A bias-free coupling photoelectrochemical system, a preparation method and application of an anode and a cathode thereof

Abstract

The application belongs to the field of photoelectrochemistry, and relates to a bias-free coupled photoelectrochemical system and a preparation method and application of an anode and a cathode thereof. The CuMo / TCS photo-cathode constructed by the application realizes synthesis of solar-driven urea from nitrate-containing wastewater and carbon dioxide at an ultra-low potential, thereby optimizing photo-generated charge transport and reducing the energy potential barrier of the COOHNH2 intermediate dehydroxylation. The bias-free coupled photoelectrochemical system of the CuMo / TCS photo-cathode and the Bi2O3 / Pt anode is successfully constructed, the Bi2O3 / Pt is used as an anode electrocatalyst, and the anode reaction is endowed with additional high-value product output. Under real sunlight, the urea yield of a 12cm 2 2 large-area photoelectrode reaches 1319.68ug h ‑1 1, the C3 product yield is 381.48umol h ‑1 1, and the application has potential practical application value.

Description

Technical Field

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

[0002] Urea (CO(NH2)2) is a crucial basic chemical product with a global annual 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 primarily relies on the Bosch-Meiser process, which requires high temperatures (150-200°C) and high pressures (150-250 bar). This process not only consumes approximately 80% of industrial ammonia production but also contributes about 1% of global carbon dioxide emissions. Therefore, developing efficient and sustainable urea synthesis methods has become one of the key issues urgently needing to be addressed in the chemical industry.

[0003] In recent years, the photoelectrochemical (PEC) method, driven by renewable energy, has emerged as a new pathway for the high-value utilization of carbon and nitrogen resources and for energy conservation and emission reduction. This method utilizes NO3... - Coupled with CO2 and converted to urea under solar energy, this process not only effectively treats nitrate-containing wastewater but also achieves resource utilization of greenhouse gases, resulting in significant environmental and economic benefits. Existing research indicates that regulating reaction conditions and constructing a synergistic catalytic system can enhance the conversion of CO2 and NO3 in the PEC system. - The CN coupling efficiency. For example, Wang et al. constructed a NiFe diatomic catalyst / TiO2 layer / nanostructure n + The p-Si photocathode achieved a Faraday efficiency (FE) of 24.2% (Proc. Natl. Acad. Sci. USA 2024, 121, e2311326121); the Mi team, on the other hand, achieved an n-Si photocathode. + Ag catalyst supported on p-Si-based GaN nanowire photocathode at -0.3V RHE Achieving an FE of up to 75.6% is attributed to the high efficiency of NO2 and COO2. - Effective CN coupling between intermediates (ACS Catal. 2024, 14, 2588-2596). Furthermore, Duan et al. used cubic Cu₂O as the photocathode material at -0.017 V. RHE 29.71 μmol g was achieved. -1 h -112.9% FE (Angew. Chem. Int. Ed. 2024, 63, e202406515). However, the current high-efficiency PEC synthesis of urea still faces many challenges. First, achieving high-selectivity C-N coupling at low potential is still limited by the insufficient reaction selectivity on the catalyst surface and the low charge transport efficiency of the semiconductor material. Second, most traditional PEC urea synthesis systems rely on an external bias, and the anode reaction is mainly the slow oxygen evolution reaction (OER), which severely limits the overall energy efficiency and product value-added of the system. Therefore, building a bias-free PEC system without an external bias, and realizing the coordinated production of high-value chemicals at the anode and the cathode, is a fundamental challenge to realize the direct solar-driven high-efficiency synthesis of urea. SUMMARY

[0004] To solve the above technical problems, the present application provides a bias-free coupled photoelectrochemical system, and a preparation method and application of an anode and a cathode thereof.

[0005] The technical solution of the present application is as follows:

[0006] A preparation step of a CuMo / TiO2 / CdS / Sb2S3 photo-cathode is as follows:

[0007] (1) Preparation of Sb2S3 semiconductor: potassium antimonyl tartrate and anhydrous sodium thiosulfate are weighed and dissolved in deionized water, and a uniform precursor solution is formed under magnetic stirring. The above-mentioned precursor solution is placed in a reaction kettle, and a fluorine-doped tin oxide (FTO) conductive glass substrate is inclined and placed in the solution with the bottom facing down. The reaction kettle is ultrasonically treated at room temperature to enhance the contact and adsorption of the precursor and the substrate. The reaction kettle is placed in an oven for heating reaction, and after the reaction is completed, it is naturally cooled overnight in the oven to obtain an initial deposition film. The deposition film is taken out and annealed at 340~360℃ for 18~22min in a nitrogen atmosphere to obtain a dense and uniform Sb2S3 semiconductor thin film;

[0008] The mass ratio of potassium antimonyl tartrate and anhydrous sodium thiosulfate in step (1) is 2.4~2.8:2.3~2.7; the heating reaction temperature is 130~140℃, and the time is 4.5~5.5h.

[0009] (2) Chemical bath deposition (CBD) of CdS layer: Deionized water was added into a beaker and heated to 45-55 °C in a water bath for 12-16 min. Cadmium sulfate (CdSO4) was added and stirred until dissolved; after heating to 58-62 °C, ammonia (NH3·H2O) was added; thiourea (SC(NH2)2) was quickly added and continued to be stirred until completely dissolved. The Sb2S3 film (with the substrate facing down) was immediately immersed in the reaction solution. The beaker was moved into a constant temperature oven at 55-65 °C for 13-17 min, and a CdS layer was deposited to form a CdS / Sb2S3 heterojunction.

[0010] The concentration of cadmium sulfate in the reaction solution in step (2) is 3.0-3.4 mg / mL, the volume concentration of ammonia is 19-23% v / v, and the concentration of thiourea is 16.5-17.5 mg / mL.

[0011] (3) Deposition of TiO2 layer (atomic layer deposition, ALD): Titanium tetrakis(dimethylamino)titanate was used as the titanium source, and deionized water was used as the oxygen source. Deposition was carried out at 115-125 °C for 400-800 cycles to form a dense TiO2 layer. After deposition, the sample was annealed at 195-205 °C for 0.8-1.2 hours under an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (referred to as TCS) structure.

[0012] (4) Electrochemical deposition and annealing of CuMo layer: Copper chloride (CuCl2), sodium molybdate (Na2MoO4), and ammonium oxalate ((NH4)2C2O4) were dissolved in deionized water; stirring was carried out at room temperature for 25-35 min; an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film-forming performance of the film layer. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode. CuMo components were uniformly deposited on the surface of TCS by electrodeposition at a potential of -0.8 V AgCl for 900 seconds. The sample after electrodeposition was annealed at 200-220 °C for 25-35 min to obtain the final CuMo / TCS multilayer photoelectrode structure.

[0013] The concentration of copper chloride in step (4) 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.

[0014] The application discloses a bias-free coupling photoelectrochemical system, which comprises a reaction tank, a workstation, a stirring device and a gas path device; the reaction tank comprises a cathode reaction tank and an anode reaction tank; the cathode reaction tank takes a CuMo / TiO2 / CdS / Sb2S3 photo-cathode as a cathode, and the anode reaction tank takes a Bi2O3 / Pt anode as an anode; a proton exchange membrane is arranged between the reaction tanks; a cathode electrolyte is 0.5 M KHCO3 and 0.5 M KNO3 saturated with CO2; and an anode electrolyte is 1 M KOH and 0.5 M glycerol.

[0015] The preparation steps of the Bi2O3 / Pt anode are as follows:

[0016] a. Commercial nickel foam (Nickel Foam, NF) is cleaned by ultrasonic cleaning, and is sequentially cleaned by deionized water, ethanol and acetone, and is dried for standby. The cleaned nickel foam is immersed in deionized water; chloroplatinic acid solution (H2PtCl6·6H2O) and concentrated hydrochloric acid (HCl) are sequentially added; polyvinylpyrrolidone (PVP) is further added; and the mixture is gently stirred until a uniform solution is formed. The reaction system is placed in a constant temperature oven, and is statically placed at 50-55 DEG C for 5.5-6.5 hours. After the reaction is completed, black deposits are formed on the surface of the electrode. The obtained electrode is taken out, washed with deionized water, dried, and annealed at 400-480 DEG C in an air atmosphere for 1.5-2.5 hours to obtain a Pt electrode.

[0017] In the step a, the volume ratio of the deionized water, the chloroplatinic acid solution and the 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; and 8-12 mg of polyvinylpyrrolidone is added per mL of deionized water.

[0018] b. Bismuth nitrate (Bi(NO3)3·5H2O) is dissolved in a mixed solution of deionized water and ethylene glycol, and is stirred until clear. A three-electrode system is adopted, the above Pt electrode is used as a working electrode, and Ag / AgCl is used as a reference electrode; Bi is deposited by electrodeposition at a potential of-0.6 V for 10 minutes. After the deposition is completed, the electrode is taken out, and is annealed at 400-480 DEG C in an air atmosphere for 1.5-2.5 hours to obtain a Bi2O3 / Pt electrode.

[0019] In the step b, the mixed solution is a mixed solution of deionized water and ethylene glycol with 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.

[0020] The above bias-free coupling photoelectrochemical system generates glyceric acid, lactic acid, and C3 chemicals such as sub-rubidic acid at the anode, and urea at the cathode; the light irradiation condition is 50-200 mW cm -2 Solar light is irradiated.

[0021] The present application directly converts NO3 - and CO2 into urea by using solar energy, and the mechanism is as follows: under light irradiation, the CuMo / TiO2 / CdS / Sb2S3 photoanode reduces NO3 - to generate NH2 intermediate, and couples with CO2 intermediate to generate CO2NH2 intermediate. Protonation of the CO2NH2 intermediate further generates the key intermediate COOHNH2, and then dehydration and a second C-N coupling step of the COOHNH2 intermediate, efficiently and selectively produce PEC urea on the photoanode, wherein the path of COOHNH2 intermediate avoids the generation of CO intermediate, and improves the synthesis efficiency of urea.

[0022] The present application has the following beneficial effects:

[0023] (1) The CuMo / TCS photoanode constructed in the present application exhibits an ultra-low onset potential (0.98 V RHE ), and the urea Faraday efficiency (FE) is as high as 73.3% at 0.4 V RHE , and the urea yield can reach 264.79 μg cm RHE h -2 -1 -1 , which shows excellent electrocatalytic activity and product selectivity. Through in-situ characterization and theoretical calculation, it is confirmed that the dehydroxylation reaction of the key intermediate COOHNH2 on the surface of the CuMo / TCS photoanode has the lowest energy barrier, effectively improves the C-N coupling reaction efficiency, and provides a clear reaction path mechanism basis for the photoelectrosynthesis of urea.

[0024] (2) The present application successfully builds a bias-free coupling photoelectrochemical (PEC) system of CuMo / TCS photoanode and Bi2O3 / Pt anode, uses Bi2O3 / Pt as an anode electrocatalyst, and uses glycerol oxidation reaction (GOR) to replace the traditional oxygen evolution reaction (OER), which significantly reduces the anode onset potential to 0.23 V RHE , effectively reduces the energy consumption of the whole photoelectrochemical system, and gives the anode reaction an additional high-value product output. In the potential interval of 0.3-0.8 V RHE , the C3 chemical selectivity of glycerol oxidation products continuously remains above 90%, and the highest is 98.58%. Under the simulated light irradiation condition of one sun, the bias-free coupling photoelectrochemical (PEC) system realizes-4.05 mA·cm -2of 12 cm 2 The unbiased device based on CuMo / TCS photoanode achieved urea production rate of 1319.68 μg·h -1 C3 product production rate of 381.48 μmol·h -1 , reaching the leading level in the unbiased PEC system, verifying the scalability and potential industrialization prospect of the system. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0026] Figure 1 are scanning electron microscope images; wherein a-d are scanning electron microscope images of TiO2 / CdS / Sb2S3, e-h are scanning electron microscope images of CuMo / TiO2 / CdS / Sb2S3.

[0027] Figure 2 are cross-sectional transmission electron microscope images and EDX spectra of CuMo / TiO2 / CdS / Sb2S3; wherein a-g are cross-sectional transmission electron microscope images, and h is an EDX spectrum.

[0028] Figure 3 are XPS spectra corresponding to a Cu LMM , b Cu 2p, c Mo 3d, d O 1s of different photoanodes.

[0029] Figure 4 are LSV curves of photoanodes; wherein a is a LSV curve of CuMo / TiO2 / CdS / Sb2S3 in different electrolytes, b is a 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 a urea FE of different catalyst-modified photoanodes.

[0030] Figure 5 are cycle tests of photoanodes; wherein a is a FE of nitrogen-containing products of CuMo / TiO2 / CdS / Sb2S3 at different potentials, b is a FE of nitrogen-containing products of CuMo / TiO2 / CdS / Sb2S3 at 0.4 V RHEStability of CuMo / TiO2 / CdS / Sb2S3 under AM 1.5G illumination, c Cyclic test of CuMo / TiO2 / CdS / Sb2S3.

[0031] Figure 6 In-situ FTIR spectra of different photoanodes; where a is the in-situ FTIR spectra of CuMo / TiO2 / CdS / Sb2S3, b is the in-situ FTIR spectra of Cu / TiO2 / CdS / Sb2S3, c is the in-situ FTIR spectra of Mo / TiO2 / CdS / Sb2S3.

[0032] Figure 7 Characterization of anodes; where a is the SEM image of Bi2O3 / Pt, b is the TEM image of Bi2O3 / Pt, c is the corresponding EDX mapping, d is the XPS spectra of Pt 4f for Bi2O3 / Pt and Pt, e is the XPS spectra of Bi 4f for Bi2O3 / Pt and Bi2O3, f is the XPS spectra of O 1s for Bi2O3 / Pt, Bi2O3 and Bi2O3 / Pt.

[0033] Figure 8 Electrochemical performance of anodes; where a is the linear sweep voltammetry curves of Bi2O3, Pt, Bi2O3 / Pt in 1 M KOH + 0.5 M glycerol, b is the yield and corresponding C3 selectivity of all C3 products on Bi2O3 / Pt at different potentials, c is the selectivity of all products and C3 yield on Pt and Bi2O3 / Pt at 0.8 V RHE under 0.6 V RHE , d is the I-t curve of Bi2O3 / Pt under cyclic test, e is the corresponding C3 yield and C3 selectivity under cyclic test.

[0034] Figure 9 CuMo / TCS || Bi2O3 / Pt system and test; where a is the schematic of PEC cell for production of urea and C3, b is the potential gain when coupled with various anode reactions in the assisted urea production process measured under two-electrode setup, c is the unbiased stability of CuMo / TiO2 / CdS / Sb2S3|| Bi2O3 / Pt tandem device, the electrolyte is refreshed every 0.5 hour, d is the urea FEs and yield of CuMo / TiO2 / CdS / Sb2S3|| Bi2O3 / Pt tandem device under unbiased condition under AM 1.5G illumination, e is the selectivity and yield of C3 on Bi2O3 / Pt under unbiased condition.

[0035] Figure 10Large unbiased PEC system and testing; where a is a digital photograph of real outdoor solar testing (1-sun: 100 mW cm -2 ), b is digital images of CuMo / TiO2 / CdS / Sb2S3 of different sizes, c is the J-V curves of CuMo / TiO2 / CdS / Sb2S3|| Bi2O3 / Pt cell under real sunlight (CuMo / TiO2 / CdS / Sb2S3 is 12 square centimeters) and simulated sunlight (CuMo / TiO2 / CdS / Sb2S3 is 4 square centimeters) irradiation, d is the selectivity of urea FE and C3 in 1 hour test, e is the urea product yield and C3 product yield of CuMo / TiO2 / CdS / Sb2S3|| Bi2O3 / Pt tandem device under laboratory and outdoor unbiased pressure test conditions. The test was carried out in Hohhot, China from 1 pm to 3 pm on June 17, 2025, f is the economic value of the unbiased voltage system. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0037] The test methods used in the following experimental examples are conventional methods unless otherwise specified. The materials, reagents, etc. used are commercially available reagents and materials unless otherwise specified. Example 1

[0038] This embodiment provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photo-cathode:

[0039] (1) Preparation of Sb2S3 semiconductor: 2.67 g of potassium antimonyl tartrate and 2.53 g of anhydrous sodium thiosulfate were weighed and dissolved in 100 mL of deionized water to form a uniform precursor solution under magnetic stirring. 28 mL of the precursor solution was taken into a 30 mL reactor, and a fluorine-doped tin oxide (FTO) conductive glass substrate was vertically placed in the solution with the bottom facing down. The reactor was subjected to ultrasonic treatment at room temperature for 10 minutes to enhance the contact and adsorption of the precursor with the substrate. The reactor was placed in a 135 °C oven for heating for 5 hours, and after the reaction was completed, the reactor was naturally cooled in the oven overnight to obtain an initial deposition film. The deposition film was taken out and annealed at 350 °C for 20 minutes in a nitrogen atmosphere to obtain a dense and uniform Sb2S3 semiconductor thin film.

[0040] (2) Chemical bath deposition (CBD) of CdS layer: 79 mL of deionized water was added to a beaker and heated to 50 °C in a water bath for 15 minutes. 0.32 g of cadmium sulfate (CdSO4) was added and stirred until dissolved; after heating to 60 °C, 21 mL of ammonia water (NH3·H2O) was added, followed by rapid addition of 1.69 g of thiourea (SC(NH2)2), and continued stirring until complete dissolution. The Sb2S3 thin film (substrate facing down) was immediately immersed in the reaction solution. The beaker was moved into a 60 °C constant temperature oven together with the sample for reaction for 15 minutes, and a CdS layer was deposited to form a CdS / Sb2S3 heterojunction.

[0041] (3) Deposition of TiO2 layer (atomic layer deposition, ALD): titanium tetrakis(dimethylamino)titanate was used as the titanium source, and deionized water was used as the oxygen source. Deposition was carried out at 120 °C for 600 cycles to form a dense TiO2 layer. After deposition was completed, the sample was annealed at 200 °C for 1 hour in an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (referred to as TCS) structure.

[0042] (4) Electrochemical deposition and annealing treatment of CuMo layer: 0.05 g of copper chloride (CuCl2), 0.24 g of sodium molybdate (Na2MoO4), and 0.25 g of ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL of deionized water; stirred at room temperature for 30 minutes; and an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance of the film layer. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode. The potential was set to -0.8 V AgClPotentiostatic electrodeposition was performed for 900 seconds to deposit CuMo components uniformly on the TCS surface. The electrodeposited sample was annealed at 210 °C for 30 minutes to obtain a final CuMo / TCS multilayer photoelectrode structure, i.e., a CuMo / TiO2 / CdS / Sb2S3 photo-cathode. Example 2

[0043] This example provides a preparation procedure of a CuMo / TiO2 / CdS / Sb2S3 photo-cathode:

[0044] (1) Preparation of Sb2S3 semiconductor: 2.4 g of potassium antimonyl tartrate and 2.7 g of anhydrous sodium thiosulfate were weighed and dissolved in 100 mL of deionized water to form a uniform precursor solution under magnetic stirring. 28 mL of the precursor solution was taken into a 30 mL reaction kettle, and a fluorine-doped tin oxide (FTO) conductive glass substrate was vertically placed in the solution with the bottom facing down. The reaction kettle was subjected to ultrasonic treatment at room temperature for 10 minutes to enhance the contact and adsorption of the precursor with the substrate. The reaction kettle was placed in a 130 °C oven for heating for 4.5 hours, and after the reaction was completed, it was naturally cooled in the oven overnight to obtain an initial deposition film. The deposition film was taken out and annealed at 340 °C for 18 minutes in a nitrogen atmosphere to obtain a dense and uniform Sb2S3 semiconductor thin film.

[0045] (2) Chemical bath deposition (CBD) of CdS layer: 79 mL of deionized water was added to a beaker and heated to 50 °C in a water bath for 15 minutes. 0.3 g of cadmium sulfate (CdSO4) was added and stirred until dissolved; after heating to 55 °C, 20 mL of ammonia water (NH3·H2O) was added; subsequently, 1.65 g of thiourea (SC(NH2)2) was quickly added and continuously stirred until completely dissolved. The Sb2S3 thin film (with the substrate facing down) was immediately immersed in the reaction solution. The beaker was moved into a 55 °C constant temperature oven together with the sample for 13 minutes of reaction to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0046] (3) Deposition of TiO2 layer (atomic layer deposition, ALD): titanium tetrakis(dimethylamino) titanate was used as the titanium source, and deionized water was used as the oxygen source. Deposition was performed at 115 °C for 600 cycles to form a dense TiO2 layer. After deposition was completed, the sample was annealed at 195 °C for 0.8 hours in an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (referred to as TCS) structure.

[0047] (4) Electrochemical deposition of CuMo layer and annealing treatment: 0.04 g of copper chloride (CuCl2), 0.23 g of sodium molybdate (Na2MoO4), and 0.225 g of ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL of deionized water; stirring for 30 minutes at room temperature; adding an appropriate amount of polyethylene glycol (PEG-2000) to improve the film forming performance of the film layer. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode. CuMo components were uniformly deposited on the surface of TCS by electrodeposition at -0.8 V AgCl for 900 seconds. The electrodeposited sample was annealed at 200 °C for 25 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure, i.e., a CuMo / TiO2 / CdS / Sb2S3 photo-cathode. Example 3

[0048] This example provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photo-cathode:

[0049] (1) Preparation of Sb2S3 semiconductor: 2.5 g of potassium antimonyl tartrate and 2.6 g of anhydrous sodium thiosulfate were weighed and dissolved in 100 mL of deionized water, and the mixture was stirred under magnetic stirring to form a uniform precursor solution. 28 mL of the above precursor solution was taken and placed in a 30 mL reaction kettle, and a fluorine-doped tin oxide (FTO) conductive glass substrate was vertically placed in the solution with the bottom facing down. The reaction kettle was subjected to ultrasonic treatment at room temperature for 10 minutes to enhance the contact and adsorption of the precursor with the substrate. The reaction kettle was placed in a 140 °C oven and heated for 5 hours, and after the reaction was completed, the reaction kettle was naturally cooled in the oven overnight to obtain an initial deposition film. The deposition film was taken out and annealed at 360 °C for 19 minutes in a nitrogen atmosphere to obtain a dense and uniform Sb2S3 semiconductor thin film.

[0050] (2) Chemical bath deposition (CBD) of CdS layer: 79 mL of deionized water was added to a beaker and heated to 50 °C in a water bath for 15 minutes. 0.34 g of cadmium sulfate (CdSO4) was added and stirred until dissolved; after heating to 65 °C, 20 mL of ammonia water (NH3·H2O) was added; then 1.7 g of thiourea (SC(NH2)2) was quickly added and continuously stirred until completely dissolved. The Sb2S3 thin film (with the substrate facing down) was immediately immersed in the reaction solution. The beaker with the sample was moved into a 58 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0051] (3) TiO2layer deposition (atomic layer deposition, ALD): using titanium tetrakis(dimethylamino)titanate as the titanium source; deionized water as the oxygen source; depositing for 600 cycles at 125 °C to form a dense TiO2layer. After deposition, the sample is annealed at 205 °C for 1.2 hours under argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (referred to as TCS) structure.

[0052] (4) Electrochemical deposition of CuMo layer and annealing treatment: 0.06 g of copper chloride (CuCl2), 0.24 g of sodium molybdate (Na2MoO4), and 0.275 g of ammonium oxalate ((NH4)2C2O4) are dissolved in 50 mL of deionized water; stirring at room temperature for 30 minutes; adding an appropriate amount of polyethylene glycol (PEG-2000) to improve the film forming performance of the film layer. A three-electrode system is used, with TCS as the working electrode and Ag / AgCl as the reference electrode. The CuMo component is uniformly deposited on the surface of TCS by electrodeposition at -0.8 V AgCl for 900 seconds. The sample after electrodeposition is annealed at 220 °C for 35 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure, i.e. CuMo / TiO2 / CdS / Sb2S3 photo-cathode. Example 4

[0053] This example provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photo-cathode:

[0054] (1) Preparation of Sb2S3semiconductor: 2.8 g of potassium antimonyl tartrate and 2.5 g of anhydrous sodium thiosulfate are weighed and dissolved in 100 mL of deionized water, and fully dissolved under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution into a 30 mL reaction kettle, and place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonic treatment is performed on the reaction kettle at room temperature for 10 minutes to enhance the contact and adsorption of the precursor with the substrate. The reaction kettle is placed in a 138 °C oven for heating for 5 hours, and after the reaction is completed, it is naturally cooled overnight in the oven to obtain an initial deposition film. The deposition film is taken out and annealed at 340 °C for 21 minutes under nitrogen atmosphere to obtain a dense and uniform Sb2S3semiconductor thin film.

[0055] (2) Chemical bath deposition (CBD) of CdS layer: 79 mL of deionized water was added into a beaker and heated to 50 °C in a water bath for 15 minutes. 0.31 g of cadmium sulfate (CdSO4) was added and stirred until dissolved; after heating to 55 °C, 20 mL of ammonia water (NH3·H2O) was added; subsequently, 1.68 g of thiourea (SC(NH2)2) was quickly added and continued to stir until completely dissolved. The Sb2S3 film (with the substrate facing down) was immediately immersed in the reaction solution. The beaker was removed together with the sample into a constant temperature oven at 63 °C for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0056] (3) Deposition of TiO2 layer (atomic layer deposition, ALD): titanium tetrakis(dimethylamino)titanate was used as the titanium source; deionized water was used as the oxygen source; 600 cycles of deposition were carried out 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 (referred to as TCS) structure.

[0057] (4) Electrochemical deposition and annealing treatment of CuMo layer: 0.045 g of copper chloride (CuCl2), 0.24 g of sodium molybdate (Na2MoO4), and 0.275 g of ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL of deionized water; stirred at room temperature for 30 minutes; and an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance of the film layer. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode. CuMo components were uniformly deposited on the surface of TCS by electrodeposition at -0.8 V AgCl for 900 seconds. The sample after electrodeposition was annealed at 210 °C for 30 minutes to obtain a final CuMo / TCS multilayer photoelectrode structure, i.e., a CuMo / TiO2 / CdS / Sb2S3 photo-cathode. Example 5

[0058] This example provides a preparation step of a CuMo / TiO2 / CdS / Sb2S3 photo-cathode:

[0059] (1) Preparation of Sb2S3 semiconductor: 2.6 g of potassium antimonyl tartrate and 2.4 g of anhydrous sodium thiosulfate were weighed and dissolved in 100 mL of deionized water to form a uniform precursor solution under magnetic stirring. 28 mL of the precursor solution was taken into a 30 mL reactor, and a fluorine-doped tin oxide (FTO) conductive glass substrate was vertically placed in the solution with the bottom facing down. The reactor was subjected to ultrasonic treatment at room temperature for 10 minutes to enhance the contact and adsorption of the precursor with the substrate. The reactor was placed in a 130 °C oven for heating for 4.5 hours, and after the reaction was completed, the reactor was naturally cooled in the oven overnight to obtain an initial deposition film. The deposition film was taken out and annealed at 350 °C for 18 minutes in a nitrogen atmosphere to obtain a dense and uniform Sb2S3 semiconductor thin film.

[0060] (2) Chemical bath deposition (CBD) of CdS layer: 79 mL of deionized water was added to a beaker and heated to 50 °C in a water bath for 15 minutes. 0.3 g of cadmium sulfate (CdSO4) was added and stirred until dissolved; after heating to 55 °C, 20 mL of ammonia water (NH3·H2O) was added; then 1.7 g of thiourea (SC(NH2)2) was quickly added and continuously stirred until completely dissolved. The Sb2S3 thin film (with the substrate facing down) was immediately immersed in the reaction solution. The beaker with the sample was moved into a 60 °C constant temperature oven for reaction for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0061] (3) Deposition of TiO2 layer (atomic layer deposition, ALD): titanium tetrakis(dimethylamino)titanate was used as the titanium source, and deionized water was used as the oxygen source. Deposition was carried out at 120 °C for 600 cycles to form a dense TiO2 layer. After deposition was completed, the sample was annealed at 200 °C for 1 hour in an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (referred to as TCS) structure.

[0062] (4) Electrochemical deposition and annealing treatment of CuMo layer: 0.05 g of copper chloride (CuCl2), 0.24 g of sodium molybdate (Na2MoO4), and 0.25 g of ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL of deionized water; stirred at room temperature for 30 minutes; and an appropriate amount of polyethylene glycol (PEG-2000) was added to improve the film forming performance of the film layer. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode. The potential was set to -0.8 V AgClPotentiostatic electrodeposition for 1200 seconds to deposit CuMo components uniformly on the TCS surface. The electrodeposited sample was annealed at 200 °C for 25 minutes to obtain the final CuMo / TCS multilayer photoelectrode structure, i.e., CuMo / TiO2 / CdS / Sb2S3 photo-cathode. Comparative Example 1

[0063] This comparative example provides a preparation procedure of a TiO2 / CdS / Sb2S3 photo-cathode:

[0064] (1) Preparation of Sb2S3 semiconductor: Take 2.67 g of potassium antimonyl tartrate and 2.53 g of anhydrous sodium thiosulfate, dissolve in 100 mL of deionized water, and fully dissolve under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reaction kettle. Put the fluorine-doped tin oxide (FTO) conductive glass substrate vertically into the solution with the bottom facing down. Ultrasonically treat the reaction kettle at room temperature for 10 minutes to enhance the contact and adsorption of the precursor with the substrate. Place the reaction kettle in a 135 °C oven and heat for 5 hours. After the reaction is completed, naturally cool in the oven overnight to obtain an initial deposition film. Take out the deposition film and anneal it at 350 °C for 20 minutes in a nitrogen atmosphere to obtain a dense and uniform Sb2S3 semiconductor thin film.

[0065] (2) Chemical bath deposition (CBD) of CdS layer: Add 79 mL of deionized water to a beaker and heat in a water bath to 50 °C 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 water (NH3·H2O); subsequently, quickly add 1.69 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3 thin film (substrate facing down) into the reaction solution. Move the beaker together with the sample into a 60 °C constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0066] (3) Deposition of TiO2 layer (atomic layer deposition, ALD): Use titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source. Perform 600 cycles of deposition at 120 °C to form a dense TiO2 layer. After deposition is complete, anneal the sample at 200 °C for 1 hour in an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (referred to as TCS) structure. Comparative Example 2

[0067] The comparative example provides a preparation step of a Cu / TiO2 / CdS / Sb2S3photocathode:

[0068] (1) Preparation of Sb2S3semiconductor: Take 2.67 g of potassium antimonyl tartrate and 2.53 g of anhydrous sodium thiosulfate, dissolve in 100 mL of deionized water, and fully dissolve under magnetic stirring to form a uniform precursor solution. Take 28 mL of the above precursor solution and place it in a 30 mL reaction kettle, and place the fluorine-doped tin oxide (FTO) conductive glass substrate vertically downward into the solution. Ultrasonically treat the reaction kettle at room temperature for 10 minutes to enhance the contact and adsorption of the precursor with the substrate. Place the reaction kettle in a 135 ℃ oven and heat for 5 hours, and after the reaction is completed, naturally cool in the oven overnight to obtain an initial deposition film. Take out the deposition film and anneal it at 350 ℃ for 20 minutes in a nitrogen atmosphere to obtain a dense and uniform Sb2S3semiconductor thin film.

[0069] (2) Chemical bath deposition (CBD) of the CdS layer: Add 79 mL of deionized water to a beaker and heat in a water bath to 50 ℃ for 15 minutes. Add 0.32 g of cadmium sulfate (CdSO4) and stir until dissolved; after heating to 60 ℃, add 21 mL of ammonia water (NH3·H2O); subsequently, quickly add 1.69 g of thiourea (SC(NH2)2) and continue stirring until completely dissolved. Immediately immerse the Sb2S3thin film (substrate downward) into the reaction solution. Move the beaker together with the sample into a 60 ℃ constant temperature oven for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3heterojunction.

[0070] (3) Deposition of the TiO2layer (atomic layer deposition, ALD): Use titanium tetrakis(dimethylamino)titanate as the titanium source and deionized water as the oxygen source; deposit for 600 cycles at 120 ℃ to form a dense TiO2layer. After deposition is complete, anneal the sample at 200 ℃ for 1 hour in an argon atmosphere to obtain a TiO2 / CdS / Sb2S3structure (referred to as TCS).

[0071] (4) Electrochemical deposition of the Cu layer and annealing treatment: Dissolve 0.05 g of copper chloride (CuCl2) and 0.25 g of ammonium oxalate ((NH4)2C2O4) in 50 mL of deionized water; stir at room temperature for 30 minutes; add an appropriate amount of polyethylene glycol (PEG-2000) to improve the film forming performance of the film layer. Use a three-electrode system with TCS as the working electrode and Ag / AgCl as the reference electrode, and deposit a Cu layer on the TCS structure at -0.8 VAgCl Potentiostatic electrodeposition was performed for 900 seconds to deposit Cu components uniformly on the TCS surface. The electrodeposited sample was annealed at 210 °C for 30 minutes to obtain a final Cu / TCS multilayer photoelectrode structure. Comparative Example 3

[0072] This comparative example provides a preparation procedure of a Mo / TiO2 / CdS / Sb2S3 photoelectrode:

[0073] (1) Preparation of Sb2S3 semiconductor: 2.67 g of potassium antimonyl tartrate and 2.53 g of anhydrous sodium thiosulfate were weighed and dissolved in 100 mL of deionized water under magnetic stirring to form a uniform precursor solution. 28 mL of the above precursor solution was taken into a 30 mL reaction kettle, and a fluorine-doped tin oxide (FTO) conductive glass substrate was vertically placed in the solution with the bottom facing down. The reaction kettle was subjected to ultrasonic treatment at room temperature for 10 minutes to enhance the contact and adsorption of the precursor with the substrate. The reaction kettle was placed in a 135 °C oven for heating for 5 hours, and after the reaction was completed, it was naturally cooled in the oven overnight to obtain an initial deposition film. The deposition film was taken out and annealed at 350 °C for 20 minutes in a nitrogen atmosphere to obtain a dense and uniform Sb2S3 semiconductor thin film.

[0074] (2) Chemical bath deposition (CBD) of CdS layer: 79 mL of deionized water was added to a beaker and heated to 50 °C in a water bath for 15 minutes. 0.32 g of cadmium sulfate (CdSO4) was added and stirred until dissolved; after heating to 60 °C, 21 mL of ammonia water (NH3·H2O) was added; subsequently, 1.69 g of thiourea (SC(NH2)2) was quickly added and continued to stir until completely dissolved. The Sb2S3 thin film (substrate facing down) was immediately immersed in the reaction solution. The beaker was removed together with the sample into a 60 °C constant temperature oven for reaction for 15 minutes to deposit a CdS layer and construct a CdS / Sb2S3 heterojunction.

[0075] (3) Deposition of TiO2 layer (atomic layer deposition, ALD): titanium tetrakis(dimethylamino)titanate was used as the titanium source; deionized water was used as the oxygen source; 600 cycles of deposition were performed at 120 °C to form a dense TiO2 layer. After deposition was completed, the sample was annealed at 200 °C for 1 hour in an argon atmosphere to obtain a TiO2 / CdS / Sb2S3 (referred to as TCS) structure.

[0076] (4) Electrochemical deposition of Mo layer and annealing treatment: 0.24 g of sodium molybdate (Na2MoO4) and 0.25 g of ammonium oxalate ((NH4)2C2O4) were dissolved in 50 mL of deionized water; stirring for 30 minutes at room temperature; adding an appropriate amount of polyethylene glycol (PEG-2000) to improve the film forming performance of the film layer. A three-electrode system was used, with TCS as the working electrode and Ag / AgCl as the reference electrode. Mo components were uniformly deposited on the surface of TCS by electrodeposition at -0.8 V AgCl for 900 seconds. The electrodeposited sample was annealed at 210 °C for 30 minutes to obtain the final Mo / TCS multilayer photoelectrode structure. Example 6

[0077] This embodiment provides an unbiased coupling photoelectrochemical system, which comprises a reaction tank, a workstation, a stirring device, and a gas path device. The reaction tank comprises a cathode reaction tank and an anode reaction tank. The CuMo / TiO2 / CdS / Sb2S3 photo-cathode prepared in Example 1 is used as the cathode of the cathode reaction tank, and the Bi2O3 / Pt anode is used as the anode of the anode reaction tank.

[0078] The preparation steps of the Bi2O3 / Pt anode are as follows:

[0079] (1) Commercial nickel foam (Nickel Foam, NF) was ultrasonically cleaned, and then sequentially cleaned with deionized water, ethanol and acetone, and dried for standby. The cleaned nickel foam was immersed in 3 mL of deionized water; 0.5 mL of chloroplatinic acid solution (H2PtCl6·6H2O) with a concentration of 120 mM and 15 μL of concentrated hydrochloric acid (HCl) were sequentially added; then 30 mg of polyvinylpyrrolidone (PVP) was added; gently stirring until all were dissolved to form a uniform solution. The above reaction system was placed in a constant temperature oven and left to stand at 54 °C for 6 hours. After the reaction was completed, black deposits were observed on the surface of the electrode. The obtained electrode was washed with deionized water and dried, and then annealed at 450 °C in an air atmosphere for 2 hours to obtain a Pt electrode.

[0080] (2) 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 the above Pt electrode as the working electrode and Ag / AgCl as the reference electrode. Bi was deposited by electrodeposition at -0.6 V for 10 minutes. After the deposition was completed, the electrode was taken out and annealed at 450 °C in an air atmosphere for 2 hours to obtain a Bi2O3 / Pt electrode. Example 7

[0081] The embodiment provides a bias-free coupling photoelectrochemical system, which comprises a reaction tank, a workstation, a stirring device and a gas path device; the reaction tank comprises a cathode reaction tank and an anode reaction tank; the CuMo / TiO2 / CdS / Sb2S3 photo-cathode prepared in the embodiment 1 is used as the cathode of the cathode reaction tank; and the Bi2O3 / Pt anode is used as the anode of the anode reaction tank.

[0082] The preparation steps of the Bi2O3 / Pt anode are as follows:

[0083] (1) Commercial nickel foam (Nickel Foam, NF) is cleaned by ultrasonic cleaning, and is sequentially cleaned by deionized water, ethanol and acetone, and is dried for standby use. The cleaned nickel foam is immersed into 2.9 mL of deionized water; 0.45 mL of a chloroplatinic acid solution (H2PtCl6·6H2O) with a concentration of 110 mM and 10 μL of concentrated hydrochloric acid (HCl) are sequentially added; 24 mg of polyvinylpyrrolidone (PVP) is further added; and the mixture is gently stirred until a uniform solution is formed. The reaction system is placed in a constant temperature oven, and is left to stand at 50°C for 5.5 hours. After the reaction is completed, a black deposit is observed on the surface of the electrode. The obtained electrode is taken out, washed with deionized water, dried, and annealed at 400°C in an air atmosphere for 2.5 hours, to obtain a Pt electrode.

[0084] (2) 0.36 mmol of bismuth nitrate (Bi(NO3)3·5H2O) is dissolved in a mixed solution of 33 mL of deionized water and 12 mL of ethylene glycol, and is stirred until clear. A three-electrode system is adopted, the above-mentioned Pt electrode is used as a working electrode, and Ag / AgCl is used as a reference electrode; Bi is deposited by electrodeposition at a potential of-0.6 V for 10 minutes. After the deposition is completed, the electrode is taken out, and is annealed at 400°C in an air atmosphere for 2.5 hours, to obtain a Bi2O3 / Pt electrode. Embodiment 8

[0085] The embodiment provides a bias-free coupling photoelectrochemical system, which comprises a reaction tank, a workstation, a stirring device and a gas path device; the reaction tank comprises a cathode reaction tank and an anode reaction tank; the CuMo / TiO2 / CdS / Sb2S3 photo-cathode prepared in the embodiment 1 is used as the cathode of the cathode reaction tank; and the Bi2O3 / Pt anode is used as the anode of the anode reaction tank.

[0086] The preparation steps of the Bi2O3 / Pt anode are as follows:

[0087] (1) Commercial nickel foam (Nickel Foam, NF) was cleaned by ultrasonic washing, and then sequentially cleaned with deionized water, ethanol and acetone, and dried for standby. The cleaned nickel foam was immersed in 3.1 mL of deionized water; 0.55 mL of chloroplatinic acid solution (H2PtCl6·6H2O) with a concentration of 130 mM and 15 μL of concentrated hydrochloric acid (HCl) were sequentially added; 36 mg of polyvinylpyrrolidone (PVP) was then added; and the mixture was gently stirred until a uniform solution was formed. The reaction system was placed in a constant temperature oven and kept at 53°C for 6 hours. After the reaction was completed, black deposits were observed on the surface of the electrode. The obtained electrode was taken out, washed with deionized water, dried, and then annealed at 480 ℃ in an air atmosphere for 2 hours to obtain a Pt electrode.

[0088] (2) 0.44 mmol of bismuth nitrate (Bi(NO3)3·5H2O) was dissolved in a mixture of 27 mL of deionized water and 18 mL of ethylene glycol, and stirred until clear. A three-electrode system was used, with the above Pt electrode 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 taken out and annealed at 480 ℃ in an air atmosphere for 1.5 hours to obtain a Bi2O3 / Pt electrode. Example 9

[0089] This embodiment provides a bias-free coupled photoelectrochemical system, which comprises a reaction tank, a workstation, a stirring device, and a gas path device. The reaction tank comprises a cathode reaction tank and an anode reaction tank. The CuMo / TiO2 / CdS / Sb2S3 photo-cathode prepared in Example 1 is used as the cathode of the cathode reaction tank, and the Bi2O3 / Pt anode is used as the anode of the anode reaction tank.

[0090] The preparation steps of the Bi2O3 / Pt anode are as follows:

[0091] (1) Commercial nickel foam (Nickel Foam, NF) was cleaned by ultrasonic washing, and then sequentially cleaned with deionized water, ethanol and acetone, and dried for standby. The cleaned nickel foam was immersed in 3 mL of deionized water; 0.55 mL of chloroplatinic acid solution (H2PtCl6·6H2O) with a concentration of 125 mM and 20 μL of concentrated hydrochloric acid (HCl) were sequentially added; 27 mg of polyvinylpyrrolidone (PVP) was then added; and the mixture was gently stirred until a uniform solution was formed. The reaction system was placed in a constant temperature oven and kept at 55°C for 5.5 hours. After the reaction was completed, black deposits were observed on the surface of the electrode. The obtained electrode was taken out, washed with deionized water, dried, and then annealed at 440°C in an air atmosphere for 2 hours to obtain a Pt electrode.

[0092] (2) 0.5 mmol of bismuth nitrate (Bi(NO3)3·5H2O) was dissolved in a mixture of 27 mL of deionized water and 18 mL of ethylene glycol, and stirred until clear. A three-electrode system was used, with the above Pt electrode 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 taken out and annealed at 470°C in an air atmosphere for 1.8 hours to obtain a Bi2O3 / Pt electrode. Example 10

[0093] This embodiment provides a bias-free coupled photoelectrochemical system, which includes a reaction tank, a workstation, a stirring device, and a gas path device. The reaction tank includes a cathode reaction tank and an anode reaction tank. The CuMo / TiO2 / CdS / Sb2S3 photo-cathode prepared in Example 1 is used as the cathode of the cathode reaction tank, and the Bi2O3 / Pt anode is used as the anode of the anode reaction tank.

[0094] The preparation steps of the Bi2O3 / Pt anode are as follows:

[0095] (1) Commercial nickel foam (Nickel Foam, NF) was cleaned by ultrasonic washing, and then sequentially cleaned with deionized water, ethanol and acetone, and dried for standby. The cleaned nickel foam was immersed in 3 mL of deionized water; 0.55 mL of chloroplatinic acid solution (H2PtCl6·6H2O) with a concentration of 125 mM and 20 μL of concentrated hydrochloric acid (HCl) were sequentially added; 27 mg of polyvinylpyrrolidone (PVP) was then added; and the mixture was gently stirred until a uniform solution was formed. The reaction system was placed in a constant temperature oven and allowed to stand at 55°C for 5.5 hours. After the reaction was completed, black deposits were observed on the surface of the electrode. The obtained electrode was taken out, washed with deionized water, dried, and then annealed at 440°C in an air atmosphere for 2 hours to obtain a Pt electrode.

[0096] (2) 0.4 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 the above Pt electrode 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 taken out and annealed at 430°C in an air atmosphere for 1.8 hours to obtain a Bi2O3 / Pt electrode. Comparative Example 4

[0097] This comparative example provides a bias-free coupled photoelectrochemical system, which includes a reaction tank, a workstation, a stirring device, and a gas path device. The reaction tank includes a cathode reaction tank and an anode reaction tank. The CuMo / TiO2 / CdS / Sb2S3 photo-cathode prepared in Example 1 is used as the cathode of the cathode reaction tank, and a Pt anode is used as the anode of the anode reaction tank.

[0098] The preparation steps of the Pt anode are as follows:

[0099] The commercial nickel foam (NF) was cleaned by ultrasonic washing, and then sequentially cleaned with deionized water, ethanol and acetone, and dried for standby use. The cleaned nickel foam was immersed in 3 mL of deionized water; 0.5 mL of a chloroplatinic acid solution (H2PtCl6·6H2O) with a concentration of 120 mM and 15 μL of concentrated hydrochloric acid (HCl) were sequentially added; 30 mg of polyvinylpyrrolidone (PVP) was then added; and gentle stirring was performed until a uniform solution was formed. The above reaction system was placed in a constant temperature oven and left to stand at 54 ℃ for 6 hours. After the reaction was completed, black deposits were observed on the surface of the electrode. The obtained electrode was taken out, washed with deionized water, dried, and then annealed at 450 ℃ in an air atmosphere for 2 hours to obtain a Pt electrode. Comparative Example 5

[0100] The present comparative example provides a bias-free coupled photoelectrochemical system, comprising a reaction tank, a workstation, a stirring device, and a gas path device; the reaction tank comprises a cathode reaction tank and an anode reaction tank, the CuMo / TiO2 / CdS / Sb2S3 photo-cathode prepared in Example 1 is used as the cathode of the cathode reaction tank, and the Bi2O3 anode is used as the anode of the anode reaction tank.

[0101] The preparation steps of the Bi2O3 anode are as follows:

[0102] 0.5 mmol of bismuth nitrate (Bi(NO3)3·5H2O) was dissolved in a mixed solution 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 deposition was completed by electrodeposition at a potential of -0.6 V for 10 minutes. After deposition, the electrode was taken out and annealed at 450 ℃ in an air atmosphere for 2 hours to obtain a Bi2O3 electrode.

[0103] Example Effect Example 1

[0104] 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 were observed by scanning electron microscopy (SEM), and the grain size of Sb2S3 was about 2.5 microns. Mo / TCS showed a shell-like morphology, and Cu and CuMo showed nanoparticle characteristics on the surface of the semiconductor, with the particle size of CuMo being 200 to 500 nm. Figure 1Cross-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 (a). Furthermore, both CuMo and Cu exhibit nanocrystalline characteristics, while the Mo catalyst displays an amorphous structure (Fig. 2b). The lattice spacing of the CuMo catalyst is 0.246 nm, corresponding to the (111) crystal plane of Cu₂O (…). Figure 2 The inter-lattice spacing (c) of Sb2S3 and CdS is slightly larger than that of Cu catalyst (0.243 nm), which may be due to the addition of Mo atoms to the Cu2O lattice. The inter-lattice spacings of the (211) and (111) planes of Sb2S3 and CdS are 0.305 nm and 0.335 nm, respectively. Figure 2 (dg), which is related to the Fast Fourier Transform Figure 1 The elemental diagram obtained by energy-dispersive X-ray spectroscopy (EDX) shows that Sb₂S₃ is encapsulated by layers of CdS and TiO₂, and Cu and Mo are uniformly distributed throughout the CuMo catalyst. Figure 2 (h).

[0105] A summary of the ICP-OES analysis results for copper and molybdenum in CuMo / TiO2 / CdS / Sb2S3 prepared in Example 1 is shown in Table 1:

[0106] Table 1 Summary of ICP-OES analysis results for copper and molybdenum in CuMo / TCS

[0107]

[0108] The ICP analysis in Table 1 shows that the atomic ratio of copper to molybdenum is approximately 3:1; XPS analysis confirmed the presence of copper, molybdenum, and oxygen. Figure 3 The Cu 2p and Cu LMM spectra show that Cu 0 Cu + and Cu 2+ The mixture (Cu) 0 (negligible), while Mo is mainly Mo 6+ The state exists. Based on these results, considering the observed oxidation states of copper and molybdenum, if all Cu in the catalyst is in the +2 state, while Mo is in the Mo2 state... 6+ If copper exists primarily in the +1 state, then the charge balance indicates that its stoichiometry is close to that of Cu3MoO6. Alternatively, if copper is predominantly in the +1 state, then the corresponding stoichiometry is approximately Cu3MoO6.4.5 Given Cu + and Cu 2+ The two substances coexist, and the actual composition may fall somewhere between these two scenarios.

[0109] Example 2 of implementation results

[0110] Photoelectrochemical measurements were performed in a closed H-type cell using a three-electrode system: 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, and carbon dioxide reduction measurements were performed for 0.5 hours at different application potentials. Before testing, the working electrode chamber was purged with carbon dioxide at a rate of 30 mL / min for at least 30 minutes. Illumination was provided by an AM 1.5G simulator with a power of 100 mW / cm². -2 The recorded potentials are based on an Ag / AgCl reference electrode and can be converted to a reversible hydrogen electrode (RHE) scale using the Nernst equation: E RHE =E (Ag / AgCl) +0.197 +0.0591 * pH. Quantification of ammonia products was performed 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; (c) 1 wt% sodium nitroferricyanide solution. 1 mL of 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 kept in the dark for 2 hours before absorbance measurement. 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. Then, 7 mg of urease was dissolved in the precursor solution, followed by the addition of 3.2 mL of cathodic electrolyte. The mixture was thoroughly homogenized and incubated at 50 °C for 1 hour. The concentration of NH3 in the electrolyte without urease was determined using the indophenol blue method. The amount of urea produced (N) was then calculated. urea ) is (N urease - N ammonia ) / 2, where N urease and N ammoniarepresent the molar amount of ammonia in the presence and absence of urease, respectively. The FE for urea synthesis was calculated using the following equation: FE = (n*F*C*V) / (60.06*Q), where F is the Faraday constant, Q is the total charge passed during electrolysis, C is the concentration of urea produced, V is the volume of 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 - ), 2 g of sulfamic acid and 0.1 g of N-(1-naphthyl)ethylenediamine dihydrochloride were dissolved in the appropriate solvent to prepare a colorimetric reagent. 0.5 mL of sample in the cathode compartment was mixed with 2 mL of deionized water and 0.1 mL of the prepared color reagent. After the reaction proceeded for 20 minutes, the absorbance was measured at a wavelength of 540 nm.

[0111] To investigate the performance of the photoelectrode in urea synthesis, we performed photoelectrochemical measurements. When the atmosphere of the electrolytic cell was switched from Ar to CO2, the current density of CuMo / TCS increased in the potential range (a in Figure 4 ), indicating that additional CO2 reduction-related reactions occurred. Figure 4 b shows the linear sweep voltammetry (LSV) curves of the photoelectrode in 0.5 M KHCO3+ 0.5 M KNO3 and CO2 bubbles. Among these samples, CuMo / TCS had the best PEC performance, with a photocurrent density of -3.98 mA cm RHE at 0 V -2 , which was higher than that of Cu / TCS (-2.62 mA cm -2 ), Mo / TCS (-1.46 mA cm -2 ), and TCS (-0.39 mA cm -2 ) at the same potential. The onset potential of CuMo / TCS (0.98 V RHE ) was much lower than that of Cu / TCS (0.87 V RHE ), Mo / TCS (0.76 V RHE ), and TCS (0.52 V RHE ). As shown in c in Figure 4 , the urea FE value of CuMo / TCS at 0.4 V RHE was as high as 73.3%, while those of Cu / TCS and Mo / TCS were 0.15 and 0 V RHEThe maximum FE values ​​were 49.90% and 36.23%, respectively. Compared with Cu / TCS and Mo / TCS, the potential for achieving optimal urea FE on CuMo / TCS is more anodic.

[0112] NO3 - Reduced to byproducts (such as NO2) - (or NH3) usually limits NO3 - The electrocatalytic conversion efficiency of CO2 to urea was investigated. We further studied the FEs (FeOs) of nitrogen-containing products on CuMo / TCS. Figure 5 (a) In the range of 0.45-0.25 V RHE In the low potential range, most NO3 - It reacts with CO2 to produce urea. However, as the potential becomes more negative, both the urea FE and nitrogen selectivity decrease due to the emergence of a more favorable competing reaction. Furthermore, CuMo / TCS was measured under intermittent illumination conditions with continuous stirring and a 100-second light-dark interval to simulate intermittent solar irradiation. In an electrolyte at pH 7, the current density of CuMo / TCS decreased to 80% of its initial value within 4 hours. Figure 5 (b) For long-term urea synthesis using photoelectrodes ( Figure 5 (c) Because the electrolyte was replaced every 0.5 hours, no significant decrease in current density was detected during the 8 cycles. Urea FE remained above 65%, and urea production also remained constant, averaging 86.01 μg cm⁻¹ per cycle. -2 .

[0113] In-situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) was used to identify key intermediates on the photocathode during PEC urea synthesis. For CuMo / TCS, the potential ranged from 0.8 V to 0 V under illumination. RHE Clear infrared signals can be observed in all of them. Figure 6 (a) Under dark conditions, no characteristic peaks were detected, confirming the important role of photogenerated charge carriers in the reaction process. Peaks at 1160, 1380, and 1667 cm⁻¹ correspond to the NH₂ intermediate, CO₂NH₂ intermediate, and COOHNH₂ intermediate, respectively, indicating the presence of a key CN-coupling intermediate. Notably, no obvious CO intermediate band was detected, indicating that the CO intermediate does not participate in the CN-coupling pathway. When the potential changes from 0.8 to 0 V... RHEAs the potential was changed, these scaling patterns gradually increased, indicating that PEC urea production on CuMo / TCS was efficient. In addition, as the potential increased, a peak corresponding to amide (O=C-NH2) appeared at ~1717 cm -1 When the potential approached 0 V RHE , an OCO intermediate band at 1404 cm -1 was identified, which means that the amount of CO2 adsorption increased, but was not timely converted into urea. On the other hand, Cu / TCS exhibited a strong NH2 intermediate band, Mo / TCS had a strong COOHNH2 intermediate signal, and both exhibited a weak N-C-N vibration ( Figure 6 in b、 Figure 6 in c). This indicates that the conversion efficiency of NH2 intermediate to urea on Cu / TCS is very low, and on Mo / TCS, the further conversion of COOHNH2 intermediate is hindered due to the lack of a synergistic C-N coupling site.

[0114] Effect Example 3

[0115] In order to improve the charge transfer rate of the anode and at the same time obtain high value-added products, we improved the design of the anode when preparing the unbiased coupling photoelectrochemical system, and designed a Bi2O3 modified platinum catalyst (referred to as Bi2O3 / Pt) which can be used for electrochemical glycerol oxidation reaction (GOR). The photoanode Bi2O3 / Pt prepared in Example 6 and the photoanode Pt prepared in Comparative Example 1 were observed by scanning electron microscope (SEM), and the Bi2O3 / Pt sample contained about 10 nanometer platinum nanoparticles at the bottom, and the surface was plated with irregular worm-like Bi2O3( Figure 7 in a). The heterojunction can be observed in the TEM image of Bi2O3 / Pt, and the lattice spacing is 0.230 nm and 0.311 nm, respectively, corresponding to the (111) plane of Pt and the (111) plane of Bi2O3( Figure 7 in b). EDS element mapping shows that oxygen is mainly related to Bi ( Figure 7 in c).

[0116] Effect Example 4

[0117] Electrochemical measurements were performed using a three-electrode system in a closed H-type battery. 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, respectively. 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 the Pt electrode, Bi₂O₃ / Pt electrode, and Bi₂O₃ electrode in 1 M KOH containing 0.5 M glycerol. Figure 8 As shown in Figure a, at 0.8V RHE Under these conditions, the current density of Bi₂O₃ / Pt reaches 406.7 mA cm⁻¹. -2 Compared to Pt (215.8 mA cm⁻¹) -2 ) and Bi2O3 (21.4 mA cm -2 The values ​​were approximately 1.9 times and 19 times higher, respectively. Furthermore, the overpotential of the Bi₂O₃ / Pt prepared in Example 6 for GOR was approximately 0.23 V. RHE The overpotential for the oxygen evolution reaction is significantly lower than that without glycerol. The exposed Bi₂O₃ facilitates the adsorption of OH intermediates, thereby reducing the kinetic barrier to glycerol oxidation and promoting a lower onset potential, which is crucial for constructing unassisted PEC devices coupled to a photocathode. High-performance liquid chromatography analysis revealed that glyceric acid (GLA) is the major product of glycerol oxidation on Bi₂O₃ / Pt at 0.3 V. RHE The selectivity at that time was 68.84% ( Figure 8 (b) In the range of 0.3-0.8 V RHE Over a wide potential range, the overall selectivity for C3 products (including GLA, lactic acid, and tartaric acid) exceeds 90% at 0.3 V. RHE It reaches a maximum value of 98.58% at 0.8 V. Furthermore, at 0.8 V... RHE At that time, the selectivity of the platinum electrode for C3 products was only 47.3% ( Figure 8 (c). The maximum C3 yield of Bi2O3 / Pt is 2.96 mmol / cm. -2 h -1 Compared with the Pt electrode prepared in Comparative Example 4 (0.98 mmol cm⁻¹), -2 h -1 The value was approximately three times higher. Furthermore, in a 10-hour cycle test, Bi₂O₃ / Pt at 0.6 V... RHEMaintain a stable current density ( Figure 8 (d). More importantly, the selectivity of the C3 product remained above 95% in each cycle, and the productivity remained stable at ~2 mmol / cm². -2 h -1 ( Figure 8 (e). These are all attributed to the synergistic effect between Bi2O3 and Pt, where Bi2O3 promotes the efficient and sustained formation of C3 products.

[0118] Example of implementation effect 5

[0119] Simultaneous production of urea and high-value-added anode products under unbiased conditions remains a significant challenge, primarily due to the high overpotential required for urea synthesis. Therefore, we have, for the first time, designed an 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 (a) Taking the unbiased coupled photoelectrochemical system prepared in Example 6 as an example. It is worth noting that the CuMo / TCS || Bi₂O₃ / Pt system at 0 V... CE The photocurrent density at that time was -4.05 mA cm⁻¹. -2 ( Figure 9 (b) This is due to internal chemical deviation caused by the pH gradient between the two compartments of the battery. Simultaneously, its photocurrent density exceeds the OER and GOR values ​​of a PEC battery with platinum foil (CuMo / TCS || platinum foil) as the anode, at 0 V. CE The values ​​were -0.07 mA cm⁻¹. -2 and -1.91 mA cm -2 (Figure 9b). This indicates that the CuMo / TCS || Bi2O3 / Pt system has high charge transfer efficiency in the symbiosis of urea and C3. Furthermore, after 3 hours of stable operation under sunlight, the current density of the unassisted PEC system remains at approximately 85% of its initial value. Figure 9 (c) After six cycles, the FE of unrefined urea decreased from 52.83% to 48.63%, and the average urea yield was 126.76 μg / cm³. -2 ( Figure 9 (d). Meanwhile, the selectivity of GLA remained around 74.1-75.3%, the selectivity of total C3 products exceeded 98%, and the average C3 yield per cycle was 35 μmol / cm³. -2 ( Figure 9 (e).

[0120] Example of implementation effect 6

[0121] In addition, we designed a large-scale unbiased PEC system to assess the feasibility of producing urea and C3 chemicals under real sunlight conditions. Figure 10 (a) Taking the system of Example 6 as an example, photocathodes of different sizes were designed. Figure 10 (b) In laboratory tests, the total current generated by a PEC device with a phototube area of ​​4 square centimeters was 10.95 mA. Figure 10 (c) Under different test conditions, the Faraday efficiency of urea is basically consistent with the selectivity of C3 chemicals. Figure 10 (d). The yields of urea and C3 chemicals reached 707.17 μg / h. -1 and 197.13 μmol h -1 The area of ​​the photoelectrode was increased to 12 cm². 2 Subsequently, the system generated a total current of 24.86 mA under outdoor conditions, with yields of urea and C3 chemicals of 1319.68 μg h⁻¹. -1 and 381.48 μmol h -1 ( Figure 10 (e). We also assessed the economic feasibility under actual solar radiation conditions ( Figure 10 (f). The system generates 0.94 × 10⁻⁶ urea and C3 chemical revenues per hour, respectively. -6 US dollars and 1062.13 × 10 -6 The system, valued at US dollars, increased the value of raw materials by more than 275 times. It provides experimental verification for the unbiased electrochemical synthesis of urea and C3 products, and has potential practical application value.

[0122] In summary, this invention constructs a CuMo / TCS photocathode for the selective synthesis of urea. This photocathode has a very low onset potential of only 0.98 V. RHE At 0.4 V RHE The FE of urea was 73.3%. 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. Simultaneously, at 0.3–0.8 V... RHE Over a wide potential range, the Bi₂O₃ / Pt anode of this application exhibits selectivity for C₃ products exceeding 90%. Importantly, we constructed a CuMo / TCS || Bi₂O₃ / Pt unbiased coupled photoelectrochemical system, which achieved 4.05 mA cm⁻¹ under simulated solar illumination. -2of 1319.68 pg h -1 a C3 chemical yield of 381.48 pmol h -1 This work not only advances the study of PEC urea synthesis, but also provides experimental validation for the development of a bias-free PEC device that converts solar energy into high-value chemicals.

[0123] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a CuMo / TiO2 / CdS / Sb2S3photocathode, characterized in that, The steps are: (1) a precursor solution containing potassium antimonyl tartrate and anhydrous sodium thiosulfate is prepared, a fluorine-doped tin oxide substrate is placed in the precursor solution, and after ultrasonic treatment, a heating reaction is carried out in a reaction kettle, and after the reaction is completed, the initial deposition film is obtained by natural cooling, and the initial deposition film is subjected to annealing reaction I to obtain an Sb2S3 semiconductor thin film; (2) a reaction solution containing cadmium sulfate, ammonia and thiourea is prepared, and then the Sb2S3 semiconductor thin film of step (1) is immersed in the reaction solution, and after constant temperature reaction, a CdS / Sb2S3 heterojunction is obtained; (3) the CdS / Sb2S3 heterojunction of step (2) is placed in a vacuum chamber with tetrakis (dimethylamino) titanium as the titanium source and deionized water as the water source for atomic layer deposition, and after deposition is completed, annealing reaction II is carried out to obtain a TiO2 / CdS / Sb2S3 structure, which is denoted as TCS; (4) a deionized water solution containing copper chloride, sodium molybdate and ammonium oxalate is prepared, and after stirring, polyethylene glycol is added to obtain a deposition solution, and the TCS of step (3) is used as the working electrode and Ag / AgCl as the reference electrode for electrochemical deposition, and the obtained deposition sample is subjected to annealing reaction III to obtain a CuMo / TiO2 / CdS / Sb2S3 photo-cathode.

2. The method for preparing a CuMo / TiO2 / CdS / Sb2S3photocathode according to claim 1, characterized in that: In step (1), the mass ratio of potassium antimonyl tartrate to anhydrous sodium thiosulfate is 2.4-2.8:2.3-2.7; the heating reaction temperature is 130-140℃, and the time is 4.5-5.5h; the annealing reaction I is carried out in a nitrogen atmosphere, the temperature is 340-360℃, and the time is 18-22min; in step (2), the concentration of cadmium sulfate in the reaction solution is 3.0-3.4mg / mL, the volume concentration of ammonia is 19-23%v / v, and the concentration of thiourea is 16.5-17.5mg / mL; the constant temperature reaction temperature is 55-65℃, and the time is 13-17min.

3. The method for preparing a CuMo / TiO2 / CdS / Sb2S3photocathode according to claim 2, characterized in that: The temperature of the atomic layer deposition in the step (3) is 115-125 ℃, the cycle number is 600 times; the atmosphere of the annealing reaction II is nitrogen, the temperature is 195-205 ℃, and the time is 0.8-1.2 h; the concentration of the copper chloride in the step (4) is 0.08-0.12 mg / mL, the concentration of the sodium molybdate is 4.6-5.0 mg / mL, and the concentration of the ammonium oxalate is 4.5-5.5 mg / mL; the potential of the electrochemical deposition is -0.8 V AgCl The potential and the deposition time are 600-1200 s; the temperature of the annealing reaction III is 200-220 ℃, and the time is 25-35 min.

4. A CuMo / TiO2 / CdS / Sb2S3 photo-cathode prepared by the method of any one of claims 1-3.

5. A bias-free coupled photoelectrochemical system, comprising a reaction cell, a working station, a stirring device, a gas path device; the reaction cell comprises a cathode reaction cell and an anode reaction cell, characterized in that: The cathode reaction tank uses the CuMo / TiO2 / CdS / Sb2S3 photo-cathode of claim 4 as the cathode.

6. The unbiased coupled photoelectrochemical system of claim 5, wherein: The anode reaction tank uses a Bi2O3 / Pt anode as the anode; the preparation steps of the Bi2O3 / Pt anode are: a. Nickel foam is immersed in deionized water, then chloroplatinic acid solution and concentrated hydrochloric acid solution are added, and finally polyvinylpyrrolidone is added, stirring until a uniform solution is formed, and then heating after standing to obtain a black precipitate, which is subjected to annealing reaction IV to obtain a Pt electrode; b. A mixed solution of bismuth nitrate is prepared as a deposition solution, and the Pt electrode of step a is used as the working electrode and Ag / AgCl as the reference electrode for electrochemical deposition, and the obtained deposition electrode is subjected to annealing reaction V to obtain a Bi2O3 / Pt anode.

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

8. Use of a bias-free 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 generating C3 chemicals on the anode; ② generating urea on the cathode.

9. Use of a bias-free coupled photoelectrochemical system according to claim 8, characterized in that: The application conditions are 50-200 mW cm -2 A solar light illuminated unbiased photocatalytic system.

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