Photoelectric cathode based on silicon nanowire substrate and preparation method and application thereof

Abstract

The invention discloses a photoelectric cathode based on a silicon nanowire substrate and a preparation method and application of the photoelectric cathode, and belongs to the technical field of photoelectrocatalytic reduction carbon dioxide materials. The preparation method disclosed by the invention comprises the following steps: adsorbing Au nanoparticles on the surface of a silicon nanowire substrate to obtain the silicon nanowire substrate adsorbed with the Au nanoparticles; a TiO2 film is deposited on the surface of a silicon nanowire substrate through an atomic layer deposition method, then a photosensitizer and a catalyst are adsorbed on the TiO2 film through the atomic layer deposition method, then the TiO2 film is coated through the atomic layer deposition method, and the photoelectric cathode based on the silicon nanowire substrate is obtained. The photocathode obtained through the method has the advantages of being stable in structure, good in carbon dioxide reduction effect and the like, and has important significance on optimizing the structure of the dye-sensitized photocathode and improving the photoelectrocatalytic carbon dioxide reduction performance of the dye-sensitized photocathode.

Description

Technical Field

[0001] The present invention belongs to the technical field of photoelectric catalytic reduction of carbon dioxide materials, and in particular relates to a photocathode based on a silicon nanowire substrate, a preparation method thereof and an application thereof. Background Art

[0002] Dye-sensitized photoelectrochemical cells (DSPECs) for photoelectrocatalytic CO2 reduction have multiple advantages such as low raw material cost, simple preparation process and adjustable surface assembly, and therefore have received great attention in the field of energy materials. In DSPECs, the CO2 reduction reaction occurs at the photocathode, which is composed of a semiconductor substrate, a photosensitizer and a catalyst. When the photosensitizer is excited by visible light and transitions from the ground state to the excited state, photogenerated electron-hole pairs are generated. The photogenerated holes are injected into the semiconductor valence band, and the photogenerated electrons migrate to the catalyst surface, driving the CO2 reduction and converting CO2 into valuable chemicals such as CO.

[0003] However, there are certain limitations in using DSPEC for CO2 reduction reaction. The catalyst in DSPEC (usually a metal complex or a molecular catalyst) is easily deactivated during long-term photoelectrochemical reactions, especially in aqueous solutions or electrolytes. The catalyst has poor stability and is prone to decomposition or degradation. The adsorption and desorption process of the catalyst on the electrode surface is unstable, which can easily lead to the loss of the catalyst, thereby affecting the continued progress of the reaction. At the same time, the photosensitizer in DSPEC (usually a dye molecule) is prone to photodegradation under light conditions, especially under strong light or long-term light. The stability of the photosensitizer is poor, resulting in a decrease in photoelectric conversion efficiency. The adsorption and desorption process of the photosensitizer on the electrode surface is unstable, which can easily lead to the loss of the photosensitizer, thereby affecting the photoelectric conversion efficiency. In addition, the CO2 reduction reaction usually produces a variety of reduction products (such as CO, HCOOH, CH4, C2H4, etc.). The DSPEC system has challenges in controlling product selectivity and it is difficult to efficiently generate a single target product. And because the CO2 reduction reaction involves a multi-electron transfer process, the reaction kinetics are slow, resulting in low photoelectric conversion efficiency and CO2 reduction efficiency of the DSPEC system.

[0004] Since the method of using DSPEC for CO2 reduction reaction has poor selectivity for CO2 reduction products and poor stability of photosensitizers and catalysts, how to improve the selectivity and stability of photo-CO2 reduction products has become the key to improving photoelectrocatalytic carbon dioxide reduction.

[0005] In summary, how to obtain a photocathode with stable structure, good photoelectrocatalytic performance, simple preparation process and high selectivity is of great significance for optimizing the structure of dye-sensitized photocathode and improving the selectivity of carbon dioxide reduction. Summary of the invention

[0006] The purpose of the present invention is to provide a photocathode based on a silicon nanowire substrate and a preparation method and application thereof, so as to improve and solve the technical problems of poor selectivity and poor stability of CO2 reduction products in existing photocathodes.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention discloses a method for preparing a photocathode based on a silicon nanowire substrate, comprising the following steps: Adsorbing Au nanoparticles on the surface of the silicon nanowire substrate to obtain a silicon nanowire substrate adsorbed with Au nanoparticles; A TiO2 film is deposited on the surface of a silicon nanowire substrate by atomic layer deposition, a photosensitizer and a catalyst are then adsorbed on the TiO2 film deposited by atomic layer deposition, and the TiO2 film is then coated by atomic layer deposition to obtain a photocathode based on a silicon nanowire substrate.

[0008] Furthermore, the preparation method of the silicon nanowire substrate is: After the silicon wafer is processed, a silicon wafer is obtained, and the silicon wafer is sequentially immersed in an AgNO3 solution for 60 to 90 min and an HF solution for 60 to 90 min, and then sequentially immersed in an HNO3 solution for 60 to 90 min and an HF solution for 5 to 10 min, to obtain a silicon nanowire substrate; The steps of processing the silicon wafer are as follows: Then, the silicon wafer was cleaned in a mixed solution of H2SO4 and H2O2 with a volume ratio of 1:1 for 20-40 min to obtain a silicon wafer; The concentrations of the AgNO3 solution and the HF solution are 0.03-0.05 M and 4.3-4.6 M, respectively.

[0009] Furthermore, the Au nanoparticles are adsorbed on the surface of the silicon nanowire substrate by immersing the silicon nanowire substrate in a HAuCl4 solution and oscillating the solution; the concentration of the HAuCl4 solution is 0.002-0.1 M.

[0010] Furthermore, the oscillation frequency is 120-150 rpm, and the oscillation time is 60-90 min.

[0011] Furthermore, the specific steps of depositing a TiO2 thin film on the surface of the silicon nanowire substrate by atomic layer deposition are: The silicon nanowire substrate is placed in a deposition chamber, and tetrakis(dimethylamino)titanium and water are used as precursors for a deposition reaction to form a TiO2 film on the surface of the silicon nanowire substrate; The deposition reaction temperature of the tetrakis(dimethylamino)titanium is 60-120°C.

[0012] Furthermore, the deposition cycle number of the TiO2 film on the surface of the silicon nanowire substrate is 15 times.

[0013] Further, the photosensitizer is a P1 photosensitizer; the catalyst is a ReC catalyst; The steps of adsorbing the photosensitizer and catalyst on the TiO2 film deposited by atomic layer deposition are: The substrate is placed in an atomic layer deposition reaction chamber to deposit a TiO2 film, then immersed in an acetonitrile solution of a P1 photosensitizer, and then a TiO2 film is deposited; then immersed in a methanol solution of a ReC catalyst, and a TiO2 film is deposited on the outermost layer; The number of deposition cycles of the photosensitizer is 5 times; the number of deposition cycles of the catalyst is 5 times; The concentration of the acetonitrile solution of the P1 photosensitizer is 0.2-0.3 mM; the concentration of the methanol solution of the ReC catalyst is 0.2-0.6 mM.

[0014] Furthermore, the specific steps of coating the TiO2 film by atomic layer deposition are as follows: The TiO2 thin film was deposited using tetrakis(dimethylamino)titanium and water as precursors to obtain a photocathode based on a silicon nanowire substrate; The deposition cycle number of the TiO2 film is 5 times.

[0015] The invention also discloses a photocathode based on a silicon nanowire substrate prepared by the preparation method.

[0016] The present invention also discloses the use of the above-mentioned photocathode based on silicon nanowire substrate in photoelectrocatalytic carbon dioxide reduction, comprising the following steps: Using a silicon nanowire-based photocathode as the working electrode, Ag / Ag + A three-electrode system is constructed using a platinum sheet as a reference electrode and a platinum sheet as a counter electrode, and a photoelectrocatalytic carbon dioxide reduction reaction is carried out in the electrolyte solution of the three-electrode system; The incident light power intensity of the light source used in the photoelectrocatalytic carbon dioxide reduction reaction is 100 mW / cm 2 , the applied bias range is -1.3~-1.9 V; The electrolyte solution is an acetonitrile solution containing 0.1 M tetrabutylammonium hexafluorophosphate.

[0017] Compared with the prior art, the present invention has the following beneficial effects: The invention discloses a method for preparing a photocathode based on a silicon nanowire substrate. Atomic layer deposition (ALD) is used to connect a photosensitizer and a catalyst on the silicon nanowire substrate, and Au particles are adsorbed on the silicon nanowire substrate. A stable photocathode can be formed without covalent bonds or ionic bonds between photosensitizer / catalyst units. The structure is more stable and the photoelectrocatalytic performance is better. The plasmon effect of the metal nanostructure is used to significantly enhance the light-matter interaction to promote the catalytic reaction, enhance the utilization of visible light, and increase the selectivity of CO2 reduction. A simple atomic layer deposition is used to coat the outermost layer of the photocathode with a TiO2 protective layer, which can maintain the stability of the catalyst during the reaction and make the photocathode structure more stable.

[0018] The present invention also discloses a photocathode based on a silicon nanowire substrate prepared by the above-mentioned preparation method. The photocathode has the advantages of stable structure and good carbon dioxide reduction effect, which is of great significance for optimizing the structure of the dye-sensitized photocathode and improving its photoelectrocatalytic water oxidation performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of a photocathode based on a silicon nanowire substrate of the present invention; Figure 2 This is a UV-visible absorption spectrum of the photocathode based on the silicon nanowire substrate prepared in Example 1 of the present invention; Figure 3 This is a Faraday effect diagram of CO2 reduction products of the photocathode based on a silicon nanowire substrate prepared in Example 1 of the present invention; Figure 4 The photocurrent-time curve of the photocathode based on the silicon nanowire substrate prepared in Example 1 of the present invention; Figure 5 This is the Nyquist diagram of the photocathode based on the silicon nanowire substrate prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0021] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0022] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0023] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0024] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0025] The present invention provides a method for preparing a photocathode based on a silicon nanowire substrate, comprising the following steps: The Au nanoparticles are adsorbed on the surface of the silicon nanowire substrate (Si NWs substrate) to obtain the silicon nanowire substrate adsorbed with Au nanoparticles (Si NWs|Au); A TiO2 film (Si NWs|Au|TiO2) was deposited on the surface of a silicon nanowire substrate by atomic layer deposition, and then the photosensitizer and catalyst were deposited and adsorbed on the TiO2 film by atomic layer deposition. The TiO2 film was then coated by atomic layer deposition to obtain a photocathode based on a silicon nanowire substrate (Si NWs|Au|TiO2|P1-TiO2|ReC-TiO2).

[0026] Preferably, the method for preparing the silicon nanowire substrate by metal-assisted chemical etching is: After the silicon wafer is processed, a silicon wafer is obtained, and the silicon wafer is immersed in an AgNO3 solution and an HF solution in sequence to obtain a silicon nanowire substrate; The steps of processing the silicon wafer are as follows: The p-type silicon wafer was ultrasonically immersed in acetone, ethanol and water for 20-30, 15-30 and 15-30 min, respectively, and then cleaned in a mixed solution of H2SO4 and H2O2 for 30-50 min to obtain a silicon wafer; The silicon wafer is immersed in the AgNO3 solution and the HF solution for 60 to 90 minutes; The concentrations of the AgNO3 solution and the HF solution are 0.03-0.05 M and 4.3-4.6 M, respectively.

[0027] Preferably, the Au nanoparticles are adsorbed on the surface of the silicon nanowire substrate by immersing the silicon nanowire substrate in a HAuCl4 solution and oscillating the solution in an oscillator; the oscillation frequency in the oscillator is 120 rpm and the time is 60 min.

[0028] Preferably, the specific steps of depositing a TiO2 thin film on the surface of the silicon nanowire substrate by atomic layer deposition are: The silicon nanowire substrate is placed in a deposition chamber, and tetrakis(dimethylamino)titanium and water are used as precursors for a deposition reaction to form a TiO2 film on the surface of the silicon nanowire substrate; The deposition reaction temperature of the tetrakis(dimethylamino)titanium is 60-120°C.

[0029] Preferably, the deposition cycle number of the TiO2 film on the surface of the silicon nanowire substrate is 15 times.

[0030] Preferably, the steps of adsorbing the photosensitizer and the catalyst onto the TiO2 film deposited by atomic layer deposition are: The substrate is placed in an atomic layer deposition reaction chamber to deposit a TiO2 film, and then immersed in an acetonitrile solution of a P1 photosensitizer to adsorb the photosensitizer; after drying, the substrate is placed in an atomic layer deposition reaction chamber to deposit a TiO2 film, and then immersed in a methanol solution of a ReC catalyst to adsorb the catalyst; The number of deposition cycles of the photosensitizer is 5 times; the number of deposition cycles of the catalyst is 5 times; The concentration of the acetonitrile solution of the P1 photosensitizer is 0.2-0.3 mM; the concentration of the methanol solution of the ReC catalyst is 0.5-0.6 mM.

[0031] The specific steps of coating TiO2 thin film by atomic layer deposition are as follows: The TiO2 thin film was deposited using tetrakis(dimethylamino)titanium and water as precursors to obtain a photocathode based on a silicon nanowire substrate; The deposition cycle number of the TiO2 film is 5 times.

[0032] The present invention also provides a photocathode based on a silicon nanowire substrate prepared by the above preparation method, the structure of which is Si NWs|Au|TiO2|4-(Bis-{4-[5-(2,2-dicyano-vinyl)- thiophene-2-yl]-phenyl}-amino)-benzoicacid(P1)-TiO2|[Re(bdpm-bpy)(CO)3Cl](ReC)-TiO2, abbreviated as Si NWs|Au|TiO2|P1-TiO2|ReC-TiO2.

[0033] The present invention also provides an application of the above-mentioned photocathode based on silicon nanowire substrate in carbon dioxide reduction, wherein the prepared photocathode is used as a working electrode, Ag / Ag + A three-electrode system was constructed using a reference electrode and a platinum sheet as a counter electrode, and a photoelectrocatalytic carbon dioxide reduction reaction was carried out in an electrolyte solution.

[0034] Preferably, the incident light power intensity of the light source used for photoelectrocatalysis is 100 mW / cm 2 , the applied bias range is -1.3~-1.9 V vs Ag / Ag + .

[0035] Preferably, the electrolyte solution is an acetonitrile solution containing 0.1 M tetrabutylammonium hexafluorophosphate.

[0036] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0037] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0038] Example 1 A method for preparing a photocathode based on a silicon nanowire substrate comprises the following steps: Si NWs were prepared by metal-assisted chemical etching. First, the p-type silicon wafer was ultrasonically immersed in acetone, ethanol and water for 20, 15 and 15 min, respectively, to remove surface impurities. It was then further cleaned in H2SO4:H2O2 (v / v = 1:1) solution for 30 min, rinsed with water and removed the surface oxide layer in HF solution (5wt%). The clean silicon wafer was immersed in solutions containing AgNO3 (0.03 M) and 4.6 M HF, respectively, at room temperature for 90 min. The silicon wafer was immersed in HNO3 solution (v / v = 1:1) for 45 min to remove residual Ag. After immersion in HF solution (5 wt%) for 5 min, vertically aligned Si NWs were obtained. The Si NWs were immersed in HAuCl4 solution (2 mM) and shaken at a frequency of 120 rpm for 60 min, and then rinsed with water to obtain a silicon nanowire substrate adsorbed with Au nanoparticles (Si NWs|Au); Si NWs|Au was placed in an ALD chamber to deposit a TiO2 layer (15 cycles) using tetrakis(dimethylamino)titanium and water as precursors at a deposition reaction temperature of 80 °C to obtain Si NWs|Au|TiO2; The photosensitizer P1 and catalyst [Ru(bda)(4-PO3H2-(CH2)3-pyr)2] (ReC) were fully mixed with acetonitrile and methanol respectively under ultrasound to prepare P1-acetonitrile and 0.2 mM ReC-methanol solutions; the Si NWs|Au-TiO2 electrode was immersed in P1-acetonitrile for 16 h, dried, and then atomic layer deposition of TiO2 was carried out on its surface using a precursor for 5 cycles of growth. The electrode was taken out and immersed in ReC-acetonitrile solution for 16 h, dried, and then atomic layer deposition of TiO2 was carried out on its surface using a precursor for 5 cycles of growth to obtain the Si NWs|Au-TiO2|P1-TiO2|ReC-TiO2 electrode.

[0039] The prepared photocathode was used for photoelectrocatalytic carbon dioxide reduction: The prepared photocathode was used as the working electrode, the platinum sheet was used as the counter electrode, and the Ag / Ag + As the reference electrode, a three-electrode system was constructed. When the incident light power intensity was 100 mW / cm 2 Under the condition of light, the carbon dioxide reduction reaction was carried out in acetonitrile solution containing 0.1 M tetrabutylammonium hexafluorophosphate, and the voltage applied to the electrode was 1.8 V vs Ag / Ag + .

[0040] Figure 1 Schematic diagram of photocathode preparation. Figure 1 It can be seen that the photocathode is mainly composed of Si NWs adsorbing Au NPS, and TiO2 thin film is deposited by ALD technology to adsorb photosensitizer and catalyst, and a TiO2 thin film protective layer is coated on the outermost layer.

[0041] Figure 2 This is the ultraviolet absorption spectrum of Si NWs|Au|TiO2|P1-TiO2|ReC-TiO2 electrode; Figure 2 It can be seen that the absorption range of the electrode is 500~800 nm, with the maximum absorption wavelength at 670 nm.

[0042] Figure 3 This is the Faraday effect diagram of CO2 reduction products of the photocathode; Figure 3It can be seen that under the application of -1.8 V bias, the Faraday efficiency of the product CO was calculated by gas chromatography quantification.

[0043] FE CO is 72.0%, corresponding to a current of -1.2 mA cm -2 .

[0044] Figure 4 is the photocurrent-time curve of the photocathode; Figure 4 It can be seen that under the application of -1.8 V bias and continuous illumination, the photocurrent density of the Si NWs|Au|TiO2|P1-TiO2|ReC-TiO2 photocathode decays by less than 15% within 3 hours, which indicates that the ALD-deposited TiO2 protective layer enhances the stability of the photocathode.

[0045] Figure 5 Nyquist plot of the photocathode. The charge transfer resistance of Si NWs|Au|TiO2-P1-TiO2|-ReC-TiO2 is the smallest at 83.9Ω.

[0046] Example 2 Si NWs|TiO2-P1-TiO2|ReC-TiO2 photocathode: Compared with Example 1, the difference is that the Si NWs substrate is not adsorbed with Au. 2 Under the illumination conditions of , controlled potential electrolysis was carried out in a carbon dioxide atmosphere under continuous simulated illumination (AM 1.5 G), and the Faradaic efficiency of the product CO was calculated by gas chromatography. The Si NWs|TiO2-P1-TiO2|ReC-TiO2 photocathode was used for carbon dioxide reduction. The Faradaic efficiency of the product CO was calculated by gas chromatography, and the maximum FE was obtained at a bias voltage of -1.9 V. CO It is 58.7%.

[0047] Example 3 Si NWs|0.5Au|TiO2|P1-TiO2|ReC-TiO2 photocathode: Compared with Example 1, the difference is that the Si NWs substrate is immersed in a HAuCl4 solution (0.5 mM) and the oscillation frequency is 120 rpm for 60 min; when the incident light power intensity is 100 mW / cm 2 Under the conditions of light, controlled potential electrolysis was carried out under continuous simulated light (AM 1.5 G) in a carbon dioxide atmosphere, and the Faradaic efficiency of the product CO was calculated by gas chromatography.

[0048] The Si NWs|0.5Au|TiO2|P1-TiO2|ReC-TiO2 photocathode was used for CO2 reduction, and the maximum CO Faraday efficiency FE was obtained at an applied bias of -1.9 V. CO It is 62%.

[0049] Example 4 Si NWs|10Au|TiO2|P1-TiO2|ReC-TiO2 photocathode: Compared with Example 1, the difference is that the Si NWs substrate is immersed in a HAuCl4 solution (0.01 M) and oscillated (120 rpm) for 60 min; when the incident light power intensity is 100 mW / cm 2 Under the conditions of light, controlled potential electrolysis was carried out under continuous simulated light (AM 1.5 G) in a carbon dioxide atmosphere, and the Faradaic efficiency of the product CO was calculated by gas chromatography.

[0050] The Si NWs|10Au|TiO2|P1-TiO2|ReC-TiO2 photocathode was used for carbon dioxide reduction, and the maximum carbon monoxide Faraday efficiency FE was obtained at an applied bias voltage of -1.9 V. CO It is 52.3%.

[0051] Example 5 Si NWs|Au|TiO2|P1-TiO2|ReC photocathode: Compared with Example 1, the difference is that the outermost layer of the Si NWs|Au|TiO2|P1-TiO2|ReC photocathode is not coated with the TiO2 protective layer by ALD.

[0052] The Si NWs|Au|TiO2|P1-TiO2|ReC photocathode was used for CO2 reduction at an incident light power intensity of 100 mW / cm 2 Under illumination conditions, the photocurrent density decays by 40% within 1 hour when a bias of -1.8 V is applied in a carbon dioxide atmosphere.

[0053] Example 6 Si NWs|Au|TiO2|P1-TiO2|ReC-TiO2 photocathode: A method for preparing a photocathode based on a silicon nanowire substrate comprises the following steps: Si NWs were prepared by metal-assisted chemical etching. First, the p-type silicon wafer was ultrasonically immersed in acetone, ethanol and water for 20, 15 and 15 min, respectively, to remove surface impurities. Then, it was further cleaned in H2SO4:H2O2 (v / v, 1:1) solution for 30 min, rinsed with water and removed the surface oxide layer in HF solution (5wt%). The clean silicon wafer was immersed in solutions containing AgNO3 (0.03 M) and 4.6 M HF, respectively, at room temperature for 90 min. The silicon wafer was immersed in HNO3 solution (v / v, 1:1) to remove residual Ag for 45 min. After being immersed in HF solution (5 wt%) for 5 min, vertically aligned Si NWs were obtained. The Si NWs were immersed in HAuCl4 solution (2 mM) and shaken at a frequency of 120 rpm for 60 min, and then rinsed with water to obtain a silicon nanowire substrate adsorbed with Au nanoparticles (Si NWs|Au); Si NWs|Au was placed in an ALD chamber to deposit a TiO2 layer (15 cycles) using tetrakis(dimethylamino)titanium and water as precursors at a deposition reaction temperature of 80 °C to obtain Si NWs|Au|TiO2; The photosensitizer P1 and catalyst [Ru(bda)(4-PO3H2-(CH2)3-pyr)2] (ReC) were fully mixed with acetonitrile and methanol respectively under ultrasound to prepare P1-acetonitrile and 0.2 mM ReC-methanol solutions; the Si NWs|Au-TiO2 electrode was immersed in P1-acetonitrile for 16 h, dried, and then atomic layer deposition of TiO2 was carried out on its surface using a precursor for 5 cycles of growth. The electrode was taken out and immersed in ReC-acetonitrile solution for 16 h, dried, and then atomic layer deposition of TiO2 was carried out on its surface using a precursor for 5 cycles of growth to obtain the Si NWs|Au-TiO2|P1-TiO2|ReC-TiO2 electrode.

[0054] The prepared photocathode was used for photoelectrocatalytic carbon dioxide reduction: Compared with Example 1, the difference is that the electrolyte solution is replaced with 0.1 M KHCO3 solution; The Si NWs|Au|TiO2|P1-TiO2|ReC-TiO2 photocathode was used for CO2 reduction at an incident light power intensity of 100 mW / cm 2 The photoelectric performance was tested under illumination conditions and a bias of -1.8 V in a carbon dioxide atmosphere. It was found that the photocurrent density decayed by less than 15% within 3 h.

[0055] Example 7 A method for preparing a photocathode based on a silicon nanowire substrate comprises the following steps: Si NWs were prepared by metal-assisted chemical etching. First, the p-type silicon wafer was ultrasonically immersed in acetone, ethanol and water for 20, 15 and 15 min, respectively, to remove surface impurities. Then, it was further cleaned in H2SO4:H2O2 (v / v, 1:1) solution for 20 min, rinsed with water and removed the surface oxide layer in HF solution (5 wt%). The clean silicon wafer was immersed in solutions containing AgNO3 (0.05 M) and 4.3 M HF, respectively, at room temperature for 60 min. The silicon wafer was immersed in HNO3 solution (v / v, 1:1) for 60 min to remove residual Ag. After being immersed in HF solution (5 wt%) for 10 min, vertically aligned Si NWs were obtained. The Si NWs were immersed in HAuCl4 solution (0.1 M) and shaken at a frequency of 150 rpm for 90 min, and then rinsed with water to obtain a silicon nanowire substrate adsorbed with Au nanoparticles (Si NWs|Au); Si NWs|Au was placed in an ALD chamber to deposit a TiO2 layer (15 cycles) using tetrakis(dimethylamino)titanium and water as precursors at a deposition reaction temperature of 60 °C to obtain Si NWs|Au|TiO2; The photosensitizer P1 and catalyst [Ru(bda)(4-PO3H2-(CH2)3-pyr)2] (ReC) were fully mixed with acetonitrile and methanol respectively under ultrasound to prepare P1-acetonitrile and 0.6 mM ReC-methanol solutions; the Si NWs|Au-TiO2 electrode was immersed in P1-acetonitrile for 16 h, dried, and then atomic layer deposition of TiO2 was carried out on its surface using a precursor for 5 cycles of growth. The electrode was taken out and immersed in ReC-acetonitrile solution for 16 h, dried, and then atomic layer deposition of TiO2 was carried out on its surface using a precursor for 5 cycles of growth to obtain the Si NWs|Au-TiO2|P1-TiO2|ReC-TiO2 electrode.

[0056] Example 8 A method for preparing a photocathode based on a silicon nanowire substrate comprises the following steps: Si NWs were prepared by metal-assisted chemical etching. First, the p-type silicon wafer was ultrasonically immersed in acetone, ethanol and water for 20, 15 and 15 min, respectively, to remove surface impurities. Then, it was further cleaned in H2SO4:H2O2 (v / v, 1:1) solution for 30 min, rinsed with water and removed the surface oxide layer in HF solution (5 wt%). The clean silicon wafer was immersed in solutions containing AgNO3 (0.03 M) and 4.6 M HF, respectively, at room temperature for 90 min. The silicon wafer was immersed in HNO3 solution (v / v, 1:1) for 45 min to remove residual Ag. After immersion in HF solution (5 wt%) for 5 min, vertically aligned Si NWs were obtained. The Si NWs were immersed in HAuCl4 solution (0.002 M) and shaken at a frequency of 120 rpm for 60 min, and then rinsed with water to obtain a silicon nanowire substrate adsorbed with Au nanoparticles (Si NWs|Au); Si NWs|Au was placed in an ALD chamber to deposit a TiO2 layer (15 cycles) using tetrakis(dimethylamino)titanium and water as precursors at a deposition reaction temperature of 80 °C to obtain Si NWs|Au|TiO2; The photosensitizer P1 and catalyst [Ru(bda)(4-PO3H2-(CH2)3-pyr)2] (ReC) were fully mixed with acetonitrile and methanol respectively under ultrasound to prepare P1-acetonitrile and 0.5 mM ReC-methanol solutions; the Si NWs|Au-TiO2 electrode was immersed in P1-acetonitrile for 16 h, dried, and then atomic layer deposition of TiO2 was performed on its surface using a precursor for 5 cycles of growth. The electrode was taken out and immersed in ReC-acetonitrile solution for 16 h. After drying, atomic layer deposition of TiO2 was performed on its surface using a precursor for 5 cycles of growth. The Si NWs|Au-TiO2|P1-TiO2|ReC-TiO2 electrode was obtained.

[0057] Example 9 A method for preparing a photocathode based on a silicon nanowire substrate comprises the following steps: Si NWs were prepared by metal-assisted chemical etching. First, the p-type silicon wafer was ultrasonically immersed in acetone, ethanol and water for 20, 15 and 15 min, respectively, to remove surface impurities. Then, it was further cleaned in H2SO4:H2O2 (v / v, 1:1) solution for 30 min, rinsed with water and removed the surface oxide layer in HF solution (5 wt%). The clean silicon wafer was immersed in solutions containing AgNO3 (0.03 M) and 4.6 M HF, respectively, at room temperature for 90 min. The silicon wafer was immersed in HNO3 solution (v / v, 1:1) for 45 min to remove residual Ag. After immersion in HF solution (5 wt%) for 5 min, vertically aligned Si NWs were obtained. The Si NWs were immersed in HAuCl4 solution (2 mM) and oscillated at 140 rpm for 80 min, and then rinsed with water to obtain a silicon nanowire substrate adsorbed with Au nanoparticles (Si NWs|Au). Si NWs|Au was placed in an ALD chamber to deposit a TiO2 layer (15 cycles) using tetrakis(dimethylamino)titanium and water as precursors at a deposition reaction temperature of 120 °C to obtain Si NWs|Au|TiO2; The photosensitizer P1 and catalyst [Ru(bda)(4-PO3H2-(CH2)3-pyr)2] (ReC) were fully mixed with acetonitrile and methanol respectively under ultrasound to prepare P1-acetonitrile and 0.5 mM ReC-methanol solutions; the Si NWs|Au-TiO2 electrode was immersed in P1-acetonitrile for 16 h, dried, and then atomic layer deposition of TiO2 was performed on its surface using a precursor for 5 cycles of growth. The electrode was taken out and immersed in ReC-acetonitrile solution for 16 h. After drying, atomic layer deposition of TiO2 was performed on its surface using a precursor for 5 cycles of growth. The Si NWs|Au-TiO2|P1-TiO2|ReC-TiO2 electrode was obtained.

[0058] Comparative Example 1 The photocathode in this comparative example is: Si NWs|Au|TiO2|ReC-TiO2 photocathode; Compared with Example 1, the difference is that the Si NWs|Au|TiO2|ReC-TiO2 photocathode does not adsorb the P1 photosensitizer. 2 Under the conditions of light, controlled potential electrolysis was carried out in a carbon dioxide atmosphere under continuous simulated light (AM 1.5G), and the Faradaic efficiency of the product CO was calculated by gas chromatography.

[0059] The Si NWs|Au|TiO2|ReC-TiO2 photocathode was used for carbon dioxide reduction, and the Faraday efficiency of the product CO was calculated by gas chromatography. The maximum FE at a bias voltage of -1.9 V was obtained. CO It is 43.2%.

[0060] Comparative Example 2 The photocathode in this comparative example is: Si NWs|TiO2-ReC-TiO2 photocathode; Compared with Example 1, the difference is that the Si NWs|TiO2-ReC-TiO2 photocathode does not adsorb Au and P1 photosensitizers. 2 Under the conditions of light, controlled potential electrolysis was carried out in a carbon dioxide atmosphere under continuous simulated light (AM 1.5G), and the Faradaic efficiency of the product CO was calculated by gas chromatography.

[0061] The Si NWs|TiO2-ReC-TiO2 photocathode was used for carbon dioxide reduction. The Faradaic efficiency of the product CO was calculated by gas chromatography, and the maximum FE was obtained at a bias voltage of -1.9 V. CO It is 14.3%.

[0062] In summary, the Si NWs|Au|TiO2|P1-TiO2|ReC-TiO2 photocathode of the present invention has a stable structure and good photoelectrocatalytic performance; wherein Au nanoparticles are adsorbed on the Si NWs substrate, and the plasmon effect of the metal nanostructure is utilized to significantly enhance the light-matter interaction to promote the catalytic reaction and increase the selectivity of CO2 reduction. The TiO2 protective layer is coated on the outermost layer using simple ALD technology to maintain the stability of the catalyst during the reaction, making the photocathode structure more stable. The strategy of utilizing the noble metal LSPR effect to improve light absorption can be extended to the efficient conversion of other catalytic systems.

[0063] The method of the present invention assembles a photocathode of a photosensitizer and a catalyst through atomic layer deposition technology, and has the characteristics of stable structure and good photoelectrocatalytic performance; the photocathode has good effect when applied in photoelectrocatalytic carbon dioxide reduction; a photocathode with surface adsorbed photosensitizer and catalyst can be formed without covalent bonds or ionic bonds between photosensitizer / catalyst units, and the structure is more stable and the photoelectrocatalytic performance is better. The silicon nanowire substrate has a large specific surface area, which can provide more active sites, which is conducive to the adsorption of photosensitizer and catalyst, thereby improving the efficiency of photoelectrocatalytic reaction; the photosensitizer and catalyst are sequentially connected on the TiO2 film through atomic layer deposition, and finally coated on the TiO2 film to form a multilayer structure, which can effectively improve the transmission efficiency of photogenerated electrons, reduce charge recombination, and further improve the photoelectrocatalytic performance. The thin film adsorbed photosensitizer and catalyst by atomic layer deposition (ALD) can achieve precise control at the nanometer level, ensure that the photosensitizer and catalyst are evenly distributed on the surface of the TiO2 film, and improve the stability and activity of the catalyst. By coating the outermost layer with TiO2 film by atomic layer deposition, the photosensitizer and catalyst can be effectively protected, preventing them from being lost or degraded during the reaction process, and improving the stability and service life of the catalyst. Atomic layer deposition (ALD) is a highly controllable thin film deposition technology that can achieve precise control at the nanometer level, simplify the traditional complex photocathode preparation process, and improve the repeatability and consistency of the preparation. By precisely adsorbing the photosensitizer (P1) and catalyst (ReC) on the TiO2 film by atomic layer deposition, the synergistic effect of the photosensitizer and catalyst can be achieved, and the selectivity and efficiency of the CO2 reduction reaction can be improved. Through the optimized design of the multilayer structure, the transmission efficiency of the photogenerated electrons can be effectively improved, the charge recombination can be reduced, and the efficiency of the CO2 reduction reaction can be further improved. The photocathode prepared by this technical solution is suitable for the photocatalytic CO2 reduction reaction, and can efficiently reduce CO2 to the target product (such as CO, HCOOH, etc.) under light conditions, with high photocatalytic efficiency and product selectivity. By constructing a three-electrode system (working electrode, reference electrode, counter electrode), efficient electrochemical control and reaction monitoring can be achieved in the photoelectrocatalytic CO2 reduction reaction, further improving the stability and controllability of the reaction. The electrolyte solution used in this technical solution is an acetonitrile solution containing tetrabutylammonium hexafluorophosphate, which has good electrochemical stability and environmental friendliness and is suitable for long-term photoelectrocatalytic reactions. This technical solution can convert CO2 into useful chemical fuel CO through the photoelectrocatalytic CO2 reduction reaction, and has high sustainability and environmental benefits.

[0064] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a photocathode based on a silicon nanowire substrate, characterized in that: The following steps are involved: Adsorbing Au nanoparticles on the surface of the silicon nanowire substrate to obtain a silicon nanowire substrate adsorbed with Au nanoparticles; A TiO2 film is deposited on the surface of a silicon nanowire substrate by atomic layer deposition, and then a photosensitizer and a catalyst are adsorbed on the TiO2 film deposited by the atomic layer deposition method, and then the TiO2 film is coated by atomic layer deposition to obtain a photocathode based on a silicon nanowire substrate.

2. The method for preparing a photocathode based on a silicon nanowire substrate according to claim 1, characterized in that: The preparation method of the silicon nanowire substrate is: After the silicon wafer is processed, a silicon wafer is obtained, and the silicon wafer is sequentially immersed in an AgNO3 solution for 60 to 90 min and an HF solution for 60 to 90 min, and then sequentially immersed in an HNO3 solution for 60 to 90 min and an HF solution for 5 to 10 min, to obtain a silicon nanowire substrate; The steps of processing the silicon wafer are as follows: Then, the silicon wafer was cleaned in a mixed solution of H2SO4 and H2O2 with a volume ratio of 1:1 for 20-40 min to obtain a silicon wafer; The concentrations of the AgNO3 solution and the HF solution are 0.03-0.05 M and 4.3-4.6 M, respectively.

3. The method for preparing a photocathode based on a silicon nanowire substrate according to claim 1, characterized in that: The Au nanoparticles are adsorbed on the surface of the silicon nanowire substrate by immersing the silicon nanowire substrate in a HAuCl4 solution and shaking it; the concentration of the HAuCl4 solution is 0.002-0.1 M.

4. The method for preparing a photocathode based on a silicon nanowire substrate according to claim 3, characterized in that: The oscillation frequency is 120-150 rpm, and the oscillation time is 60-90 min.

5. The method for preparing a photocathode based on a silicon nanowire substrate according to claim 1, characterized in that: The specific steps of depositing a TiO2 film on the surface of the silicon nanowire substrate by atomic layer deposition are: The silicon nanowire substrate is placed in a deposition chamber, and tetrakis(dimethylamino)titanium and water are used as precursors for a deposition reaction to form a TiO2 film on the surface of the silicon nanowire substrate; The deposition reaction temperature of the tetrakis(dimethylamino)titanium is 60-120°C.

6. The method for preparing a photocathode based on a silicon nanowire substrate according to claim 5, characterized in that: The deposition cycle number of the TiO2 film on the surface of the silicon nanowire substrate is 15 times.

7. The method for preparing a photocathode based on a silicon nanowire substrate according to claim 1, characterized in that: The photosensitizer is a P1 photosensitizer; the catalyst is a ReC catalyst; The steps of adsorbing the photosensitizer and catalyst on the TiO2 film deposited by atomic layer deposition are: The substrate is placed in an atomic layer deposition reaction chamber to deposit a TiO2 film, then immersed in an acetonitrile solution of a P1 photosensitizer, and then a TiO2 film is deposited; then immersed in a methanol solution of a ReC catalyst, and a TiO2 film is deposited on the outermost layer; The number of deposition cycles of the photosensitizer is 5 times; the number of deposition cycles of the catalyst is 5 times; The concentration of the acetonitrile solution of the P1 photosensitizer is 0.2-0.3 mM; the concentration of the methanol solution of the ReC catalyst is 0.2-0.6 mM.

8. The method for preparing a photocathode based on a silicon nanowire substrate according to claim 1, characterized in that: The specific steps of coating TiO2 thin film by atomic layer deposition are as follows: The TiO2 thin film was deposited using tetrakis(dimethylamino)titanium and water as precursors to obtain a photocathode based on a silicon nanowire substrate; The deposition cycle number of the TiO2 film is 5 times.

9. A photocathode based on a silicon nanowire substrate, characterized in that: The method is prepared by any one of claims 1 to 8.

10. The use of the photocathode based on silicon nanowire substrate according to claim 9 in photoelectrocatalytic carbon dioxide reduction, characterized in that: The following steps are involved: Using a silicon nanowire-based photocathode as the working electrode, Ag / Ag + A three-electrode system is constructed using a platinum sheet as a reference electrode and a platinum sheet as a counter electrode, and a photoelectrocatalytic carbon dioxide reduction reaction is carried out in the electrolyte solution of the three-electrode system; The incident light power intensity of the light source used in the photoelectrocatalytic carbon dioxide reduction reaction is 100 mW / cm 2 , the applied bias range is -1.3~-1.9 V; The electrolyte solution is an acetonitrile solution containing 0.1 M tetrabutylammonium hexafluorophosphate.

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