A one-dimensional nitride-doped Ag / WO 3 nanorod electrocatalyst, its preparation method and application

Abstract

The present invention belongs to the field of electrocatalysis, relates to nitrate reduction, particularly to the synthesis of ammonia by nitrate reduction in acidic media, and discloses a one-dimensional nitride-doped Ag / WO3 nanorod electrocatalyst, its preparation method and application. For the first time, a stable one-dimensional nitride-doped WO3 nanorod is synthesized in this application, and Ag species with poor hydrogen evolution activity are decorated on it for rapidly reducing nitrate to ammonia under acidic conditions. This catalyst improves the adsorption of nitrate, reduces the energy barrier of the rate-determining step, thereby greatly improving the efficiency of ammonia synthesis and reducing HER at the amperometric current density. This work provides in-depth insights into acidic nitrate reduction in ammonia electrosynthesis and develops corrosion-resistant electrocatalysts for energy conversion.

Description

Technical Field

[0001] The present invention belongs to the field of electrocatalysis, relates to nitrate reduction, and particularly refers to the synthesis of ammonia by nitrate reduction. Background Art

[0002] Electrocatalytic reduction of nitrate to ammonia (NO 3 RR) has received extensive attention in the Haber-Bosch alternative process for ammonia synthesis. Great efforts have been made to study the selective electrocatalysts for NO 3 RR under alkaline / neutral conditions. Although the recently reported catalysts have high Faradaic efficiencies (FEs) for NH 3 , to achieve the optimal performance for ammonia production from nitrate, it is usually necessary to generate nitrite by-products and a large overpotential at the beginning stage. According to the reaction equation of NO 3 - + 6H 2 O + 8e - → NH 3 + 9OH - under alkaline / neutral conditions, NO 3 RR involves nine proton-coupled electron transfers, where protons are generated through an additional water dissociation step (H 2 O → H* + OH*), which may lead to a too large overpotential and slow kinetics, thus limiting the performance of NO 3 RR. On the contrary, compared with alkaline / neutral conditions, direct nitrate reduction in acidic media (which contains wastewater commonly present in industrial processes) has unique advantages, such as enhancing the multi-protonation step of NO 3 - , and improving the conversion rate of NO 3 - to NH 3 . As the acidity of the reaction increases, abundant protons can be provided for the continuous hydrogenation reaction of NO 3 - , thus ensuring an increase in the conversion rate of NO 3 - and generating NH 3 more efficiently. Therefore, it is highly desirable to develop NO 3 RR that conforms to industrial processes in an acidic environment and avoids additional costs and energy consumption. However, designing a robust catalyst for acidic NO 3 RR is a huge challenge, which requires high catalytic activity, high selectivity, and high durability.

[0003] The hydrogen evolution reaction (HER) inevitably becomes NO 3Competitive reactions of RR, especially under acidic conditions. Reported catalysts (such as Cu, Co, and Ni transition metals) are usually unstable in acidic media and are rarely available for acidic NO 3 RR. Due to the enhanced competitive HER under acidic conditions, these catalysts also suffer from the problem of reduced NH 3 FE. To address these issues, Zhi et al. reported the potential of iron phthalocyanine / titanium dioxide nanosheets to selectively and rapidly reduce nitrate to ammonia in acidic media, with an NH 3 yield as high as 17.4 mg h -1 cm -2 and an NH 3 FE of 90.6%. Chen and his colleagues fabricated RhNi bis(cyclopentadienyl)titanium with a lattice-compressed Rh-skin type structure, which showed a stability of 400 hours for acidic NO 3 RR. The Rh-skin atoms inhibited the Rh dissolution caused by NO 2 * / NH 2 * adsorption, improving the electrocatalytic stability of acidic electrochemical nitrate reduction. However, it is still difficult to meet the industrial requirements. Summary of the Invention

[0004] To meet the industrial requirements, the present invention provides an electrocatalyst that can rapidly 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 / WO 3 nanorod electrocatalyst and its preparation method and application.

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

[0006] A preparation method of a one-dimensional nitride-doped Ag / WO 3 nanorod electrocatalyst, the steps are as follows:

[0007] (1) The carbon cloth is oxidized in a 60-70% HNO 3 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 homogeneous 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 WO 3 nanowires are washed with deionized water and dried overnight at 70 °C.

[0008] (2) The preparation method of Ag / N-WO 3 is to mix WO 3The nanowires are immersed in 4 - 6 mM Ag 2 SO 4 solution for 1 - 2 minutes. The Ag 2 SO 4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in an NH 3 atmosphere at 500 - 550 °C for 2 - 2.5 hours with a heating rate of 5 - 6 °C / min to obtain Ag / N - WO 3 .

[0009] The Ag / WO 3 nanorod electrocatalyst prepared by the above method.

[0010] The above Ag / WO 3 nanorod electrocatalyst is applied to the electrocatalytic reduction of nitrate to ammonia in industrialization.

[0011] The above electrocatalysis is an electrocatalytic reaction under strong acid conditions.

[0012] A three - electrode system, which uses Ag / N - WO 3 as the working electrode.

[0013] The above three - electrode system also includes a reference electrode, a counter electrode, a cathode cell and an anode cell; both the cathode cell and the anode cell contain strong acidic solutions.

[0014] Specifically, the three - electrode H - Cell used consists of a working electrode, a saturated calomel electrode (SCE) as the reference electrode and a platinum foil as the counter electrode; it is divided into a cathode cell (33 mL 0.5 M KNO 3 + 0.5 M H 2 SO 4 ) and an anode cell (40 mL 0.5 M H 2 SO 4 ) by an anion - exchange membrane (Nafion 117 membrane). Ag / N - WO 3 is used as the working electrode.

[0015] The present invention has the following beneficial effects:

[0016] 1. For the first time, the present application constructs a one - dimensional nitride - doped Ag / WO 3 nanorod electrocatalyst, and decorates it with Ag species with poor hydrogen evolution activity for rapidly reducing nitrate to ammonia under acidic conditions. WO 3 has excellent stability under acidic conditions. This catalyst changes NO 3 by introducing Ag single atoms on the WO 3The reaction path of RR was further nitrided to enhance its adsorption of NO at low reduction potential, thus achieving efficient and stable nitrate reduction to ammonia in a strong acid environment. 3 - The adsorption of NO was enhanced, enabling efficient and stable nitrate reduction to ammonia in a strong acid environment.

[0017] 2. Ag / N-WO 3 For the electrocatalyst in the potential range of -0.6 to -0.2 V RHE the Faradaic efficiency (FE) of ammonia production by the catalyst was close to 99.32 ± 3.66%. At -0.4 V RHE the maximum FE was ~100%. At -0.55 V RHE the maximum production rate of NH 3 reached 5.24 ± 0.41 mmol h -1 cm -2 . Impressively, the catalyst could maintain an industrially relevant current density of 480 mA cm -2 for over 1000 hours, with the FE stable at around 94%. Experimental results and theoretical calculations showed that the nitrate adsorption was improved, and the single silver atoms and nitridation treatment reduced the energy barrier of the rate-determining step, thus greatly enhancing the efficiency of ammonia synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] 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.

[0019] Figure 1 Scanning electron microscope images of a-c WO 3 , d-f Ag / WO 3 and g-i Ag / N-WO 3 .

[0020] Figure 2 Characterization diagrams of WO 3 , Ag / WO 3 and Ag / N-WO 3 ; where a is the XRD pattern and b is the Raman spectrum.

[0021] Figure 3 The preparation optimization process of Ag / N-WO 3 .

[0022] Figure 4 For Ag / N-WO 3Electrochemical tests with or without nitrate (NO 3 - ); where a is the LSV curve of 0.5 M H 3 Ag / N-WO 3 Ag / WO 3 and WO 2 SO 4 + 0.5 M KNO 3 after 80% iR correction; b is the LSV curve of WO 3 Ag / WO 3 and Ag / N-WO 3 in 0.5 M H 2 SO 4 ; c is the Tafel slope plot of the corresponding catalyst; d is the Nyquist plot of the corresponding catalyst; e is the Cdl plot of WO 3 Ag / WO 3 and Ag / N-WO 3 ; f is the Faraday efficiency and yield of NH 3 Ag / N-WO 3 Ag / WO 3 and WO RHE at -0.4 V 3 .

[0023] Figure 5 are the Faraday efficiency and ammonia yield of NH 3 for different catalysts at different potentials; where a is WO 3 ; b is Ag / WO 3 ; c is Ag / N-WO 3 .

[0024] Figure 6 are the stability tests of NO 3 RR electrocatalysts; where a is the I-t curve of ammonia synthesis measured cyclically for Ag / N-WO 3 at -0.4 V RHE ; b is the continuous stability measurement of Ag / N-WO RHE at -0.4 V 3 ; c is the long-term stability test of NO RHE RR on Ag / N-WO 3 at -0.3 V 3 using a continuous flow system in an H-type cell. The arrow mark indicates electrolyte replacement.

[0025] Figure 7 are at different potentials, 600 - 1000 cm -1In-situ Raman spectra of different catalysts within a certain range; where a is WO 3 、b is Ag / WO 3 and c is Ag / N-WO 3 .

[0026] Figure 8 In-situ Raman spectra of different catalysts within the range of 1000 - 1700 cm -1 at different potentials; where a is WO 3 、b is Ag / WO 3 and c is Ag / N-WO 3 .

[0027] Figure 9 Electrochemical thin-layer in-situ Fourier transform infrared spectra of NO 2 RR on different catalysts in 0.5 M H 4 SO 3 + 0.5 M KNO 3 ; where a is WO 3 、b is Ag / WO 3 and c is Ag / N-WO 3 .

[0028] Figure 10 Electrochemical online DEMS results of NO 3 RR on different catalysts; where a is Ag / N-WO 3 、b is Ag / WO 3 and c is WO 3 . Detailed implementation manners

[0029] 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 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 shall fall within the protection scope of the present invention.

[0030] The test methods used in the following experimental examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0031] Example 1

[0032] A preparation method of a one-dimensional nitride-doped Ag / WO 3 nanorod electrocatalyst, the steps are as follows:

[0033] (1) The carbon cloth is treated with HNO 3(65 wt%) was treated by oxidation for 12 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate hydrate (50.0 mM) was dissolved in 20.0 mL of ultrapure water, and then magnetically stirred for 20 minutes to obtain a homogeneous solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed into the solution and reacted at 180 °C for 16 hours to obtain WO 3 nanowires were washed with deionized water and dried overnight at 70 °C.

[0034] (2)The preparation method of Ag / N-WO 3 was to immerse the WO 3 nanowires into 5 mM Ag 2 SO 4 solution for 2 minutes. The Ag 2 SO 4 solution should be ultrasonically treated overnight. The sample was dried at room temperature for 30 minutes. Finally, the above sample was annealed in an NH 3 atmosphere at 500 °C for 2 hours with a heating rate of 5 °C / min to obtain Ag / N-WO 3 .

[0035] Example 2

[0036] A preparation method of a one-dimensional nitride-doped Ag / WO 3 nanorod electrocatalyst, the steps are as follows:

[0037] (1)The carbon cloth was treated by oxidation in HNO 3 (60 wt%) at 75 °C for 10 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate hydrate (40.0 mM) was dissolved in 20.0 mL of ultrapure water, and then magnetically stirred for 25 minutes to obtain a homogeneous solution. The above solution was transferred to an autoclave, and then the carbon cloth was placed into the solution and reacted at 170 °C for 15 hours to obtain WO 3 nanowires were washed with deionized water and dried overnight at 70 °C.

[0038] (2)The preparation method of Ag / N-WO 3 was to immerse the WO 3 nanowires into 4 mM Ag 2 SO 4 solution for 1 minute. The Ag 2 SO 4 solution should be ultrasonically treated overnight. The sample was dried at room temperature for 30 minutes. Finally, the above sample was annealed in an NH 3 atmosphere at 530 °C for 2 hours with a heating rate of 5.5 °C / min to obtain Ag / N-WO 3 .

[0039] Example 3

[0040] A preparation method of a one-dimensional nitride-doped Ag / WO 3 nanorod electrocatalyst, the steps are as follows:

[0041] (1) The carbon cloth is oxidized in HNO 3 (70 wt%) at 78 °C for 13 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (45.0 mM) is dissolved in 20.0 mL of ultrapure water, and then magnetically stirred for 30 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 190 °C for 18 hours to obtain WO 3 nanowires are washed with deionized water and dried overnight at 70 °C.

[0042] (2) The preparation method of Ag / N-WO 3 is to immerse the WO 3 nanowires in 6 mM Ag 2 SO 4 solution for 1.5 minutes. The Ag 2 SO 4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in an NH 3 atmosphere at 550 °C for 2.5 hours with a heating rate of 6 °C / min to obtain Ag / N-WO 3 .

[0043] Example 4

[0044] A preparation method of a one-dimensional nitride-doped Ag / WO 3 nanorod electrocatalyst, the steps are as follows:

[0045] (1) The carbon cloth is oxidized in HNO 3 (65 wt%) at 80 °C for 14 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate dodecahydrate (50.0 mM) is dissolved in 20.0 mL of ultrapure water, and then 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 190 °C for 16 hours to obtain WO 3 nanowires are washed with deionized water and dried overnight at 70 °C.

[0046] (2) The preparation method of Ag / N-WO 3 is to immerse the WO 3 nanowires in 4 mM Ag 2 SO 4 solution for 2 minutes, Ag2 SO 4 The solution should be sonicated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in an NH 3 atmosphere at 500 °C for 2 hours with a heating rate of 5 °C / min to obtain Ag / N-WO 3 .

[0047] Example 5

[0048] A preparation method of a one-dimensional nitride-doped Ag / WO 3 nanorod electrocatalyst, the steps are as follows:

[0049] (1) The carbon cloth is oxidized in HNO 3 (70 wt%) at 79 °C for 14 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate hydrate (48.0 mM) is dissolved in 20.0 mL of ultrapure water, and then magnetically stirred for 20 minutes to obtain a homogeneous solution. The above solution is transferred to an autoclave, and then the carbon cloth is placed in the solution and reacted at 170 °C for 18 hours to obtain WO 3 nanowires are washed with deionized water and dried overnight at 70 °C.

[0050] (2) The preparation method of Ag / N-WO 3 is to immerse the WO 3 nanowires in 6 mM Ag 2 SO 4 solution for 2 minutes. The Ag 2 SO 4 solution should be sonicated overnight. The sample is dried at room temperature for 30 minutes. Finally, the above sample is annealed in an NH 3 atmosphere at 550 °C for 2 hours with a heating rate of 5 °C / min to obtain Ag / N-WO 3 .

[0051] Comparative Example 1

[0052] The preparation method of WO 3 nanowires is as follows:

[0053] (1) The carbon cloth is oxidized in HNO 3 (65 wt%) at 80 °C for 12 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Ammonium metatungstate hydrate (50.0 mM) is dissolved in 20.0 mL of ultrapure water, and then magnetically stirred for 20 minutes to obtain a homogeneous solution. The above solution is transferred to an autoclave, and then the carbon cloth is placed in the solution and reacted at 180 °C for 16 hours to obtain WO 3 nanowires are washed with deionized water and dried overnight at 70 °C.

[0054] (2) Finally, anneal the above sample in an O 2 atmosphere at 500 °C for 2 hours with a heating rate of 5 °C / min to obtain WO 3 .

[0055] Comparative Example 2

[0056] Preparation method of Ag / WO 3 :

[0057] (1) The carbon cloth is oxidized in HNO 3 (65 wt%) at 80 °C for 12 hours, then ultrasonically cleaned with deionized water and ethanol, and dried in air. Dissolve ammonium metatungstate hydrate (50.0 mM) in 20.0 mL of ultrapure water, then stir magnetically for 20 minutes to obtain a homogeneous solution. Transfer the above solution to an autoclave, then put the carbon cloth into the solution, react at 180 °C for 16 hours, and wash the obtained WO 3 nanowires with deionized water and dry overnight at 70 °C. Finally, anneal the above sample in an O 2 atmosphere at 500 °C for 2 hours with a heating rate of 5 °C / min to obtain WO 3 .

[0058] (2) The preparation method of Ag / WO 3 is to immerse the WO 3 nanowires in 5 mM Ag 2 SO 4 solution for 2 minutes. The Ag 2 SO 4 solution should be ultrasonically treated overnight. The sample is dried at room temperature for 30 minutes. Finally, anneal the above sample in an O 2 atmosphere at 500 °C for 2 hours with a heating rate of 5 °C / min to obtain Ag / WO 3 .

[0059] Example of implementation effect 1

[0060] For the Ag / N-WO 3 prepared in Example 1, the WO 3 prepared in Comparative Example 1, and the Ag / WO 3 prepared in Comparative Example 2, scanning electron microscopy (SEM) observation was carried out. As Figure 1 shown, it can be seen that Ag / N-WO 3 is in the form of nanorods loaded on the carbon cloth, and there is no obvious change in the morphology of WO 3 , Ag / WO 3 and Ag / N-WO 3 ( Figure 1). Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the Ag concentration on Ag / N-WO 3 was 0.42 wt.% (Table 1).

[0061] Table 1 ICP-MS analysis of three substances

[0062]

[0063] WO 3 , Ag / WO 3 and Ag / N-WO 3 X-ray diffraction (XRD) patterns showed the characteristic peaks of hexagonal tungsten trioxide (JCPDS No. 85-2460) ( Figure 2 a). Due to the extremely low Ag phase content, no peaks related to it were observed. The (002) and (200) interplanar spacings of Ag / N-WO 3 were shortened from 4.9 nm of WO 3 and Ag / WO 3 to 4.5 nm, which can be attributed to the lattice distortion caused by nitrogen doping reported previously. As shown by the Raman spectra in Figure 2 b, the bands at 270 and 328 cm -1 were attributed to the deformation mode of O-W-O, while the bands below 183 cm -1 corresponded to the lattice mode. The bands at 806 and 712 cm -1 were related to the asymmetric and symmetric stretching vibrations of terminal O-W-O. It could be observed that the O-W-O stretching vibration peaks underwent a red shift. For WO 3 and Ag / WO 3 , the peaks were located at 806 cm -1 and 712 cm -1 respectively, while for Ag / N-WO 3 , they were shifted to 718 cm -1 and 647 cm -1 respectively, which was attributed to the redistribution of electron density on WO 3 due to the nitridation treatment.

[0064] Example of implementation effect 2

[0065] Electrochemical NO 3 RR measurements were carried out using a CHI760E electrochemical analyzer. The three-electrode H-Cell used consisted of a working electrode, a saturated calomel electrode (SCE) as the reference electrode, and a platinum foil as the counter electrode; it was divided into a cathode cell (33 mL 0.5 M KNO 3 + 0.5 M H 2 SO4 ), and the anodic cell (40 mL of 0.5 M H 2 SO 4 ). Ag / N-WO 3 , Ag / WO 3 , and WO 3 were used as the working electrodes. The scanning rate of linear sweep voltammetry (LSV) was 5 mV s -1 . For the catalytic potential, we calibrated it using 80% of the solution internal resistance (iR). All potentials were calibrated to RHE according to the following formula:

[0066] E RHE = E SCE + 0.0591×pH (1)

[0067] where E SCE represents the experimental applied potential. Electrochemical impedance spectroscopy (EIS) was measured at -0.25 V RHE with an amplitude of 5 mV at frequencies from 15 kHz to 0.001 Hz. The electrochemical double-layer capacitance (Cdl) was obtained by CV cycling at potentials from -0.1 to 0.3 V RHE , and then a linear fit was performed on this curve, and the slope was the Cdl value. The measurement formula for the electrochemically active surface area (ECSA) is:

[0068] ECSA = Cdl / Cs (2)

[0069] The Faradaic efficiency (FE) of NH3 was calculated as follows:

[0070] (3)

[0071] where Q represents the total applied charge (C), Q NH3 is the charge required to produce NH 3 , n is the number of electron transfers (8 for 1 mole of NH 3 ), V is the volume of the cathode solution in the cathode chamber (33 mL), c NH3 is the concentration of the produced NH 3 , and F is the Faraday constant (96.485 C mol -1 ). To ensure the accuracy of the experiment, we conducted three independent experiments separately and measured the error bars.

[0072] The yield of the product was calculated as follows:

[0073] (4)

[0074] Among them, 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 correspond to the standard deviation of three independent measurements, and the central value of the error bars is the average of the three independent measurements.

[0075] 1. We evaluated the electrochemical nitrate reduction reaction (NO 3 RR) performance of WO 3 , Ag / WO 3 and Ag / N-WO 3 in an acidic H-type electrolytic cell. First, Figure 3 shows the optimization of the NO 2 RR activity on Ag / N-WO 4 for different Ag 3 SO 3 concentrations, ammonia annealing temperatures, and nitrate concentrations in the electrolyte. The linear sweep voltammetry (LSV) curves of Ag / N-WO 3 with or without nitrate (NO 3 - ) were recorded (a in Figure 4 and b in Figure 4 ). In the presence of nitrate, the current density of Ag / N-WO 3 increased, indicating that the nitrate reduction process occurred. As shown in a of Figure 4 , compared with the original WO 3 , Ag / WO 3 and Ag / N-WO 3 showed better performance in the LSV curves, especially in terms of the chronoamperometric current density. Among these samples, Ag / N-WO 3 showed the best activity, with a current density of 1 A cm RHE ² at -0.53 V - (reversible hydrogen electrode potential) and an onset potential of 0 V RHE . Figure 4 c and Figure 4 d show that Ag / N-WO 3 has the lowest Tafel slope and Nyquist plot, indicating the fastest electron transfer frequency. The electrochemically active surface area (ECSA) shows that the double-layer capacitance (CdI, 357.68 mF cm 3 ) of Ag / N-WO -2 is larger than that of Ag / WO 3 (331.46 mF cm -2 ) and WO 3 (66.28 mF cm -2 ) (e in Figure 4 ), confirming that among these catalysts, Ag / N-WO 3Essentially has the highest activity.

[0076] Figure 4 Figure f shows the Faraday efficiencies (FEs) and ammonia yields of the catalysts used at -0.4 V. RHE Among these samples, Ag / N-WO 3 exhibits the highest Faraday efficiency and ammonia yield, which represents the best NO 3 RR performance reported to date in acidic electrolytes. We further investigated the Faraday efficiency and ammonia yield of Ag / N-WO 3 at different potentials ( Figure 5 a). As can be seen from Figure 3 Figure c, Ag / N-WO 3 maintains a Faraday efficiency above 90% in the wide potential range from -0.2 to -0.6 V RHE and reaches the highest Faraday efficiency of 99.32 ± 4% at -0.4 V RHE . At an industrial high current density, the ammonia yield is the highest at -0.5 V RHE and is 5.24 ± 0.41 mmol h -1 cm -2 . The increased Faraday efficiency and ammonia yield at larger potentials indicate that the catalyst has a high selectivity for the electroreduction of NO 3 to NH 3 compared to Ag / WO 3 - and WO 3 ( Figure 5 Figure b and Figure 5 Figure c). In addition, as the potential gradually increases in the negative direction, the current density increases linearly without a decrease, indicating that the competition between NO 3 - and H ＋ on the electrode surface weakens.

[0077] In addition to activity and selectivity, the stability of the NO 3 RR electrocatalyst is also a crucial parameter in potential practical applications. We conducted 20 consecutive chronoamperometry experiment cycles on Ag / N-WO 3 ( Figure 6 Figure a), and at -0.4 V RHE , all Faraday efficiencies (FEs) for NO 3 RR are approximately 97% ( Figure 6 Figure b). In addition, the long-term stability of electrochemical NO 3 RR was evaluated by chronoamperometry measurements using a continuous flow system in a H-type electrolytic cell. Ag / N-WO 3Maintain a stable current density of approximately 480 mA cm after 1000 hours -1 , and a stable ammonia Faraday efficiency of 95% ( Figure 6 c) in 3 , indicating that this catalyst can continuously catalyze NO

[0078] 2. We used in-situ Raman spectroscopy to study the changes in the WO 3 substrate during the NO 3 RR reaction process. During the NO 3 RR process, as the cathode voltage gradually increased, the characteristic Raman peaks of tungsten oxide corresponding to the three samples of Ag / N-WO 3 , Ag / WO 3 and WO 3 all disappeared and gradually underwent a blue shift ( Figure 7 ). This is because during the nitrate reduction process, electrons are transferred from nitrate to WO 3 , resulting in a change in the electronic structure of WO 3 . This electron transfer may change the energy band structure of WO 3 , thereby affecting the lattice vibration mode of WO 3 and causing the Raman peak to blue shift.

[0079] To determine the intermediates involved in the NO 3 RR process, we used in-situ Raman spectroscopy in the potential range of 0 to -0.6 V RHE . The Raman spectra of Ag / N-WO Figure 8 , Ag / WO 3 and WO 3 at different potentials during NO 3 RR are shown in 3 . The peak at 1048 cm -1 in the Raman spectrum is attributed to the symmetric stretching vibration of NO 3 - ions, indicating the presence of NO 3 - in the electrolyte. After applying the cathode potential, the vibration peak at 1382 cm -1 gradually appears, and this peak is attributed to a specific mode of surface-adsorbed *NO 3 - . It is worth noting that the surface adsorption peak of *NO 3 on the Ag / N-WO 3 sample appears at 0 V RHE , significantly earlier than the Ag / WO 3 and WO 3 samples, indicating that the formation of the Ag-N bond helps to enhance *NO3 Adsorption on the WO 3 substrate. Meanwhile, the Raman peak at 1351 cm -1 belongs to the symmetric stretching vibration of NO 2 . As the cathode voltage is gradually applied, the *NO 3 - peak gradually disappears, while the NO 2 peak is significantly enhanced, which clearly indicates that NO 3 - is reduced to NO 3 - . In addition, for Ag / N-WO 3 , a vibration peak at 1218 cm RHE appears starting from -0.2 V -1 , and this peak is enhanced at more negative cathode potentials, which can be attributed to the adsorbed NO 2 . In the Ag / N-WO 3 and Ag / WO 3 samples, the appearance and disappearance of *NOH and *NH can be observed at 1551 cm -1 and 150 cm -1 respectively, which indicates that the catalytic path of NO 3 RR belongs to the NOH path, and the overall peak intensity on the Ag / N-WO 3 sample is in a weak state, which means the formation of the Ag-N bond promotes the rapid consumption of reaction intermediates (such as *NOH and *NH), thus driving the NO 3 RR to proceed rapidly and continuously. In addition, in the in-situ Raman spectrogram of WO 3 ( Figure 8 c), the *NOH and *NH at 1551 cm -1 and 1500 cm -1 cannot be observed, which indicates that the formation of Ag single atoms changes the catalytic pathway of NO 3 RR on the WO 3 substrate. The obvious peaks at 1613 cm -1 and 1591 cm -1 are attributed to the asymmetric vibrations of NH 2 and *NH 3 . The *NH 3 peak on Ag / N-WO 3 is significantly stronger than that on Ag / WO 3 and WO 3 samples, which indicates that Ag / N-WO 3 is more favorable for the NO 3 RR reaction.

[0080] To comprehensively elucidate the reaction mechanism, in-situ Fourier transform infrared (FTIR) spectroscopy was employed to study the information of adsorbed substances at the electrode-electrolyte interface during the NO 3 RR process. Figure 9 The FTIR spectra of Ag / N-WO 3 , Ag / WO 3 and WO 3 in H 2 SO 4 containing nitrate are shown. As depicted, the negative peak at approximately 1360 cm -1 corresponds to NO 3 - , while the positive peaks correspond to the deoxygenation intermediates (*NO at approximately 1674 cm -1 ), *NO -1 at approximately 1275 cm 2 ), the hydrogenation intermediates (*NH -1 at approximately 3098 cm 2 , *NH -1 OH at approximately 1128 cm 2 ) and the generated NH 3 (*NH -1 at approximately 3250 cm 3 , NH -1 at approximately 1480 cm 4 + ). Additionally, compared with the WO 3 sample ( Figure 9 c), during the entire NO 3 RR process, after introducing Ag single atoms, the H-O-H stretching vibration (1625 cm 3 ) of H 3 O in the Ag / N-WO 2 and Ag / WO -1 samples is significantly enhanced. This confirms that when Ag single atoms serve as catalytic sites, H 2 O can be effectively dissociated, thereby generating a large number of stable *H. During the NO 3 RR process, as the cathode potential is gradually applied, the appearance time of the deoxygenation intermediate and the hydrogenation intermediate on the nitrided Ag / N-WO 3 is earlier than that on the Ag / WO 3 . This clearly indicates that the formation of the Ag-N bond enhances the adsorption of *NO 3 and reduces the energy barriers for deoxygenation and hydrogenation during the NO 3 RR process. This conclusion is also consistent with the electrocatalytic experimental data.

[0081] To clarify the specific reaction pathway during the electroreduction of nitrate, in-situ differential electrochemical mass spectrometry (DEMS) was used to monitor the reaction intermediates. Under the same range and test conditions, there are some obvious differences in the intermediates and products of Ag / N-WO 3 ( Figure 10 a), Ag / WO 3 ( Figure 10 b), and WO 3 ( Figure 10 c). The signals of H 2 , N 2 , and N 2 O are weak, demonstrating the high selectivity of the Ag-N active sites towards NH 3 . Considering that N-N coupling is energetically unfavorable, other complex multi-nitrogen intermediates are not considered here. When using Ag / N-WO 3 as the catalyst, the signal intensities of the intermediates related to NH 3 (NH 3 , NH 2 , NH) are much stronger, which corresponds to the high NH 3 yield. Importantly, several key intermediates determining the selectivity towards NH 3 can be observed on Ag / N-WO 3 and Ag / WO 3 , but not on WO 3 . These intermediates are NO, nitroxyl (NHO), and hydroxylamine (NH 2 OH), where NHO is a unique intermediate on the path to generating NH 3 . This indicates that the introduction of Ag single atoms changes the reaction pathway of NO 3 RR, thereby improving the NO 3 RR catalytic activity of the WO 3 substrate. The in-situ experimental results imply a possible reaction pathway: *NO 2 → *NO → *NHO → *NHOH → *NH 2 OH → *NH → *NH 2 → *NH 3 .

[0082] The nitrate reduction reaction (NO 3 - -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.

[0083] WO3 Tungsten trioxide, as a semiconductor material, exhibits significant application potential in nitrate reduction under acidic conditions due to its unique electronic structure and catalytic properties. WO 3 It has good semiconductor characteristics and a suitable bandgap structure, enabling it to effectively absorb light energy and participate in electrocatalytic reactions. Moreover, through nanostructure design (such as nanosheets, nanowires) and heterostructure construction (such as composite with ZIF-67), its specific surface area and the number of active sites can be significantly increased. WO 3 It shows good chemical stability in an acidic environment and is suitable for nitrate reduction in acidic electrolytes.

[0084] WO 3 WO-based catalysts exhibit broad application prospects in nitrate reduction under acidic conditions. By efficiently reducing nitrate, it can be converted into harmless nitrogen or ammonia, thereby purifying industrial wastewater containing nitrates. Synthesizing ammonia through electrochemical nitrate reduction realizes resource recovery and energy utilization. And it can be applied in acidic soils or water bodies to reduce nitrate pollution.

[0085] 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 within 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 the Ag / WO3 nanorod electrocatalyst described in claim 6 as a 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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