An iron-doped copper oxide catalyst, its preparation method and application in electrocatalytic synthesis of ammonia from nitrate

Abstract

The present invention relates to the technical field of electrocatalytic materials, and discloses an iron-doped copper oxide catalyst, a preparation method thereof, and an application thereof in electrocatalytic nitrate synthesis of ammonia. The method includes: using CuCl2 as a metal precursor and ascorbic acid as a reducing agent, obtaining Cu2O nanoparticles through a hydrothermal precipitation method; subsequently, adding Cu2O into a solution containing FeSO4, adding sodium borohydride, centrifuging, washing, and drying, and obtaining an iron-doped copper oxide nitrate electroreduction catalyst rich in defects and with uniformly dispersed metals through a pyrolytic reduction method with programmed temperature rise. The electrocatalytic material obtained by the method of the present invention has a large catalytic active area, relatively rich defect sites and oxygen vacancies, improves the nitrate adsorption and activation effect, promotes the supply of active hydrogen by constructing stable heterogeneous active sites, improves the product selectivity and Faraday efficiency in NO3RR, and has good durability.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic materials, and particularly relates to an iron-doped copper oxide catalyst, a preparation method thereof, and an application thereof in electrocatalytic synthesis of ammonia from nitrate. Background Art

[0002] Electrocatalytic nitrate reduction (NO3RR) provides a win-win opportunity for environmental remediation and resource recovery by using renewable electricity to control nitrate (NO3 - ) pollution in water and produce high-value ammonia (NH3), and has become a promising NH3 synthesis technology to replace the traditional H-B process.

[0003] However, the generation efficiency and selectivity of NH3 under neutral conditions are limited by the competitive hydrogen (H2) and nitrogen (N2) generation processes. Therefore, designing and constructing efficient electrocatalysts to regulate the selectivity of NO3RR products is of great significance for realizing the efficient synthesis of NH3 under neutral conditions.

[0004] Active non-noble metal copper has an orbital similar to the lowest unoccupied molecular orbital of NO3 - , and its orbital can form a coordination bond with the lone pair electrons of nitrogen, which is beneficial to the adsorption and activation of NO3 . Therefore, it is widely used in NO3RR research. However, copper-based electrocatalysts have problems such as large overpotential, easy accumulation of intermediate nitrite, and limited hydrogenation ability. d - adsorption and activation, and is widely used in NO3RR research. However, copper-based electrocatalysts have problems such as large overpotential, easy accumulation of intermediate nitrite, and limited hydrogenation ability.

[0005] Therefore, the optimized design of copper-based catalysts is the key to realizing the efficient reduction of electrocatalytic NO3 - to NH3. Summary of the Invention

[0006] The purpose of the present invention is to address the above problems existing in the prior art, and propose a preparation method of an iron-doped copper oxide catalyst, which can achieve a high NH3 yield when used for electrocatalytic reduction of nitrate to ammonia, and solve the problems of low selectivity and low Faraday efficiency of reducing low-concentration nitrate to NH3 under neutral conditions.

[0007] To achieve the above purpose, the first aspect of the present invention provides a preparation method of an iron-doped copper oxide catalyst, and the method includes the following steps:

[0008] (1) Add CuCl2·2H2O to deionized water and dissolve it uniformly to form solution I; add NaOH to deionized water and dissolve it to form solution II; add ascorbic acid to deionized water and dissolve it to form solution III;

[0009] Add the solution I dropwise to the solution II, mix evenly to obtain a mixed solution 1, and stir magnetically at room temperature for 30 min; add the solution III dropwise to the above mixed solution 1, and stir magnetically at room temperature for 1 h to obtain a mixed solution 2;

[0010] Place the mixed solution 2 in a water bath at 80 °C and heat for 2 h, then let it stand at room temperature. After the temperature drops to room temperature, take the precipitate, wash it with deionized water, transfer it to a centrifuge for centrifugation, perform the washing and centrifugation 6 times, and then place it in a vacuum dryer at -50 °C for 24 h to obtain Cu2O powder;

[0011] (2) Add the Cu2O powder to the deionized aqueous solution containing FeSO4·7H2O, ultrasonically treat for 30 min, and stir magnetically for 1 h to obtain a mixed solution A; add the deionized aqueous solution containing sodium borohydride dropwise to the mixed solution A, stir magnetically for 3 h, let it stand, perform centrifugation, and wash with deionized water. Perform the washing and centrifugation 6 times, and then place it in a vacuum dryer at -50 °C for 24 h, grind and sieve to obtain Cu2O-Fe powder;

[0012] (3) Perform stepwise temperature-rising calcination treatment on the Cu2O-Fe powder to obtain Cu x O-Fe.

[0013] Preferably, in step (1), the mass ratio of the CuCl2·2H2O, the NaOH, and the ascorbic acid is 1:2 - 3:1 - 2.

[0014] More preferably, in step (1), the dropping rate of the solution I and the solution III is 1 drop / second.

[0015] Preferably, in steps (1) and (2), the conditions for the centrifugation treatment at least satisfy: the rotation speed is 12000 rpm, the time is 10 min, and the temperature is 10 °C.

[0016] Preferably, in step (2), the mass ratio of the Cu2O powder, the FeSO4·7H2O, and the sodium borohydride is 1:1.9 - 7.8:2.8.

[0017] More preferably, in step (2), the dropping rate of the deionized aqueous solution containing sodium borohydride is 1 drop / second.

[0018] Preferably, in step (3), the stepwise temperature-rising calcination treatment includes: placing the Cu2O-Fe powder in a magnetic boat, then transferring it to a tubular furnace, and under a nitrogen atmosphere, heating it at a rate of 5 °C·min -1 to 300 °C, and holding at this temperature for 5 h, then naturally cooling, and heating at a rate of 5 °C·min -1Heat up to 550 °C at a rate of, hold for 5 h at this temperature, and cool naturally.

[0019] The second aspect of the present invention is an iron-doped copper oxide catalyst prepared by the method described in the first aspect of the present invention.

[0020] The third aspect of the present invention provides the application of the iron-doped copper oxide catalyst described in the second aspect of the present invention in the electrocatalytic synthesis of ammonia from nitrate.

[0021] The method provided by the present invention at least also has the following beneficial effects:

[0022] (1) The present invention combines a simple co-precipitation method and a pyrolysis reduction method to provide a preparation method for an iron-doped copper oxide catalyst, including: using CuCl2 as a metal precursor and ascorbic acid as a reducing agent, obtaining Cu2O nanoparticles through a hydrothermal precipitation method; subsequently, adding Cu2O to a solution containing FeSO4, adding sodium borohydride, and after centrifugation, washing, and drying, obtaining an iron-doped copper oxide nitrate electroreduction catalyst with rich defects and uniform metal dispersion through a programmed temperature pyrolysis reduction method. The preparation process of the present invention is simple. On the basis of improving the catalytic activity of the copper-based catalyst, it can reduce the preparation cost of the catalyst. The electrocatalytic material prepared by this method has a large catalytic activity area, rich defect sites and oxygen vacancies, and a high current density, thereby improving the nitrate adsorption and activation effect, and promoting the supply of active hydrogen by constructing stable heterogeneous active sites, improving the product selectivity and Faraday efficiency in NO3RR, and having good durability.

[0023] (2) In the iron-doped copper oxide catalyst prepared by the present invention, copper and iron are uniformly dispersed, and copper exists in the 0, +1, and +2 valence states at the same time. When used as a catalytic cathode material for NO3RR to efficiently and stably electrocatalyze low-concentration nitrate to ammonia under near-neutral conditions, in a 0.5 mol·L -1 K2SO4 and 100 mg·L -1 KNO3 electrolyte (pH = 6.53), the ammonia production rate can reach 1.6 mg·h -1 ·mg 催化剂 -1 , the ammonia selectivity is 94.7%, the Faraday efficiency can reach 91.7%, and it has a small Tafel slope, electrochemical impedance, and a large catalytic activity area. In 10 cyclic experiments, the ammonia production rate, selectivity, and Faraday efficiency are maintained at 1.4 - 1.6 mg·h -1 ·mg 催化剂 -1, at the levels of 88.4~95.7% and 84.1~92.3%, it has excellent recycling effect and long-term stability. The technical solution of the present invention provides a promising idea for the design of highly active and stable near-neutral low-concentration NO3RR catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is the X-ray diffraction spectrogram of the materials obtained in Example 1 and Comparative Example 1 of the present invention;

[0025] Figure 2 is the Cu obtained in Example 1 of the present invention x scanning electron microscope test result diagram of O-Fe-1;

[0026] Figure 3 is the Cu obtained in Example 1 of the present invention x transmission electron microscope test result diagram of O-Fe-1;

[0027] Figure 4 is the Cu obtained in Example 1 of the present invention x high-resolution transmission electron microscope test result diagram of O-Fe-1;

[0028] Figure 5 is the Cu obtained in Example 1 of the present invention x high-angle annular dark-field STEM and elemental distribution diagram of O-Fe-1;

[0029] Figure 6 is the Cu obtained in Example 1 of the present invention x X-ray photoelectron spectrogram of Cu 2p of O-Fe-1 obtained in Example 1 and Cu obtained in Comparative Example 1 x O;

[0030] Figure 7 is the Cu obtained in Example 1 of the present invention x X-ray photoelectron spectrogram of Fe 2p in O-Fe-1;

[0031] Figure 8 is the Cu obtained in Example 1 of the present invention x X-ray photoelectron spectrogram of O 1s in O-Fe-1 obtained in Example 1 and Cu obtained in Comparative Example 1 x O;

[0032] Figure 9 is the performance comparison diagram of LSV curves when the materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention are used as working electrodes, respectively, in an electrolyte without NO3 - electrolyte and an electrolyte containing NO3 - ;

[0033] Figure 10Open circuit potential test diagrams of the materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention when used as working electrodes;

[0034] Figure 11 When the materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention are used as working electrodes, in electrolytes containing NO3 - electrolytes, and electrolytes without NO3 - Electrochemical impedance spectroscopy test diagrams;

[0035] Figure 12 Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x O double-capacitance slope diagrams when used as working electrodes;

[0036] Figure 13 Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x O Tafel slope diagrams when used as working electrodes;

[0037] Figure 14 Cu obtained in Comparative Example 1 x O CV curves in electrolytes without NO3 - when used as a working electrode;

[0038] Figure 15 Cu obtained in Example 1 of the present invention x O-Fe-1 CV curves in electrolytes without NO3 - when used as a working electrode;

[0039] Figure 16 Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x O performance comparison diagrams for electrocatalytic NO3RR tests at different potentials when used as working electrodes;

[0040] Figure 17 Cu obtained in Example 1 of the present invention x NO3RR performance diagrams of O-Fe-1 in electrolytes with different initial pH values;

[0041] Figure 18 Cu obtained in Example 1 of the present invention x O-Fe-1 catalytic activity test diagrams for continuous 10-cycle reuse in electrocatalytic NO3RR when used as a working electrode;

[0042] Figure 19 Cu obtained in Example 1 of the present invention xThe graph of the leaching amount of metal ions in the electrolyte during 10 consecutive cycles when O-Fe-1 is used as the working electrode;

[0043] Figure 20 is the Cu obtained in Example 1 of the present invention x The scanning electron microscope image after 10 consecutive cycles when O-Fe-1 is used as the working electrode;

[0044] Figure 21 is the Cu obtained in Example 1 of the present invention x The X-ray diffraction spectrogram before and after 10 consecutive cycles when O-Fe-1 is used as the working electrode;

[0045] Figure 22 is the Cu obtained in Example 1 of the present invention at a low current density x The test graph of the electrocatalytic stability performance of O-Fe-1. Detailed implementation manners

[0046] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0047] In the present invention, "Cu x O" in " x " means that the Cu in this material exhibits multiple valence states, such as Cu x O can be expressed as Cu / CuO / Cu2O.

[0048] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, the raw materials are commercially available products.

[0049] Example 1

[0050] This example is used to provide a preparation method of an iron-doped copper oxide catalyst, and this method includes the following steps:

[0051] (1) Add 2 mg of CuCl2·2H2O to 20 mL of deionized water and dissolve it uniformly to form Solution I; add 5 mg of NaOH to 5 mL of deionized water and dissolve it to form Solution II; add 3 mg of ascorbic acid to 5 mL of deionized water and dissolve it to form Solution III;

[0052] The solution I was dropped into the solution II at a rate of 1 drop per second, and uniformly mixed to obtain a mixed solution 1, which was magnetically stirred at room temperature for 30 min; the solution III was dropped into the above mixed solution 1 at a rate of 1 drop per second, and magnetically stirred at room temperature for 1 h to obtain a mixed solution 2;

[0053] The mixed solution 2 was placed in a preheated water bath, heated at 80 °C for 2 h, then left to stand at room temperature. After the temperature dropped to room temperature, the precipitate was taken, washed with deionized water, transferred to a centrifuge for centrifugation. The washing and centrifugation were carried out 6 times, and then vacuum dried at -50 °C for 24 h to obtain Cu2O powder;

[0054] The conditions of the centrifugation were as follows: rotation speed was 12000 rpm, temperature was 10 °C, and time was 10 min.

[0055] (2) 0.1 g of Cu2O powder was added to 30 mL of deionized water solution containing 0.39 g of FeSO4·7H2O, ultrasonically treated for 30 min, and magnetically stirred for 1 h to obtain a mixed solution A; 20 mL of deionized water solution containing 0.28 g of sodium borohydride was added to the mixed solution A at a rate of 1 drop per second, magnetically stirred for 3 h, left to stand, centrifuged, and washed with deionized water. The washing and centrifugation were carried out 6 times, and then vacuum dried at -50 °C for 24 h, ground, and passed through a 200-mesh sieve to obtain Cu2O-Fe powder;

[0056] The conditions of the centrifugation were as follows: rotation speed was 12000 rpm, temperature was 10 °C, and time was 10 min.

[0057] (3) The Cu2O-Fe powder was placed in a magnetic boat and then transferred to a tube furnace. Under a nitrogen atmosphere, it was heated to 300 °C at a rate of 5 °C·min -1 and held at this temperature for 5 h, then naturally cooled. It was heated to 550 °C at a rate of 5 °C·min -1 and held at this temperature for 5 h, then naturally cooled to obtain an iron-doped copper oxide catalyst, denoted as Cu x O-Fe-1.

[0058] Example 2

[0059] This example was carried out according to the method of Example 1, except that in step (2), the mass ratio of the Cu2O powder, the FeSO4·7H2O, and the sodium borohydride was 1:1.9:2.8, and the remaining steps and parameters were the same as those in Example 1. Finally, an iron-doped copper oxide catalyst was prepared, denoted as Cu x O-Fe-2.

[0060] Example 3

[0061] This example is carried out according to the method of Example 1. The difference is that in step (2), the mass ratio of the Cu2O powder, the FeSO4·7H2O, and the sodium borohydride is 1:7.8:2.8, and the remaining steps and parameters are the same as those in Example 1. Finally, an iron-doped copper oxide catalyst is prepared, denoted as Cu x O-Fe-3.

[0062] Comparative Example 1

[0063] This example is carried out according to the method of Example 1. The difference is that the Cu2O powder prepared in step (1) does not go through step (2) and directly enters step (3) to prepare a copper oxide catalyst, denoted as Cu x O, and the remaining steps and parameters are the same as those in Example 1.

[0064] Test Example 1

[0065] The materials obtained in the above Example 1 and Comparative Example 1 were tested by X-ray diffraction spectroscopy, and the results are as Figure 1 shown.

[0066] It can be seen from Figure 1 that the diffraction peaks of the Cu x O obtained in Comparative Example 1 at 35.5°, 36.5°, 38.7°, and 43.2° respectively correspond to the crystal planes of CuO (-111), Cu2O (111), CuO (111), and Cu (111). This indicates that Cu x O is a multiphase structure containing multiple valence states of Cu. The diffraction peaks of the Cu x O-Fe-1 obtained in Example 1 of the present invention at 33.2°, 35.4°, 35.5°, and 43.2° respectively correspond to the crystal planes of Fe2O3 (104), Fe3O4 (311), CuO (-111), Cu2O (111), and Cu (111). This indicates that Fe has been successfully doped into Cu x O containing multiple valence states of Cu to form iron oxides.

[0067] Test Example 2

[0068] The materials obtained in the above Example 1 were tested for morphology and structure characterization, and the results are as Figures 2 - 6 shown.

[0069] Among them, Figure 2 is the scanning electron microscope test result diagram of the Cu x O-Fe-1 obtained in Example 1 of the present invention, Figure 3 is the transmission electron microscope test result diagram of the Cu x O-Fe-1 obtained in Example 1 of the present invention, Figure 4 is the Cu obtained in Example 1 of the present inventionx High-resolution transmission electron microscope test result diagram of O-Fe-1, Figure 5 which is Cu obtained in Example 1 of the present invention x High-angle annular dark field STEM and elemental distribution diagram of O-Fe-1.

[0070] It can be seen from Figure 2 that the Cu obtained in Example 1 of the present invention x O-Fe-1 presents a sheet formed by the aggregation of a large number of nanoparticles. It can be seen from Figure 3 and Figure 4 that the Cu obtained in Example 1 of the present invention x O-Fe-1 has a clear interface. The lattice spacings in the outer region are 0.246nm, 0.251nm, and 0.206nm respectively, which match the crystal planes of Cu2O (111), CuO (-111), and Cu (111). The lattice spacings in the inner region are 0.256nm and 0.262nm, corresponding to the crystal planes of Fe3O4 (311) and Fe2O3 (104) respectively. It can be seen from Figure 5 that Cu element, Fe element, and O element are evenly distributed, indicating that Fe is evenly doped into Cu x O.

[0071] Test Example 3

[0072] X-ray photoelectron spectroscopy characterization tests were carried out on the materials obtained in Example 1 and Comparative Example 1 above, and the results are as Figures 6 - 8 shown.

[0073] Among them, Figure 6 is the X-ray photoelectron spectroscopy diagram of Cu 2p of Cu x O-Fe-1 obtained in Example 1 of the present invention and Cu x O obtained in Comparative Example 1, Figure 7 is the X-ray photoelectron spectroscopy diagram of Fe 2p in Cu x O-Fe-1 obtained in Example 1 of the present invention, Figure 8 is the X-ray photoelectron spectroscopy diagram of O 1s in Cu x O-Fe-1 obtained in Example 1 of the present invention and Cu x O obtained in Comparative Example 1.

[0074] It can be seen from Figure 6 that in Cu x O, the fitting peaks at 932.4, 934.1, 952.1, and 953.7 eV respectively correspond to Cu 0 / 1+ (23.9 at%), Cu 2+ (21.8 at%), Cu 0 / 1+ (14.7 at%) and Cu2+ (10.5 at%); in Cu x In CuO-Fe-1, the peaks at 931.6, 934.1, 951.4, and 953.5 eV correspond to Cu 0 / 1+ (42.9 at%), Cu 2+ (18.6 at%), Cu 0 / 1+ (17.8 at%), and Cu 2+ (8.3 at%), where the proportions of Cu 0 / 1+ are all relatively large. After doping with Fe, the proportion of the Cu x peak in CuO-Fe-1 increases and the peak centers shift 0.8 and 0.7 eV towards lower binding energies respectively, indicating that Fe doping leads to an increase in the electron density of Cu 0 / 1+ , the local electronic structure is regulated, which helps to adjust the Cu 0 / 1+ band center, promote electron transfer, and improve the NO3RR performance. d As can be seen from

[0075] From Figure 7 it can be known that in the CuO-Fe-1 obtained in Example 1 of the present invention, the fitting peaks at 709.3 / 722.5, 710.7 / 724.0, and 713.4 / 726.2 eV correspond to Fe x (11.1 / 11.3 at%), Fe 0 (14.3 / 7.1 at%), and Fe 2+ (15.3 / 15.5 at%), where the proportion of the Fe 3+ peak area is the largest. 3+ As can be seen from

[0076] From Figure 8 it can be known that in the O 1s spectra of CuO and CuO-Fe-1, peaks O1, O2, and O3 are fitted at 528.9 and 529.1, 530.5 and 530.1, and 532.1 and 531.5 eV respectively, corresponding to lattice oxygen (Cu-O or Fe-O), low-coordination oxygen defect sites, and surface hydroxyl groups (-OH). The obvious negative shifts of about 0.4 and 0.6 eV of peaks O2 and O3 in O 1s after doping with Fe may be due to the charge redistribution at the CuO-Fe-1 interface, resulting in the transfer of electrons from Fe to CuO x , which provides an important basis for the electron interaction between Fe atoms and CuO x . x In CuO-Fe-1, the peaks at 931.6, 934.1, 951.4, and 953.5 eV correspond to Cu x (42.9 at%), Cu x (18.6 at%), Cu xThe proportions of peaks O2 and O3 of O-Fe-1 increased significantly, indicating that Fe doping would cause local structural distortion or introduce more surface defects, increasing the surface catalytic active sites, which was also the reason for the decrease in the proportion of peak O1. The increase in surface defects and active sites could enhance the adsorption and activation of intermediates, promote electron enrichment, and improve the NO3RR activity.

[0077] Test Example 4

[0078] The materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1 above were tested for their electrochemical properties, and the results were as Figures 9 - 11 .

[0079] Specifically, a standard three-electrode test system was used, with 0.5 mol·L -1 K2SO4 and 100 mg·L -1 KNO3 as the electrolyte, an Ag / AgCl electrode as the reference electrode, a Pt wire electrode as the counter electrode, and Cu x O-Fe-1 obtained in Example 1 of the present invention, Cu x O-Fe-2 obtained in Example 2, Cu x O-Fe-3 obtained in Example 3 or Cu x O obtained in Comparative Example 1 as the working electrode. Linear sweep voltammetry (LSV) tests were carried out at a scan rate of 10 mV·s -1 ; the open circuit potential (OCP) test lasted for 400 seconds; the electrochemical impedance spectroscopy (EIS) test was carried out in the frequency range of 10 -2 Hz to 10 6 Hz.

[0080] Figure 9 This is a comparison chart of the LSV curve performance of Cu x O-Fe-1 obtained in Example 1 of the present invention, Cu x O-Fe-2 obtained in Example 2, Cu x O-Fe-3 obtained in Example 3 and Cu x O obtained in Comparative Example 1 as the working electrode in electrolytes without NO3 - and electrolytes containing NO3 - . It can be seen from Figure 9 that the presence of NO3 - in the electrolyte significantly increased the current density, and under the same potential conditions, the current density corresponding to the Cu x O-Fe-1 electrode prepared in Example 1 was significantly greater than that of the Cu x O-Fe-3 prepared in Example 3, the Cu x O-Fe-2 prepared in Example 2 and the Cu x O prepared in Comparative Example 1.

[0081] Figure 10 For the Cu obtained in Example 1 of the present invention x O-Fe-1, the Cu obtained in Example 2 x O-Fe-2, the Cu obtained in Example 3 x O-Fe-3 and the Cu obtained in Comparative Example 1 x O as the open circuit potential test diagram of the working electrode. From Figure 10 it can be seen that the stable potential of the Cu obtained in Example 1 x O-Fe-1 is 0.22V vs . RHE, the stable potential of the Cu obtained in Example 2 x O-Fe-2 is 0.17V vs .RHE, the Cu obtained in Example 3 x O-Fe-3 has a stable potential of 0.20V vs . RHE, the stable potential of the Cu obtained in Comparative Example 1 x O is 0.05V vs . RHE, indicating that under the condition of no power supply, Cu x O-Fe-1 has significantly stronger adsorption ability for NO3 - than Cu x O-Fe-3, Cu x O-Fe-2 and Cu x O, which is more conducive to the further activation of NO3 - .

[0082] Figure 11 For the Cu obtained in Example 1 of the present invention x O-Fe-1, the Cu obtained in Example 2 x O-Fe-2, the Cu obtained in Example 3 x O-Fe-3 and the Cu obtained in Comparative Example 1 x O as the working electrode, respectively in the electrolyte containing NO3 - and the electrolyte without NO3 - electrochemical impedance spectroscopy test diagram. From Figure 11 it can be seen that Cu x O, Cu x O-Fe-1, Cu x O-Fe-2 and Cu x O-Fe-3 in the electrolyte containing NO3 - the diameter of the EIS semicircle is significantly smaller than that in the electrolyte without adding NO3 - , indicating that adding NO3 - to the electrolyte can significantly reduce the resistance of the reaction interface. In the electrolyte containing NO3 - , Cu xThe EIS semicircle diameter of O-Fe-1 is the smallest, indicating that appropriate Fe doping significantly reduces the charge transfer resistance, meaning that Cu x O-Fe-1 has the strongest charge transfer ability.

[0083] Test Example 5

[0084] The materials obtained in Example 1 and Comparative Example 1 above were subjected to electrochemical performance tests and electrocatalytic nitrate reduction performance tests, and the results are as Figures 12 - 17 . Specifically, a standard three-electrode test system was used, and 0.5 mol·L -1 K2SO4 and 100 mg·L -1 KNO3 were used as the electrolyte, an Ag / AgCl electrode was used as the reference electrode, a Pt wire electrode was used as the counter electrode, and Cu x O-Fe-1 obtained in Example 1 of the present invention or Cu x O obtained in Comparative Example 1 was used as the working electrode.

[0085] The electrochemically active surface area (ECSA) was tested by cyclic voltammetry (CV) in the non-Faraday region at scanning rates of 10 mV·s -1 , 20 mV·s -1 , 40 mV·s -1 , 60 mV·s -1 , 80 mV·s -1 and 100 mV·s -1 ; the Tafel curve was carried out at a scanning rate of 10 mV·s -1 ; cyclic voltammetry (CV) was carried out at a scanning rate of 10 mV·s -1 in the range where the initial potential was -0.6 V, -0.7 V, -0.8 V, and -0.9 V vs. RHE and the termination potential was 1.2 V vs. RHE; chronopotentiometry was used to carry out NO3RR tests at constant potentials of -1.2 V, -1.0 V, -0.9 V, -0.8 V, -.7 V, -0.6 V, -0.4 V, and -0.2 V vs.RHE; an inductively coupled plasma emission spectrometer was used to detect the leaching amounts of metal Cu and Fe ions in the electrolyte; chronopotentiometry was used to carry out stability tests at a constant current density of 35 mA·cm -2 .

[0086] Figure 12 For Cu x O-Fe-1 obtained in Example 1 of the present invention and Cu xDouble-capacitance slope plot when O is used as the working electrode. The electrochemically active surface area (ECSA) estimated from the double-layer capacitance (Cdl) is an important indicator for evaluating the performance of electrocatalyst for NO3RR. Electrocatalysts with a larger Cdl have more active sites and higher NO3RR activity. From Figure 12 it can be seen that the Cdl of Cu x O-Fe-1 is 3.3 mF·cm -2 , higher than that of Cu x O (1.5 mF·cm -2 ), indicating that Cu x O-Fe-1 can expose more catalytically active sites and has higher intrinsic activity. The larger ECSA of Cu x O-Fe-1 can be attributed to the lattice distortion caused by appropriate Fe doping and the introduction of more oxygen vacancy defects, resulting in the exposure of more active sites.

[0087] Figure 13 This is the Tafel slope plot of Cu x O-Fe-1 obtained in Example 1 of the present invention and Cu x O obtained in Comparative Example 1 when used as the working electrode. From Figure 13 it can be seen that the Tafel slope of the Cu x O-Fe-1 electrode is 120.7 mV·dec -1 , far better than that of Cu x O (262.1 mV·dec -1 ), indicating that the Fe doping in Cu x O-Fe-1 significantly reduces the NO3RR overpotential, enhances its conductivity and electron transfer ability, and has a higher electrode reaction rate.

[0088] Figure 14 This is the CV curve of Cu x O obtained in Comparative Example 1 when used as the working electrode in an electrolyte without NO3−, Figure 15 This is the CV curve of Cu x O-Fe-1 obtained in Example 1 of the present invention when used as the working electrode in an electrolyte without NO3−. From Figure 14 and Figure 15 it can be seen that obvious oxidation peaks can be observed in the range of -0.5 to 1.0 V vs. RHE, indicating that active hydrogen ( ) is generated and adsorbed on the electrode surface during the reduction process and then oxidized during the oxidation process, and the oxidation peak intensity on the Cu x O-Fe-1 electrode is higher than that on the Cu x O, indicating that Cu x O-Fe-1 has a stronger supply ability.

[0089] Figure 16 Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x O as the working electrode, performance comparison diagram of electrocatalytic NO3RR test at different potentials. As can be seen from Figure 16 it, in the range of -1.2~0.2V vs. RHE, the NH3 yield, Faraday efficiency (FE) and NH3 selectivity shown by the Cu x O-Fe-1 electrode generally show a trend of first increasing and then decreasing. Cu x O-Fe-1 achieves the highest NO3RR yield (1.6mg·h -1 ·mg cat -1 Converted to 2.5mg·h -1 ·cm -2 ), FE (91.7%) and high NH3 selectivity (94.7%) at -0.8V vs. RHE potential, and its NO3RR catalytic performance is significantly better than that of Cu x O (NH3 yield: 0.8mg·h -1 ·mg cat -1 ; FE: 60.6%; selectivity: 82.1%).

[0090] Figure 17 Cu obtained in Example 1 of the present invention x O-Fe-1 NO3RR performance diagram in different initial pH electrolytes. As can be seen from Figure 17 it, high NH3 yields (1.3~1.6mg·h -1 ·mg cat -1 ), NH3 selectivity (92.1%~95.2%) and FE (85.5%~95.9%) can be achieved for NO3RR under different initial pH (3~11) conditions, indicating that the Cu x O-Fe-1 electrocatalyst prepared in this application has good NO3RR activity and stability in a wide pH range.

[0091] Test Example 6

[0092] The obtained material in Example 1 above was tested for electrochemical stability performance, and the results are as Figures 18 - 22 .

[0093] Among them, Figure 18 Cu obtained in Example 1 of the present invention x O-Fe-1 as the working electrode, catalytic activity test diagram of continuous 10 - cycle utilization for electrocatalytic NO3RR. As can be seen from Figure 18It can be seen that during 10 cycles of reuse, the NH3 production rate remains at 1.4 - 1.6 mg·h -1 ·mg cat -1 , the NH3 selectivity remains at 88.4% - 95.7%, and the FE remains at 84.1% - 92.3%, indicating that Cu x O - Fe - 1 always maintains good catalytic activity and stability.

[0094] Figure 19 This is the graph of the leaching amount of metal ions in the electrolyte during 10 consecutive cycles when Cu x O - Fe - 1 obtained in Example 1 of the present invention is used as the working electrode. It can be seen from Figure 19 that overall, the leaching amounts of metal Cu and Fe ions decrease with the increase of the number of cycles until they cannot be detected. The metal leaching amount is much lower than the limit values of the surface water environmental quality standard (GB3838 - 2025) in China (for Class II water, Cu ≤ 1.0 mg·L -1 and Fe ≤ 0.3 mg·L -1 ), indicating that the Cu x O - Fe - 1 catalytic material has excellent chemical stability.

[0095] Figure 20 This is the scanning electron microscope image of Cu x O - Fe - 1 obtained in Example 1 of the present invention after 10 consecutive cycles when used as the working electrode, Figure 21 This is the X - ray diffraction spectrum of Cu x O - Fe - 1 obtained in Example 1 of the present invention before and after 10 consecutive cycles when used as the working electrode. It can be seen from the figure that before and after 10 consecutive cycles, the apparent morphology and crystal structure of Cu x O - Fe - 1 obtained in Example 1 of the present invention have no obvious changes, indicating that the Cu x O - Fe - 1 catalytic material has good stability during long - term NO3RR operation.

[0096] Figure 22 This is the test graph of the electrocatalytic stability performance of Cu x O - Fe - 1 obtained in Example 1 of the present invention at low current density. It can be seen from the figure that at a constant current density of 35 mA·cm -2 , the stability of the sample is evaluated during long - term continuous operation. During continuous operation for 40 h at a current density of 35 mA·cm -2 , the potential is stable at about - 0.8V vs . RHE, and the fluctuation is only within a range of 72 mV. Within the first 15 h, the FE is maintained within the range of 90.8% - 94.5%, and the FE drops to 74.7% only after 30 - 40 h, indicating that the Cu xThe O-Fe-1 electrocatalyst also exhibits good long-term operation stability at low current densities.

[0097] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A preparation method of an iron-doped copper oxide catalyst, characterized in that, The method includes the following steps: (1) Add CuCl2·2H2O to deionized water and dissolve it uniformly to form Solution I; add NaOH to deionized water and dissolve it to form Solution II; add ascorbic acid to deionized water and dissolve it to form Solution III; Drop the Solution I into the Solution II, mix uniformly to obtain Mixed Solution 1, and magnetically stir for 30 min at room temperature; drop the Solution III into the above Mixed Solution 1, and magnetically stir for 1 h at room temperature to obtain Mixed Solution 2; Place the Mixed Solution 2 in a water bath at 80 °C and heat for 2 h, then let it stand at room temperature. After the temperature drops to room temperature, take the precipitate, wash it with deionized water, transfer it to a centrifuge for centrifugation, perform the washing and centrifugation 6 times, and then place it in a vacuum dryer at -50 °C for 24 h to obtain Cu2O powder; (2) Add the Cu2O powder to the deionized water solution containing FeSO4·7H2O, ultrasonically treat for 30 min, and magnetically stir for 1 h to obtain Mixed Solution A; drop the deionized water solution containing sodium borohydride into the Mixed Solution A, magnetically stir for 3 h, let it stand, perform centrifugation, and wash with deionized water. Perform the washing and centrifugation 6 times, and then place it in a vacuum dryer at -50 °C for 24 h, grind and sieve to obtain Cu2O-Fe powder; (3) The Cu2O-Fe powder is subjected to stepwise temperature-rising calcination treatment to obtain Cu x O-Fe, where x indicates that Cu in this material exhibits multiple valence states, and Cu x O can be expressed as Cu / CuO / Cu2O.

2. The method according to claim 1, wherein In step (1), the mass ratio of the CuCl2·2H2O, the NaOH, and the ascorbic acid is 1:2 - 3:1 - 2.

3. The method according to claim 1 or 2, wherein In step (1), the dropping rate of the Solution I and the Solution III is 1 drop / second.

4. The method according to claim 1 or 2, wherein In steps (1) and (2), the conditions of the centrifugation treatment at least satisfy: the rotation speed is 12000 rpm, the time is 10 min, and the temperature is 10 °C.

5. The method according to claim 1 or 2, wherein In step (2), the mass ratio of the Cu2O powder, the FeSO4·7H2O, and the sodium borohydride is 1:1.9 - 7.8:2.

8.

6. The method according to claim 1 or 2, wherein In step (2), the dropping rate of the deionized water solution containing sodium borohydride is 1 drop / second.

7. The method according to claim 1 or 2, wherein In step (3), the staged heating and calcination treatment includes: placing the Cu2O-Fe powder in a magnetic boat, then transferring it to a tube furnace, and under a nitrogen atmosphere, heating it to 300 °C at a rate of 5 °C·min −1 , holding at this temperature for 5 h, and then naturally cooling. Then heating it to 550 °C at a rate of 5 °C·min −1 , holding at this temperature for 5 h, and then naturally cooling.

8. An iron-doped copper oxide catalyst prepared by the method according to any one of claims 1 - 7.

9. Application of the iron-doped copper oxide catalyst according to claim 8 in electrocatalytic synthesis of ammonia from nitrate.

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