Cobalt modified multistage heterostructure catalyst and preparation method and application thereof

Abstract

The invention provides a cobalt modified multistage heterostructure catalyst and a preparation method and application thereof, and belongs to the technical field of ammonia synthesis. The cobalt modified Con-Cu3P / Cu catalyst is prepared by depositing copper and cobalt on a substrate step by step and then carrying out calcination, phosphorization and electrochemical reduction. In the catalyst, the metal Co mainly exists in the catalyst in the form of an elementary substance, Cu exists in the form of elementary substance Cu and monovalent Cu3P, and the problem that protonation of an intermediate is limited is solved by modifying and regulating an electronic structure through Co. The Co-Cu3P / Cu catalyst is used for electro-catalysis nitrate reduction reaction (NO3RR), and sustainable green ammonia (NH3) synthesis and nitrate (NO3 <->) pollutant removal can be achieved.

Description

Technical Field

[0001] This invention relates to the field of ammonia synthesis technology, and in particular to a cobalt-modified multi-level heterostructure catalyst, its preparation method, and its application. Background Technology

[0002] Ammonia (NH3) is a key high-value commodity chemical in agricultural fertilizers, chemical manufacturing, and energy sectors. The Haber-Bosch process (400-550°C, 15-25 MPa) remains the primary method for ammonia production, relying heavily on fossil fuel consumption and generating significant carbon dioxide emissions. Currently, developing new, green, and sustainable methods for the synthesis of NH3 under mild conditions has become a research hotspot. The electrocatalytic reduction of nitrates (NO3RR) is a promising alternative method, utilizing renewable electricity to reduce nitrates (NO3) to nitrogen oxides. - The NO3 in the water is converted into NH3. This not only achieves carbon-free NH3 synthesis, but also simultaneously treats NO3 in the water. - Pollution control holds unique significance for the coordinated management of energy and the environment. However, NO3RR is plagued by complex multi-electron / proton transfer processes and unstable reaction intermediates, leading to significant challenges in its reaction efficiency and product selectivity. Therefore, there is an urgent need to develop efficient and stable electrocatalysts to promote the practical application of NO3RR technology.

[0003] Copper-based catalysts are widely used in NO3RR (electrocatalytic nitrate reduction reaction) due to their excellent economic feasibility and moderate binding affinity for a variety of substrates. The high availability of its electronic configuration Cu (3d¹⁰ 4s¹) endows it with a strong electron-donating ability, making Cu a core element in NO3RR. - The adsorption at the active sites of the copper-based cathode dominates the NO3RR, in which copper and NO3... - The significant binding affinity of NO2 accelerated - The rate of formation determines the steps. However, due to NO2 - Accumulation on copper leads to NO3RR exhibiting lower NH3 concentrations at low overpotentials. This is considering that NO3RR involves a series of hydrogenation reactions, where... The formation of H species also plays a decisive role in the efficient production of NH3. The poor H2O dissociation activity of copper-based catalysts hinders NO3 production. -Complete hydrogenation to NH3. Therefore, an effective strategy is to dope with foreign elements to modify the electronic structure of the catalyst and optimize the reaction pathway. For example, Wang et al. (https: / / doi.org / 10.1021 / acscatal.4c05954, Jiajia Wang, Zhuodong Ou, Chengbo Dong, Mengying Su, Amjad Ali, Artem V. Kuklin, Hans Ågren, Glib V. Baryshnikov, Yang Liu, Xue Zhao, and Haibo Zhang) synthesized boron-doped copper (BDCu) and demonstrated that boron doping enhances water activation and proton H adsorption ( ). H), and significantly increased NO3 - The conversion rate to NH3. Furthermore, Cu3P-based cathodes have been used for the electrocatalytic hydrogenation of N2 to NH3. However, the strong coordination of phosphides covers the active sites of Cu and reduces electron transfer capability, which in turn impairs the overall performance of NO3RR.

[0004] Therefore, existing NO3RR catalysts have the following drawbacks: 1) Low catalytic efficiency: Traditional NO3RR catalysts (such as single-metal or bimetallic catalysts) have low Faradaic efficiency (FE) and yield for NH3, making it difficult to meet industrial requirements. Key intermediates (such as...) 1) NO: At high concentrations, the protonation process is limited, leading to blocked reaction pathways and further reducing catalytic efficiency. 2) Poor selectivity of Cu-based catalysts: Existing Cu-based catalysts easily generate byproducts (such as N2O, NO2, etc.) in NO3RR, reducing the selectivity of NH3 and increasing the cost of subsequent separation and purification. Although phosphide catalysts (such as Cu3P / Cu) have certain activity, insufficient electronic structure regulation results in high reaction energy barriers, making it difficult to improve selectivity. 3) Insufficient stability: Traditional catalysts are prone to structural collapse or deactivation of active sites during long-term operation, leading to performance degradation and affecting the reliability of industrial applications. 4) High cost and poor scalability: Noble metal-based catalysts (such as Pt, Pd) are expensive and difficult to use on a large scale; while the preparation process of transition metal phosphide (TMP) catalysts is complex, posing challenges to large-scale production. Summary of the Invention

[0005] The purpose of this invention is to provide a cobalt-modified hierarchical heterostructure catalyst, its preparation method, and its application, overcoming the challenge of limited protonation of key intermediates at high concentrations in the electrocatalytic nitrate reduction reaction (NO3RR), thereby achieving efficient and sustainable green ammonia (NH3) synthesis and nitrate (NO3) reduction. - Pollutant removal.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing a cobalt-modified hierarchical heterostructure catalyst, comprising the following steps: The substrate was subjected to a first electrodeposition in a copper-containing source solution to obtain a copper deposit. The copper deposit was subjected to a second electrodeposition in a cobalt-containing source solution to obtain a cobalt-copper deposit. The cobalt-copper deposit was calcined in air to obtain Co-CuO; The Co-CuO was phosphated under phosphorus source conditions to obtain the phosphated product; Under constant current conditions, the phosphating product was electrochemically reduced in an alkaline solution to obtain a cobalt-modified multi-level heterostructure catalyst.

[0007] Preferably, the copper source in the copper-containing solution includes copper sulfate; the copper source solution also includes sulfuric acid and sodium chloride; the molar ratio of sulfuric acid to copper source in the copper-containing solution is 1:0.1 to 1:1; and the molar ratio of copper source to sodium chloride is 10:1 to 5:2.

[0008] Preferably, the current density of the first electrodeposition is 50~100 mA / cm². 2 The deposition time is 30~120 min.

[0009] Preferably, the cobalt source in the cobalt source solution includes cobalt sulfate; the cobalt source solution also includes sodium chloride; and the molar ratio of cobalt source to sodium chloride in the cobalt source solution is 1:1.

[0010] Preferably, the current density of the second electrodeposition is 10~50 mA / cm². 2 The deposition time is 30-90 minutes; The calcination temperature is 300℃ and the time is 4~8h.

[0011] Preferably, the phosphorus source includes NaH2PO2; the phosphating conditions include: a nitrogen atmosphere and a temperature of 300-350°C. o C, the time is 2 hours.

[0012] Preferably, the alkali used in the alkaline solution includes sodium carbonate; the concentration of the alkaline solution is 1.5 mol / L; and the current density of the electrochemical reduction is 100 mA / cm². 2 Time ≥ 2 hours.

[0013] The present invention provides a cobalt-modified hierarchical heterostructure catalyst prepared by the preparation method described above, comprising a Cu3P / Cu support and Co supported on the Cu3P / Cu support, forming a Co-Cu3P interface and having a hierarchical heterostructure.

[0014] Preferably, the Co loading in the cobalt-modified hierarchical heterostructure catalyst is 0.02~0.1 wt%.

[0015] This invention provides the application of the cobalt-modified hierarchical heterostructure catalyst described above in the electrocatalytic nitrate reduction reaction.

[0016] To address the challenge of developing highly active and selective catalysts for the NO3RR reaction, which suffers from limited protonation of key intermediates at high concentrations, this invention provides a method for preparing a cobalt-modified hierarchical heterostructure catalyst. The method involves stepwise deposition of copper and cobalt on a substrate, followed by calcination, phosphating, and electrochemical reduction to prepare a cobalt-modified Co-Cu3P / Cu catalyst. In this catalyst, metallic Co exists primarily in elemental form, while Cu exists as elemental Cu and monovalent Cu3P. This Co-Cu3P / Cu catalyst, used for the electrocatalytic nitrate reduction reaction (NO3RR), enables sustainable green ammonia (NH3) synthesis and nitrate (NO3-) pollutant removal.

[0017] This invention innovatively constructs a Co-Cu3P / Cu composite catalytic system through Co modification technology. This system promotes water decomposition to generate the reducing medium H through Co element, and achieves efficient H retention through interface engineering, thereby significantly accelerating the hydrogenation reaction of N intermediate and improving the selectivity of NH3 synthesis. Crucially, this composite system synergistically solves the dual problems of nitrite (NO2-) accumulation in traditional copper-based catalysts and low electron transfer efficiency in the metal phosphide Cu3P / Cu system. Its mechanism of action is as follows: the introduction of Co regulates the electron density of active sites through electronic synergistic effects, inhibiting the excessive formation of NO2- intermediates; simultaneously, the synergistic catalytic centers at the Co-Cu3P / Cu hierarchical heterogeneous interface form electron transport channels, promoting the NO3- reduction reaction to proceed efficiently at a more negative potential (<-0.4 vs. RHE), thereby avoiding nitrite accumulation and improving reaction efficiency.

[0018] The present invention has the following beneficial effects: Enhancing Catalytic Efficiency and Selectivity: A multi-scale active site distribution is formed through the design of a Co-modified cuprous phosphide hierarchical heterostructure (Co-Cu3P / Cu) composite interface, enhancing electron transfer and intermediate adsorption capabilities. Co regulates the electronic structure of Cu3P / Cu, promoting key hydrogenation steps, optimizing the reaction pathway, and suppressing the formation of byproducts (such as N2O and NO2). This synergistically regulates NO3- reduction and hydrogenation processes, thereby improving catalytic activity and NH3 selectivity, significantly increasing the Faraday efficiency (up to 87.8%) and yield (up to 36.7 mg h⁻¹) of NH3. -1 cm -2 At -0.2 V vs. RHE, the NH3 Faraday efficiency is ≥85%, and the yield is ≥30 mg. ¹ c ². The NH3 Faraday efficiency and yield of the catalyst of this invention are significantly higher than those of traditional bimetallic and phosphide catalysts, representing a technological breakthrough. Therefore, this invention solves the problem of limited protonation of intermediates by modifying the electronic structure with Co.

[0019] Enhanced structural stability: The multi-level heterogeneous structure design utilizes the synergistic effect of multiple active sites of Co, Cu3P and Cu to provide more active sites while dispersing reaction stress, reducing the deactivation of active sites in the catalyst during long-term operation and extending its service life.

[0020] Reduce costs and enable scalable applications: Use non-precious metals (Co, Cu) and phosphating processes to reduce raw material costs; optimize preparation processes (such as chemical vapor deposition, electrochemical deposition, etc.) to achieve large-scale production and promote the industrial application of NO3RR technology in green ammonia synthesis and nitrate pollutant removal.

[0021] The results of the examples show that Co performs better in optimizing Cu3P / Cu activity. 0.05 -Cu3P / Cu (79.1%) exhibited a higher NO3- conversion rate than Cu3P / Cu (48.4%), demonstrating that Co modification accelerated the reduction process of NO3- and NO2- on Cu3P / Cu. Meanwhile, Co... 0.05 -Cu3P / Cu exhibits a superior NO2-NH3 hydrogenation process, with a higher NH3FE (87.8%) compared to Co-Cu (45.2%). Therefore, Co... 0.05 The highest NH3 yield of 36.7 mg h was obtained after reacting Cu3P / Cu at -0.2 V vs RHE potential for 2 hours. -1 cm -2 In addition, Co 0.05-Cu3P / Cu exhibits excellent electrochemical activity, demonstrating its superior charge transfer and hydrogenation capabilities, as evidenced by a minimal Rct (3.1 Ω) and a high reduction current density of -187.6 mA / cm² at -0.2 V. 2 Tafel slope proof Co 0.05 -Cu3P / Cu exhibits a moderate HER process, promoting the simultaneous conversion of NO3- to NO2- and NO2- to NH3. Co 0.05 -Cu3P / Cu can serve as an attractive catalyst for the electrochemical reduction of nitrates. This invention provides a new strategy for the design of transition metal phosphide (TMP) heterostructure catalysts, promotes the development of industrial ammonia synthesis technology based on NO3RR, and provides a new strategy for developing multi-component catalysts for efficient NH3 production and wastewater treatment. Attached Figure Description

[0022] Figure 1 SEM images of the Cu electrode in Comparative Example 1 at different magnifications; Figure 2 Here are SEM images of Co-Cu at different magnifications in Comparative Example 2; Figure 3 SEM images of Cu3P / Cu at different magnifications in Comparative Example 3; Figure 4 Co in Example 1 0.02 SEM images of Cu3P / Cu electrodes at different magnifications; Figure 5 Co in Example 1 0.05 SEM images of Cu3P / Cu electrodes at different magnifications; Figure 6 Co in Example 1 0.1 SEM images of Cu3P / Cu electrodes at different magnifications; Figure 7 Co in Example 1 0.05 -EDS mapping diagram of Cu3P / Cu; Figure 8 Co in Example 1 0.05 TEM image of Cu3P / Cu; Figure 9 Co in Example 1 0.05 HAADF-STEM image of Cu3P / Cu; Figure 10 In Example 1, Co 0.05 HRTEM image of Cu3P / Cu; Figure 11 Cu, Co-Cu, Cu3P / Cu and Co0.05 XRD pattern of Cu3P / Cu; Figure 12 Co in Example 1 0.05 CuO x XRD patterns of CuO-CuCl electrodes; Figure 13 The NO3- conversion efficiency (CE), NH3 Faradaic efficiency, and NH3 yield of the NO3RR process on different catalysts are shown. Figure 14 For nitrogen species during NO3RR, in (a) Cu, (b) Co-Cu, (c) Cu3P / Cu, and (d) Co 0.02 -Cu3P / Cu, (e)Co 0.05 -Cu3P / Cu and (f)Co 0.1 Concentration curves on Cu3P / Cu; Figure 15 NO3RR at different potentials for Cu, Co-Cu, Cu3P / Cu and Co 0.05 -Cu3P / Cu conversion efficiency (a), NH3 Faraday efficiency (b) and NH3 yield (c); Figure 16 Cu, Co-Cu, Cu3P / Cu and Co 0.05 AC impedance diagram of Cu3P / Cu, with the inset being a magnified view of a portion; Figure 17 Cu, Co-Cu, Cu3P / Cu and Co 0.05 CV plot of Cu3P / Cu; Figure 18 Cu, Co-Cu, Cu3P / Cu and Co 0.05 Fitting plot of the double-layer capacitance (Cdl) of Cu3P / Cu; Figure 19 Cu, Co-Cu, Cu3P / Cu and Co 0.05 LSV curve of Cu3P / Cu in 0.5M Na2SO4; Figure 20 Cu, Co-Cu, Cu3P / Cu and Co 0.05 Tafel slope of Cu3P / Cu; Figure 21 For Co 0.05 LSV curves of Cu3P / Cu with different NO3- concentrations in 0.5 M Na2SO4; Figure 22 Cu, Co-Cu, Cu3P / Cu and Co 0.05LSV comparison chart of Cu3P / Cu in 0.5 M NaSO4 with or without 100 mM NO3-; Figure 23 For Co 0.05 C / C0 curve of nitrate during 10 NO3RR cycles of Cu3P / Cu; Figure 24 For Co 0.05 Nitrate conversion (CE), ammonia faradaic efficiency (NH3FE), and ammonia yield (NH3 yield) for a 10-cycle NO3RR process of Cu3P / Cu. Figure 25 For Co 0.05 SEM (a) and HRTEM (b) images and XRD spectra (c) after the Cu3P / Cu cycling reaction. Detailed Implementation

[0023] In this invention, unless otherwise specified, the raw materials or reagents required for preparation are all commercially available products well known to those skilled in the art.

[0024] This invention provides a method for preparing a cobalt-modified hierarchical heterostructure catalyst, comprising the following steps: The substrate was subjected to a first electrodeposition in a copper-containing source solution to obtain a copper deposit. The copper deposit was subjected to a second electrodeposition in a cobalt-containing source solution to obtain a cobalt-copper deposit. The cobalt-copper deposit was calcined in air to obtain Co-CuO; The Co-CuO was phosphated under phosphorus source conditions to obtain the phosphated product; Under constant current conditions, the phosphating product was electrochemically reduced in an alkaline solution to obtain a cobalt-modified multi-level heterostructure catalyst.

[0025] In this invention, the substrate is preferably nickel foam or cobalt foam, more preferably nickel foam. Nickel foam is inexpensive and structurally stable, and its performance is minimally affected after the substrate is encapsulated in copper.

[0026] Before using the foamed nickel, the present invention preferably cuts the foamed nickel and then ultrasonically cleans it for 15 minutes in 0.01M hydrochloric acid solution, acetone and deionized water to remove surface impurities.

[0027] The present invention does not impose any special limitation on the size of the substrate, which can be adjusted according to the requirements; in the embodiments of the present invention, it is specifically 1 cm × 1 cm.

[0028] In this invention, the copper source in the copper-containing solution preferably includes copper sulfate; the copper source solution preferably also includes sulfuric acid and sodium chloride; the molar ratio of sulfuric acid to copper source in the copper-containing solution is preferably 1:0.1 to 1:1, more preferably 1:0.5; the molar ratio of copper source to sodium chloride is preferably 10:1 to 5:2, more preferably 5:1; the molar ratio of sulfuric acid, sodium chloride, and copper source in the copper-containing solution is more preferably 1:0.1:0.5. In this invention, the concentration of sulfuric acid in the copper-containing solution is preferably 1 mol / L, the concentration of sodium chloride is preferably 0.1 mol / L, and the concentration of copper source is preferably 0.5 mol / L. The solvent used in the copper-containing solution of this invention is preferably water.

[0029] In this invention, the current density of the first electrodeposition is preferably 50~100 mA / cm². 2 The deposition time is preferably 30-120 min, more preferably 60-90 min. This invention deposits Cu and CuCl on a substrate using constant current electrodeposition.

[0030] After completing the first electrodeposition, the present invention preferably rinses the sample thoroughly with deionized water, soaks it for 5 minutes, and then immerses the resulting copper deposit in a cobalt-containing source solution for the second electrodeposition.

[0031] In this invention, the cobalt source in the cobalt-containing source solution preferably includes cobalt sulfate; the cobalt source solution preferably also includes sodium chloride; the molar ratio of the cobalt source to sodium chloride in the cobalt-containing source solution is preferably 1:1. In this invention, the concentration of the cobalt source in the cobalt-containing source solution is preferably 50 mM, and the concentration of sodium chloride is preferably 50 mM.

[0032] The solvent used in the cobalt-containing source solution of the present invention is preferably water.

[0033] In this invention, the current density of the second electrodeposition is preferably 10~50 mA / cm². 2 More preferably 20~30 mA / cm 2 The deposition time is preferably 30-90 min, more preferably 60 min. This invention uses a second electrodeposition process to deposit elemental Co onto a copper deposit.

[0034] After the second electrodeposition is completed, the present invention preferably places the obtained electrode in a muffle furnace for calcination.

[0035] In this invention, the calcination temperature is preferably 300°C, and the calcination time is preferably 4-8 hours, more preferably 6-8 hours. This invention uses calcination to perform thermal oxidation, forming a metal oxide, CuO.

[0036] In this invention, Co-CuO is preferably placed in a tube furnace, and a phosphorus source is placed 1 cm upstream of the material. Phosphating is carried out by heating in a nitrogen flow.

[0037] In this invention, the phosphorus source preferably includes NaH2PO2 (which decomposes at 300°C to produce phosphine gas); the phosphating conditions preferably include: a nitrogen atmosphere and a temperature of 300-350°C. o C, more preferably 300~320 o C, time is 2h, heating rate is 5 o C min -1 The preferred flow rate of the nitrogen gas is 100 mL / min. During the phosphating process, by controlling the phosphating temperature and time, some Cu is phosphated to form Cu3P.

[0038] In this invention, the alkali used in the alkaline solution preferably includes sodium carbonate; the concentration of the alkaline solution is preferably 1.5 mol / L; this invention does not have a special limitation on the ratio of the alkaline solution to the phosphating product, as long as the amount of alkaline solution is sufficient. The solvent used in the alkaline solution of this invention is preferably water. Electrochemical reduction in sodium carbonate solution can stabilize the components, reducing unstable oxidized components and thus relatively fixing the active components during the reaction.

[0039] In this invention, the current density of the electrochemical reduction is preferably 100 mA / cm². 2 The preferred time is ≥2 hours, more preferably 2 hours. This invention uses an electrochemical reduction current to completely reduce the phosphating product.

[0040] The present invention provides a cobalt-modified hierarchical heterostructure catalyst prepared by the preparation method described above, comprising a Cu3P / Cu support and Co supported on the Cu3P / Cu support, forming a Co-Cu3P interface and having a hierarchical heterostructure.

[0041] In this invention, the Co loading in the cobalt-modified hierarchical heterostructure catalyst is 0.02~0.1 wt%, more preferably 0.03~0.08 wt%, and even more preferably 0.05~0.06 wt%.

[0042] This invention provides the application of the cobalt-modified hierarchical heterostructure catalyst described above in the electrocatalytic nitrate reduction reaction. This invention does not impose any particular limitation on the method of application; any method well-known in the art can be used.

[0043] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0044] Unless otherwise specified, the experimental methods described in the various embodiments of this invention are conventional methods; unless otherwise specified, the reagents and raw materials described below are all commercially available.

[0045] Example 1

[0046] Cut the nickel foam into 1 cm × 2 cm pieces and ultrasonically clean them for 15 minutes in 0.01 M hydrochloric acid solution, acetone and deionized water. A 1 cm × 1 cm piece of nickel foam was immersed in a mixed solution containing 1 M H₂SO₄, 0.1 M NaCl, and 0.5 M CuSO₄ at 100 mA / cm⁻¹. 2 Cu and CuCl were deposited on nickel foam by constant current electrodeposition at a current density of 20 mA / cm². After 60 min of electrodeposition, the sample was thoroughly rinsed with deionized water and soaked for 5 min. Subsequently, the copper deposit was immersed in a mixed solution of 50 mM CoSO₄ and 50 mM NaCl at a current density of 20 mA / cm². 2 Co was electrodeposited by constant current at a current density of 30 min, 60 min, and 90 min, respectively. The resulting electrodeposited electrode was placed in a muffle furnace and calcined at 300 °C for 8 h in air atmosphere, then naturally cooled to room temperature. The resulting product is denoted as Co. n CuO x ( n (This represents the Co loading obtained by adjusting the Co electrodeposition time). Prepared Co n CuO x Place them separately in a tube furnace, with NaH2PO2 positioned 1 cm upstream of the material, and heat in a nitrogen flow (100 mL / min) at a rate of 5... o C min -1 The sample was heated at a heating rate of 300°C. o After being kept at C for 2 hours, the phosphated sample was dissolved in 1.5 M Na2CO3 solution at 100 mAcm⁻¹. -2 Electrochemical reduction with constant current for 2 hours yielded Co. n -Cu3P / Cu (Co loading n = 0.02, 0.05, or 0.1, corresponding to Co deposition times of 30 min, 60 min, and 90 min respectively), the products are denoted as Co. 0.02 -Cu3P / Cu, Co 0.05 -Cu3P / Cu and Co 0.1 -Cu3P / Cu.

[0047] Comparative Example 1

[0048] Preparation of Cu: A 1 cm × 1 cm piece of nickel foam was immersed in a mixed solution of 1 M H₂SO₄, 0.1 M NaCl, and 0.5 M CuSO₄ at 100 mA / cm². 2 At a current density of 100 mA / cm², Cu and CuCl were deposited on nickel foam using a constant current technique for 60 min. The electrodes were then washed with a large amount of deionized water and soaked for 5 min, followed by rapid air drying. The dried electrodes were placed in a muffle furnace and calcined at a constant temperature of 300 °C for 8 h in an air atmosphere. After cooling to room temperature, CuO-CuCl was obtained. The CuO-CuCl was then subjected to a current density of 100 mA / cm². 2 A Cu electrode was obtained by electrochemical reduction in 1.5 M Na2CO3 solution for 2 h under constant current.

[0049] Comparative Example 2

[0050] Preparation of Co-Cu: A 1 cm × 1 cm nickel foam was immersed in a mixed solution of 1 M H₂SO₄, 0.1 M NaCl, and 0.5 M CuSO₄ at 100 mA / cm². 2 Cu and CuCl were deposited on nickel foam using a constant current technique at a current density of 60 min. The foam was then washed with sufficient deionized water and soaked for 5 min, followed by immersion in a mixed solution of 20 mM (NH4)2SO4 and 20 mM CoSO4 at 20 mA / cm². 2 Co was deposited under constant current at a given current density for 60 minutes. The dried electrode was then calcined in a muffle furnace at 300°C in air for 8 hours, followed by cooling to room temperature. The resulting material was Co-CuO. x， Then use 100mA / cm 2 Co-Cu was obtained by electrochemical reduction in 1.5M Na2CO3 solution for 2 hours under constant current.

[0051] Comparative Example 3

[0052] Preparation of Cu3P / Cu: CuO-CuCl samples with dimensions of 1 cm × 1 cm prepared in Comparative Example 1 were loaded into a tube furnace. NaH2PO2 was introduced at a short distance of 1 cm upstream of the tube furnace. The sample was heated to 300°C in a nitrogen flow (100 mL / min) at a heating rate of 5°C / min and held at 300°C for 2 h. The resulting phosphating sample was then dissolved in 1.5 M Na2CO3 solution at a heating rate of 100 mA / cm. 2 Electrochemical reduction with constant current for 2 h yielded Cu3P / Cu.

[0053] Characterization of catalysts

[0054] 1) Co-Cu3P / Cu samples with different Co loadings were synthesized by a stepwise method. First, a Cu-CuCl substrate was prepared by electrodeposition. Then, Co was further electrodeposited, followed by heat treatment in air and phosphine atmosphere generated by NaH2PO2. Finally, Co species were anchored onto Cu in Cu3P / Cu by electrochemical reduction. The Co content in Co-Cu3P / Cu could be adjusted by the electrodeposition time of Co. The elemental contents of Cu and Co on different electrodes were measured by ICP (Table 1).

[0055] Table 1. Elemental mass of Cu, Co, and P in the catalysts of Example 1 and Comparative Examples 1-3 determined by ICP-AES.

[0056] Table 1 shows that Cu, Cu3P / Cu and Co n -Cu3P / Cu (n=0.02, 0.05 and 0.1) have similar copper mass contents, Co n In Cu3P / Cu (n=0.02, 0.05, and 0.1), the cobalt content increases with increasing Co electrodeposition time. Co-Cu, without phosphating treatment, is directly electrochemically reduced and reacts with Co. 0.05 -Cu3P / Cu have similar cobalt quality.

[0057] 2) Figure 1 The images show SEM images of the Cu electrode in Comparative Example 1 at different magnifications. Figure 2 Here are SEM images of Co-Cu at different magnifications in Comparative Example 2; from Figure 1 and Figure 2 As can be seen, Cu exhibits a porous structure formed by overlapping nanosheets, while Co-Cu exhibits a columnar structure composed of irregular particles growing on a framework substrate. This rich structure increases the surface roughness of the electrode and creates abundant pores for electron mass transfer.

[0058] Figure 3 SEM images of Cu3P / Cu at different magnifications in Comparative Example 3; Figure 4 Co in Example 1 0.02 SEM images of Cu3P / Cu electrodes at different magnifications; Figure 5 Co in Example 1 0.05 SEM images of Cu3P / Cu electrodes at different magnifications; Figure 6 Co in Example 1 0.1 SEM images of the Cu3P / Cu electrode at different magnifications; by Figures 3-6 It can be seen that after the phosphating process, Co n-Cu3P / Cu (n=0.02, 0.05 and 0.1) exhibit partial structural softening, forming a multi-level structure composed of dense particles of approximately 40-120 nm in size.

[0059] 3) Figure 7 Co in Example 1 0.05 - EDS mapping diagram of Cu3P / Cu; clearly verifying Co 0.05 The uniform distribution of copper, cobalt and phosphorus in -Cu3P / Cu.

[0060] 4) Figure 8 Co in Example 1 0.05 TEM image of Cu3P / Cu. Figure 8 Showcasing Co 0.05 - The multilevel structure of Cu3P / Cu, the multilevel heterostructure includes Cu, Cu3P and Co.

[0061] Figure 9 Co in Example 1 0.05 HAADF-STEM image of Cu3P / Cu; High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image and corresponding elemental mapping image show that Cu, Co, C and O elements are uniformly distributed throughout the particles.

[0062] Figure 10 In Example 1, Co 0.05 -HRTEM image of Cu3P / Cu; A clear heterostructure with well-defined interfaces was observed in the high-resolution TEM (HRTEM) image, with planar distances of 0.18 nm, 0.20 nm and 0.23 nm for clear lattice fringes, corresponding to the (200) plane of Cu, the (300) plane of Cu3P and the (111) plane of Co, respectively.

[0063] 5) Figure 11 Cu, Co-Cu, Cu3P / Cu and Co 0.05XRD pattern of Co-Cu3P / Cu; X-ray diffraction pattern identified diffraction peaks corresponding to Cu, Cu3P, and Co in Co-Cu3P / Cu. Characteristic peaks of cubic Cu (JCPDS 04-0836) (111), (200), and (220) crystal planes were observed at 43.5°, 50.6°, and 74.1°. Strong diffraction peaks of hexagonal Cu3P (JCPDS71-2261) appeared at 36.0°, 45.1°, and 46.1°. Characteristic peaks of cubic Co (JCPDS15-0806) (111), (200), and (220) crystal planes were observed at 44.2°, 51.5°, and 75.8°. Notably, no oxidized Co crystal form was detected during the synthesis of Co-Cu3P / Cu. Figure 12 ). Figure 12 Co in Example 1 0.05 CuO x XRD patterns of CuO-CuCl electrodes.

[0064] Application test cases

[0065] Electrocatalytic reduction of nitrate: NO3RR was performed on a CHI760E electrochemical workstation (China Ltd.) using a closed H-type electrolytic cell separated by a Nafion N117 proton exchange membrane. A three-electrode system was employed: the prepared sample served as the working electrode (controlled geometry: 1 × 0.5 cm²), a saturated calomel electrode (SCE) served as the reference electrode, and Ti / Ru-Ir was used as the reference electrode. A mixed metal oxide (MMO) electrode was used as the counter electrode. The electrolyte was a 0.5 M Na₂SO₄ aqueous solution (pH adjusted to 12), with 50 mL added to both the cathode and anode chambers; the cathode chamber also contained a 100 mM NaNO₃ aqueous solution. The potential was calibrated to the reversible hydrogen electrode (RHE) using the following equation: ERHE = ESCE + 0.059 × pH + 0.24. Before NO₃RR, the potential was calibrated at 5 mV s in the potential range of 0.5 to -0.7 V vs. RHE. -1 The reaction was carried out by linear sweep voltammetry (LSV) at a rate of [missing value] until the polarization curve stabilized. Subsequently, NO3RR was performed with stirring (800 rpm) at a constant potential of -0.2 V vs. RHE. All reactions were carried out at room temperature under an Ar atmosphere.

[0066] 1) Evaluate the electrochemical NO3RR performance of the prepared catalyst in a custom H-type electrolyzer with a standard three-electrode system.

[0067] Figure 13 The NO3- conversion efficiency (CE), NH3 Faradaic efficiency, and NH3 yield of the NO3RR process on different catalysts are given.

[0068] Figure 14 For nitrogen species during NO3RR, in (a) Cu, (b) Co-Cu, (c) Cu3P / Cu, and (d) Co 0.02 -Cu3P / Cu, (e)Co 0.05 -Cu3P / Cu and (f)Co 0.1 Concentration curves on Cu3P / Cu.

[0069] Depend on Figures 13-14 It can be seen that after 2 hours of reaction, Cu exhibits high NO3- reduction activity, with a NO3- conversion efficiency (CE) as high as 92.9%. Figure 13 However, it only achieved a low NH3 Faraday efficiency of 11.7% (NH3 FE) and 2.6 mgh. -1 cm -2 The low NH3 yield is attributed to the low selectivity of NH3 and the severe accumulation of NO2- on the copper electrode. Figure 14 In contrast, the Cu3P / Cu catalyst exhibited higher NH3 selectivity, resulting in 92.8% NH3 FE and 27.6 mgh. -1 cm -2 The NH3 yield was high, while its NO3- conversion efficiency was only 48.4%. Compared with Cu, the Co-Cu catalyst maintained excellent NH3 FE (45.2%) and NH3 yield (12.4 mgh). -1 cm -2 However, the problem of NO2- accumulation still exists. It is worth noting that Co modification significantly optimizes the activity of Cu3P / Cu. 0.05 -Cu3P / Cu achieved a NO3- conversion efficiency of 79.1%, higher than Cu3P / Cu's 48.4%, indicating that Co accelerates the reduction process of NO3- and NO2-. Simultaneously, Co-Cu3P / Cu exhibited a good NO2- to NH3 hydrogenation process, with a higher NH3 FE (87.8%) compared to Co-Cu (45.2%). Specifically, excessive cobalt loading may lead to particle aggregation, resulting in decreased activity. Figure 6 Therefore, Co 0.05 -Cu3P / Cu exhibits excellent NO3RR behavior, achieving 36.7 mgh -1 cm -2 Maximum NH3 production.

[0070] 2) Electrochemical NO3RR was performed under different applied potentials to further demonstrate that Co 0.05 -Applicability of Cu3P / Cu.

[0071] Figure 15 NO3RR at different potentials for Cu, Co-Cu, Cu3P / Cu and Co 0.05 -Cu3P / Cu conversion efficiency (a), NH3 Faradaic efficiency (b), and NH3 yield (c). For example... Figure 15 As shown, within the range of 0.0 V to -0.4 V vs. RHE, increasing the potential promotes further reduction of NO2- on Cu and Co-Cu, mainly manifested as a significant increase in NH3 FE and a small change in NO3- conversion efficiency. The unique dependence of NO3- conversion on external potential is largely attributed to the redox reaction of NO3- reduction to NO3- at Cu sites. In contrast, increasing the potential from 0.0 V to -0.2 V enhances the reduction of NO2- on Cu3P / Cu and Co-Cu. 0.05 The selective conversion of NO3- and NH3 on Cu3P / Cu leads to a gradual increase in the production of NH3FE and NH3. Compared to Cu3P / Cu, when the potential increases from -0.2V to -0.4V, Co... 0.05 The conversion efficiency of Cu3P / Cu and NH3FE were significantly improved, indicating that Co 0.05 -Cu3P / Cu can efficiently convert NO3- to NH3 at -0.2 V.

[0072] 3) Efficient interfacial mass transfer and rapid electron transfer are indispensable prerequisites for high NO3RR activity. Charge transfer resistance (Rct), corresponding to the semicircle diameter in the Nyquist plot, is a key descriptor of electrocatalytic kinetics (a lower Rct indicates faster electron transfer), as measured by EIS. Figure 16 As shown.

[0073] Figure 16 Cu, Co-Cu, Cu3P / Cu and Co 0.05 The AC impedance diagram of Cu3P / Cu is shown in the inset, which is a magnified view of a portion of the diagram. Figure 16 As shown, in the catalyst, Co 0.05 The lowest Rct (3.1 Ω) was observed in Cu3P / Cu, lower than Cu3P / Cu (5.8 Ω), Co-Cu (5.7 Ω), and Cu (6.9 Ω), indicating a more favorable charge transfer kinetic for NO3RR. Furthermore, in the low-frequency region, Co showed better charge transfer dynamics compared to Cu. 0.05 -Cu3P / Cu, Cu3P / Cu, and Co-Cu exhibit steeper Warburg slopes, indicating superior mass transfer performance.

[0074] 4) The electrochemical active surface area (ECSA) is directly proportional to the number of accessible active sites. Quantification is achieved by cyclic voltammetry (CV) using a double-layer capacitor (Cdl) within a non-Radidatic potential window at different scan rates (5-50 mV s⁻¹). Figure 17 ).

[0075] Figure 17 Cu, Co-Cu, Cu3P / Cu and Co 0.05 CV plot of Cu3P / Cu. Figure 18 Cu, Co-Cu, Cu3P / Cu and Co 0.05 Fitting plot of the double layer capacitance (Cdl) of Cu3P / Cu.

[0076] like Figure 17 As shown, the CV curves reveal a linear relationship between current and scan rate, with no obvious Faraday peak, confirming the pure capacitive behavior and validating the ECSA estimate based on Cdl. The linear fit between the capacitor current (Δj / 2) and scan rate yields Co. n The Cdl value of -Cu3P / Cu is approximately 200~300 mF / cm. 2 ( Figure 18 ).

[0077] 5) The water decomposition performance of different materials was compared using LSV curves. Figure 19 ). Figure 19 Cu, Co-Cu, Cu3P / Cu and Co 0.05 LSV curves of Cu3P / Cu in 0.5M Na2SO4. (By...) Figure 19 Calculation, obtained Figure 20 . Figure 20 Cu, Co-Cu, Cu3P / Cu and Co 0.05 The Tafel slope of -Cu3P / Cu. The Tafel slope reflects the intrinsic properties and electrocatalytic reaction kinetics, and is related to the rate-determining step of water splitting (…). Figure 20 ). with Cu (257.1 mV dec) -1 Compared to Cu, Co-Cu and Cu3P / Cu exhibit smaller Tafel slopes (241.1 and 255.0 mV dec). -1 This indicates that the water splitting process is faster. Similarly, Co 0.05 -Cu3P / Cu exhibits a good Tafel slope (247.2 mV dec). -1 This can promote the further hydrogenation of NO2- adsorbed on the surface.

[0078] 6) The preliminary NO3- reduction activity was evaluated using LSV in solutions with different NO3- concentrations. Figure 21 ). Figure 21 For Co 0.05 LSV curves of Cu3P / Cu with different NO3- concentrations in 0.5 M Na2SO4. Figure 22Cu, Co-Cu, Cu3P / Cu and Co 0.05 LSV comparison chart of -Cu3P / Cu in 0.5 M NaSO4 with or without 100 mM NO3-. Figure 23 For Co 0.05 C / C0 curve of nitrate during 10 NO3RR cycles of Cu3P / Cu.

[0079] The reduction peak current increases with increasing nitrate concentration, indicating that the reduction peak is a current response generated by nitrate reduction rather than a current response generated by the redox reaction of the material itself. Figure 21 Co 0.05 The peak current density of -Cu3P / Cu increases monotonically with NO3- concentration. Figure 22 In the presence of 100 mM NO3-, it reaches -187.6 mA cm⁻¹ at -0.2 V relative to RHE. -2 It is significantly higher than that of Cu (-92.6 mA cm⁻¹). -2 ), Co-Cu (-104.1 mA cm⁻¹) -2 Cu3P / Cu (-147.6 mA cm⁻¹) -2 () Figure 23 ).

[0080] Based on the above discussion, this invention proposes a synergistic mechanism for NO3RR on Co-Cu3P / Cu. In this heterostructure, the copper surface is the main active site, preferentially adsorbing and activating NO3-. Simultaneously, water decomposition occurs at the Cu3P sites to produce... H is then supplied to Cu and Co sites as needed, thereby synergistically promoting the successive hydrogenation steps of NO3RR. Although Cu3P / Cu exhibits a low conversion efficiency of NO3- to NH3, the incorporation of appropriate amounts of Co into Cu3P / Cu can effectively modulate the adsorption strength of key intermediates, optimize deoxygenation and hydrogenation kinetics, and thus significantly improve NO3RR performance.

[0081] 7) Co was evaluated over 10 consecutive reuse cycles. 0.05 - The reusability and stability of Cu3P / Cu catalysts.

[0082] Figure 24 For Co 0.05 Nitrate conversion (CE), ammonia faradaic efficiency (NH3FE), and ammonia yield (NH3 yield) for a 10-cycle NO3RR process of Cu3P / Cu.

[0083] like Figure 24As shown, the conversion efficiency of NO3- remained stable in the range of 75.9-80.4%. Furthermore, the NH3 yield (32.4-38.7 mg h⁻¹) remained relatively stable. -1 cm -1 It also exhibited excellent stability in terms of ) and NH3 FE (81.0-89.2%). Figure 24 ).

[0084] 8) Figure 25 For Co 0.05 SEM (a) and HRTEM (b) images and XRD spectra (c) after Cu3P / Cu cycling reaction; Figure 25 The results showed that its morphology or crystal structure did not change significantly compared to the fresh catalyst. These findings collectively confirm the presence of Co. 0.05 The high stability of the Cu3P / Cu catalyst, which exhibits excellent NO3RR performance, provides a green and sustainable strategy for the resource utilization of nitrate-containing wastewater.

[0085] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-modified hierarchical heterostructure catalyst, characterized in that, Includes the following steps: The substrate was subjected to a first electrodeposition in a copper-containing source solution to obtain a copper deposit. The copper deposit was subjected to a second electrodeposition in a cobalt-containing source solution to obtain a cobalt-copper deposit. The cobalt-copper deposit was calcined in air to obtain Co-CuO; The Co-CuO was phosphated under phosphorus source conditions to obtain the phosphated product; Under constant current conditions, the phosphating product was electrochemically reduced in an alkaline solution to obtain a cobalt-modified multi-level heterostructure catalyst.

2. The preparation method according to claim 1, characterized in that, The copper source solution contains copper sulfate as the copper source; the copper source solution also contains sulfuric acid and sodium chloride; the molar ratio of sulfuric acid to copper source in the copper source solution is 1:0.1 to 1:1; the molar ratio of copper source to sodium chloride is 10:1 to 5:

2.

3. The preparation method according to claim 1 or 2, characterized in that, The current density of the first electrodeposition is 50~100 mA / cm². 2 The deposition time is 30~120 min.

4. The preparation method according to claim 1, characterized in that, The cobalt source solution includes cobalt sulfate as the cobalt source; the cobalt source solution also includes sodium chloride; the molar ratio of cobalt source to sodium chloride in the cobalt source solution is 1:

1.

5. The preparation method according to claim 1 or 4, characterized in that, The current density of the second electrodeposition is 10~50 mA / cm². 2 The deposition time is 30-90 minutes; The calcination temperature is 300℃ and the time is 4~8h.

6. The preparation method according to claim 1, characterized in that, The phosphorus source includes NaH2PO2; the phosphating conditions include: a nitrogen atmosphere and a temperature of 300-350°C. o C, the time is 2 hours.

7. The preparation method according to claim 1, characterized in that, The alkaline solution used includes sodium carbonate; the concentration of the alkaline solution is 1.5 mol / L; the current density of the electrochemical reduction is 100 mA / cm². 2 Time ≥ 2 hours.

8. The cobalt-modified hierarchical heterostructure catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that, It includes a Cu3P / Cu support and Co loaded on the Cu3P / Cu support, forming a Co-Cu3P interface, and has a multi-level heterostructure.

9. The cobalt-modified hierarchical heterostructure catalyst according to claim 8, characterized in that, In the cobalt-modified hierarchical heterostructure catalyst, the Co loading is 0.02~0.1 wt%.

10. The application of the cobalt-modified hierarchical heterostructure catalyst according to claim 8 or 9 in the electrocatalytic nitrate reduction reaction.

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