Nickel phosphide composite TiO2 nanotube array and preparation method and application thereof

Abstract

The invention belongs to the technical field of photoelectrocatalysis, and particularly relates to a nickel phosphide composite TiO2 nanotube array and a preparation method and application thereof. The heterojunction modified titanium dioxide nanotube array is constructed by using nickel phosphide with specific concentration, and the nickel phosphide with enhanced charge density near Fermi level has higher conductivity, chemical stability and better activity, and is beneficial to improvement of electron transfer rate. Research finds that electrons under optical excitation tend to be transferred from TiO2 to Ni2P, the Ni2P modifies the electronic structure of the TiO2 nanotube, and the remarkable change of the electronic structure can cause electron transition and improve the electron-hole separation efficiency, so that the photoelectrocatalysis performance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectrocatalysis, and particularly relates to a nickel phosphide composite TiO2 nanotube array, a preparation method thereof, and an application thereof. Background Art

[0002] Using semiconductor photocatalysts for solar-driven electrochemical (PEC) water splitting for clean and inexpensive hydrogen production is considered the cleanest and most efficient hydrogen production method. TiO2 has been widely used in the field of photocatalysis due to its low cost, good stability, and non-toxicity. However, problems such as a wide bandgap of photogenerated carrier pairs, slow charge transfer, and high recombination rate seriously hinder the practical application of TiO2 in PEC water splitting under sunlight. Growing one-dimensional TiO2 nanotube arrays (TNTAs) with an acceptable specific surface area by self-organized anodic oxidation of a titanium substrate is considered an ideal candidate for a PEC anode.

[0003] However, the existing TiO2 nanotube arrays have low photoelectrochemical performance and cannot fully meet the actual needs. Summary of the Invention

[0004] The purpose of the present invention is to provide a nickel phosphide composite TiO2 nanotube array, a preparation method thereof, and an application thereof. The nickel phosphide composite TiO2 nanotube array provided by the present invention has excellent photoelectrochemical performance.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides a nickel phosphide composite TiO2 nanotube array, including a titanium dioxide nanotube array and nickel phosphide forming a heterojunction with the titanium dioxide nanotube array; the heterojunction is a Schottky junction.

[0007] Preferably, the diameter of the tubes in the titanium dioxide nanotube array is 100 - 120 nm, and the length of the tubes is 22 - 25 μm.

[0008] Preferably, the atomic ratio of titanium ions to nickel ions in the nickel phosphide composite TiO2 nanotube array is 140 - 1500.

[0009] The present invention also provides a preparation method of the nickel phosphide composite TiO2 nanotube array according to the above scheme, including the following steps:

[0010] Mixing the titanium dioxide nanotube array, Ni salt, and a dispersion solvent, performing a first impregnation and then drying to obtain a pretreated titanium dioxide nanotube array;

[0011] Mixing the pretreated titanium dioxide nanotube array, an alkali metal hydroxide, and a good solvent, performing a second impregnation to obtain an electrode;

[0012] Anneal the electrode and hypophosphite by mixing them to obtain the nickel phosphide composite TiO2 nanotube array.

[0013] Preferably, the preparation method of the titanium dioxide nanotube array includes the following steps: Mix a Ti sheet and a fluorinated ethylene glycol solution for first anodization, and then successively perform second anodization, ethylene glycol immersion, and annealing.

[0014] Preferably, after the first anodization, ultrasonication of the obtained product in water is further included; the frequency of the ultrasonication is 60 - 100 kHz, and the time is 10 - 30 min.

[0015] Preferably, the temperature of the first impregnation is room temperature, and the time is 2 - 3 h; the temperature of the second impregnation is room temperature, and the time is 5 - 30 min.

[0016] Preferably, the molar ratio of the alkali metal hydroxide to the hypophosphite is 1:1 - 2.

[0017] Preferably, the temperature of the annealing is 300 - 500 °C, and the heat preservation time is 1 - 3 h; the second annealing is carried out in a protective atmosphere.

[0018] The present invention also provides the application of the nickel phosphide composite TiO2 nanotube array described in the above solution or the nickel phosphide composite TiO2 nanotube array obtained by the preparation method described in the above solution in the field of photoelectrocatalysis.

[0019] The present invention provides a nickel phosphide composite TiO2 nanotube array. For the nickel phosphide composite TiO2 nanotube array provided by the present invention, a heterojunction is constructed by nickel phosphide with a specific concentration to modify the titanium dioxide nanotube array. Compared with traditional catalysts such as Ni(OH)2, nickel phosphide (Ni2P) with enhanced charge density near the Fermi level has higher electrical conductivity, chemical stability, and better activity, which is beneficial to the improvement of the electron transfer rate; in addition, PO4 generated on the surface of Ni2P 3- promotes the occurrence of the proton-coupled electron transfer process.

[0020] The present invention has found through research that under light excitation, electrons are more inclined to transfer from TiO2 to Ni2P. Ni2P modifies the electronic structure of the TiO2 nanotube. This significant change in the electronic structure will lead to electron transitions, improve the separation efficiency of electron-hole pairs, and thus improve the photoelectrocatalytic performance. In addition, the Schottky junction is formed by the contact between a metal and a semiconductor. The Schottky junction promotes the separation of photo-generated carriers through the built-in electric field and band bending, reduces recombination, improves the photoelectric conversion efficiency, reduces the overpotential, and enhances light absorption, thereby significantly improving the photoelectrochemical performance of the material. The nickel phosphide composite TiO2 nanotube array provided by the present invention has excellent photoelectrochemical performance, is simple and efficient, and has stable effects.

[0021] The present invention also provides a method for preparing the nickel phosphide composite TiO2 nanotube array described in the above solution. Through the electrochemical anodic oxidation method and the impregnation method, the present invention obtains a TiO2 nanotube array photoanode composite with Ni2P nanoparticles, which has good uniformity, faster photoelectric response speed, avoids the recombination process of minority carriers, and forms a relatively high Schottky barrier to suppress dark current, and has broad application prospects.

[0022] The present invention also provides the application of the nickel phosphide composite TiO2 nanotube array described in the above solution or the nickel phosphide composite TiO2 nanotube array obtained by the preparation method described in the above solution in the field of photoelectrocatalysis. The nickel phosphide composite TiO2 nanotube array provided by the present invention has excellent photoelectrochemical performance, low cost, and good stability, and is suitable for use in the field of photoelectrocatalysis, especially for the preparation of clean energy such as hydrogen. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0024] Figure 1 It is the preparation flow chart of the nickel phosphide composite TiO2 nanotube array (Ni2P / TNTAs) of the present invention;

[0025] Figure 2 It is the XRD pattern of Ni2P / TNTAs prepared in Examples 1 to 3; in the figure, X in Ni2P / TNTAs-X is the nickel ion concentration coefficient;

[0026] Figure 3 It is the SEM diagram of TNTAs (a and d), Ni(OH)2 / TNTAs (b and e) and Ni2P / TNTAs (c and f);

[0027] Figure 4 It is the TEM diagram of TNTAs (a) and Ni2P / TNTAs (d);

[0028] Figure 5 It is the HRTEM diagram of TNTAs (b) and Ni2P / TNTAs (e);

[0029] Figure 6 It is the SAED diagram of TNTAs (c) and Ni2P / TNTAs (f);

[0030] Figure 7Element distribution map of Ni2P / TNTAs;

[0031] Figure 8 XPS spectrum of Ni2P / TNTAs;

[0032] Figure 9 DOS diagram of Ni2P / TNTAs. Specific implementation mode

[0033] The present invention provides a nickel phosphide composite TiO2 nanotube array, which includes a titanium dioxide nanotube array and nickel phosphide forming a heterojunction with the titanium dioxide nanotube array; the heterojunction is a Schottky junction.

[0034] The nickel phosphide composite TiO2 nanotube array provided by the present invention includes a titanium dioxide nanotube array; the diameter of the tubes in the titanium dioxide nanotube array can be 100-120 nm, specifically 105 nm, 110 nm or 115 nm, and the length of the tubes can be 22-25 μm, specifically 23 μm or 24 μm.

[0035] The nickel phosphide composite TiO2 nanotube array provided by the present invention includes nickel phosphide; the atomic ratio of titanium ions to nickel ions in the nickel phosphide composite TiO2 nanotube array can be 140-1500, specifically 1458.67, 1250, 1000, 750, 500, 306.199 or 147.426.

[0036] The present invention also provides a preparation method of the nickel phosphide composite TiO2 nanotube array described in the above scheme, including the following steps:

[0037] Mix the titanium dioxide nanotube array, Ni salt and dispersion solvent for the first impregnation and then dry to obtain a pretreated titanium dioxide nanotube array;

[0038] Mix the pretreated titanium dioxide nanotube array, alkali metal hydroxide and good solvent for the second impregnation to obtain an electrode;

[0039] Anneal the electrode and NaH2PO2 to obtain the nickel phosphide composite TiO2 nanotube array.

[0040] The present invention mixes the titanium dioxide nanotube array, Ni salt and dispersion solvent (to obtain a first mixed solution) for the first impregnation and then dries to obtain a pretreated titanium dioxide nanotube array. In the present invention, the preparation method of the titanium dioxide nanotube array may include the following steps: mixing a Ti sheet and a fluorinated ethylene glycol solution for the first anodization, and then sequentially performing the second anodization, ethylene glycol soaking and annealing (denoted as the first annealing).

[0041] In the present invention, the Ti sheet can be pretreated before use; the pretreatment can be: polishing the Ti sheet until it is bright, placing it in acetone for ultrasonic treatment, taking out the Ti sheet, washing it, and then drying it.

[0042] In the present invention, the time of the ultrasonic treatment can be 30 - 60 min, specifically 40 min or 50 min; the washing can be water washing; the water used for the water washing can be deionized water; the drying can be drying in an oven; the equipment for the drying can be an oven.

[0043] In the present invention, the fluorinated ethylene glycol solution can include NH4F and ethylene glycol; the concentration of NH4F in the fluorinated ethylene glycol solution can be 0.1 - 0.5 wt.%, specifically 0.2 wt.%, 0.25 wt.%, 0.3 wt.%, 0.36 wt.% or 0.4 wt.%; the fluorinated ethylene glycol solution can be an aqueous solution of fluorinated ethylene glycol; the concentration of water in the aqueous solution of fluorinated ethylene glycol can be 1 - 2.2 vol.%, specifically 1.2 vol.%, 1.5 vol.%, 1.8 vol.% or 2 vol.%.

[0044] In the present invention, the temperature of the first anodization can be 20 - 50 °C, specifically 25 °C, 30 °C, 35 °C, 40 °C or 45 °C, and the time can be 1 - 3 h, specifically 1.5 h, 2 h or 2.5 h; the first anodization can be carried out under a constant potential condition; the voltage of the constant potential can be 10 - 60 V, specifically 20 V, 30 V, 40 V or 50 V.

[0045] In the present invention, after the first anodization, it can further include ultrasonic treatment of the obtained product in water; the frequency of the ultrasonic treatment can be 60 - 100 kHz, specifically 70 kHz, 80 kHz or 90 kHz, and the time can be 10 - 30 min, specifically 15 min, 20 min or 25 min. In the present invention, titanium nanotubes are removed by ultrasonic treatment.

[0046] In the present invention, the temperature of the second anodization can be 20 - 50 °C, specifically 25 °C, 30 °C, 35 °C, 40 °C or 45 °C, and the time can be 1 - 3 h, specifically 1.5 h, 2 h or 2.5 h; the second anodization can be carried out under a constant potential condition; the voltage of the constant potential can be 10 - 60 V, specifically 20 V, 30 V, 40 V or 50 V.

[0047] In the present invention, the reagent used for the ethylene glycol immersion can be ethylene glycol.

[0048] In the present invention, the temperature of the ethylene glycol immersion can be room temperature, and the time can be 10 to 15 h, specifically 11 h, 12 h, 13 h, or 14 h.

[0049] In the present invention, the temperature of the first annealing can be 300 to 900 °C, specifically 400 °C, 500 °C, 600 °C, 700 °C, or 800 °C, and the heat preservation time can be 2 to 3 h, specifically 2.2 h, 2.4 h, 2.7 h, or 2.8 h; the first annealing can be carried out in an air atmosphere.

[0050] In the present invention, before the first annealing, it may further include heating up the product system of the ethylene glycol immersion; the heating rate can be 0.5 to 1.2 °C / min, specifically 0.8 °C / min or 1 °C / min.

[0051] In the present invention, before using the titanium dioxide nanotube array, it may further include washing and drying the titanium dioxide nanotube array; the washing can be rinsing with deionized water; the drying temperature can be 20 to 60 °C, specifically 30 °C, 40 °C, or 50 °C, and the heat preservation time can be 1 to 2 h, specifically 1.2 h, 1.5 h, or 1.8 h; the drying can be carried out in an air atmosphere.

[0052] In the present invention, the Ni salt can include one or several of Ni(NO3)2 and nickel sulfate.

[0053] In the present invention, the dispersion solvent can include water.

[0054] In the present invention, the concentration of the Ni salt in the first mixed solution can be 1 to 10 mM, specifically 2 mM, 4 mM, 6 mM, or 8 mM.

[0055] In the present invention, the temperature of the first impregnation can be room temperature, and the time can be 2 to 3 h, specifically 2.2 h, 2.5 h, or 2.8 h. Through the first impregnation in the present invention, the titanium dioxide nanotube array is fully wetted by the first mixed solution.

[0056] In the present invention, the drying temperature can be 20 to 60 °C, specifically 30 °C, 40 °C, or 50 °C, and the heat preservation and drying time can be 1 to 3 h, specifically 1.5 h, 2 h, or 2.5 h; the drying atmosphere can be air.

[0057] After obtaining the pretreated titanium dioxide nanotube array, the present invention mixes the pretreated titanium dioxide nanotube array, an alkali metal hydroxide, and a good solvent (to obtain a second mixed solution) for a second impregnation to obtain an electrode (denoted as Ni(OH)2 / TNTAs). In the present invention, the alkali metal hydroxide may include one or more of potassium hydroxide and sodium hydroxide.

[0058] In the present invention, the good solvent may be water; the water may be deionized water.

[0059] In the present invention, the concentration of KOH in the second mixed solution may be 0.5 - 2 M, specifically 1 M or 1.5 M.

[0060] In the present invention, the temperature of the second impregnation may be room temperature, and the time may be 5 - 30 min, specifically 5 min, 10 min, 15 min, 20 min, 25 min, or 30 min. Through the second impregnation, the present invention obtains a Ni(OH)2 coating.

[0061] In the present invention, after the second impregnation, it may further include washing the obtained product; the washing reagent may be water; the water may be deionized water; the number of washing times may be more than 1 time.

[0062] After obtaining the electrode, the present invention mixes the electrode and hypophosphite for annealing (denoted as the second annealing) to obtain the nickel phosphide composite TiO2 nanotube array. In the present invention, the hypophosphite may include one or more of NaH2PO2 and potassium dihydrogen hypophosphite; the molar ratio of the alkali metal hydroxide to the hypophosphite may be 1:1 - 2, specifically 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8, or 1:2.

[0063] In the present invention, before the second annealing, it may further include heating to the temperature of the second annealing; the heating rate may be 0.5 - 2 °C / min, specifically 0.8 °C / min, 1 °C / min, 1.2 °C / min, 1.5 °C / min, 1.7 °C / min, or 1.9 °C / min; the heating may be carried out in a protective atmosphere; the protective atmosphere may be an inert gas; the inert gas may be argon.

[0064] In the present invention, the temperature of the second annealing may be 300 - 500 °C, specifically 330 °C, 350 °C, 380 °C, 400 °C, 420 °C, 450 °C, or 480 °C, and the holding time may be 1 - 3 h, specifically 1.5 h, 2 h, or 2.5 h; the second annealing may be carried out in a protective atmosphere; the protective atmosphere may be an inert gas; the inert gas may be argon.

[0065] The preparation process of the nickel phosphide composite TiO2 nanotube array of the present invention is as follows Figure 1 shown. In the present invention, a titanium dioxide nanotube array, a Ni salt, and a dispersion solvent are mixed and subjected to a first impregnation and then dried to obtain a pretreated titanium dioxide nanotube array; then the pretreated titanium dioxide nanotube array, an alkali metal hydroxide, and a good solvent are mixed and subjected to a second impregnation to obtain an electrode; thereafter, the electrode and hypophosphite are mixed and annealed to obtain the nickel phosphide composite TiO2 nanotube array.

[0066] The present invention also provides the application of the nickel phosphide composite TiO2 nanotube array described in the above solution or the nickel phosphide composite TiO2 nanotube array obtained by the preparation method described in the above solution in the field of photoelectrocatalysis.

[0067] The nickel phosphide composite TiO2 nanotube array provided by the present invention has excellent photoelectrochemical performance, low cost, and good stability, and is suitable as a photoelectrocatalyst for use in the field of photoelectrocatalysis, especially for the preparation of clean energy such as hydrogen.

[0068] In order to further illustrate the present invention, the solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the protection scope of the present invention.

[0069] Comparative Example 1

[0070] First, a pretreated Ti sheet is added to a fluorinated ethylene glycol solution containing 0.36 wt.% NH4F and 1.8 vol.% H2O, and first anodized at a constant potential of 60 V and a temperature of 25 °C for 1 h to obtain a TiO2 nanotube array. The TiO2 nanotube array is ultrasonically removed in water for 30 min and then second anodized at a constant potential of 60 V and a temperature of 25 °C for 1.5 h. The prepared product is soaked in an ethylene glycol solution for 12 h and then annealed in air at 400 °C for 2 h with a heating rate of 0.8 °C / min to obtain pure TNTAs.

[0071] Example 1

[0072] First, pure TNTAs were prepared according to Comparative Example 1. The TNTAs were rinsed with deionized water and then dried in air. The TNTAs were fully wetted with a 1 mM Ni(NO3)2 solution for 2 h and then dried in air for 1 h. After that, the wetted TNTAs were immersed in a 1 M KOH solution for 5 min and washed with deionized water to obtain an electrode, denoted as Ni(OH)2 / TNTAs. Subsequently, Ni(OH)2 / TNTAs and excessive NaH2PO2 (an aqueous solution of 1 M NaH2PO2, with the molar ratio of KOH to NaH2PO2 being 1:1) were annealed at 400 °C for 2 h in argon at a ramp rate of 0.8 °C / min to obtain Ni2P / TNTAs.

[0073] Example 2

[0074] First, pure TNTAs were prepared according to Comparative Example 1. The TNTAs were rinsed with deionized water and then dried in air. The TNTAs were fully wetted with a 5 mM Ni(NO3)2 solution for 3 h and then dried in air for 1 h. After that, the wetted TNTAs were immersed in a 1 M KOH solution for 20 min and washed with deionized water to obtain an electrode, denoted as Ni(OH)2 / TNTAs. Subsequently, Ni(OH)2 / TNTAs and excessive NaH2PO2 (an aqueous solution of 1 M NaH2PO2, with the molar ratio of KOH to NaH2PO2 being 1:1) were annealed at 400 °C for 2 h in argon at a ramp rate of 0.8 °C / min to obtain Ni2P / TNTAs.

[0075] Example 3

[0076] First, pure TNTAs were prepared according to Comparative Example 1. The TNTAs were rinsed with deionized water and then dried in air. The TNTAs were fully wetted with a 10 mM Ni(NO3)2 solution for 2.5 h and then dried in air for 1 h. After that, the wetted TNTAs were immersed in a 1 M KOH solution for 30 min and washed with deionized water to obtain an electrode, denoted as Ni(OH)2 / TNTAs. Subsequently, Ni(OH)2 / TNTAs and excessive NaH2PO2 (an aqueous solution of 1 M NaH2PO2, with the molar ratio of KOH to NaH2PO2 being 1:1) were annealed at 400 °C for 2 h in argon at a ramp rate of 0.8 °C / min to obtain Ni2P / TNTAs.

[0077] Test Example 1

[0078] XRD pattern analysis was performed on the Ni2P / TNTAs prepared in Examples 1 to 3, with TiO2 and Ni2P as the control groups, and the results are as Figure 2 shown. According to Figure 2It can be seen that for the products obtained with nickel ion concentrations in the range of 1 - 10 mM, the XRD patterns show diffraction peaks of anatase titanium dioxide. However, perhaps due to the very small particle size of the nickel ions and their highly uniform dispersion on the surface of TNTAs with a low loading amount, no obvious diffraction peaks of nickel phosphide were detected (TiO2 - PDF#21 - 1272, Ni2P - PDF#74 - 1385); there is no obvious new phase formed at the Ni2P / TNTAs interface in the figure, indicating the formation of a Schottky junction.

[0079] Test Example 2

[0080] SEM tests were conducted on the Ni(OH)2 / TNTAs and Ni2P / TNTAs prepared in Example 1 and the TNTAs prepared in Comparative Example 1, and the results are as Figure 3 shown. According to Figure 3 It can be seen that the nanotube growth of the three samples is uniformly distributed and dense, but no nanoparticles were observed on the surface, probably because of their too low loading amount; the SEM image has a clear interface without obvious diffusion or reaction layer, further indicating the formation of a Schottky junction.

[0081] Test Example 3

[0082] TEM tests were conducted on the Ni2P / TNTAs prepared in Example 1 and the TNTAs prepared in Comparative Example 1, and the results are as Figure 4 shown. According to Figure 4 It can be seen that nickel phosphide was successfully compounded onto the titanium dioxide nanotube array.

[0083] Test Example 4

[0084] HRTEM tests were conducted on the Ni2P / TNTAs prepared in Example 1 and the TNTAs prepared in Comparative Example 1, and the results are as Figure 5 shown. According to Figure 5 It can be seen that nickel phosphide was successfully compounded onto the titanium dioxide nanotube array, and the lattice spacing of nickel phosphide can be calculated.

[0085] Test Example 5

[0086] SAED tests were conducted on the Ni2P / TNTAs prepared in Example 1 and the TNTAs prepared in Comparative Example 1, and the results are as Figure 6 shown. According to Figure 6 It can be seen that nickel phosphide was successfully compounded onto the titanium dioxide nanotube array, and the diffraction rings of nickel phosphide can be calculated.

[0087] Test Example 6

[0088] Elemental distribution tests were conducted on the Ni2P / TNTAs prepared in Example 1, and the results are as Figure 7 shown. According to Figure 7It can be seen that nickel phosphide has been successfully compounded onto the titanium dioxide nanotube array, and trace amounts of nickel and phosphorus elements have been detected.

[0089] Test Example 7

[0090] The Ni2P / TNTAs prepared in Example 1 were subjected to XPS testing, and the results are as Figure 8 shown. According to Figure 8 what can be seen, nickel phosphide has been successfully compounded onto the titanium dioxide nanotube array, and the 2p peak of nickel element has been detected.

[0091] Test Example 8

[0092] The Ni2P / TNTAs prepared in Examples 1 to 3 and the TNTAs prepared in Comparative Example 1 were subjected to optoelectronic performance testing. The testing method was as follows: first measure the open-circuit potential (ocp), then scan the cyclic voltammetry (CV), then measure the linear sweep voltammetry (LSV), and finally measure the current-time (I-t). The test results showed that compared with the unmodified pure TNTAs in Comparative Example 1, the Ni2P / TNTAs prepared in Examples 1 to 3, especially the Ni2P / TNTAs prepared in Example 2, exhibited more efficient optoelectrocatalytic performance; when the bias voltage was 1.4 V (vs. Ag / AgCl), the photocurrent density of the photoanode of Ni2P / TNTAs in Example 2 was 0.25 mA / cm 2 , which was significantly higher than that of pure TNTAs and was 12.50 times the photocurrent density (0.02 mA / cm 2 ) of the TNTAs photoanode under the same conditions; under AM 1.5G, 1.4 V (vs. Ag / AgCl), the photocurrent of Comparative Example 1 was 0.31 mA / cm 2 , and the photocurrents of Examples 1 to 3 were 0.72 mA / cm 2 , 1.63 mA / cm 2 and 0.58 mA / cm 2 . Accordingly, it was further proved that a Schottky junction was formed in Ni2P / TNTAs.

[0093] Test Example 9

[0094] The Ni2P / TNTAs prepared in Examples 1 to 3 and the TNTAs prepared in Comparative Example 1 were subjected to optoelectrocatalytic hydrogen production performance testing. The testing method was as follows: a xenon lamp was used as the light source to vertically irradiate the surface of the sample, and the electrolyte was 66 mL of 0.1 M Na2SO4 solution; before the reaction started, the reaction system was evacuated to eliminate the influence of dissolved oxygen in the electrolyte, and circulating cooling water was used to keep the reaction temperature constant; the test was carried out for 3 h, and 1 mL of gas was manually injected every half hour through a syringe and sent to a gas chromatograph for test analysis through N2 carrier gas. The test results showed that the optoelectronic combined hydrogen production amount of Ni2P / TNTAs was high, and the hydrogen production amount was 182.96 μmol / cm 2, Comparative Example 1 was only 31.26 μmol / cm 2 .

[0095] Test Example 10

[0096] The DOS detection was performed on the Ni2P / TNTAs prepared in Example 1, and the results are as Figure 9 shown. According to Figure 9 it can be seen that Ni2P modified the electronic structure of the TiO2 nanotubes. This significant change in the electronic structure would lead to electron transitions, improve the separation efficiency of electron-hole pairs, and thus improve the photoelectrocatalytic performance.

[0097] As can be seen from the above examples, the nickel phosphide composite TiO2 nanotube array provided by the present invention has excellent photoelectrochemical performance, good uniformity, and is simple and efficient.

[0098] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A nickel phosphide composite TiO2 nanotube array, characterized in that, It includes a titanium dioxide nanotube array and nickel phosphide that forms a heterojunction with the titanium dioxide nanotube array; the heterojunction is a Schottky junction.

2. The nickel phosphide composite TiO2 nanotube array according to claim 1, wherein In the titanium dioxide nanotube array, the diameter of the tubes is 100 - 120 nm, and the length of the tubes is 22 - 25 μm.

3. The nickel phosphide composite TiO2 nanotube array according to claim 1 or 2, characterized in that, In the nickel phosphide composite TiO2 nanotube array, the atomic ratio of titanium ions to nickel ions is 140 - 1500.

4. The preparation method of the nickel phosphide composite TiO2 nanotube array according to any one of claims 1 to 3, characterized in that, It includes the following steps: Mix the titanium dioxide nanotube array, Ni salt, and a dispersing solvent, conduct a first impregnation and then dry to obtain a pretreated titanium dioxide nanotube array; Mix the pretreated titanium dioxide nanotube array, an alkali metal hydroxide, and a good solvent, conduct a second impregnation to obtain an electrode; Mix the electrode and hypophosphite and conduct annealing to obtain the nickel phosphide composite TiO2 nanotube array.

5. The preparation method according to claim 4, characterized in that, The preparation method of the titanium dioxide nanotube array includes the following steps: Mix a Ti sheet and a fluorinated ethylene glycol solution, conduct a first anodic oxidation, and then successively conduct a second anodic oxidation, ethylene glycol immersion, and annealing.

6. The preparation method according to claim 5, characterized in that, After the first anodic oxidation, it also includes ultrasonicating the obtained product in water; the frequency of the ultrasonic wave is 60 - 100 kHz, and the time is 10 - 30 min.

7. The preparation method according to claim 4, characterized in that, The temperature of the first impregnation is room temperature, and the time is 2 - 3 h; the temperature of the second impregnation is room temperature, and the time is 5 - 30 min.

8. The preparation method according to claim 4 or 7, characterized in that, The molar ratio of the alkali metal hydroxide to the hypophosphite is 1:1 - 2.

9. The preparation method according to claim 4, wherein The temperature of the annealing is 300 - 500 °C, and the heat preservation time is 1 - 3 h; the second annealing is carried out in a protective atmosphere.

10. Application of the nickel phosphide composite TiO2 nanotube array according to any one of claims 1 - 3 or the nickel phosphide composite TiO2 nanotube array obtained by the preparation method according to any one of claims 4 - 9 in the field of photoelectrocatalysis.

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