.

[0021] The photocathode of this application, with g-C3N4 modified GaN nanopillars, not only promotes the reduction reaction at the electrode / electrolyte interface and enhances charge separation efficiency, but also, when used in photoelectrochemical cells for hydrogen production through water splitting, prevents photoelectrochemical corrosion of the GaN nanopillars in the electrolyte. Furthermore, g-C3N4, as a metal-free electrocatalyst, is suitable for sustainable water splitting systems, further enhancing the stability of the photoelectrode and improving the overall photoelectric performance of the device.

[0022] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of this application will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0023] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.

[0024] Figure 1 This is a schematic diagram of the structure of the g-C3N4 modified GaN nanopillar photoelectrode of this application;

[0025] Figure 2 SEM images of GaN nanopillars, g-C3N4 two-dimensional nanosheets, and g-C3N4-modified GaN nanopillar photoelectrode surfaces;

[0026] Figure 3 The current-voltage relationship of g-C3N4 modified GaN nanopillar photoelectrode material and comparative material in photoelectrochemical hydrogen production system under a certain bias voltage is shown in the figure.

[0027] Figure 4The bias photoelectric conversion efficiency of g-C3N4 modified GaN nanopillar photoelectrode material and comparative material in a photoelectrochemical hydrogen production system under a certain bias voltage is shown in the figure. Detailed Implementation

[0028] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this application. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0029] In existing technologies, type II heterostructure photoelectrode materials formed by Cu2O microcrystals and GaN are used in PEC water splitting. While electrodepositing Cu2O microcrystals onto an epitaxial GaN layer on a Si(111) substrate can achieve efficient PEC water splitting under no bias voltage, the poor stability of Cu2O makes it difficult to maintain an efficient, continuous, and stable hydrogen and oxygen production process. Therefore, the efficiency and stability of photoelectrode materials in PEC water splitting applications are two aspects that need continuous improvement.

[0030] Therefore, this application provides a g-C3N4 modified GaN nanopillar photoelectrode material, photocathode, photoelectrochemical cell, and their preparation method and application, thereby providing an effective strategy for achieving efficient PEC water splitting to produce hydrogen.

[0031] This application provides a g-C3N4 modified GaN nanopillar photoelectrode material, characterized in that it includes a Si substrate, on which a GaN nanopillar layer is grown, and the surface of the GaN nanopillar is modified with a g-C3N4 layer.

[0032] Graphite-like carbon nitride (g-C3N4) is a planar two-dimensional sheet structure material similar to graphene. g-C3N4 has a wide absorption spectrum and can perform photocatalysis under ordinary visible light without requiring ultraviolet light. Furthermore, g-C3N4 possesses very suitable semiconductor band edge positions, meeting the thermodynamic requirements for photocatalytic water splitting to produce hydrogen and oxygen. Due to the delocalized electrons in its carbon network, it can effectively collect electrons from the photoelectrode and rapidly transfer them to the counter electrode.

[0033] Therefore, g-C3N4, as a low-cost, high-efficiency, and stable water-splitting material, shows greater promise, especially for sustainable water splitting applications. It can also serve as a highly efficient metal-free electrocatalyst, significantly improving the performance of water splitting systems. Using g-C3N4 can further improve the PEC performance of GaN nanopillar photoelectrodes. By using g-C3N4, not only is the absorption spectral range of the photoelectrode material broadened, but the onset potential is also effectively reduced, promoting the dissociation, transport, and oxidation of charge carriers at the electrode / electrolyte interface, greatly improving the photoelectric conversion efficiency of the nanopillars, thus achieving highly efficient photoelectrochemical water splitting for hydrogen production. Furthermore, g-C3N4 modification can prevent photoelectrochemical corrosion of GaN nanopillars in the electrolyte, and as a metal-free electrocatalyst, g-C3N4 is suitable for sustainable water splitting systems, further enhancing the stability of the photoelectrode and improving the overall photoelectric performance of the material.

[0034] In one embodiment, the Si substrate is ultra-low resistivity silicon with a resistivity of less than 1 Ω·cm. Preferably, the Si substrate is selected from Si(111) crystal planes (conductivity <0.005 Ω).

[0035] In one embodiment, the silicon substrate undergoes cleaning and annealing.

[0036] The cleaning process involves first removing organic contaminants from the Si substrate surface using an organic solvent, then treating the Si substrate with an HF solution to remove the surface oxide layer, and finally drying it with high-purity dry nitrogen. The annealing process involves placing the cleaned Si substrate in a reaction chamber and annealing it at 900–980°C for 10–30 minutes to obtain a reconstructed surface. Preferably, the removal of organic contaminants from the Si substrate surface using an organic solvent involves sequentially cleaning in acetone and anhydrous ethanol, followed by rinsing with water; the HF solution has a mass concentration of 5–20%.

[0037] In one embodiment, the GaN nanopillar layer is grown on the Si substrate using molecular beam epitaxy. The GaN nanopillars have a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rods / m³. -2 .

[0038] In one embodiment, the process conditions for growing the GaN nanopillar layer on the Si substrate using molecular beam epitaxy are as follows:

[0039] The temperature of the Si substrate was controlled at 430–970℃, the rotation speed of the Si substrate was 5–10 r / min, and the equivalent pressure of the Ga beam was 1.2 × 10⁻⁶. -7 ~1.4×10 -7GaN nanopillars were grown on Si substrates using a nitrogen flow rate of 1–5 sccm, a plasma source power of 200–400 W, and a growth time of 2–4 h.

[0040] In one embodiment, the g-C3N4 layer is prepared by spin-coating a g-C3N4 suspension onto the surface of GaN nanopillars.

[0041] The spin coating conditions were as follows: rotation speed of 500–2500 r / min; concentration of g-C3N4 suspension of 0.5–2.5 mg / mL; and volume of g-C3N4 suspension of 10–50 μL.

[0042] Preferably, the spin coating conditions are: a rotation speed of 1000-1500 r / min; a concentration of g-C3N4 suspension of 1-1.5 mg / mL; and a volume of g-C3N4 suspension of 20-40 μL.

[0043] In one embodiment, the g-C3N4 suspension is prepared by dispersing C3N4 in ethanol containing 2% Naifion.

[0044] Preferably, the g-C3N4 suspension is prepared by dispersing 1 mg of C3N4 in 1 mL of ethanol containing 2% Naifion to obtain a g-C3N4 suspension with a concentration of 1 mg / mL.

[0045] This application also provides a method for preparing g-C3N4 modified GaN nanopillar photoelectrode material, including the following steps:

[0046] GaN nanopillars were grown on a Si substrate using molecular beam epitaxy.

[0047] g-C3N4 was loaded onto GaN nanopillars using a spin-coating method, followed by annealing, to prepare the g-C3N4-modified GaN nanopillar photoelectrode material.

[0048] The Si substrate temperature was controlled at 430–970℃, the Si substrate rotation speed at 5–10 r / min, and the Ga beam equivalent pressure at 1.2 × 10⁻⁶. -7 ~1.4×10 -7 GaN nanopillars were grown on Si substrates using a nitrogen flow rate of 1–5 sccm, a plasma source power of 200–400 W, and a growth time of 2–4 h. The resulting GaN nanopillars had a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rods / m³. -2 .

[0049] A g-C3N4 layer was loaded onto the GaN nanopillars using a spin-coating method, followed by annealing. The spin-coating conditions were as follows: spin speed 500–2500 r / min; g-C3N4 suspension concentration 0.5–2.5 mg / mL; g-C3N4 suspension volume 10–50 μL.

[0050] Preferably, the spin coating conditions are: a rotation speed of 1000-1500 r / min; a concentration of g-C3N4 suspension of 1-1.5 mg / mL; and a volume of g-C3N4 suspension of 20-40 μL.

[0051] In one embodiment, the g-C3N4 suspension is prepared by dispersing C3N4 in ethanol containing 2% Naifion.

[0052] In one embodiment, the annealing conditions are: an annealing temperature of 50–150°C and an annealing time of 5–20 min. Preferably, the annealing conditions are: an annealing temperature of 90–100°C and an annealing time of 10–15 min.

[0053] This application also provides a photocathode comprising any of the g-C3N4 modified GaN nanopillar photoelectrode materials described above.

[0054] The g-C3N4 modified GaN nanopillar photoelectrode material of this application, under illumination, photoexcites electrons on the conduction band CB of GaN to recombine with holes on the valence band of C3N4, thereby forming a Z-type heterojunction. This significantly reduces the recombination of photogenerated electrons / holes, allowing electrons on the conduction band of C3N4 to transfer into the solution and undergo a reduction reaction to generate hydrogen gas.

[0055] In addition to illumination, a bias voltage of -0.8V is applied in this embodiment to achieve better results. The -0.8V bias voltage can increase the catalytic effect; while further increasing the voltage takes into account the withstand capability of the photoelectrode. Although applying a larger voltage can increase the catalytic effect, the photoelectrode may be denatured under high voltage, and simply increasing the voltage significantly will cause photoelectrocatalysis to become electrocatalysis, which contradicts the original design intention of the photomaterial.

[0056] In one embodiment, a Ti-Au alloy is used to connect a wire to the back side of a Si substrate containing a g-C3N4-modified GaN nanopillar photoelectrode material to obtain the photocathode. The photocathode is a heterostructure electrode.

[0057] This application also provides a photoelectrochemical cell, including a photoanode, a photocathode as described above, and an electrolyte; the photoanode and photocathode are respectively placed in the electrolyte.

[0058] In one embodiment, the electrolyte is a 0.08–0.12 mol / L Na₂SO₄ solution, and the pH of the electrolyte is 8–10.

[0059] The aforementioned photoelectrochemical cell is used in the photoelectrochemical water splitting for hydrogen production, where hydrogen is produced under sunlight irradiation.

[0060] The following specific examples will provide further details.

[0061] Example 1

[0062] A photocathode prepared from g-C3N4 modified GaN nanopillar photoelectrode material and its preparation method thereof, comprising the following steps:

[0063] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005Ω);

[0064] (2) Photocathode fabrication: Molecular beam epitaxy was used, with the Si substrate temperature controlled at 900℃, the Si substrate rotation speed at 10 r / min, and the Ga beam equivalent pressure at 1.4 × 10⁻⁶. -7 GaN nanopillars were grown on Si substrates using a nitrogen flow rate of 1–5 sccm, a plasma source power of 200–400 W, and a growth time of 2–4 h. The GaN nanopillars had a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rods / μm. -2 Then, g-C3N4 two-dimensional nanosheets were loaded onto GaN nanopillars by spin coating, and the photoelectrode was annealed. The spin coating conditions were: rotation speed of 1000 r / min; concentration of g-C3N4 two-dimensional nanosheet suspension of 1 mg / mL; volume of g-C3N4 two-dimensional nanosheet suspension of 20 μL; annealing conditions were: annealing temperature of 100℃ and annealing time of 10 min, to obtain g-C3N4 modified GaN nanopillar photoelectrode material.

[0065] (3) A photocathode is fabricated by connecting a wire to the back side of a Si substrate modified with g-C3N4 GaN nanopillar photoelectrode material using a Ti-Au alloy. The area of ​​the photoelectrode is a 0.5*0.5cm square.

[0066] Example 2

[0067] A photocathode prepared from g-C3N4 modified GaN nanopillar photoelectrode material and its preparation method thereof, comprising the following steps:

[0068] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005Ω).

[0069] (2) Photocathode fabrication: Molecular beam epitaxy was used, with the Si substrate temperature controlled at 900℃, the Si substrate rotation speed at 10 r / min, and the Ga beam equivalent pressure at 1.4 × 10⁻⁶. -7 GaN nanopillars were grown on Si substrates using a nitrogen flow rate of 1–5 sccm, a plasma source power of 200–400 W, and a growth time of 2–4 h. The GaN nanopillars had a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rods / μm. -2 Then, g-C3N4 two-dimensional nanosheets were spin-coated onto GaN nanopillars, followed by annealing of the photoelectrode. The spin-coating conditions were: spin speed 1000 r / min; concentration of g-C3N4 two-dimensional nanosheet suspension 1 mg / mL; volume of g-C3N4 two-dimensional nanosheet suspension 30 μL; annealing conditions were: annealing temperature 100℃; annealing time 10 min; thus, g-C3N4 modified GaN nanopillar photoelectrode material was obtained.

[0070] (3) A photocathode was fabricated by connecting a wire to the back side of a Si substrate containing a g-C3N4-modified GaN nanopillar photoelectrode material using a Ti-Au alloy. The structure is as follows: Figure 1 As shown; the area of ​​the photoelectrode is a 0.5*0.5cm square. The SEM image of the surface structure is shown below. Figure 2 As shown.

[0071] Example 3

[0072] A photocathode prepared from g-C3N4 modified GaN nanopillar photoelectrode material and its preparation method thereof, comprising the following steps:

[0073] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005Ω).

[0074] (2) Photocathode fabrication: Molecular beam epitaxy was used, with the Si substrate temperature controlled at 900℃, the Si substrate rotation speed at 10 r / min, and the Ga beam equivalent pressure at 1.4 × 10⁻⁶. -7 GaN nanopillars were grown on Si substrates using a nitrogen flow rate of 1–5 sccm, a plasma source power of 200–400 W, and a growth time of 2–4 h. The GaN nanopillars had a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rods / μm. -2Then, g-C3N4 two-dimensional nanosheets were loaded onto GaN nanopillars via spin coating, followed by annealing of the photoelectrode. The spin coating conditions were: rotation speed 1000 r / min; concentration of g-C3N4 two-dimensional nanosheet suspension 1 mg / mL; volume of g-C3N4 two-dimensional nanosheet suspension 40 μL; annealing conditions were: annealing temperature 100℃; annealing time 10 min, resulting in g-C3N4 modified GaN nanopillar photoelectrode material.

[0075] (3) A photocathode is fabricated by connecting a wire to the back side of a Si substrate modified with g-C3N4 GaN nanopillar photoelectrode material using a Ti-Au alloy. The area of ​​the photoelectrode is a 0.5*0.5cm square.

[0076] Comparative Example 1

[0077] A photocathode made of GaN nanopillar photoelectrode material and its preparation method thereof, comprising the following steps:

[0078] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005Ω).

[0079] (2) Photocathode fabrication: Molecular beam epitaxy was used, with the Si substrate temperature controlled at 900℃, the Si substrate rotation speed at 10 r / min, and the Ga beam equivalent pressure at 1.4 × 10⁻⁶. -7 GaN nanopillars were grown on Si substrates using a nitrogen flow rate of 1–5 sccm, a plasma source power of 200–400 W, and a growth time of 2–4 h. The GaN nanopillars had a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rods / μm. -2 ;

[0080] (3) A photocathode was fabricated by connecting a wire to the back side of a GaN nanopillar photoelectrode material Si substrate using a Ti-Au alloy; the area of ​​the photoelectrode was a 0.5*0.5cm square; the SEM image of the surface structure is shown below. Figure 2 As shown.

[0081] Comparative Example 2

[0082] A photocathode made of g-C3N4 photoelectrode material and its preparation method thereof, comprising the following steps:

[0083] (1) Substrate selection: n-type Si was used as the substrate (conductivity <0.005Ω).

[0084] (2) Photocathode fabrication: g-C3N4 two-dimensional nanosheets were loaded onto an n-type Si substrate by spin coating, and then the photocathode was annealed. The spin coating conditions were: rotation speed of 1000 r / min; concentration of g-C3N4 two-dimensional nanosheet suspension of 1 mg / mL; volume of g-C3N4 two-dimensional nanosheet suspension of 30 μL; annealing conditions were: annealing temperature of 100℃ and annealing time of 10 min.

[0085] (3) A photocathode was fabricated by connecting a wire to the back side of a g-C3N4 photoelectrode material Si substrate using a Ti-Au alloy; the area of ​​the photoelectrode was a 0.5*0.5cm square; the SEM image of the surface structure is shown below. Figure 2 As shown.

[0086] Performance testing:

[0087] Construction of the photoelectrochemical cell: The photocathodes prepared in Examples 1-3 and Comparative Examples 1-2 were connected in series with a Pt electrode. The photoanode and photocathode were placed in an electrolyte solution of 0.1 M Na₂SO₄ (pH = 7). Parallel light was used as the light source. The photoelectrochemical hydrogen production system was used for solar-powered hydrogen production under a bias voltage of -0.8 V. The current-voltage relationship in the photoelectrochemical hydrogen production system under a certain bias voltage is as follows: Figure 3 As shown; the bias photoelectric conversion efficiency in the photoelectrochemical hydrogen production system under a certain bias voltage is as follows: Figure 4 As shown in the figure; the obtained bias photoelectric conversion efficiency is shown in Table 1;

[0088] Table 1

[0089] Serial Number Photoelectric conversion efficiency at -0.8V bias / % Example 1 0.32 Example 2 5.87 Example 3 0.79 Comparative Example 1 0.13 Comparative Example 2 0.47

[0090] As can be seen from Examples 1-3, for silicon wafers of the same area, the photoelectric conversion efficiency under -0.8V bias changes significantly with decreasing volumes of spin-coated g-C3N4 (20 μL, 30 μL, and 40 μL). When the volume of spin-coated g-C3N4 is 30 μL, the photoelectric conversion efficiency under -0.8V bias reaches 5.87%. This is because the accumulated g-C3N4 NSs has the best shell density and catalytic performance on the GaN NRs core, effectively acting as a surface passivation layer. This layer suppresses the defect states of photocarriers and the surface recombination of photocarriers, promoting good charge transfer at the photocathode / electrolyte interface. Furthermore, when the C3N4 loading is too high, it completely covers the GaN, resulting in a decrease in catalytic effect. Comparative Example 1, without g-C3N4 modification, showed a photoelectric conversion efficiency of only 0.13% at -0.8V bias. Comparative Example 2, using pure C3N4 as the photocathode material, exhibited better performance than GaN, achieving a photoelectric conversion efficiency of 0.47% at -0.8V bias. This was significantly higher than the 20 μL g-C3N4 spin-coated material in Example 1. These findings demonstrate that by selecting g-C3N4 as the modification material and loading it onto GaN nanopillars, this method effectively improves the photoelectric conversion efficiency of pure GaN.

[0091] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.

[0092] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.

[0093] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this application, and these should all be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A photocathode, characterized in that, The photocathode comprises a g-C3N4 modified GaN nanopillar photoelectrode material; the g-C3N4 modified GaN nanopillar photoelectrode material includes a Si substrate, on which a GaN nanopillar layer is grown, and the surface of the GaN nanopillar is modified with a g-C3N4 layer. The Ti-Au alloy is used to connect the wire to the back side of the Si substrate of the g-C3N4 modified GaN nanopillar photoelectrode material to obtain the photocathode.

2. The photocathode according to claim 1, characterized in that, GaN nanopillars were grown on a Si substrate using molecular beam epitaxy. g-C3N4 was loaded onto GaN nanopillars using a spin-coating method, followed by annealing, to prepare the g-C3N4-modified GaN nanopillar photoelectrode material.

3. The photocathode according to claim 2, characterized in that, The GaN nanopillars have a height of 100–400 nm, a diameter of 30–100 nm, and a density of 100–300 rod / m³. -2 .

4. The photocathode according to claim 2, characterized in that, The process conditions for growing the GaN nanopillar layer on the Si substrate using molecular beam epitaxy are as follows: The temperature of the Si substrate was controlled at 430–970℃, the rotation speed of the Si substrate was 5–10 r / min, and the equivalent pressure of the Ga beam was 1.2 × 10⁻⁶. -7 ~1.4×10 -7 GaN nanopillars were grown on Si substrates using a nitrogen flow rate of 1–5 sccm, a plasma source power of 200–400 W, and a growth time of 2–4 h.

5. The photocathode according to claim 2, characterized in that, The spin coating conditions were as follows: rotation speed of 500–2500 r / min; concentration of g-C3N4 suspension of 0.5–2.5 mg / mL; and volume of g-C3N4 suspension of 10–50 μL.

6. The photocathode according to claim 5, characterized in that, The annealing conditions are: annealing temperature of 50-150℃ and annealing time of 5-20min.

7. A photoelectrochemical cell, characterized in that, It includes a photoanode, a photocathode as described in any one of claims 1-6, and an electrolyte; the electrolyte is a 0.08-0.12 mol / L Na2SO4 solution, and the pH of the electrolyte is 7.

8. The application of the photoelectrochemical cell according to claim 7 in photoelectrochemical water splitting for hydrogen production, characterized in that, The photoelectrochemical cell produces hydrogen under sunlight.

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