Preparation method and application of copper-nickel double-atom modified MXene-based electrocatalyst

Abstract

The invention relates to a preparation method and application of a copper-nickel double-atom modified MXene-based electrocatalyst. According to the method, CuNiDA / MXene is obtained through acid leaching of CuNi / MXene with hydrochloric acid, copper-nickel diatoms with low metal loading capacity are obtained, and residual copper-nickel alloy nanoparticles in the molten salt etching process are successfully converted into the copper-nickel diatoms to be loaded on an MXene substrate in situ; the obtained copper-nickel diatom modified MXene-based electrocatalyst has copper-nickel diatoms coordinated by oxygen functional groups, so that the adsorption of reaction intermediates is enhanced, and the electrocatalytic performance is further improved. The prepared electrocatalyst shows the ammonia yield as high as 59225 [mu] g h <-1 > mg CuNi atom <-1 > and the Faraday efficiency as high as 94.8% in a reaction system for reducing nitrite into ammonia, and has the industrial prospect of green and sustainable synthesis of ammonia.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic ammonia synthesis catalysts, and specifically relates to a copper-nickel diatom-modified MXene-based electrocatalyst and a preparation method thereof. Background Art

[0002] Ammonia is a high-value chemical widely used in industries such as chemical, agriculture and energy. In addition, due to its easy transportation, zero carbon emissions and high energy density, ammonia has become a promising clean energy carrier with great application potential. At present, the large-scale production of ammonia mainly relies on the energy-intensive Haber-Bosch process, which is accompanied by large amounts of carbon dioxide emissions and considerable energy consumption. Considering global warming, there is an urgent need to develop an environmentally friendly green ammonia synthesis technology. In recent years, electrocatalytic synthesis of ammonia powered by renewable energy and using water and nitrogen-containing substances as proton sources and nitrogen sources has shown great application potential. As a pollutant widely present in nature, nitrite has a low reduction potential, an easily breakable N=O bond (204kJmol -1 ) and high solubility in water. Therefore, electrocatalytic reduction of nitrite to synthesize ammonia is not only beneficial to the removal of nitrogen-containing pollutants, but also enables the sustainable synthesis of green ammonia.

[0003] As the core of the electrocatalytic nitrite reduction reaction, the design of the electrocatalyst directly determines the yield and Faradaic efficiency of ammonia synthesis. Currently, relevant technologies for preparing electrocatalysts for electrocatalytic reduction of nitrite to ammonia have been reported. Patent CN120291121A discloses a copper-modified wheel-shaped tungstophosphate electrocatalyst for electrocatalytic reduction of nitrite to ammonia synthesis. Although the Faradaic efficiency of its ammonia synthesis reaches 92.42%, due to the lack of active sites caused by the single metal modification, the ammonia yield is only 3617.6μg h -1 mg cat -1 , which is far from meeting the demand for industrial ammonia synthesis. Patent CN119461329A discloses a carbon-coated cobalt phosphide-loaded carbon nitride electrocatalyst for electrocatalytic reduction of nitrite to synthesize ammonia. Although the ammonia yield is increased to 6700.89 μg h -1 cm -2 However, since the ammonia yield is still less than 10,000 μg, there is still a large gap between the requirements for large-scale ammonia production.

[0004] Therefore, designing and preparing an electrocatalyst with both high ammonia yield and high Faradaic efficiency with industrial prospects is of great significance for environmentally friendly large-scale ammonia synthesis. Summary of the Invention

[0005] The purpose of the present invention is to address the limitations of current technologies and to provide a method for preparing and applying a MXene-based electrocatalyst modified with copper-nickel diatoms. This method avoids the use of traditional hazardous fluorine-containing etching reagents through a molten salt etching strategy, and then obtains CuNiDA / MXene by acid leaching CuNi / MXene with hydrochloric acid, thereby obtaining copper-nickel diatoms with a low metal loading. The copper-nickel alloy nanoparticles remaining during the molten salt etching process are successfully converted into copper-nickel diatoms and in situ loaded on the MXene substrate; the obtained copper-nickel diatom-modified MXene-based electrocatalyst has copper-nickel diatoms coordinated by oxygen functional groups, wherein the introduction of nickel single atoms causes the d-band center of the copper single atom to shift toward the Fermi level, thereby enhancing the adsorption of reaction intermediates and further improving the electrocatalytic performance. The electrocatalyst prepared by the present invention exhibits an energy conversion rate of up to 59225 μg h in the reaction system of nitrite reduction to ammonia. -1 mg CuNi atom％ -1 The ammonia yield and Faradaic efficiency of 94.8% achieve both high ammonia yield and high Faradaic efficiency at a low non-precious metal loading, and have the industrial prospect of green and sustainable ammonia synthesis.

[0006] The technical solution of the present invention is:

[0007] A method for preparing a copper-nickel diatom-modified MXene-based electrocatalyst, the method comprising the following steps:

[0008] (1) Ti3AlC2 MAX powder, copper chloride dihydrate, nickel chloride hexahydrate, sodium chloride, and potassium chloride were mixed in an agate mortar and placed in an argon-filled glove box and ground for 15–20 min.

[0009] The molar ratio of Ti3AlC2 MAX powder, copper chloride dihydrate, nickel chloride hexahydrate, sodium chloride and potassium chloride is 1:1.5-2:1.5-2:2-4:2-4;

[0010] (2) The ground mixture was transferred to a corundum boat and placed in a tube furnace. The temperature was raised to 700-800°C under argon protection and maintained for 24-28 hours before being cooled naturally.

[0011] (3) washing the cooled powder with deionized water 3 to 5 times and then freeze-drying it for 18 to 24 hours to obtain a CuNi / MXene catalyst;

[0012] (4) placing the CuNi / MXene catalyst in hydrochloric acid and stirring for 24 to 28 hours to remove unstable copper-nickel nanoparticles;

[0013] (5) The acid-leached powder was washed with deionized water for 6 to 8 times and then freeze-dried for 18 to 24 hours to obtain a CuNiDA / MXene catalyst, i.e., a copper-nickel diatom-modified MXene-based electrocatalyst.

[0014] The heating rate in step (2) is 4 to 6°C / min.

[0015] The concentration of hydrochloric acid in step (4) is 2M to 5M.

[0016] The invention relates to an application method of the copper-nickel diatom-modified MXene-based electrocatalyst prepared by the method, which is characterized in that the electrocatalytic reduction of nitrite to synthesize ammonia is used.

[0017] Specifically, the steps include: electrolyzing the electrolyte for 1 to 2 hours using a constant voltage method in a three-electrode system to obtain ammonia;

[0018] In the three-electrode system, carbon paper loaded with a MXene-based electrocatalyst modified with copper and nickel diatoms, Ag / AgCl, and a platinum sheet served as the working electrode, reference electrode, and counter electrode, respectively. The electrolytic cell was an H-type electrolytic cell with a Nafion 117 membrane as the diaphragm. The electrolyte consisted of a 0.1-0.5 M K2SO4 solution containing 0.1-0.5 M KNO2.

[0019] In the working electrode, 0.5 to 1 mg of catalyst is loaded per 1 square centimeter of carbon paper;

[0020] The voltage range of electrolysis is -0.2V to -0.7V.

[0021] The essential features of the present invention are:

[0022] The present invention constructs a copper-nickel diatomic structure coordinated by oxygen functional groups and loaded onto MXene, wherein the introduction of nickel single atoms shifts the d-band center of the copper single atom toward the Fermi level, thereby enhancing the adsorption of reaction intermediates and further improving the electrocatalytic performance.

[0023] The researchers first thoroughly ground several different chemical powders together to form a uniform molten salt during the second high-temperature annealing step, which improves the etching effect. At the same time, sodium chloride and potassium chloride provide a molten salt environment and help lower the melting point of the overall molten reaction, resulting in better etching results. The molten salt etching strategy then avoids the use of traditional hazardous fluorine-containing etching reagents (such as hydrofluoric acid), greatly improving experimental safety. During the molten salt etching process, due to the favorable Gibbs free energy and redox potential differences, the copper and nickel ions in copper chloride dihydrate and nickel chloride hexahydrate oxidize the aluminum atoms in the MAX phase to volatile aluminum chloride. The copper and nickel ions are then reduced together to form copper-nickel alloy nanoparticles that are in situ loaded on the MXene. Then, the copper-nickel alloy nanoparticles were etched into copper-nickel diatoms through a simple hydrochloric acid leaching strategy, thereby obtaining a copper-nickel diatom-modified MXene-based electrocatalyst (CuNiDA / MXene); due to the introduction of nickel single atoms, the d-band center of the copper single atom shifted toward the Fermi level, thereby enhancing the adsorption of reaction intermediates in the electrocatalytic ammonia synthesis process, further improving the ammonia yield and Faraday efficiency.

[0024] The present invention has the following beneficial effects:

[0025] 1. The electrocatalyst preparation of the present invention can successfully etch the MAX phase into MXene through a molten salt etching strategy without the use of traditional hazardous fluorine-containing etching reagents.

[0026] 2. The present invention cleverly etches the copper-nickel alloy nanoparticles left over from the molten salt etching strategy into copper-nickel diatoms through a simple acid leaching strategy. The introduction of nickel single atoms shifts the d-band center of the copper single atom toward the Fermi level, thereby enhancing the adsorption of reaction intermediates. This not only greatly improves the yield of electrocatalytic ammonia synthesis, but also improves the Faraday efficiency.

[0027] 3. Since both copper and nickel are non-precious metals and the metal loading of copper-nickel diatoms is extremely low, this effectively reduces the preparation cost of the catalyst, thus showing good industrial prospects.

[0028] 4. The introduction of nickel atoms can effectively adjust the electronic structure of copper atoms, causing the d-band center of copper atoms to shift toward the Fermi level, thereby enhancing the adsorption of reaction intermediates in the electrocatalytic synthesis of ammonia. Generally speaking, the initial adsorption step in the electrocatalytic synthesis of ammonia determines the reaction rate. Compared with the copper single atom modified MXene-based electrocatalyst (CuSA / MXene), CuNiDA / MXene has a higher adsorption rate in the initial adsorption step (NO2 -+* → *The Gibbs free energy in NO2) decreases from -1.1eV to -2.11eV, which indicates that the introduction of nickel atoms effectively enhances the adsorption of copper atoms on nitrite. On the other hand, CuNiDA / MXene has a significant effect on the rate-determining step ( * NH+H2O→ * NH2+OH - ) is 0.16 eV, which is significantly lower than 0.33 eV of CuSA / MXene. This further illustrates that the introduction of nickel atoms effectively enhances the adsorption capacity of copper atoms, thereby improving the performance of electrocatalytic ammonia synthesis.

[0029] 5. Thanks to the enhanced adsorption of copper atoms on reaction intermediates induced by the introduction of nickel atoms, the copper-nickel double-atom modified MXene-based electrocatalyst also showed an extremely high ammonia yield (59225 μg h) in the electrocatalytic nitrite reduction reaction. -1 mg CuNiatom％ -1 ) and a satisfactory Faradaic efficiency (94.8%). The ammonia yield of the copper-nickel diatomic modified MXene-based electrocatalyst prepared by the present invention is close to 60 mg h -1 mg CuNi atom％ -1 , and the Faradaic efficiency is close to 95%, which can simultaneously achieve high ammonia yield and high Faradaic efficiency, which provides inspiration and direction for the preparation of ammonia synthesis electrocatalysts with low metal loading, high activity and high selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a scanning electron microscope image of the electrocatalyst prepared in Example 1.

[0031] Figure 2 This is a transmission electron microscope image of the electrocatalyst prepared in Example 1.

[0032] Figure 3 These are the X-ray diffraction patterns of the electrocatalysts prepared in Examples 1, 2, and 3.

[0033] Figure 4 The X-ray photoelectron spectra of the electrocatalysts prepared in Examples 1, 2, and 3 are shown in FIG. Figure 4 a is the high-resolution C1s XPS spectrum, Figure 4 b is the high-resolution Ti 2p XPS spectrum, Figure 4 c is the high-resolution Cu 2p XPS spectrum; Figure 4 d is the high-resolution Ni 2p XPS spectrum;

[0034] Figure 5is the Tafel slope of the electrocatalysts prepared in Examples 1, 2, and 3.

[0035] Figure 6 Electrochemical impedance spectroscopy of the electrocatalysts prepared in Examples 1, 2, and 3.

[0036] Figure 7 Linear sweep voltammetry curves of the electrocatalysts prepared in Examples 1, 2, and 3 in electrolyte.

[0037] Figure 8 The yield of ammonia synthesis of the electrocatalysts prepared in Examples 1, 2, and 3.

[0038] Figure 9 The Faradaic efficiency of ammonia synthesis of the electrocatalysts prepared in Examples 1, 2, and 3. DETAILED DESCRIPTION

[0039] The following is a complete and clear description of the specific implementation steps of the present invention and the accompanying drawings. It is necessary to point out that the specific implementation of the present invention is not limited to these descriptions. For those skilled in the art to which the present invention belongs, other embodiments or inferences obtained without making innovative contributions should be considered to fall within the scope of protection of the present invention.

[0040] The Ti3AlC2 MAX (titanium aluminum carbide) described in the present invention is a well-known material and is commercially available. The present invention uses the product of Jilin Province - Technology Co., Ltd., but is not limited thereto.

[0041] Example 1:

[0042] The specific preparation method of the copper-nickel diatomic modified MXene-based electrocatalyst is as follows:

[0043] (1) 1 mol of Ti3AlC2 MAX powder, 1.5 mol of copper chloride dihydrate, 1.5 mol of nickel chloride hexahydrate, 2 mol of sodium chloride, and 2 mol of potassium chloride were mixed and placed in a glove box filled with argon atmosphere and ground in an agate mortar for 15 min.

[0044] (2) The above mixture was transferred into a covered corundum boat and placed into a tube furnace. The mixture was heated at 4 °C min under argon protection. -1 The temperature was raised to 750 °C at a heating rate and kept at that temperature for 24 hours before being cooled naturally.

[0045] (3) After cooling, the obtained powder was washed three times with deionized water and freeze-dried for 24 hours to obtain the CuNi / MXene catalyst.

[0046] (4) The prepared CuNi / MXene catalyst was added to a 2 M HCl solution and stirred for 24 h to remove unstable CuNi nanoparticles.

[0047] (5) The acid-leached mixture was washed with deionized water until neutral and then freeze-dried for 24 hours to obtain the CuNiDA / MXene catalyst.

[0048] The morphology of CuNiDA / MXene catalyst was observed using scanning electron microscopy (SEM). Figure 1 As shown, the Ti3AlC2 MAX precursor was successfully etched into an accordion shape under the action of CuCl2 and NiCl2 molten salts and no CuNi alloy particles were observed on the surface and between the layers of MXene, which indicates the successful preparation of MXene and the atomic-level dispersion of copper and nickel.

[0049] The morphology and structure of CuNiDA / MXene catalyst were analyzed using transmission electron microscopy (TEM). Figure 2 As shown, the CuNiDA / MXene catalyst displays a layered structure of multilayer nanosheets, and no lattice of any metal nanoparticles is observed, further demonstrating the complete removal of CuNi and gold nanoparticles.

[0050] The phase composition and crystal structure of CuNiDA / MXene were characterized by X-ray diffraction (XRD). Figure 3 Only characteristic peaks at 7.9° and 16.1° are observed, which are attributed to the (002) and (004) crystal planes of Ti3C2 MXene, respectively, indicating that the Al layer in Ti3AlC2 MAX was successfully etched and the MXene was successfully prepared. In addition, no characteristic peaks related to metal nanoparticles were observed, indicating that copper and nickel are atomically dispersed on the MXene substrate.

[0051] The surface bonding information and chemical state of CuNiDA / MXene catalyst were analyzed by X-ray photoelectron spectroscopy (XPS). Figure 4 As shown in a, the presence of C-Ti bond (281.6 eV) was observed in the high-resolution C1s XPS spectrum. Figure 4 As shown in b, in the high-resolution Ti 2p XPS spectrum, the peaks observed can be deconvoluted into Ti-C(I) bonds (454.7 / 460.4eV), Ti-C(II) bonds (455.5 / 461.2eV), Ti-Cl bonds (456.6 / 462.8eV) and Ti-O bonds (458.1 / 464.0eV). Among them, the appearance of Ti-C(I) bonds and Ti-C(II) bonds indicates the successful preparation of MXene. At the same time, the characteristic peaks of Ti-O bonds and Ti-Cl bonds indicate that the functional groups of MXene contain O and Cl groups, which come from oxidation during the washing process and molten salt etching process, respectively. Figure 4As shown in c, the high-resolution Cu 2p XPS spectra of CuNiDA / MXene can be fitted with Cu 0 / 1+ and Cu 2+ Characteristic peak. Compared with CuSA / MXene, the Cu 2p binding energy of CuNiDA / MXene shifts to a lower binding energy by 0.18 eV. Interestingly, the opposite pattern is observed in the high-resolution Ni 2p XPS spectra of NiSA / MXene and CuNiDA / MXene. Figure 4 As shown in Figure d, the Ni 2p binding energy of CuNiDA / MXene shifts toward higher binding energies by 0.17 eV compared to NiSA / MXene. These results indicate that electron rearrangement occurs between Cu and Ni, with Cu receiving electrons donated by Ni. Notably, CuNiDA / MXene exhibits no intrinsic metal valence (zero valence), further demonstrating the effective removal of metal nanoparticles by the acid etching strategy and the atomic-level dispersion of metal sites.

[0052] The reaction kinetics of CuNiDA / MXene was evaluated using the Tafel slope. Figure 5 As shown in Figure 3, the Tafel slope of CuNiDA / MXene is only 47.3 mV / dec, which indicates that CuNiDA / MXene has faster reaction kinetics for nitrite reduction.

[0053] The electrochemical resistance of CuNiDA / MXene was tested using electrochemical impedance spectroscopy. Figure 6 As shown in the figure, CuNiDA / MXene exhibits a smaller semicircle diameter and a higher straight line slope in the high-frequency and low-frequency regions, which indicates that the copper-nickel diatoms reduce the charge transfer resistance and promote ion diffusion.

[0054] The electrocatalytic ammonia synthesis performance of CuNiDA / MXene was studied by linear sweep voltammetry. Figure 7 As shown in Figure 2, CuNiDA / MXene exhibited the highest current density (52.3 mA cm -2 ), which indicates that CuNiDA / MXene has excellent ability to electrocatalyze nitrite reduction to synthesize ammonia.

[0055] The specific steps include: (1) using a three-electrode system to conduct an electrochemical experiment on the electrocatalytic reduction of nitrite to synthesize ammonia on a Shanghai Chenhua CHI-760E electrochemical workstation, in which an area of ​​1 cm 2The carbon paper-supported catalyst, Ag / AgCl, and platinum sheet were used as the working electrode, reference electrode, and counter electrode, respectively. (2) The electrolysis test was carried out in an H-type electrolytic cell separated by a Nafion 117 membrane, which contained an electrolyte of 0.1M KNO2 and 0.5M K2SO4. The Nafion 117 membrane was pretreated by first treating it in a 5wt% H2O2 solution at 80°C for 1 hour and soaking it in deionized water for 30 minutes, and then soaking it in H2SO4 at 80°C for 1 hour and soaking it in deionized water at 80°C for 30 minutes to treat the impurities that may exist on the Nafion 117 membrane. (3) The preparation steps of the working electrode are as follows: 10 mg of the catalyst was dispersed in a mixed solution (50 μL Nafion solution + 0.45 mL deionized water + 0.45 mL anhydrous ethanol) and ultrasonically treated for half an hour to form a uniform catalyst ink. 50 μL of the catalyst ink was dropped on a 1 cm 2 on carbon paper and allowed to dry naturally. (4) All electrolysis potentials involved in this work are reversible hydrogen electrode (RHE) potentials, and the conversion formula is E(RHE) = E(Ag / AgCl) + 0.059 × pH + 0.197. (5) The electrocatalyst was subjected to a chronoamperometric test for 1 hour at different electrolysis potentials, and the electrolysis potential range was -0.2V to -0.7V. (6) After the chronoamperometric test, 2 mL of electrolyte was taken out and the ammonia synthesized by the electrocatalyst was qualitatively and quantitatively analyzed by UV spectrophotometer.

[0056] The amount of ammonia synthesis in the electrolyte after CuNiDA / MXene was electrolyzed under the chronoamperometry was detected using an ultraviolet spectrophotometer. Figure 8 As shown in Figure 2, the ammonia yield of CuNiDA / MXene reached 59225 μgh at an applied voltage of -0.6 V. -1 mg CuNiatom％ -1 , which has the potential for application in large-scale synthesis of ammonia. Figure 8 The CuNiDA / MXene, CuSA / MXene and NiSA / MXene involved in the test were all tested using a three-electrode system on a CHI-760E electrochemical workstation. The three-electrode system is based on an area of ​​1 cm 2 Carbon paper-supported catalyst, Ag / AgCl, and platinum sheet served as the working electrode, reference electrode, and counter electrode, respectively. Chronoamperometry was used for electrolysis testing. The applied voltage range was -0.2 V to -0.7 V (constant voltage). The electrolyte consisted of 0.1 M KNO₂ and 0.5 M K₂SO₄. Ammonia yield after electrolysis was measured using a UV spectrophotometer.

[0057] The corresponding Faradaic efficiency was calculated using the ammonia yields obtained by CuNiDA / MXene at different voltages. Figure 9 As shown, the Faradaic efficiency of CuNiDA / MXene in the voltage range of electrolysis is almost maintained above 80% and the Faradaic efficiency at an applied voltage of -0.4 V is as high as 94.8%, which proves that the electronic regulation of copper-nickel diatoms effectively improves the selectivity of the electrocatalytic nitrite reduction reaction.

[0058] Example 2

[0059] The other steps are the same as those in Example 1, except that nickel chloride hexahydrate is not added in step (1) of Example 1, and the obtained sample is a copper single atom-modified MXene-based electrocatalyst load (CuSA / MXene);

[0060] The phase composition and crystal structure of CuSA / MXene were characterized by X-ray diffraction (XRD). Figure 3 Only characteristic peaks at 7.9° and 16.1° are observed, which are attributed to the (002) and (004) crystal planes of Ti3C2 MXene, respectively, indicating that the Al layer in Ti3AlC2 MAX was successfully etched and the MXene was successfully prepared. In addition, no characteristic peaks related to metal nanoparticles were observed, indicating that copper is atomically dispersed on the MXene substrate.

[0061] The surface bonding information and chemical state of CuSA / MXene catalyst were analyzed by X-ray photoelectron spectroscopy (XPS). Figure 4 As shown in a, the presence of C-Ti bond (281.6 eV) was observed in the high-resolution C1s XPS spectrum. Figure 4 As shown in b, in the high-resolution Ti 2p XPS spectrum, the peaks observed can be deconvoluted into Ti-C(I) bonds (454.7 / 460.4eV), Ti-C(II) bonds (455.5 / 461.2eV), Ti-Cl bonds (456.6 / 462.8eV) and Ti-O bonds (458.1 / 464.0eV). Among them, the appearance of Ti-C(I) bonds and Ti-C(II) bonds indicates the successful preparation of MXene. At the same time, the characteristic peaks of Ti-O bonds and Ti-Cl bonds indicate that the functional groups of MXene contain O and Cl groups, which come from oxidation during the washing process and molten salt etching process, respectively. Figure 4 As shown in c, the high-resolution Cu 2p XPS spectra of CuSA / MXene can be fitted with Cu 0 / 1+ and Cu 2+It is noteworthy that CuSA / MXene does not exhibit the intrinsic valence state of the metal (zero valence), which further demonstrates the effective removal of metal nanoparticles by the acid etching strategy and the atomic-level dispersion of metal sites.

[0062] The reaction kinetics of CuSA / MXene was evaluated using the Tafel slope. Figure 5 As shown in Figure 3, CuSA / MXene exhibits a Tafel slope of 131.2 mV / dec, which indicates that the reaction kinetics of CuSA / MXene's electrocatalytic synthesis of ammonia is slow.

[0063] The electrochemical resistance of CuSA / MXene was tested using electrochemical impedance spectroscopy. Figure 6 As shown in the figure, CuSA / MXene exhibits the largest semicircle diameter and smaller straight line slope in the high-frequency and low-frequency regions, which indicates that the electrochemical impedance of copper single atoms is the highest, which is not conducive to electrochemical reactions.

[0064] The electrocatalytic ammonia synthesis performance of CuSA / MXene was studied by linear sweep voltammetry. Figure 7 As shown in Figure 2, CuSA / MXene exhibited the lowest current density (42.6 mA cm -2 ), which indicates that CuSA / MXene has a relatively poor ability to electrocatalyze nitrite reduction to synthesize ammonia.

[0065] The electrocatalytic performance of CuSA / MXene was analyzed by linear sweep voltammetry. Figure 7 As shown in the graph, the current density of CuSA / MXene at each potential is smaller than that of CuNiDA / MXene, indicating that the electrocatalytic activity of CuSA / MXene in the reduction of nitrate to ammonia is lower than that of CuNiDA / MXene.

[0066] The amount of ammonia synthesis in the electrolyte after CuSA / MXene electrolysis at different constant voltages was detected using an ultraviolet spectrophotometer. Figure 8 As shown in Figure 2, the ammonia yield of CuSA / MXene at an applied voltage of −0.6 V was 16059 μg h -1 mg Cu atom％ -1 .

[0067] The Faradaic efficiency was calculated using the ammonia yield of CuSA / MXene electrocatalyst at different voltages. Figure 9 As shown, the CuSA / MXene electrocatalyst exhibited a Faradaic efficiency of 50.6% at an applied voltage of −0.4 V.

[0068] The ammonia yield and Faradaic efficiency of CuSA / MXene were 16059 μg h -1 mg Cu atom％ -1 The adsorption of CuNiDA / MXene on the reaction intermediates during electrocatalytic ammonia synthesis is weak due to the lack of nickel single atoms, which hinders the rapid electrocatalytic nitrate reduction and thus reduces the performance of electrocatalytic ammonia synthesis.

[0069] Example 3

[0070] The other steps are the same as those in Example 1, except that copper chloride dihydrate is not added in step (1) of Example 1, and the obtained sample is a nickel single atom-modified MXene-based electrocatalyst load (NiSA / MXene);

[0071] The phase composition and crystal structure of NiSA / MXene were characterized by X-ray diffraction (XRD). Figure 3 Only characteristic peaks at 7.9° and 16.1° are observed, which are attributed to the (002) and (004) crystal planes of Ti3C2 MXene, respectively, indicating that the Al layer in Ti3AlC2 MAX was successfully etched and the MXene was successfully prepared. In addition, no characteristic peaks related to metal nanoparticles were observed, indicating that copper is atomically dispersed on the MXene substrate.

[0072] The surface bonding information and chemical state of NiSA / MXene catalyst were analyzed by X-ray photoelectron spectroscopy (XPS). Figure 4 As shown in a, the presence of C-Ti bond (281.6 eV) was observed in the high-resolution C1s XPS spectrum. Figure 4 As shown in b, in the high-resolution Ti 2p XPS spectrum, the peaks observed can be deconvoluted into Ti-C(I) bonds (454.7 / 460.4eV), Ti-C(II) bonds (455.5 / 461.2eV), Ti-Cl bonds (456.6 / 462.8eV) and Ti-O bonds (458.1 / 464.0eV). Among them, the appearance of Ti-C(I) bonds and Ti-C(II) bonds indicates the successful preparation of MXene. At the same time, the characteristic peaks of Ti-O bonds and Ti-Cl bonds indicate that the functional groups of MXene contain O and Cl groups, which come from oxidation during the washing process and molten salt etching process, respectively. Figure 4 As shown in d, the high-resolution Ni 2p XPS spectra of NiSA / MXene can be fitted to the Ni 2+It is noteworthy that NiSA / MXene does not exhibit the intrinsic valence state of the metal (zero valence), which further demonstrates the effective removal of metal nanoparticles by the acid etching strategy and the atomic-level dispersion of metal sites.

[0073] The reaction kinetics of NiSA / MXene was evaluated using the Tafel slope. Figure 5 As shown in Figure 3, NiSA / MXene exhibits a Tafel slope of 113.4 mV / dec, which indicates that the reaction kinetics of NiSA / MXene's electrocatalytic synthesis of ammonia is slow.

[0074] The electrochemical resistance of NiSA / MXene was tested using electrochemical impedance spectroscopy. Figure 6 As shown, NiSA / MXene exhibits a larger semicircle diameter and a smaller straight line slope in the high-frequency and low-frequency regions, which indicates that the electrochemical impedance of nickel single atoms is the highest, which is not conducive to electrochemical reactions.

[0075] The electrocatalytic ammonia synthesis performance of NiSA / MXene was studied by linear sweep voltammetry. Figure 7 As shown in Figure 2, NiSA / MXene exhibited a lower current density (49.2 mA cm -2 ), which indicates that NiSA / MXene has a relatively poor ability to electrocatalyze nitrite reduction to synthesize ammonia.

[0076] The electrocatalytic performance of NiSA / MXene was analyzed by linear sweep voltammetry. Figure 7 As shown in the graph, the current density of NiSA / MXene at each potential is smaller than that of CuNiDA / MXene, indicating that the electrocatalytic activity of NiSA / MXene in the reduction of nitrate to ammonia is lower than that of CuNiDA / MXene.

[0077] The amount of ammonia synthesis in the electrolyte after NiSA / MXene electrolysis at different constant voltages was detected using an ultraviolet spectrophotometer. Figure 8 As shown in Figure 2, the ammonia yield of NiSA / MXene at an applied voltage of −0.6 V was 28231 μg h -1 mg Ni atom％ -1 .

[0078] The Faradaic efficiency was calculated using the ammonia yield of NiSA / MXene electrocatalyst at different voltages. Figure 9 As shown, the NiSA / MXene electrocatalyst exhibited a Faradaic efficiency of 71.3% at an applied voltage of −0.4 V.

[0079] The ammonia yield and Faradaic efficiency of NiSA / MXene were 28231 μg h -1 mg Ni atom％ -1 The adsorption of nitrate in the CuNiDA / MXene layer is 71.3% and 71.3%, which are both lower than those of CuNiDA / MXene. Due to the lack of active sites (copper atoms) for the electrocatalytic nitrate reduction reaction, the energy barrier of the initial adsorption step of electrocatalytic ammonia synthesis is high, which reduces the reaction kinetics of electrocatalytic ammonia synthesis.

[0080] Example 4

[0081] The other steps are the same as those in Example 1, except that the annealing temperature in step (2) of Example 1 is replaced by 800°C from 750°C;

[0082] The obtained material properties are close;

[0083] Example 5

[0084] The other steps are the same as in Example 1, except that the heating rate in step (2) of Example 1 is increased from 4°C min -1 Replaced with 6℃min -1 ;

[0085] The obtained material properties are close;

[0086] Example 6

[0087] The other steps are the same as those in Example 1, except that the pyrolysis time in step (2) of Example 1 is replaced by 28 hours from 24 hours;

[0088] The obtained material properties are close;

[0089] In summary, the electrocatalyst prepared by the present invention has an extremely high ammonia yield and a satisfactory Faradaic efficiency. It not only has the application potential for large-scale ammonia synthesis, but also solves the challenge of the current electrocatalysts for ammonia synthesis that is difficult to achieve both high yield and high Faradaic efficiency. By introducing nickel single atoms, the electronic structure of copper single atoms can be effectively adjusted, causing the d-band center of copper single atoms to shift toward the Fermi level, thereby enhancing the adsorption of reaction intermediates by CuNiDA / MXene during the electrocatalytic ammonia synthesis process. Thanks to the electronic structure regulation effect between copper and nickel single atoms, CuNiDA / MXene exhibits an extremely high ammonia yield and a high Faradaic efficiency in the electrocatalytic nitrite reduction reaction, providing inspiration for the sustainable development and large-scale production of electrocatalytic ammonia synthesis.

[0090] The above content is only an example and explanation of the concept of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be considered as the scope of protection of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and equivalent changes made by using the technical content disclosed above, which are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

[0091] Matters not covered by the present invention are known technologies.

Claims

1. A method for preparing a copper-nickel diatomic modified MXene-based electrocatalyst, characterized by: The method comprises the following steps: (1) Ti3AlC2 MAX powder, copper chloride dihydrate, nickel chloride hexahydrate, sodium chloride, and potassium chloride were mixed in an agate mortar and placed in an argon-filled glove box and ground for 15–20 min. The molar ratio of Ti3AlC2 MAX powder, copper chloride dihydrate, nickel chloride hexahydrate, sodium chloride and potassium chloride is 1:1.5-2:1.5-2:2-4:2-4; (2) The ground mixture was transferred to a corundum boat and placed in a tube furnace. The temperature was raised to 700-800°C under argon protection and maintained for 24-28 hours before being cooled naturally. (3) washing the cooled powder with water and freeze-drying it for 18 to 24 hours to obtain a CuNi / MXene catalyst; (4) placing the CuNi / MXene catalyst in hydrochloric acid and stirring for 24 to 28 hours; (5) The acid-leached powder was washed with water and then freeze-dried for 18 to 24 hours to obtain a CuNiDA / MXene catalyst, i.e., a copper-nickel diatom-modified MXene-based electrocatalyst.

2. The method for preparing a copper-nickel diatom-modified MXene-based electrocatalyst according to claim 1, wherein: The heating rate in step (2) is 4 to 6°C / min.

3. The method for preparing a copper-nickel diatom-modified MXene-based electrocatalyst according to claim 1, wherein: The concentration of hydrochloric acid in step (4) is 2M to 5M.

4. Use of the copper-nickel diatomic modified MXene-based electrocatalyst prepared by the method of claim 1, characterized in that: Used for electrocatalytic reduction of nitrite to synthesize ammonia.

5. The use according to claim 4, characterized in that The method comprises the following steps: electrolyzing an electrolyte for 1 to 2 hours using a constant voltage method in a three-electrode system to obtain ammonia; In the three-electrode system, carbon paper loaded with a MXene-based electrocatalyst modified with copper and nickel diatoms, Ag / AgCl, and a platinum sheet served as the working electrode, reference electrode, and counter electrode, respectively. The electrolytic cell was an H-type cell with a Nafion 117 membrane as the diaphragm. The electrolyte consisted of a 0.1-0.5M K2SO4 solution containing 0.1-0.5M KNO2. In the working electrode, 0.5 to 1 mg of catalyst is loaded per 1 square centimeter of carbon paper; The voltage range of electrolysis is -0.2V to -0.7V.

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