A preferentially oriented ta3n5 photoanode and a preparation method thereof

Abstract

This invention belongs to the field of photoelectrode material preparation technology for photoelectrode fabrication in photoelectrochemical water splitting, specifically a preferred-oriented Ta3N5 photoanode and its preparation method. This method utilizes an electron beam evaporation system and a high-temperature nitriding method to form a specifically oriented Ta3N5 inducing layer on a Nb substrate, and then achieves the orientation-continuous growth of the main Ta3N5 thin film. By adjusting the type of metal material in the inducing layer, the preferred orientation of the Ta3N5 crystal planes can be controlled, thereby achieving the regulation of the photoelectrochemical water splitting performance of the Ta3N5 thin film. This method has good structural repeatability and can be extended to the growth of different substrates and other material systems.

Description

Technical Field

[0001] This invention belongs to the field of photoelectrochemical water splitting photoelectrode material preparation technology, specifically relating to a preferred orientation Ta3N5 photoanode and its preparation method. Background Technology

[0002] With the increasing severity of global environmental problems and the energy crisis, the development of clean, low-carbon alternative energy sources has become an urgent need for sustainable development. Photoelectrochemical (PEC) water splitting for hydrogen production has attracted much attention due to its ability to directly convert solar energy into chemical energy. Among numerous photoanode materials, Ta3N5 stands out for its superior physical properties. As an n-type semiconductor with a band gap of approximately 2.1 eV, Ta3N5 can absorb solar spectra with wavelengths less than 600 nm; its conduction and valence bands span the redox potential of water, giving it thermodynamic potential for achieving overall water splitting. Theoretical studies show that Ta3N5 can achieve a maximum saturation photocurrent density of 12.9 mA / cm² under standard sunlight irradiation. 2 The solar-to-hydrogen STH conversion efficiency is 15.9%.

[0003] Currently, Ta3N5 photoanode thin films are typically prepared by high-temperature nitriding of oxide precursors. However, existing methods often result in randomly oriented polycrystalline structures, leading to a high number of grain boundaries and easy recombination and loss of photogenerated carriers during transport. Furthermore, different crystal planes exhibit significant differences in carrier transport characteristics, further affecting their photoelectric performance. Therefore, there is an urgent need to develop a new method for preferentially growing Ta3N5 thin films to effectively control their photoelectrochemical water splitting performance. Summary of the Invention

[0004] The purpose of this invention is to provide a preferentially oriented Ta3N5 photoanode and its preparation method, thereby solving the technical problem of difficulty in effectively controlling the crystal orientation during the preparation of existing Ta3N5 thin films. By achieving preferential growth of Ta3N5 thin films on specific crystal planes, a new technical approach is provided for controlling the photoelectrochemical water splitting performance of Ta3N5 thin films.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a preferred-oriented Ta3N5 photoanode includes the following steps:

[0007] Step 1: Provide the substrate, clean it, and dry it.

[0008] Step 2: Sequentially deposit a first layer of Ta2O5 precursor film and a metal film on the substrate treated in Step 1; the metal film is a Pt film or a Ni film.

[0009] Step 3: Perform a first high-temperature nitriding treatment on the sample obtained in Step 2 to obtain a Ta3N5 induced layer;

[0010] Step 4: Deposit a second Ta2O5 precursor film on the surface of the Ta3N5 induced layer;

[0011] Step 5: Perform a second high-temperature nitriding treatment on the sample obtained in Step 4 to transform the second Ta2O5 precursor film into a Ta3N5 host precursor film; the Ta3N5 induction layer serves as a crystal growth template to induce the orientation continuation growth of the Ta3N5 host precursor film, forming a Ta3N5 film with preferred crystal orientation.

[0012] Step 6: Fabricate an ohmic contact on the back side of the sample obtained in Step 5 and encapsulate it to obtain a Ta3N5 photoanode.

[0013] A preferred orientation Ta3N5 photoanode, characterized in that it is prepared by the above-mentioned preferred orientation Ta3N5 photoanode preparation method, and the Ta3N5 photoanode has a preferred orientation feature along the (023) crystal plane or the (110) crystal plane.

[0014] This invention provides a method for preparing a preferentially oriented Ta3N5 photoanode. Combining an electron beam evaporation system with a high-temperature nitriding method, a Ta3N5 induction layer with specific orientation characteristics is first formed on a Nb substrate. Based on this, a Ta3N5 main film is further deposited and nitrided to achieve continuous growth with the preferred orientation. By controlling the type of metal material used in the induction layer, the formation mode of the initial crystal nuclei and the subsequent crystal growth orientation can be affected, thereby adjusting the preferred orientation characteristics of the final Ta3N5 film. The orientation characteristics obtained under different induction conditions differ in charge transport behavior, making the photoelectrochemical water splitting performance of the Ta3N5 photoanode tunable.

[0015] Compared with existing technologies, this preparation method can stably construct preferentially grown Ta3N5 films with good repeatability and controllability, and can be extended to the growth of other substrates and materials. Attached Figure Description

[0016] Figure 1 This is a process flow diagram of the present invention;

[0017] Figure 2 XRD patterns of Ta3N5 thin films in Examples 1, 2 and Comparative Example 1;

[0018] Figure 3 Photocurrent-voltage curves of the Ta3N5 photoanodes in Examples 1, 2 and Comparative Example 1;

[0019] Figure 4The graphs show the bias-assisted photoelectric conversion efficiency curves of the Ta3N5 photoanodes in Examples 1, 2 and Comparative Example 1. Detailed Implementation

[0020] To better explain the purpose, structure, and effects of this invention, the invention will be further described in detail below with reference to the accompanying drawings and specific examples. It should be noted that the specific examples are only for explaining the invention and should not be construed as limiting the scope of protection of this invention. All equivalent substitutions, improvements, or modifications made within the spirit and principles of this invention are included within the scope of protection of this invention.

[0021] This invention provides a method for preparing a preferentially oriented Ta3N5 photoanode. The method involves first preparing a Ta3N5 inducing layer with specific orientation characteristics through two steps: electron beam evaporation and high-temperature nitriding. Subsequently, the orientation of the Ta3N5 substrate film is continuously grown on this layer. By changing the structure of the inducing layer, the orientation of the film growth can be controlled. The process flow diagram is shown below. Figure 1 As shown, the invention comprises six steps: ultrasonic cleaning of the substrate, sequential deposition of a Ta2O5 precursor film and a metal film using an electron beam evaporation system, high-temperature nitriding to prepare a Ta3N5 induced layer, re-deposition of the Ta2O5 precursor film, high-temperature nitriding to prepare a preferentially oriented Ta3N5 film, and preparation of a preferentially oriented Ta3N5 photoanode. The technical solution of this invention will be described in detail below with reference to specific parameter ranges.

[0022] Step 1, Substrate Cleaning: Select a metal Nb sheet as the substrate, and ultrasonically clean the substrate for 10-20 minutes in sequence with a precision detergent, deionized water, acetone and isopropanol, and then dry it with a nitrogen gun.

[0023] Step 2: Deposition of Ta₂O₅ precursor film and metal film: Place the cleaned substrate into the sample tray of the electron beam evaporation system. Simultaneously, place the crucible containing Ta₂O₅ as the oxide precursor and the crucible containing Pt or Ni metal into their respective deposition sources. Close the system vacuum chamber door and evacuate to 5 × 10⁻⁻⁻⁵. 6 ~1×10⁻ 5 Torr. During Ta₂O₅ deposition, oxygen was introduced into the system at a rate of 1–10 sccm, with a deposition rate of 1–5 Å / s and a deposition thickness of 100–300 nm. A quartz oscillator was used to monitor and control the deposition rate and thickness of the source in real time during the deposition process. After Ta₂O₅ deposition was completed, the vacuum level was allowed to return to 5 × 10⁻⁻⁻⁴. 6 ~1×10⁻ 5 Torr is then used to deposit a metal thin film. The deposition rate of the metal thin film is 0.1–0.3 Å / s, and the deposition thickness is 2–10 nm.

[0024] Step 3: First high-temperature nitriding to prepare the Ta3N5 induced layer: The sample (Ta2O5 / Pt or Ta2O5 / Ni) obtained in Step 2 was placed in a quartz boat and sealed in a high-temperature tube furnace, and high-temperature nitriding was carried out under an NH3 atmosphere. The nitriding conditions were: NH3 gas flow rate 100-300 sccm, temperature 800-1050℃, and time 1-12 hours, to obtain the Ta3N5 induced layer.

[0025] Step 4: Deposit the second Ta2O5 precursor film: Place the sample obtained in step 3 into the sample tray of the electron beam evaporation system and repeat the Ta2O5 film deposition process in step 2.

[0026] Step 5: Second High-Temperature Nitriding for Preferred Orientation of Ta3N5 Thin Film: The Ta3N5 / Pt / Ta2O5 or Ta3N5 / Ni / Ta2O5 sample obtained in Step 4 is placed in a quartz boat and sealed in a high-temperature tube furnace for a second high-temperature nitriding under an NH3 atmosphere. The nitriding conditions are within the process parameter range described in Step 3, transforming the second Ta2O5 layer into a Ta3N5 host film. Under the template effect of the lower Ta3N5 inducing layer, orientation continuation growth is achieved, ultimately forming a Ta3N5 thin film with preferred crystal orientation.

[0027] Step 6: Prepare photoanode: Use indium metal to weld the wire to the back of the sample obtained in step 5, and then use epoxy resin to encapsulate and cover it to form an ohmic contact, thus preparing a Ta3N5 photoanode with preferred crystal orientation.

[0028] Example 1: Preparation of (023) preferred orientation Ta3N5 photoanode using Pt as the metal induction layer.

[0029] The Ta3N5 photoanode prepared according to the preferred scheme described in this embodiment has the following specific parameters:

[0030] Substrate: Metal Nb sheet with a thickness ≥ 0.07 mm and a purity ≥ 99.98%, cleaned for 15 minutes according to step 1.

[0031] Deposition process: According to the preferred scheme in step 2, vacuum degree 5×10⁻ 6 During the deposition of Torr Ta2O5, 5 sccm of O2 was introduced, resulting in a deposition rate of 5 Å / s and a thickness of 200 nm; the deposition rate of the metal Pt thin film was 0.2 Å / s and the thickness was 5 nm.

[0032] First nitriding: Following the preferred scheme in step 3, with NH3 purity of 99.999% and a gas flow rate of 200 sccm, the temperature is increased to 1025℃ at 10℃ / min and held at that temperature for 6 hours to obtain the Ta3N5 induced layer.

[0033] Second deposition: Following the preferred scheme in step 4, deposit Ta2O5 with a thickness of 600 nm.

[0034] Second nitriding: According to the preferred scheme of step 5, the NH3 gas flow rate is 280 sccm, the temperature is 1025℃, and the time is 6 hours to obtain a Ta3N5 thin film with preferred orientation of (023) crystal plane.

[0035] Encapsulation: Prepare the photoanode according to step 6.

[0036] Example 2: Fabrication of a (110) preferred-oriented Ta3N5 photoanode using Ni as the metal induction layer:

[0037] This embodiment is basically the same as Embodiment 1, except that the metal film deposited in step 2 is Ni, with a deposition rate of 0.2 Å / s and a thickness of 5 nm. All other parameters are the same as in Embodiment 1.

[0038] Comparative Example 1: The steps are the same as in Example 1, except that the metal layer deposition process in step 2 is omitted, and only 200nm Ta3N5 without obvious orientation is prepared as a comparison.

[0039] Figure 2 The XRD patterns of the Ta3N5 thin films in Examples 1, 2, and Comparative Example 1 are shown. It is readily apparent that the diffraction patterns of the Ta3N5 thin films prepared in the three examples correspond to the orthorhombic crystal structure of Ta3N5 (JCPDS no. 79-1533-Ta3N5), indicating that the introduction of the metal does not introduce other impurity phases. Furthermore, a comparison reveals that the Ta3N5 thin film in Example 1 exhibits a significantly enhanced diffraction peak intensity at 2θ = 31.45°, indicating that under these preparation conditions, the Ta3N5 thin film undergoes preferential growth along the (023) crystal plane; while the Ta3N5 thin film in Example 2 shows a slightly enhanced diffraction peak intensity at 2θ = 24.49°, indicating that under these preparation conditions, the Ta3N5 thin film undergoes preferential growth along the (110) crystal plane; the Ta3N5 thin film in Comparative Example 1, without the introduction of metal, does not exhibit a clear preferred orientation characteristic, thus proving that the change in crystal orientation originates from the metal-induced layer, rather than the process itself.

[0040] To further analyze the influence of different crystal plane orientations on carrier transport behavior, the effective carrier mass of the two crystal planes mentioned above was theoretically calculated, and the results are shown in Table 1 below.

[0041] Table 1 Effective carrier mass for two crystal planes (unit: m0)

[0042]

[0043] As shown in Table 1, the (023) direction has a smaller effective carrier mass, which is theoretically more conducive to carrier migration, providing a theoretical basis for the influence of crystal plane modulation on photoelectric performance.

[0044] Figure 3 and Figure 4 The figures show the photocurrent-voltage curves and bias-assisted photoelectric conversion efficiency curves of the Ta3N5 photoanodes in Examples 1, 2, and Comparative Example 1, respectively. Before performing photoelectrochemical water splitting, NiCoFe-B needs to be deposited on the surface of the Ta3N5 photoanode. i Oxygen-producing co-catalyst. From Figure 3 , Figure 4 As can be seen, compared with conventional Ta3N5 films, the sample with the (023) preferred orientation structure exhibits higher photocurrent density and energy conversion efficiency, while the sample with the (110) preferred orientation structure has relatively poor photoelectric performance.

[0045] In summary, this invention combines an electron beam evaporation system with a high-temperature nitriding method to prepare a preferentially oriented Ta3N5 photoanode. By changing the metal material used in the inducing layer, this method yields Ta3N5 films preferentially grown along different crystal planes. Due to the differences in carrier migration across different crystal planes, the photoelectrochemical water splitting performance of the Ta3N5 photoanode exhibits tunability.

[0046] In summary, this invention combines an electron beam evaporation system with a high-temperature nitriding method to prepare a preferentially oriented Ta3N5 photoanode. By changing the metal material used in the inducing layer, this method yields Ta3N5 films preferentially grown along different crystal planes. Due to the differences in carrier migration across different crystal planes, the photoelectrochemical water splitting performance of the Ta3N5 photoanode exhibits tunability.

Claims

1. A method for preparing a preferred-oriented Ta3N5 photoanode, characterized in that, Includes the following steps: Step 1: Provide the substrate, clean it, and dry it. Step 2: Sequentially deposit a first layer of Ta2O5 precursor film and a metal film on the substrate treated in Step 1; the metal film is a Pt film or a Ni film. Step 3: Perform a first high-temperature nitriding treatment on the sample obtained in Step 2 to obtain a Ta3N5 induced layer; Step 4: Deposit a second Ta2O5 precursor film on the surface of the Ta3N5 induced layer; Step 5: Perform a second high-temperature nitriding treatment on the sample obtained in Step 4 to transform the second Ta2O5 precursor film into a Ta3N5 host precursor film; the Ta3N5 induction layer serves as a crystal growth template to induce the orientation continuation growth of the Ta3N5 host precursor film, forming a Ta3N5 film with preferred crystal orientation. Step 6: Fabricate an ohmic contact on the back side of the sample obtained in Step 5 and encapsulate it to obtain a Ta3N5 photoanode.

2. The method for preparing a preferred-oriented Ta3N5 photoanode according to claim 1, characterized in that, The substrate used in step 1 is a niobium sheet with a purity of ≥99.98% and a thickness of ≥0.07mm.

3. The preferred orientation Ta3N5 photoanode and its preparation method according to claim 1, characterized in that, The cleaning and drying method in step 1 is as follows: the substrate is ultrasonically cleaned sequentially with detergent, deionized water, acetone and isopropanol, and then dried with a nitrogen gun.

4. The method for preparing a preferred-oriented Ta3N5 photoanode according to claim 1, characterized in that, The thickness of the metal thin film in step 2 is 2~10nm.

5. The preferred orientation Ta3N5 photoanode and its preparation method according to claim 1, characterized in that, In step 2, the deposition thickness of the first Ta2O5 precursor film is 100~300nm; in step 4, the deposition thickness of the second Ta2O5 precursor film is 600nm.

6. The method for preparing a preferred-oriented Ta3N5 photoanode according to claim 1, characterized in that, The first Ta2O5 precursor film and metal film in step 2, and the second Ta2O5 precursor film in step 4, are all deposited using an electron beam evaporation system. When depositing the first or second Ta2O5 precursor film, oxygen is introduced into the system at a rate of 1–10 sccm, and the deposition rate is 1–5 Å / s; when depositing the metal film, the deposition rate is 0.1–0.3 Å / s.

7. The method for preparing a preferred-oriented Ta3N5 photoanode according to claim 1, characterized in that, The conditions for the first high-temperature nitriding treatment in step 3 are as follows: under an NH3 atmosphere, the gas flow rate is 100~300 sccm, the temperature is 800~1050℃, and the time is 1~12 hours.

8. The method for preparing a preferred-oriented Ta3N5 photoanode according to claim 1, characterized in that, The conditions for the second high-temperature nitriding treatment in step 5 are: 1025°C in an NH3 atmosphere for 6 hours.

9. A preferred orientation Ta3N5 photoanode, characterized in that, The Ta3N5 photoanode is prepared by any one of the preparation methods described in claims 1 to 8, and the photoanode has a preferred orientation along the (023) crystal plane or the (110) crystal plane.

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