Ag-FeOOH electrocatalyst, hydrogel enhanced electrocatalytic electrode as well as preparation method and application of Ag-FeOOH electrocatalyst and hydrogel enhanced electrocatalytic electrode

Abstract

The invention provides an Ag-FeOOH electrocatalyst, a hydrogel enhanced electrocatalytic electrode as well as a preparation method and application of the Ag-FeOOH electrocatalyst and the hydrogel enhanced electrocatalytic electrode, and belongs to the field of electrocatalysis. In the Ag-FeOOH electrocatalyst, the Ag catalytic site is mainly responsible for the conversion process from NO3 <-> to NO2 <->, the FeOOH site is responsible for the conversion process from NO2 <-> to NH3, and under the synergistic catalysis of the two sites, NO3 <-> is rapidly converted into NH3. Gel NDI is further loaded on the surface of the Ag-FeOOH electrocatalyst, and after a conductive polymer PPy is introduced into the gel NDI, the removal rate of NO3 <->-N and the selectivity of NH4 < + >-N of the catalytic electrode under the same potential are improved.

Description

Technical Field

[0001] This invention relates to the field of electrocatalysis technology, specifically to an Ag-FeOOH electrocatalyst, a hydrogel-reinforced electrocatalytic electrode, its preparation method, and its application. Background Technology

[0002] The importance of water resources to the Earth is self-evident, yet nitrate pollution of water is increasingly severe. Highly efficient pathways for electrocatalytic nitrate reduction have attracted researchers' attention. The mechanism of electrocatalytic NRA is still under investigation, and research into the catalytic mechanism is crucial for the study of electrocatalytic nitrate reduction. To date, researchers have devoted considerable effort to studying the mechanisms that promote nitrate reduction. Recent studies have focused on introducing new catalytic active sites to construct synergistic effects. These studies are mainly concentrated in materials science, chemical engineering, and catalysis. For example, by anchoring metal atoms to the surface of oxides or carbon materials, atomic-level high efficiency can be achieved, and new catalytic active sites can be introduced. These composite materials, through strategies such as spatial separation and electronic modulation, construct synergistic effects, significantly improving catalytic performance.

[0003] Developing an electrocatalyst with excellent electrical properties and stability for the reduction of nitrates is an important research direction. Summary of the Invention

[0004] To further improve the efficiency, ammonium selectivity, and ammonium yield of electrocatalyst NRA, this invention provides an electrocatalyst with excellent electrical properties and stability for nitrate reduction, as well as a hydrogel-reinforced electrocatalytic electrode, aiming to solve the problems of insufficient catalytic performance and inadequate stability of existing electrocatalysts.

[0005] To achieve the above objectives, the present invention provides an Ag-FeOOH electrocatalyst with dual catalytic active sites, wherein the Ag-FeOOH electrocatalyst comprises FeOOH nanowires and Ag nanoparticles grown on the FeOOH nanowires.

[0006] Furthermore, the Ag-FeOOH electrocatalyst is hydrophilic, and the Ag nanoparticles are grown on the tips of FeOOH nanowires via an electrochemical reduction method.

[0007] This invention also provides a method for preparing an Ag-FeOOH electrocatalyst with dual catalytic active sites, which is prepared in two steps by hydrothermal treatment and electroplating. The specific steps are as follows: (1) The titanium mesh was placed in a mixed solution containing FeCl3·6H2O and Na2SO4. After hydrothermal reaction at 60°C for 12 hours under normal pressure, it was rinsed three times with deionized water and dried at 60°C to obtain a precursor catalyst containing FeOOH nanowires. (2) The precursor catalyst was used as the working electrode and electroplated in a three-electrode system. The electroplating solution used was a mixed solution containing AgNO3. After electroplating, the electrode was rinsed three times with deionized water and dried at 60°C to obtain Ag-FeOOH electrocatalyst with dual catalytic active sites.

[0008] Further, the electroplating solution is a mixed solution containing 3.55g Na2SO4, 0.32g Na3C6H5O7, and 0.024g AgNO3, and the electroplating is performed at -0.35 V. vs. Electrolysis for 30 seconds was tested at RHE potential using the It test.

[0009] Furthermore, the FeOOH nanowires are uniformly distributed on the titanium mesh.

[0010] The present invention also provides a hydrogel-reinforced electrocatalytic electrode, wherein the electrocatalytic electrode is based on an Ag-FeOOH electrocatalyst, and hydrogel is loaded in situ on the substrate to form a hydrogel-reinforced electrocatalytic electrode.

[0011] Furthermore, the hydrogel has a porous structure inside.

[0012] Furthermore, the hydrogel's porous structure also includes a conductive polymer introduced through in-situ polymerization. The conductive polymer is preferably polypyrrole.

[0013] This invention also provides a method for preparing a hydrogel-enhanced electrocatalytic electrode, which forms an NDI / Ag-FeOOH electrode by in-situ supporting NDI hydrogel on an Ag-FeOOH electrocatalyst. The specific process for synthesizing NDI / Ag-FeOOH is as follows: (1) Using N,N'-methylenebisacrylamide as a crosslinking agent and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone as a photoinitiator, N,N-dimethylacrylamide and N-acryloyloxysuccinimide were copolymerized in dimethyl sulfoxide to form a precursor solution A containing a covalent scaffold of NA. (2) Place the Ag-FeOOH electrocatalyst in a mold, add the prepared precursor solution A to the mold, so that Ag-FeOOH is wetted by the precursor solution; place the membrane under an LED ultraviolet UV curing lamp for 2 hours to obtain the electrode ND / Ag-FeOOH; (3) The electrode ND / Ag-FeOOH was immersed in anhydrous DMSO solution containing 4,4'-iminodiphenylamine (IDA) for 8 h to replace the oxysuccinimide group, thus obtaining electrode NDI / Ag-FeOOH; (4) The electrode NDI / Ag-FeOOH is first soaked in FeCl3 solution, and then the electrode is transferred to pyrrole aqueous solution and left to stand for 12 hours to allow the internal conductive network polypyrrole to polymerize and form electrode NDI-PPy / Ag-FeOOH.

[0014] This invention also provides the application of Ag-FeOOH electrocatalyst in the electrocatalytic reduction of nitrates.

[0015] The present invention also provides the application of a hydrogel-enhanced electrocatalytic electrode in the electrocatalytic reduction of nitrates.

[0016] The present invention also provides a Zn-NO3 - The battery includes an Ag-FeOOH electrocatalyst with dual catalytic active sites or a gel-enhanced electrocatalytic electrode.

[0017] Compared with the prior art, the present invention has the following advantages.

[0018] The present invention introduces Ag nanoparticles into the FeOOH surface through electrochemical reduction, which has the following significant advantages: (1) By introducing Ag catalytic active sites, the NO3- content is increased. - To NO2 - Rate, coordinating NO2 on FeOOH - To NH4 + The conversion process improves the overall efficiency of the electrocatalytic NRA of the catalytic material; the Ag catalytic sites of Ag-FeOOH are mainly responsible for NO3. - To NO2 - In the conversion process, the FeOOH site is responsible for NO2. - The conversion to NH3, under the synergistic catalytic action of two sites, NO3... - It is rapidly converted into NH3. (2) NO3 based on different feed ratios - With NO2 - Mixed electrolyte, utilizing the dual active sites of Ag and FeOOH for NO3 - With NO2 - The conversion efficiencies differ, and by coordinating and optimizing the electrocatalytic NRA process, a superior ammonium yield can be obtained. Specifically, Ag-FeOOH at -0.85 V... vs. It exhibits excellent electrocatalytic performance at the RHE potential, with 97.56% ammonium selectivity and 92.45% NO3- selectivity. - Conversion rate and 3.21 mg h -1 cm -2 The ammonium yield. Simultaneously, Ag-FeOOH-based Zn-NO3 - The battery also exhibits excellent performance, while meeting pollution control and energy conversion standards.

[0019] For NDI-PPy / Ag-FeOOH, its internal pores and hydrophilic properties, combined with the surface-loaded hydrogel design, significantly improve the stability of the original substrate catalytic material. Introducing the conductive polymer PPy into the surface-loaded gel NDI significantly enhances the stability of the catalytic electrode at the same potential for NO3-. - -N removal rate and NH4 + The selectivity of -N was improved, and this phenomenon was also observed in the catalytic electrodes PAM-PPy / Ag-FeOOH and PAM / Ag-FeOOH. This indicates that the conductive polymer PPy introduced into the gel matrix not only improves the conductivity of the catalytic electrode, but also improves the efficiency of the electrocatalytic NRA process. Attached Figure Description

[0020] Figure 1 (a) Figure 1 (b) is a SEM image of Ag-FeOOH prepared in Example 1; Figure 1 Figure (c) shows the HRTEM image of Ag-FeOOH; Figure (d) shows the TEM electron image and EDS test results of Ag-FeOOH. Figure 2 (a) XPS full spectra of Ag, FeOOH and Ag-FeOOH; Figure 2 (b) XPS spectra of FeOOH and Ag-FeOOH in the Fe 2p region; Figure 2 (c) XPS spectra of FeOOH and Ag in the Ag 3d region; Figure 2 (d) is the XRD pattern of Ag-FeOOH; Figure 2 (e) shows the contact angle test results for Ti, Ag, FeOOH and Ag-FeOOH; Figure 3 (a) Ag, FeOOH, and Ag-FeOOH in the presence of 100 ppm NO3 - -N is present in 0.5M Na2SO4 electrolyte and reacts with Ag-FeOOH in the absence of NO3. - LSV curve of -N in 0.5M Na2SO4 electrolyte; Figure 3 (b) shows the nitrate conversion and ammonia selectivity of Ag-FeOOH at different potentials; Figure 3 (c) Ammonia yield and Faraday efficiency of Ag-FeOOH at different potentials; Figure 3 (d) represents NO3 during the electrolysis experiment. - -N, NO2 - -N, NH4 + -N concentration change curve over time (-0.85V) vs. RHE); Figure 3(e) Whether to add NO3 - Ammonium yield of Ag-FeOOH in N-type electrolytes; Figure 3 (f) represents Ag-FeOOH at -0.85V vs. NO3 in cyclic experiments under RHE - Removal rate and ammonia selectivity data; Figure 4 (a) 4 (b) Figure 4 (c) Ag, FeOOH, and Ag-FeOOH are respectively treated with different NO3- - With NO2 - LSV curve at the specified ratio; Figure 5 The catalytic electrode NDI-PPy / Ag-FeOOH was prepared in 0.5M Na2SO4 and 100ppm NO3. - In the -N electrolyte, 5(a) represents NO3 at different potentials. - -N removal rate and NH4 + Selectivity; 5(b) shows NO3 at different potentials - -N removal rate and NH4 + The Faraday efficiency FE 5(c) of NH4 at different potentials + Yield; 5(d) is at -0.85V vs NO3 under the RHE potential window - -N, NO2 - -N, NH4 + -N change over time; 5(e) shows the ammonium yield of NDI-PPy / Ag-FeOOH in Na2SO4 electrolyte with and without nitrate; 5(f) shows the nitrate conversion and selectivity of NDI-PPy / Ag-FeOOH and NDI / Ag-FeOOH after continuous cycling tests; Figure 6 For 0.5M Na2SO4 and 100ppm NO3 - In the N-electrolyte, the nitrate removal rate and ammonium selectivity of catalytic electrodes 6(a) NDI / Ag-FeOOH, 6(b) PVA / Ag-FeOOH, 6(c) PAM / Ag-FeOOH; 6(d) SA / Ag-FeOOH, 6(e) ND / Ag-FeOOH, and 6(f) PAA / Ag-FeOOH at different potentials; Figure 7 Containing 100ppm NO3 - NO3- in electrolytes of N- and 0.5M Na2SO4 at different potentials at 7(a)- -N removal rate and 7(b) NH4 + -N selectivity; NO3- of PAM-PPy / Ag-FeOOH and PAM / Ag-FeOOH at different potentials at 7(c) - -N removal rate and (d) NH4 + -N selectivity. Detailed Implementation

[0021] The embodiments of the technical solution of the present invention will be described in further detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited thereto. Example 1

[0022] A method for preparing an Ag-FeOOH electrocatalyst with dual catalytic active sites includes the following steps: (1) The pretreated titanium mesh was placed in a 50 mL mixed solution containing 0.03 M FeCl3·6H2O and 0.03 M Na2SO4. After hydrothermal reaction at 60 °C for 12 h under normal pressure, the catalyst FeOOH was obtained. After rinsing three times with deionized water, it was dried at 60 °C for later use.

[0023] (2) The precursor catalyst prepared above was used as the working electrode for electroplating in a three-electrode system. The electroplating solution was a 50 ml mixed solution containing 3.55 g Na₂SO₄, 0.32 g Na₃C₆H₅O₇, and 0.024 g AgNO₃. Electroplating was performed at -0.35 V. vs. Electrolysis was performed at RHE potential for 30 seconds using It test. Electrode materials with different Ag contents were synthesized using different concentrations of AgNO3. The electroplated electrodes were then rinsed three times with deionized water and dried at 60°C for later use.

[0024] Figure 1 (a)- Figure 1 (b) is a SEM image of Ag-FeOOH prepared in Example 1. The SEM image shows that dense and uniform FeOOH nanowires are grown on the Ti mesh, and the Ag nanoparticles grown at the tips of the FeOOH nanowires increase both conductivity and catalytic active sites. Meanwhile, the HRTEM test results for Ag-FeOOH are as follows: Figure 1 As shown in (c), smaller Ag nanoparticles are grown on FeOOH nanowires, and the 0.12 nm and 0.24 nm lattice fringes correspond to the (2 2 2) and (1 1 1) crystal planes of Ag, respectively, while the 0.33 nm lattice fringes correspond to the (2 1 1) crystal plane of FeOOH. Finally, from... Figure 1In the EDS test of Ag-FeOOH (d), the distribution of Ag elements corresponds to the transmission image, proving the successful introduction of Ag sites.

[0025] The XPS test results for Ag, FeOOH and Ag-FeOOH prepared in Example 1 are as follows: Figure 2 As shown in (a)-2(c), for Ag-FeOOH, the diffraction peak with a binding energy of 731.1 eV in the Fe 2p spectrum corresponds to Fe 2p. 3 / 2 For FeOOH, the Fe 2p spectrum corresponds to Fe 2p 3 / 2 The binding energy is 731.6 eV. Simultaneously, the Ag 3d spectrum of Ag-FeOOH shows Ag 3d... 5 / 2 The binding energy of the diffraction peak is 368.5 eV, while the Ag 3d spectrum of pure Ag shows Ag 3d... 5 / 2 The binding energy of the diffraction peak is 360.1 eV. This is achieved by comparing the Fe 2p of Ag-FeOOH and FeOOH. 3 / 2 Binding energy indicates that the Fe 2p binding energy increases after the introduction of Ag sites. 3 / 2 The binding energy of Ag-FeOOH and pure Ag underwent a negative shift; by comparing Ag-FeOOH with Ag 3d... 5 / 2 The binding energy shows that the Ag introduced onto the FeOOH surface has a Ag 3d 5 / 2 The binding energy of FeOOH has shifted positively, indicating that the Ag introduced on the FeOOH surface through electrochemical reduction has altered the original electronic structure. Specifically, electrons flow from FeOOH to Ag. The strong interaction between Fe and Ag has changed the electronic structure of the metal center, thereby affecting the electrocatalytic activity of Ag-FeOOH.

[0026] Figure 2 (d) XRD testing and analysis of the synthesized Ag-FeOOH showed that the material exhibited diffraction peaks of both FeOOH and Ag, indicating successful synthesis. As shown in 2(e), the contact angles of Ti, Ag, FeOOH, and Ag-FeOOH are not entirely the same. Ti and Ag are hydrophilic, while FeOOH is hydrophilic. The material after introducing Ag onto the FeOOH surface through electrochemical reduction remains hydrophilic. In the study of electrocatalytic ammonium nitrate production, it was found that the hydrophilicity of the material facilitates electrolyte transport and enhances the electrocatalytic rate.

[0027] To investigate the current response of catalysts to NRA, this invention measured the current response of Ag, FeOOH, and Ag-FeOOH in the presence of NO3. - -N electrolytes and Ag-FeOOH do not contain NO3. - LSV curves in solutions of -N electrolytes. For example... Figure 3As shown in (a), in the presence of NO3 - In N-type electrolyte solutions, Ag-FeOOH exhibits a stronger current response compared to both Ag and FeOOH, indicating that the Ag-FeOOH catalyst has a stronger response to NRA. Furthermore, the LSV curve clearly shows that the current is within -0.7V. vs. A deviation begins to appear at the RHE point, and this deviation becomes more pronounced with increasing voltage. This indicates that the catalyst begins to react with NO3 at this site. - The electrocatalytic reduction response is determined. Therefore, a voltage range of -0.7V to -0.9V is chosen. vs. RHE was used as a voltage window for subsequent performance testing. For example... Figure 3 As shown in (b) and 3(c), from -0.7V vs. RHE to -0.9V vs. RHE, NO3 - The removal rate and ammonium yield gradually increased at -0.85V. vs. The NO3 content reaches its peak at RHE. - The removal rate, ammonium selectivity, Faraday efficiency, and ammonium yield were 92.45%, 97.56%, 89.58%, and 3.21 mg / h, respectively. -1 cm -2 Subsequently, NO3 was assessed. - -N, NO2 - -N, NH4 + The change in -N concentration over time was evaluated, and the curve is shown in... Figure 3 (d) When the voltage is constant at -0.85V vs. When RHE occurs, NO3 - -N decreases rapidly, NH4 + The rapid increase in -N indicates a rapid conversion of nitrate to ammonium. Simultaneously, NO2... - The concentration of the -N intermediate product initially increased and then decreased during the reaction, and the concentration became negligible, indicating excellent ammonium selectivity of the material. Performance tests were conducted on the same catalyst over 10 cycles. Figure 3 As shown in (e). The results above show that after multiple cycles of testing, the nitrate conversion, ammonium selectivity, and ammonium yield did not show significant decline, confirming the excellent stability of the catalyst.

[0028] To investigate the role and mechanism of introducing Ag nano-ions via electrochemical reduction on the FeOOH surface in the electrocatalytic NRA reaction, NO3 was designed... - With NO2 - Mixed feed experiments were conducted to observe the effects of Ag, FeOOH, and Ag-FeOOH on different NO3- concentrations. - With NO2- LSV curves under mixed feed ratios. For example... Figure 4 (a), 4 (b) and Figure 4 As shown in (c), the current response of Ag differs under different proportions. Interestingly, with the increase of NO3... - With increasing NO2 content, the current response of the electrode gradually increases; the current response of FeOOH also varies under different ratios. The current response of FeOOH is characterized by increasing NO2 content. - With increasing content, the current response of the electrode gradually increases; however, Ag-FeOOH exhibits an irregular response under different feed ratios, with NO3 showing the most significant increase. - With NO2 - A mixed feed ratio of 70:30 exhibits the best current response.

[0029] Another embodiment of the present invention involves loading a porous gel onto the surface of a developed substrate material, Ag-FeOOH, introducing target groups onto the synthesized covalent scaffold using a simple and mild substitution reaction, and then introducing a conductive polymer through in-situ polymerization to enhance the gel's positive role in electrocatalytic NRA. Example 2

[0030] A method for preparing a hydrogel-enhanced electrocatalytic electrode NDI / Ag-FeOOH is described below: (1) Using N,N'-methylenebisacrylamide (30 mM) as a crosslinking agent and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (30 mM) as a photoinitiator, N,N-dimethylacrylamide (3.0 M) and N-acryloyloxysuccinimide (30 MM) were copolymerized in dimethyl sulfoxide to form a covalent scaffold.

[0031] (2) Place the synthesized dry Ag-FeOOH in a mold, add the prepared precursor solution A to the mold, so that Ag-FeOOH is wetted by the precursor solution; place the film under an LED ultraviolet UV curing lamp for 2 hours to obtain the electrode ND / Ag-FeOOH. (3) The electrode ND / Ag-FeOOH was immersed in anhydrous DMSO solution containing 4,4'-iminodiphenylamine (IDA) (30 mM) for 8 h to replace the oxysuccinimide group, and a new electrode NDI / Ag-FeOOH was obtained.

[0032] (4) The electrode NDI / Ag-FeOOH was first soaked in 1.0 M FeCl3 solution for 1 h, and then the electrode was transferred to a pyrrole aqueous solution containing 0.1 wt% and left to stand for 12 h to allow the internal conductive network polypyrrole to polymerize and form electrode NDI-PPy / Ag-FeOOH.

[0033] Example 2 synthesized a conductive gel NDI-PPy on an Ag-FeOOH surface through polymerization, displacement, and repolymerization at room temperature. The pores inside the gel NDI-PPy facilitate mass transfer during the electrocatalytic process. To improve the conductivity of the gel, Fe was used inside the gel NDI. 3+ The initiation of polymerized conductive network polypyrrole and the electrode's good hydrophilicity have a positive effect on mass transfer in electrocatalytic reactions.

[0034] Subsequently, the NDI-PPy / Ag-FeOOH ratio was measured in 0.5 M Na2SO4 and 100 ppm NO3. - Electrocatalytic NRA electrolysis experiments were conducted at different potentials in the -N electrolyte. For example... Figure 5 As shown in (a)-5(c), from -0.7V vs. RHE to -0.9V vs. RHE, at -0.85V vs. The value is reached at RHE, NO3 - -N removal rate, ammonium selectivity, Faraday efficiency, and ammonium yield were 89.34%, 94.27%, 89.53%, and 2.95 mg h, respectively. -1 cm -2 Subsequently, during the electrolysis experiment, NO3 was... - -N, NO2 - -N, NH4 + The concentration of -N was detected, such as Figure 5 As shown in (d). When the voltage is constant at -0.85V vs. When RHE occurs, NO3 - -N decreases rapidly, NH4 + The rapid increase in -N indicates a rapid conversion of nitrate to ammonium. Simultaneously, NO2... - The concentration of the -N intermediate showed a trend of first increasing and then decreasing during the reaction, and the concentration was almost negligible, indicating that the material has excellent ammonium selectivity. Comparative experiments were conducted in blank Na₂SO₄ solution, as shown... Figure 5 As shown in (e). The results show that NO3 was not added. - The amount of ammonium produced in the electrolyte is almost negligible, preliminarily indicating that the ammonium produced in the solution originates entirely from the electrocatalytic NRA. To further evaluate the stability of the catalysts, cyclic performance tests were conducted on NDI-PPy / Ag-FeOOH and Ag-FeOOH, such as... Figure 5As shown in (f). Experimental results show that Ag-FeOOH exhibited good stability in the first 10 cycles, but both the removal rate and selectivity decreased in the 11th to 13th cycles; while NDI-PPy / Ag-FeOOH showed good stability after 15 cycles. - The conversion rate and selectivity showed no significant decline, confirming the catalyst's excellent cycle stability. In summary, NDI-PPy / Ag-FeOOH exhibits excellent catalytic performance, with its NO3- content remaining stable. - The conversion rate, Faraday efficiency, selectivity, and ammonium yield were 89.64%, 90.46%, 87.94%, and 2.95 mg / h, respectively. -1 cm -2 Furthermore, the stability of the original substrate catalytic material was significantly improved by using a conductive gel designed with surface loading.

[0035] Comparative Example 1 The difference between Comparative Example 1 and Example 2 is that step (2) is not performed, that is, the hydrogel in the electrode prepared in Comparative Example 1 is a gel ND that is not replaced.

[0036] Comparative Examples 2-6 differ from Example 2 only in the type of hydrogel. The hydrogels in Comparative Examples 2-6 are polyacrylamide (PAM) hydrogel, polyvinyl alcohol (PVA), sodium alginate (SA) hydrogel, and polyacrylic acid (PAA) hydrogel, respectively.

[0037] Hydrogels containing NDI, polyacrylamide (PAM), polyvinyl alcohol (PVA), and sodium alginate (SA) contain different functional groups and exhibit different electrocatalytic NRA properties. The test results are as follows: Figure 6 As shown. Specifically, the catalytic electrode NDI / Ag-FeOOH with NDI hydrogel supported on its surface affects NO3. - The removal rate was the highest, and its selectivity was also the highest, with removal rates of 78.81%, 79.20%, 87.88%, and 89.56% at the four potentials, and selectivity of 91.33%, 94.97%, 95.73%, and 96.26%, respectively. In contrast, the catalytic electrode ND / Ag-FeOOH formed by the gel ND without the final replacement reaction showed removal rates of 75.23%, 76.62%, 84.13%, and 86.77% at the four potentials, and selectivity of 89.50%, 93.07%, 93.82%, and 94.33%, respectively. The comparison shows that the amine and aromatic groups introduced in the third replacement reaction can improve the catalytic performance of the substrate material to a certain extent.

[0038] In further cyclic testing, the electrodes exhibited varying degrees of stability. NDI / Ag-FeOOH maintained good stability throughout, while NO3... - The average removal rate was 86.07%; PAM / Ag-FeOOH also maintained good stability, NO3 - The average removal rate was 78.84%; however, the stability of ND / Ag-FeOOH showed a significant decrease after four cycles of testing. A comparison of gel NDI and ND surprisingly revealed that the amine and aromatic groups introduced through the substitution reaction had a positive effect on electrode stability. Then, the NO3- removal rate of PVA / Ag-FeOOH was... - The average removal rate was 73.95%. After four cycles of testing, severe gel detachment occurred. This was because PVA lacked sufficient internal pores, hindering mass transfer in the electrocatalytic NRA process and preventing the escape of gases generated during electrolysis, leading to gel detachment. PAA hydrogels, with their abundant carboxyl groups, also exhibited severe gel detachment, resulting in a significant decrease in the cyclic stability of the catalytic electrode. In contrast, NDI synthesized through a substitution reaction, simultaneously introducing amine groups and twice the amount of aromatic groups into the gel network, shares with PAM a large number of internal amine groups and internal pores for mass and gas transfer, thus maintaining better electrode stability.

[0039] Comparative Example 7 differs from Example 2 only in that it does not include step (4).

[0040] At 100ppm NO3 - The electrolysis test results of NDI-PPy / Ag-FeOOH and NDI / Ag-FeOOH in electrolytes of -N and 0.5M Na2SO4 are as follows: Figure 7 As shown, for NDI-PPy / Ag-FeOOH and NDI / Ag-FeOOH, after introducing the conductive polymer PPy into the surface-loaded gel NDI, the NO3 at the catalytic electrode under the same potential... - -N removal rate and NH4 + The selectivity of -N was improved, and this phenomenon was also observed in the catalytic electrodes PAM-PPy / Ag-FeOOH and PAM / Ag-FeOOH. This indicates that the conductive polymer PPy introduced into the gel matrix not only improves the conductivity of the catalytic electrode, but also improves the efficiency of the electrocatalytic NRA process.

Claims

1. An Ag-FeOOH electrocatalyst with dual catalytic active sites, characterized in that, The Ag-FeOOH electrocatalyst comprises FeOOH nanowires and Ag nanoparticles grown on the FeOOH nanowires.

2. The dual-catalytic active site Ag-FeOOH electrocatalyst according to claim 1, characterized in that, The Ag-FeOOH electrocatalyst is hydrophilic, and the Ag nanoparticles are grown on the tips of FeOOH nanowires via an electrochemical reduction method.

3. A method for preparing an Ag-FeOOH electrocatalyst with dual catalytic active sites as described in claim 1 or 2, characterized in that, It is prepared by a two-step method involving hydrothermal treatment and electroplating, with the specific steps as follows: (1) The titanium mesh was placed in a mixed solution containing FeCl3·6H2O and Na2SO4. After hydrothermal reaction at 60°C for 12 hours under normal pressure, it was rinsed three times with deionized water and dried at 60°C to obtain a precursor catalyst containing FeOOH nanowires. (2) The precursor catalyst was used as the working electrode and electroplated in a three-electrode system. The electroplating solution used was a mixed solution containing AgNO3. After electroplating, the electrode was rinsed three times with deionized water and dried at 60°C to obtain Ag-FeOOH electrocatalyst with dual catalytic active sites.

4. The preparation method according to claim 3, characterized in that, The electroplating solution is a mixed solution containing 3.55g Na2SO4, 0.32g Na3C6H5O7, and 0.024g AgNO3, and the electroplating is performed at -0.35 V. vs. Electrolysis for 30 s at RHE potential was tested, and the FeOOH nanowires were uniformly distributed on the titanium mesh.

5. A hydrogel-reinforced electrocatalytic electrode, characterized in that, The electrocatalyst electrode is based on the Ag-FeOOH electrocatalyst of claim 1 or 2 or the Ag-FeOOH electrocatalyst prepared by any one of claims 3-4, and hydrogel is loaded in situ on the substrate to form a hydrogel-enhanced electrocatalyst electrode.

6. The electrocatalytic electrode according to claim 5, characterized in that, The hydrogel has a porous structure inside, and the porous structure of the hydrogel also includes a conductive polymer introduced through in-situ polymerization.

7. A method for preparing a hydrogel-enhanced electrocatalytic electrode, characterized in that, The NDI / Ag-FeOOH electrode is formed by in-situ loading NDI hydrogel onto the Ag-FeOOH electrocatalyst prepared by the method described in claim 1 or 2 or by any one of claims 3-5. The specific process for synthesizing NDI / Ag-FeOOH is as follows: (1) Using N,N'-methylenebisacrylamide as a crosslinking agent and 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone as a photoinitiator, N,N-dimethylacrylamide and N-acryloyloxysuccinimide were copolymerized in dimethyl sulfoxide to form a precursor solution A containing a covalent scaffold of NA. (2) Place the Ag-FeOOH electrocatalyst in a mold, add the prepared precursor solution A to the mold, so that Ag-FeOOH is wetted by the precursor solution; place the membrane under an LED ultraviolet UV curing lamp for 2 hours to obtain the electrode ND / Ag-FeOOH; (3) The electrode ND / Ag-FeOOH was immersed in anhydrous DMSO solution containing 4,4'-iminodiphenylamine (IDA) for 8 h to replace the oxysuccinimide group, thus obtaining electrode NDI / Ag-FeOOH; (4) The electrode NDI / Ag-FeOOH is first soaked in FeCl3 solution, and then the electrode is transferred to pyrrole aqueous solution and left to stand for 12 hours to allow the internal conductive network polypyrrole to polymerize and form electrode NDI-PPy / Ag-FeOOH.

8. The application of an electrocatalyst as described in claim 1 or 2, or an Ag-FeOOH electrocatalyst prepared by any one of claims 3-4, in the electrocatalytic reduction of nitrates.

9. The application of a hydrogel-enhanced electrocatalytic electrode as described in any one of claims 5-6 or a hydrogel-enhanced electrocatalytic electrode prepared by the preparation method described in claim 7 in the electrocatalytic reduction of nitrates.

10. A Zn-NO3 - The battery, characterized in that, The battery includes the electrocatalyst according to claim 1 or 2, or the Ag-FeOOH electrocatalyst prepared by the preparation method according to any one of claims 3-4, or the hydrogel-enhanced electrocatalytic electrode according to any one of claims 5-6, or the hydrogel-enhanced electrocatalytic electrode prepared by the preparation method according to claim 7.

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