Preparation method and application of co-doped feohh catalyst

Abstract

The application discloses a preparation method of a Co-doped FeOOH catalyst and application thereof, and comprises the following steps: adding ferric chloride and cobalt chloride hexahydrate into an organic solvent, ultrasonic mixing and dissolving to form a uniform mixed solution; adding sodium nitrate into the mixed solution, stirring at room temperature to obtain a uniform mixed solution; adding hydrochloric acid solution dropwise into the mixed solution, transferring into a polytetrafluoroethylene-lined high-pressure reaction kettle, and performing hydrothermal reaction; cooling to room temperature after the reaction is completed; centrifuging, washing and vacuum drying the obtained precipitate with ethanol and ultrapure water; and cooling the obtained product after drying to room temperature to obtain the product Co-doped FeOOH catalyst. The application first proposes a catalyst suitable for high-performance electrochemical synthesis of ammonia, preferably a 6% Co-FeOOH catalyst, and realizes the best ammonia catalysis effect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of electrochemical synthesis of ammonia catalysts, and particularly relates to a preparation method of a Co-doped FeOOH catalyst and application thereof. BACKGROUND

[0002] Electrocatalytic nitrogen fixation in aqueous solution is considered as a very promising method for ammonia synthesis, although the Faraday efficiency and ammonia production of the process are low, so it is necessary to develop a high-efficiency, clean and safe catalyst to promote the nitrogen reduction process.

[0003] Ammonia (NH3) is one of the most important chemicals in chemical production, and is widely used in many fields such as industry, agriculture, medicine, etc. However, most of NH3 is synthesized by Haber-Bosch process, which requires high temperature and high pressure conditions and produces a large amount of carbon dioxide emissions. Therefore, it is crucial to develop sustainable ammonia synthesis under mild conditions. In recent years, electrocatalytic nitrogen reduction reaction (NRR) has attracted much attention due to its mild reaction conditions and renewable characteristics. However, the N≡N bond is difficult to break and the competitive HER reaction leads to low selectivity and Faraday efficiency of NRR.

[0004] So far, noble metal-based catalysts are still the most effective electrocatalysts for NRR. However, these metals are rare elements, and the scarcity and high cost of these noble metals greatly hinder their large-scale practical application.

[0005] Recently, non-noble metal-based electrocatalysts are attractive for NRR due to their low cost and high content. For example: iron-based materials, especially FeOOH. Due to the open structure of iron, low cost, natural abundance and environmental friendliness, it is a kind of excellent catalyst that can be recycled. However, the poor electrical conductivity (about 10 -5 Scm -1 ) of FeOOH is still a major challenge, which seriously limits its electrocatalytic performance. SUMMARY

[0006] The purpose of this section is to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0007] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0008] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art, and to provide a preparation method of a Co-doped FeOOH catalyst.

[0009] To solve the above technical problems, the present application provides the following technical solutions: a preparation method of a Co-doped FeOOH catalyst, comprising,

[0010] Iron trichloride and cobalt chloride hexahydrate are added to an organic solvent, ultrasonic mixing and dissolution are performed to form a uniform mixed solution;

[0011] Sodium nitrate is added to the mixed solution, and stirring is performed at room temperature to obtain a uniform mixed solution;

[0012] Hydrochloric acid solution is added dropwise to the mixed solution, and the solution is transferred to a polytetrafluoroethylene-lined high-pressure reaction kettle for hydrothermal reaction;

[0013] After the reaction is completed, the obtained precipitate is centrifuged, washed with ethanol and ultrapure water, and vacuum dried;

[0014] The product obtained after drying is cooled to room temperature to obtain the product Co-doped FeOOH catalyst.

[0015] As a preferred scheme of the preparation method of the present application, wherein: the organic solvent comprises ethanol.

[0016] As a preferred scheme of the preparation method of the present application, wherein: the molar ratio of cobalt to iron in the Co-doped FeOOH catalyst is x%, wherein x = 0, 2, 4, 6, 8, 10.

[0017] As a preferred scheme of the preparation method of the present application, wherein: the molar concentration of the hydrochloric acid is 0.09M.

[0018] As a preferred scheme of the preparation method of the present application, wherein: the molar ratio of iron trichloride to sodium nitrate is 12:1.

[0019] As a preferred scheme of the preparation method of the present application, wherein: the stirring time at room temperature is 30-60 min.

[0020] As a preferred scheme of the preparation method of the present application, wherein: the hydrothermal reaction, wherein the reaction temperature is 100-120℃, and the reaction time is 3h.

[0021] As a preferred scheme of the preparation method of the present application, wherein: the vacuum drying, wherein the temperature is 60℃, and the time is 12h.

[0022] Another object of the present application is to overcome the deficiencies in the prior art and provide a Co-doped FeOOH catalyst prepared by the preparation method.

[0023] Another object of the present application is to overcome the deficiencies in the prior art and provide a Co-doped FeOOH catalyst prepared by the preparation method. Another object of the present application is to overcome the deficiencies in the prior art and provide a Co-doped FeOOH catalyst prepared by the preparation method.

[0024] Advantages of the present application:

[0025] (1) The present application improves the performance of electrochemical synthesis of ammonia in Co-doped FeOOH catalyst. The FeOOH-based catalyst exhibits certain electrochemical synthesis of ammonia performance. The strong synergistic effect of loading Co and FeOOH improves the activity, selectivity and stability of Co / FeOOH for electrochemical synthesis of ammonia, so that the ammonia yield is increased from 15.9 μg·h -1 mg -1 cat to 28.2 μg·h -1 mg -1 cat .

[0026] (2) The doped Co element can improve the electronic conductivity, which enhances the conductivity of the catalyst, is conducive to the improvement of the performance of the catalyst and the acceleration of the N2 activation process. The modification of FeOOH with Co not only effectively optimizes the adsorption energy of nitrogen-containing intermediates, but also provides abundant active sites for catalytic NRR, thereby enhancing the activity. At the same time, the doping of Co causes the expansion of the FeOOH lattice, which improves the utilization rate of FeOOH, and N2 has more active sites, so the adsorption process is accelerated, which promotes the catalytic reaction to occur more easily.

[0027] (3) The present application realizes the best ammonia catalytic effect under the premise of not damaging FeOOH by adding different amounts of Co. The present application first proposes a catalyst suitable for high-performance electrochemical synthesis of ammonia, and optimizes 6% Co / FeOOH to realize the best ammonia catalytic effect. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0029] Figure 1 Electrochemical synthesis of ammonia performance diagram of FeOOH sample prepared for the present application embodiment 1.

[0030] Figure 2 Electrochemical synthesis of ammonia performance diagram of 2% Co-FeOOH sample prepared for the present application embodiment 2.

[0031] Figure 3 Electrochemical synthesis of ammonia performance diagram of 4% Co-FeOOH sample prepared for the present application embodiment 3.

[0032] Figure 4Electrochemical ammonia synthesis performance chart of 6% Co-FeOOH sample prepared for the present embodiment 4.

[0033] Figure 5 Ammonia production performance chart of all samples prepared in the present invention under the applied voltage of-0.9V (vs. Ag / AgCl).

[0034] Figure 6 XRD chart of Co-doped FeOOH with different proportions prepared in the present embodiment 1, 5 and 6. DETAILED DESCRIPTION

[0035] In order to make the above objectives, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention will be described in detail below with reference to the embodiments of the present invention.

[0036] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and those skilled in the art can make similar generalizations without departing from the connotation of the present invention, therefore the present invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present invention. "In one embodiment" appearing in different places in the present specification does not mean the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments.

[0038] Electrochemical ammonia synthesis performance evaluation in the present embodiment:

[0039] Firstly, 5mg of catalyst and 5mg of carbon black (mass ratio 1:1) are dissolved in a mixture of 0.1mL of Nafion dispersion and 0.9mL of anhydrous ethanol (volume ratio 1:9), and are uniformly dispersed by ultrasonic dispersion to prepare a catalyst suspension (ink), which is uniformly dropped on 6 pieces of carbon paper to prepare a working electrode, so that the single-piece carbon catalyst loading is 0.35mg / cm 2 ;

[0040] All electrochemical tests are carried out by electrochemical workstation (CH Instruments, 760E) for electrochemical ammonia synthesis test at normal temperature and pressure, and the electrolytic cell is a double-chamber sealed H-type electrolytic cell separated by Nafion-117 membrane (DuPont), 45mL of 0.1mol·L -1 Na2SO4 electrolyte is added to the cathode chamber and the anode chamber respectively.

[0041] A three-electrode system was used, the working electrode prepared above was used as the cathode, a platinum electrode and KCl saturated Ag / AgCl were used as the counter electrode and reference electrode respectively.

[0042] To ensure the gas saturation of the electrolyte, high-purity nitrogen or argon was continuously introduced into the cathode of the electrolyte cell at a rate of 20 mL·min -1 for 30 min;

[0043] Secondly, the working electrode was scanned by linear sweep method (LSV) to determine the optimal voltage for catalyst testing;

[0044] Finally, the chronoamperometry test (i-t) was carried out under the condition of applying the optimal voltage and introducing nitrogen, and the indigo phenol blue method was used to detect the concentration of ammonia in the product;

[0045] That is, after the test, the absorbance of the electrolyte was tested, the ammonia content in the electrolyte was calculated through the standard curve, and the electrochemical synthesis rate of ammonia of the catalyst was calculated;

[0046] The calculated ammonia generation rate was used as an index to evaluate the catalytic activity of the catalyst.

[0047] Example 1

[0048] (1) Synthesis method of FeOOH catalyst:

[0049] Dissolve 12 mmol of ferric chloride and 1 mmol of sodium nitrate in 100 mL of ethanol, ultrasonically mix and dissolve to form a uniform mixed solution;

[0050] Add a few drops of 0.09M hydrochloric acid solution to the above mixed solution and stir for 2 minutes;

[0051] Place the above solution in a magnetic stirrer under water bath heating condition;

[0052] Move the mixed solution to a stainless steel high-pressure reaction kettle made of polytetrafluoroethylene, and react at 120℃ for 3h.

[0053] Cool to room temperature after the reaction is completed, and the obtained precipitate is centrifuged several times with ethanol and ultrapure water, washed and vacuum dried; the product FeOOH catalyst is obtained.

[0054] (2) Performance evaluation of electrochemical synthesis of ammonia:

[0055] According to the electrochemical test calculation, the FeOOH used has certain electrochemical synthesis activity of ammonia, and the ammonia generation rate is 15.90μg·h -1 mg -1 cat .

[0056] Example 2

[0057] Preparation method of 2% Co-FeOOH catalyst:

[0058] Preparation and testing of a 2% Co-FeOOH catalyst with a cobalt to iron molar ratio of 2:100:

[0059] (1) Weigh out 12 mmol of ferric nitrate nonahydrate, 0.24 mmol of cobalt chloride hexahydrate and 1 mmol of sodium nitrate and dissolve them in 100 mL of ethanol. Mix and dissolve by sonication to form a homogeneous solution.

[0060] (2) Transfer the mixture to a high-pressure reactor lined with polytetrafluoroethylene and react it in an oven at 120°C for 3 hours.

[0061] (3) After the reaction is completed, cool to room temperature and remove the reaction vessel. Wash the precipitate three times with ethanol and deionized water by centrifugation.

[0062] (4) The product was dried in a vacuum drying oven at 60℃ for 12h to obtain a yellow product, namely the Co-doped FeOOH catalyst;

[0063] After preparing the above catalyst as a working electrode and conducting electrochemical ammonia synthesis tests, it was found that the 2% Co-FeOOH catalyst exhibited good electrochemical ammonia synthesis performance, with an ammonia synthesis rate of 21.00 μg·h⁻¹. -1 mg -1 cat Its catalytic performance is higher than that of FeOOH.

[0064] Example 3

[0065] Preparation method of 4% Co-FeOOH nanomaterials:

[0066] Same as in Example 2, using the same synthesis method, with the amount of cobalt chloride hexahydrate added being 0.48 mmol, and all other parameters remaining unchanged. The final product was named 4% Co-FeOOH.

[0067] After preparing the above catalyst into a working electrode and conducting electrochemical ammonia synthesis tests, from... Figure 3 The performance graph shows that the 4% Co-FeOOH catalyst exhibits good electrochemical ammonia synthesis performance, with an ammonia synthesis rate of 22.80 μg·h⁻¹. -1 mg -1 cat Its catalytic performance is higher than that of FeOOH.

[0068] Example 4

[0069] Preparation method of 6% Co-FeOOH nanomaterials:

[0070] The same synthetic method was used as in Example 2, the amount of cobalt chloride hexahydrate was 0.72 mmol, and the rest was the same, and the final product was named 6%Co-FeOOH.

[0071] After the above catalyst was prepared into a working electrode for electrochemical synthesis of ammonia test, it was found that the 6%Co-FeOOH catalyst had good electrochemical synthesis of ammonia performance, and the synthesis rate of ammonia was 28.20 μg·h -1 mg -1 cat , and the catalytic performance was higher than that of FeOOH.

[0072] Example 5

[0073] 8%Co-FeOOH nanomaterial preparation method:

[0074] The same synthetic method was used as in Example 2, the amount of cobalt chloride hexahydrate was 0.96 mmol, and the rest was the same, and the final product was named 8%Co-FeOOH.

[0075] From the XRD of Figure 6 , it can be seen that 8%Co-FeOOH was successfully synthesized.

[0076] After the above catalyst was prepared into a working electrode for electrochemical synthesis of ammonia test, it was found that the 8%Co-FeOOH catalyst had good electrochemical synthesis of ammonia performance, and the synthesis rate of ammonia was 19.50 μg·h -1 mg -1 cat , and the catalytic performance was higher than that of FeOOH.

[0077] Example 6

[0078] 10%Co-FeOOH nanomaterial preparation method:

[0079] The same synthetic method was used as in Example 2, the amount of cobalt chloride hexahydrate was 1.2 mmol, and the rest was the same, and the final product was named 10%Co-FeOOH.

[0080] From the XRD of Figure 6 , it can be seen that 10%Co-FeOOH was successfully synthesized.

[0081] After the above catalyst was prepared into a working electrode for electrochemical synthesis of ammonia test, it was found that the 10%Co-FeOOH catalyst had good electrochemical synthesis of ammonia performance, and the synthesis rate of ammonia was 16.60 μg·h -1 mg -1 cat , and the catalytic performance was higher than that of FeOOH.

[0082] The XRD pattern of FeOOH prepared in Example 1 of this invention is shown in the figure. Figure 1 ;Depend on Figure 1 It can be seen that the catalyst FeOOH was successfully synthesized.

[0083] The electrochemical ammonia synthesis performance of the FeOOH, 2% Co-FeOOH, and 6% Co-FeOOH samples prepared in Examples 1, 2, and 4 of this invention are shown in the figure. Figure 1 , Figure 2 , Figure 4 The optimal ammonia catalysis effect is achieved by using 6% Co-FeOOH.

[0084] The performance characteristics of all prepared samples in this invention are shown in the graph. Figure 5 ;

[0085] Depend on Figure 5 It is evident that different amounts of Co doping do affect catalyst performance. This can be attributed to the following: as the amount of Co increases, when Co ions enter the FeOOH lattice, the FeOOH lattice becomes distorted, increasing oxygen vacancies and altering the chemical properties and electronic structure of the Co-FeOOH sample. Co doping also leads to decreased crystallinity, inhibiting FeOOH grain growth. Smaller grains improve crystal dispersion, exposing more active sites and enhancing catalyst activity. Therefore, appropriate Co doping increases oxygen vacancies on the catalyst surface, thereby improving catalytic performance.

[0086] Comparative Example 1

[0087] Preparation method of 2% La-FeOOH catalyst:

[0088] Preparation and testing of 2% La-FeOOH catalyst with a lanthanum to iron molar ratio of 2:100:

[0089] (2) Weigh 12 mmol ferric nitrate nonahydrate, 0.24 mmol lanthanum nitrate, 7.5 mmol ammonium fluoride and 18 mmol urea and dissolve them in 100 mL ethanol. Mix and dissolve by sonication to form a homogeneous solution.

[0090] (2) Transfer the mixture to a high-pressure reactor lined with polytetrafluoroethylene and react it in an oven at 90°C for 36 hours.

[0091] (3) After the reaction is completed, cool to room temperature and remove the reaction vessel. Wash the precipitate three times with ethanol and deionized water by centrifugation.

[0092] (4) The product, namely La-doped FeOOH catalyst, was obtained by drying in a vacuum drying oven at 60℃ for 12h.

[0093] After preparing the above catalyst as a working electrode and conducting electrochemical ammonia synthesis tests, it was found that the ammonia synthesis rate of the 2% La-FeOOH catalyst was 7.64 μg·h⁻¹. -1 mg -1 cat Its performance is lower than that of FeOOH (15.90 μg·h). -1 mg -1 cat .

[0094] Comparative Example 2

[0095] Preparation method of 4% La-FeOOH catalyst:

[0096] Similar to Comparative Example 1, the same synthesis method was used, with the addition of 0.48 mmol of lanthanum nitrate to control the La / Fe molar ratio at 4%.

[0097] After preparing the above catalyst as a working electrode and conducting electrochemical ammonia synthesis tests, it was found that the ammonia synthesis rate of the 4% La-FeOOH catalyst was 9.37 μg·h⁻¹. -1 mg -1 cat Its performance is lower than that of FeOOH (15.90 μg·h). -1 mg -1 cat .

[0098] Comparative Example 3

[0099] Preparation method of 6% La-FeOOH catalyst:

[0100] Similar to Comparative Example 1, the same synthesis method was used, with 0.72 mmol of lanthanum nitrate added to control the La / Fe molar ratio at 6%.

[0101] After preparing the above catalyst as a working electrode and conducting electrochemical ammonia synthesis tests, it was found that the ammonia synthesis rate of the 6% La-FeOOH catalyst was 11.03 μg·h⁻¹. -1 mg -1 cat Its performance is lower than that of FeOOH (15.90 μg·h). -1 mg -1 cat .

[0102] The Co-doped FeOOH is used as an electrochemical catalyst to improve the performance of electrochemical synthesis of ammonia for the first time, the original structure of FeOOH is retained, Co is successfully doped on the FeOOH carrier, the typical structure of transition metal-based catalyst, one of iron oxyhydroxide, has shown certain electrochemical synthesis of ammonia performance in electrochemical synthesis of ammonia, and the activity and selectivity of Co-FeOOH in electrochemical synthesis of ammonia are improved in the interaction of Co and FeOOH, so that the ammonia yield is increased from 15.90 mu g.h -1 mg -1 cat to 28.20 mu g.h -1 mg -1 cat .

[0103] Meanwhile, in the preparation method of the high-performance electrochemical ammonia synthesis catalyst, the ethanol and deionized water are washed, centrifuged by a centrifuge, and then dried at 60 DEG C under vacuum to remove the residual organic solvent, so that the measured performance is more accurate.

[0104] Electrochemical synthesis of ammonia is considered to be the most potential method, compared with the high-temperature and high-pressure Haber-Bosch method, the energy consumption can be reduced by 20%, and the reaction is not limited by thermodynamics, and theoretically the single-pass hydrogen conversion rate can reach 100%. Especially, ammonia is synthesized by electrocatalytic nitrogen reduction reaction (NRR) from nitrogen and water at low temperature and normal pressure, the reaction conditions are mild, the raw materials are easy to obtain, the demand for hydrogen produced by fossil fuels is crossed, and it is expected to become a green ammonia synthesis technology for sustainable development in the future.

[0105] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not limited, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the present application.

Claims

1. A method for preparing a Co-doped FeOOH catalyst, characterized by: comprising, adding ferric chloride and cobalt chloride hexahydrate into an organic solvent, ultrasonic mixing and dissolving to form a uniform mixed solution; adding sodium nitrate into the mixed solution, stirring at room temperature to obtain a uniform mixed solution, and the molar ratio of ferric chloride to sodium nitrate is 12:1; adding hydrochloric acid solution dropwise into the mixed solution, transferring into a polytetrafluoroethylene lined high-pressure reaction kettle, and hydrothermal reaction; cooling to room temperature after the reaction is completed, centrifuging, washing and vacuum drying the obtained precipitate with ethanol and ultrapure water; cooling the obtained product to room temperature after drying to obtain a product Co-doped FeOOH catalyst; the molar ratio of cobalt to iron in the Co-doped FeOOH catalyst is x%, wherein x=2, 4, 6, 8, 10.

2. The production method according to claim 1, characterized by: the organic solvent comprises ethanol.

3. The production method according to claim 1, wherein: the molar concentration of the hydrochloric acid is 0.09M.

4. The production method according to claim 1, wherein: the stirring time at room temperature is 30-60min.

5. The production method according to claim 1, wherein: the hydrothermal reaction, wherein the reaction temperature is 100-120℃, and the reaction time is 3h.

6. The production method according to claim 5, characterized by: the vacuum drying, wherein the temperature is 60℃, and the time is 12h.

7. The Co-doped FeOOH catalyst prepared by the preparation method in any one of claims 1-6.

8. The application of the Co-doped FeOOH catalyst in claim 7 in electrochemical synthesis of ammonia.

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