A CuOs / CdS / SSS photocathode, its preparation method and application

Abstract

The present invention belongs to the field of chemical engineering, and relates to photoelectrochemical synthesis. The present invention provides a CuOs / CdS / SSS photocathode, a preparation method thereof, and an application thereof. By constructing a copper osmium catalyst deposited on an Sb2(S,Se)3-based semiconductor as a photocathode, the photocathode reaches a photocurrent density of 5.6 mA cm RHE at 0 V ‑2 . Under AM 1.5G illumination, it has an ultra-low onset potential of 0.86 V RHE and a Faraday efficiency of 96.98%. The glycerol oxidation reaction on a bismuth ruthenium modified titanium dioxide photoanode is used to replace the oxygen evolution reaction to achieve bias-free ammonia production. In a bias-free system, the photocathode coupled with the BiRu / TiO2 photoanode shows a stable photocurrent response of 1.4 mA cm ‑2 . Under AM 1.5G illumination, the Faraday efficiency of the ammonia product exceeds 97%. Solar-driven ammonia production from waste nitrate is realized, thereby optimizing the photocarrier transport path.

Description

Technical Field

[0001] The present invention belongs to the field of chemical engineering, and relates to photoelectrochemical synthesis, particularly nitrate reduction and ammonia synthesis. Background Art

[0002] Ammonia is the second most produced chemical globally and is a key precursor for fertilizers and fine chemicals. However, the traditional energy-intensive Haber-Bosch ammonia synthesis process generates a large amount of carbon emissions. Secondly, with the development of industry, agriculture and animal husbandry, and human activities, the accumulation of nitrates in the environment has gradually attracted the attention of the ecological environment field. Sustainable solar energy makes it an option for renewable energy applications. The photoelectrochemical nitrate reduction reaction for ammonia production is a promising approach carried out at ambient temperature and pressure, without carbon dioxide emissions, and is expected to achieve a closed-loop nitrogen cycle and generate economic benefits. However, since the conversion of nitrate to ammonia involves an eight-electron transfer process, its solar-to-ammonia conversion efficiency is low, the selectivity is poor, and the onset potential is high. This performance is mainly due to the low utilization rate of solar flux and slow charge transport in the photoanode. On the one hand, compared with photoelectrochemical nitrate reduction, the hydrogen evolution reaction becomes more competitive. On the other hand, nitrite, as an incomplete reduction product of nitrate, poses a threat to the selectivity and yield of ammonia. The application with publication number CN 114672822 A provides a three-dimensional self-supporting electrode material of inverse perovskite nitride for nitrate reduction to ammonia, improving the performance of the electrode material from the perspectives of conductivity and active area; the application with publication number CN119221026A provides a dual-mode nanoporous silver / silver cobalt bimetallic tandem catalyst, improving the efficiency of ammonia synthesis by increasing active sites. However, there has been no in-depth study on how to utilize highly selective photoelectrochemical nitrate reduction to ammonia and achieve light-driven ammonia synthesis without an external voltage, which is extremely promising. Summary of the Invention

[0003] To solve the above technical problems, the present invention proposes a CuOs / CdS / SSS photocathode and its preparation method and application.

[0004] The technical solution of the present invention is realized as follows:

[0005] On the one hand, the present application provides a preparation method of a CuOs / CdS / SSS photocathode, and the steps are as follows:

[0006] (1) Add thiourea, cadmium sulfate hydrate and ammonia water to deionized water to obtain a precursor solution;

[0007] (2) Immerse Sb2(S, Se)3 in the precursor solution and carry out annealing reaction I in air to obtain CdS / Sb2(S,Se)3;

[0008] (3) In the presence of a titanium source and an oxygen source, TiO₂ / CdS / Sb₂(S, Se)₃ with a deposited TiO₂ passivation layer is obtained by atomic layer deposition of CdS / Sb₂(S, Se)₃, and then annealing reaction II is carried out in an inert atmosphere to prepare CdS / SSS;

[0009] (4) CdS / SSS is immersed in a mixed alcohol solution of CuOs, and then annealing reaction III is carried out in an inert atmosphere to obtain a CuOs / CdS / SSS photocathode.

[0010] In the above step (1), the mass ratio of thiourea, cadmium sulfate hydrate and ammonia water is 1 - 3:1:85; the concentration of ammonia water is 20 - 30% wt; the volume ratio of ammonia water to deionized water is 2 - 4:10.

[0011] In the above step (2), the soaking temperature is 55 - 75 °C and the time is 5 - 15 minutes, and the temperature of annealing reaction I is 150 - 300 °C and the time is 1 - 3 hours.

[0012] In the above step (3), the titanium source is titanium bis(ethylcyclopentadienyl) (99% purity); the oxygen source is water.

[0013] The temperature of the above atomic layer deposition is 100 - 150 °C, and the number of cycles is 400 - 600 times; the temperature of annealing reaction II is 150 - 300 °C and the time is 1 - 3 hours.

[0014] In the above step (4), the solvent in the mixed alcohol solution of CuOs is a mixture of ethanol and isopropanol with a volume ratio of 2 - 5:1; the concentration of CuOs in the mixed alcohol solution of CuOs is 1 - 5 mg / mL. The preparation method of CuOs used in this application is as follows: CuO powder reacts completely with a 4 - 8 g / L NaBH₄ solution, is centrifuged and collected, dried in vacuum, and ground for 3 hours to obtain Cu powder. The obtained Cu powder is immersed in an aqueous solution containing 1 - 4 mM OsCl₃ and 1 M HCl for a displacement reaction to obtain CuOs powder.

[0015] The temperature of the above annealing reaction III is 250 - 450 °C and the time is 10 - 30 minutes.

[0016] In the second aspect, a CuOs / CdS / SSS photocathode prepared by the above method is claimed.

[0017] In the third aspect, the application of the CuOs / CdS / SSS photocathode in nitrate reduction and ammonia production is claimed.

[0018] In a fourth aspect, there is a request for protection of an apparatus for photoelectrochemical ammonia synthesis, which includes a reference electrode, a counter electrode, a cathode reaction cell, and an anode reaction cell; the cathode reaction cell uses a CuOs / CdS / SSS photocathode as the cathode, and the anode reaction cell uses the counter electrode as the anode.

[0019] Further, the reference electrode is an Ag / AgCl reference electrode; the counter electrode is a Pt electrode.

[0020] When this electrode system operates, the CdS / SSS light-absorbing layer is excited by light to generate electron-hole pairs. The photo-generated electrons are extracted into the electrolyte through the heterojunction interface between CdS and Sb2(S, Se)3. At the same time, the surface catalyst layer on the CuOs improves the surface reaction kinetics, promotes the nitrate reduction reaction process, and enhances the selectivity for ammonia.

[0021] The present invention has the following beneficial effects:

[0022] 1. The present invention has developed a high-performance PEC cell using an Sb2(S, Se)3 photocathode and deposited a copper osmium electrocatalyst (CuOs / CdS / SSS) for selective light-driven nitrate reduction to obtain highly efficient ammonia products. In particular, compared with traditional photoanodes, it exhibits higher performance at low overpotentials. In addition, unbiased ammonia production is achieved through coupling with the glycerol oxidation reaction. The CuOs / CdS / SSS photocathode coupled with the glycerol oxidation photoanode shows a stable light response of 1.4 mA cm -2 and the Faradaic efficiency of the ammonia product exceeds 90%. Under AM 1.5G intensity illumination, efficient conversion of nitrate to ammonia is achieved without applying any potential. This work promotes the development of producing value-added products from low-value / waste compounds.

[0023] 2. The present invention has realized solar-driven production of ammonia from waste nitrate by constructing a copper osmium catalyst deposited on an Sb2(S, Se)3-based semiconductor, thereby optimizing the photo-carrier transport path. The obtained photocathode reaches a photocurrent density of 5.6 mAcm RHE at 0 V -2 and has an ultra-low onset potential of 0.86 V RHE and a Faradaic efficiency of 96.98% under AM 1.5G illumination. We further use the glycerol oxidation reaction (GOR) on a bismuth ruthenium-modified titanium dioxide (BiRu / TiO2) photoanode instead of the oxygen evolution reaction to achieve unbiased ammonia production. In the unbiased system, the CuOs / CdS / SSS photocathode coupled with the BiRu / TiO2 photoanode shows a stable light response of 1.4 mA cm -2 and the Faradaic efficiency of the ammonia product exceeds 97% under AM 1.5G illumination.

[0024] 3. This application has developed a high-performance PEC cell using an Sb2(S, Se)3 photocathode and deposited a copper osmium electrocatalyst (CuOs / CdS / SSS) for selective PEC NO3RR to obtain highly efficient ammonia products. The resulting photocathode reaches a photocurrent density of 5.6 mA cm RHE at 0 V -2 with an ultra-low onset potential of 0.86 V RHE . In particular, compared with traditional photoanodes, it exhibits higher performance at low overpotentials. In addition, we have employed a glycerol oxidation reaction on a bismuth ruthenium decorated titanium oxide photoanode to achieve unbiased ammonia production without an external voltage. Moreover, the performance is maintained for 10 hours without significant degradation, which is the best performance among all reported unbiased PEC cells to date. This work promotes the development of producing value-added products from low-value / waste compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 shows the PEC NO3RR performance of CdS / SSS-5, CdS / SSS-10, and CdS / SSS-15 samples.

[0027] Figure 2 is a schematic diagram of electrode synthesis and scanning electron microscope images, where a is the schematic diagram of electrode synthesis; b is CdS / SSS; c is Cu / CdS / SSS; d is CuOs / CdS / SSS.

[0028] Figure 3 is a linear sweep voltammogram, where a is the linear sweep voltammogram of different samples in an acidic nitrate solution; b is the onset potential curve of the samples; c is the linear sweep voltammogram of different samples in an acidic solution without nitrate.

[0029] Figure 4Test results of CuOs / TiO2 / CdS / Sb2(S, Se)3 for simulating nitrate removal and ammonia production; where a is the Faradaic efficiency of ammonia production of CuOs / CdS / SSS at different potentials; b is the ammonia production rate of CuOs / CdS / SSS at different potentials; c is the ammonia selectivity of CuOs / CdS / SSS at different potentials; d is the ammonia production rate and Faradaic efficiency of CuOs / CdS / SSS at different nitrate concentrations; e is the Faradaic efficiency of CuOs / CdS / SSS for nitrite at different potentials; f is the chronoamperometry curve of CuOs / TiO2 / CdS / Sb2(S, Se)3 at 1.0 V RHE under; g is the cyclic durability test of CuOs / CdS / SSS.

[0030] Figure 5 For in-situ electrochemical test analysis; where a is on-line differential electrochemical mass spectrometry analysis; b is in-situ Fourier transform infrared spectroscopy analysis of Cu / CdS / SSS; c is in-situ Fourier transform infrared spectroscopy analysis of Cu / CdS / SSS; d is the hydrogen radical electron paramagnetic resonance spectrum of CuOs / CdS / SSS in the absence of nitrate; e is the hydrogen radical electron paramagnetic resonance spectrum of CuOs / CdS / SSS in the presence and absence of nitrate.

[0031] Figure 6 For the coupling experiment result diagram; where a is the schematic diagram of the coupling device without bias voltage; b is the chronoamperometry curve under the condition of no bias voltage; c is the production efficiency of each product. Specific implementation manners

[0032] Next, in combination with the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0033] The test methods used in the following experimental examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used are all reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0034] Cadmium sulfate hydrate was purchased from Beijing Innochem Science & Technology Co., Ltd., CAS: 7790-84-3.

[0035] Ammonia water is liquid ammonia, CAS: 7664-41-7.

[0036] The preparation steps of the raw material Sb2(S, Se)3 photocathode are as follows: Dissolve 1.33 g of potassium antimonyl tartrate and 1.98 g of sodium thiosulfate pentahydrate in 100 mL of deionized water. Subsequently, transfer 20 mL of the solution to a 30 mL reactor. Place the fluorine-doped tin oxide substrate (1×2 cm 2 ) face down in the reactor and heat it at 135 °C for 1 hour to form a seed layer on the substrate. Next, dissolve 1.33 g of potassium antimonyl tartrate, 1.98 g of sodium thiosulfate pentahydrate and 0.061 g of selenium in 100 mL of deionized water at 75 °C, and perform the second hydrothermal method at 135 °C for 4 hours. Then heat the film at 250 °C for 20 minutes in a nitrogen atmosphere to form the Sb2(S, Se)3 photocathode.

[0037] Example 1

[0038] A method for preparing a CdS / SSS photocathode in this example is as follows:

[0039] (1) Add 0.114 g of thiourea, 0.063 g of cadmium sulfate hydrate and 6 mL of ammonia water to 20 mL of deionized water to obtain a precursor solution;

[0040] (2) Immerse the prepared Sb2(S, Se)3 in the above precursor solution at 65 °C for 5, 10, and 15 minutes respectively to deposit CdS, and then anneal it in air at 200 °C for 1 hour to form CdS / Sb2(S, Se)3;

[0041] (3) At 120 °C, use titanium tetrakis(dimethylamino) and water as the titanium source and oxygen source respectively, and deposit a TiO2 passivation layer on CdS / Sb2(S, Se)3 by atomic layer deposition (ALD). A total of 600 ALD cycles are carried out, and then anneal it at 200 °C under Ar conditions for 1 hour to obtain the CuOs / CdS / SSS photocathode.

[0042] The samples prepared above are respectively labeled as CdS / SSS-5 (immersed for 5 minutes), CdS / SSS-10 (immersed for 10 minutes) and CdS / SSS-15 (immersed for 15 minutes) according to the different CdS immersion times.

[0043] Then, a Pt sheet was used as the anode counter electrode, CdS / SSS-5, CdS / SSS-10, and CdS / SSS-15 were used as the cathode working electrodes respectively, Ag / AgCl was used as the reference electrode. The cathode and the reference electrode were inserted into the cathode cell, the Pt sheet was inserted into the anode cell, and the cathode cell and the anode cell were separated by a Nafion117 membrane. The electrolytes for the cathode and the anode were 0.5 M potassium sulfate + 0.1 M potassium nitrate solution, and the pH was adjusted to 2 with sulfuric acid. The test was carried out using a CHI660 electrochemical workstation to measure the linear voltammetric curve of the test electrode, with the scanning range of 1.0 V RHE -0.0 V RHE , the scanning rate was 10 mV / s, and the cathode was irradiated with calibrated AM1.5G light intensity, and the reaction was carried out at room temperature.

[0044] The PEC NO3RR performance of the CdS / SSS-5, CdS / SSS-10, and CdS / SSS-15 samples was tested, and the results are as Figure 1 shown. It can be seen from Figure 1 that the loading time of the CdS layer significantly affected the photoelectrochemical reaction activity of the samples, and the optimal condition was soaking for 10 min. The optimal CuOs / CdS / SSS sample was prepared according to this condition.

[0045] Example 2

[0046] A preparation method of a CuOs / CdS / SSS photocathode in this example is as follows:

[0047] (1) 0.114 g of thiourea, 0.063 g of cadmium sulfate hydrate and 6 mL of ammonia water were added to 20 mL of deionized water to obtain a precursor solution;

[0048] (2) The prepared Sb2(S, Se)3 was soaked in the above precursor solution at 65 °C for 10 minutes to deposit CdS, and then annealed in air at 200 °C for 1 hour to form CdS / Sb2(S, Se)3;

[0049] (3) At 120 °C, titanium tetrakis(dimethylamino) and water were used as the titanium source and the oxygen source respectively, and a TiO2 passivation layer was deposited on CdS / Sb2(S, Se)3 by atomic layer deposition (ALD). A total of 600 ALD cycles were carried out, and then annealed in Ar at 200 °C for 1 hour. The sample prepared above was denoted as CdS / SSS;

[0050] (4) For CuOs decoration, at room temperature, CuO powder reacts completely with an 8 g / L NaBH4 solution, and the product is collected by centrifugation and dried under vacuum, then ground for 3 hours to obtain Cu powder. The obtained Cu powder is immersed in an aqueous solution containing 1 mM OsCl3 and 1 M HCl for a displacement reaction to obtain CuOs powder. 4 mg of the obtained CuOs powder is ultrasonically dispersed in a 1 mL mixed solution of ethanol and isopropanol with a volume ratio of 3:1, and then annealed at 250 °C for 20 minutes in an Ar atmosphere. The CuOs is loaded onto the prepared CdS / SSS surface to obtain the final CuOs / CdS / SSS photocathode.

[0051] The CuOs / TiO2 / Sb2(S, Se)3 photocathode is fabricated by a two-step hydrothermal method, and the preparation principle is as Figure 2 shown in a of the figure. Briefly, first, a Sb2S3 seed layer is prepared on a fluorine-doped tin oxide (FTO) substrate using the hydrothermal method. After that, a Sb2(S, Se)3 light absorption layer is formed during the second hydrothermal process by adding selenium urea to the precursor. During the reaction process, a gradient doping rich in selenium is formed at the bottom of the film. CdS is deposited as a transfer layer on the top surface of selenium urea, and then an amorphous TiO2 protective layer is deposited (the obtained electrode is labeled as CdS / SSS). Finally, a copper-osmium-based co-catalyst is modified on CdS / SSS by cyclic voltammetry, and the sample is denoted as CuOs / CdS / SSS. For comparison, a Cu co-catalyst deposited on the CdS / SSS photocathode (labeled as Cu / CdS / SSS) is synthesized.

[0052] The morphological structures of the related photocathodes are observed by scanning electron microscopy (SEM). The original SSS and CdS / SSS show dense grains with a size of about 500 ± 100 nm. The CuOs catalyst shows a nanoparticle structure on the surface of CuOs / CdS / SSS, which is similar to the nanoparticle structure of Cu / CdS / SSS. The SEM images of the electrodes are as Figure 2 shown.

[0053] Example 3

[0054] A preparation method of a CuOs / CdS / SSS photocathode in this example is as follows:

[0055] (1) Add 0.063 g of thiourea, 0.063 g of cadmium sulfate hydrate, and 6 mL of ammonia water to 20 mL of deionized water to obtain a precursor solution;

[0056] (2) Immerse the prepared Sb2(S, Se)3 in the above precursor solution at 55 °C for 10 minutes to deposit CdS, and then anneal in air at 150 °C for 1.5 hours to form CdS / Sb2(S, Se)3;

[0057] (3) At 100 °C, using titanium tetrakis(dimethylamino) and water as the titanium source and oxygen source respectively, a TiO2 passivation layer was deposited on CdS / Sb2(S, Se)3 by atomic layer deposition (ALD). A total of 500 ALD cycles were carried out, and then annealed at 150 °C for 1 hour under Ar conditions. The sample prepared above was denoted as CdS / SSS;

[0058] (4) For CuOs modification, CuO powder was completely reacted with a 4 g / L NaBH4 solution, centrifuged, collected, vacuum dried, and ground for 3 hours to obtain Cu powder. The obtained Cu powder was immersed in an aqueous solution containing 3 mM OsCl3 and 1 M HCl for a displacement reaction to obtain CuOs powder. The obtained CuOs powder was dispersed in a mixed solution of 1 mL ethanol and isopropanol with a volume ratio of 2:1, and then annealed at 300 °C for 25 minutes in an Ar atmosphere. CuOs was loaded onto the surface of the prepared CdS / SSS to obtain the final CuOs / CdS / SSS photocathode.

[0059] Example 4

[0060] A preparation method of a CuOs / CdS / SSS photocathode in this example is as follows:

[0061] (1) 0.189 grams of thiourea, 0.063 grams of cadmium sulfate hydrate and 8 mL of ammonia water were added to 20 mL of deionized water to obtain a precursor solution;

[0062] (2) The prepared Sb2(S, Se)3 was immersed in the above precursor solution at 70 °C for 10 minutes to deposit CdS, and then annealed in air at 200 °C for 1 hour to form CdS / Sb2(S, Se)3.

[0063] (3) At 130 °C, using titanium tetrakis(dimethylamino) and water as the titanium source and oxygen source respectively, a TiO2 passivation layer was deposited on CdS / Sb2(S, Se)3 by atomic layer deposition (ALD). A total of 400 ALD cycles were carried out, and then annealed at 250 °C for 3 hours under Ar conditions. The sample prepared above was denoted as CdS / SSS.

[0064] (4) For CuOs decoration, the CuO powder reacts completely with the 5 g / L NaBH4 solution, is centrifuged for collection and dried under vacuum, and ground for 3 hours to obtain Cu powder. The obtained Cu powder is immersed in an aqueous solution containing 2 mM OsCl3 and 1 M HCl for a displacement reaction to obtain CuOs powder. The obtained CuOs powder is dispersed in a mixed solution of 1 mL ethanol and isopropanol with a volume ratio of 4:1, and then annealed at 250 °C for 30 minutes in an Ar atmosphere. The CuOs is loaded onto the prepared CdS / SSS surface to obtain the final CuOs / CdS / SSS photocathode.

[0065] Example 5

[0066] A method for preparing a CuOs / CdS / SSS photocathode in this example is as follows:

[0067] (1) Add 0.102 grams of thiourea, 0.063 grams of cadmium sulfate hydrate, and 10 mL of ammonia water to 20 mL of deionized water to obtain a precursor solution;

[0068] (2) Immerse the prepared Sb2(S, Se)3 in the above precursor solution at 75 °C for 10 minutes to deposit CdS, and then anneal in air at 200 °C for 3 hours to form CdS / Sb2(S, Se)3;

[0069] (3) At 120 °C, use tetrakis(dimethylamino)titanium and water as the titanium source and oxygen source respectively, and deposit a TiO2 passivation layer on CdS / Sb2(S, Se)3 by atomic layer deposition (ALD). A total of 500 ALD cycles are carried out, and then anneal at 150 °C for 1 hour under Ar conditions. The above-prepared sample is denoted as CdS / SSS;

[0070] (4) For CuOs decoration, the CuO powder reacts completely with the 8 g / L NaBH4 solution, is centrifuged for collection and dried under vacuum, and ground for 3 hours to obtain Cu powder. The obtained Cu powder is immersed in an aqueous solution containing 4 mM OsCl3 and 1 M HCl for a displacement reaction to obtain CuOs powder. The obtained CuOs powder is dispersed in a mixed solution of 1 mL ethanol and isopropanol with a volume ratio of 5:1, and then annealed at 450 °C for 10 minutes in an Ar atmosphere. The CuOs is loaded onto the prepared CdS / SSS surface to obtain the final CuOs / CdS / SSS photocathode.

[0071] Example of implementation effect 1

[0072] An apparatus for photoelectrochemical ammonia synthesis, comprising a reference electrode, a counter electrode, a cathode reaction cell, and an anode reaction cell; the cathode reaction cell uses the CuOs / CdS / SSS photocathode prepared in Example 2 as the cathode, and the anode reaction cell uses the counter electrode as the anode. Specifically, in the specific experimental process: a Pt sheet is used as the anode counter electrode, CuOs / CdS / SSS is used as the cathode working electrode, Ag / AgCl is used as the reference electrode, the cathode and the reference electrode are inserted into the cathode cell, the Pt sheet is inserted into the anode cell, and the cathode cell and the anode cell are separated by a Nafion117 membrane. The electrolyte is a 0.5 M potassium sulfate solution with or without 0.1 M potassium nitrate, and sulfuric acid is used to adjust the pH to 2. All electrochemical tests are performed using a CHI660 electrochemical workstation. The linear voltammetry curve of the test electrode is scanned in the range of 1.0 V RHE - 0.0 V RHE , and the scanning rate is 10 mV / s. All potentials are calibrated to RHE according to the following formula:

[0073] E RHE = E SCE + 0.0591×pH (1)

[0074] where E SCE represents the experimental applied potential. The cathode is irradiated with calibrated AM1.5G light intensity and the reaction is carried out at room temperature. The durability test is carried out using chronoamperometry. The Faraday efficiency and yield tests are calculated by chronoamperometry tests for a certain period of time. The calculation formula for the NH3 Faraday efficiency (FE) is as follows;

[0075] (2)

[0076] where Q represents the total coulomb quantity (C) in the chronoamperometry test, Q NH3 is the coulomb quantity required to produce NH3, n is the number of electron transfers (8 for 1 mole of NH3), V is the volume of the cathode solution in the cathode chamber (30 mL), c NH3 is the concentration of the produced NH3, and F is the Faraday constant (96.485 C mol -1 ). To ensure the accuracy of the experiment. We carried out three independent experiments respectively and measured the error bars.

[0077] The yield of the product is calculated according to the following formula:

[0078] (3)

[0079] Where V is the volume of the electrolyte in the cathode chamber, t is the electrolysis time, and m is the area of the photoelectrode. The error bars correspond to the standard deviation of three independent measurements, and the center value of the error bars is the average of three independent measurements. The cathode was illuminated by a calibrated AM1.5G light intensity +, and the reaction was carried out at room temperature.

[0080] 1. The nitrate reduction performance of the photocathode was measured in an H-type electrolytic cell with 0.5 M K2SO4 and 0.1 M KNO3 (pH=2) under AM 1.5G irradiation without iR correction. Figure 3 As shown in a, under dark conditions, the photocathode has no obvious photocurrent density. Under one sun illumination, the original SSS at 0 V RHE The following shows -1.57 mA cm -2 CdS / SSS and CuOs / CdS / SSS show increased photocurrent density at the tested potentials, respectively, at 0 V RHE and -3.37 mA cm -2 and -5.6 mA cm -2 It is worth noting that in the range of 0.4 to 0.8 V RHE In the potential range of 2.3 V, Cu / CdS / SSS and CuOs / CdS / SSS exhibit similar photocurrent densities. The onset potentials of Cu / CdS / SSS and CuOs / CdS / SSS shift significantly to 0.84 V, respectively. RHE and 0.86 V RHE , significantly better than SSS (0.42 V RHE ) and CdS / SSS (0.63V RHE ) of the starting potential ( Figure 3 b). This proves that the modification of Cu or CuOs cocatalyst can promote the conversion of nitrate. At the same time, the photocathode with a more positive onset potential can prevent the competitive hydrogen evolution reaction (HER). - Compared with the photocathode without adding NO3 - In the case of Figure 3 c), which indicates high nitrate reduction activity of the photocathode. Note that compared with Cu / CdS / SSS (0.17 mA cm −2 ) compared to 0 V RHE The photocurrent density of CoOs / CdS / SSS in the electrolyte without nitrate addition is -0.26 mAcm -2 The increase in the HER activity of CoOs / CdS / SSS may be related to the ability of Os co-catalyst to adsorb hydrogen protons.

[0081] 2. This application also evaluated the Faraday efficiency (FE), ammonia production, and the durability of the electrode ( Figure 4 ). As Figure 4 shown in a of RHE , the ammonia Faraday efficiency of CdS / SSS was 35.6% at 0.1 V. As the potential shifted positively, the ammonia Faraday efficiency decreased, indicating that its slow charge carrier dynamics hindered the conversion of nitrate to ammonium. The ammonia Faraday efficiency of Cu / CdS / SSS was 70.4% at 0.1 V RHE and decreased as the potential shifted positively. At high overpotential conditions, the Faraday efficiency of ammonia was relatively high, indicating the inertness of copper towards the hydrogen evolution reaction. In contrast, the average ammonia Faraday efficiency of CuOs / CdS / SSS was greater than 90% in the potential range of 0.1 to 0.8 V RHE and reached a maximum of 96.98% at 0.6 V RHE . Figure 4 As shown in b of + , the NH4 RHE yield of CuOs / CdS / SSS was the highest among these photocathodes, reaching 19.87 μmol h -1 cm -2 at 0.1 V -1 cm -2 , higher than that of Cu / CdS / SSS (15.10 μmol h -1 cm -2 ) and CdS / SSS (2.25 μmol h- 1 cm -2 ). The selectivity of ammonia indicated that the selectivity of CuOs / CdS / SSS gradually increased as the potential shifted negatively and reached 95% at -0.2 V RHE ( Figure 4 c). The average NH4 + selectivity of CuOs / CdS / SSS at the measured potential was approximately 99%, significantly higher than that of Cu / CdS / SSS (38.9%) and CdS / SSS (23.3%). These results indicate that the deposition of the CuOs catalyst improved the reaction kinetics of the photocathode. In addition, the NH4 + yield and Faraday efficiency were also affected by the concentration of the nitrate source. CuOs / CdS / SSS showed that when the nitrate concentration increased from 10 mM to 200 mM, the ammonia yield increased from 1.18 μmol h -1 cm -2 to 5.67 μmol h -1 cm -2 , and the average Faraday efficiency exceeded 96% ( Figure 4d). This indicates that the electrode can maintain a high selectivity for active hydrogen during the nitrate reduction process within a wide range of nitrate concentrations, thus enabling efficient intermediate hydrogen generation.

[0082] Nitrite is the main by-product during the nitrate reduction process, seriously affecting the hydrogenation reduction process of nitrate. Therefore, we investigated the performance of the corresponding photocathode in generating nitrite, as Figure 4 shown in e). Except for CdS / SSS, Cu / CdS / SSS generates a large amount of nitrite at the measured potentials. During long-term operation, the catalytic activity and product yield of CuOs / CdS / SSS were further studied. The photocathode had a stable photocurrent density at 0.6 and 0.4 V RHE for 6 hours, and its average Faraday efficiency remained at 93% within 12 hours ( Figure 4 shown in f). In addition, this sample maintained stable ammonia production and Faraday efficiency during 20 cyclic tests ( Figure 4 shown in g), indicating that this photocathode has good stability.

[0083] 3. Online differential electrochemical mass spectrometry (DEMS) and in-situ Fourier transform infrared spectroscopy (FTIR) were used to explore the potential reaction mechanism and detect the intermediate species generated on the photocathode during the PEC NO3RR reaction under illumination. Figure 5 a shows the function of the mass-to-charge ratio (m / z) signal recorded on CuOs / CdS / SSS as a function of time, along with 5 subsequent cyclic voltammetry scans (each cycle including a chronoamperometry scan at 0.6 V RHE ). The m / z signals at 46, 30, 31, 33, and 17 correspond to NO2, NO, NOH, NH2OH, and NH3 respectively. This result implies a possible reaction pathway: *NO2 → *NO → *NOH → *NHOH → *NH2OH → *NH → *NH2 → *NH3.

[0084] From Figure 5 the in-situ Fourier transform infrared measurement results in b and c, it can be seen that at 0.8 V RHE , the peak of *NO2 appears at ~1241 cm -1 , representing the nitrite formed during nitrate reduction on Cu / CdS / SSS. The intensity of this peak increases with the increase of the applied potential, reaching a more negative range. The peak related to *NH appears at 1432 cm -1 , while the characteristic peak of *NOH appears at 1365 cm -1 . As the potential changes from 0.8 V RHE to 0.3 VRHE , a small peak at 1125 cm -1 can be observed. This is the -N-O- stretching vibration of hydroxylamine (NH2OH), which is a key intermediate in the formation of NH3. It should be noted that compared with Cu / CdS / SSS, the potential at which these hydrogenation intermediates appear on CuOs / CdS / SS is more positive, which confirms the fast hydrogenation kinetics of the CuOs catalyst for nitrogen-oxygen intermediates. In addition, a series of weak peaks related to the *NO signal appear at ~1589 cm -1 on Cu / CdS / SSS, while these peaks are not observed on CuOs / CdS / SSS. Instead, a *H2O peak at 1645 cm -1 can be observed on CuOs / CdS / SSS. This means that *H can be effectively separated from H2O and promote the formation of NH3 by transferring to nitrogen-oxygen intermediates. To evaluate the amount of hydrogen radicals (*H) generated or consumed during the nitrate reduction process, electron paramagnetic resonance (EPR) analysis was carried out using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a radical trapping reagent. As shown in Figure 5 d, in the absence of nitrate, Os / CdS / SSS and CuOs / CdS / SSS show similar but stronger DMPO-*H signals than Cu / CdS / SSS (the intensity ratio of nine characteristic peaks is 1:1:2:1:2:1:2:1:1:1), indicating that *H is preferentially adsorbed on Os or CuOs sites compared with Cu sites. In the presence of nitrate, almost no DMPO-*H signal can be detected on CuOs / CdS / SSS ( Figure 5 e). This proves that the *H generated on the surface of CuOs / CdS / SSS is rapidly consumed during the hydrogenation of surface-active nitrogen-containing intermediates, resulting in excellent ammonia production and Faraday efficiency.

[0085] Example of implementation effect 2

[0086] To demonstrate the ability of the tandem cell to achieve load-free operation, we integrated a CuOs / CdS / SSS photocathode with a BiRu / TiO2 photoanode to achieve unassisted production of ammonia and three-carbon products (C3). Specifically, during the specific experiment: a two-electrode electrochemical cell system was used. The BiRu / TiO2 electrode was used as the anode, and CuOs / CdS / SSS was used as the cathode. The cathode electrolyte was a 0.5 M potassium sulfate solution containing 0.1 M potassium nitrate, and the pH was adjusted to 2 using sulfuric acid. The anode electrolyte was a 0.1 M glycerol solution, and the pH value was adjusted to 2 using sulfuric acid. The cathode compartment and the anode compartment were separated by a Nafion117 ion exchange membrane. The anode and cathode were irradiated with calibrated AM1.5G light intensity, and the reaction was carried out at room temperature. This device is a bias-free device and does not require an external voltage to be applied. The chronoamperometric data of this device were collected by a CHI660 electrochemical workstation. The product yields were detected by an ultraviolet-visible spectrophotometer and liquid chromatography.

[0087] The test results are as Figure 6 shown in a of. This system consists of two photo electrodes, which are connected by copper wires in a two-chamber reactor. The bias-free photoelectrochemical system on CuOs / CdS / SSS‖BiRu / TiO2 shows a stable ~1.4 mA cm -2 photo response for 10 hours ( Figure 6 shown in b of). The yields of ammonia and C3 increase with time. After 10 hours, the cumulative yields of ammonia and C3 reach 55.12 μmol cm -1 and 132.52 μmol cm -1 respectively ( Figure 6 shown in c of). This provides a practical application for the direct conversion of solar energy into high-value chemicals by bias-free PEC synthesis.

[0088] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a CuOs / CdS / SSS photocathode, characterized in that, The steps are as follows: (1) Add thiourea, cadmium sulfate hydrate, and ammonia water to deionized water to obtain a precursor solution; (2) Immerse Sb2(S, Se)3 in the precursor solution and perform annealing reaction I in air to obtain CdS / Sb2(S, Se)3; (3) In the presence of a titanium source and an oxygen source, CdS / Sb2(S, Se)3 is deposited with a TiO2 passivation layer by atomic layer deposition, and then annealing reaction II is carried out in an inert atmosphere to prepare CdS / SSS; (4) Immerse CdS / SSS in a mixed alcohol solution of CuOs, and then carry out annealing reaction III in an inert atmosphere to obtain a CuOs / CdS / SSS photocathode; The preparation steps of the CuOs are as follows: CuO powder reacts completely with a 4 - 8 g / L NaBH4 solution, centrifugally collected and vacuum dried, and ground for 3 hours to obtain Cu powder; the obtained Cu powder is immersed in an aqueous solution containing 1 - 4 mM OsCl3 and 1 M HCl for a displacement reaction to obtain CuOs.

2. The preparation method of the CuOs / CdS / SSS photocathode according to claim 1, characterized in that: In step (1), the mass ratio of thiourea, cadmium sulfate hydrate, and ammonia water is 1 - 3:1:85; the concentration of ammonia water is 25 - 30% wt; the volume ratio of ammonia water to deionized water is 2 - 4:

10.

3. The preparation method of the CuOs / CdS / SSS photocathode according to claim 2, characterized in that: In step (2), the soaking temperature is 55 - 75 °C, the time is 5 - 15 minutes, the temperature of annealing reaction I is 150 - 300 °C, and the time is 1 - 3 hours.

4. The preparation method of the CuOs / CdS / SSS photocathode according to claim 3, wherein: In step (3), the titanium source is titanium bis(ethylcyclopentadienyl); the oxygen source is water.

5. The preparation method of the CuOs / CdS / SSS photocathode according to claim 4, characterized in that: The temperature of the atomic layer deposition is 100 - 150 °C, and the number of cycles is 400 - 600 times; the temperature of annealing reaction II is 150 - 300 °C, and the time is 1 - 3 hours.

6. The preparation method of the CuOs / CdS / SSS photocathode according to claim 5, characterized in that: In step (4), the solvent in the mixed alcohol solution of CuOs is a mixture of ethanol and isopropanol with a volume ratio of 2 - 5:1; the concentration of CuOs in the mixed alcohol solution of CuOs is 1 - 5 mg / mL.

7. The preparation method of the CuOs / CdS / SSS photocathode according to claim 6, characterized in that: The temperature of annealing reaction III is 150 - 300 °C, and the time is 10 - 30 minutes.

8. A CuOs / CdS / SSS photocathode prepared by the method according to any one of claims 1 - 7.

9. The application of the CuOs / CdS / SSS photocathode according to claim 8 in nitrate reduction and ammonia production.

10. An apparatus for photoelectrochemical ammonia synthesis, characterized in that: It includes a reference electrode, a counter electrode, a cathode reaction cell, and an anode reaction cell; the cathode reaction cell uses the CuOs / CdS / SSS photocathode according to claim 8 as the cathode, and the anode reaction cell uses the counter electrode as the anode.

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