阅读说明：本技术 磷、氧共掺杂的铜基催化剂及其制备方法和应用 (Phosphorus and oxygen co-doped copper-based catalyst and preparation method and application thereof ) 是由 杜沣 郭春显 谭子轩 姚智坤 于 2021-10-26 设计创作，主要内容包括：本发明公开了一种磷、氧共掺杂的铜基催化剂、其制备方法和其在电催化硝酸根还原合成氨中的应用。该制备方法以铜盐和亚磷酸盐的水溶液作为电解液,采用三电极体系进行恒电位电沉积反应,其中以泡沫镍片为工作电极,清洗并干燥后即得到均匀生长于所述泡沫镍片表面的磷、氧共掺杂的铜基催化剂。恒电位共沉积的方法能够使磷、氧均匀掺杂在铜基催化剂表面,杂原子的掺杂能够调节铜周围的电子结构,使其比纯铜催化剂具有更高的催化活性。且相比于金属掺杂的催化剂,磷、氧共掺杂的铜基催化剂成本低,经济效益高,适合产业化和商业化。(The invention discloses a phosphorus and oxygen co-doped copper-based catalyst, a preparation method thereof and application thereof in synthesizing ammonia by electrocatalysis nitrate reduction. The preparation method comprises the steps of taking an aqueous solution of copper salt and phosphite as an electrolyte, carrying out constant potential electrodeposition reaction by adopting a three-electrode system, cleaning and drying a foam nickel sheet serving as a working electrode to obtain the phosphorus and oxygen co-doped copper-based catalyst uniformly growing on the surface of the foam nickel sheet. The constant potential codeposition method can enable phosphorus and oxygen to be uniformly doped on the surface of the copper-based catalyst, and the doping of the heteroatom can adjust the electronic structure around the copper, so that the copper-based catalyst has higher catalytic activity than a pure copper catalyst. Compared with a metal-doped catalyst, the phosphorus-oxygen co-doped copper-based catalyst is low in cost and high in economic benefit, and is suitable for industrialization and commercialization.)

1. The preparation method of the phosphorus and oxygen co-doped copper-based catalyst is characterized by comprising the following steps of:

dissolving copper salt and phosphite with anions of oxygen-containing acid radicals in water to prepare electrolyte;

step two, carrying out constant potential electrodeposition reaction by adopting a three-electrode system, wherein the potential range is-1.6 to-1.8V, and the working electrode of the three-electrode system is a foamed nickel sheet;

and step three, after the reaction is finished, cleaning and drying the foam nickel sheet subjected to the constant potential electrodeposition reaction to obtain the phosphorus and oxygen co-doped copper-based catalyst growing on the surface of the foam nickel sheet.

2. The production method according to claim 1, wherein the copper salt whose anion is an oxo acid group is copper nitrate and/or copper sulfate.

3. The method according to claim 1, wherein the phosphite is sodium phosphite and/or potassium phosphite.

4. The method according to claim 1, wherein the molar ratio of copper ions to phosphite in the electrolyte is 1:0.8 to 1: 1.2.

5. The method according to claim 4, wherein the concentration of copper ions in the electrolyte is 0.08 to 0.13 mol/L.

6. The preparation method according to claim 1, wherein the time of the potentiostatic electrodeposition reaction is 100 to 700 seconds.

7. The preparation method according to claim 1, wherein the temperature in the drying process is 45-55 ℃ and the drying time is 6-9 h.

8. The preparation method according to claim 1, wherein in the second step, before the reaction is started, the method further comprises the step of pretreating the nickel foam sheet: and cleaning the foamed nickel sheet by using an organic solvent and/or an inorganic acid.

9. The method according to claim 8, wherein the organic solvent is acetone or ethanol, and the inorganic acid is hydrochloric acid or sulfuric acid.

10. The preparation method according to claim 1, wherein the counter electrode of the three-electrode system is a platinum foil or a carbon rod, and the reference electrode is a saturated calomel electrode or an Ag/AgCl electrode.

11. A phosphorus-oxygen co-doped copper-based catalyst prepared by the preparation method of any one of claims 1 to 10.

12. Use of a phosphorus and oxygen co-doped copper-based catalyst according to claim 11 for the electrocatalytic nitrate reduction synthesis of ammonia.

13. The application of claim 12, wherein the electrocatalytic nitrate radical reduction ammonia synthesis reaction adopts a saturated calomel electrode as a reference electrode, a platinum foil as a counter electrode and a foamed nickel sheet loaded with the phosphorus and oxygen co-doped copper-based catalyst as a working electrode, and the nitrate radical-containing aqueous solution is electrolyzed, wherein the voltage of the electrolysis process is-0.40V.

Technical Field

The invention belongs to the technical field of catalytic materials, and particularly relates to a phosphorus and oxygen co-doped copper-based catalyst and a preparation method and application thereof.

Background

Ammonia is one of the most important chemical raw materials in modern industrial and agricultural production, and the yield of ammonia directly promotes the development of global industry and industry. At present, the industrial synthesis method of ammonia is mainly a Haber-Bosch method, which requires huge energy consumption, and discharges a large amount of greenhouse gases in the reaction process, thus being not beneficial to energy conservation and environmental protection.

The electrochemical reduction of nitrate to prepare ammonia means that nitrate is reduced and degraded on the surface of a cathode electrode by applying a certain voltage to a reaction electrode in an electrolytic cell containing nitrate. Compared with the traditional Haber-Bosch method, the electrochemical reduction method has lower requirements on equipment, does not generate a large amount of production waste, and has more excellent economical efficiency and environmental compatibility. In addition, human domestic sewage is rich in nitrate, and the nitrate discharged into the environment can be reduced into harmful nitrite under the action of microorganisms. Therefore, the method for preparing ammonia by electrochemically reducing nitrate in water can realize the virtuous cycle of nitrogen element and meet the requirement of green development.

The conversion of nitrate to ammonia requires an 8 electron transfer process, the actual potential of which is usually lower than that of the hydrogen evolution reaction, and a large number of electrons are used for the reduction of hydrogen ions in water, resulting in unnecessary consumption of electric energy and ultimately a reduction in faraday efficiency. In order to solve this problem, some electrocatalysts with high activity are used to improve the activity of electrochemical reduction of nitrate. The copper-based catalyst has good adsorption capacity to nitrate radicals, can inhibit hydrogen evolution reaction to a certain extent, and can improve electron transfer efficiency in a system due to the excellent conductivity of copper, so that the copper-based catalyst is a catalytic material with good development prospect. When pure copper is used as the catalytic material, the catalytic active sites on the surface are limited, resulting in low nitrate reduction efficiency. The current research direction is generally to dope the copper-based catalyst with suitable metal heteroatoms, such as Ni, Pd, Pt (R) ((R))J. Am. Chem. Soc. 2020, 142, 5702; J. Phys. Chem. C 2009, 113, 290–297;Nature Communications 2019,10,5812) Etc. to change the electronic structure of the base metal, thereby improving catalytic activity. However, these metals are not economical due to their high price, and thus are difficult to be industrialized and commercialized.

Disclosure of Invention

In view of the above-mentioned deficiencies of the prior art, an object of the present invention is to provide a phosphorus and oxygen co-doped copper-based catalyst and a preparation method thereof, wherein the preparation method is simple and environment-friendly, and the synthesized catalyst has good catalytic performance and lower cost compared with metal doping. The invention also aims to apply the phosphorus and oxygen co-doped copper-based catalyst in the reaction for electrochemically reducing nitrate to synthesize ammonia so as to improve the nitrate conversion rate, the ammonia yield, the Faraday efficiency and the ammonia selectivity of the reaction.

In order to achieve the purpose, the invention provides the following technical scheme:

a preparation method of a phosphorus and oxygen co-doped copper-based catalyst comprises the following steps: 1) and dissolving copper salt and phosphite in deionized water to prepare electrolyte. The anion of the copper salt is an oxygen-containing acid radical ion, and the copper salt needs to have good water solubility, so that copper nitrate and/or copper sulfate are/is preferred, the electron losing capability of nitrate and sulfate is weaker than that of hydroxide ions in water, and therefore, the copper nitrate and the sulfate do not participate in the reaction in the electrolytic process, and unnecessary energy consumption and production waste are prevented from being generated. The cation of the phosphite has weaker electron obtaining capability than that of copper ions, and the phosphite also has good water solubility, so that sodium phosphite and/or potassium phosphite are preferred, and the copper ions obtain electrons before the sodium ions and/or potassium ions in the electrolytic process, so that the sodium ions and/or potassium ions do not react in the electrolytic system, and unnecessary energy consumption is prevented. 2) A three-electrode system is adopted to carry out constant potential electrodeposition reaction, the voltage range of the constant potential electrodeposition reaction is-1.6 to-1.8V, and the phosphorus and oxygen co-doped copper-based catalyst with good electrocatalysis performance can be prepared in the potential range. Wherein the working electrode of the three-electrode system is a foamed nickel sheet. 3) And cleaning and drying the foam nickel sheet subjected to the constant potential electrodeposition reaction to obtain the phosphorus and oxygen co-doped copper-based catalyst growing on the surface of the foam nickel sheet.

The invention adopts a constant potential electrodeposition method to carry out one-step co-electrodeposition reaction, so that the phosphorus and oxygen co-doped copper-based catalyst is uniformly loaded on the surface of the foam nickel sheet. The synthesis method is simple and easy to operate, and does not generate environmental pollutants in the preparation process. The doping of phosphorus and oxygen can adjust the electronic structure around copper, so that the copper catalyst has higher catalytic activity than a pure copper catalyst. Compared with a metal-doped catalyst, the phosphorus-oxygen co-doped copper-based catalyst has low cost and high economic benefit, and is suitable for industrialization and commercialization.

The molar ratio of the divalent copper ions to the phosphite radicals in the electrolyte is preferably 1: 0.8-1: 1.2, and the concentration of the divalent copper ions in the electrolyte is preferably 0.08-0.13 mol/L. In the preparation process of the electrolyte, the copper salt and the phosphite can be fully dissolved in the deionized water by adopting an ultrasonic dispersion method, and the ultrasonic dispersion time is preferably 0.5-3 h.

The time of the constant potential electrodeposition reaction is related to the compactness of the surface of the prepared catalyst, and if the reaction time is short, the surface of the foam nickel sheet cannot be effectively covered, so that the reaction space is not favorably utilized; if the reaction time is too long, the obtained catalyst has too large surface density and is not easy to expose active sites. Therefore, the reaction time can be controlled within 100-700 s, preferably 250-550 s, so as to obtain a catalyst surface which is completely covered and has moderate density on the foamed nickel sheet substrate.

After the constant potential electrodeposition reaction is finished, the foam nickel sheet loaded with the phosphorus and oxygen co-doped copper-based catalyst needs to be cleaned. The cleaning agent can be selected from deionized water, ethanol or a mixture of deionized water and ethanol in a certain proportion, and the cleaning agent is used for washing the foamed nickel sheet loaded with the phosphorus and oxygen co-doped copper-based catalyst for multiple times so as to remove the residual electrolyte on the surface. And after washing, drying in an oven, wherein the drying temperature is preferably set to be 45-55 ℃, and the drying time is preferably 6-9 h. Under the conditions of the drying temperature and the drying time, most of moisture in the prepared catalyst can be effectively removed, the removal of the moisture in the prepared catalyst can accurately measure the mass change of the working electrode before and after preparation, and the catalyst is favorable for quick combination with reactants in the subsequent application process. In addition, under the conditions of the drying temperature and the drying time, the more obvious surface oxidation phenomenon can not be caused, so that the phenomenon that the activity of the catalyst is reduced due to the surface oxidation is relieved. The oven can be selected from a vacuum oven, and the catalyst is further prevented from being oxidized in the drying process.

The preparation method can further comprise a process of pretreating the foamed nickel sheet to remove stains on the surface of the foamed nickel sheet. The pretreatment process can be carried out by soaking and ultrasonic cleaning the foamed nickel sheet by selecting an organic solvent and/or a low-concentration acid, for example, the organic solvent can be acetone, and the acid can be hydrochloric acid. The acetone has certain lipid solubility and water solubility, can effectively remove oil stains on the surface of the foamed nickel sheet, and the hydrochloric acid aqueous solution with certain concentration can remove oxides on the surface of the foamed nickel sheet. The step of pretreating the nickel foam sheet can enable the phosphorus and oxygen co-doped copper-based catalyst to be more uniformly loaded on the surface of the nickel foam sheet, and prevent the collapse or the falling off of the active substances. Of course, other reagents may be selected to pre-treat the nickel foam sheet, such as ethanol, dilute sulfuric acid, and the like. The pretreatment step can also further comprise a process of washing away residual reagents on the foamed nickel sheet by using deionized water and drying the foamed nickel sheet, wherein the drying method can be natural blow drying at room temperature or oven drying. To prevent the nickel foam sheet from being oxidized during the drying process, a vacuum oven may be preferred.

The counter electrode of the three-electrode system can be selected from a platinum foil electrode or a carbon rod electrode, and the reference electrode of the three-electrode system can be selected from a saturated calomel electrode or an Ag/AgCl electrode.

The foam nickel sheet as the working electrode can be selected from a foam nickel sheet with the thickness of 0.2 cm, and the area of the working electrode is preferably 0.5 cm² ~ 2 cm²。

The phosphorus and oxygen co-doped copper-based catalyst provided by the invention is synthesized by any preparation method. In the catalyst, phosphorus and oxygen are mainly doped on the surface of copper, and the electronic structure around the copper is adjusted, so that the d-band center of the copper moves to a deep energy level, and the binding energy of a reaction intermediate is further improved.

The invention also relates to the application of the phosphorus and oxygen co-doped copper-based catalyst in synthesizing ammonia by electrocatalysis nitrate reduction. When the potential is applied to be-0.40V (relative to a reversible hydrogen electrode: vs. RHE), the foamed nickel sheet loaded by the phosphorus and oxygen co-doped copper-based catalyst is used as a working electrode to perform nitrate radical electro-reduction reaction, the nitrate radical conversion rate can reach 91.09%, and 1.22mmol ‧ h^-1‧cm^-2NH of (2)₃Yield, faradaic efficiency of 91.72% and selectivity to 67.80% ammonia. And faradaic efficiency and NH at 8 hours of continuous cycling₃The yield is not obviously attenuated, which indicates that the phosphorus and oxygen co-doped copper-based catalyst has good stability.

The invention has the beneficial effects that: 1) the invention provides a phosphorus and oxygen co-doped copper-based catalyst, wherein the doping of phosphorus and oxygen can adjust the electronic structure around copper, so that the catalyst has better catalytic activity than a pure copper catalyst, and compared with the doping of metal heteroatoms, the doping of phosphorus and oxygen has low requirements on reagents, better economy and easy control of production cost; 2) the phosphorus and oxygen co-doped copper-based catalyst is synthesized in one step by adopting a constant potential electrodeposition preparation method, the method is simple to operate, has low requirements on equipment, does not generate harmful production waste, and is suitable for industrialization; 3) the phosphorus and oxygen co-doped copper-based catalyst is applied to the reaction for synthesizing ammonia by electrocatalysis nitrate reduction, and the reaction can reach the nitrate conversion rate of 91.09 percent and 1.22 mmol.h^-1·cm^-2NH of (2)₃The yield, faradaic efficiency of 91.72% and selectivity to 67.80% ammonia, and still good stability over 8 hours of continuous cycling.

Drawings

In order to more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

Fig. 1a is an SEM image of the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1.

FIG. 1b is an EDS profile of the Cu element in the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1.

FIG. 1c is an EDS profile of element P in the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1.

FIG. 1d is an EDS profile of the O element in the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1.

Fig. 2a is a TEM image and SAED image of the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1.

FIG. 2b is a HRTEM image of the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1.

FIG. 2c is a Cu test of HRTEM of the P-O-codoped Cu-based catalyst prepared in example 1₂Lattice spacing of the O (111) plane.

FIG. 2d is the lattice spacing of the Cu (111) plane obtained by HRTEM testing of the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1.

Fig. 3a is an XPS comparison of a phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 and an oxygen doped copper-based catalyst prepared in comparative example 1.

FIG. 3b is an enlarged view of the region 130-136 eV shown in FIG. 3 a.

Fig. 4 is a PDOS plot of the copper d-bands for the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 and the oxygen doped copper-based catalyst prepared in comparative example 1.

Fig. 5 is a graph of the change in nitrate conversion and faraday efficiency at different potentials for the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1.

FIG. 6 is NH of a 4-cycle test at-0.40V potential for a phosphorus and oxygen co-doped copper-based catalyst prepared in example 1₃Yield and faraday efficiency profiles.

Fig. 7 is a graph comparing LSVs before and after nitrate addition for the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 and the oxygen doped copper-based catalyst prepared in comparative example 1.

Figure 8 is a graph comparing the faradaic efficiency, nitrate conversion, and ammonia selectivity at a potential of-0.40V for the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 and the oxygen doped copper-based catalyst prepared in comparative example 1.

Detailed Description

The technical solutions in the specific embodiments of the present invention will be clearly and completely described below, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1:

a preparation method of a phosphorus and oxygen co-doped copper-based catalyst comprises the following steps:

(1) 2.42 g of copper nitrate trihydrate and 2.16g of sodium phosphite are weighed and added into 100 mL of deionized water, and the mixture is continuously stirred until the copper nitrate trihydrate and the sodium phosphite are completely dissolved, so that the electrolyte is prepared.

(2) A foam nickel sheet with the thickness of 0.2 cm is taken and cut into a rectangular shape of 0.5 cm multiplied by 2 cm. And (3) sequentially using 30 mL of acetone and 30 mL of hydrochloric acid aqueous solution with the concentration of 3 mol/L to ultrasonically clean the foamed nickel sheet for 5 min respectively so as to remove oil stains and oxidation films on the surface of the foamed nickel sheet. And repeatedly washing with deionized water to remove residual reagents on the surface of the foam nickel sheet, performing ultrasonic treatment in 30 mL of deionized water for 5 min, and finally drying under room-temperature environmental conditions to obtain the foam nickel sheet with a clean surface.

(3) Pouring the prepared electrolyte into an electrolytic cell, taking a platinum foil as a counter electrode, taking a saturated calomel electrode as a reference electrode, taking a pretreated foam nickel sheet as a working electrode to perform constant potential electrodeposition reaction, setting the voltage to be-1.7V, and setting the reaction time to be 400 s.

(4) And after the reaction is finished, taking down the foamed nickel sheet, respectively washing with deionized water and ethanol, and then putting into an oven for drying at the drying temperature of 55 ℃ for 6 hours to obtain the phosphorus and oxygen co-doped copper-based catalyst uniformly loaded on the surface of the foamed nickel sheet.

Example 2:

a preparation method of a phosphorus and oxygen co-doped copper-based catalyst comprises the following steps:

(1) 2.02 g of copper nitrate trihydrate and 2.16g of sodium phosphite are weighed and added into 100 mL of deionized water, and the mixture is continuously stirred until the copper nitrate trihydrate and the sodium phosphite are completely dissolved, so that the electrolyte is prepared.

(2) A nickel foam sheet with a thickness of 0.2 cm was cut into a rectangular shape of 1 cm. times.2 cm. And (3) sequentially using 30 mL of acetone and 30 mL of hydrochloric acid aqueous solution with the concentration of 3 mol/L to ultrasonically clean the foamed nickel sheet for 5 min respectively so as to remove oil stains and oxidation films on the surface of the foamed nickel sheet. And repeatedly washing with deionized water to remove residual reagents on the surface of the foam nickel sheet, performing ultrasonic treatment in 30 mL of deionized water for 5 min, and finally drying under room-temperature environmental conditions to obtain the foam nickel sheet with a clean surface.

(3) Pouring the prepared electrolyte into an electrolytic cell, taking a platinum foil as a counter electrode, taking a saturated calomel electrode as a reference electrode, taking a pretreated foam nickel sheet as a working electrode to perform constant potential electrodeposition reaction, setting the voltage to be-1.65V, and setting the reaction time to be 500 s.

(4) And after the reaction is finished, taking down the foamed nickel sheet, respectively washing with deionized water and ethanol, and then putting into an oven for drying at the drying temperature of 45 ℃ for 9 hours to obtain the phosphorus and oxygen co-doped copper-based catalyst uniformly loaded on the surface of the foamed nickel sheet.

Example 3:

a preparation method of a phosphorus and oxygen co-doped copper-based catalyst comprises the following steps:

(1) 3.03 g of copper nitrate trihydrate and 2.16g of sodium phosphite are weighed and added into 100 mL of deionized water, and the mixture is continuously stirred until the copper nitrate trihydrate and the sodium phosphite are completely dissolved, so that the electrolyte is prepared.

(2) A nickel foam sheet with a thickness of 0.2 cm was cut into a rectangular shape of 1 cm × 1 cm. And (3) sequentially using 30 mL of acetone and 30 mL of hydrochloric acid aqueous solution with the concentration of 3 mol/L to ultrasonically clean the foamed nickel sheet for 5 min respectively so as to remove oil stains and oxidation films on the surface of the foamed nickel sheet. And repeatedly washing with deionized water to remove residual reagents on the surface of the foam nickel sheet, performing ultrasonic treatment in 30 mL of deionized water for 5 min, and finally drying under room-temperature environmental conditions to obtain the foam nickel sheet with a clean surface.

(3) Pouring the prepared electrolyte into an electrolytic cell, taking a platinum foil as a counter electrode, taking a saturated calomel electrode as a reference electrode, taking a pretreated foam nickel sheet as a working electrode to perform constant potential electrodeposition reaction, setting the voltage to be-1.6V, and setting the reaction time to be 300 s.

(4) And after the reaction is finished, taking down the foamed nickel sheet, respectively washing with deionized water and ethanol, and then putting into an oven for drying at the drying temperature of 50 ℃ for 7.5 hours to obtain the phosphorus and oxygen co-doped copper-based catalyst uniformly loaded on the surface of the foamed nickel sheet.

Comparative example 1:

a copper-based catalyst doped with oxygen alone was prepared in the same manner as in example 1, except that the electrolyte in comparative example 1 contained only 2.42 g of copper nitrate trihydrate.

Characterization of phosphorus and oxygen-codoped copper-based catalysts

The phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 was used as a test sample, and was characterized by a Scanning Electron Microscope (SEM), an X-ray spectroscopy (EDS), a Transmission Electron Microscope (TEM), a Selective Area Electron Diffraction (SAED), and a High Resolution Transmission Electron Microscope (HRTEM).

The elemental compositions of the phosphorus-oxygen co-doped copper-based catalyst and the oxygen-doped copper-based catalyst were compared and tested using X-ray photoelectron spectroscopy (XPS) with the oxygen-doped copper-based catalyst of comparative example 1 as a control sample. And the state-splitting density (PDOS) of the copper d-band in the two catalysts is calculated to explore the influence of phosphorus doping on the center of the copper d-band.

The characterization results are specifically described and analyzed below with reference to the accompanying drawings:

FIG. 1a is an SEM image of a phosphorus and oxygen co-doped copper-based catalyst prepared in example 1, and the catalyst obtained by the potentiostatic electrodeposition method has a bulk structure as shown in FIG. 1 a. Fig. 1b, 1c and 1d are EDS (electron-deposition spectroscopy) surface scans of Cu, P and O elements in the catalyst, respectively, and it can be seen from the views that the distribution states of the Cu, P and O elements on the surface of the catalyst are uniformly distributed, which illustrates that a copper-based catalyst with uniform co-doping of P and O can be obtained by adopting a constant potential electrodeposition manner.

Fig. 2a is a TEM image and SAED image of the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1. The SAED detection shows not only crystal faces of Cu (111) and Cu (200), but also detects Cu₂O (111) plane, illustrating O element to form Cu₂The mode of O is doped into the catalyst. FIG. 2b is a HRTEM image of the P-O-codoped copper-based catalyst prepared in example 1, with partial magnification showing the lattice spacing observed, as shown in FIGS. 2c and 2d, for Cu₂The lattice spacing of the O (111) plane is 0.246 nm, the lattice spacing of the Cu (111) plane is 0.208 nm, and further shows that in addition to the generation of the simple substance Cu, part of Cu is generated in the electrodeposition process₂O。Cu₂The copper ions in O have a tendency to change valence state, thus making it more catalytically active than Cu alone.

XPS detection was performed to verify whether the phosphorus element was doped successfully, using the prepared oxygen-doped catalyst alone as a control sample in comparative example 1. As shown in fig. 3a, in the XPS full scan spectrum, characteristic peaks corresponding to O1 s and Cu 2p appeared for the oxygen-doped copper-based catalyst alone. The phosphorus and oxygen co-doped copper-based catalyst shows characteristic peaks corresponding to P2P, O1 s and Cu 2P. FIG. 3b is an enlarged view of the range of 130-136 eV in FIG. 3a, the XPS spectrum of the Cu-based catalyst co-doped with P and oxygen shows a distinct P2P peak at 133 eV, while the XPS spectrum of the Cu-based catalyst doped with oxygen alone shows no P2P peak at the same position, indicating that P and O are both doped on the surface of the Cu-based catalyst during the preparation process of the Cu-based catalyst co-doped with P and oxygen.

To investigate the effect of phosphorus doping on the electronic structure around copper, the density of the states of the copper d-band of the phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 and the oxygen doped copper-based catalyst prepared in comparative example 1 were calculated. As shown in fig. 4, the copper d band center in the oxygen-doped copper-based catalyst alone is-2.590 eV, and the copper d band center in the phosphorus and oxygen-co-doped copper-based catalyst is-2.611 eV, and after phosphorus doping, the copper d band center moves to a deep level, which results in an increase in the bonding strength of the active sites and reaction intermediates on copper, thereby improving catalytic activity. The specific mechanism of the displacement of the center of the copper d-band affecting the catalytic activity is described in the prior art and is not described herein.

Application of phosphorus and oxygen co-doped copper-based catalyst in electrocatalysis of nitrate radical reduction synthesis of ammonia

The phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 was used as a test sample, and the oxygen-doped copper-based catalyst prepared in comparative example 1 was used as a control sample, and the catalytic activities of the two catalysts in the reaction of synthesizing ammonia by electrocatalysis of nitrate reduction are detected.

Faraday efficiency, nitrate conversion, ammonia selectivity and NH related to the experimental procedure₃The yield was calculated as follows:

faraday efficiency = (zxvxc)_NH3× F）/（M_NH3× i × t）

Nitrate conversion = (C)₀-C_NO3 ^-）/C× 100%

Ammonia selectivity = C_NH3/（C₀-C_NO3 ^-）× 100%

NH₃Yield = (V × C)_NH3)/（S × t）

Wherein Z is 1molNH generated in the reaction process₃Number of transferred electrons (Z =8 in this reaction), V is electrolyte volume (L), C_NH3For the resulting ammonia concentration (mg/L), F is the Faraday constant (F = 96485C ∙ mol)^-1），M_NH3Is NH₃Relative to the molecular mass, i is the current magnitude (mA), t is the electrolysis time (h), C₀Is the initial concentration of nitrate (mg/L), C_NO3 ^-As the concentration of nitrate (mg/L) after the reaction, S is the electrode area (cm)²）。

The initial concentration of the nitrate, the concentration of the nitrate after the reaction, and the concentration of the ammonia generated were determined colorimetrically.

1. Potential optimization for electrocatalytic nitrate reduction ammonia synthesis reaction

The phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 was used as a test sample to investigate the change trend of the faradaic efficiency and nitrate conversion rate of the reaction at different potentials to obtain a better applied potential.

1) The reaction conditions for synthesizing ammonia by electrocatalysis nitrate radical reduction are as follows:

electrolyte solution: 1 mol/L potassium hydroxide and 1400 ppm potassium nitrate aqueous solution.

An electrolytic cell: and (4) an H-shaped pool.

Three-electrode system: a saturated calomel electrode is used as a reference electrode, a platinum foil electrode is used as a counter electrode, and a foam nickel sheet loaded with a phosphorus and oxygen co-doped copper-based catalyst is used as a working electrode.

Testing parameters: the voltage was set at-0.45V, -0.40V, -0.35V, or-0.30V (vs. reversible hydrogen electrode: vs. RHE), and the sweep rate was set at 2 mV/s.

2) And (3) testing results:

as shown in FIG. 5, when the voltages were-0.45V, -0.40V, -0.35V and-0.30V, the conversion rates of nitrate in the electrocatalytic ammonia synthesis reaction by nitrate reduction were 91.4%, 91.1%, 84.7% and 78.2%, respectively, and the faradaic efficiencies were 85.5%, 91.7%, 88.8% and 86.1%, respectively. It can be seen that when the applied potentials were-0.45V, and 0.40V, the nitrate conversion reached a higher value and tended to be stable. The Faraday efficiency is volcano-shaped curve before and after-0.40V. Therefore, considering the nitrate conversion and the Faraday efficiency in combination, the preferred applied voltage for the reaction is-0.40V.

2. Stability test

The phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 was used as a test sample to investigate the stability of the catalytic performance of the catalyst in the reaction of electrocatalytic reduction of nitrate to ammonia for multiple cycles.

1) The reaction conditions for synthesizing ammonia by electrocatalysis nitrate radical reduction are as follows:

electrolyte solution: 1 mol/L potassium hydroxide and 1400 ppm potassium nitrate aqueous solution.

An electrolytic cell: and (4) an H-shaped pool.

Three-electrode system: a saturated calomel electrode is used as a reference electrode, a platinum foil electrode is used as a counter electrode, and a foam nickel sheet loaded with a phosphorus and oxygen co-doped copper-based catalyst is used as a working electrode.

Testing parameters: the voltage was set at-0.40V (vs. RHE), the sweep rate was set at 2 mV/s, and the test time per cycle was 2 h.

2) And (3) testing results:

the stability test was run through 4 cycles of 2 h each, with NH in each cycle after completion₃The yield and the faraday efficiency were tested while replacing the new electrolyte and performing the next cycle test with the same working electrode. 4 cycles of NH as shown in FIG. 6₃The yield is 1.22mmol · h respectively^-1·cm^-2、1.19 mmol·h^-1·cm^-2、1.24 mmol·h^-1·cm^-2And 1.19 mmol · h^-1·cm^-2The relative standard deviation was 2.0%. The faradaic efficiencies of the 4 cycles were 91.8%, 88.7%, 88.3%, and 89.6%, respectively, with a relative standard deviation of 1.7%. It can be seen that the NH of this reaction was measured in 4 cycles for a total of 8 h₃The relative standard deviations of both yield and faraday efficiency are low. Therefore, the catalyst has good stability in the electrocatalysis of the reaction for synthesizing ammonia by reducing nitrate radicals, and can be continuously used.

3. Comparison of catalytic Activity

(1) Linear voltammetric sweep test

The phosphorus and oxygen co-doped copper-based catalyst prepared in example 1 and the oxygen doped catalyst prepared in comparative example 1 were subjected to a linear voltammetric sweep test in an electrolyte solution with or without nitrate, respectively.

1) And (3) testing conditions are as follows:

electrolyte solution: the nitrate-free electrolyte consists of 1 mol/L potassium hydroxide aqueous solution; the electrolyte containing nitrate was composed of 1 mol/L potassium hydroxide and 1400 ppm potassium nitrate aqueous solution.

An electrolytic cell: and (4) an H-shaped pool.

Three-electrode system: a saturated calomel electrode is used as a reference electrode, a platinum foil electrode is used as a counter electrode, and a foam nickel sheet loaded with a phosphorus and oxygen co-doped copper-based catalyst or an oxygen doped copper-based catalyst is used as a working electrode.

Testing parameters: the voltage was set to 0.1 to-0.48V (vs. RHE), and the sweep rate was set to 2 mV/s.

2) Test results

As shown in fig. 7, the LSV curves corresponding to the phosphorus, oxygen co-doped copper-based catalyst and oxygen doped copper-based catalyst both showed low current densities when nitrate was not contained in the electrolyte. The LSV curves corresponding to the phosphorus, oxygen co-doped copper-based catalyst and oxygen doped copper-based catalyst both showed a rapid increase in current density when 1400 ppm of potassium nitrate was added to the electrolyte, indicating that both catalysts are nitrate sensitive. Compared with a single oxygen-doped copper-based catalyst, when a foamed nickel sheet loaded with a phosphorus and oxygen co-doped copper-based catalyst is used as a working electrode, the system has higher current density, and the co-doping of phosphorus and oxygen enables the copper-based catalyst to have better catalytic activity and to show stronger sensitivity to nitrate.

(2) Faraday efficiency, nitrate conversion, ammonia selectivity, and NH in different catalyst systems₃Comparison of yields

Using the phosphorus-oxygen co-doped copper-based catalyst prepared in example 1 as a test sample and the oxygen-doped copper-based catalyst prepared in comparative example 1 as a control sample, the Faraday efficiency, nitrate conversion, ammonia selectivity and NH in the electrocatalytic nitrate reduction ammonia synthesis reaction using the two as catalysts were respectively tested₃Yield.

1) And (3) testing conditions are as follows:

electrolyte solution: 1 mol/L potassium hydroxide and 1400 ppm potassium nitrate aqueous solution.

An electrolytic cell: and (4) an H-shaped pool.

Three-electrode system: a saturated calomel electrode is used as a reference electrode, a platinum foil electrode is used as a counter electrode, and a foam nickel sheet loaded with a phosphorus and oxygen co-doped copper-based catalyst or an oxygen doped copper-based catalyst is used as a working electrode.

Testing parameters: the voltage was set to-0.40V (vs. RHE) and the sweep rate was set to 2 mV/s.

2) Test results

As shown in FIG. 8, when a nickel foam sheet loaded with an oxygen-doped copper-based catalyst is used as a working electrode, the faradaic efficiency, the nitrate conversion rate and the ammonia selectivity of the reaction for synthesizing ammonia by electrocatalysis of nitrate reduction are 83.1%, 68.7% and 56.5%, respectively, and NH is calculated₃The yield was 0.77 mmol · h^-1·cm^-2. When a foamed nickel sheet loaded with a phosphorus and oxygen co-doped copper-based catalyst is taken as a working electrode, the faradaic efficiency, the nitrate conversion rate and the ammonia selectivity of the reaction for synthesizing ammonia by electrocatalysis of nitrate reduction are respectively 91.7%, 91.1% and 67.8%, and simultaneously, NH is obtained by calculation₃The yield was 1.22 mmol. h^-1·cm^-2. It can be seen that the phosphorus and oxygen co-doped copper-based catalyst has better catalytic performance than the copper-based catalyst doped with oxygen alone for the electrocatalytic nitrate reduction ammonia synthesis reaction.

The invention adopts a constant potential electrodeposition method to prepare the phosphorus and oxygen co-doped copper-based catalyst, and test results such as EDS, TEM, HRTEM, SAED and XPS and the like show successful doping of phosphorus and oxygen. PDOS demonstrated that phosphorus doping can modulate the electronic structure around copper, shifting the copper d-band center to a deep level, which helps to modulate the binding energy of the reaction intermediates, thereby affecting electrocatalytic activity. The LSV curve shows that the catalytic system of the phosphorus, oxygen co-doped copper based catalyst has a higher current density when nitrate is present than the catalytic system of the oxygen doped copper based catalyst alone, indicating that it has a stronger nitrate sensitivity. The phosphorus and oxygen co-doped copper-based catalyst is applied to electrocatalysis of ammonia synthesis by nitrate reduction, and the catalyst system can achieve the nitrate conversion rate of 91.09 percent and 1.22mmol ‧ h^-1‧cm^-2The yield of NH3, the faradaic efficiency of 91.72 percent and the selectivity of 67.80 percent of ammonia are high, and no obvious attenuation phenomenon appears under 8-hour continuous cycle test, which shows that the catalyst has good catalytic activity and stability for the reaction of synthesizing ammonia by reducing nitrate, and has application prospect.

The phosphorus and oxygen co-doped copper-based catalyst, the preparation method thereof and the application thereof in the reaction of electrocatalytic reduction of nitrate to synthesize ammonia provided by the invention are described in detail, specific examples are used herein to illustrate the phosphorus and oxygen co-doped copper-based catalyst, the preparation method thereof and the application thereof, and the description of the above examples is only used to help understanding the method and the core idea of the invention. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.