Iodine-doped copper nanoparticle catalyst and preparation method thereof, and method for synthesizing ammonia catalyst through electro-catalysis nitrate reduction

Abstract

The invention discloses an iodine-doped copper nanoparticle catalyst and a preparation method thereof, and a method for synthesizing an ammonia catalyst through electro-catalytic reduction of nitrate, and belongs to the technical field of electro-catalytic reduction. On the basis of an electrostatic spinning confinement carbonization strategy, the carbon nanofiber loaded iodine-doped copper nanoparticles are constructed, and efficient ammonia production through nitrate electrocatalytic reduction is achieved through the multifunctional synergistic effect of the component I. The structure and electronic characteristics of the material can be synchronously regulated and controlled through I doping, I serves as a structure stabilizer to inhibit Cu NPs agglomeration and improve dispersion uniformity, meanwhile, nitrate adsorption activation sites are optimized through surface electron reconstruction, and a carbon fiber substrate is induced to form abundant defects so as to enhance charge transfer efficiency. The catalyst shows excellent electrocatalytic activity and selectivity, remarkably improves the ammonia synthesis efficiency in a wide potential range and effectively inhibits side reactions, has certain cycle stability, is suitable for nitrate wastewater treatment and green ammonia synthesis scenes, and has wide industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic materials, and in particular relates to an iodine-doped copper nanoparticle catalyst and a preparation method thereof, and a catalyst method for synthesizing ammonia by electrocatalytic nitrate reduction. Background Art

[0002] Ammonia (NH3) is an important chemical raw material with widespread applications in various fields. However, the traditional Haber–Bosch process is characterized by high energy consumption and high carbon dioxide emissions, which can easily lead to energy and environmental problems. The electrocatalytic nitrogen reduction reaction (NRR) and the electrocatalytic nitrate reduction reaction (NO3RR) have become increasingly researched topics. The NRR is limited by difficulties in N2 activation, interference from the hydrogen evolution reaction (HER), and low N2 solubility. However, the eNO3RR holds greater potential due to its low nitrate bond energy, high solubility, and advantages in pollutant removal. However, the NO3RR involves complex electron / proton transfer processes, resulting in low product selectivity and slow reaction kinetics, limiting its further development. Therefore, the development of highly active, selective, and stable electrocatalysts is crucial.

[0003] Precious metal catalysts offer excellent catalytic performance but are expensive. Cu-based catalysts, due to their excellent d-orbital alignment with the LUMOπ* orbital of NO⁻ ...

[0004] The present invention aims to develop efficient Cu-based electrocatalysts, optimize NO3RR performance through electronic structure regulation and carrier synergy, solve the problems of low activity and poor selectivity of existing catalysts, and provide a new strategy for the green synthesis of NH3. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, the present invention provides a doped copper nanoparticle catalyst (I-Cu NPs / CNFs) and its preparation method, as well as a method for electrocatalytic nitrate reduction to synthesize ammonia. By utilizing an I doping strategy, precise regulation of Cu active sites is achieved, and the ultimately prepared catalyst is highly efficient and stable.

[0006] The technical solution adopted by the present invention to solve the technical problem is: a method for preparing an iodine-doped copper nanoparticle catalyst, the method comprising the following steps:

[0007] (1) Dispersing copper salt, iodide and nanofiber precursor in an organic solvent to obtain a uniform and transparent spinning solution;

[0008] (2) spinning the electrospinning solution prepared in step (1) by an electrospinning method to obtain a precursor nanofiber membrane;

[0009] (3) placing the nanofiber membrane prepared in step (2) in an air atmosphere, calcining at a constant heating rate and keeping the temperature, and performing sufficient pre-oxidation treatment;

[0010] (4) The pre-oxidized fiber membrane prepared in step (3) is heated under an inert gas atmosphere at 2-10°C min -1 The heating rate was raised to 1000 °C and kept constant for 2 to 5 h; after the heat treatment was completed, it was naturally cooled to room temperature to obtain I-Cu NPs / CNFs material.

[0011] In one embodiment, the molar concentration of the copper salt in the spinning solution in step (1) is 0.03-0.05 mmol g -1 , the copper salt is one or two of copper chloride, copper nitrate, and copper acetate.

[0012] In one embodiment, the mass fraction of the iodide in step (1) is 1.0 wt% to 3.5 wt%; the iodide is one or both of ammonium iodide and sodium iodide.

[0013] In one embodiment, the fiber precursor in step (1) includes one or more of polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, and polymethyl methacrylate;

[0014] In one embodiment, the organic solvent in step (1) is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, ethanol, water, and acetone.

[0015] In one embodiment, the precursor solution in step (1) contains carbon fiber precursor in an amount of 10 to 15% by weight.

[0016] In one embodiment, the spinning voltage in step (2) is 15-25 kV, the distance from the receiving device to the spinning needle is 10-20 cm, and the solution flow rate is 0.2-0.4 mL h -1 .

[0017] In one embodiment, the heating rate of the high temperature treatment in step (3) is 2-10 °C min -1 , pre-oxidation is to raise the temperature to 180-250℃ and keep calcining for 2-5 hours;

[0018] In one embodiment, the inert gas in step (4) is one of argon and nitrogen, preferably argon.

[0019] The second object of the present invention is to provide an I-Cu NPs / CNFs catalyst prepared by the above method.

[0020] The third object of the present invention is to provide a method for electrocatalytic nitrate synthesis of ammonia, wherein the method uses the above-mentioned I-Cu NPs / CNFs as an electrocatalyst.

[0021] In one embodiment, the method specifically includes the following:

[0022] The electrochemical reaction was conducted using a three-electrode system and an H-type electrolytic cell on a CHI 660E electrochemical workstation. The I-Cu NPs / CNFs catalyst material served as the working electrode, a platinum sheet served as the counter electrode, and an alkaline Hg / HgO electrode served as the reference electrode. The electrolyte consisted of a 1 M KOH solution containing 0.1 M KNO₃. Ar was purged through the solution for 30 minutes before the experiment and continued to flow during the test phase to maintain an inert atmosphere and drive off byproduct hydrogen.

[0023] The voltage range of the electrocatalytic synthesis of NH3 test was -0.25~-0.75V vs. RHE.

[0024] The beneficial effects of the present invention are as follows: 1) the present invention combines electrospinning technology with high-temperature graphitization to prepare iodine-doped copper nanoparticle catalysts (I-Cu NPs / CNFs), whose three-dimensional porous carbon nanofiber network provides a high specific surface area and a fast mass transfer channel, which is conducive to electron transport; 2) the introduction of I effectively inhibits the agglomeration of Cu nanoparticles during high-temperature treatment by utilizing the confinement effect and strong electronic interaction of carbon nanofibers, so that the Cu nanoparticles are uniformly dispersed on the carbon fibers, exposing more active sites; 3) I regulates the electronic structure of Cu through the electron transfer effect, induces the expansion of the Cu lattice and increases its electron density, inhibits side reactions, and promotes the continued reduction of nitrite to NH3, thereby further improving the catalytic activity; 4) I, with its unique electronic properties and steric hindrance effect, not only significantly optimizes the electronic structure of Cu NPs, but also successfully achieves the uniform dispersion and electronic structure optimization of Cu NPs on CNFs, making its surface electron-rich, and effectively inhibits the agglomeration of Cu NPs through strong metal-support interaction; 5) the I-Cu The NPs / CNFs catalyst exhibited excellent electrocatalytic activity and stability in the eNO3RR reaction; the FE at -0.45 V was 83.81% and the yield was 10.7 mg h -1 mg cat. -1 During the 10-cycle stability test at -0.45 V, the NH3 yield and FE fluctuated only slightly, which provides an efficient catalyst for the green synthesis of NH3 and the treatment of nitrogen-containing wastewater. I doping gives the catalyst excellent stability. This work not only reveals the unique advantages of I doping in regulating the electronic structure and dispersibility of metal catalysts, but also provides an innovative strategy of "electronic regulation-structural confinement" synergy for the design of efficient Cu-based NO3RR catalysts, opening up a new path for green NH3 synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a microscopic morphology of the catalyst I-Cu NPs / CNFs obtained in Example 1 of the present invention; wherein, Figure 1 (a) is the scanning electron microscopy (SEM) image of I-Cu NPs / CNFs. Figure 1 (b) Transmission electron microscopy (TEM) image of I-Cu NPs / CNFs. Figure 1 (c) is the size distribution diagram of I-Cu NPs in I-Cu NPs / CNFs. Figure 1 (d) STEM-EDX element distribution image of I-Cu NPs / CNFs.

[0026] Figure 2 This is a microscopic morphology of the catalyst Cu NPs / CNFs obtained in Comparative Example 1 of the present invention; wherein, Figure 2 (a) is the SEM image of Cu NPs / CNFs. Figure 2 (b) TEM image of Cu NPs / CNFs.

[0027] Figure 3 The X-ray diffraction patterns (XRD) and Raman spectra (Raman) of catalysts I-Cu NPs / CNFs and Cu NPs / CNFs obtained in Example 1 of the present invention and Comparative Example 1 are shown.

[0028] Figure 4 The microscopic morphology of the catalyst CNFs and I-CNFs obtained in Comparative Example 2-3 of the present invention is shown in FIG. Figure 4 (a) and (b) are SEM images of CNFs and I-CNFs, respectively.

[0029] Figure 5 These are the XRD patterns and Raman patterns of the catalyst I-CNFs and CNFs obtained in Comparative Examples 2-3 of the present invention.

[0030] Figure 6 1 are X-ray photoelectron spectroscopy (XPS) graphs of catalysts I-Cu NPs / CNFs and Cu NPs / CNFs obtained in Example 1 of the present invention and Comparative Example 1.

[0031] Figure 7 The figures show the electrocatalytic nitrate reduction reaction kinetics of the catalysts I-Cu NPs / CNFs, Cu NPs / CNFs, I-CNFs and CNFs obtained in Example 1 of the present invention and Comparative Examples 1-3, wherein 7 (a) is the LSV curves of the four materials in a 1 M KOH electrolyte containing 0.1 M KNO3, and 7 (b) is a comparison of the LSV curves of Cu NPs / CNFs and I-Cu NPs / CNFs in the presence or absence of 0.1 M KNO3 in 1 M KOH.

[0032] Figure 8 The performance of catalysts I-Cu NPs / CNFs and Cu NPs / CNFs obtained in Example 1 of the present invention and Comparative Example 1 in NO3RR to NH3 in 1 M KOH electrolyte containing 0.1 M KNO3; wherein, Figure 8 (a) Faradaic efficiency of NH3 production of I-Cu NPs / CNFs and Cu NPs / CNFs at different voltages; Figure 8 (b) NH3 production rates of I-Cu NPs / CNFs and Cu NPs / CNFs at different voltages; Figure 8 (c) NH3 current density of I-Cu NPs / CNFs and Cu NPs / CNFs at different voltages; Figure 8 (d) Nitrite production (NO2) by I-Cu NPs / CNFs and Cu NPs / CNFs at different voltages − ) of the Faraday efficiency.

[0033] Figure 9 The electrochemical impedance spectroscopy diagrams of catalysts I-Cu NPs / CNFs and Cu NPs / CNFs obtained in Example 1 of the present invention and Comparative Example 1 are shown.

[0034] Figure 10 This is a stability test of the catalyst I-Cu NPs / CNFs obtained in Example 1 of the present invention in the NO3RR to NH3 production at -0.45 V in a 1 M KOH electrolyte containing 0.1 M KNO3.

[0035] Figure 11 The effect of different I doping amounts in Examples 1-3 on the performance of I-Cu NPs / CNFs catalysts in NO3RR to NH3 (mass fraction).

[0036] Figure 12 The effect of Cu precursor loading on the performance of I-Cu NPs / CNFs catalyst for NO3RR to NH3 in Example 1 and Examples 4-5. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand the solutions of the present invention, the following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts should fall within the scope of protection of the present invention.

[0038] Example 1

[0039] A method for preparing iodine-doped copper nanoparticle catalyst (I-Cu NPs / CNFs) comprises the following steps:

[0040] (1) Take 0.8 mmol (0.4 mmol g -1 ) copper chloride and 0.5 g of ammonium iodide (1.35 wt%) were added to 20 g of a 10 wt% N,N-dimethylformamide solution and magnetically stirred to obtain a homogeneous, transparent solution. The mixed solution was transferred to a syringe for electrospinning. The anode voltage was 17 kV, the cathode voltage was 1 kV, the needle was 15 cm from the metal roller, and the spinning speed was 0.36 mL h. -1 , that is, the precursor nanofiber membrane is obtained.

[0041] (2) Cut the precursor nanofiber membrane into pieces and place them on graphite sheets, which are then placed in a tube furnace and heated at 2 °C min -1 The heating rate was raised to 230 °C and maintained for 3 h, so that the fiber membrane could form a stable structure and effectively prevent the fiber from being damaged during the carbonization process. -1 The temperature was raised to 1000°C at a rate of 1000°C and kept constant for 3 hours. The film was then naturally cooled to room temperature to obtain the I-Cu NPs / CNFs catalyst.

[0042] Example 2

[0043] The only difference from Example 1 is that in step (1), the amount of ammonium iodide added was adjusted to 0.3 g (1.35 wt%), and the other parameters and conditions were the same as those in Example 1. 1.35I-Cu NPs / CNFs catalyst was prepared by electrospinning and calcination at 1000°C.

[0044] Example 3

[0045] The only difference from Example 1 is that in step (1), the iodide was adjusted to sodium iodide, and the addition amount was 0.7 g (3.08 wt%). The other parameters and conditions were the same as those in Example 1. 3.08I-Cu NPs / CNFs catalyst was prepared by electrospinning and high-temperature calcination at 1000°C.

[0046] Example 4

[0047] The only difference from Example 1 is that in step (1), the copper salt is adjusted to copper nitrate, and the addition amount is 0.6 mmol (i.e., 0.3 mmol g-1). The other parameters and conditions are the same as those in Example 1. The I-0.3Cu NPs / CNFs catalyst is prepared by electrospinning and high-temperature calcination at 1000°C.

[0048] Example 5

[0049] The only difference from Example 1 is that in step (1), the amount of copper salt added is adjusted to 1.0 mmol (i.e., 0.5 mmolg-1), and the other parameters and conditions are the same as those in Example 1. The I-0.5Cu NPs / CNFs catalyst is prepared by electrospinning and high-temperature calcination at 1000°C.

[0050] Example 6

[0051] The only difference from Example 1 is that in step (2), the heating rate of pre-oxidation and high-temperature calcination is adjusted to 5 °C min-1, and the other parameters and conditions are the same as those in Example 1. Cu NPs / CNFs catalyst is prepared by electrospinning and high-temperature calcination at 1000 °C.

[0052] Example 7

[0053] The only difference from Example 1 is that in step (2), the heating rate of pre-oxidation and high-temperature calcination is adjusted to 10 °C min-1, and the other parameters and conditions are the same as those in Example 1. Cu NPs / CNFs catalyst is prepared by electrospinning and high-temperature calcination at 1000 °C.

[0054] Comparative Example 1:

[0055] The preparation method of Cu NPs / CNFs material comprises the following steps:

[0056] (1) 0.8 mmol of copper chloride dihydrate was added to 20 g of 10 wt% N,N-dimethylformamide solution and a uniform and transparent solution was obtained by magnetic stirring. The mixed solution was transferred to a syringe for electrospinning. The anode voltage was 17 kV, the cathode voltage was 1 kV, the needle was 15 cm away from the metal roller, and the pushing speed was 0.36 mL h -1 , that is, the precursor nanofiber membrane is obtained.

[0057] (2) Cut the precursor nanofiber membrane into pieces and place them on graphite sheets, which are then placed in a tube furnace and heated at 2 °C min -1 The heating rate was raised to 230 °C and maintained for 3 h, so that the fiber membrane could form a stable structure and effectively prevent the fiber from being damaged during the carbonization process. -1 The heating rate was raised to 1000°C and kept constant for 3 hours. The film was then naturally cooled to room temperature to obtain the Cu NPs / CNFs catalytic material.

[0058] Comparative Example 2:

[0059] The preparation method of I-CNFs material comprises the following steps:

[0060] (1) 0.5 g of ammonium iodide was added to 20 g of 10 wt% N,N-dimethylformamide solution and a uniform and transparent solution was obtained by magnetic stirring. The mixed solution was transferred to a syringe for electrospinning. The anode voltage was 17 kV, the cathode voltage was 1 kV, the needle was 15 cm away from the metal roller, and the pushing speed was 0.36 mL h -1 , that is, the precursor nanofiber membrane is obtained.

[0061] (2) Cut the precursor nanofiber membrane into pieces and place them on graphite sheets, which are then placed in a tube furnace and heated at 2 °C min -1 The heating rate was raised to 230 °C and maintained for 3 h, so that the fiber membrane could form a stable structure and effectively prevent the fiber from being damaged during the carbonization process. -1 The temperature was raised to 1000°C at a constant rate for 3 h, and the membrane was then naturally cooled to room temperature to obtain the I-CNFs catalytic material.

[0062] Comparative Example 3:

[0063] The preparation method of CNFs material comprises the following steps:

[0064] (1) 20 g of 10 wt% N,N-dimethylformamide solution was stirred magnetically to obtain a homogeneous and transparent solution. The mixed solution was transferred to a syringe for electrospinning. The anode voltage was 17 kV, the cathode voltage was 1 kV, the needle was 15 cm away from the metal roller, and the pushing speed was 0.36 mL h. -1 , that is, the precursor nanofiber membrane is obtained.

[0065] (2) Cut the precursor nanofiber membrane into pieces and place them on graphite sheets, which are then placed in a tube furnace and heated at 2 °C min -1 The heating rate was raised to 230 °C and maintained for 3 h, so that the fiber membrane could form a stable structure and effectively prevent the fiber from being damaged during the carbonization process. -1 The heating rate was raised to 1000°C and kept constant for 3 hours. The membrane was then naturally cooled to room temperature to obtain the CNFs catalytic material.

[0066] Figure 1 (a-b) Field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) images of I-Cu NPs / CNFs. The I-Cu NPs / CNFs exhibit randomly distributed nanofiber morphology with diameters ranging from 100 to 200 nm, forming a unique three-dimensional network structure. TEM images demonstrate that the I-Cu NPs are uniformly dispersed and anchored on the fiber surface and in the internal pores. The I-Cu NPs exhibit no significant agglomeration, indicating good dispersion and sufficient exposure of surface active sites. Figure 1 The particle size distribution in (c) shows that the average size of I-Cu NPs is 10.6 ± 2.5 nm. Figure 1(d) STEM-EDX elemental distribution image of I-Cu NPs / CNFs. The image clearly shows the uniform distribution of Cu, I, and N elements on the CNFs. It is inferred that the spatial confinement effect of the carbon fiber backbone and the lattice distortion caused by I doping synergistically inhibit the migration and aggregation of Cu NPs. Furthermore, I doping further stabilizes the dispersion by enhancing the interfacial interaction between Cu NPs and CNFs. This unique structure endows the material with a high active site density and a three-dimensional conductive network, providing an ideal mass-electron transport interface for electrocatalytic reactions.

[0067] Figure 2 The SEM and TEM images in (ab) show the morphology of Cu NPs / CNFs. Figure 2 From the SEM image in (a), it can be observed that the Cu NPs / CNFs fiber surface exhibits significant Cu NPs agglomeration, and the aggregate size distribution is in the range of 50~200 nm. Figure 2 The TEM image in (b) further reveals the heterogeneous distribution of Cu NPs. This phenomenon is in stark contrast to the I-doped I-Cu NPs / CNFs system. This suggests that relying solely on the confinement of CNFs is insufficient to suppress NP aggregation. I doping modulates Cu lattice stress and interfacial energy, forming a synergistic stabilization mechanism with the spatial confinement effect, thereby significantly improving the dispersion of CuNPs.

[0068] Figure 3 (a-b) are X-ray diffraction (XRD) patterns of I-Cu NPs / CNFs and Cu NPs / CNFs. The XRD of Cu NPs / CNFs shows three diffraction peaks at 43.3°, 50.5°, and 74.2°, corresponding to the (111), (200), and (220) planes of face-centered cubic (fcc) Cu crystals (JCPDS No. 04-0836), respectively. Figure 3 The XRD pattern (b) shows that compared with Cu NPs / CNFs, the diffraction peaks corresponding to the (111) and (200) planes of I-Cu NPs / CNFs shift towards lower angles by 0.11° and 0.12°, respectively. This shift is attributed to the incorporation of I atoms into the Cu lattice structure, which increases the interplanar spacing and induces lattice distortion. It is worth noting that no characteristic diffraction peaks of Cu-I compounds were detected in the XRD spectrum, further supporting that I enters the Cu lattice through doping. Figure 3(c) is the Raman spectrum of I-Cu NPs / CNFs and Cu NPs / CNFs. By calculating the ID / IG ratio, it was found that the undoped Cu NPs / CNFs was 1.17, while the I-Cu NPs / CNFs increased to 1.27, an increase of 9.1%, indicating that the introduction of I leads to further disorder of the carbon lattice, providing abundant active sites and electron transfer paths for the catalytic reaction.

[0069] Figure 4 The SEM images in (a-b) show the morphologies of I-CNFs and CNFs. To clarify the regulatory effect of I doping on the microstructure of CNFs, the morphologies of I-CNFs and CNFs were systematically standardized. Figure 4 As shown in the SEM image of CNFs in (a), undoped CNFs present a three-dimensional network structure, with single fibers being smooth cylindrical with diameters uniformly distributed in the range of 100-200 nm, and the fibers forming a porous skeleton through random cross-linking. Figure 4 As shown in the SEM image of I-CNFs (b), the introduction of I increases the diameter of the main fibers to a range of 200–300 nm, while finer fibers with diameters of approximately 50 nm appear in some regions. Notably, these ultrafine fibers do not exist independently but are embedded within the main fiber network through branching growth, forming a synergistic "coarse-fine" composite three-dimensional system that effectively increases the density of surface active sites.

[0070] Figure 5 (a) and Figure 5 (b) XRD and Raman spectra of I-CNFs and CNFs, respectively. Figure 5 As shown in (a), the XRD patterns of I-CNFs and CNFs are similar, both showing two broad peaks at 24° and 43°, which are attributed to the (002) and (101) crystal plane reflections of the amorphous graphitic carbon matrix, respectively. Figure 5 As shown in (b), Raman spectroscopy was further used to reveal the microstructural evolution of the carbon matrix. The ID / IG value of I-CNFs was significantly improved from 0.94 of CNFs to 1.03. This change confirmed that I doping effectively induced the sp 2 The reconstruction of the hybrid structure can be inferred that the embedding of I atoms leads to the amorphization of carbon fibers. This high defect density carbon skeleton helps to improve the electron transfer efficiency and the accessibility of active sites.

[0071] Figure 6 (ad) show the XPS spectra of I-Cu NPs / CNFs and Cu NPs / CNFs. Figure 6As shown in (ab), the full spectrum analysis confirmed that all samples had Cu element signals, while the characteristic peak of I element was only in the I-Cu NPs / CNFs composite system, which was consistent with the EDS element mapping analysis. Figure 6 (c) Cu 2p high-resolution spectrum shows that four groups of characteristic peaks appear in the Cu NPs / CNFs comparison sample, among which the Cu 2p peaks with binding energies at 932.9 eV and 952.6 eV are 3 / 2 With Cu 2p 1 / 2 orbital corresponds to Cu 1+ or Cu 0 Mixed state (Cu 1+ / 0 ), while the double peaks at 935.5 eV and 955.1 eV with higher binding energy are attributed to Cu 2 + When the I element is introduced to construct the I-Cu NPs / CNFs system, the XPS binding energy of Cu shows an overall negative shift: Cu 1+ / 0 The corresponding Cu 2p 3 / 2 and Cu 2p 1 / 2 The main peaks shifted to 932.5 eV and 952.3 eV, respectively, and Cu 2+ The corresponding orbital peaks of shift to 935.1 eV and 954.4 eV. Combined with the fact that the electronegativity of I is significantly higher than that of Cu, it can be inferred that the shift is due to the strong electron attraction of I on Cu, which promotes the transfer of electrons from Cu to it and forms local electron-rich Cu sites. Figure 6 From the high-resolution spectrum of I3d in (d), we can see that I exists in the form of I⁻, where I 3d 5 / 2 and I 3d 3 / 2 The peak positions of the orbitals are 618.9 eV and 630.4 eV, respectively, whereas Cu NPs / CNFs do not contain the element I. Further XRD phase analysis revealed no characteristic diffraction peaks for CuI compounds, indicating that the I atoms are embedded in the carbon matrix via doping rather than forming a coordination complex with Cu. This conclusion provides key evidence for the interaction mechanism between Cu and I, demonstrating that I can modulate the electron density of adjacent Cu sites through charge transfer. Furthermore, the introduction of I atoms into the carbon lattice can induce the formation of defect structures, synergistically optimizing the exposure of active centers and the reactant adsorption configuration. This dual-action regulation of electronic and geometric structures provides a critical structural foundation for subsequent catalytic performance.

[0072] Figure 7(a) Linear sweep voltammetry (LSV) curves of the four materials in a mixed solution of 1 M KOH and 0.1 M KNO3. It can be observed that the current density of I-CNFs is increased compared with CNFs. After loading Cu NPs, the current density of I-Cu NPs / CNFs further increases to -127.5 mA cm −2 , compared to Cu NPs / CNFs (75.2 mA cm −2 ) increased by 41.4%. This result indicates that I doping not only increases the intrinsic activity of the carbon support, but also may improve the synergistic catalytic performance through strong metal-support interaction (SMSI). Figure 7 (b) It can be seen that compared with the HER test in 1 M KOH alone, after the introduction of 0.1 M KNO3, I-Cu NPs / CNFs showed a larger current response and a lower starting potential, further revealing the high NO3RR activity of I-Cu NPs / CNFs.

[0073] Figure 8 (a-b) show the Faradaic efficiency and NH3 yield of I-Cu NPs / CNFs and Cu NPs / CNFs at different potentials. It is worth noting that I-Cu NPs / CNFs has the highest NH3 selectivity at -0.45 V, reaching 83.81%, and the NH3 yield is 10.7 mg h -1 mg cat. -1 However, the FE of Cu NPs / CNFs at this voltage was only 64.4%, with a yield of 2.3 mg h -1 mg cat. -1 It may be due to the intrinsic active defects of Cu, which promotes NO3 - The peak of Cu NPs / CNFs appeared at a more negative −0.55 V vs. RHE, with a FE of 70.1% and an NH3 yield of 7.5 mg h -1 mg cat. -1 , its performance is still lower than that of I-Cu NPs / CNFs. In addition, as the potential further increases, the NO3RR of all samples decreases, but the attenuation of I-CuNPs / CNFs is slower. It is speculated that the confinement effect of its carrier on *H inhibits the HER competition of active sites, because HER as a competitive side reaction will affect the performance of NO3RR. Figure 8 As shown in (c), the partial current density of NH3 gradually increases with the increase of applied potential. At -0.45 V vs. RHE, the partial current density of I-Cu NPs / CNFs is 15.4 mA cm-2 , which is 4 mA cm corresponding to Cu NPs / CNFs -2 At a high voltage of -0.75 V vs. RHE, the maximum partial current density of I-CuNPs / CNFs is 47.6 mA cm -2 , compared with 26.8 mA cm for Cu NPs / CNFs. -2 Significant improvement. Figure 8 As shown in (d), in the low overpotential region of -0.25 V, Cu NPs / CNFs generate NO2 − The FE of I-Cu NPs / CNFs was 21.5%, while that of I-Cu NPs / CNFs was only 2.5%. This indicates that I doping significantly reduced the NO2 - As the potential shifts negatively, both NO2 - The FE of Cu NPs / CNFs showed a monotonically decreasing trend, but the value of I-Cu NPs / CNFs was always lower than that of Cu NPs / CNFs. This phenomenon further proves that I doping effectively inhibits NO2 - The desorption of NH3 is promoted.

[0074] Figure 9 As shown in Figure 2, Nyquist plots of I-Cu NPs / CNFs and Cu NPs / CNFs were obtained using electrochemical impedance spectroscopy. The arc radius of I-Cu NPs / CNFs was the smallest (4.5 Ω), much smaller than that of Cu NPs / CNFs (5.7 Ω), indicating lower charge transfer resistance. This result further demonstrates that I doping can modulate the electronic structure of Cu, thereby improving charge transfer at the cathode and facilitating NO₃RR.

[0075] Figure 10 The stability test of I-Cu NPs / CNFs was performed for 10 cycles with the electrolyte replaced every hour, and no significant attenuation of the Faradaic efficiency and NH3 yield was detected, indicating that I-Cu NPs / CNFs have good stability.

[0076] Figure 11 The FE and NH3 yield of the electrocatalytic synthesis of NH3 over I-Cu NPs / CNFs catalytic materials with different I addition amounts are shown. When 0.3 g (1.35 wt%) of ammonium iodide was added, the FE and NH3 yield of the 1.35I-Cu NPs / CNFs catalytic material reached the highest values ​​of 70.4% and 8.4 mg h at -0.45 V vs. RHE. -1 mg cat. -1When the amount of ammonium iodide increased to 0.7 g (3.08 wt%), the corresponding FE and yield of NH3 reached the highest values ​​of 72.4% and 12.1 mg h -1 mg cat. -1 It is worth noting that although the NH3 yield of 3.08I-Cu NPs / CNFs is higher than that of I-Cu NPs / CNFs at the optimal ratio (10.7mg h -1 mg cat. -1 ), but its FE is significantly lower than the latter's 83.81%. This phenomenon suggests that excessive I doping may reduce the selectivity of the catalyst surface active sites for NH3 or trigger other side reaction pathways, thereby affecting the selectivity for the target product NH3.

[0077] Figure 12 The effects of different Cu loadings on the catalytic performance of I-Cu NPs / CNFs with fixed doping (0.5 g ammonium iodide) were investigated. -1 At -0.45 V vs. RHE, the Faradaic efficiency and NH3 yield of I-0.3Cu NPs / CNFs catalytic material reached the highest values ​​of 66.9% and 3.9 mg h -1 mg cat. -1 When the Cu salt loading increased to 0.5 mmol g -1 At the same potential, the FE and yield of NH3 of I-0.5Cu NPs / CNFs were the highest, reaching 76.0% and 13.6 mg h-1, respectively. -1 mg cat. -1 Similarly, when the Cu loading was too high, reaching 0.5 mmol g -1 When 0.4 mmol g -1 Cu loading of 100 μg / min is the optimal point for balancing yield and selectivity at a fixed doping level. Too high a loading may lead to agglomeration of Cu NPs, thereby reducing the number of effective active sites and lowering the selectivity.

[0078] The above specific embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for preparing iodine-doped copper nanoparticle catalyst, characterized in that: The method comprises the following steps: (1) Dispersing copper salt, iodide and nanofiber precursor in an organic solvent to obtain a uniform and transparent spinning solution; (2) spinning the electrospinning solution prepared in step (1) by an electrospinning method to obtain a precursor nanofiber membrane; (3) placing the nanofiber membrane prepared in step (2) in an air atmosphere, heating the temperature to 180-260° C. at a constant heating rate and keeping the temperature, for sufficient pre-oxidation treatment; (4) The pre-oxidized fiber membrane prepared in step (3) is heated under an inert gas atmosphere at 2-10°C / min. -1 The heating rate was raised to 1000°C and kept constant for 2 to 5 hours. After the heat treatment, it was naturally cooled to room temperature to obtain carbon nanofiber-supported I-Cu NPs / CNFs material.

2. The preparation method according to claim 1, characterized in that The molar concentration of copper salt in the spinning solution in step (1) is 0.03-0.05 mmol g -1 , the copper salt is one or two of copper chloride, copper nitrate, and copper acetate; the mass fraction of the iodide in step (1) is 1.0wt%~3.5wt%; the iodide is one or two of ammonium iodide and sodium iodide.

3. The preparation method according to claim 1, characterized in that The fiber precursor described in step (1) includes one or more of polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl alcohol, and polymethyl methacrylate.

4. The preparation method according to claim 1, characterized in that The organic solvent described in step (1) is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, ethanol, water, and acetone.

5. The preparation method according to claim 1, characterized in that The precursor solution in step (1) contains a carbon fiber precursor in an amount of 10 to 15 wt %.

6. The preparation method according to claim 1, characterized in that The spinning voltage in step (2) is 15-25 kV, the distance from the receiving device to the spinning needle is 10-20 cm, and the solution flow rate is 0.2-0.4 mL h -1 .

7. The preparation method according to claim 1, characterized in that The heating rate in step (3) is 2~10℃min -1 , pre-oxidation is to raise the temperature to 180-250℃ and keep calcining for 2-5 hours.

8. The preparation method according to claim 1, characterized in that The holding time in step (4) is 3 hours; the inert gas in step (4) is one of argon and nitrogen.

9. A I-Cu NPs / CNFs catalyst, characterized by: Prepared by the method described in any one of 1-8.

10. A method for electrocatalytic nitrate reduction to synthesize ammonia catalyst, characterized in that: The method utilizes the I-Cu NPs / CNFs in claim 9 as an electrocatalyst.

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