One-dimensional nitride doped Ag / WO3 nanorod electrocatalyst as well as preparation method and application thereof

Abstract

The invention belongs to the field of electrocatalysis, relates to nitrate reduction, in particular to ammonia synthesis through nitrate reduction under an acid medium, and discloses a one-dimensional nitride doped Ag / WO3 nanorod electrocatalyst as well as a preparation method and application thereof. The stable one-dimensional nitride doped WO3 nanorod is synthesized for the first time, and Ag species with poor hydrogen evolution activity are decorated on the one-dimensional nitride doped WO3 nanorod and used for rapidly reducing nitrate into ammonia under the acidic condition. The catalyst improves the adsorption of nitrate, and reduces the energy barrier of the step of determining the rate, thereby greatly improving the efficiency of ammonia synthesis and reducing the HER under the ampere current density. The work provides deep insight for reduction of acidic nitrate in ammonia electrosynthesis, and a corrosion-resistant electrocatalyst for energy conversion is developed.

Description

Technical Field

[0001] The invention belongs to the field of electrocatalysis and relates to nitrate reduction, in particular to nitrate reduction to synthesize ammonia. Background Art

[0002] Electrocatalytic nitrate reduction to ammonia (NO3RR) has attracted much attention in the Haber-Bosch process for ammonia synthesis. Significant efforts have been devoted to the investigation of selective electrocatalysts for NO3RR under alkaline / neutral conditions. Although recently reported catalysts have high Faradaic efficiencies (FEs) for NH3, optimal performance for nitrate reduction to ammonia is usually achieved with the production of nitrite as a byproduct and large overpotentials at the beginning. - + 6H2O + 8e - → NH3+ 9OH - The reaction equation under alkaline / neutral conditions, NO3RR involves nine proton-coupled electron transfers, where protons are generated through an additional water dissociation step (H2O → H* + OH*), which may result in excessive overpotentials and slow kinetics, thus limiting the performance of NO3RR. In contrast, direct nitrate reduction under acidic media (which contain wastewater commonly found in industrial processes) has unique advantages compared to alkaline / neutral conditions, such as enhanced NO3 - Multiple protonation steps increase NO3 - The conversion rate to NH3. As the acidity of the reaction increases, it can be NO3 - The continuous hydrogenation reaction provides abundant protons, thereby ensuring the improvement of NO3 - The conversion rate can be increased and NH3 can be generated more efficiently. Therefore, it is highly desirable to develop NO3RR in acidic environment that is compatible with industrial processes and avoids additional cost and energy consumption. However, designing robust catalysts for acidic NO3RR is a great challenge, requiring high catalytic activity, high selectivity, and high durability.

[0003] The hydrogen evolution reaction (HER) inevitably becomes a competing reaction for NO3RR, especially under acidic conditions. Reported catalysts (such as Cu, Co, and Ni transition metals) are usually unstable in acidic media and are rarely used for acidic NO3RR. These catalysts also suffer from the problem of reduced NH3FE due to the enhanced competitive HER under acidic conditions. To address these issues, Zhi et al. reported the potential of Fephthalocyanine / TiO2 nanosheets for the selective and rapid reduction of nitrate to ammonia in acidic media, with a high NH3 yield of 17.4 mg h -1 cm -2, NH3FE is 90.6%. Chen and his colleagues have produced RhNi bi-titanocenes with a lattice-compressed Rh-skin-type structure, whose acidic NO3RR stability can reach 400 hours. Rh-skin atoms inhibit Rh dissolution caused by NO2* / NH2* adsorption and improve the electrocatalytic stability of acidic electrochemical nitrate reduction. Despite this, it is still difficult to meet industrial requirements. Summary of the invention

[0004] In order to meet the requirements of industrialization, an electrocatalyst is proposed in the present invention which can quickly reduce nitrate to ammonia at a high current density under acidic conditions and has high stability. The present application provides a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst and its preparation method and application.

[0005] The technical solution of the present invention is achieved in this way: A method for preparing a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst, comprising the following steps: (1) The carbon cloth is oxidized in a 60-70% HNO3 solution at 75-80°C for 10-14 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Then, it is added to an ultrapure aqueous solution of ammonium metatungstate dodecahydrate with a concentration of 2-2.5 mol / L, and magnetically stirred for 20 minutes to obtain a uniform solution. The above solution is transferred to an autoclave, and then the carbon cloth is placed in the solution and reacted at 170-190°C for 15-18 hours. The obtained WO3 nanowires are washed with deionized water and dried at 70°C overnight.

[0006] (2) The preparation method of Ag / N-WO3 is to immerse the WO3 nanowires in a 4-6mM Ag2SO4 solution for 1-2 minutes, and the Ag2SO4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in an NH3 atmosphere at 500-550°C for 2-2.5 hours with a heating rate of 5-6°C / min to obtain Ag / N-WO3.

[0007] Ag / WO3 nanorod electrocatalyst prepared by the above method.

[0008] The above-mentioned Ag / WO3 nanorod electrocatalyst is used in the industrial electrocatalytic reduction of nitrate to synthesize ammonia.

[0009] The above electrocatalysis is an electrocatalytic reaction under strong acid conditions.

[0010] A three-electrode system, wherein Ag / N-WO3 is used as a working electrode.

[0011] The three-electrode system further comprises a reference electrode, a counter electrode, a cathode pool and an anode pool; the cathode pool and the anode pool both contain a strong acid solution.

[0012] Specifically, the three-electrode H-Cell used was composed of a working electrode, a saturated calomel electrode (SCE) as a reference electrode, and a platinum foil as a counter electrode; it was divided into a cathode pool (33 mL 0.5 M KNO3+0.5 M H2SO4) and an anode pool (40 mL 0.5 M H2SO4) by an anion membrane (Nafion 117 membrane). Ag / N-WO3 was used as the working electrode.

[0013] The present invention has the following beneficial effects: 1. This application first constructs a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst and decorates it with Ag species with poor hydrogen evolution activity, which is used to quickly reduce nitrate to ammonia under acidic conditions. WO3 has excellent stability under acidic conditions. The catalyst introduces Ag single atoms on the WO3 substrate to change the reaction path of NO3RR, and further nitridation treatment is performed to enhance its NO3 reduction under low reduction potential. - The adsorption effect of nitrate can achieve efficient and stable nitrate reduction to synthesize ammonia in a strong acid environment.

[0014] 2. Ag / N-WO3 electrocatalyst at -0.6~-0.2 V RHE The Faradaic efficiency (FE) of the catalyst for ammonia production is close to 99.32±3.66% at -0.4 V. RHE The maximum value of FE is ~100% at -0.55 V RHE The maximum NH3 yield reached 5.24 ± 0.41 mmol h -1 cm -2 Impressively, the catalyst was able to -2 The FE was stabilized at about 94% at an industrially relevant current density for more than 1000 hours. The experimental results and theoretical calculations show that nitrate adsorption is improved, and the single silver atom and nitridation treatment reduce the energy barrier of the rate-determining step, thereby greatly improving the efficiency of ammonia synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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.

[0016] Figure 1 SEM images of ac WO3, df Ag / WO3 and gi Ag / N-WO3.

[0017] Figure 2 Characterization diagrams of WO3, Ag / WO3 and Ag / N-WO3; a is the XRD pattern and b is the Raman spectrum.

[0018] Figure 3 Optimize the preparation process of Ag / N-WO3.

[0019] Figure 4 Ag / N-WO3 in the presence or absence of nitrate (NO3 - ) in the presence of ; a is the LSV curve of 0.5 M H2SO4 + 0.5 M KNO3 on Ag / N-WO3, Ag / WO3 and WO3 after 80% iR correction; b is the LSV curve of WO3, Ag / WO3 and Ag / N-WO3 in 0.5 M H2SO4; c is the Tafel slope diagram of the corresponding catalyst; d is the Nyquist diagram of the corresponding catalyst; e is the Cdl diagram of WO3, Ag / WO3 and Ag / N-WO3; f is the Cdl diagram of Ag / N-WO3, Ag / WO3 and WO3 at -0.4 V RHE Faradaic efficiency and yield of NH3 under different conditions.

[0020] Figure 5 are the Faraday efficiency and ammonia yield of NH3 for different catalysts at different potentials; where a is WO3; b is Ag / WO3; c is Ag / N-WO3.

[0021] Figure 6 The stability test of NO3RR electrocatalyst; a is Ag / N-WO3 at -0.4 V RHE It curve of ammonia synthesis measured under cyclic conditions; b is at -0.4 V RHE Continuous stability measurement of Ag / N-WO3 under conditions; c is a continuous flow system in an H-type battery at -0.3 V RHE The long-term stability of NO3RR on Ag / N-WO3 was tested under 3.5 % RH and 2.5 % RH. The arrows indicate electrolyte replacement.

[0022] Figure 7 600 - 1000 cm at different potentials -1 In situ Raman spectra of different catalysts in the range; a is WO3, b is Ag / WO3 and c is Ag / N-WO3.

[0023] Figure 81000 - 1700 cm at different potentials -1 In situ Raman spectra of different catalysts in the range; a is WO3, b is Ag / WO3 and c is Ag / N-WO3.

[0024] Fig. 9 In situ Fourier transform infrared spectra of electrochemical thin layer NO3RR on different catalysts in 0.5 M H2SO4 + 0.5 M KNO3; a is WO3, b is Ag / WO3 and c is Ag / N-WO3.

[0025] Fig.10 Electrochemical online DEMS results of NO3RR on different catalysts; a is Ag / N-WO3, b is Ag / WO3 and c is WO3. 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] Example 1 A method for preparing a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst, comprising the following steps: (1) The carbon cloth was oxidized in HNO3 (65wt%) at 80℃ for 12 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (50.0 mM) was dissolved in 20.0 mL ultrapure water and then magnetically stirred for 20 minutes to obtain a uniform solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed in the solution and reacted at 180℃ for 16 hours. The obtained WO3 nanowires were washed with deionized water and dried at 70℃ overnight.

[0029] (2) The preparation method of Ag / N-WO3 is to immerse WO3 nanowires in 5 mM Ag2SO4 solution for 2 minutes, and the Ag2SO4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in NH3 atmosphere at 500℃ for 2 hours with a heating rate of 5℃ / min to obtain Ag / N-WO3.

[0030] Example 2 A method for preparing a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst, comprising the following steps: (1) The carbon cloth was oxidized in HNO3 (60wt%) at 75℃ for 10 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (40.0 mM) was dissolved in 20.0 mL ultrapure water and then magnetically stirred for 25 minutes to obtain a uniform solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed in the solution and reacted at 170℃ for 15 hours. The obtained WO3 nanowires were washed with deionized water and dried at 70℃ overnight.

[0031] (2) The preparation method of Ag / N-WO3 is to immerse WO3 nanowires in 4mM Ag2SO4 solution for 1 minute, and the Ag2SO4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in NH3 atmosphere at 530℃ for 2 hours with a heating rate of 5.5℃ / min to obtain Ag / N-WO3.

[0032] Example 3 A method for preparing a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst, comprising the following steps: (1) The carbon cloth was oxidized in HNO3 (70wt%) at 78℃ for 13 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (45.0 mM) was dissolved in 20.0 mL ultrapure water and then magnetically stirred for 30 minutes to obtain a uniform solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed in the solution and reacted at 190℃ for 18 hours. The obtained WO3 nanowires were washed with deionized water and dried at 70℃ overnight.

[0033] (2) The preparation method of Ag / N-WO3 is to immerse WO3 nanowires in a 6 mM Ag2SO4 solution for 1.5 minutes, and the Ag2SO4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in an NH3 atmosphere at 550°C for 2.5 hours with a heating rate of 6°C / min to obtain Ag / N-WO3.

[0034] Example 4 A method for preparing a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst, comprising the following steps: (1) The carbon cloth was oxidized in HNO3 (65wt%) at 80℃ for 14 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (50.0 mM) was dissolved in 20.0 mL ultrapure water and then magnetically stirred for 20 minutes to obtain a uniform solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed in the solution and reacted at 190℃ for 16 hours. The obtained WO3 nanowires were washed with deionized water and dried at 70℃ overnight.

[0035] (2) The preparation method of Ag / N-WO3 is to immerse WO3 nanowires in 4 mM Ag2SO4 solution for 2 minutes, and the Ag2SO4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in NH3 atmosphere at 500℃ for 2 hours with a heating rate of 5℃ / min to obtain Ag / N-WO3.

[0036] Example 5 A method for preparing a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst, comprising the following steps: (1) The carbon cloth was oxidized in HNO3 (70wt%) at 79°C for 14 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (48.0 mM) was dissolved in 20.0 mL ultrapure water and then magnetically stirred for 20 minutes to obtain a uniform solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed in the solution and reacted at 170°C for 18 hours. The obtained WO3 nanowires were washed with deionized water and dried at 70°C overnight.

[0037] (2) The preparation method of Ag / N-WO3 is to immerse WO3 nanowires in a 6 mM Ag2SO4 solution for 2 minutes, and the Ag2SO4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in an NH3 atmosphere at 550℃ for 2 hours with a heating rate of 5℃ / min to obtain Ag / N-WO3.

[0038] Comparative Example 1 The preparation method of WO3 nanowires is as follows: (1) The carbon cloth was oxidized in HNO3 (65wt%) at 80℃ for 12 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (50.0 mM) was dissolved in 20.0 mL ultrapure water and then magnetically stirred for 20 minutes to obtain a uniform solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed in the solution and reacted at 180℃ for 16 hours. The obtained WO3 nanowires were washed with deionized water and dried at 70℃ overnight.

[0039] (2) Finally, the sample was annealed in an O2 atmosphere at 500°C for 2 hours with a heating rate of 5°C / min to obtain WO3.

[0040] Comparative Example 2 The preparation method of Ag / WO3 comprises the following steps: (1) The carbon cloth was oxidized in HNO3 (65wt%) at 80℃ for 12 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (50.0 mM) was dissolved in 20.0 mL ultrapure water, and then magnetically stirred for 20 minutes to obtain a uniform solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed in the solution and reacted at 180℃ for 16 hours. The obtained WO3 nanowires were washed with deionized water and dried at 70℃ overnight. Finally, the above sample was annealed in an O2 atmosphere at 500℃ for 2 hours with a heating rate of 5℃ / min to obtain WO3.

[0041] (2) The preparation method of Ag / WO3 is to immerse WO3 nanowires in a 5 mM Ag2SO4 solution for 2 minutes, and the Ag2SO4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in an O2 atmosphere at 500°C for 2 hours with a heating rate of 5°C / min to obtain Ag / WO3.

[0042] Implementation effect example 1 The Ag / N-WO3 prepared in Example 1, the WO3 prepared in Comparative Example 1, and the Ag / WO3 prepared in Comparative Example 2 were observed by scanning electron microscope (SEM). Figure 1 As shown, it can be seen that Ag / N-WO3 is loaded on the carbon cloth in the form of nanorod structure, and no obvious changes were found in the morphology of WO3, Ag / WO3 and Ag / N-WO3 ( Figure 1 ). Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the Ag concentration on Ag / N-WO3 was 0.42 wt.% (Table 1).

[0043] Table 1 ICP-MS analysis of three substances The X-ray diffraction (XRD) patterns of WO3, Ag / WO3 and Ag / N-WO3 show the characteristic peaks of hexagonal tungsten trioxide (JCPDS No. 85-2460) ( Figure 2 (a). Since the content of Ag phase is very low, no peaks related to it are observed. The (002) and (200) phase spacing of Ag / N-WO3 is shortened to 4.5 nm from 4.9 nm of WO3 and Ag / WO3, which can be attributed to the lattice distortion caused by nitrogen doping as previously reported. Figure 2The Raman spectrum of (b) shows that the -1 The band at 183 cm is attributed to the deformation mode of OWO, while the band at 183 cm -1 The following bands correspond to lattice modes. 806 and 712 cm -1 The bands at are related to the antisymmetric and symmetric stretching vibrations of the terminal OWO. It can be observed that the stretching vibration peak of OWO is red-shifted, and for WO3 and Ag / WO3, the peaks are located at 806 cm -1 and 712 cm -1 , while for Ag / N-WO3, they shift to 718 cm -1 and 647 cm -1 , which is attributed to the redistribution of electron density on WO3 caused by nitridation treatment.

[0044] Implementation effect example 2 Electrochemical NO3RR measurements were performed using a CHI760E electrochemical analyzer. The three-electrode H-Cell used consisted of a working electrode, a saturated calomel electrode (SCE) as a reference electrode, and a platinum foil as a counter electrode; it was divided into a cathode cell (33 mL 0.5 M KNO3+ 0.5 M H2SO4) and an anode cell (40 mL 0.5 M H2SO4) by an anion membrane (Nafion117 membrane). Ag / N-WO3, Ag / WO3, and WO3 were used as working electrodes. The scan rate of linear sweep voltammetry (LSV) was 5 mVs -1 For the catalytic potentials, we used 80% of the internal resistance (iR) of the solution for calibration. 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. Electrochemical impedance spectroscopy (EIS) at -0.25 V RHE The electrochemical double layer capacitance (Cdl) was measured at -0.1 to 0.3 V at a frequency of 15 kHz to 0.001 Hz with an amplitude of 5 mV. RHE The curve is obtained by CV cycle at a potential of , and then a linear fit is performed on the curve, and its slope is the Cdl value. The measurement formula of electrochemically active surface area (ECSA) is: ECSA = Cdl / Cs (2) The calculation formula of NH3 Faradaic efficiency (FE) is as follows: (3) Where Q represents the total coulombs (C) applied, Q NH3is the amount of coulombs required to produce NH3, n is the number of electrons transferred (8 for 1 mol NH3), V is the volume of the cathode solution in the cathode compartment (33 ml), c NH3 is the concentration of NH3 produced, and 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.

[0045] The yield of the product is calculated as follows: (4) Where V is the volume of the electrolyte in the cathode chamber, t is the electrolysis time, and m is the mass of the catalyst. The error bars are equivalent to the standard deviation of three independent measurements, and the center value of the error bar is the average of three independent measurements.

[0046] 1. We evaluated the electrochemical nitrate reduction reaction (NO3RR) performance of WO3, Ag / WO3, and Ag / N-WO3 in an H-type electrolytic cell under acidic conditions. First, Figure 3 The optimization of NO3RR activity on Ag / N-WO3 for different Ag2SO4 concentrations, ammonia annealing temperatures, and nitrate concentrations in the electrolyte is demonstrated. The activity of Ag / N-WO3 in the presence or absence of nitrate (NO3 - ) in the presence of linear sweep voltammetry (LSV) curves ( Figure 4 A and Figure 4 b). In the presence of nitrate, the current density of Ag / N-WO3 increases, indicating that nitrate reduction occurs. Figure 4 As shown in Figure 1, Ag / WO3 and Ag / N-WO3 exhibit better performance in the LSV curves compared to pristine WO3, especially in terms of chronocurrent density. Among these samples, Ag / N-WO3 exhibits the best activity, with a peak at -0.53 V. RHE The current density reached 1 A cm at the reversible hydrogen electrode potential. - ², the starting potential is 0V RHE . Figure 4 Medium c and Figure 4 Figure d shows that Ag / N-WO3 has the lowest Tafel slope and Nyquist plot, indicating that its electron transfer frequency is the fastest. The electrochemically active surface area (ECSA) shows that the double layer capacitance (CdI, 357.68 mF cm) of Ag / N-WO3 -2 ) than Ag / WO3 (331.46 mF cm -2 ) and WO3 (66.28 mF cm -2 ) is larger ( Figure 4 (e), confirming that among these catalysts, Ag / N-WO3 has the highest intrinsic activity.

[0047] Figure 4 Figure 5 shows the -0.4 V RHE The Faradaic efficiencies (FEs) and ammonia yields of the catalysts used under different potentials are shown in Table 1. Among these samples, Ag / N-WO3 exhibits the highest Faradaic efficiency and ammonia yield, which represents the best NO3RR performance reported in acidic electrolytes to date. We further studied the Faradaic efficiency and ammonia yield of Ag / N-WO3 at different potentials ( Figure 5 a). From Figure 3 From c, we can see that Ag / N-WO3 is between -0.2 and -0.6 V RHE The Faraday efficiency is maintained above 90% over a wide potential range, and at -0.4 V RHE The Faraday efficiency is the highest at 99.32 ± 4% at -0.5 V at industrial high current density. RHE The ammonia yield was the highest at 5.24 ± 0.41 mmol h -1 cm -2 The improved Faradaic efficiency and ammonia yield at higher potentials indicate that this catalyst is superior to Ag / WO3 and WO3 for NO3 - Electroreduction to NH3 is highly selective ( Figure 5 Medium b and Figure 5 In addition, as the potential gradually increases in the negative direction, the current density increases linearly without decreasing, which indicates that NO3 - With H ＋ The competition between them has weakened.

[0048] In addition to activity and selectivity, the stability of NO3RR electrocatalysts is also a crucial parameter in potential practical applications. We performed 20 consecutive chronoamperometric experiments on Ag / N-WO3 ( Figure 6 In a), at -0.4V RHE All Faradaic efficiencies (FEs) for NO3RR are about 97% ( Figure 6 In addition, the long-term stability of the electrochemical NO3RR was evaluated by chronoamperometry measurements using a continuous flow system in an H-type electrolytic cell. Ag / N-WO3 maintained approximately 480 mA cm after 1000 h. -1 The stable current density and the stable ammonia Faraday efficiency of 95% ( Figure 6 (c), indicating that the catalyst can continuously catalyze NO3RR and represents an unprecedented ultrastable acidic electrocatalyst.

[0049] 2. We used in-situ Raman spectroscopy to study the changes in the WO3 substrate during the NO3RR reaction. During the NO3RR process, as the cathode voltage gradually increased, the characteristic tungsten oxide Raman peaks corresponding to the three samples of Ag / N-WO3, Ag / WO3 and WO3 disappeared and gradually blue-shifted ( Figure 7 ). This is because during the nitrate reduction process, electrons are transferred from nitrate to WO3, causing the electronic structure of WO3 to change. This electron transfer may change the band structure of WO3, thereby affecting the lattice vibration mode of WO3, resulting in a blue shift in the Raman peak.

[0050] To identify the intermediates involved in the NO3RR process, we used a 0 to −0.6 V RHE In situ Raman spectroscopy was used in the potential range of Figure 8 The Raman spectra of Ag / N-WO3, Ag / WO3 and WO3 at different potentials in NO3RR are shown in Figure 2. -1 The peak at is attributed to NO3 - Symmetric stretching vibration of ions indicates the presence of NO3 in the electrolyte - After applying the cathode potential, 1382 cm -1 The vibration peak of - It is worth noting that the surface adsorption peak of *NO3 on the Ag / N-WO3 sample is at 0 V. RHE This indicates that the formation of Ag-N bonds helps to enhance the adsorption of *NO3 on the WO3 substrate. -1 The Raman peak at belongs to the symmetric stretching vibration of NO2. As the cathode voltage is gradually applied, *NO3 - The NO2 peak gradually disappeared, while the NO2 peak increased significantly, which clearly showed that NO3 - Reduced to NO3 - In addition, for Ag / N-WO3, from -0.2 V RHE 1218 cm begins to appear -1 The vibration peak of Ag / N-WO3 and Ag / WO3 samples is at 1551 cm -1 and 150 cm -1The appearance and disappearance of *NOH and *NH can be observed, which indicates that the catalytic pathway of NO3RR belongs to the NOH pathway, and the overall peak intensity on the Ag / N-WO3 sample is in a weak state, which means that the formation of Ag-N bonds promotes the rapid consumption of reaction intermediates (such as *NOH and *NH), thereby promoting the rapid and continuous NO3RR. In addition, in the in-situ Raman spectrum of WO3 ( Figure 8 c) The 1551 cm -1 and 1500 cm -1 The formation of single Ag atoms changes the catalytic pathway of NO3RR on WO3 substrate. -1 and 1591 cm -1 The obvious peaks at are attributed to the antisymmetric vibration of NH2 and *NH3. The *NH3 peak on Ag / N-WO3 is significantly stronger than that on Ag / WO3 and WO3 samples, indicating that Ag / N-WO3 is more conducive to the NO3RR reaction.

[0051] In order to fully elucidate the reaction mechanism, in situ Fourier transform infrared (FTIR) spectroscopy was used to investigate the information of adsorbed species at the electrode-electrolyte interface during the NO3RR process. Fig. 9 The FTIR spectra of Ag / N-WO3, Ag / WO3, and WO3 in H2SO4 containing nitrate are shown. As shown in the figure, around 1360 cm -1 The negative peak at corresponds to NO3 - , while the positive peak corresponds to the deoxy intermediate (about 1674 cm -1 *NO, about 1275 cm -1 *NO2 at 3098 cm -1 *NH2 at about 1128 cm -1 *NH2OH at 3250 cm -1 *NH3 at about 1480 cm -1 NH4 + In addition, compared with the WO3 sample ( Fig. 9 Compared with (c), in the whole NO3RR process, after the introduction of Ag single atoms, the HOH stretching vibration (1625cm -1) is significantly enhanced. This confirms that when Ag single atoms are used as catalytic sites, H2O can effectively dissociate to produce a large amount of stable *H. During the NO3RR process, as the cathode potential is gradually applied, the deoxygenation intermediates and hydrogenation intermediates on the nitrided Ag / N-WO3 appear earlier than on Ag / WO3. This clearly shows that the formation of Ag-N bonds enhances the adsorption of *NO3 and reduces the energy barriers for deoxygenation and hydrogenation during the NO3RR process. This conclusion is also consistent with the electrocatalytic experimental data.

[0052] In order to clarify the specific reaction path during the nitrate electroreduction process, in situ differential electrochemical mass spectrometry (DEMS) was used to monitor the reaction intermediates. Under the same range and test conditions, Ag / N-WO3 ( Fig.10 a), Ag / WO3 ( Fig.10 b) and WO3 ( Fig.10 The intermediates and products in (c) show some obvious differences. The signals of H2, N2 and N2O are weak, which proves that the Ag-N active site has high selectivity for NH3. Considering that NN coupling is energetically unfavorable, other complex multi-nitrogen intermediates are not considered here. When Ag / N-WO3 is used as the catalyst, the signal intensity of NH3-related intermediates (NH3, NH2, NH) is much stronger, which corresponds to the high NH3 yield. Importantly, several key intermediates that determine the selectivity toward NH3 can be observed on Ag / N-WO3 and Ag / WO3, but not on WO3. These intermediates are NO, nitramide (NHO) and hydroxylamine (NH2OH), among which NHO is a unique intermediate on the path to generate NH3. This indicates that the introduction of single Ag atoms changes the reaction path of NO3RR, thereby improving the NO3RR catalytic activity of WO3 substrate. The in situ experimental results suggest a possible reaction pathway, namely *NO2→*NO→*NHO→*NHOH→*NH2OH→*NH→*NH2→*NH3.

[0053] Nitrate reduction reaction (NO3 - -RR) is of great significance in environmental protection and resource recovery. Traditional nitrate treatment methods (such as biological denitrification and physical separation) have problems such as low efficiency, high cost or secondary pollution. Electrochemical nitrate reduction technology has become a promising alternative due to its mild reaction conditions, environmental friendliness and potential for coupling with renewable energy.

[0054] As a semiconductor material, WO3 (tungsten trioxide) shows significant application potential in nitrate reduction under acidic conditions due to its unique electronic structure and catalytic properties. WO3 has good semiconductor properties and a suitable band gap structure, which can effectively absorb light energy and participate in electrocatalytic reactions. And its specific surface area and the number of active sites can be significantly improved through nanostructure design (such as nanosheets, nanowires) and heterostructure construction (such as composite with ZIF-67). WO3 shows good chemical stability in acidic environments and is suitable for nitrate reduction in acidic electrolytes.

[0055] WO3-based catalysts show broad application prospects in nitrate reduction under acidic conditions. Nitrate can be efficiently reduced and converted into harmless nitrogen or ammonia, thereby purifying industrial wastewater containing nitrates. Ammonia can be synthesized through electrochemical nitrate reduction to achieve resource recovery and energy utilization. It can also be used in acidic soils or water bodies to reduce nitrate pollution.

[0056] 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 one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst, characterized in that: The steps are: (1) The carbon cloth is oxidized with concentrated nitric acid, ultrasonically cleaned, dried, and then placed in an aqueous solution of ammonium metatungstate for heating to obtain WO3 nanowires; (2) The WO3 nanowires are immersed in a Ag2SO4 solution. The obtained product is dried and then annealed in an ammonia atmosphere to obtain Ag / N-WO3.

2. The method for preparing the one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst according to claim 1, characterized in that: The mass fraction of concentrated nitric acid in step (1) is 60-70%; the concentration of the aqueous solution of ammonium metatungstate is 2-2.5 mol / L.

3. The method for preparing the one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst according to claim 2, characterized in that: The oxidation treatment is carried out at a temperature of 75-80°C and for a time of 10-14 hours; the heating reaction is carried out at a temperature of 170-190°C and for a time of 15-18 hours.

4. The method for preparing the one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst according to claim 1, characterized in that: The concentration of the Ag2SO4 solution in step (2) is 4-6 mM.

5. The method for preparing the one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst according to claim 4, characterized in that: The WO3 nanowires are immersed in the Ag2SO4 solution for 1-2 minutes; the annealing reaction temperature is 500-550°C, the time is 2-2.5 hours, and the annealing heating rate is 5-6°C / min.

6. Ag / WO3 nanorod electrocatalyst prepared by the method described in any one of claims 1 to 5.

7. Use of the Ag / WO3 nanorod electrocatalyst according to claim 6 in the industrial electrocatalytic reduction of nitrates to synthesize ammonia.

8. The use according to claim 7, characterized in that: The electrocatalysis is an electrocatalytic reaction under strong acid conditions.

9. A three-electrode system, characterized in that: The three-electrode system uses Ag / N-WO3 as the working electrode.

10. The three-electrode system according to claim 9, characterized in that: The three-electrode system further comprises a reference electrode, a counter electrode, a cathode pool and an anode pool; the cathode pool and the anode pool both contain a strong acid solution.

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