CuOs / CdS / SSS photocathode and preparation method and application thereof

Abstract

The invention belongs to the field of chemistry and chemical engineering, relates to photoelectrochemical synthesis, and provides a CuOs / CdS / SSS photocathode and a preparation method and application thereof. A copper osmium catalyst deposited on a Sb2 (S, Se) 3-based semiconductor is constructed to serve as a photocathode, the photocathode reaches the photocurrent density of 5.6 mA cm <-2 > under 0 VRHE, and under illumination of AM 1.5 G, the photocathode has the ultralow initial potential of 0.86 VRHE and the Faraday efficiency of 96.98%. Glycerol oxidation reaction on the bismuth ruthenium modified titanium oxide photo-anode is adopted to replace oxygen evolution reaction, and bias-voltage-free ammonia production is achieved. In an unbiased system, a photocathode coupled with the BiRu / TiO2 photoanode shows stable photoresponse of 1.4 mA cm <-2 >, and under illumination of AM 1.5 G, the Faraday efficiency of an ammonia product exceeds 97%. The production of ammonia from waste nitrate driven by solar energy is realized, so that a photo-carrier transmission path is optimized.

Description

Technical Field

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

[0002] Ammonia is the second most produced chemical in the world and is a key precursor for fertilizers and fine chemicals. However, the traditional energy-intensive Haber-Bosch ammonia synthesis process produces a large amount of carbon emissions. Secondly, with the development of industry, agriculture and animal husbandry and human activities, the accumulation of nitrate in the environment has gradually attracted attention in the field of ecological environment. Sustainable solar energy makes it an option for renewable energy applications. The photoelectrochemical nitrate reduction reaction for the production of ammonia is a promising way to carry out at ambient temperature and pressure, without carbon dioxide emissions, and is expected to achieve a closed loop of the nitrogen cycle and generate economic benefits. However, since the conversion of nitrate to ammonia involves an eight-electron transfer process, its solar conversion to ammonia has low efficiency, poor selectivity, and poor starting potential. This performance is mainly due to the low utilization of solar flux and slow charge transfer in the photoelectrode. On the one hand, compared with the 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 antiperovskite phase nitride for nitrate reduction to ammonia, which improves the performance of the electrode material from the perspective of conductivity and active area; the application with publication number CN119221026A provides a dual-mode nanoporous silver / silver-cobalt bimetallic tandem catalyst, which improves the efficiency of ammonia synthesis by increasing active sites. However, how to use highly selective photoelectrochemical nitrate reduction to ammonia and realize light-driven ammonia synthesis without applied voltage has not been studied in depth, which is extremely promising. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a CuOs / CdS / SSS photocathode and a preparation method and application thereof.

[0004] The technical solution of the present invention is achieved in this way: On the one hand, the present application provides a method for preparing a CuOs / CdS / SSS photocathode, the steps being as follows: (1) adding thiourea, cadmium sulfate hydrate and ammonia water into deionized water to obtain a precursor solution; (2) Sb 2 (S, Se) 3 Soaked in the precursor solution, annealed in air to obtain CdS / Sb 2 (S,Se) 3 ; (3) CdS / Sb 2 (S, Se) 3 In the presence of a titanium source and an oxygen source, TiO is deposited by atomic layer deposition. 2 TiO passivation layer 2 / CdS / Sb 2 (S, Se) 3 , and then annealing reaction II is carried out in an inert atmosphere to obtain CdS / SSS; (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.

[0005] 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; and the volume ratio of ammonia water to deionized water is 2-4:10.

[0006] In the above step (2), the immersion temperature is 55-75°C and the time is 5-15 minutes, and the annealing reaction I is at a temperature of 150-300°C and the time is 1-3 hours.

[0007] In the above step (3), the titanium source is tetrakis(dimethylamino)titanium (99% purity); and the oxygen source is water.

[0008] The temperature of the atomic layer deposition is 100-150° C., and the number of cycles is 400-600 times; the temperature of the annealing reaction II is 150-300° C., and the time is 1-3 hours.

[0009] The solvent in the mixed alcohol solution of CuOs in the above step (4) is a mixture of ethanol and isopropanol in a volume ratio of 2 to 5:1; the concentration of CuOs in the mixed alcohol solution of CuOs is 1 to 5 mg / mL. The preparation method of CuOs used in this application is: CuO powder is mixed with 4 to 8 g / L NaBH 4 The solution was completely reacted, collected by centrifugation and vacuum dried, and ground for 3 hours to obtain Cu powder. The obtained Cu powder was immersed in a solution containing 1~4 mM OsCl 3 The CuOs powder was obtained by substitution reaction in an aqueous solution of 1 M HCl.

[0010] The temperature of the annealing reaction III is 250-450° C. and the time is 10-30 minutes.

[0011] In the second aspect, protection is sought for the CuOs / CdS / SSS photocathode prepared using the above method.

[0012] Thirdly, we request protection for the application of CuOs / CdS / SSS photocathode in nitrate reduction and ammonia production.

[0013] The fourth aspect requests protection for a device for photoelectrochemical synthesis of ammonia, comprising 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 a cathode, and the anode reaction cell uses a counter electrode as an anode.

[0014] Furthermore, the reference electrode is an Ag / AgCl reference electrode; and the counter electrode is a Pt electrode.

[0015] When the electrode system is working, the CdS / SSS light-absorbing layer is excited by light to generate electron-hole pairs. The photogenerated electrons pass through CdS and Sb 2 (S, Se) 3 The heterogeneous interface is extracted into the electrolyte, and the CuOs surface catalyst layer improves the surface reaction kinetics, promotes the nitrate reduction reaction process, and improves the selectivity for ammonia.

[0016] The present invention has the following beneficial effects: 1. The present invention has developed a method using Sb 2 (S, Se) 3 The photocathode of the high-performance PEC cell was deposited with a copper-osmium electrocatalyst (CuOs / CdS / SSS) for selective light-driven nitrate reduction to obtain efficient ammonia production. In particular, it showed improved performance at low overpotentials compared with conventional photoelectrodes. In addition, bias-free ammonia production was achieved by coupling with the glycerol oxidation reaction. The CuOs / CdS / SSS photocathode coupled with the glycerol oxidation photoanode showed a high photocatalytic efficiency of 1.4 mA cm -2 The stable photoresponse, the Faradaic efficiency of the ammonia product exceeding 90%, and the efficient conversion of nitrate to ammonia under AM 1.5G intensity illumination without any applied potential were achieved. This work promotes the development of value-added products from low-value / waste compounds.

[0017] 2. The present invention constructs a deposited Sb 2 (S, Se) 3 The copper-osmium catalyst on the base semiconductor realizes the solar-driven production of ammonia from waste nitrate, thereby optimizing the photocarrier transport path. The resulting photocathode RHE Down to 5.6 mAcm -2 The photocurrent density is 0.86 V under AM 1.5G illumination. RHE The ultra-low onset potential and 96.98% Faradaic efficiency were achieved. We further used bismuth-ruthenium-modified titanium oxide (BiRu / TiO 2 ) photoanode to replace the oxygen evolution reaction, achieving unbiased ammonia production. In the unbiased system, the BiRu / TiO 2The photoanode-coupled CuOs / CdS / SSS photocathode showed a high performance of 1.4 mA cm -2 The photoresponse is stable, and the Faradaic efficiency of ammonia production exceeds 97% under AM 1.5G illumination.

[0018] 3. This application has developed a method using Sb 2 (S, Se) 3 High-performance PEC cells with photocathode and deposited copper-osmium electrocatalyst (CuOs / CdS / SSS) for selective PEC NO 3 RR to obtain efficient ammonia production. The resulting photocathode is at 0V RHE down to 5.6 mA cm -2 The photocurrent density is 0.86 V RHE The ultra-low onset potential of the photoelectrodes shows improved performance at low overpotentials, especially when compared to conventional photoelectrodes. Furthermore, we employed the glycerol oxidation reaction on a bismuth-ruthenium-decorated titanium oxide photoanode to achieve bias-free ammonia production without an applied voltage. Moreover, the performance was maintained for 10 h without noticeable degradation, which is the best performance among all unbiased PEC cells reported to date. This work advances the development of value-added products from low-value / waste compounds. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 PEC NO of CdS / SSS-5, CdS / SSS-10 and CdS / SSS-15 samples 3 RR performance.

[0021] Figure 2 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.

[0022] Figure 3 It is a linear scanning voltammetry curve diagram, where a is the linear scanning voltammetry curve of different samples in acidic nitrate solution; b is the starting potential curve of the sample; and c is the linear scanning voltammetry curve of different samples in acidic solution without nitrate.

[0023] Figure 4 CuOs / TiO2 / CdS / Sb 2 (S, Se) 3 Test results of simulated nitrate removal and ammonia generation; a is the Faradaic efficiency of ammonia production of CuOs / CdS / SSS at different potentials; b is the ammonia yield of CuOs / CdS / SSS at different potentials; c is the ammonia selectivity of CuOs / CdS / SSS at different potentials; d is the ammonia yield 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 selectivity of CuOs / TiO 2 / CdS / Sb 2 (S, Se) 3 At 1.0 V RHE a is the chronoamperometric curve under the conditions of CuOs / CdS / SSS; g is the cycle durability test of CuOs / CdS / SSS.

[0024] Figure 5 It is an electrochemical in-situ test analysis; wherein a is an online differential electrochemical mass spectrometry analysis; b is an in-situ Fourier transform infrared spectroscopy analysis of Cu / CdS / SSS; c is an in-situ Fourier transform infrared spectroscopy analysis of Cu / CdS / SSS; d is the hydrogen radical paramagnetic resonance spectrum of CuOs / CdS / SSS in the absence of nitrate; e is the hydrogen radical paramagnetic resonance spectrum of CuOs / CdS / SSS in the presence and absence of nitrate.

[0025] Figure 6 It is the coupling experiment result diagram; a is the schematic diagram of the coupling device without bias; b is the chronoelectric current curve under the condition of no bias; c is the output efficiency of each product. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the experimental methods used in the following experimental examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0028] Cadmium sulfate hydrate was purchased from Beijing Inokai Technology Co., Ltd., CAS: 7790-84-3.

[0029] Ammonia water is liquid ammonia, CAS: 7664-41-7.

[0030] Raw material Sb 2 (S, Se) 3 The preparation steps of the photocathode are as follows: 1.33 g potassium antimony tartrate and 1.98 g sodium thiosulfate pentahydrate were dissolved in 100 mL of deionized water. Subsequently, 20 mL of the solution was transferred to a 30 mL reactor. A fluorine-doped tin oxide substrate (1 × 2 cm 2 ) was placed face down in a reactor and heated at 135°C for 1 hour to form a seed layer on the substrate. Next, 1.33 g of potassium antimony tartrate, 1.98 g of sodium thiosulfate pentahydrate, and 0.061 g of selenium were dissolved in 100 ml of deionized water at 75°C and a second hydrothermal treatment was performed at 135°C for 4 hours. The film was then heated at 250°C for 20 minutes under a nitrogen atmosphere to form a Sb 2 (S, Se) 3 Photocathode.

[0031] Example 1 A method for preparing a CdS / SSS photocathode in this embodiment comprises the following steps: (1) Add 0.114 g of thiourea, 0.063 g of cadmium sulfate hydrate and 6 ml of aqueous ammonia to 20 ml of deionized water to obtain a precursor solution; (2) Prepare Sb 2 (S, Se) 3 The CdS was deposited by soaking in the above precursor solution at 65 °C for 5, 10, and 15 min, respectively, and then annealed at 200 °C in air for 1 hour to form CdS / Sb 2 (S, Se) 3 ; (3) At 120 °C, tetrakis(dimethylamino)titanium and water were used as titanium source and oxygen source, respectively, to deposit the CdS / Sb 2 (S, Se) 3 TiO 2 The passivation layer was deposited for a total of 600 ALD cycles and then annealed at 200 °C for 1 h under Ar to produce the CuOs / CdS / SSS photocathode.

[0032] The samples prepared above were marked as CdS / SSS-5 (immersion for 5 minutes), CdS / SSS-10 (immersion for 10 minutes) and CdS / SSS-15 (immersion for 15 minutes) according to different CdS immersion times.

[0033] Then, the 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, Ag / AgCl was used as the reference electrode, the cathode and the reference electrode were inserted into the cathode slot, the Pt sheet was inserted into the anode slot, and the cathode slot and the anode slot were separated by a Nafion117 membrane. The cathode and anode electrolytes were 0.5 M potassium sulfate + 0.1 M potassium nitrate solution, and sulfuric acid was used to adjust the pH to 2. The test was performed using a CHI660 electrochemical workstation, and the linear voltammetric curve of the test electrode was scanned at a 1.0 V interval. RHE -0.0V RHE , the scan rate was 10 mV / s, the cathode was irradiated with a calibrated AM1.5G light intensity, and the reaction was carried out at room temperature.

[0034] Test PEC NO of CdS / SSS-5, CdS / SSS-10 and CdS / SSS-15 samples 3 RR performance, the results are as follows Figure 1 As shown by Figure 1 It can be seen that the loading time of the CdS layer significantly affects the photoelectrochemical reaction activity of the sample, among which immersion time of 10 minutes is the optimal condition. The optimal CuOs / CdS / SSS sample was prepared according to this condition.

[0035] Example 2 A method for preparing a CuOs / CdS / SSS photocathode in this embodiment comprises the following steps: (1) Add 0.114 g of thiourea, 0.063 g of cadmium sulfate hydrate and 6 ml of aqueous ammonia to 20 ml of deionized water to obtain a precursor solution; (2) Prepare Sb 2 (S, Se) 3 The CdS was deposited by soaking in the above precursor solution at 65 °C for 10 min, and then annealed at 200 °C in air for 1 h to form CdS / Sb 2 (S, Se) 3 ; (3) At 120 °C, tetrakis(dimethylamino)titanium and water were used as titanium source and oxygen source, respectively, to deposit the CdS / Sb 2 (S, Se) 3 TiO 2 For the passivation layer, a total of 600 ALD cycles were performed, followed by annealing at 200 °C for 1 h under Ar conditions. The samples prepared above were denoted as CdS / SSS; (4) For CuOs decoration, CuO powder was mixed with 8 g / L NaBH at room temperature. 4The solution was completely reacted, collected by centrifugation and vacuum dried, and ground for 3 hours to obtain Cu powder. The obtained Cu powder was immersed in a solution containing 1 mM OsCl 3 4 mg of the obtained CuOs powder was ultrasonically dispersed in a mixed solution of 1 mL of ethanol and isopropanol with a volume ratio of 3:1, and then annealed at 250 °C in an Ar atmosphere for 20 min to load CuOs on the prepared CdS / SSS surface to obtain the final CuOs / CdS / SSS photocathode.

[0036] CuOs / TiO 2 / Sb 2 (S, Se) 3 The photocathode was fabricated by a two-step hydrothermal method. Figure 2 In brief, Sb was first prepared on a fluorine-doped tin oxide (FTO) substrate using a hydrothermal method. 2 S 3 Afterwards, Sb is formed in the second hydrothermal process in the precursor by the addition of selenourea. 2 (S, Se) 3 Light absorption layer. During the reaction, a gradient doping rich in selenium is formed at the bottom of the film. CdS is deposited on the top surface of selenourea as a transfer layer, and then amorphous TiO 2 The protective layer (the obtained electrode is labeled as CdS / SSS). Finally, the copper-osmium-based co-catalyst was modified on CdS / SSS by cyclic voltammetry, and the sample was denoted as CuOs / CdS / SSS. For comparison, a Cu co-catalyst deposited on a CdS / SSS photocathode was synthesized (labeled as Cu / CdS / SSS).

[0037] The morphology of the photocathodes was observed by scanning electron microscopy (SEM). The original SSS and CdS / SSS showed dense grains with a size of about 500 ± 100 nm. The CuOs catalyst showed a nanoparticle structure on the surface of CuOs / CdS / SSS, which was similar to the nanoparticle structure of Cu / CdS / SSS. The SEM images of the electrodes are shown in Figure 2. Figure 2 shown.

[0038] Example 3 A method for preparing a CuOs / CdS / SSS photocathode in this embodiment comprises the following steps: (1) adding 0.063 g of thiourea, 0.063 g of cadmium sulfate hydrate and 6 ml of aqueous ammonia to 20 ml of deionized water to obtain a precursor solution; (2) Prepare Sb 2 (S, Se) 3The CdS was deposited by soaking in the above precursor solution at 55 °C for 10 min, and then annealed in air at 150 °C for 1.5 h to form CdS / Sb 2 (S, Se) 3 ; (3) At 100°C, tetrakis(dimethylamino)titanium and water were used as titanium source and oxygen source, respectively, to deposit the CdS / Sb 2 (S, Se) 3 TiO 2 For the passivation layer, 500 ALD cycles were performed, followed by annealing at 150 °C for 1 h under Ar conditions. The samples prepared above were denoted as CdS / SSS. (4) For CuOs modification, CuO powder was mixed with 4 g / L NaBH 4 The solution was completely reacted, collected by centrifugation and vacuum dried, and ground for 3 hours to obtain Cu powder. The obtained Cu powder was immersed in a solution containing 3 mM OsCl 3 The CuOs powder was obtained by substitution reaction in an aqueous solution of 1 M HCl, and 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 min in an Ar atmosphere to load CuOs on the prepared CdS / SSS surface to obtain the final CuOs / CdS / SSS photocathode.

[0039] Example 4 A method for preparing a CuOs / CdS / SSS photocathode in this embodiment comprises the following steps: (1) adding 0.189 g of thiourea, 0.063 g of cadmium sulfate hydrate and 8 ml of aqueous ammonia to 20 ml of deionized water to obtain a precursor solution; (2) Prepare Sb 2 (S, Se) 3 The CdS was deposited by immersing in the above precursor solution at 70 °C for 10 min, and then annealed at 200 °C in air for 1 h to form CdS / Sb 2 (S, Se) 3 .

[0040] (3) At 130 °C, tetrakis(dimethylamino)titanium and water were used as titanium source and oxygen source, respectively, to deposit the CdS / Sb 2 (S, Se) 3 TiO 2 The passivation layer was subjected to 400 ALD cycles in total, and then annealed at 250 °C for 3 h under Ar conditions. The sample prepared above was recorded as CdS / SSS.

[0041] (4) For CuOs decoration, CuO powder was mixed with 5 g / L NaBH 4 The solution was completely reacted, collected by centrifugation and vacuum dried, and ground for 3 hours to obtain Cu powder. The obtained Cu powder was immersed in a solution containing 2 mM OsCl 3 The CuOs powder was obtained by substitution reaction in an aqueous solution of 1 M HCl, and the obtained CuOs powder was 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 min in an Ar atmosphere to load CuOs on the prepared CdS / SSS surface to obtain the final CuOs / CdS / SSS photocathode.

[0042] Example 5 A method for preparing a CuOs / CdS / SSS photocathode in this embodiment comprises the following steps: (1) Add 0.102 g of thiourea, 0.063 g of cadmium sulfate hydrate and 10 ml of aqueous ammonia to 20 ml of deionized water to obtain a precursor solution; (2) Prepare Sb 2 (S, Se) 3 The CdS was deposited by immersing in the above precursor solution at 75 °C for 10 min, and then annealed at 200 °C in air for 3 h to form CdS / Sb 2 (S, Se) 3 ; (3) At 120 °C, tetrakis(dimethylamino)titanium and water were used as titanium source and oxygen source, respectively, to deposit the CdS / Sb 2 (S, Se) 3 TiO 2 For the passivation layer, 500 ALD cycles were performed, followed by annealing at 150 °C for 1 h under Ar conditions. The samples prepared above were denoted as CdS / SSS. (4) For CuOs decoration, CuO powder was mixed with 8 g / L NaBH 4 The solution was completely reacted, collected by centrifugation and vacuum dried, and ground for 3 hours to obtain Cu powder. The obtained Cu powder was immersed in a solution containing 4 mM OsCl 3 The CuOs powder was obtained by substitution reaction in an aqueous solution of 1 M HCl, and the obtained CuOs powder was 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 min in an Ar atmosphere to load CuOs on the prepared CdS / SSS surface to obtain the final CuOs / CdS / SSS photocathode.

[0043] Implementation effect example 1 A device for photoelectrochemical synthesis of ammonia, 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 slot, the Pt sheet is inserted into the anode slot, and the cathode slot and the anode slot are separated by a Nafion117 membrane. The electrolyte is a 0.5 M potassium sulfate solution containing or not containing 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 voltammetric curve of the test electrode is scanned at a range of 1.0 V RHE - 0.0 V RHE , with a scan rate of 10 mV / s. All potentials were calibrated to RHE using the following formula: E RHE = E SCE + 0.0591×pH (1) Among them, E SCE Representative experimental applied potential. The cathode was illuminated by calibrated AM1.5G light intensity and the reaction was carried out at room temperature. Durability test was performed using chronoamperometry. Faraday efficiency and yield test were calculated by chronoamperometry test for a certain time. NH 3 The calculation formula of Faradaic efficiency (FE) is as follows; (2) Where Q represents the total coulombs (C) in the chronoamperometry test, Q NH3 It produces NH 3 The required coulomb quantity, n is the number of electrons transferred (for 1 mol NH 3 , is 8), V is the volume of the cathode solution in the cathode chamber (30 ml), c NH3 The NH produced 3 concentration, F is the Faraday constant (96.485 C mol -1 To ensure the accuracy of the experiment, we conducted three independent experiments and measured the error bars.

[0044] The yield of the product is calculated as follows: (3) 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.

[0045] 1. Under AM 1.5G irradiation without iR correction, at 0.5 MK 2 SO 4 and 0.1 M KNO 3 The nitrate reduction performance of the photocathode was measured in an H-type electrolytic cell at pH = 2. 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 demonstrates that the modification of Cu or CuOs cocatalysts can promote the conversion of nitrates. At the same time, the photocathode with a more positive onset potential can prevent the competitive hydrogen evolution reaction (HER). 3 - Compared with the photocathode without adding NO 3 - 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.

[0046] 2. This application also evaluates the Faradaic efficiency (FE), ammonia production and durability of the electrode ( Figure 4 ).like Figure 4 As shown in a, CdS / SSS at 0.1 V RHE The ammonia Faraday efficiency is 35.6% at 0.1 V. As the potential shifts positively, the ammonia Faraday efficiency decreases, indicating that its slow charge carrier kinetics hinders the conversion of nitrate to ammonium. RHE The ammonia Faradaic efficiency is 70.4% at 0.1 to 0.8 V and decreases with positive potential. The high Faradaic efficiency of ammonia at high overpotentials indicates the inertness of copper to the hydrogen evolution reaction. In contrast, CuOs / CdS / SSS has a low Faradaic efficiency at 0.1 to 0.8 V. RHE The average ammonia Faradaic efficiency is greater than 90% in the potential range of 0.6 V. RHE The maximum value is 96.98%. Figure 4 As shown in b, the NH 4 + The yield is the highest among these photocathodes, at 0.1 V RHE The value was as low as 19.87 μmol h -1 cm -2 , which is higher than Cu / CdS / SSS (15.10 μmol h -1 cm -2 ) and CdS / SSS (2.25 μmol h- 1 cm -2 The selectivity of ammonia shows that when the potential shifts negatively, the selectivity of CuOs / CdS / SSS gradually increases. RHE 95% ( Figure 4 (c) The average NH of CuOs / CdS / SSS at the measured potential 4 + The selectivity is about 99%, which is significantly higher than that of Cu / CdS / SSS (38.9%) and CdS / SSS (23.3%). These results indicate that the deposition of CuOs catalyst improves the reaction kinetics of the photocathode. 4 + The yield and Faradaic efficiency were also affected by the concentration of 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 Increased to 5.67 μmol h -1 cm -2 , the average Faradaic efficiency exceeds 96% ( Figure 4 This indicates that the electrode can maintain high selectivity for active hydrogen during nitrate reduction over a wide range of nitrate concentrations, leading to efficient intermediate hydrogen generation.

[0047] Nitrite is the main byproduct in the nitrate reduction process and seriously affects the hydrogenation reduction process of nitrate. Therefore, we investigated the performance of the corresponding photocathodes in producing nitrite, such as Figure 4 In addition to CdS / SSS, Cu / CdS / SSS produces a large amount of nitrite at the measured potential. The catalytic activity and product yield of CuOs / CdS / SSS were further studied during long-term operation. RHE The photocurrent density under the condition remained stable within 6 hours, and its Faraday efficiency remained at an average value of 93% within 12 hours ( Figure 4 In addition, the sample maintained a stable ammonia production and Faradaic efficiency during the 20 cycle test ( Figure 4 (g), which indicates that the photocathode has good stability.

[0048] 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 PEC NO under light irradiation. 3 Intermediate species generated at the photocathode during the RR reaction. Figure 5 Figure a shows the mass-to-charge ratio (m / z) signal recorded on CuOs / CdS / SSS as a function of time, while five subsequent voltammetric scan cycles were performed (each cycle included a RHE The m / z signals at 46, 30, 31, 33, and 17 were correlated with NO 2 、NO、NOH、NH 2 OH and NH 3 Correspondingly, this result suggests a possible reaction pathway, namely, *NO 2 →*NO→*NOH→*NHOH→*NH 2 OH→*NH→*NH 2 →*NH 3 .

[0049] from Figure 5 In situ Fourier transform infrared measurements can be seen in b and c. RHE When *NO 2 The peak appears at ~1241 cm -1 The peak intensity increases with the applied potential to a more negative range. The peak associated with *NH appears at 1432 cm -1 The characteristic peak of *NOH appears at 1365 cm-1 As the potential increases from 0.8 V RHE to 0.3 V RHE , we can observe 1125 cm -1 The small peak at 2 OH)'s -NO- stretching vibration is NH 3 It is important to note that these hydrogenation intermediates appear at more positive potentials on CuOs / CdS / SS compared to Cu / CdS / SS, confirming the fast hydrogenation kinetics of the N-oxygen intermediates over the CuOs catalyst. -1 A series of weak peaks related to *NO signals appeared at 1645 cm-1, while these peaks were not observed on CuOs / CdS / SSS. -1 *H 2 O peak. This means that *H can effectively 2 O and promotes NH 3 To evaluate the amount of hydrogen radicals (*H) produced or consumed during nitrate reduction, electron paramagnetic resonance (EPR) analysis was performed using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a radical trapping agent. Figure 5 As shown in Figure d, in the absence of nitrate, Os / CdS / SSS and CuOs / CdS / SSS showed similar but stronger DMPO-*H signals than Cu / CdS / SSS (the intensity ratio of the nine characteristic peaks was 1:1:2:1:2:1:2:1:1:1), indicating that *H was preferentially adsorbed on Os or CuOs sites compared with Cu sites. In the presence of nitrate, almost no DMPO-*H signal was detected on CuOs / CdS / SSS ( Figure 5 This demonstrates that the *H generated on the CuOs / CdS / SSS surface is rapidly consumed during the hydrogenation of surface-active nitrogen-containing intermediates, resulting in excellent ammonia yield and Faradaic efficiency.

[0050] Implementation effect example 2 To demonstrate the ability of the tandem cell to achieve no-load operation, a CuOs / CdS / SSS photocathode was coupled to a BiRu / TiO 2 The photoanode was integrated to achieve unassisted ammonia and three-carbon products (C 3 ) production. Specifically, in the specific experimental process: a dual-electrode electrochemical cell system is used. BiRu / TiO 2The electrode is used as the anode, CuOs / CdS / SSS is used as the cathode, the cathode electrolyte is a 0.5 M potassium sulfate solution containing 0.1 M potassium nitrate, and sulfuric acid is used to adjust the pH to 2. The anode electrolyte is a glycerol solution with a concentration of 0.1 M, and the pH value is adjusted to 2 by sulfuric acid. The cathode tank and the anode tank are separated by a Nafion117 ion exchange membrane. The cathode and anode are irradiated with a calibrated AM1.5G light intensity and react at room temperature. The device is a bias-free device and does not require an external voltage. The chronoamperometric data of the device are collected by a CHI660 electrochemical workstation. The product yield is detected by a UV-visible spectrophotometer and liquid chromatography.

[0051] Test results such as Figure 6 As shown in Figure 1, the system consists of two photoelectrodes connected by copper wires in a two-chamber reactor. 2 The unbiased photoelectrochemical system on the PDMS exhibited a stable ~1.4 mA cm-2 under AM 1.5G illumination. -2 Photoresponse 10 hours ( Figure 6 b). Ammonia and C 3 The production of ammonia and C increased with time. After 10 hours, 3 The cumulative yields of -1 and 132.52 μmol cm -1 ( Figure 6 This provides practical applications for unbiased PEC synthesis to directly convert solar energy into high-value-added chemicals.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a CuOs / CdS / SSS photocathode, characterized in that: Here are the steps: (1) adding thiourea, cadmium sulfate hydrate and ammonia water into deionized water to obtain a precursor solution; (2) Soak Sb2(S, Se)3 in a precursor solution and perform annealing reaction I in air to obtain CdS / Sb2(S, Se)3; (3) CdS / Sb2(S, Se)3 with a TiO2 passivation layer deposited by atomic layer deposition in the presence of a titanium source and an oxygen source is then subjected to annealing reaction II in an inert atmosphere to obtain CdS / SSS; (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.

2. The method for preparing the CuOs / CdS / SSS photocathode according to claim 1, characterized in that: In the 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; and the volume ratio of ammonia water to deionized water is 2-4:

10.

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

4. The method for preparing the CuOs / CdS / SSS photocathode according to claim 3, characterized in that: In step (3), the titanium source is tetrakis(dimethylamino)titanium; and the oxygen source is water.

5. The method for preparing 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 the annealing reaction II is 150-300° C., and the time is 1-3 hours.

6. The method for preparing the CuOs / CdS / SSS photocathode according to claim 5, characterized in that: The solvent in the mixed alcohol solution of CuOs in step (4) is a mixture of ethanol and isopropanol in 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 method for preparing the CuOs / CdS / SSS photocathode according to claim 6, characterized in that: The temperature of the 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 to 7.

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

10. A device for photoelectrochemical synthesis of ammonia, characterized in that: The invention comprises 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 a cathode, and the anode reaction cell uses the counter electrode as an anode.

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