Iron-doped copper oxide catalyst, preparation method thereof and application of iron-doped copper oxide catalyst in electro-catalysis of nitrate to synthesize ammonia

Abstract

The invention relates to the technical field of electro-catalysis materials, and discloses an iron-doped copper oxide catalyst, a preparation method thereof and application of the iron-doped copper oxide catalyst in electro-catalysis of nitrate to synthesize ammonia. The method comprises the steps that CuCl2 serves as a metal precursor, ascorbic acid serves as a reducing agent, and Cu2O nanoparticles are obtained through a hydrothermal precipitation method; then, Cu2O is added into a solution containing FeSO4, sodium borohydride is added, centrifugal washing and drying are carried out, and the iron-doped copper oxide nitrate electroreduction catalyst which is rich in defects and uniform in metal dispersion is obtained through a programmed heating pyrolysis reduction method. The electro-catalytic material obtained by adopting the method disclosed by the invention has a relatively large catalytic active area and relatively abundant defect sites and oxygen vacancies, the nitrate adsorption and activation effects are improved, the supply of active hydrogen is promoted by constructing stable heterogeneous active sites, the product selectivity and Faraday efficiency in NO3RR are improved, and the electro-catalytic material has good durability.

Description

Technical Field

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

[0002] Electrocatalytic nitrate reduction (NO 3 RR) is a project to control nitrate (NO) in water using renewable electricity. 3 - ) pollution and produce high value-added ammonia (NH 3 ), provides a win-win opportunity for environmental restoration and resource recovery, and has become a promising NH to replace the traditional HB process 3 Synthesis technology.

[0003] However, under neutral conditions, NH 3 The generation efficiency and selectivity of hydrogen are affected by the competitive hydrogen (H 2 ) and nitrogen (N 2 ) generation process. Therefore, it is necessary to design and construct efficient electrocatalysts to regulate NO 3 The selectivity of RR products is important for achieving NH 3 The efficient synthesis is of great significance.

[0004] The active non-precious metal copper has NO 3 - Similar lowest unoccupied molecular orbital Track, its d The orbital can form a coordination bond with the lone pair of electrons of nitrogen, which is beneficial to NO 3 - adsorption and activation, widely used in NO 3 However, copper-based electrocatalysts have problems such as large overpotential, easy accumulation of intermediate nitrite, and limited hydrogenation capacity.

[0005] Therefore, the optimal design of copper-based catalysts is an important way to achieve electrocatalytic NO 3 - Efficient reduction to NH 3 The key. Summary of the invention

[0006] The purpose of the present invention is to solve the above problems in the prior art and to provide a method for preparing an iron-doped copper oxide catalyst, which can achieve high NH 3 Yield, solving the problem of reducing low concentration nitrate to NH under neutral conditions 3 The problem of low selectivity and low Faradaic efficiency.

[0007] In order to achieve the above object, the first aspect of the present invention provides a method for preparing an iron-doped copper oxide catalyst, the method comprising the following steps: (1) CuCl 2 ·2H 2 O was added to deionized water and uniformly dissolved to form solution I; NaOH was added to deionized water and dissolved to form solution II; ascorbic acid was added to deionized water and dissolved to form solution III;

[0008] The solution I was added dropwise to the solution II, mixed evenly to obtain a mixed solution 1, and magnetically stirred at room temperature for 30 minutes; the solution III was added dropwise to the mixed solution 1, and magnetically stirred at room temperature for 1 hour to obtain a mixed solution 2;

[0009] The mixed solution 2 was placed in a water bath at 80°C for 2 hours, then allowed to stand at room temperature, and the precipitate was washed with deionized water and transferred to a centrifuge for centrifugal treatment. The washing and centrifugal treatment were repeated 6 times, and then placed in a vacuum dryer at -50°C for 24 hours to obtain Cu 2 O powder;

[0010] (2) Cu 2 O powder is added to the FeSO 4 7H 2 O in a deionized water solution, ultrasonically treated for 30 minutes, and magnetically stirred for 1 hour to obtain a mixed solution A; the deionized water solution containing sodium borohydride was added dropwise to the mixed solution A, magnetically stirred for 3 hours, allowed to stand, centrifuged, and washed with deionized water. The washing and centrifugation were performed 6 times, and then placed at -50 ° C for vacuum drying for 24 hours, ground and sieved to obtain Cu 2 O-Fe powder;

[0011] (3) Cu 2 O-Fe powder is subjected to stage-by-stage calcination to obtain Cu x O-Fe.

[0012] Preferably, in step (1), the CuCl 2 ·2H 2 The mass ratio of O, the NaOH and the ascorbic acid is 1:2~3:1~2.

[0013] Further preferably, in step (1), the dropping speed of the solution I and the solution III is 1 second / drop.

[0014] Preferably, in step (1) and step (2), the centrifugal treatment conditions at least meet the following conditions: rotation speed of 12000 rpm, time of 10 min, and temperature of 10°C.

[0015] Preferably, in step (2), the Cu 2 O powder, the FeSO 4 7H 2 O. The mass ratio of the sodium borohydride is 1:1.9~7.8:2.8.

[0016] Further preferably, in step (2), the dropping speed of the deionized water solution containing sodium borohydride is 1 second / drop.

[0017] Preferably, in step (3), the staged temperature rise calcination treatment comprises: 2 The O-Fe powder was placed in a magnetic boat and then transferred to a tube furnace. The temperature was set at 5 °C min under a nitrogen atmosphere. -1 The temperature was raised to 300°C at a rate of 5°C / min and kept at this temperature for 5 h. The mixture was then cooled naturally and heated to 300°C / min at a rate of 5°C / min. -1 The temperature was raised to 550°C at a rate of , and kept at this temperature for 5 h, and then cooled naturally.

[0018] 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.

[0019] The third aspect of the present invention provides the use of the iron-doped copper oxide catalyst described in the second aspect of the present invention in electrocatalytic nitrate synthesis of ammonia.

[0020] The method provided by the present invention also has at least the following beneficial effects: (1) The present invention adopts a simple coprecipitation and thermal reduction method to provide a method for preparing an iron-doped copper oxide catalyst, comprising: 2 As metal precursor, ascorbic acid as reducing agent, Cu was obtained by hydrothermal precipitation method. 2 O nanoparticles; then, Cu 2 O added containing FeSO 4 Sodium borohydride is added to the solution, and after centrifugal washing and drying, a defect-rich, metal-uniformly dispersed iron-doped copper oxide nitrate electro-reduction catalyst is obtained by a programmed temperature pyrolysis reduction method. The preparation process of the present invention is simple, and on the basis of improving the catalytic activity of the copper-based catalyst, the preparation cost of the catalyst can be reduced. The electrocatalytic material prepared by this method has a large catalytic active area, abundant defect sites and oxygen vacancies, and a high current density, thereby improving the nitrate adsorption and activation effect, and by constructing stable heterogeneous active sites, promoting the supply of active hydrogen, and increasing NO 3 The product selectivity and Faradaic efficiency in RR are high, and it has good durability.

[0021] (2) The iron-doped copper oxide catalyst prepared by the present invention has copper and iron uniformly dispersed, wherein copper exists at 0, +1 and +2 valences at the same time, and acts as a NO 3 RR's catalytic cathode material is used to efficiently and stably electrocatalyze low-concentration nitrate to produce ammonia under near-neutral conditions. -1 K 2 SO 4 and 100mg·L -1 KNO 3 In the electrolyte (pH 6.53), the ammonia yield 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 active area. In 10 cycles, the ammonia yield, selectivity and Faraday efficiency are maintained at 1.4~1.6 mg·h -1 mg 催化剂 -1 , 88.4~95.7% and 84.1~92.3%, with excellent recycling effect and long-term stability. The technical solution of the present invention is a highly active, stable near-neutral low-concentration NO 3 The design of RR catalysts provides a promising approach. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is an X-ray diffraction spectrum of the materials obtained in Example 1 of the present invention and Comparative Example 1;

[0023] Figure 2 The Cu obtained in Example 1 of the present invention x Scanning electron microscope test results of O-Fe-1;

[0024] Figure 3 The Cu obtained in Example 1 of the present invention x Transmission electron microscope test results of O-Fe-1;

[0025] Figure 4 The Cu obtained in Example 1 of the present invention x High-resolution transmission electron microscopy test results of O-Fe-1;

[0026] Figure 5 The Cu obtained in Example 1 of the present invention x High-angle annular dark-field STEM and elemental distribution of O-Fe-1;

[0027] Figure 6 The Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1x X-ray photoelectron spectrum of Cu 2p of O;

[0028] Figure 7 The Cu obtained in Example 1 of the present invention x X-ray photoelectron spectrum of Fe 2p in O-Fe-1;

[0029] Figure 8 The Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x X-ray photoelectron spectrum of O 1s in O;

[0030] Fig. 9 When the materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention are used as working electrodes, the materials are respectively 3 - Electrolyte, containing NO 3 - LSV curve performance comparison chart in electrolyte;

[0031] Fig.10 This is an open circuit potential test diagram when the materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1 of the present invention are used as working electrodes;

[0032] Fig.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, the materials are respectively 3 - Electrolyte, NO-free 3 - Electrochemical impedance spectroscopy test diagram in electrolyte;

[0033] Fig.12 The Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x Dual capacitance slope diagram when O is used as the working electrode;

[0034] Fig.13 The Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x Tafel slope plot when O is used as the working electrode;

[0035] Fig.14 The Cu obtained in Comparative Example 1 x When O is used as the working electrode, in the absence of NO 3 - CV curves in electrolyte;

[0036] Fig.15 The Cu obtained in Example 1 of the present inventionx When O-Fe-1 is used as the working electrode, in the absence of NO 3 - CV curves in electrolyte;

[0037] Fig.16 The Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x When O was used as the working electrode, electrocatalysis of NO was performed at different potentials. 3 Performance comparison chart of RR test;

[0038] Fig.17 The Cu obtained in Example 1 of the present invention x O-Fe-1 in electrolytes with different initial pH values 3 RR performance graph;

[0039] Fig.18 The Cu obtained in Example 1 of the present invention x When O-Fe-1 was used as the working electrode, it was used for electrocatalytic NO for 10 consecutive cycles. 3 Catalytic activity test diagram of RR;

[0040] Fig.19 The Cu obtained in Example 1 of the present invention x When O-Fe-1 is used as the working electrode, the amount of metal ions leached from the electrolyte during 10 consecutive cycles;

[0041] Fig. 20 The Cu obtained in Example 1 of the present invention x Scanning electron microscopy image after 10 consecutive cycles when O-Fe-1 was used as the working electrode;

[0042] Fig.21 The Cu obtained in Example 1 of the present invention x X-ray diffraction spectra of O-Fe-1 before and after 10 consecutive cycles when used as the working electrode;

[0043] Fig. 22 At low current density, the Cu obtained in Example 1 of the present invention x O-Fe-1 electrocatalytic stability performance test diagram. DETAILED DESCRIPTION

[0044] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0045] In the present invention, "Cu x O" in" x " indicates that the Cu in the material is in multiple valence states, such as Cu x O can be expressed as Cu / CuO / Cu 2 O.

[0046] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, the raw materials are all commercially available.

[0047] Example 1

[0048] This example is used to provide a method for preparing an iron-doped copper oxide catalyst, and the method comprises the following steps: (1) 2 mg CuCl 2 ·2H 2 O was added to 20 mL of deionized water and uniformly dissolved to form solution I; 5 mg of NaOH was added to 5 mL of deionized water and dissolved to form solution II; 3 mg of ascorbic acid was added to 5 mL of deionized water and dissolved to form solution III;

[0049] The solution I was added dropwise to the solution II at a rate of 1 second / drop, and the mixture was uniformly mixed to obtain a mixed solution 1, and the mixture was magnetically stirred for 30 minutes at room temperature; the solution III was added dropwise to the mixed solution 1 at a rate of 1 second / drop, and the mixture was magnetically stirred for 1 hour at room temperature to obtain a mixed solution 2;

[0050] The mixed solution 2 was placed in a preheated water bath, heated at 80°C for 2h, and then allowed to stand at room temperature. The precipitate was washed with deionized water and transferred to a centrifuge for centrifugal treatment. The washing and centrifugal treatment were repeated 6 times, and then placed at -50°C for vacuum drying for 24h to obtain Cu 2 O powder;

[0051] The centrifugal treatment conditions are as follows: rotation speed of 12000 rpm, temperature of 10° C., and time of 10 min.

[0052] (2) 0.1 g Cu 2 O powder was added to contain 0.39 g FeSO 4 7H 2O in 30 mL deionized water solution, ultrasonically treated for 30 min, and magnetically stirred for 1 h to obtain a mixed solution A; 20 mL deionized water solution containing 0.28 g sodium borohydride was added to the mixed solution A at a rate of 1 second / drop, magnetically stirred for 3 h, allowed to stand, centrifuged, and washed with deionized water. The washing and centrifugation were performed 6 times, and then placed at -50 ° C for 24 h in vacuum drying, ground, and passed through a 200-mesh sieve to obtain Cu 2 O-Fe powder;

[0053] The centrifugal treatment conditions are as follows: rotation speed of 12000 rpm, temperature of 10° C., and time of 10 min.

[0054] (3) Cu 2 The O-Fe powder was placed in a magnetic boat and then transferred to a tube furnace. The temperature was set at 5 °C min under a nitrogen atmosphere. -1 The temperature was raised to 300°C at a rate of 5°C / min and kept at this temperature for 5 h. The mixture was then cooled naturally and heated to 300°C / min at a rate of 5°C / min. -1 The temperature was raised to 550°C at a rate of 1.5 ℃ and kept at this temperature for 5 h. The catalyst was cooled naturally to obtain an iron-doped copper oxide catalyst, which was recorded as Cu x O-Fe-1.

[0055] Example 2

[0056] This example is carried out according to the method of Example 1, except that in step (2), the Cu 2 O powder, the FeSO 4 7H 2 O, the mass ratio of the sodium borohydride is 1:1.9:2.8, and the remaining steps and parameters are the same as those in Example 1. Finally, the iron-doped copper oxide catalyst is obtained, denoted as Cu x O-Fe-2.

[0057] Example 3

[0058] This example is carried out according to the method of Example 1, except that in step (2), the Cu 2 O powder, the FeSO 4 7H 2 O, the mass ratio of the sodium borohydride is 1:7.8:2.8, and the remaining steps and parameters are the same as those in Example 1. Finally, the iron-doped copper oxide catalyst is obtained, denoted as Cu x O-Fe-3.

[0059] Comparative Example 1

[0060] This example is carried out according to the method of Example 1, except that the Cu prepared in step (1) 2 The O powder does not go through step (2) and directly enters step (3) to obtain a copper oxide catalyst, denoted as Cux O, the remaining steps and parameters are the same as in Example 1.

[0061] Test Example 1

[0062] The materials obtained in Example 1 and Comparative Example 1 were subjected to X-ray diffraction spectrum test, and the results are as follows: Figure 1 shown.

[0063] Depend on Figure 1 It can be seen that the Cu obtained in Comparative Example 1 x O have diffraction peaks at 35.5°, 36.5°, 38.7°, and 43.2°, corresponding to CuO (-111), Cu 2 O (111), CuO (111), Cu (111) crystal planes, which indicates that Cu x O is a multi-phase structure, containing multivalent Cu. x The diffraction peaks of O-Fe-1 at 33.2°, 35.4°, 35.5°, and 43.2° correspond to Fe 2 O 3 (104), Fe 3 O 4 (311), CuO (-111), Cu 2 O(111) and Cu(111) crystal planes, indicating that Fe was successfully doped into Cu containing multivalent Cu. x O, forming iron oxides.

[0064] Test Example 2

[0065] The morphology and structure of the material obtained in Example 1 were tested. Figure 2~Figure 6 shown.

[0066] in, Figure 2 Cu obtained in Example 1 of the present invention x Scanning electron microscope test results of O-Fe-1, Figure 3 Cu obtained in Example 1 of the present invention x Transmission electron microscope test results of O-Fe-1. Figure 4 Cu obtained in Example 1 of the present invention x High-resolution transmission electron microscopy test results of O-Fe-1, Figure 5 Cu obtained in Example 1 of the present invention x High-angle annular dark-field STEM and element distribution map of O-Fe-1.

[0067] Depend on Figure 2 It can be seen that the Cu obtained in Example 1 of the present invention x O-Fe-1 is in the form of a sheet formed by the aggregation of a large number of nanoparticles. Figure 3 and Figure 4 It can be seen that the Cu obtained in Example 1 of the present invention x O-Fe-1 has a clear interface, and the lattice spacings in the outer regions are 0.246nm, 0.251nm, and 0.206nm, respectively, which is similar to Cu 2 O (111), CuO (-111), and Cu (111) crystal planes match, and the lattice spacing in the inner region is 0.256nm and 0.262nm, corresponding to Fe 3 O 4 (311) and Fe 2 O 3 (104) crystal plane. Figure 5 It can be seen that Cu, Fe and O are evenly distributed, indicating that Fe is evenly doped into Cu. x In O.

[0068] Test Example 3

[0069] The materials obtained in Example 1 and Comparative Example 1 were subjected to X-ray photoelectron spectroscopy characterization test, and the results are as follows: Figure 6~Figure 8 shown.

[0070] in, Figure 6 The Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x X-ray photoelectron spectrum of Cu 2p of O, Figure 7 Cu obtained in Example 1 of the present invention x X-ray photoelectron spectrum of Fe 2p in O-Fe-1, Figure 8 Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x X-ray photoelectron spectrum of O 1s in O.

[0071] Depend on Figure 6 It can be seen that in Cu x O, the fitted peaks at 932.4, 934.1, 952.1, and 953.7 eV correspond to Cu 0 / 1+ (23.9 at%), Cu 2+ (21.8 at%), Cu 0 / 1+ (14.7 at%) and Cu 2+ (10.5 at%); in Cu x In O-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%), Cu0 / 1+ (17.8at%) and Cu 2+ (8.3 at%), of which Cu 0 / 1+ After doping with Fe, Cu x Cu in O-Fe-1 0 / 1+ The peak proportion increased and the peak center moved toward the low binding energy direction by 0.8 and 0.7 eV, respectively, which indicates that Fe doping leads to Cu 0 / 1+ The increase in electron density and the regulation of the local electronic structure are helpful to regulate the Cu d With center, promote electron transfer, increase NO 3 RR performance.

[0072] Depend on Figure 7 It can be seen that the Cu obtained in Example 1 of the present invention x In O-Fe-1, the fitted peaks at 709.3 / 722.5, 710.7 / 724.0, and 713.4 / 726.2 eV correspond to Fe 0 (11.1 / 11.3at%), Fe 2+ (14.3 / 7.1at%) and Fe 3+ (15.3 / 15.5at%), of which Fe 3+ The peak area accounts for the largest proportion.

[0073] Depend on Figure 8 It can be seen that Cu x O and Cu x In the O 1s spectrum of O-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-coordinated oxygen defect sites, and surface hydroxyl groups (-OH). Peaks O2 and O3 in O 1s show obvious negative shifts of about 0.4 and 0.6 eV after Fe doping, which may be due to the Cu x Charge redistribution at the O-Fe-1 interface results in electron transfer from Fe to Cu x O, which is the Fe atom and Cu x The electronic interaction between O and Cu provides an important basis. x The proportion of peak O2 and peak O3 of O-Fe-1 is significantly enhanced, indicating that Fe doping will cause local structural distortion or introduce more surface defects, increase the surface catalytic active sites, which is also the reason for the decrease in the proportion of peak O1. The increase in surface defects and active sites can enhance the adsorption and activation of intermediates, promote electron enrichment, and increase NO 3 RR activity.

[0074] Test Example 4

[0075] The electrochemical performance of the materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1 was tested. The results are as follows: Figure 9~Figure 11 .

[0076] Specifically, a standard three-electrode test system was used, using 0.5 mol·L -1 K 2 SO 4 and 100mg·L -1 KNO 3 The electrolyte was the Ag / AgCl electrode as the reference electrode, the Pt wire electrode as the counter electrode, and the Cu obtained in Example 1 of the present invention was used. x O-Fe-1, Cu obtained in Example 2 x O-Fe-2, Cu obtained in Example 3 x O-Fe-3 or Cu obtained in Comparative Example 1 x O was used as the working electrode. At 10 mV·s -1 Linear sweep voltammetry (LSV) tests were performed at a scan rate of 10 s; open circuit potential (OCP) tests lasted for 400 s; and electrochemical impedance spectroscopy (EIS) tests were performed at a scan rate of 10 -2 Hz~10 6 Hz frequency range.

[0077] Fig. 9 Cu obtained in Example 1 of the present invention x O-Fe-1, Cu obtained in Example 2 x O-Fe-2, Cu obtained in Example 3 x O-Fe-3 and Cu obtained in Comparative Example 1 x O as the working electrode in the absence of NO 3 - The electrolyte contains NO 3 - LSV curve performance comparison chart in electrolyte. Fig. 9 It can be seen that the electrolyte contains NO 3 - The current density is significantly increased, and under the same potential conditions, the Cu prepared in Example 1 x The current density corresponding to the O-Fe-1 electrode is significantly greater than that of the Cu prepared in Example 3. x O-Fe-3, Cu prepared in Example 2 x O-Fe-2 and Cu prepared in Comparative Example 1 x O.

[0078] Fig.10 Cu obtained in Example 1 of the present invention x O-Fe-1, Cu obtained in Example 2 x O-Fe-2, Cu obtained in Example 3x O-Fe-3 and Cu obtained in Comparative Example 1 x Open circuit potential test diagram when O is used as the working electrode. Fig.10 It can be seen that the Cu obtained in Example 1 x The stable potential of O-Fe-1 is 0.22V vs . RHE, Cu obtained in Example 2 x The stable potential of O-Fe-2 is 0.17V vs .RHE, Cu obtained in Example 3 x The stable potential of O-Fe-3 is 0.20V vs . RHE, Cu obtained in Comparative Example 1 x The stable potential of O is 0.05 V vs . RHE, indicating that Cu x O-Fe-1 versus NO 3 - The adsorption capacity is significantly stronger than Cu x O-Fe-3、Cu x O-Fe-2 and Cu x O, more favorable to NO 3 - Further activation.

[0079] Fig.11 Cu obtained in Example 1 of the present invention x O-Fe-1, Cu obtained in Example 2 x O-Fe-2, Cu obtained in Example 3 x O-Fe-3 and Cu obtained in Comparative Example 1 x O as the working electrode, respectively in the presence of NO 3 - Electrolyte, NO-free 3 - Electrochemical impedance spectroscopy test diagram in electrolyte. Fig.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 NO 3 - The EIS semicircle diameter in the electrolyte is significantly larger than that without adding NO. 3 - The electrolyte is smaller, indicating that NO 3 - It can significantly reduce the resistance of the reaction interface. 3 - In the electrolyte, Cu xThe EIS semicircle diameter of O-Fe-1 is the smallest, indicating that appropriate Fe doping significantly reduces the charge transfer resistance, which means that Cu x O-Fe-1 has the strongest charge transfer ability.

[0080] Test Example 5

[0081] The electrochemical performance test and electrocatalytic nitrate reduction performance test of the materials obtained in Example 1 and Comparative Example 1 were performed. The results are as follows: Figure 12~Figure 17 Specifically, a standard three-electrode test system was used, using 0.5 mol·L -1 K 2 SO 4 and 100mg·L -1 KNO 3 The electrolyte was the Ag / AgCl electrode as the reference electrode, the Pt wire electrode as the counter electrode, and the Cu obtained in Example 1 of the present invention was used. x O-Fe-1 or Cu obtained in Comparative Example 1 x O as the working electrode.

[0082] The electrochemically active surface area (ECSA) was measured at a scan rate of 10 mV·s -1 , 20mV·s -1 , 40mV·s -1 、60mV·s -1 , 80mV·s -1 and 100mV·s -1 The non-Faraday range under the condition of cyclic voltammetry (CV) was used for testing; the Tafel curve was measured at 10 mV·s -1 The scan rate of cyclic voltammetry (CV) was 10 mV·s -1 The scan rate was carried out in the range of initial potential of -0.6 V, -0.7 V, -0.8 V and -0.9 V vs. RHE and termination potential of 1.2 V vs. RHE. The NO was detected by chronopotentiometry at constant potential 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. 3 RR test; inductively coupled plasma emission spectrometer was used to detect the leaching amount of metal Cu and Fe ions in the electrolyte; chronopotentiometry was used at 35 mA cm -2 The stability test was carried out at a constant current density.

[0083] Fig.12 Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 xThe double 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 a good indicator of the electrocatalyst NO 3 An important indicator of RR performance, electrocatalysts with large Cdl have more active sites and higher NO 3 RR activity. Fig.12 It can be seen that Cu x The Cdl of O-Fe-1 is 3.3 mF·cm -2 , higher than Cu x O (1.5mF cm -2 ), indicating that Cu x O-Fe-1 can expose more catalytic active sites and has higher intrinsic activity. x The larger ECSA of O-Fe-1 can be attributed to the lattice distortion caused by moderate Fe doping and the introduction of more oxygen vacancy defects, which expose more active sites.

[0084] Fig.13 Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x Tafel slope diagram when O is used as working electrode. Fig.13 It can be seen that Cu x The Tafel slope of the O-Fe-1 electrode is 120.7 mV·dec -1 , much better than Cu x O(262.1mV·dec -1 ), indicating that Cu x Fe doping in O-Fe-1 significantly reduces the NO 3 RR overpotential enhances its conductivity and electron transfer ability, and has a higher electrode reaction rate.

[0085] Fig.14 Cu obtained in Comparative Example 1 x When O is used as the working electrode, in the absence of NO 3 −CV curves in electrolyte, Fig.15 Cu obtained in Example 1 of the present invention x When O-Fe-1 is used as the working electrode, in the absence of NO 3 −CV curve in electrolyte. Fig.14 and Fig.15 It can be seen that an obvious oxidation peak can be observed in the range of -0.5~1.0V vs. RHE, which indicates that active hydrogen ( ) is generated during the reduction process and adsorbed on the electrode surface, and then oxidized during the oxidation process, and Cu x The oxidation peak intensity on O-Fe-1 electrode is higher than that on Cu x O, Cux O-Fe-1 has a strong supply ability.

[0086] Fig.16 Cu obtained in Example 1 of the present invention x O-Fe-1 and Cu obtained in Comparative Example 1 x When O was used as the working electrode, electrocatalysis of NO was performed at different potentials. 3 Performance comparison chart of RR test. Fig.16 It can be seen that in the range of -1.2~0.2V vs. RHE, Cu x The NH 3 Yield, Faradaic efficiency (FE) and NH 3 The overall selectivity shows a trend of first increasing and then decreasing. x O-Fe-1 achieved the highest NO at -0.8 V vs. RHE potential. 3 RR yield (1.6 mg·h -1 mg cat -1 Converted to 2.5 mg·h -1 cm -2 ), FE (91.7%) and high NH 3 Selectivity (94.7%), its NO 3 The catalytic performance of RR is significantly better than that of Cu x O(NH 3 Yield: 0.8 mg·h -1 mg cat -1 ; FE: 60.6%; selectivity: 82.1%).

[0087] Fig.17 Cu obtained in Example 1 of the present invention x O-Fe-1 in electrolytes with different initial pH values 3 RR performance diagram. Fig.17 It can be seen that under different initial pH (3~11) conditions, NO 3 RR can achieve high NH 3 Yield (1.3~1.6mg·h -1 mg cat -1 )、NH 3 Selectivity (92.1%~95.2%) and FE (85.5%~95.9%), it can be seen that the Cu prepared in this application x O-Fe-1 electrocatalyst has good NO 3 RR activity and stability.

[0088] Test Example 6

[0089] The electrochemical stability performance test of the material obtained in Example 1 was carried out, and the results are as follows: Figure 18 to Figure 22 .

[0090] in, Fig.18 Cu obtained in Example 1 of the present invention x When O-Fe-1 was used as the working electrode, it was used for electrocatalytic NO for 10 consecutive cycles. 3 The catalytic activity test diagram of RR. Fig.18 It can be seen that during the 10-time recycling process, NH 3 The yield was maintained at 1.4~1.6mg·h -1 mg cat -1 , NH 3 The selectivity was maintained at 88.4%~95.7%, and the FE was maintained at 84.1%~92.3%, indicating that Cu x O-Fe-1 always maintains good catalytic activity and stability.

[0091] Fig.19 Cu obtained in Example 1 of the present invention x When O-Fe-1 is used as the working electrode, the amount of metal ions leached from the electrolyte during 10 consecutive cycles. Fig.19 It can be seen that the leaching amount of metal Cu and Fe ions decreases with the increase of the number of cycles until it cannot be detected. The leaching amount of metals is far lower than the limit value of my country's surface water environmental quality standard (GB3838-2025) (Class II water Cu≤1.0mg·L -1 and Fe≤0.3mg·L -1 ), indicating that Cu x O-Fe-1 catalytic material has excellent chemical stability.

[0092] Fig. 20 Cu obtained in Example 1 of the present invention x When O-Fe-1 is used as the working electrode, the scanning electron microscope image after 10 consecutive cycles is shown. Fig.21 Cu obtained in Example 1 of the present invention x When O-Fe-1 is used as the working electrode, the X-ray diffraction spectrum before and after 10 consecutive cycles. As can be seen from the figure, the Cu obtained in Example 1 of the present invention is x The apparent morphology and crystal structure of O-Fe-1 have not changed significantly, indicating that Cu x O-Fe-1 catalytic material in long-term NO 3 RR has good stability during operation.

[0093] Fig. 22Under low current density, the Cu obtained in Example 1 of the present invention x O-Fe-1 electrocatalytic stability performance test diagram. As shown in the figure, at 35mA·cm -2 The stability of the sample was evaluated by long-term continuous operation at a constant current density of 35 mA cm -2 During the continuous operation of 40h at the current density, the potential was stable at -0.8V vs . RHE, the fluctuation is only within 72mV. In the first 15h, FE is maintained in the range of 90.8%~94.5%, and FE drops to 74.7% after 30~40h, indicating that the Cu prepared in this application x The O-Fe-1 electrocatalyst also exhibits good long-term operation stability at low current density.

[0094] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for preparing an iron-doped copper oxide catalyst, characterized in that: The method comprises 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; The solution I was added dropwise to the solution II, mixed evenly to obtain a mixed solution 1, and magnetically stirred at room temperature for 30 minutes; the solution III was added dropwise to the mixed solution 1, and magnetically stirred at room temperature for 1 hour to obtain a mixed solution 2; The mixed solution 2 was placed in a water bath at 80°C for 2 hours, and then allowed to stand at room temperature. After the temperature dropped to room temperature, the precipitate was taken, washed with deionized water, and transferred to a centrifuge for centrifugal treatment. The washing and centrifugal treatments were repeated 6 times, and then the solution was placed in a vacuum dryer at -50°C for 24 hours to obtain Cu2O powder. (2) Adding Cu2O powder to a deionized water solution containing FeSO4·7H2O, ultrasonically treating for 30 min, and magnetically stirring for 1 h to obtain a mixed solution A; adding a deionized water solution containing sodium borohydride dropwise to the mixed solution A, magnetically stirring for 3 h, allowing to stand, centrifuging, and washing with deionized water. The washing and centrifuging were repeated 6 times, and then vacuum dried at −50°C for 24 h, and ground and sieved to obtain Cu2O-Fe powder; (3) The Cu2O-Fe powder is subjected to a step-by-step temperature calcination treatment to obtain Cu x O-Fe.

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 speed of the solution I and the solution III is 1 second / drop.

4. The method according to claim 1 or 2, wherein: In step (1) and step (2), the centrifugal treatment conditions at least meet the following conditions: rotation speed of 12000 rpm, time of 10 min, and temperature of 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 speed of the deionized water solution containing sodium borohydride is 1 second / drop.

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

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

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

Images