Unbiased coupling photoelectrochemical system and preparation method and application of anode and cathode of unbiased coupling photoelectrochemical system

Abstract

The invention belongs to the field of photoelectrochemistry, and relates to an unbiased coupling photoelectrochemistry system and a preparation method and application of an anode and a cathode of the unbiased coupling photoelectrochemistry system. The CuMo / TCS photocathode constructed by the invention realizes synthesis of solar-driven urea by using nitrate-containing wastewater and carbon dioxide under ultralow potential, so that photogenerated charge transfer is optimized, and the energy potential barrier of COOHNH2 intermediate dehydroxylation is reduced. According to the invention, an unbiased coupling photoelectrochemical system of a CuMo / TCS photocathode and a Bi2O3 / Pt anode is successfully established, Bi2O3 / Pt is adopted as an anode electrocatalyst, and additional high-value product output is given to the anode reaction. Under real sun illumination, the urea yield of the large-area photoelectrode of 12 cm < 2 > reaches 1319.68 [mu] g h <-1 >, the yield of a C3 product is 381.48 [mu] mol h <-1 >, and potential practical application value is achieved.

Description

Technical Field

[0001] The invention belongs to the field of photoelectrochemistry and relates to the synthesis of urea and the preparation of C3 chemicals. Background Art

[0002] Urea (CO(NH2)2) is a vital basic chemical product with an annual global production exceeding 100 million tons. It is widely used in agricultural fertilizers, food production, and the synthesis of fine chemical raw materials such as melamine and polyurethane. Traditional urea production relies primarily on the Bosch-Meiser process, which operates under high temperature (150-200°C) and high pressure (150-250 bar). This process consumes approximately 80% of industrial ammonia production and contributes approximately 1% of global CO2 emissions. Therefore, developing efficient and sustainable urea synthesis methods has become a key challenge in the chemical industry.

[0003] In recent years, the use of renewable energy driven photoelectrochemical (PEC) method for urea synthesis has become a new path to achieve high value utilization of carbon and nitrogen resources and energy conservation and emission reduction. - The conversion of CO2 into urea under solar-driven conditions can not only effectively treat nitrate-containing wastewater, but also realize the resource utilization of greenhouse gases, with significant environmental and economic benefits. Studies have shown that regulating reaction conditions and constructing a synergistic catalytic system can improve the conversion of CO2 and NO3 in the PEC system. - For example, Wang et al. constructed a NiFe diatomic catalyst / TiO2 layer / nanostructure n + p-Si photocathode, achieved a Faradaic Efficiency (FE) of 24.2% (Proc. Natl. Acad. Sci. USA 2024, 121, e2311326121); the Mi team + Ag catalyst was loaded on p-Si based GaN nanowire photocathode at -0.3V RHE The FE of up to 75.6% was obtained under the condition of NO2 and COO. - Effective CN coupling between intermediates (ACS Catal. 2024, 14, 2588-2596). In addition, Duan et al. used cubic Cu2O as the photocathode material and RHE 29.71 μmol g -1 h -1and a urea formation rate of 12.9% (Angew. Chem. Int. Ed. 2024, 63, e202406515). However, the current efficient PEC synthesis of urea still faces many challenges. First, the realization of highly selective CN coupling at low potential is still limited by the insufficient selectivity of the catalyst surface reaction and the low charge transfer efficiency of the semiconductor material. Second, traditional PEC urea synthesis systems mostly rely on an external bias, and their anode reaction is mainly a slow oxygen evolution reaction (OER), which seriously limits the overall energy efficiency of the system and product value-added. Therefore, constructing an unbiased PEC system that does not require an external bias and achieving the coordinated production of high-value chemicals at the anode and cathode is a fundamental challenge for achieving efficient urea synthesis directly driven by solar energy. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention proposes a bias-free coupled photoelectrochemical system and a method for preparing and applying the anode and cathode thereof.

[0005] The technical solution of the present invention is achieved as follows: Preparation steps of a CuMo / TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh potassium antimonyl tartrate and anhydrous sodium thiosulfate, dissolve them in deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Place the above precursor solution in a reactor, and place the fluorine-doped tin oxide (FTO) conductive glass substrate tilted downward into the solution. Ultrasonicate the reactor at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in an oven for heating and reaction. After the reaction is completed, naturally cool it in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 340~360℃ in a nitrogen atmosphere for 18~22 minutes to obtain a dense and uniform Sb2S3 semiconductor film; In the step (1), the mass ratio of potassium antimony tartrate to anhydrous sodium thiosulfate is 2.4-2.8:2.3-2.7; the heating reaction temperature is 130-140° C. and the time is 4.5-5.5 h.

[0006] (2) Chemical bath deposition (CBD) of the CdS layer: Add deionized water to a beaker and heat it in a water bath to 45-55°C for 12-16 minutes. Add cadmium sulfate (CdSO4) and stir until dissolved. After heating to 58-62°C, add ammonia (NH3·H2O). Quickly add thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Move the beaker and the sample into a constant temperature oven at 55-65°C for 13-17 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction. In the step (2), the concentration of cadmium sulfate in the reaction solution is 3.0-3.4 mg / mL, the volume concentration of ammonia water is 19-23% v / v, and the concentration of thiourea is 16.5-17.5 mg / mL.

[0007] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, the TiO2 layer was deposited at 115-125°C for 400-800 cycles to form a dense TiO2 layer. After deposition, the sample was annealed at 195-205°C in an argon atmosphere for 0.8-1.2 hours to obtain a TiO2 / CdS / Sb2S3 (TCS) structure.

[0008] (4) Electrochemical deposition and annealing of CuMo layer: Dissolve copper chloride (CuCl2), sodium molybdate (Na2MoO4) and ammonium oxalate ((NH4)2C2O4) in deionized water; stir at room temperature for 25-35 minutes; add appropriate amount of polyethylene glycol (PEG-2000) to improve the film forming performance. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode, at -0.8 V AgCl Electrodeposition was performed for 900 seconds at a potential to uniformly deposit the CuMo component on the TCS surface. The electrodeposited sample was annealed at 200-220°C for 25-35 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure.

[0009] In step (4), the concentration of copper chloride is 0.08-0.12 mg / mL, the concentration of sodium molybdate is 4.6-5.0 mg / mL, and the concentration of ammonium oxalate is 4.5-5.5 mg / mL.

[0010] A bias-free coupled photoelectrochemical system comprises a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell comprises a cathode reaction cell and an anode reaction cell, wherein the cathode reaction cell uses a CuMo / TiO2 / CdS / Sb2S3 photocathode as the cathode, and the anode reaction cell uses a Bi2O3 / Pt anode as the anode; the reaction cells are separated by a proton exchange membrane, the cathode electrolyte is 0.5 M KHCO3 and 0.5 M KNO3 saturated with CO2, and the anode electrolyte is 1 M KOH and 0.5 M glycerol.

[0011] The preparation steps of the Bi2O3 / Pt anode are as follows: a. Commercial nickel foam (NF) was ultrasonically cleaned, then rinsed sequentially with deionized water, ethanol, and acetone, and dried for later use. The cleaned nickel foam was immersed in deionized water. Chloroplatinic acid solution (HPtCl6·6H2O) and concentrated hydrochloric acid (HCl) were added sequentially. Polyvinylpyrrolidone (PVP) was then added and gently stirred until completely dissolved to form a homogeneous solution. The reaction system was placed in a constant temperature oven at 50–55°C for 5.5–6.5 hours. After the reaction was complete, a black deposit was observed on the electrode surface. The resulting electrode was removed, rinsed thoroughly with deionized water, dried, and annealed in air at 400–480°C for 1.5–2.5 hours to obtain a Pt electrode.

[0012] In step a, the volume ratio of deionized water, chloroplatinic acid solution, and concentrated hydrochloric acid solution is 2.9-3.1:0.45-0.55:0.01-0.02; the concentration of the chloroplatinic acid solution is 110-130 mM; 8-12 mg of polyvinyl pyrrolidone is added per mL of deionized water; b. Dissolve bismuth nitrate (Bi(NO₃)₃·5H₂O) in a mixture of deionized water and ethylene glycol and stir until the solution is clear. Using a three-electrode system, use the aforementioned Pt electrode as the working electrode and Ag / AgCl as the reference electrode. Electrodeposit Bi at -0.6 V for 10 minutes. After deposition, remove the electrode and anneal it in air at 400–480°C for 1.5–2.5 hours to obtain a Bi₂O₃ / Pt electrode.

[0013] The mixed solution in step b is a mixed solution of deionized water and ethylene glycol in a volume ratio of 1.8-2.2:0.8-1.2; the concentration of bismuth nitrate is 0.008-0.012 mmol / mL.

[0014] The unbiased coupled photoelectrochemical system produces C3 chemicals such as glyceric acid, lactic acid, and tartaric acid at the anode and urea at the cathode. The illumination conditions are 50-200 mW cm -2 Sunlight is used for exposure.

[0015] This application uses solar energy to directly convert NO3 - The mechanism of converting NO3 into urea is as follows: Under light, CuMo / TiO2 / CdS / Sb2S3 photocathode converts NO3 into urea. - The NH2 intermediate produced by reduction couples with the CO2 intermediate to form the CO2NH2 intermediate. The protonation of the CO2NH2 intermediate further produces the key COOHNH2 intermediate. The subsequent dehydration of the COOHNH2 intermediate and the second CN coupling step efficiently and selectively produce PEC urea on the photocathode. In particular, the use of the COOHNH2 intermediate pathway avoids the production of the CO intermediate and improves the efficiency of urea synthesis.

[0016] The present invention has the following beneficial effects: (1) The CuMo / TCS photocathode constructed in this invention exhibits an ultra-low onset potential (0.98 V RHE ), at 0.4V RHE The Faradaic efficiency (FE) of urea is as high as 73.3% at 0.1 V. RHE The urea yield can reach 264.79 μg cm -2 h -1 , showing excellent electrocatalytic activity and product selectivity. Through in situ characterization and theoretical calculations, it was confirmed that the dehydroxylation reaction of the key intermediate COOHNH2 on the CuMo / TCS photocathode surface has the lowest energy barrier, effectively improving the efficiency of the CN coupling reaction and providing a clear reaction pathway mechanism for the photoelectric synthesis of urea.

[0017] (2) The present invention successfully built a bias-free coupled photoelectrochemical (PEC) system of CuMo / TCS photocathode and Bi2O3 / Pt anode, using Bi2O3 / Pt as the anode electrocatalyst and replacing the traditional oxygen evolution reaction (OER) with glycerol oxidation reaction (GOR), which significantly reduced the anode starting potential to 0.23 V. RHE , effectively reducing the energy consumption of the entire photoelectrochemical system and giving the anode reaction additional high-value product output. RHE The C3 chemical selectivity of glycerol oxidation products remained above 90% within the potential range, reaching a maximum of 98.58%. The unbiased coupled photoelectrochemical (PEC) system achieved a -4.05 mA·cm -2 Photocurrent density. Based on an area of ​​12 cm2 The unbiased device constructed with a CuMo / TCS photocathode achieved a urea yield of 1319.68 μg·h under real sunlight irradiation. -1 , C3 product yield 381.48 μmol·h -1 , reaching the leading level in the unbiased PEC system, verifying the scalability and potential industrialization prospects of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 are scanning electron microscope images; ad are scanning electron microscope images of TiO2 / CdS / Sb2S3 and eh CuMo / TiO2 / CdS / Sb2S3.

[0020] Figure 2 are the cross-sectional transmission electron microscope images and EDX spectra of CuMo / TiO2 / CdS / Sb2S3; ag is the cross-sectional transmission electron microscope image and h is the EDX spectrum.

[0021] Figure 3 For different photocathodes corresponding to a Cu LMM , b Cu 2p, c Mo 3d, d O 1s XPS spectrum.

[0022] Figure 4 are the LSV curves of the photocathode; a is the LSV curve of CuMo / TiO2 / CdS / Sb2S3 in different electrolytes, b is the LSV curve of CuMo / TiO2 / CdS / Sb2S3, Cu / TiO2 / CdS / Sb2S3, Mo / TiO2 / CdS / Sb2S3, TiO2 / CdS / Sb2S3 in CO2-saturated 0.5 M KHCO3+0.5 M KNO3, and c is the urea FE of the photocathode modified with different catalysts.

[0023] Figure 5 Cyclic test of the photocathode; a FE of nitrogen-containing products of CuMo / TiO2 / CdS / Sb2S3 at different potentials, b CuMo / TiO2 / CdS / Sb2S3 at 0.4 V RHEStability under conditions of c, cycling test of CuMo / TiO2 / CdS / Sb2S3.

[0024] Figure 6 In situ infrared spectra of different photocathodes; a is the in situ infrared spectrum of CuMo / TiO2 / CdS / Sb2S3, b is the in situ infrared spectrum of Cu / TiO2 / CdS / Sb2S3, and c is the in situ infrared spectrum of Mo / TiO2 / CdS / Sb2S3.

[0025] Figure 7 Characterization of the anode; where a is the scanning electron microscope image of Bi2O3 / Pt, b is the transmission electron microscope image of Bi2O3 / Pt, c is the corresponding EDX spectrum, d XPS spectrum of Bi2O3 / Pt and Pt corresponding to Pt 4f, e XPS spectrum of Bi2O3 / Pt and Bi2O3 corresponding to Bi 4f, f XPS spectrum of Bi2O3 / Pt, Bi2O3 and Bi2O3 / Pt corresponding to O 1s.

[0026] Figure 8 is the electrochemical performance of the anode; where a is the linear sweep voltammetry curve of Bi2O3, Pt, and Bi2O3 / Pt in 1 M KOH+0.5 M glycerol, b is the yield of all C3 products on Bi2O3 / Pt and the corresponding C3 selectivity at different potentials, and c is the yield of all C3 products on Bi2O3 / Pt at 0.8 V RHE Selectivity of Pt and Bi2O3 / Pt for all products and C3 yield, d is 0.6V RHE It curve of Bi2O3 / Pt cycle test under the following conditions, e is the corresponding C3 yield and C3 selectivity in the cycle test.

[0027] Figure 9 Figure 3 is the CuMo / TCS || Bi2O3 / Pt system and test; a is a schematic diagram of the PEC cell for producing urea and C3, b is the potential gain when coupled with various anodic reactions during unassisted urea production measured in a two-electrode setup, c is the unbiased stability of the CuMo / TiO2 / CdS / Sb2S3|| Bi2O3 / Pt tandem device with the electrolyte refreshed every 0.5 h, d is the urea FEs and yield of the CuMo / TiO2 / CdS / Sb2S3|| Bi2O3 / Pt tandem device under unbiased conditions under AM 1.5G illumination, and e is the selectivity and yield of Bi2O3 / Pt for C3 under unbiased conditions.

[0028] Figure 10A large unbiased PEC system and test; a is a digital photo of a real outdoor solar test (1-sun: 100 mW cm -2 (a) a digital image of CuMo / TiO2 / CdS / Sb2S3 cells of different sizes; (b) JV curves of the CuMo / TiO2 / CdS / Sb2S3||Bi2O3 / Pt cell under real sunlight (12 square centimeters for CuMo / TiO2 / CdS / Sb2S3) and simulated sunlight (4 square centimeters for CuMo / TiO2 / CdS / Sb2S3); (d) urea FE and C3 selectivity in a 1-hour test; (e) urea and C3 product yields of the CuMo / TiO2 / CdS / Sb2S3||Bi2O3 / Pt tandem device under laboratory and outdoor unbiased test conditions. The test was conducted in Hohhot, China, from 1:00 PM to 3:00 PM on June 17, 2025; (f) economic value of the unbiased system. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; the materials and reagents used are commercially available reagents and materials unless otherwise specified. Example 1

[0031] This embodiment provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh 2.67 g potassium antimonyltartrate and 2.53 g anhydrous sodium thiosulfate, dissolve them in 100 mL deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reactor. Place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonicate the reactor for 10 minutes at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in a 135 °C oven and heat for 5 hours. After the reaction is completed, cool it naturally in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 350 °C in a nitrogen atmosphere for 20 minutes to obtain a dense and uniform Sb2S3 semiconductor film.

[0032] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat it to 50 °C in a water bath for 15 minutes. Add 0.32 g of cadmium sulfate (CdSO4) and stir until dissolved. After heating to 60 °C, add 21 mL of ammonia (NH3·H2O) and quickly add 1.69 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Transfer the beaker and the sample to a 60 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0033] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, 600 cycles of deposition were performed at 120°C to form a dense TiO2 layer. After deposition, the sample was annealed at 200°C for 1 hour under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (TCS) structure.

[0034] (4) Electrochemical deposition and annealing of CuMo layer: 0.05 g copper chloride (CuCl2), 0.24 g sodium molybdate (Na2MoO4) and 0.25 g ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL deionized water; stirred at room temperature for 30 minutes; an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode, at -0.8 V AgClElectrodeposition was performed at a potential of 900 seconds to uniformly deposit the CuMo component on the TCS surface. The electrodeposited sample was annealed at 210°C for 30 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure, namely, the CuMo / TiO2 / CdS / Sb2S3 photocathode. Example 2

[0035] This embodiment provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh 2.4 g potassium antimonyltartrate and 2.7 g anhydrous sodium thiosulfate, dissolve them in 100 mL deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reactor. Place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonicate the reactor for 10 minutes at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in a 130 °C oven and heat for 4.5 hours. After the reaction is completed, cool it naturally in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 340 °C in a nitrogen atmosphere for 18 minutes to obtain a dense and uniform Sb2S3 semiconductor film.

[0036] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat it to 50 °C in a water bath for 15 minutes. Add 0.3 g of cadmium sulfate (CdSO4) and stir until dissolved. After heating to 55 °C, add 20 mL of ammonia (NH3·H2O). Subsequently, quickly add 1.65 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Transfer the beaker and the sample to a 55 °C constant temperature oven for 13 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0037] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, 600 cycles of deposition were performed at 115°C to form a dense TiO2 layer. After deposition, the sample was annealed at 195°C for 0.8 h under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (TCS) structure.

[0038] (4) Electrochemical deposition and annealing of CuMo layer: 0.04 g copper chloride (CuCl2), 0.23 g sodium molybdate (Na2MoO4) and 0.225 g ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL deionized water; stirred at room temperature for 30 minutes; an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode, at -0.8 V AgCl Electrodeposition was performed at a potential for 900 seconds to uniformly deposit the CuMo component on the TCS surface. The electrodeposited sample was annealed at 200°C for 25 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure, namely, the CuMo / TiO2 / CdS / Sb2S3 photocathode. Example 3

[0039] This embodiment provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh 2.5 g of potassium antimonyltartrate and 2.6 g of anhydrous sodium thiosulfate, dissolve them in 100 mL of deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reactor. Place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonicate the reactor for 10 minutes at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in a 140 °C oven and heat for 5 hours. After the reaction is completed, cool it naturally in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 360 °C in a nitrogen atmosphere for 19 minutes to obtain a dense and uniform Sb2S3 semiconductor film.

[0040] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat it to 50 °C in a water bath for 15 minutes. Add 0.34 g of cadmium sulfate (CdSO4) and stir until dissolved. After heating to 65 °C, add 20 mL of ammonia (NH3·H2O). Subsequently, quickly add 1.7 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Transfer the beaker and the sample to a 58 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0041] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, 600 cycles of deposition were performed at 125°C to form a dense TiO2 layer. After deposition, the sample was annealed at 205°C for 1.2 hours under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (TCS) structure.

[0042] (4) Electrochemical deposition and annealing of CuMo layer: 0.06 g copper chloride (CuCl2), 0.24 g sodium molybdate (Na2MoO4) and 0.275 g ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL deionized water; stirred at room temperature for 30 minutes; an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode, at -0.8 V AgCl Electrodeposition was performed at a potential of 900 seconds to uniformly deposit the CuMo component on the TCS surface. The electrodeposited sample was annealed at 220°C for 35 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure, namely, the CuMo / TiO2 / CdS / Sb2S3 photocathode. Example 4

[0043] This embodiment provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh 2.8 g of potassium antimonyltartrate and 2.5 g of anhydrous sodium thiosulfate, dissolve them in 100 mL of deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reactor. Place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonicate the reactor for 10 minutes at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in an oven at 138 °C and heat for 5 hours. After the reaction is completed, cool it naturally in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 340 °C for 21 minutes in a nitrogen atmosphere to obtain a dense and uniform Sb2S3 semiconductor film.

[0044] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat it to 50 °C in a water bath for 15 minutes. Add 0.31 g of cadmium sulfate (CdSO4) and stir until dissolved. After heating to 55 °C, add 20 mL of ammonia (NH3·H2O). Subsequently, quickly add 1.68 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Transfer the beaker and the sample to a 63 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0045] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, 600 cycles of deposition were performed at 123°C to form a dense TiO2 layer. After deposition, the sample was annealed at 200°C for 1 hour under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (TCS) structure.

[0046] (4) Electrochemical deposition and annealing of CuMo layer: 0.045 g copper chloride (CuCl2), 0.24 g sodium molybdate (Na2MoO4) and 0.275 g ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL deionized water; stirred at room temperature for 30 minutes; an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode, at -0.8 V AgCl Electrodeposition was performed at a potential of 900 seconds to uniformly deposit the CuMo component on the TCS surface. The electrodeposited sample was annealed at 210°C for 30 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure, namely, the CuMo / TiO2 / CdS / Sb2S3 photocathode. Example 5

[0047] This embodiment provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh 2.6 g of potassium antimonyl tartrate and 2.4 g of anhydrous sodium thiosulfate, dissolve them in 100 mL of deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reactor. Place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonicate the reactor for 10 minutes at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in a 130 °C oven and heat for 4.5 hours. After the reaction is completed, cool it naturally in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 350 °C in a nitrogen atmosphere for 18 minutes to obtain a dense and uniform Sb2S3 semiconductor film.

[0048] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat it to 50 °C in a water bath for 15 minutes. Add 0.3 g of cadmium sulfate (CdSO4) and stir until dissolved. After heating to 55 °C, add 20 mL of ammonia (NH3·H2O). Subsequently, quickly add 1.7 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Transfer the beaker and the sample to a 60 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0049] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, 600 cycles of deposition were performed at 120°C to form a dense TiO2 layer. After deposition, the sample was annealed at 200°C for 1 hour under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (TCS) structure.

[0050] (4) Electrochemical deposition and annealing of CuMo layer: 0.05 g copper chloride (CuCl2), 0.24 g sodium molybdate (Na2MoO4) and 0.25 g ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL deionized water; stirred at room temperature for 30 minutes; an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode, at -0.8 V AgClElectrodeposition was performed at a potential of 1200 seconds to uniformly deposit the CuMo component on the TCS surface. The electrodeposited sample was annealed at 200°C for 25 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure, namely, the CuMo / TiO2 / CdS / Sb2S3 photocathode. Comparative Example 1

[0051] This comparative example provides a preparation step of a TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh 2.67 g potassium antimonyltartrate and 2.53 g anhydrous sodium thiosulfate, dissolve them in 100 mL deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reactor. Place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonicate the reactor for 10 minutes at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in a 135 °C oven and heat for 5 hours. After the reaction is completed, cool it naturally in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 350 °C in a nitrogen atmosphere for 20 minutes to obtain a dense and uniform Sb2S3 semiconductor film.

[0052] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat it to 50 °C in a water bath for 15 minutes. Add 0.32 g of cadmium sulfate (CdSO4) and stir until dissolved. After heating to 60 °C, add 21 mL of ammonia (NH3·H2O). Subsequently, quickly add 1.69 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Transfer the beaker and the sample to a 60 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0053] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, 600 cycles of deposition were performed at 120°C to form a dense TiO2 layer. After deposition, the sample was annealed at 200°C for 1 hour under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (TCS) structure. Comparative Example 2

[0054] This comparative example provides a preparation step of a Cu / TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh 2.67 g potassium antimonyltartrate and 2.53 g anhydrous sodium thiosulfate, dissolve them in 100 mL deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reactor. Place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonicate the reactor for 10 minutes at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in a 135 °C oven and heat for 5 hours. After the reaction is completed, cool it naturally in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 350 °C in a nitrogen atmosphere for 20 minutes to obtain a dense and uniform Sb2S3 semiconductor film.

[0055] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat it to 50 °C in a water bath for 15 minutes. Add 0.32 g of cadmium sulfate (CdSO4) and stir until dissolved. After heating to 60 °C, add 21 mL of ammonia (NH3·H2O). Subsequently, quickly add 1.69 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Transfer the beaker and the sample to a 60 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0056] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, 600 cycles of deposition were performed at 120°C to form a dense TiO2 layer. After deposition, the sample was annealed at 200°C for 1 hour under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (TCS) structure.

[0057] (4) Electrochemical deposition and annealing of Cu layer: 0.05 g copper chloride (CuCl2) and 0.25 g ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL deionized water; stirred at room temperature for 30 minutes; an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode, at -0.8 V AgClElectrodeposition was performed for 900 seconds at a potential to uniformly deposit the Cu component on the TCS surface. The electrodeposited sample was annealed at 210°C for 30 minutes to obtain the final Cu / TCS multilayer photoelectrode structure. Comparative Example 3

[0058] This comparative example provides a preparation step of a Mo / TiO2 / CdS / Sb2S3 photocathode: (1) Preparation of Sb2S3 semiconductor: Weigh 2.67 g potassium antimonyltartrate and 2.53 g anhydrous sodium thiosulfate, dissolve them in 100 mL deionized water, and fully dissolve them under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reactor. Place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonicate the reactor for 10 minutes at room temperature to enhance the contact and adsorption between the precursor and the substrate. Place the reactor in a 135 °C oven and heat for 5 hours. After the reaction is completed, cool it naturally in the oven overnight to obtain the initial deposited film. Take out the deposited film and anneal it at 350 °C in a nitrogen atmosphere for 20 minutes to obtain a dense and uniform Sb2S3 semiconductor film.

[0059] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat it to 50 °C in a water bath for 15 minutes. Add 0.32 g of cadmium sulfate (CdSO4) and stir until dissolved. After heating to 60 °C, add 21 mL of ammonia (NH3·H2O). Subsequently, quickly add 1.69 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 film (substrate facing down) in the reaction solution. Transfer the beaker and the sample to a 60 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0060] (3) Deposition of the TiO2 layer (atomic layer deposition, ALD): Using titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source, 600 cycles of deposition were performed at 120°C to form a dense TiO2 layer. After deposition, the sample was annealed at 200°C for 1 hour under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (TCS) structure.

[0061] (4) Electrochemical deposition and annealing of Mo layer: 0.24 g sodium molybdate (Na2MoO4) and 0.25 g ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL deionized water; stirred at room temperature for 30 minutes; an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode, at -0.8 V AgCl Electrodeposition was performed at a potential of 900 seconds to uniformly deposit the Mo component on the TCS surface. The electrodeposited sample was annealed at 210°C for 30 minutes to obtain the final Mo / TCS multilayer photoelectrode structure. Example 6

[0062] This embodiment provides an unbiased coupled photoelectrochemical system, including a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell includes a cathode reaction cell and an anode reaction cell, the cathode reaction cell uses the CuMo / TiO2 / CdS / Sb2S3 photocathode prepared in Example 1 as the cathode, and the anode reaction cell uses a Bi2O3 / Pt anode as the anode.

[0063] The preparation steps of Bi2O3 / Pt anode are as follows: (1) Commercial nickel foam (NF) was ultrasonically cleaned, then washed with deionized water, ethanol, and acetone, and dried for later use. The cleaned nickel foam was immersed in 3 mL of deionized water; 0.5 mL of 120 mM chloroplatinic acid solution (H2PtCl6·6H2O) and 15 μL of concentrated hydrochloric acid (HCl) were added in sequence; 30 mg of polyvinylpyrrolidone (PVP) was added; and the mixture was gently stirred until all dissolved to form a uniform solution. The above reaction system was placed in a constant temperature oven at 54 °C for 6 hours. After the reaction was completed, a black deposit was observed on the electrode surface. The obtained electrode was removed, rinsed thoroughly with deionized water, dried, and annealed at 450 °C in air for 2 hours to obtain a Pt electrode.

[0064] (2) Dissolve 0.5 mmol of bismuth nitrate (Bi(NO₃)₃·5H₂O) in a mixture of 30 mL of deionized water and 15 mL of ethylene glycol and stir until the solution is clear. A three-electrode system is used, with the aforementioned Pt electrode as the working electrode and Ag / AgCl as the reference electrode. Electrodeposition is performed at a potential of -0.6 V for 10 minutes to complete the deposition of Bi. After deposition, the electrode is removed and annealed at 450°C in air for 2 hours to obtain a Bi₂O₃ / Pt electrode. Example 7

[0065] This embodiment provides an unbiased coupled photoelectrochemical system, including a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell includes a cathode reaction cell and an anode reaction cell, the cathode reaction cell uses the CuMo / TiO2 / CdS / Sb2S3 photocathode prepared in Example 1 as the cathode, and the anode reaction cell uses a Bi2O3 / Pt anode as the anode.

[0066] The preparation steps of Bi2O3 / Pt anode are as follows: (1) Commercial nickel foam (NF) was ultrasonically cleaned, then washed with deionized water, ethanol, and acetone, and dried for later use. The cleaned nickel foam was immersed in 2.9 mL of deionized water; 0.45 mL of 110 mM chloroplatinic acid solution (H2PtCl6·6H2O) and 10 μL of concentrated hydrochloric acid (HCl) were added in sequence; 24 mg of polyvinylpyrrolidone (PVP) was added; and the mixture was gently stirred until all dissolved to form a uniform solution. The above reaction system was placed in a constant temperature oven at 50°C for 5.5 hours. After the reaction was completed, a black deposit was observed on the electrode surface. The obtained electrode was removed, rinsed thoroughly with deionized water, dried, and annealed at 400°C in air for 2.5 hours to obtain a Pt electrode.

[0067] (2) Dissolve 0.36 mmol of bismuth nitrate (Bi(NO₃)₃·5H₂O) in a mixture of 33 mL of deionized water and 12 mL of ethylene glycol and stir until the solution is clear. A three-electrode system is used, with the aforementioned Pt electrode as the working electrode and Ag / AgCl as the reference electrode. Electrodeposition is performed at a potential of -0.6 V for 10 minutes to complete the deposition of Bi. After deposition, the electrode is removed and annealed at 400°C in air for 2.5 hours to obtain a Bi₂O₃ / Pt electrode. Example 8

[0068] This embodiment provides an unbiased coupled photoelectrochemical system, including a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell includes a cathode reaction cell and an anode reaction cell, the cathode reaction cell uses the CuMo / TiO2 / CdS / Sb2S3 photocathode prepared in Example 1 as the cathode, and the anode reaction cell uses a Bi2O3 / Pt anode as the anode.

[0069] The preparation steps of Bi2O3 / Pt anode are as follows: (1) Commercial nickel foam (NF) was ultrasonically cleaned, then washed with deionized water, ethanol, and acetone, and dried for later use. The cleaned nickel foam was immersed in 3.1 mL of deionized water; 0.55 mL of 130 mM chloroplatinic acid solution (H2PtCl6·6H2O) and 15 μL of concentrated hydrochloric acid (HCl) were added in sequence; 36 mg of polyvinylpyrrolidone (PVP) was added; and the mixture was gently stirred until all the solution was dissolved to form a uniform solution. The above reaction system was placed in a constant temperature oven at 53°C for 6 hours. After the reaction was completed, a black deposit was observed on the electrode surface. The obtained electrode was removed, rinsed thoroughly with deionized water, dried, and annealed at 480°C in air for 2 hours to obtain a Pt electrode.

[0070] (2) Dissolve 0.44 mmol of bismuth nitrate (Bi(NO₃)₃·5H₂O) in a mixture of 27 mL of deionized water and 18 mL of ethylene glycol and stir until the solution is clear. A three-electrode system is used, with the aforementioned Pt electrode as the working electrode and Ag / AgCl as the reference electrode. Electrodeposition is performed at a potential of -0.6 V for 10 minutes to complete the deposition of Bi. After deposition, the electrode is removed and annealed at 480°C in air for 1.5 hours to obtain a Bi₂O₃ / Pt electrode. Example 9

[0071] This embodiment provides an unbiased coupled photoelectrochemical system, including a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell includes a cathode reaction cell and an anode reaction cell, the cathode reaction cell uses the CuMo / TiO2 / CdS / Sb2S3 photocathode prepared in Example 1 as the cathode, and the anode reaction cell uses a Bi2O3 / Pt anode as the anode.

[0072] The preparation steps of Bi2O3 / Pt anode are as follows: (1) Commercial nickel foam (NF) was ultrasonically cleaned, then washed with deionized water, ethanol, and acetone, and dried for later use. The cleaned nickel foam was immersed in 3 mL of deionized water; 0.55 mL of 125 mM chloroplatinic acid solution (H2PtCl6·6H2O) and 20 μL of concentrated hydrochloric acid (HCl) were added in sequence; 27 mg of polyvinylpyrrolidone (PVP) was added; and the mixture was gently stirred until all the solution was dissolved to form a uniform solution. The above reaction system was placed in a constant temperature oven at 55°C for 5.5 hours. After the reaction was completed, a black deposit was observed on the electrode surface. The obtained electrode was removed, rinsed thoroughly with deionized water, dried, and annealed at 440°C in air for 2 hours to obtain a Pt electrode.

[0073] (2) Dissolve 0.5 mmol of bismuth nitrate (Bi(NO₃)₃·5H₂O) in a mixture of 27 mL of deionized water and 18 mL of ethylene glycol and stir until the solution is clear. A three-electrode system is used, with the aforementioned Pt electrode as the working electrode and Ag / AgCl as the reference electrode. Electrodeposition is performed at a potential of -0.6 V for 10 minutes to complete Bi deposition. After deposition, the electrode is removed and annealed at 470°C in air for 1.8 hours to obtain a Bi₂O₃ / Pt electrode. Example 10

[0074] This embodiment provides an unbiased coupled photoelectrochemical system, including a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell includes a cathode reaction cell and an anode reaction cell, the cathode reaction cell uses the CuMo / TiO2 / CdS / Sb2S3 photocathode prepared in Example 1 as the cathode, and the anode reaction cell uses a Bi2O3 / Pt anode as the anode.

[0075] The preparation steps of Bi2O3 / Pt anode are as follows: (1) Commercial nickel foam (NF) was ultrasonically cleaned, then washed with deionized water, ethanol, and acetone, and dried for later use. The cleaned nickel foam was immersed in 3 mL of deionized water; 0.55 mL of 125 mM chloroplatinic acid solution (H2PtCl6·6H2O) and 20 μL of concentrated hydrochloric acid (HCl) were added in sequence; 27 mg of polyvinylpyrrolidone (PVP) was added; and the mixture was gently stirred until all the solution was dissolved to form a uniform solution. The above reaction system was placed in a constant temperature oven at 55°C for 5.5 hours. After the reaction was completed, a black deposit was observed on the electrode surface. The obtained electrode was removed, rinsed thoroughly with deionized water, dried, and annealed at 440°C in air for 2 hours to obtain a Pt electrode.

[0076] (2) Dissolve 0.4 mmol of bismuth nitrate (Bi(NO₃)₃·5H₂O) in a mixture of 30 mL of deionized water and 15 mL of ethylene glycol and stir until the solution is clear. A three-electrode system is used, with the aforementioned Pt electrode as the working electrode and Ag / AgCl as the reference electrode. Electrodeposition is performed at a potential of -0.6 V for 10 minutes to complete the deposition of Bi. After deposition, the electrode is removed and annealed at 430°C in air for 1.8 hours to obtain a Bi₂O₃ / Pt electrode. Comparative Example 4

[0077] This comparative example provides an unbiased coupled photoelectrochemical system, including a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell includes a cathode reaction cell and an anode reaction cell, the cathode reaction cell uses the CuMo / TiO2 / CdS / Sb2S3 photocathode prepared in Example 1 as the cathode, and the anode reaction cell uses a Pt anode as the anode.

[0078] The preparation steps of Pt anode are as follows: Commercial nickel foam (NF) was ultrasonically cleaned, rinsed sequentially with deionized water, ethanol, and acetone, and dried for later use. The cleaned nickel foam was immersed in 3 mL of deionized water. 0.5 mL of a 120 mM chloroplatinic acid solution (HPtCl6·6H2O) and 15 μL of concentrated hydrochloric acid (HCl) were added sequentially. 30 mg of polyvinylpyrrolidone (PVP) was then added and gently stirred until completely dissolved to form a homogeneous solution. The reaction system was placed in a thermostatic oven at 54°C for 6 hours. After the reaction was complete, a black deposit was observed on the electrode surface. The resulting electrode was removed, rinsed thoroughly with deionized water, dried, and annealed at 450°C in air for 2 hours to obtain a Pt electrode. Comparative Example 5

[0079] This comparative example provides an unbiased coupled photoelectrochemical system, including a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell includes a cathode reaction cell and an anode reaction cell, the cathode reaction cell uses the CuMo / TiO2 / CdS / Sb2S3 photocathode prepared in Example 1 as the cathode, and the anode reaction cell uses a Bi2O3 anode as the anode.

[0080] The preparation steps of Bi2O3 anode are as follows: 0.5 mmol of bismuth nitrate (Bi(NO₃)₃·5H₂O) was dissolved in a mixture of 30 mL of deionized water and 15 mL of ethylene glycol and stirred until clear. A three-electrode system was used, with NF as the working electrode and Ag / AgCl as the reference electrode. Bi was deposited by electrodeposition at a potential of -0.6 V for 10 minutes. After deposition, the electrode was removed and annealed at 450°C in air for 2 hours to obtain a Bi₂O₃ electrode. Implementation effect example 1

[0081] Scanning electron microscopy (SEM) observations of the CuMo / TiO2 / CdS / Sb2S3 prepared in Example 1, the TiO2 / CdS / Sb2S3 prepared in Comparative Example 1, the Cu / TiO2 / CdS / Sb2S3 prepared in Comparative Example 2, and the Mo / TiO2 / CdS / Sb2S3 prepared in Comparative Example 3 revealed that the grain size of Sb2S3 was approximately 2.5 μm. Mo / TCS exhibited a shell-like morphology, and both Cu and CuMo exhibited nanoparticle characteristics on the semiconductor surface, with the CuMo particle size ranging from 200 to 500 nm ( Figure 1 Cross-sectional transmission electron microscopy (TEM) images of CuMo / TCS show that the interfaces between the CuMo, CdS, TiO2, and Sb2S3 layers are very clear. The thicknesses of the Sb2S3, CdS, and TiO2 layers are ~2.5 μm, ~50 nm, and ~60 nm, respectively ( Figure 2 In addition, both CuMo and Cu exhibit nanocrystalline features, while the Mo catalyst exhibits an amorphous structure (Figure 2b). The lattice spacing of the CuMo catalyst is 0.246 nm, corresponding to the (111) crystal plane of Cu2O ( Figure 2 (c), slightly larger than the 0.243 nm of the Cu catalyst, which may be due to the addition of Mo atoms in the Cu2O lattice. The lattice spacing of the (211) and (111) planes of Sb2S3 and CdS are 0.305 and 0.335 nm, respectively ( Figure 2dg), which is similar to the fast Fourier transform Figure 1 Energy dispersive X-ray spectroscopy (EDX) elemental mapping showed that Sb2S3 was surrounded by CdS and TiO2 layers, and Cu and Mo were uniformly distributed throughout the CuMo catalyst ( Figure 2 Middle h).

[0082] The summary of ICP-OES analysis results of copper and molybdenum in CuMo / TiO2 / CdS / Sb2S3 prepared in Example 1 is shown in Table 1: Table 1 Summary of ICP-OES analysis results of copper and molybdenum in CuMo / TCS

[0083] From the ICP analysis in Table 1, we can see that the atomic ratio of copper to molybdenum is about 3:1; XPS analysis confirms the presence of copper, molybdenum and oxygen ( Figure 3 ), where Cu 2p and Cu LMM spectra show Cu 0 、Cu + and Cu 2+ mixture (Cu 0 can be ignored), while Mo is mainly Mo 6+ Based on these results, considering the observed oxidation states of copper and molybdenum, if all the Cu in the catalyst is in the +2 state and Mo is in the form of Mo 6+ Alternatively, if the copper is predominantly in the +1 state, the corresponding stoichiometry is approximately Cu3MoO6. 4.5 Given that Cu + and Cu 2+ The two substances coexist, and the actual composition may be between the two situations. Implementation effect example 2

[0084] Photoelectrochemical measurements were performed in a closed H-cell using a three-electrode system with a CuMo / TCS working electrode, an Ag / AgCl reference electrode, and a platinum foil counter electrode. A Nafion 117 membrane separated the working and counter electrodes. The electrolyte consisted of 0.5 M KNO₃ and 0.5 M KHCO₃. CO₂ reduction measurements were performed at various applied potentials for 0.5 h. Prior to the test, the working electrode chamber was purged with CO₂ at a rate of 30 ml / min for at least 30 min. Illumination was provided by an AM 1.5G simulator with a power of 100 mW cm⁻¹. -2The recorded potential is based on an Ag / AgCl reference electrode and can be converted to the reversible hydrogen electrode (RHE) scale using the Nernst equation: E RHE =E (Ag / AgCl) +0.197+0.0591*pH. Ammonia production was quantified using the indophenol blue method. The chromogenic reagents were as follows: (a) 1 M NaOH solution containing 5 wt% sodium citrate and 5 wt% salicylic acid; (b) 0.05 M sodium hypochlorite solution; and (c) 1 wt% sodium nitroferricyanide solution. A 1 mL electrolyte sample was extracted and mixed sequentially with 1 mL of reagent (a), 0.5 mL of reagent (b), and 0.1 mL of reagent (c). The resulting mixture was stored in the dark for 2 hours before measuring absorbance. Urea concentration was determined using the urease hydrolysis method. A precursor solution was prepared by dissolving 0.5 g of EDTA-Na2 and 2.46 g of K2HPO4 in 500 mL of deionized water. 7 mg of urease was then dissolved in the precursor solution, and 3.2 mL of catholyte was added. The mixture was thoroughly homogenized and incubated at 50°C for 1 hour. The NH3 concentration in the electrolyte without urease was determined using the indophenol blue method. The amount of urea produced (N urea ) is (N urease -N ammonia ) / 2, where N urease and N ammonia represents the molar amount of ammonia in the presence and absence of urease, respectively. The FE for urea synthesis is calculated using the following formula: FE = (n*F*C*V) / (60.06*Q), where F is the Faraday constant, Q is the total charge passed during the electrolysis process, C is the concentration of urea produced, V is the volume of the electrolyte, and n is the number of electrons transferred in the electrochemical reaction. For the electrochemical coupling of CO2 and nitrate, n is 16. To detect nitrite (NO2 - Prepare a colorimetric reagent by dissolving 2 g of aminosulfonic acid and 0.1 g of N-(1-naphthyl)ethylenediamine dihydrochloride in an appropriate solvent. Mix 0.5 mL of the sample in the cathode compartment with 2 mL of deionized water and 0.1 mL of the prepared colorimetric reagent. After 20 minutes of reaction, measure the absorbance at 540 nm.

[0085] To investigate the performance of the photocathode in urea synthesis, we performed photoelectrochemical measurements. When switching the electrolyzer atmosphere from Ar to CO2, the current density of CuMo / TCS increases over the potential range ( Figure 4 (a) This indicates that additional CO2 reduction-related reactions occurred. Figure 4Figure b shows the linear sweep voltammetry (LSV) curves of the photocathode in 0.5 M KHCO3 + 0.5 M KNO3 and CO2 bubbles. Among these samples, CuMo / TCS has the best PEC performance, with a peak at 0 V. RHE The photocurrent density is -3.98 mA cm -2 , exceeding the Cu / TCS (-2.62 mA cm -2 )、Mo / TCS(-1.46 mA cm -2 ) and TCS (−0.39 mA cm -2 The onset potential of CuMo / TCS (0.98 V RHE ) is much lower than Cu / TCS (0.87 V RHE )、Mo / TCS(0.76 V RHE ) and TCS (0.52 V RHE ).like Figure 4 As shown in c, CuMo / TCS at 0.4 V RHE The urea FE value is as high as 73.3% at 0.15 V and 0 V, while Cu / TCS and Mo / TCS have the same FE value at 0.15 V and 0 V. RHE The maximum FE values ​​at 400 nm and 800 nm are 49.90% and 36.23%, respectively. The potential for achieving the optimal FE of urea on CuMo / TCS is more anodic than that on Cu / TCS and Mo / TCS.

[0086] NO3 - Reduced to by-products (such as NO2 - or NH3) usually limits NO3 - and the electrocatalytic conversion efficiency of CO2 to urea. We further studied the FEs of nitrogen-containing products on CuMo / TCS ( Figure 5 (a). At 0.45-0.25 V RHE In the low potential range, most of NO3 - Reacts with CO2 to form urea. However, as the potential becomes more negative, both the urea FE and nitrogen selectivity decrease due to the emergence of more favorable competing reactions. CuMo / TCS was also measured under continuous stirring and intermittent lighting conditions with 100-second light-dark intervals to simulate intermittent solar irradiation. In an electrolyte with a pH of 7, the current density of CuMo / TCS dropped to 80% of its initial value within 4 hours ( Figure 5 (b). For long-term urea synthesis of photoelectrodes ( Figure 5In Figure c), no significant decrease in current density was detected over the eight cycles because the electrolyte was replaced every 0.5 h. The urea FE remained above 65%, and the urea yield also remained constant, averaging 86.01 μg cm per cycle. -2 .

[0087] In situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to identify key intermediates on the photocathode during the PEC urea synthesis process. For CuMo / TCS, the potential was changed from 0.8 to 0 V under light irradiation. RHE Clear infrared signals can be observed ( Figure 6 (a), while no characteristic peaks were detected under dark conditions, confirming the important role of photogenerated charge carriers in the reaction process. The peaks at 1160, 1380, and 1667 cm⁻¹ correspond to NH₂ intermediates, CO₂NH₂ intermediates, and COOHNH₂ intermediates, respectively, indicating the presence of key CN coupling intermediates. Notably, no obvious CO intermediate band was detected, indicating that the CO intermediate is not involved in the CN coupling pathway. When the potential is increased from 0.8 to 0 V, the reaction is carried out under dark conditions. RHE These scaling modes gradually increase with the change of potential, indicating that the generation of PEC urea on CuMo / TCS is effective. In addition, the peak at ~1717 cm -1 A peak corresponding to amide (O=C-NH2) appears at RHE 1404 cm -1 The OCO intermediate band at is identified, which means that the amount of CO2 adsorbed increases but is not converted into urea in time. On the other hand, Cu / TCS shows a strong NH2 intermediate band, and Mo / TCS has a strong COOHNH2 intermediate signal. At the same time, both show weak NCN vibrations ( Figure 6 Middle b, Figure 6 This indicates that the conversion of the NH2 intermediate to urea is very inefficient on Cu / TCS, while on Mo / TCS, the further conversion of the COOHNH2 intermediate is hindered due to the lack of cooperative CN coupling sites. Implementation effect example 3

[0088] To improve the charge transfer rate at the anode and simultaneously produce high-value-added products, we designed a Bi2O3-modified platinum catalyst (called Bi2O3 / Pt) for the electrochemical glycerol oxidation reaction (GOR) during the preparation of an unbiased coupled photoelectrochemical system. Scanning electron microscopy (SEM) observations of the Bi2O3 / Pt photoanode prepared in Example 6 and the Pt photoanode prepared in Comparative Example 1 revealed that the Bi2O3 / Pt sample contained approximately 10-nanometer platinum nanoparticles at the bottom and irregular worm-like Bi2O3 ( Figure 7 In the TEM image of Bi2O3 / Pt, a heterogeneous interface can be observed, with lattice spacings of 0.230 nm and 0.311 nm, corresponding to the (111) plane of Pt and the (111) plane of Bi2O3, respectively ( Figure 7 b). EDS elemental mapping shows that oxygen is mainly associated with Bi ( Figure 7 Middle c). Implementation effect example 4

[0089] Electrochemical measurements were performed in a closed H-type cell using a three-electrode system. The working electrodes were the Bi2O3 / Pt anode prepared in Example 6, the Pt anode prepared in Comparative Example 4, and the Bi2O3 anode prepared in Comparative Example 5. The reference electrode was Hg / HgO, and the counter electrode was platinum foil. The electrolyte consisted of 1 M KOH and 0.5 M glycerol. The measured Hg / HgO potential was converted to RHE using the following formula: E RHE =E (Hg / HgO) +0.098+0.0591*pH. We evaluated the electrochemical activities of Pt electrode, Bi2O3 / Pt electrode and Bi2O3 electrode in 1 M KOH containing 0.5 M glycerol. Figure 8 As shown in a, at 0.8V RHE Under these conditions, the current density of Bi2O3 / Pt reached 406.7 mA cm -2 , compared with Pt (215.8 mA cm -2 ) and Bi2O3 (21.4 mA cm -2 ) are about 1.9 times and 19 times higher, respectively. In addition, the overpotential of Bi2O3 / Pt prepared in Example 6 for GOR is about 0.23 V RHE, which is significantly lower than the overpotential of the oxygen evolution reaction in the absence of glycerol. The exposed Bi2O3 facilitates the adsorption of OH intermediates, thereby reducing the kinetic barrier of glycerol oxidation and promoting a lower onset potential, which is crucial for constructing an unassisted PEC device coupled with a photocathode. By high-performance liquid chromatography analysis, glyceric acid (GLA) is the main product of glycerol oxidation on Bi2O3 / Pt, with a peak at 0.3 V. RHE The selectivity is 68.84% ( Figure 8 b). At 0.3-0.8 V RHE The total selectivity of C3 products (including GLA, lactic acid, and tartaric acid) exceeded 90% over a wide potential range. RHE The maximum value reaches 98.58%. In addition, at 0.8 V RHE When the platinum electrode has a selectivity of only 47.3% for C3 products ( Figure 8 (c) The maximum C3 yield of Bi2O3 / Pt was 2.96 mmol cm -2 h -1 , compared with the Pt electrode prepared in Comparative Example 4 (0.98 mmol cm -2 h -1 ) is about three times higher. In addition, in the 10-hour cycle test, Bi2O3 / Pt RHE Maintain a stable current density ( Figure 8 More importantly, the selectivity of C3 products remained above 95% in each cycle, and the productivity was stable at ~2 mmol cm -2 h -1 ( Figure 8 These are attributed to the synergistic effect between Bi2O3 and Pt, in which Bi2O3 promotes the efficient and continuous formation of C3 products. Implementation effect example 5

[0090] The simultaneous production of urea and high-value-added anode products under bias-free conditions remains a significant challenge, primarily due to the high overpotential required for urea synthesis. Therefore, we designed for the first time the integration of a CuMo / TCS photocathode with a Bi2O3 / Pt anode for the production of high-value unassisted PEC urea and C3 products ( Figure 9 In a) the unbiased coupled photoelectrochemical system prepared in Example 6 is used as an example. It is worth noting that the CuMo / TCS||Bi2O3 / Pt system is CE The photocurrent density is -4.05 mA cm -2 ( Figure 9(b) This is due to the internal chemical deviation caused by the pH gradient between the two compartments of the cell. At the same time, its photocurrent density exceeds the OER and GOR values ​​of the PEC cell with platinum foil (CuMo / TCS || platinum foil) as the anode. CE and -0.07 mA cm -2 and −1.91 mA cm -2 (Figure 9b). This indicates that the CuMo / TCS || Bi2O3 / Pt system has a high charge transfer efficiency in the symbiosis of urea and C3. In addition, after 3 hours of stable operation under solar irradiation, the current density of the unassisted PEC system still remains at about 85% of the initial value ( Figure 9 (c) After six cycles, the unbiased urea FE decreased from 52.83% to 48.63%, and the average urea yield was 126.76 μg cm -2 ( Figure 9 Meanwhile, the selectivity of GLA remained at around 74.1–75.3%, the selectivity of total C3 products exceeded 98%, and the average C3 yield per cycle was 35 μmol cm -2 ( Figure 9 Middle e). Implementation Effect Example 6

[0091] In addition, we designed a large-scale unbiased PEC system to evaluate the feasibility of producing urea and C3 chemicals under real sunlight conditions ( Figure 10 a) Take the system of Example 6 as an example, and design photocathodes of different sizes ( Figure 10 In laboratory tests, a PEC device with a photodiode area of ​​4 square centimeters produced a total current of 10.95 mA ( Figure 10 Under different test conditions, the Faradaic efficiency of urea and the selectivity of C3 chemicals are basically consistent ( Figure 10 The yields of urea and C3 chemicals reached 707.17 μg h -1 and 197.13 μmol h -1 Expanding the photoelectrode area to 12 cm 2 After that, the system generated a total current of 24.86 mA under outdoor conditions, and the production of urea and C3 chemicals was 1319.68 μg h -1 and 381.48 μmol h -1 ( Figure 10 We also evaluated the economic feasibility under actual sunlight conditions ( Figure 10The system generates 0.94× 10 -6 US dollars and 1062.13 × 10 -6 The system provides experimental verification for the unbiased electrochemical synthesis of urea and C3 products and has potential practical application value.

[0092] In summary, the present invention has constructed a CuMo / TCS photocathode for selective synthesis of urea. The onset potential of the photocathode is very low, only 0.98 V RHE , at 0.4 V RHE The FE of urea was 73.3% when the urea was prepared. In situ characterization and theoretical calculations confirmed that the key intermediate COOHNH2 exhibited the lowest energy barrier in the dehydroxylation step, thus achieving efficient PEC urea production on CuMo / TCS. RHE Over a wide potential range, the Bi2O3 / Pt anode of this application exhibits a selectivity of over 90% for C3 products. Importantly, we constructed a CuMo / TCS || Bi2O3 / Pt unbiased coupled photoelectrochemical system that achieved 4.05 mA cm under simulated illumination of one sun. -2 In addition, under real light irradiation, the urea yield of the large-sized photoelectrode was 1319.68 μg h -1 The chemical yield of C3 was 381.48 μmol h -1 This work not only advances research on PEC urea synthesis but also provides experimental validation for the development of unbiased PEC devices for converting solar energy into high-value chemicals.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a CuMo / TiO2 / CdS / Sb2S3 photocathode, characterized in that: The steps are: (1) Preparing a precursor solution containing potassium antimony tartrate and anhydrous sodium thiosulfate, placing a fluorine-doped tin oxide substrate in the precursor solution, performing a heating reaction in a reactor after ultrasonic treatment, and cooling the substrate naturally after the reaction to obtain an initial deposited film. The initial deposited film is subjected to annealing reaction I to obtain a Sb2S3 semiconductor thin film; (2) preparing a reaction solution containing cadmium sulfate, ammonia water and thiourea, then immersing the Sb2S3 semiconductor film in step (1) in the reaction solution, and reacting at a constant temperature to obtain a CdS / Sb2S3 heterojunction; (3) The CdS / Sb2S3 heterojunction prepared in step (2) is placed in a vacuum chamber with tetrakis(dimethylamino)titanium as a titanium source and deionized water as a water source for atomic layer deposition. After the deposition is completed, annealing reaction II is performed to obtain a TiO2 / CdS / Sb2S3 structure, which is denoted as TCS. (4) Prepare a deionized water solution containing copper chloride, sodium molybdate, and ammonium oxalate, stir, and add polyethylene glycol to obtain a deposition solution, perform electrochemical deposition using the TCS of step (3) as a working electrode and Ag / AgCl as a reference electrode, and anneal the obtained deposited sample to obtain a CuMo / TiO2 / CdS / Sb2S3 photocathode through reaction III.

2. The method for preparing the CuMo / TiO2 / CdS / Sb2S3 photocathode according to claim 1, wherein: In the step (1), the mass ratio of potassium antimony tartrate to anhydrous sodium thiosulfate is 2.4-2.8:2.3-2.7; the temperature of the heating reaction is 130-140° C. and the time is 4.5-5.5 h; the atmosphere of the annealing reaction I is nitrogen, the temperature is 340-360° C., and the time is 18-22 min; in the step (2), the concentration of cadmium sulfate in the reaction solution is 3.0-3.4 mg / mL, the volume concentration of ammonia water is 19-23% v / v, and the concentration of thiourea is 16.5-17.5 mg / mL; the temperature of the isothermal reaction is 55-65° C. and the time is 13-17 min.

3. The method for preparing the CuMo / TiO2 / CdS / Sb2S3 photocathode according to claim 2, wherein: In step (3), the temperature of atomic layer deposition is 115-125°C, and the number of cycles is 600 times; the atmosphere of annealing reaction II is nitrogen, the temperature is 195-205°C, and the time is 0.8-1.2 hours; in step (4), the concentration of copper chloride is 0.08-0.12 mg / mL, the concentration of sodium molybdate is 4.6-5.0 mg / mL, and the concentration of ammonium oxalate is 4.5-5.5 mg / mL; the potential of electrochemical deposition is -0.8 V AgCl The potential and deposition time are 600~1200s; the temperature of annealing reaction III is 200~220℃ and the time is 25~35min.

4. A CuMo / TiO2 / CdS / Sb2S3 photocathode prepared by the method according to any one of claims 1 to 3.

5. An unbiased coupled photoelectrochemical system comprising a reaction cell, a workstation, a stirring device, and a gas path device; the reaction cell comprises a cathode reaction cell and an anode reaction cell, characterized in that: The cathode reaction cell uses the CuMo / TiO2 / CdS / Sb2S3 photocathode described in claim 4 as the cathode.

6. The unbiased coupled photoelectrochemical system according to claim 5, characterized in that: The anode reaction cell uses a Bi2O3 / Pt anode as the anode; the preparation steps of the Bi2O3 / Pt anode are as follows: a. Nickel foam was immersed in deionized water, followed by the addition of chloroplatinic acid solution and concentrated hydrochloric acid solution, and finally polyvinylpyrrolidone. The solution was stirred until a homogeneous solution was formed. The solution was allowed to stand and heated to obtain a black precipitate. The black precipitate was annealed in reaction IV to obtain a Pt electrode. b. Prepare a mixed solution of bismuth nitrate as a deposition solution, using the Pt electrode of step a as the working electrode and Ag / AgCl as the reference electrode for electrochemical deposition. The deposited electrode was annealed to obtain a Bi2O3 / Pt anode.

7. The unbiased coupled photoelectrochemical system according to claim 6, wherein: In step a, the volume ratio of ionized water, chloroplatinic acid solution, and concentrated hydrochloric acid solution is 2.9-3.1:0.45-0.55:0.01-0.02; the concentration of the chloroplatinic acid solution is 110-130 mM; 8-12 mg of polyvinyl pyrrolidone is added per mL of deionized water; the static heating temperature is 50-55° C. and the time is 5.5-6.5 hours; the mixed solution in step b is a mixed solution of deionized water and ethylene glycol in a volume ratio of 1.8-2.2:0.8-1.2; and the concentration of bismuth nitrate is 0.008-0.012 mmol / mL.

8. Use of the unbiased coupled photoelectrochemical system according to any one of claims 5 to 7, characterized in that: The application is selected from any one of the following: ① Producing C3 chemicals at the anode; ②Urea is produced at the cathode.

9. The use of the unbiased coupled photoelectrochemical system according to claim 8, characterized in that: The conditions for the application are 50-200 mW cm -2 Bias-free coupled photoelectrochemical system under sunlight irradiation.

Images