Ni monatomic zinc oxide catalyst and application thereof in electro-catalytic synthesis of urea

Abstract

The invention relates to a Ni monatomic doped zinc oxide electrocatalyst and application thereof in electrocatalytic synthesis of urea. Ni in the catalyst is anchored to ZnO crystal lattices in a monatomic form to form a Ni-O-Zn atomic-scale interface, Ni-Ni coordination does not exist, and the catalyst is prepared by adopting a hydrothermal method. The catalyst is loaded on a conductive substrate, CO2 and NO3 <-> are synergistically reduced in a CO2 saturated KHCO3 / KNO3 mixed electrolyte to generate urea, the urea yield is 41.38 mmol h <-1 > gcat <-1 > at-0.8 V (vs RHE), and the Faraday efficiency is 31.47%. Compared with Ni nano-particle loaded ZnO and non-doped ZnO, the catalyst has the advantages that the yield and selectivity of urea are remarkably improved, and the catalyst is suitable for efficiently synthesizing urea under mild conditions.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical catalysis and synthesis technology, specifically relating to a method for preparing a Ni single-atom doped zinc oxide electrocatalyst and its application in the synergistic electroreduction of carbon dioxide and nitrate to synthesize urea. Background Technology

[0002] Urea (CO(NH2)2) is one of the world's most produced and widely used nitrogen compounds. It is an important source of nitrogen fertilizer in agricultural production and a crucial raw material in the pharmaceutical, fine chemical, and energy chemical industries. Currently, the Bosch-Meiser process is commonly used in industry to produce urea. This process typically requires first synthesizing ammonia through the Haber-Bosch process, and then reacting the ammonia with carbon dioxide under high temperature and pressure conditions of approximately 150–200 °C and 150–250 bar to produce urea. This process is energy-intensive and involves large amounts of CO2 emissions, making it difficult to meet the requirements of "dual carbon targets" and green sustainable development.

[0003] Electrochemical synergistic reduction of CO2 and nitrogen-containing species (such as N2, NO2) - NO3 - Synthesizing urea (e.g., NO3) under ambient temperature and pressure conditions is considered a potential technological route to replace traditional high-temperature and high-pressure thermocatalytic processes. - It has a lower N=O bond energy and is more easily activated under mild conditions; meanwhile, NO3 - NO3 is widely present in industrial wastewater, agricultural runoff, and domestic sewage, with high concentrations and stable sources. - As a nitrogen source in the electrosynthesis of urea system, it has the dual significance of pollution control and resource utilization.

[0004] Theoretically, the *CO intermediate produced by the CO2 electroreduction reaction (CO2RR) is electrophilic, while NO3... - The *NH2 intermediate produced by the electroreduction reaction (NO3RR) is nucleophilic, and the two can undergo CN coupling at the electrode surface to generate urea. However, CO2RR and NO3RR have significant differences in thermodynamic barriers and kinetic pathways, making it difficult to match the formation rates of *CO and *NH2. The adsorption strength of *CO on many catalysts is uncontrollable, exhibiting either excessive adsorption leading to migration inhibition or insufficient adsorption resulting in inadequate surface coverage, thus limiting the CN coupling efficiency. Furthermore, NO3RR readily generates deeply reduced byproducts such as NH3, further reducing urea selectivity.

[0005] Currently used for CO2 and NO3 -Catalysts for the electrosynthesis of urea include noble metals and their alloys, transition metal oxides / nitrides, oxides enriched with oxygen vacancies, and single / dual-atom catalysts supported on carbon supports. For example, oxygen-vacancy-rich ZnO porous nanosheets can be used for the synthesis of CO2 and NO3. - To synthesize urea, Ru-doped CeO2 nanorods can achieve CO2 and NO3 reactions. - For efficient electrosynthesis of urea, Fe-Ni or Ni-Mo dual-atom-site catalysts significantly improve urea yield and Faradaic efficiency through bimetallic synergy. However, the above catalytic systems still have the following common problems: (1) The reaction kinetics of CO2RR and NO3RR are difficult to synchronize, and the intermediates *CO and *NH x The generation and enrichment of these elements are difficult to regulate in a coordinated manner. (2) The catalyst surface lacks precise control over the adsorption energy of CO, which often manifests as excessively strong or weak adsorption, limiting the migration of CO and coupling with CN. (3) The active sites of catalysts are mostly nanoparticles or randomly distributed metal sites, and the interface structure and electronic structure are difficult to design precisely. (4) NO3RR easily forms deep reduction byproducts such as NH3, resulting in low urea selectivity.

[0006] Therefore, it is necessary to develop a novel catalytic system with a well-defined atomic-level interface structure, and to simultaneously control the adsorption energy and surface migration behavior of intermediates in a single catalytic system to achieve CO2 and NO3 reactions. - The efficient synergistic reduction and CN bond construction enable efficient and green urea electrosynthesis under mild conditions. Summary of the Invention

[0007] Purpose of the invention The purpose of this invention is to provide a Ni single-atom doped zinc oxide electrocatalyst and its preparation method, and to apply this catalyst to CO2 and NO3. - The synergistic electroreduction synthesis of urea solves the problem of synergistic electroreduction of CO2 and NO3. - This study addresses the problems of intermediate formation mismatch, restricted CO adsorption and migration, and low CN coupling efficiency in urea preparation, and achieves efficient and highly selective synthesis of urea under mild conditions.

[0008] Technical solution To achieve the above-mentioned objectives, the present invention adopts the following technical solution.

[0009] 1) A Ni single-atom-doped zinc oxide electrocatalyst is provided, the electrocatalyst comprising a ZnO support and Ni single-atom active sites dispersed on the ZnO support; the Ni single atoms form a Ni-O-Zn atomic-level interface structure with Zn atoms through O atoms, and the catalyst does not contain a Ni-Ni coordination structure. Preferably, Ni is in the form of Ni... 2+ The valence state exists, and its coordination environment is mainly Ni-O and Ni-O-Zn. The mass fraction of Ni in the electrocatalyst is 0.1–5.0 wt%, preferably 0.5–2.0 wt%, and more preferably about 1.47 wt%. The ZnO support has a wurtzite crystal phase, exhibiting a regular hexagonal prismatic or nanorod morphology, with a specific surface area of ​​10–50 m². 2 / g, preferably about 21.7 m 2 / g.

[0010] (2) A method for preparing the above-mentioned electrocatalyst, comprising: A zinc source and a nickel source are dissolved in an alcohol solvent to form a homogeneous solution. An alkaline solution is added to the solution to obtain a precursor solution containing Zn and Ni. The precursor solution is subjected to a hydrothermal reaction to allow Ni to be incorporated into the ZnO lattice, forming a Ni-O-Zn atomic interface structure. The reaction product is washed and dried to obtain a Ni-doped zinc oxide catalyst. The zinc source is preferably zinc acetate, the nickel source is preferably nickel acetate, the alcohol solvent is preferably ethanol, and the alkaline solution is preferably an aqueous KOH solution. The hydrothermal reaction temperature is 120–200 °C, and the reaction time is 6–24 h. The Ni loading can be controlled within the above range by adjusting the ratio of zinc to nickel sources, the hydrothermal reaction temperature, and the reaction time. The preferred molar ratio of zinc to nickel sources is 100:1 to 5:1. The drying step is carried out at 40–120 °C for 6–24 h; optionally, the obtained electrocatalyst is annealed at 200–500 °C in an inert or reducing atmosphere to further adjust the crystallinity and defect concentration of the material.

[0011] (3) Provides a method for synergistic reduction of CO2 and NO3 under electrochemical conditions using the above-mentioned Ni single-atom doped zinc oxide electrocatalyst. - Methods for synthesizing urea include: The catalyst was supported on a conductive substrate as the cathode working electrode, with an Ag / AgCl electrode as the reference electrode and an inert metal electrode as the counter electrode, to construct a three-electrode electrolysis system; a CO2-saturated KHCO3 / NO3-containing electrolyte was used. - A mixed electrolyte is used as the cathode electrolyte, and constant potential electrolysis is performed at a specific potential. The urea yield and urea Faradaic efficiency are calculated by quantitatively analyzing the urea content in the cathode electrolyte. Preferably, the cathode electrolyte is a CO2-saturated KHCO3 solution mixed with NO3... -A mixed solution in which the concentration of KHCO3 is 0.05–1.0 mol / L and NO3 is... - The salt concentration is 0.01–1.0 mol / L; the electrolysis potential is -0.5–-1.0 V (relative to a reversible hydrogen electrode). The conductive substrate can be carbon paper, carbon cloth, glassy carbon electrode, or metal foam, and the catalyst loading is 0.1–5.0 mg / cm³. 2 .

[0012] Catalyst preparation method The present invention also provides a method for preparing the above-mentioned catalyst, comprising: The zinc and nickel sources are dissolved in an alcohol solvent to form a homogeneous solution; An alkaline solution was added to the solution to obtain a precursor solution containing Zn and Ni; The precursor solution is subjected to a hydrothermal reaction to induce Ni doping into the ZnO lattice and form a Ni-O-Zn atomic interface structure. The reaction products were washed and dried to obtain a Ni single-atom-doped zinc oxide catalyst.

[0013] Preferably, the zinc source is zinc acetate, the nickel source is nickel acetate, the alcohol solvent is ethanol, the alkaline solution is KOH aqueous solution, the hydrothermal reaction temperature is 120–200 °C, and the time is 6–24 h.

[0014] Electrocatalytic synthesis of urea This invention also provides a method for the synergistic reduction of CO2 and NO3 under electrochemical conditions using the above-mentioned Ni single-atom doped zinc oxide electrocatalyst. - Methods for synthesizing urea include: The catalyst is loaded onto a conductive substrate and used as the cathode working electrode; A three-electrode system was constructed using an Ag / AgCl electrode as the reference electrode and an inert metal as the counter electrode. Alkaline electrolytes saturated with CO2 and containing NO3 - The electrolyte mixture is used as the cathode electrolyte, and constant potential electrolysis is performed at a specific potential. The urea yield and Faraday efficiency were calculated by quantitatively analyzing the urea content produced in the electrolyte.

[0015] Preferably, the cathode electrolyte is a mixed solution of CO2-saturated 0.1 mol / L KHCO3 and 0.1 mol / L KNO3, with an electrolysis potential of -0.5 to -1.0 V (relative to the reversible hydrogen electrode).

[0016] Beneficial effects Compared with the prior art, the present invention has the following beneficial effects: (1) By anchoring Ni in the ZnO lattice in the form of single atoms, a stable Ni-O-Zn atomic interface is constructed, which realizes the fine control of the local electronic structure of Ni sites, enabling Ni sites to efficiently adsorb and activate CO2 to generate *CO, while giving *CO a moderate adsorption strength, thus achieving a balance between "stable existence" and "transferable reaction".

[0017] (2) The Ni-O-Zn interface structure enables CO to overflow from Ni sites to Zn sites, while NO3... - On the catalyst surface, reduction intermediates such as *NO2, *NO, *NH, and *NH2 are gradually generated through multiple electron transfer steps. *NH2 enriched at Zn-related sites and *CO that migrates to Zn sites undergo CN coupling at the interface to generate the *CONH2 intermediate, which is then further formed into urea, effectively improving CN coupling efficiency and urea selectivity.

[0018] (3) At a potential of -0.8 V (vs RHE), the Ni of the present invention SA ZnO catalyst used for CO2 and NO3 - During synergistic electroreduction, a urea yield of 41.38 mmol / h can be achieved. –1 g cat –1 The urea Faradaic efficiency is 31.47%. (Compared to Ni...) NP Compared to ZnO catalysts, Ni SA The urea yield of Ni / ZnO is approximately 1.9 times that of Ni, and the urea Faradaic efficiency is approximately 1.9 times that of Ni. SA The urea yield of / ZnO is approximately 2.3 times that of the former, and the urea Faradaic efficiency is approximately 2.6 times that of the latter. These results indicate that the Ni single-atom sites and the Ni-O-Zn interface structure have a significant synergistic regulatory effect on the formation and migration behavior of intermediates.

[0019] (4) The present invention uses a hydrothermal method to prepare the catalyst. The process conditions are mild and the steps are simple. The raw materials are readily available and easy to scale up. At the same time, the Ni single atom sites still maintain a stable coordination environment and crystal phase structure after long-term electrolysis and multiple cycles. The catalyst has good electrochemical stability and reusability, and is suitable for promotion and application in the field of electrochemical urea synthesis. Attached Figure Description

[0020] Figure 1 For Ni SA XRD pattern of ZnO catalyst; Figure 2 For Ni SA SEM image of the ZnO catalyst; Figure 3For Ni SA Elemental mapping diagram of ZnO catalyst; Figure 4 For Ni SA XPS plot of ZnO catalyst; Figure 5 For Ni SA XAFS diagram of Ni K-edge in ZnO catalyst; Figure 6 For Ni SA / ZnO、Ni NP / Yield variation curves of urea synthesis using ZnO and ZnO catalysts at different potentials; Figure 7 For Ni SA / ZnO、Ni NP / Faraday efficiency curves of ZnO and ZnO catalysts for urea synthesis at different potentials; Figure 8 Ni after cyclic electrolysis SA XPS plot of ZnO catalyst; Figure 9 Ni after cyclic electrolysis SA XRD pattern of ZnO catalyst. Detailed Implementation

[0021] The following embodiments are used to further illustrate the present invention, but do not constitute a limitation thereof. For those skilled in the art, any equivalent modifications or substitutions made without departing from the spirit and substance of the present invention should fall within the protection scope of the present invention.

[0022] Unless otherwise stated, all reagents and solvents used in the following examples are commercially available analytical grade or chemically pure, and experimental conditions are conducted at room temperature and normal pressure unless otherwise specified.

[0023] Example 1: Preparation of Ni single-atom doped ZnO catalyst 1. Preparation of precursor solution Weigh 0.877 g of zinc acetate and 0.0498 g of nickel acetate, add them to 40 mL of anhydrous ethanol, and stir magnetically for about 1 h at room temperature to obtain a clear and homogeneous solution.

[0024] 2. Add alkaline solution 40 mL of 0.1 mol / L KOH solution was gradually added dropwise to the above solution while stirring was maintained during the addition. After the addition was completed, stirring was continued for about 6 h to obtain a viscous precursor solution.

[0025] 3. Hydrothermal reaction The precursor solution was transferred to a stainless steel high-pressure reactor lined with polytetrafluoroethylene and reacted at 150 °C for 20 h. After the reaction was completed, the mixture was allowed to cool naturally to room temperature.

[0026] 4. Washing and drying The obtained solid product was separated by centrifugation and washed thoroughly three times each with deionized water and ethanol to remove residual impurities. The washed solid was then vacuum dried at 60 °C for 12 h to obtain a Ni single-atom doped ZnO catalyst, denoted as Ni. SA / ZnO.

[0027] 5. Structural Characterization XRD characterization results are as follows Figure 1 As shown, the product retains the typical ZnO wurtzite crystal phase, and no diffraction peaks of metallic Ni or NiO were observed. Figure 2 The SEM images show that the sample has a regular hexagonal columnar structure with a complete morphology; Figure 3 EDS elemental mapping shows that Ni is uniformly distributed on the ZnO support; Figure 4 XPS and Figure 5 XAFS characterization results show that Ni mainly exists as Ni 2+ The morphology exists, and no peaks related to Ni-Ni bonds appear in the spectrum. Only characteristic signals of Ni-O and Ni-O-Zn are observed, proving that a stable Ni-O-Zn atomic interface structure has been formed, and Ni is highly dispersed in the form of single atoms.

[0028] Ni SA Typical structural parameters of the / ZnO catalyst are listed in Table 1.

[0029] From Table 1 and Figures 1-5 It can be seen that the Ni obtained by this invention SA The Ni loading in the ZnO catalyst is moderate, the specific surface area is at a medium-to-high level, and the distances between Ni-O and Ni-Zn are within a reasonable range. This proves that Ni is anchored to the ZnO lattice in the form of single atoms, constructing a stable Ni-O-Zn atomic interface, which provides a structural basis for the fine control of the adsorption and migration of intermediates in subsequent electrochemical reactions.

[0030] Example 2: Ni SA Electrochemical performance testing of ZnO catalyst 1. Preparation of working electrode Weigh 2 mg Ni SAZnO powder was mixed with 950 μL of isopropanol and 50 μL of 5 wt% Nafion solution and ultrasonically dispersed for 30 min to obtain a uniform catalyst ink. 50 μL of this catalyst ink was drop-coated onto a 1 cm × 1.5 cm sheet of carbon paper and allowed to dry naturally to obtain a catalyst-supported electrode with a catalyst loading of approximately 0.1 mg / cm². 2 .

[0031] 2. Electrolytic cell and electrolyte An H-type electrolytic cell was used, with the anode and cathode chambers separated by a proton exchange membrane. The cathode electrolyte was a CO2-saturated mixed solution of 0.1 mol / L KHCO3 + 0.1 mol / L KNO3, with a total volume of 40 mL; the anolyte was a 0.1 mol / L KHCO3 + 0.1 mol / L KNO3 solution. Before electrolysis, CO2 was introduced into the cathode electrolyte at a rate of 30–50 mL / min for at least 30 min to ensure complete electrolyte saturation.

[0032] 3. Electrochemical testing conditions A three-electrode system was constructed on an electrochemical workstation, using Ni SA The ZnO-supported electrode is used as the working electrode, the Ag / AgCl (saturated KCl) electrode as the reference electrode, and the Pt sheet as the counter electrode. All potentials are converted to their values ​​relative to the reversible hydrogen electrode (RHE) using the following formula: First, a linear sweep voltammetry (LSV) test was performed in the potential range of 0 to -1.5 V (vs RHE) to determine the overall current response; then constant potential electrolysis was performed at selected potentials (such as -0.6 V, -0.8 V (vs RHE)) for 2 hours each time.

[0033] 4. Product Analysis and Performance Evaluation The concentration of urea in the cathode electrolyte was quantitatively analyzed using the diacetyl monooxime colorimetric method. Urea yield was calculated using the following formula: Urea yield Among them, C urea V is the urea concentration (mmol / L), V is the cathode electrolyte volume (L), and m is the urea concentration. cat t represents the mass of catalyst on the cathode electrode (g), and t represents the electrolysis time (h).

[0034] Urea Faraday efficiency FE urea Calculate using the following formula: Where n is CO2+NO3 -The number of electrons required for conversion to urea (16), F is the Faraday constant (96485 C mol). -1 Q represents the total amount of electricity (C) during the constant potential electrolysis process.

[0035] Under the same conditions, a Ni nanoparticle-supported ZnO catalyst (Ni NP The electrocatalytic performance of ZnO and undoped ZnO catalysts in synthesizing urea was compared. The performance of different catalysts at various potentials is listed in Table 2.

[0036] Table 2 Ni SA / ZnO、Ni NP Performance of ZnO and ZnO catalysts in urea synthesis at different potentials From Table 2 and Figure 6 , Figure 7 It can be seen that at a potential of -0.8 V (vs RHE), Ni SA The ZnO catalyst exhibited the highest yield and Faraday efficiency for urea production, significantly outperforming Ni. NP / ZnO and ZnO catalysts compared. Among them, Ni SA The urea yield of / ZnO is approximately 2.3 times that of ZnO, and the Faraday efficiency is approximately 2.6 times that of ZnO, indicating that Ni single-atom sites and the Ni-O-Zn atomic interface promote the reaction of CO2 and NO3. - It played a key role in the synergistic electroreduction synthesis of urea.

[0037] Example 3: Urea Source Control Experiment This embodiment is used to verify that the urea products in the system of the present invention originate from CO2 and NO3. - The reduction is synergistic with electroreduction, rather than originating from a single substrate or electrolyte impurities. Unless otherwise specified, the catalyst preparation method and electrode preparation method used in this embodiment are the same as in Examples 1 and 2.

[0038] 1. Electrolysis conditions settings The same H-type electrolytic cell and three-electrode system as in Example 2 were used: the working cathode electrode was Ni. SA The electrode was ZnO-supported, the reference electrode was Ag / AgCl (saturated KCl), and the counter electrode was a Pt sheet. The test temperature was (25±2)℃. Electrolysis was performed at a constant potential of -0.8 V (vs RHE) for 2 h under the following three different conditions: Condition A (complete system): The cathode electrolyte is a CO2-saturated mixed solution of 0.1 mol / L KHCO3 + 0.1 mol / L KNO3, with CO2 continuously introduced at a flow rate of 30 mL / min; Condition B (without NO3) - (CO2 only): The cathode electrolyte is a 0.1 mol / L KHCO3 solution saturated with CO2 (excluding NO3). - CO2 is continuously introduced at a flow rate of 30 mL / min; Condition C (No CO2, only NO3) - The cathode electrolyte is an Ar-saturated solution of 0.1 mol / L KHCO3 + 0.1 mol / L KNO3, with Ar continuously introduced at a flow rate of 30 mL / min.

[0039] 2. Product Analysis After electrolysis, 1 mL of the cathode electrolyte sample was taken, and the urea concentration was quantitatively analyzed using the diacetyl monooxime colorimetric method. Simultaneously, NH3 was detected using the indophenol blue method, and NO2 was detected using the Griess colorimetric method. - Other nitrogen-containing products. The calculation methods for urea yield and urea Faraday efficiency are the same as in Example 2.

[0040] 3. Results and Analysis Ni under different conditions SA The urea formation of the / ZnO catalyst is listed in Table 3.

[0041] Table 3 Ni under different substrate conditions SA Comparison of urea formation with ZnO catalyst As can be seen from Table 3, only when CO2 and NO3 are present simultaneously... - Under condition A, a significant concentration of urea can be detected in the cathode electrolyte; however, under conditions B and C, urea formation is almost undetectable, and the urea yield and FE... urea All values ​​are close to 0. The above results indicate that the urea in the system of this invention mainly originates from CO2 and NO3. - The synergistic electroreduction process effectively eliminates interference from single substrates or impurities.

[0042] Example 4: Ni SA Long-term stability and cycling performance of ZnO catalysts This embodiment is used to evaluate Ni. SA / ZnO catalyst in CO2 and NO3 - The stability of long-term electrolysis and multiple cycles during the synergistic electroreduction synthesis of urea. Unless otherwise specified, the catalyst preparation, electrode preparation, electrolytic cell structure, and electrolyte composition in this embodiment are the same as those in Example 2.

[0043] 1. Long-term constant potential electrolysis stability In a CO2-saturated 0.1 mol / L KHCO3 + 0.1 mol / L KNO3 mixed electrolyte, Ni SA The ZnO electrode was used as the cathode, and constant potential electrolysis was performed at a potential of -0.8 V (vs RHE) for a total electrolysis time of 10 h. The change in current density over time was recorded, and samples were taken at 2 h, 4 h, 6 h, 8 h, and 10 h of electrolysis to determine the urea yield and urea Faradaic efficiency in the cathode electrolyte.

[0044] Typical data for long-term electrolysis processes are listed in Table 4.

[0045] Table 4 Ni SA Stability of ZnO catalyst under long-term constant potential electrolysis As shown in Table 4, during the continuous constant potential electrolysis for 10 h, Ni SA The current density of the ZnO catalyst remains essentially at -16 mA cm⁻¹. -2 The urea yield and urea Faraday efficiency remained relatively stable throughout the test, with no significant degradation observed. These characteristics indicate that the catalyst exhibits good performance in the CO2 and NO3 reactions. - It exhibits good electrochemical stability and resistance to deactivation in the synergistic reduction system.

[0046] 2. Stability after multiple electrolysis cycles Under the same electrolysis conditions as in Example 4.1, the same Ni SA Multiple constant-potential electrolysis experiments were conducted using a ZnO-loaded electrode. Each electrolysis session lasted 2 hours. After each electrolysis cycle, the electrode surface was lightly rinsed with deionized water and ethanol, dried, and then the next electrolysis cycle was performed. The total number of cycles was 10. The urea yield and urea Faradaic efficiency were measured after each electrolysis cycle, and the corresponding current density was recorded. The results are listed in Table 5.

[0047] Table 5 Ni SA / ZnO catalyst multiple cycle electrolysis performance As shown in Table 5, in 10 consecutive electrolysis cycles, Ni SA The current density, urea yield, and urea Faradaic efficiency of the / ZnO catalyst remained relatively stable across cycles, with only slight fluctuations and no obvious decline trend, indicating that the catalyst has good cycle durability and reusability.

[0048] 3. Comparison of structures before and after stability assessment To further verify Ni SAThe structural stability of the / ZnO catalyst after long-term electrolysis and multiple cycles was assessed by XPS and XRD characterization of the catalyst before and after electrolysis. Figure 8 Ni after cyclic electrolysis SA XPS plot of ZnO catalyst Figure 9 Ni after cyclic electrolysis SA XRD pattern of ZnO catalyst.

[0049] Test results show that after long-term electrolysis and cyclic use, Ni SA The XRD pattern of the ZnO catalyst still shows the typical ZnO wurtzite crystal phase, with no new metallic Ni or NiO peaks appearing; the position and shape of the Ni 2p main peak in the XPS spectrum remain basically unchanged, and Ni still predominates as Ni. 2+ The presence of this morphology indicates that Ni single atoms remain stably anchored in the ZnO lattice, further corroborating the excellent structural stability of the catalyst of this invention.

[0050] Industrial applicability The catalyst preparation process of this invention uses only common raw materials such as zinc acetate, nickel acetate, and KOH, and can be completed through hydrothermal reaction at 120–200 °C and low-temperature drying. It is suitable for scale-up production in conventional stirred tanks and hydrothermal reactors. The electrolysis system uses water-soluble KHCO3 / KNO3 electrolyte and operates in the range of room temperature and -0.5 to -1.0 V (vs RHE). It does not require high temperature, high pressure, or precious metal electrodes, and is easy to couple with existing electrolysis equipment and renewable energy power sources, showing good prospects for industrial application.

Claims

1. A Ni single-atom-doped zinc oxide electrocatalyst, characterized in that: The electrocatalyst comprises a ZnO support and Ni single-atom active sites dispersed on the ZnO support; the Ni single atoms form a Ni-O-Zn atomic-level interface structure with Zn atoms through O atoms; and there is no Ni-Ni coordination structure in the electrocatalyst.

2. The electrocatalyst according to claim 1, characterized in that: The Ni single atom is Ni 2+ Valence states exist, and the coordination environment of Ni is mainly Ni-O and Ni-O-Zn.

3. The electrocatalyst according to claim 1 or 2, characterized in that: The electrocatalyst contains Ni with a mass fraction of 0.5–2.0 wt%, more preferably 1.47 wt%; the ZnO support has a wurtzite crystal phase, exhibiting a regular hexagonal prismatic or nanorod morphology, with a specific surface area of ​​10–50 m². 2 / g.

4. A method for preparing the electrocatalyst according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Dissolve the zinc source and nickel source in an alcohol solvent and stir to obtain a homogeneous solution; (2) Add an alkaline solution to the solution and continue stirring to obtain a precursor solution; (3) The precursor solution is subjected to a hydrothermal reaction to obtain a solid product; (4) The solid product is washed and dried to obtain Ni single-atom doped ZnO electrocatalyst.

5. The preparation method according to claim 4, characterized in that: The zinc source is zinc acetate, the nickel source is nickel acetate, the alcohol solvent is ethanol, and the alkaline solution is KOH aqueous solution; the hydrothermal reaction temperature is 120-200 °C, and the time is 6-24 h; the molar ratio of the zinc source to the nickel source is 100:1-5:

1.

6. The preparation method according to claim 4 or 5, characterized in that: The drying step is carried out at 40–120 °C for 6–24 h; and optionally, it further includes annealing the electrocatalyst at 200–500 °C in an inert or reducing atmosphere.

7. A method for synergistically reducing CO2 and NO3 under electrochemical conditions using the Ni single-atom doped zinc oxide electrocatalyst according to any one of claims 1 to 3. - The method for synthesizing urea is characterized by, include: The electrocatalyst was loaded onto a conductive substrate as the cathode working electrode to construct a three-electrode electrolysis system. Containing CO2 and NO3 - An aqueous solution was used as the cathode electrolyte, and constant potential electrolysis was performed under an applied negative potential. During electrolysis, CO2 and NO3... - A reduction reaction occurs simultaneously on the cathode surface to generate urea.

8. The method according to claim 7, characterized in that: The cathode electrolyte is a mixed solution composed of CO2-saturated KHCO3 and nitrate-containing electrolyte, wherein the concentration of KHCO3 is 0.05–1.0 mol / L and NO3- is... - The salt concentration is 0.01–1.0 mol / L; the applied potential is -0.5–-1.0 V (relative to the reversible hydrogen electrode).

9. The method according to claim 7 or 8, characterized in that: The conductive substrate is any one of carbon paper, carbon cloth, glassy carbon electrode, or metal foam; the electrocatalyst loading in the cathode working electrode is 0.1–5.0 mg / cm³. 2 .

10. The method according to any one of claims 7 to 9, characterized in that: At a potential of -0.8 V (relative to the reversible hydrogen electrode), the method achieves a urea Faradaic efficiency of not less than 30% and a urea yield of not less than 35 mmol / h based on catalyst mass. –1 g cat –1 .

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