Preparation method and application of cobalt-iron alloy catalyst

Abstract

The invention belongs to the technical field of electrocatalytic nitrate reduction synthesis of ammonia, and particularly relates to a preparation method of a cobalt-iron alloy catalyst, which at least comprises the following steps: 1, preparing a cobalt-iron oxide precursor by adopting an epoxide gel method; and 2, mixing the cobalt-iron oxide precursor powder obtained in the step 1 with an alcohol solvent, water and a Nafion solution, carrying out ultrasonic treatment to prepare ink, spraying the ink on a current collector, and then carrying out electroreduction on a loaded cathode material with a constant current in an electrolyte protected by argon to generate the cobalt-iron alloy catalyst. Compared with the prior art, the CoxFey alloy catalyst with a lattice expansion effect and an adjustable electronic structure is prepared by combining an alloying strategy with an in-situ electrochemical reduction method, so that the problem of adsorption-activation imbalance of an intermediate of a Co-based catalyst in a low-concentration NO3 <-> environment is relieved, and the practical process of electro-catalysis NO3 <-> RR for low-concentration NO3 <-> wastewater treatment is accelerated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of electrocatalytic nitrate reduction to synthesize ammonia. In particular, it relates to a method for preparing a cobalt-iron alloy cathode catalyst by combining an epoxide gel method with electrochemical reduction, and its application in electrocatalytic nitrate reduction to synthesize ammonia. BACKGROUND

[0002] Groundwater is an important fresh water resource for human survival. However, in recent years, affected by human activities, the content of NO3 - in groundwater has seriously exceeded the standard of the World Health Organization (WHO) for drinking water (NO3 - concentration limit of 50 mg / L -1 ), not only threatening human health, but also leading to a decline in the quality of agricultural products. Previous studies have explored Cu, Ru, Pd, Co and other transition metal-based catalysts for electrocatalytic NO3RR to synthesize ammonia. Among them, cobalt-based materials have a low energy barrier for the dissociation of NO2* and NO*, which promotes the desorption of NO3 - and its intermediates, thereby accelerating the subsequent hydrogenation step and exhibiting excellent ammonia selectivity, making them ideal candidates for NO3RR.

[0003] Previous studies have evaluated the catalytic performance of Co-based catalysts under high concentration of NO3 - , at which the competitive HER can be effectively inhibited. However, under high NO3 - concentration, even if the electrolysis time is extended, the removal rate of nitrate is still insufficient, and the remaining NO3 - concentration is still much higher than the drinking water standard. It is worth noting that the NO3 - concentration in common water pollution is usually low, generally below 0.2 M. Therefore, designing Co-based electrocatalysts that adapt to low NO3 - concentration conditions to achieve rapid NO3 - -to-NH3 conversion has important value, but still faces great challenges.

[0004] Studies have shown that NO3RR includes two key processes: deoxidation and hydrogenation steps. For the deoxidation process, the affinity of NO3 - directly affects the overall reaction rate, and the enrichment of NO3 - around the active site can enhance effective collisions and improve catalytic performance. In addition, H2O adsorption and dissociation play a crucial role in initiating the NO3RR process, and the generated *H helps the subsequent hydrogenation step. Therefore, optimizing H2O adsorption is crucial for improving *H availability. However, NO3 -Both H2O and H2 are electron-donating groups, which will compete for the active sites. Too strong or too weak adsorption of intermediates on the surface of electrocatalysts will lead to poisoning or serious accumulation in the electrolyte, which will hinder the overall activity. Therefore, achieving moderate adsorption and desorption of intermediates on the surface of the catalyst is a key challenge to achieve efficient catalytic reaction.

[0005] Therefore, the present application aims to provide a preparation method and application of a cobalt-iron alloy catalyst, which prepares Co x Fe y alloy catalyst with lattice expansion effect and adjustable electronic structure by alloying strategy combined with in-situ electrochemical reduction method, alleviates the adsorption-activation imbalance problem of intermediates in Co-based catalysts in low-concentration NO3 - environment, and accelerates the practicalization process of electrocatalytic NO3RR for low-concentration NO3 - wastewater treatment. SUMMARY

[0006] The present application aims to provide a preparation method and application of a cobalt-iron alloy catalyst, which prepares Co x Fe y alloy catalyst with lattice expansion effect and adjustable electronic structure by alloying strategy combined with in-situ electrochemical reduction method, alleviates the adsorption-activation imbalance problem of intermediates in Co-based catalysts in low-concentration NO3 - environment, and accelerates the practicalization process of electrocatalytic NO3RR for low-concentration NO3 - wastewater treatment.

[0007] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A preparation method of a cobalt-iron alloy catalyst, at least comprising the following steps:

[0009] Firstly, a cobalt-iron oxide precursor is prepared by an epoxide gel method: a cobalt source and an iron source are dissolved in a solvent, after ultrasonic water bath dissolution, an alkylene oxide is added for stirring to form a brown gel, the gel is aged, and then vacuum drying is performed to obtain a brown powder, which is the cobalt-iron oxide precursor; as a mild proton consumer, the epoxide gradually adjusts the pH value of the solution, promotes the controllable hydrolysis-crosslinking reaction of metal cations, and finally forms a three-dimensional gel network. Compared with the rapid pH mutation caused by the traditional alkaline system (such as OH-, CO3 2- and NH3, etc.), this slow gelation process effectively inhibits element segregation, providing a uniform precursor structure basis for the construction of cobalt-iron alloy in subsequent electro-reduction treatment.

[0010] In the second step, the cobalt iron oxide precursor powder obtained in the first step is mixed with ethanol (or methanol), water and perfluorosulfonic acid type polymer solution to form ink by ultrasonication, which is then sprayed on the current collector to form a cathode (anode is a platinum sheet or graphite rod). Subsequently, the loaded cathode material is electro-reduced in an argon-protected electrolyte at a constant current or constant voltage to generate a cobalt iron alloy catalyst. 3+ The hydrolysis ability is much stronger than Co 2+ , the strongest hydroxylation effect, OH - Fe 3+ Consumption, the formation of polyhydroxy iron compounds, rather than with Co 2+ After drying, amorphous iron oxide and cobalt oxide gel are formed, which are further reduced to CoFe alloy under the driving of negative potential. Cobalt iron oxide precursors with different cobalt iron ratios lead to the formation of cobalt iron alloys with different ratios after electroreduction. x Fe y The addition of an appropriate amount of Fe into the alloy induces a certain lattice expansion, stretching the Co-Fe bond length and achieving an electron transfer effect. This intermetallic charge transfer-induced surface charge redistribution optimizes the electronic structure of the alloy, enhancing the adsorption and activation of nitrogen-containing intermediates, thereby alleviating the adsorption-activation imbalance of the intermediates to a certain extent.

[0011] As an improvement to the preparation method of the cobalt-iron alloy catalyst of the present invention, the cobalt source is at least one of cobalt chloride hexahydrate, cobalt nitrate hexahydrate and cobalt sulfate heptahydrate, the iron source is at least one of ferric chloride hexahydrate and ferric nitrate nonahydrate, the solvent is at least one of isopropanol, methanol, ethanol and ethylene glycol, and the alkylene oxide is at least one of propylene oxide, cis-2,3-butylene oxide, 1,2-butylene oxide, epichlorohydrin, epifluorohydrin and epibromohydrin.

[0012] As an improvement to the preparation method of the cobalt-iron alloy catalyst of the present invention, the molar ratio of the Co element to the Fe element in the cobalt-iron alloy catalyst is 0.1 to 10:1.

[0013] As an improvement to the preparation method of the cobalt-iron alloy catalyst of the present invention, the molar ratio of the Co element to the Fe element in the cobalt-iron alloy catalyst is 1:1.

[0014] As an improvement to the preparation method of the cobalt-iron alloy catalyst of the present invention, the current collector is at least one of carbon paper, carbon cloth, carbon felt, foam copper and foam nickel.

[0015] As an improvement to the preparation method of the cobalt-iron alloy catalyst of the present invention, the electrolyte is alkaline or neutral, the alkaline electrolyte is KOH or NaOH; the neutral electrolyte is K2SO4, Na2SO4, KClO4 or NaClO4.

[0016] As an improvement of the preparation method of the cobalt-iron alloy catalyst of the present application, the current of the constant current electro-reduction in the second step is -50 to -5000 mAcm -2 , or the voltage of the constant voltage electro-reduction is -0.1 to 20 V, and the time of the electro-reduction is 1 to 100 minutes, so as to achieve the purpose of fully reducing the oxide precursor to generate the cobalt-iron alloy.

[0017] The present application also provides an application of the catalyst of the present application in the electro-catalytic reduction of nitrate to synthesize ammonia.

[0018] Compared with the prior art, the present application has at least the following beneficial effects:

[0019] Firstly, the present application provides a method based on the combination of the epoxide gel method and in-situ electro-reduction, to prepare a Co x Fe y alloy catalyst with lattice expansion effect and adjustable electronic structure.

[0020] Secondly, Co1Fe1 achieves the best ammonia Faraday efficiency (FE NH3 ) of 90.0% and the highest ammonia yield (Y -1 ) of 55.5 mgh -2 cm NH3 .

[0021] Thirdly, in the long-term stability test of 10 h, Co1Fe1 maintains the FE NH3 of about 85%, and has excellent structural stability.

[0022] Fourthly, under the conditions of low-concentration NO3 - of 0.02 M and 0.05 M, Co1Fe1 achieves the FE NH3 of >80% in a wide potential interval (-0.1 to -0.3 V vs. RHE).

[0023] Fifthly, Co1Fe1 achieves the NO3 - removal rate of 99.5% in the treatment of low-concentration nitrate-containing wastewater of 0.02 M, and the residual NO3 - concentration can reach the WHO drinking water standard. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The XRD patterns of the Co2Fe1, Co 1.5 Fe1, Co1Fe1, Co1Fe 1.5 and Co1Fe2 catalysts in Example 1 of the present application.

[0025] Figure 2This is the characterization of the Co1Fe1 catalyst in Example 1 of the invention, where (a) is a TEM image of the Co1Fe1 catalyst, (b) is an HR-TEM image of the Co1Fe1 catalyst, and (c) is an EDS mapping image of the Co1Fe1 catalyst.

[0026] Figure 3 The SEM images of different catalysts in Example 1 of the invention, where (a) is Co2Fe1 and (b) is Co 1.5 Fe1, (c) is Co1Fe1, (d) is Co1Fe 1.5 , (e) is Co1Fe2.

[0027] Figure 4 In Example 2 of the present invention, Co2Fe1, Co 1.5 Fe1, Co1Fe1, Co1Fe 1.5 NO3RR performance diagram of Co1Fe2 catalysts, where (a) is the LSV curve in 1.0MKOH electrolyte containing 0.1MKNO3, and (b) is the ammonia Faraday efficiency (FE) at different potentials. NH3 ), (c) is the ammonia yield (Y NH3 ).

[0028] Figure 5 The NO3RR performance of Co1Fe1 in Example 2 of the present invention in 1.0M KOH electrolyte containing 0.02M, 0.05M and 0.1M KNO3, where (a) is the FE at different potentials NH3 , (b) is Y at different potentials NH3 .

[0029] Figure 6 The long-term stability test of NO3RR for the Co1Fe1 catalyst in Example 2 of the present invention was carried out in a 1.0MKOH electrolyte containing 0.1MKNO3 at a potential of -0.3V vs. RHE for 5 cycles (2 hours per cycle), where (a) is FE NH3 and Y NH3 , (b) is the chronopotentiometry (CP) curve.

[0030] Figure 7 This is the material characterization of Co1Fe1 after continuous electrolysis for 10 hours at a potential of -0.3 V vs. RHE in Example 2 of the invention, where (ab) are HR-TEM images, (c) is an EDSmapping image, and (d) is an XRD spectrum.

[0031] Figure 8The concentration of NO3 - , NO2 - , NH3 as a function of time and their corresponding N product selectivity for the 10 hours potentiostatic electrolysis at -0.3 V vs. RHE in 1.0 M KOH electrolyte containing 0.02 M KNO3 for Example 2 of the invention. DETAILED DESCRIPTION

[0032] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0033] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in the following description. In other instances, well-known methods have not been described in detail in order to avoid unnecessarily obscuring the present application.

[0034] In order to make the above objectives, features and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0035] Example 1

[0036] Co x Fe y Preparation of alloy catalysts:

[0037] (1) Chemical raw materials used in the preparation process: cobalt chloride hexahydrate, ferric chloride hexahydrate, isopropyl alcohol, propylene oxide, ethanol, water, 5wt% Nafion solution, potassium hydroxide, potassium nitrate, argon, TORAY TGP-H-060 carbon paper; instruments and equipment used in the preparation process: vacuum drying oven, plasma cleaning instrument, electrochemical workstation, H-type electrolytic cell, ultrasonic cleaning instrument.

[0038] (2) Preparation of Co1Fe1 alloy catalyst:

[0039] 87.8 mg of cobalt chloride hexahydrate and 100.6 mg of ferric chloride hexahydrate were dissolved in 1 mL of isopropyl alcohol, and after 30 minutes of ultrasonic water bath dispersion, 2 mL of propylene oxide was added and stirred for 5 minutes to form a brown gel. The gel was aged for 24 hours, and then vacuum dried at 80°C overnight to obtain a brown powder. 10 mg of Co1Fe1-OP powder was mixed with 980 μL of ethanol, 980 μL of water and 40 μL of 5wt% Nafion solution for 30 minutes to prepare an ink, which was sprayed on a 0.5 x 0.5 cm 2 of oxygen plasma treated carbon paper (mass loading of 2 mg cm -2) forming the cathode (anode was a platinum sheet). Subsequently, the cathode material was reduced galvanostatically in 1 M KOH electrolyte under argon protection at -500 mA cm -2 The supported cathode material was reduced galvanostatically for 30 min to form the Co1Fe1 alloy catalyst.

[0040] (3) Preparation of Co2Fe1 alloy catalyst

[0041] Co1Fe1-OP powder was mixed with 980 μL ethanol, 980 μL water and 40 μL 5 wt% Nafion solution for 30 min under sonication to form an ink, which was sprayed onto a 0.5 x 0.5 cm 2 of oxygen plasma treated carbon cloth (mass loading of 2 mg cm -2 ) forming the cathode (anode was a graphite rod). Subsequently, the cathode material was reduced galvanostatically in 1 M KOH electrolyte under argon protection at -100 mA cm -2 The supported cathode material was reduced galvanostatically for 40 min to form the Co2Fe1 alloy catalyst.

[0042] (4) Preparation of Co 1.5 Fe1 alloy catalyst

[0043] Co1Fe1-OP powder was mixed with 980 μL ethanol, 980 μL water and 40 μL 5 wt% Nafion solution for 30 min under sonication to form an ink, which was sprayed onto a 0.5 x 0.5 cm 2 of oxygen plasma treated carbon felt (mass loading of 2 mg cm -2 ) forming the cathode (anode was a platinum sheet). Subsequently, the cathode material was reduced galvanostatically in 1 M NaOH electrolyte under argon protection at -1000 mA cm -2 The supported cathode material was reduced galvanostatically for 50 min to form the Co 1.5 Fe1 alloy catalyst.

[0044] (5) Preparation of Co1Fe 1.5 alloy catalyst

[0045] 70.2 mg of cobalt chloride hexahydrate and 120.7 mg of ferric chloride hexahydrate were dissolved in 1 mL of isopropanol and dispersed in a water bath with ultrasound for 30 minutes. 2 mL of propylene oxide was added and stirred for 5 minutes to form a brown gel. The gel was aged for 24 hours and then dried in a vacuum at 80°C overnight to obtain a brown powder. 10 mg of Co1Fe1-OP powder was mixed with 980 μL of ethanol, 980 μL of water, and 40 μL of 5 wt% Nafion solution and ultrasound-treated for 30 minutes to prepare an ink, which was then sprayed on a 0.5 × 0.5 cm 2 On the copper foam treated with oxygen plasma (mass loading of 2 mg cm -2 ) to form a cathode (graphite rod for anode). Then, the loaded cathode material was reduced in a 1M potassium sulfate electrolyte under argon protection at a constant voltage of -10V for 30 minutes to generate Co1Fe 1.5 Alloy catalyst.

[0046] (6) Preparation of Co1Fe2 alloy catalyst

[0047] 58.5 mg of cobalt chloride hexahydrate and 134.1 mg of ferric chloride hexahydrate were dissolved in 1 mL of isopropanol and dispersed in a water bath with ultrasound for 30 minutes. 2 mL of propylene oxide was added and stirred for 5 minutes to form a brown gel. The gel was aged for 24 hours and then dried in a vacuum at 80°C overnight to obtain a brown powder. 10 mg of Co1Fe1-OP powder was mixed with 980 μL of ethanol, 980 μL of water, and 40 μL of 5 wt% Nafion solution and ultrasound-treated for 30 minutes to prepare an ink, which was then sprayed on a 0.5 × 0.5 cm 2 On the nickel foam treated with oxygen plasma (mass loading of 2 mg cm -2 ) to form a cathode (anode using platinum sheet). Subsequently, the supported cathode material was reduced at a constant voltage of -15 V for 20 minutes in a 1M sodium sulfate electrolyte under argon protection to generate a Co1Fe2 alloy catalyst.

[0048] Co x Fe y Structural characterization of alloy catalysts:

[0049] In this example, X-ray diffractometer (XRD) and field emission scanning electron microscope (SEM) were used to characterize the crystal structure and morphology of the above five catalysts; transmission electron microscope (TEM) was used to measure Co1Fe1.

[0050] Depend on Figure 1 From the XRD pattern, we can see that from Co2Fe1→Co1Fe 1.5With the increase of Fe ratio, the position of CoFe(110) diffraction peak in the alloy shifts to low angle (45.2°→44.8°) relative to the standard Co7Fe3 alloy (PDF #65-4131), indicating that alloying process with higher Fe component substitution may make Co x Fe y The (110) crystal plane of the alloy produces lattice expansion phenomenon, resulting in elongated Co-Fe bond, which is beneficial to the improvement of electronic transfer and conductivity of the catalyst.

[0051] By TEM characterization ( Figure 2 (a-b)), it can be observed that the lattice spacing of 0.202 nm, 0.143 nm and 0.103 nm are attributed to the (110), (020) and (220) crystal planes of CoFe alloy, respectively, which confirms the existence of CoFe alloy. Figure 2 In the EDS-mapping diagram shown in FIG. 1c, Co and Fe elements are uniformly distributed and well mixed.

[0052] By SEM characterization ( Figure 3 ), it can be observed that Co2Fe1 is the alloy with the least Fe content, which presents a smooth nanosheet morphology. When the amount of Fe doping is increased, the morphology of the alloy begins to change to a rough litchi-like particle. Although Co 1.5 There are still a small amount of sheet structures in Co1Fe1 alloy, but in Co1Fe1, they have completely changed into smaller litchi-like particles. Continue to increase the content of Fe, Co1Fe 1.5 The particle size of the spherical particles in Co1Fe2 and Co1Fe2 begins to increase to about 200-300 nm, which may be accompanied by a decrease in specific surface area.

[0053] Example 2

[0054] The Co x Fe y alloy catalyst prepared in Example 1 was used to test the performance of low-concentration NO3RR.

[0055] (1) Test details:

[0056] The present application adopts a three-electrode system, and performs electrochemical tests in an H-type electrolytic cell. The temperature of the experimental environment is maintained at room temperature. All electrochemical tests are performed by using a French BioLogic SP-300 type electrochemical workstation. The cathode and anode chambers are respectively 60 mL of 1.0M KOH catholyte containing 0.02M, 0.05M or 0.1M KNO3 and 1.0M KOH anolyte. The electrolytes in the two chambers are separated by a pretreated Nafion 117 (DuPont) proton exchange membrane. The pretreatment process of the ion membrane includes two steps: first, water bath heating at 80℃ for 1 hour in a 5wt% hydrogen peroxide solution, and then water bath heating at 80℃ for 1 hour in a 0.5M sulfuric acid solution. This process aims to activate the membrane and eliminate absorbed ammonia. The effective area of the working electrode is 0.5×0.5cm 2 . The counter electrode is a high-purity graphite rod, and the reference electrode is a Hg / HgO electrode filled with 1.0M KOH. All tests are performed by using Ar gas to purge the cathode electrolyte for 30 minutes before starting to remove air in the system. All test potentials (vs. Hg / HgO) are converted into potential values relative to the reversible hydrogen electrode (RHE) by the Nernst equation, which is converted by the following formula:

[0057] E (vs. RHE) = E (vs. Hg / HgO) + 0.098V + 0.0592×pH

[0058] The starting point of the linear sweep voltammetry (LSV) curve is set as the open circuit potential, and the scanning end point is dynamically adjusted to -0.5 to -0.7V vs. RHE according to the pre-experiment results to avoid abnormal current response caused by strong reducing potential. A slow scanning rate of 10mVs -1 is used to ensure the quasi-steady-state measurement condition, and 100% iR compensation is applied.

[0059] The chronoamperometry (CA) test is performed at a constant potential of -0.1 to -0.4V vs. RHE for 15 minutes. The cathode chamber is maintained at a stirring rate of 400rpm, and the electrolyte is collected after electrolysis for product detection.

[0060] Long-term stability test: In a customized three-electrode H-type electrolytic cell, the long-term stability test of NO3RR is performed at a constant potential of -0.3V vs. RHE for 5 cycles (2 hours per cycle). The cathode chamber and the anode chamber are respectively 60mL of 1.0M KOH+0.1M KNO3 and 1.0M KOH. The electrolyte is sampled and replaced every hour. The amount of ammonia generated in the catholyte is quantitatively analyzed by the indigo phenol blue method.

[0061] The nitrate-containing wastewater treatment test was conducted in a custom three-electrode H-type electrolyzer. The cathode and anode chambers contained 60 mL of 1.0 M KOH catholyte containing 0.02 M KNO₃ and 1.0 M KOH anolyte, respectively. The test was conducted at a potential of -0.3 V vs. RHE for 10 hours, with 1 mL samples collected every two hours for product analysis. Ammonia production in the catholyte was quantified using the indophenol blue method.

[0062] (2) Test results:

[0063] First, we tested Co in 1.0MKOH electrolyte containing 0.1MKNO3 x Fe y The LSV curve of the alloy catalyst, such as Figure 4 (a) After component optimization, Co1Fe1 exhibited the lowest reaction overpotential η and the largest current density, indicating that it has good NO3RR activity. We further tested Co x Fe y Ammonia Faraday efficiency (FE) of the alloy catalyst in different potential ranges NH3 ) and ammonia yield (Y NH3 ),like Figure 4 (bc) As Co x Fe y The increase of Fe content in the alloy (Co2Fe1→Co 1.5 Fe1→Co1Fe1), FE NH3 It gradually improved until the Co / Fe ratio was 1, and Co1Fe1 reached the maximum FE at -0.3Vvs.RHE. NH3 (90.0%), reaching the maximum Y at -0.4V vs. RHE NH3 (55.5mgh -1 cm -2 This performance optimization may be due to the fact that the appropriate Fe doping in the alloy causes the lattice of the Co1Fe1 alloy to expand and the Co-Fe bond to be stretched, thereby adjusting the electronic structure of Co1Fe1, enhancing the adsorption and activation of nitrogen-containing intermediates, and ultimately improving the FE NH3 and Y NH3 When the Fe content increases further (Co1Fe1→Co1Fe 1.5 →Co1Fe2), FE NH3 and Y NH3 The inhibition of NO3RR may be due to the better water dissociation ability of Fe, which provides excess *H and aggravates the occurrence of competitive HER, thus leading to a sharp decline in NO3RR performance.

[0064] To verify the application potential of Co1Fe1 in NO3RR at lower concentrations, we tested its FE in 1.0M KOH electrolyte containing 0.02M and 0.05M KNO3. NH3 and Y NH3 ,like Figure 5 The results show that the FE of Co1Fe1 in a wide potential range (-0.1~-0.3Vvs.RHE) NH3 All are >80%, proving that its performance advantage in NO3RR can be achieved at low concentration NO3 - It is maintained under electrolyte conditions, which broadens the application scenarios of Co1Fe1.

[0065] The stability test of Co1Fe1 catalyst was carried out in 1.0MKOH electrolyte containing 0.1MKNO3 for 10h at a potential of -0.3V vs. RHE ( Figure 6 The results show that the Co1Fe1 catalyst has a high FE NH3 Maintained at around 85%, Y NH3 Always greater than 26mgh -1 cm -2 , showing good ammonia production stability.

[0066] The structural analysis of the sample after the reaction showed that the Co1Fe1 catalyst exhibited a stable lattice structure. HR-TEM analysis showed ( Figure 7 (ab)), the characteristic lattice fringes of 0.207 nm clearly correspond to the (110) crystal plane of CoFe alloy, and its atomic-level orderly arrangement remains intact after the reaction. EDS-mapping further confirms ( Figure 7 (c)), the Co and Fe bimetallic components remain uniformly dispersed at the nanoscale, and no element segregation occurs. In the XRD diffraction pattern, the characteristic peak of the CoFe(110) crystal plane shows a high degree of consistency before and after the reaction ( Figure 7 (d)). These data systematically confirm that the Co1Fe1 catalyst can maintain a stable crystal structure and chemical composition during long-term stability testing.

[0067] The present invention systematically evaluated the denitrification performance of Co1Fe1 catalyst under simulated industrial wastewater treatment conditions. Figure 8 As shown, under the optimized potential condition of -0.3Vvs.RHE, for a low concentration of 0.02M NO3 - Water, through 10 hours of constant current electrolysis process to achieve efficient conversion of pollutants. Test data shows that the system NO3 - The removal rate is as high as 99.5%, and the residual NO3 in the final product - The concentration dropped to 5.9 mg / L -1, which is significantly lower than the World Health Organization (WHO) guideline for safe drinking water (50 mg L -1 ). These performance indicators verify the potential of Co1Fe1 system for industrial application in the advanced treatment of wastewater containing low concentration of NO3 - .

[0068] According to the disclosure and teachings of the above specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present application is not limited to the specific embodiments disclosed and described above, and some modifications and changes of the present application should fall within the protection scope of the claims of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of description and do not constitute any limitation on the present application.

Claims

1. A method for preparing a cobalt-iron alloy catalyst, characterized in that: At least the following steps are included: The first step is to prepare a cobalt iron oxide precursor using an epoxide gel method: a cobalt source and an iron source are dissolved in a solvent, dissolved in an ultrasonic water bath, and then alkylene oxide is added and stirred to form a brown gel. The gel is then aged at room temperature and atmospheric pressure, and then vacuum dried to obtain a brown powder, which is the cobalt iron oxide precursor. In the second step, the cobalt iron oxide precursor powder obtained in the first step is mixed with an alcohol solvent, water and a perfluorosulfonic acid polymer solution by ultrasonication to form an ink, which is sprayed on a current collector to form a working electrode. Subsequently, the loaded cathode material is electro-reduced at a constant current or constant voltage in an argon-protected electrolyte to generate a cobalt iron alloy catalyst; the alcohol solvent is methanol or ethanol.

2. The method for preparing a cobalt-iron alloy catalyst according to claim 1, wherein: The cobalt source is at least one of cobalt chloride hexahydrate, cobalt nitrate hexahydrate and cobalt sulfate heptahydrate, the iron source is at least one of ferric chloride hexahydrate and ferric nitrate nonahydrate, the solvent is at least one of isopropanol, methanol, ethanol and ethylene glycol, and the alkylene oxide is at least one of propylene oxide, cis-2,3-butylene oxide, 1,2-butylene oxide, epichlorohydrin, epifluorohydrin and epibromohydrin.

3. The method for preparing the cobalt-iron alloy catalyst according to claim 1, wherein: In the cobalt-iron alloy catalyst, the molar ratio of Co element to Fe element is 0.1 to 10:

1.

4. The method for preparing the cobalt-iron alloy catalyst according to claim 3, wherein: In the cobalt-iron alloy catalyst, the molar ratio of Co element to Fe element is 1:

1.

5. The method for preparing a cobalt-iron alloy catalyst according to claim 1, wherein: The current collector is at least one of carbon paper, carbon cloth, carbon felt, foam copper and foam nickel.

6. The method for preparing a cobalt-iron alloy catalyst according to claim 1, wherein: The electrolyte is alkaline or neutral. The alkaline electrolyte is KOH or NaOH; the neutral electrolyte is K2SO4, Na2SO4, KClO4 or NaClO4.

7. The method for preparing a cobalt-iron alloy catalyst according to claim 1, wherein: The constant current used for electroreduction in the second step is -50 to -5000 mA cm -2 , or the constant voltage used is -0.1 to 20 V, and the time of electroreduction is 1 to 100 minutes.

8. Use of the catalyst according to any one of claims 1 to 7 in electrocatalytic nitrate reduction to synthesize ammonia.

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