CN115838936A - Chromium zinc ferrochromium (ZnCr) 2-x Fe x O 4 ) Spinel electrocatalyst and preparation method and application thereof - Google Patents

Abstract

The invention discloses a zinc ferrate chromite spinel electrocatalyst, a preparation method and application thereof. The method comprises the following specific steps: weighing zincate, chromate and ferrite according to a certain proportion, dissolving in deionized water, and adjusting pH to 10 with sodium hydroxide aqueous solution _～ 12, transferring the mixture into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, carrying out hydrothermal reaction for a certain time at a certain temperature, after the reaction, centrifugally separating to remove supernatant, washing the mixture with deionized water for multiple times, and carrying out vacuum drying to obtain the catalyst precursor. Finally, the catalyst precursor is placed in a horseRoasting in a muffle furnace, naturally cooling to room temperature, and grinding to obtain the needed electrocatalyst. The method for preparing the catalyst has the advantages of easily available raw materials, low cost, simple operation, good controllability and easy mass production; the prepared catalyst is adopted, KOH aqueous solution is taken as electrolyte, nitrogen is taken as raw material gas, and the ammonia production rate and Faraday efficiency of the electrochemical synthesis of ammonia are high.

Description

Chromium zinc ferrochromium (ZnCr) 2-x Fe x O 4 ) Spinel electrocatalyst and preparation method and application thereof

Technical Field

The invention relates to zinc ferrochromate (ZnCr) _2-x Fe _x O ₄ ) A preparation method of a spinel electrocatalyst and application thereof in electrochemical synthesis of ammonia.

Background

Ammonia is one of the chemicals produced in large quantities worldwide, with annual yields exceeding 1.82 million tons, and is used primarily as a synthetic fertilizer. The ammonia also has the advantages of high hydrogen content (mass ratio up to 17.6%), high energy density, easy liquefaction and the like, and is expected to become a clean hydrogen storage carrier. Currently, ammonia is produced by the catalytic Haber-Bosch process from nitrogen and hydrogen at high temperature and pressure (300-500 ℃, 200-300 atm), large-scale factories and high investment are required, energy consumption accounts for about 1-2% of the global total energy consumption, and simultaneously, 1.5% of the global carbon dioxide is discharged annually. Therefore, the realization of the high-efficiency synthesis of ammonia at normal temperature and normal pressure is demanded by people. The electrochemical synthesis of ammonia takes water as a hydrogen source, can be carried out at normal temperature and normal pressure, can be driven by electric energy converted from green energy sources such as solar energy or wind energy, can thoroughly overcome the problems of energy consumption, pollution, safety and the like in the synthesis of ammonia by a Haber-Bosch method, and is considered as a potential ammonia synthesis substitution technology. However, the electrocatalytic nitrogen reduction ammonia synthesis catalyst at core position has been so far severely limited by the linear relationship of adsorption energy, and the catalytic activity and selectivity are still at low level. To N ₂ Strongly adsorbing early transition metal elements (elements on the left side of the periodic table) such as chromium (Cr), vanadium (V) and manganese (Mn), easily forming stable nitride phases in the reaction atmosphere of ammonia synthesis, hinderingThe subsequent hydrogenation step is adopted, and the activity of the synthetic ammonia is poor; and to N ₂ Relatively weakly adsorbed late transition metals (right elements of the periodic Table) such as ruthenium (Ru) and iron (Fe) due to their relatively moderate N ₂ The adsorption energy shows excellent activity of electrocatalytic synthesis of ammonia, but the adsorption to hydrogen is strong, the Hydrogen Evolution Reaction (HER) cannot be effectively inhibited, the selectivity is not ideal, and how to break through the constraint relation becomes the kinetic bottleneck of the development of the electrochemical synthesis of ammonia at present. Therefore, it is a great problem for scientists to develop a catalyst material that can break the limitation of the linear relationship.

Spinel (structural general formula is AB) ₂ O ₄ ) The spinel material has a cubic crystal structure, oxygen ions are in cubic close packing, divalent cations A occupy tetrahedral gaps of four-time coordination, trivalent cations B occupy octahedral gaps of six-time coordination, the A-site and B-site cation types of the spinel material can be regulated, the distribution of the cations has great influence on the performance of the spinel material, and the spinel material is widely used in the fields of magnetic materials, microwave dielectric materials, humidity-sensitive and gas-sensitive materials, chemical catalysis and the like. The literature (journal of Hebei university (Nature science edition), 2012, 12 (6): 619-622) adopts a solid phase method to prepare ZnO and Fe ₂ O ₃ 、Cr ₂ O ₃ Grinding the raw materials, and roasting at high temperature to prepare ZnCr _2-x Fe _x O ₄ (x =0,0.3,0.5,0.8,1.0) spinel and use as a magnetic material, it was found that high temperatures above 1100 ℃ were required to successfully dope Fe in the B-site ³⁺ And the prepared material has low purity and contains Cr ₂ O ₃ And ZnO, etc., which affect further applications. The literature (Results in Physics,2021, 104622) uses zinc nitrate, nickel nitrate, chromium nitrate and ferric nitrate powder as raw materials to prepare Ni with Zn at A position partially substituted by Ni and Cr for glycine fuel by a microwave combustion method _0.4 Zn _0.6-x Cr _x Fe ₂ O ₄ (x is more than or equal to 0.0 and less than or equal to 0.6) series spinels and is used as a magnetic material. Seeking a simple and controllable B site doped Fe ³⁺ Pure ZnCr of (5) _2-x Fe _x O ₄ The synthesis method has important significance.

Disclosure of Invention

In order to solve the technical problems mentioned in the background technology, the invention provides a preparation method and application of a chromite zinc ferrite spinel electrocatalyst _2-x Fe _x O ₄ The (x =0,0.4,0.8,1.2,1.6,2) electrocatalyst avoids the linear relation limitation on a single transition metal to a certain extent through the synergistic effect of Cr and Fe active sites, and realizes the high-efficiency electrocatalytic synthesis of ammonia.

The technical scheme of the invention is as follows: a preparation method of a zinc ferrate spinel electrocatalyst comprises the following specific steps:

firstly, weighing zincate, chromate and ferrite according to a certain proportion, dissolving in a solvent, then adding an alkali solution to adjust the pH = 10-12, then carrying out hydrothermal reaction, and carrying out post-treatment to obtain a dried catalyst precursor.

The molar ratio of the zincate, the chromate and the ferrite is 1 (2-x), x is more than 0 and less than 2;

the hydrothermal synthesis temperature range is 150-200 ℃;

secondly, roasting the catalyst precursor obtained after drying in the first step in a muffle furnace, naturally cooling to room temperature, and grinding to obtain the needed electrocatalyst;

further, in the above technical solution, in the first step, the solvent is deionized water; the alkali solution is 3.0-6.0mol/L sodium hydroxide or potassium hydroxide water solution.

Further, in the above technical scheme, in the first step, the hydrothermal reaction and the post-treatment are carried out by transferring the metal precursor into a hydrothermal reaction kettle with a polytetrafluoroethylene lining, carrying out hydrothermal reaction for a certain time at a certain temperature, after the reaction, centrifugally separating to remove the supernatant to obtain the catalyst precursor, washing with deionized water for 3 times, and vacuum drying.

Furthermore, in the technical scheme, in the first step, the hydrothermal synthesis time is in the range of 4-12 hours, and the vacuum drying temperature is in the range of 60-80 ℃.

Further, in the above technical solution, in the first step, the zincate includes zinc chloride, zinc sulfate, zinc nitrate and zinc acetate; chromates include chromium chloride, chromium sulfate, and chromium nitrate; ferrites include ferric chloride, ferric sulfate, and ferric nitrate; the concentration of the zincate is 0.05 to 0.2mol/L.

Furthermore, in the above technical scheme, in the second step, the roasting temperature is in the range of 300-500 ℃, and the roasting time is in the range of 0.5-3 hours.

Further, in the above technical solution, in the first step, the zincate, chromate and ferrite are respectively zinc acetate, chromium chloride and ferric chloride, the molar ratio of the zinc acetate to the chromium chloride to the ferric chloride is 1.2; in the second step, the roasting temperature is 400 ℃ and the roasting time is 1 hour.

The invention provides a pure chromium zinc ferrite spinel electrocatalyst obtained by the method, which is prepared by a general formula of ZnCr _2-x Fe _x O ₄ 2-x and x respectively represent the atomic ratio of each element, and x is larger than 0 and smaller than 2.

Further, in the above technical solution, x is selected from any number of 0.4,0.8,1.2,1.6.

The invention provides an application of the electrocatalyst prepared by the method in the electrochemical synthesis of ammonia, which comprises the following specific steps: the prepared electrocatalyst is loaded on a carbon felt to be used as a cathode, the carbon felt without the catalyst is used as an anode, KOH aqueous solution is used as electrolyte, high-purity nitrogen is blown to the cathode at a certain flow rate (200 ml/min), and then a direct current power supply is connected to carry out electrolysis under constant voltage (1.5-2.5V) at room temperature and normal pressure, so that the electrocatalyst has excellent performance of electrochemically reducing nitrogen to produce ammonia.

The invention has the following beneficial effects: (1) The catalyst has the advantages of easily obtained raw materials for preparation, low cost, simple operation, good controllability and easy mass production. (2) The catalyst for electrochemically synthesizing ammonia prepared by the invention is nano zinc ferrate spinel. (3) The prepared electrocatalyst takes 0.1mol/LKOH aqueous solution as electrolyte and nitrogen as raw material gas, and the ammonia production rate and Faraday efficiency of the electrochemical synthesis ammonia can respectively reach 29.26 mu g h ^-1 cm ^-2 And 18.41%. The term "faradaic efficiency" refers to the percentage of actual ammonia production versus the electrochemical theory of ammonia production.

Drawings

FIG. 1 is the XRD pattern of the catalyst prepared in example 1;

FIG. 2 shows ZnCr obtained in example 1 ₂ O ₄ 、ZnCr _1.2 Fe _0.8 O ₄ And ZnFe ₂ O ₄ XPS characterization results of the catalyst;

FIG. 3 shows ZnCr obtained in example 1 _1.2 Fe _0.8 O ₄ The TEM and HRTEM characterization results of the catalysts;

FIG. 4 shows ZnCr obtained in example 1 ₂ O ₄ 、ZnCr _1.2 Fe _0.8 O ₄ And ZnFe ₂ O ₄ The nitrogen temperature programmed desorption result of the catalyst;

FIG. 5 the performance of the catalyst prepared in example 1 for the electrochemical synthesis of ammonia at 2.1V;

FIG. 6 ZnCr obtained by example 1 _1.2 Fe _0.8 O ₄ The current density of the catalyst for synthesizing ammonia under different electrolysis voltages;

FIG. 7 ZnCr obtained by example 1 _1.2 Fe _0.8 O ₄ The ammonia production rate and the Faraday efficiency of the catalyst for synthesizing ammonia under different electrolysis voltages;

FIG. 8 XRD pattern of sample prepared according to comparative example 1;

figure 9 XRD pattern of the sample prepared in comparative example 2.

Detailed Description

The above-mentioned aspects of the present invention will be described in further detail by examples.

Example 1

(1) According to the chemical formula ZnCr _2-x Fe _x O ₄ (x =0,0.4,0.8,1.2,1.6,2) in the ratio of 1 (2-x) x weighing 5mmol of zinc acetate and corresponding amount of chromium chloride and ferric chloride, dissolving in deionized water to obtain 6 solutions with different ratios, adjusting the pH of the solution to be = 10-12 by using 3.0mol/L sodium hydroxide aqueous solution, adding water to make the total volume of the solution be 50ml, and then respectively transferring the solution into a container with the water to be mixed with the solutionCarrying out hydrothermal reaction for 8 hours in 6 hydrothermal reaction kettles with polytetrafluoroethylene liners at 180 ℃, after the reaction, centrifugally separating and removing supernatant to obtain 6 catalyst precursors, washing the catalyst precursors for 3 times by using deionized water, and drying the catalyst precursors in vacuum for later use.

(2) And (3) roasting the dried catalyst precursors in a muffle furnace at 400 ℃ for 1 hour respectively, naturally cooling to room temperature, and grinding to obtain the needed electrocatalyst.

X-ray diffraction (XRD) analysis of the catalyst obtained in example 1 revealed from fig. 1 that all samples have similar XRD patterns with distinct characteristic diffraction peaks near 2 θ =18.4 °,30.3 °,35.7 °,43.4 °,53.9 °,57.4 ° and 63.1 ° and are assigned to ZnCr ₂ O ₄ Spinel standard card PDF No.22-1107 and ZnFe ₂ O ₄ The (111), (220), (311), (400), (422), (511) and (440) crystal faces of spinel standard card PDF No.22-1012, and no other miscellaneous peaks appear, indicating that the prepared catalyst has a spinel structure and no miscellaneous phase. With increasing Fe content (x value), all characteristic diffraction peaks move to small angles of 2 θ. For the diffraction peak corresponding to the (311) crystal face appearing in the XRD spectral line, according to the formula 1/d of the interplanar spacing ² _hkl ＝(h ² +k ² +l ² )/a ² And Bragg equation n λ =2d _hkl sin θ (where a is the lattice constant, h, k and l are the lattice plane Miller indices, d _hkl The (311) interplanar spacing for catalysts of different compositions was calculated for the interplanar spacing of the (h, K, l) planes, n being the order of the diffraction, typically n =1, λ being the X-ray wavelength, cu ka 1 (λ =0.15406 nm), θ being the diffraction angle, and calculations showed that the lattice constant a increased from 0 to 2 when the value of X increased from 0 to 2

Is gradually increased to->

It is shown that an increase in Fe content leads to lattice expansion, which is mainly due to the larger radius of Fe ³⁺ Ion->

With relatively small radius substituted for spinel octahedral centres

As a result, octahedral-centered Cr is also shown ³⁺ Partially coated with Fe ³⁺ Together, form a homogeneous, single phase spinel crystal.

ZnCr obtained in example 1 ₂ O ₄ ,ZnCr _1.2 Fe _0.8 O ₄ And ZnFe ₂ O ₄ The catalyst was characterized by X-ray photoelectron spectroscopy (XPS), in FIG. 2a the spectrum of Zn 2p showed 2 peaks at binding energies of 1021.4eV and 1044.3eV, while the spectrum of Zn LMM Auger (FIG. 2 b) showed a peak at Auger electron kinetic energy of about-989 eV which is different from that of metallic Zn (992 eV), indicating Zn is in the form of Zn ²⁺ The valence state. Comparative ZnCr ₂ O ₄ And ZnCr _1.2 Fe _0.8 O ₄ The spectrum of Cr 2p (FIG. 2 c) shows that the difference between the two is not obvious, and the Cr 2p appears at the binding energies of 578.8 and 576.5eV _3/2 Peaks, cr 2p at 588.3 and 586.2eV binding energies _1/2 Peak, indicating that the valence of Cr is Cr ³⁺ 。ZnCr _1.2 Fe _0.8 O ₄ With ZnFe ₂ O ₄ The spectrum of Fe2p is similar (FIG. 2 d), with Fe2p appearing at 711.0 and 713.5eV binding energies _3/2 Peak at Fe2p _3/2 Typical Fe appears on one side of the binding energy of peak height ³⁺ Satellite peak, indicating that the valence state of Fe is Fe ³⁺ 。

ZnCr obtained in example 1 _1.2 Fe _0.8 O ₄ The catalyst is characterized by a Transmission Electron Microscope (TEM) (figure 3), and it can be seen that the particle size distribution of the catalyst is in a narrow range, the average particle size is about 6.6nm, and a Selective Area Electron Diffraction (SAED) spectrogram has obvious diffraction rings of (311), (400), (422) and (440) crystal faces, which indicates that the catalyst is in a polycrystalline structure; the crystal grains are characterized by a high-resolution transmission electron microscope (HRTEM) and have crystal lattice stripes with regular arrangement and 0.252nm and 0.209nm intervals, which are respectively assigned to the (311) crystal face and the (400) crystal face, and the crystal lattice stripes are consistent with XRD results.

Example 2

To implementationZnCr obtained in example 1 ₂ O ₄ 、ZnCr _1.2 Fe _0.8 O ₄ And ZnFe ₂ O ₄ Nitrogen temperature programmed desorption of catalyst (N) ₂ TPD) in order to determine the chemisorption performance of the catalysts prepared on nitrogen, the results being shown in figure 4 and table 1. Chemisorption favors the elongation of the nitrogen N.ident.N bond for activation, but for nitrogen reduction to ammonia, it is desirable that the nitrogen adsorption strength be moderate, neither too strong nor too weak. As can be seen from FIG. 4, before Fe was introduced, znCr ₂ O ₄ Nitrogen desorption peaks appeared at 209.3 and 436.7 ℃; similarly, znFe ₂ O ₄ Obvious desorption peaks appear at 220.7 ℃ and 371.9 ℃, which shows that the two have stronger chemical adsorption to nitrogen, and ZnCr after the Fe is introduced _1.2 Fe _0.8 O ₄ The nitrogen desorption peak temperature drop of (a) was at 184.5 c, indicating that the introduction of Fe reduced the chemisorption strength to nitrogen. It is noteworthy that ZnCr can be seen from Table 1 _1.2 Fe _0.8 O ₄ The adsorption capacity to nitrogen is not obviously reduced and is still 0.950cm ³ N ₂ Cat/g, with ZnCr ₂ O ₄ Amount of adsorption at 209.3 ℃ (0.945 cm) ³ N ₂ Kcat.) shows that the introduction of Fe improves the adsorption performance of the catalyst to nitrogen and solves the problem that the pure Cr-based spinel catalyst is too strong in nitrogen adsorption.

TABLE 1N ₂ Peak temperature of TPD and desorption N ₂ Volume of

Example 3

ZnCr prepared in example 1 _2-x Fe _x O ₄ (x =0,0.4,0.8,1.2,1.6,2) was tested for ammonia performance in electrochemical synthesis. Loading the prepared electrocatalyst on a carbon felt as a cathode, blowing nitrogen to the cathode at a flow rate of 200ml/min by taking a 0.1mol/L KOH aqueous solution as an electrolyte and a carbon felt as an anode, switching on a power supply, carrying out constant-voltage electrolysis under a voltage of 2.1V, analyzing and measuring ammonia gas generated by electrolysis, and obtaining a resultReferring to FIG. 5, it can be seen that ZnCr _1.2 Fe _0.8 O ₄ The ammonia generating rate and the Faraday efficiency (x = 0.8) are as high as 29.26 mu g h ^-1 cm ^-2 And 8.16% of ZnCr ₂ O ₄ (x = 0) is significantly improved, mainly by introducing Fe which improves the chemisorption and activation properties of the catalyst towards nitrogen, while ZnFe ₂ O ₄ The ammonia production rate and faraday efficiency (x = 2.0) was the lowest, indicating that more HER side reactions may occur with this catalyst.

Example 4

The difference from example 1 is in voltage, and this example examines the performance of electrochemically synthesizing ammonia at different electrolytic voltages. Referring to FIG. 6, FIG. 6 shows ZnCr _1.2 Fe _0.8 O ₄ The current density curves at different electrolysis voltages, as can be seen from the figure, the electrolysis current density remains stable over the electrolysis time as the electrolysis proceeds, indicating a smooth electrochemical reaction on the catalyst. FIG. 7 shows ZnCr _1.2 Fe _0.8 O ₄ As a result of the performance of electrocatalytic ammonia production, it can be seen that when the voltage was 1.5V, 10.08. Mu. G h was obtained ^-1 cm ^-2 The ammonia production rate and the Faraday efficiency of 18.41 percent are increased, the electrolytic current is increased almost linearly along with the increase of the voltage, the ammonia production rate is also increased synchronously, and the maximum ammonia production rate of 29.26 mu g h is obtained at 2.1V ^-1 cm ^-2 The Faraday efficiency was 8.16% at this time.

Example 5

This example is similar to example 1, and is different in that: step (1) zinc acetate, chromium chloride and ferric chloride in corresponding amounts are weighed according to the proportion of 1.1.2 _1.2 Fe _0.8 O ₄ . When 2.1V constant voltage electrolysis is carried out, the ammonia production rate is 28.43 mu g h ^-1 cm ^-2 Faradaic efficiency was 8.09%.

Comparative example 1

In order to be in contact with the catalyst prepared in example 1 (ZnCr) _1.6 Fe _0.4 O ₄ ) By contrast, replacement of Cr by Co, znCo according to the formula _1.6 Fe _0.4 O ₄ Ratio 1 given5mmol of zinc acetate and corresponding amounts of cobalt chloride and iron chloride were weighed out and dissolved in deionized water, and the procedure was as in example 1. Adjusting the pH of the solution to be 10-12 by using 3.0mol/L sodium hydroxide aqueous solution, adding water to make the total volume of the solution be 50ml, then transferring the solution into a hydrothermal reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction at 180 ℃ for 8 hours, after the reaction, centrifugally separating to remove supernatant fluid to obtain a catalyst precursor, washing the catalyst precursor for 3 times by using deionized water, and drying the catalyst in vacuum. Roasting the obtained product for 1 hour at 400 ℃ in a muffle furnace, naturally cooling the obtained product to room temperature, and grinding the obtained product to obtain the needed electrocatalyst.

XRD analysis of the sample obtained in comparative example 1 was performed, and as can be seen from FIG. 8, the XRD spectrum of the sample obtained by the preparation was identical to that of ZnCr in example 1 _1.6 Fe _0.4 O ₄ The XRD patterns (see x =0.4 in fig. 1) are clearly different, with distinct diffraction peaks at 2 θ =31.8 °,34.4 °,36.3 °,47.6 °,56.6 °,62.9 ° and 67.9 °, attributed to ZnO (standard card PDF No. 36-1451). Distinct characteristic diffraction peaks, attributed to ZnCo, appear at 2 θ =18.9 °,31.2 °,36.8 °,44.7 °,59.3 °,65.1 ° and 63.1 ° ₂ O ₄ Spinel (Standard card PDF No. 23-1390), indicating that the sample prepared in comparative example 1 contains ZnO and ZnCo ₂ O ₄ And (4) phase. It is noted that, though according to the formula ZnCo _1.6 Fe _0.4 O ₄ The given stoichiometric ratio 1 ₂ O ₄ No other miscellaneous peaks except the matched diffraction peak appear, especially no ZnFe appears ₂ O ₄ The consistent series of characteristic diffraction peaks for spinel (PDF No. 22-1012) indicates that the sample prepared in comparative example 1 does not contain ZnFe ₂ O ₄ Spinel phase, the synthesis reaction of ferric chloride added to the raw material does not produce any iron-containing crystalline species of interest (no unwanted peaks), or only amorphous Fe-based species. Thus, the sample prepared in comparative example 1 had a crystal structure other than pure ZnCo _1.6 Fe _0.4 O ₄ Spinel, but ZnO and ZnCo ₂ O ₄ A mixture of spinels.

Sample obtained in comparative example 1When the product is electrolyzed at constant voltage of 2.1V, the ammonia production rate is 6.38 mu g h ^-1 cm ^-2 Much lower than the ZnCr prepared in example 1 _1.6 Fe _0.4 O ₄ Catalyst (20.83 μ g h) ^-1 cm ^-2 ) (ii) a The Faraday efficiency was 4.91%, which is also lower than that of ZnCr prepared in example 1 _1.6 Fe _0.4 O ₄ Catalyst (5.07%).

Comparative example 2

For the purpose of the catalyst synthesized in example 1 (ZnCr) _1.6 Fe _0.4 O ₄ ) By contrast, replacing Fe by Co, znCr according to the formula _1.6 Co _0.4 O ₄ Given a ratio of 1.6.

FIG. 9 is an XRD spectrum of the sample prepared in comparative example 2, and from FIG. 9, it can be seen that the XRD spectrum of the sample obtained by the preparation is identical to that of ZnCr in example 1 _1.6 Fe _0.4 O ₄ The XRD patterns (see x =0.4 in fig. 1) are similar, and distinct characteristic diffraction peaks appear near 2 θ =18.4 °,30.3 °,35.7 °,43.4 °,57.4 ° and 63.1 °, which are assigned to ZnCr ₂ O ₄ Spinel (Standard card PDF No. 22-1107) and ZnCo ₂ O ₄ Spinel (Standard card PDF No. 23-1390), and no other peaks were present, indicating that the sample prepared in comparative example 2 had ZnCr _1.6 Co _0.4 O ₄ Spinel structure and no impurity phase. When 2.1V constant voltage electrolysis is carried out, the ammonia production rate is 14.34 mu g h ^-1 cm ^-2 The Faraday efficiencies were 4.26%, which were lower than those of ZnCr prepared in example 1 _1.6 Fe _0.4 O ₄ A catalyst.

The foregoing embodiments illustrate the principles, principal features and advantages of the invention, and it will be understood by those skilled in the art that the invention is not limited to the foregoing embodiments, which are merely illustrative of the principles of the invention, and that various changes and modifications may be made therein without departing from the scope of the principles of the invention.

Claims (10)

1. A preparation method of a zinc ferrate chromite spinel electrocatalyst is characterized by comprising the following steps: the method comprises the following specific steps:

firstly, weighing zincate, chromate and ferrite according to a certain proportion, dissolving the zincate, the chromate and the ferrite in a solvent, and then adding an alkali solution to adjust the pH =10 _～ 12, carrying out hydrothermal reaction, and carrying out post-treatment to obtain a dried catalyst precursor;

the molar ratio of the zincate, the chromate and the ferrite is 1 (2-x), x is more than 0 and less than 2;

the hydrothermal synthesis temperature range is 150-200 ℃;

and step two, roasting the catalyst precursor obtained after drying in the step one in a muffle furnace, naturally cooling to room temperature, and grinding to obtain the needed electrocatalyst.

2. The method of claim 1, wherein: in the first step, the solvent is deionized water; the alkali solution is 3.0-6.0mol/L sodium hydroxide or potassium hydroxide water solution.

3. The method of claim 1, wherein: in the first step, the hydrothermal reaction and the post-treatment are that the metal precursor is transferred into a hydrothermal reaction kettle with a polytetrafluoroethylene lining for hydrothermal reaction for a certain time at a certain temperature, after the reaction, the catalyst precursor is obtained after the supernatant is removed by centrifugal separation, washed for 3 times by deionized water and dried in vacuum.

4. The method of claim 3, wherein: in the first step, the hydrothermal synthesis time is in the range of 4 hours _～ The vacuum drying temperature is between 60 ℃ and 80 ℃ within 12 hours.

5. The method of claim 1, wherein: in the first step, the zincate comprises zinc chloride, zinc sulfate, zinc nitrate and zinc acetate; chromates include chromium chloride, chromium sulfate, and chromium nitrate; ferrites include ferric chloride, ferric sulfate, and ferric nitrate; the concentration of the zincate is 0.05 to 0.2mol/L.

6. The method of claim 1, wherein: in the second step, the roasting temperature is 300-500 ℃ and the roasting time is 0.5-3 hours.

7. The method of claim 1, wherein: in the first step, the zincate, the chromate and the ferrite are respectively zinc acetate, chromium chloride and iron chloride, the molar ratio of the zinc acetate to the chromium chloride to the iron chloride is 1.2; in the second step, the roasting temperature is 400 ℃ and the roasting time is 1 hour.

8. Claim 1 of the oil _～ 7 the zinc chromite spinel electrocatalyst obtained by the process according to any one of claims, characterized in that: is represented by the general formula ZnCr _2-x Fe _x O ₄ 2-x and x respectively represent the atomic ratio of each element, and x is larger than 0 and smaller than 2.

9. Zinc chromite spinel electrocatalyst prepared by the process of claim 8, characterised in that: x is any number of 0.4,0.8,1.2,1.6.

10. According to claim 1 _～ 7, the application of the electrocatalyst prepared by the method in the electrochemical synthesis of ammonia is characterized by comprising the following specific steps: the prepared electrocatalyst is loaded on a carbon felt as a cathode, the carbon felt without the catalyst is used as an anode, KOH aqueous solution is used as electrolyte, high-purity nitrogen is blown to the cathode at a certain flow rate, and then a direct current power supply is switched on for electrolysis.

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