Preparation method and application of Co-doped FeOOH catalyst

Abstract

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

Description

Technical Field

[0001] The invention belongs to the field of electrochemical ammonia synthesis catalysts, and specifically relates to a preparation method of a Co-doped FeOOH catalyst and application thereof. Background Art

[0002] Electrocatalytic nitrogen fixation in aqueous solution is considered a promising method for ammonia synthesis. However, the process has low Faradaic efficiency and ammonia yield, so it is necessary to develop an efficient, 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, and medicine. However, most NH3 is synthesized using the Haber-Bosch process, which requires high temperature and high pressure conditions and produces large amounts of carbon dioxide emissions. Therefore, it is crucial to develop sustainable ammonia synthesis under mild conditions. In recent years, the electrocatalytic nitrogen reduction reaction (NRR) has attracted much attention due to its mild reaction conditions and renewable characteristics. However, the difficult-to-break N≡N bond and the competitive HER reaction result in low selectivity and Faraday efficiency of NRR.

[0004] So far, noble metal-based catalysts remain 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-precious metal-based electrocatalysts have become attractive for NRR due to their low cost and high abundance. For example, iron-based materials, especially FeOOH, are a class of excellent recyclable catalysts due to their open structure, low cost, natural abundance, and environmental friendliness. However, FeOOH has poor conductivity (about 10 -5 Scm -1 ) remains a major challenge, severely limiting its electrocatalytic performance. Summary of the invention

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

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

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

[0009] In order to solve the above technical problems, the present invention provides the following technical solution: a method for preparing a Co-doped FeOOH catalyst, comprising:

[0010] Adding ferric chloride and cobalt chloride hexahydrate into an organic solvent, mixing and dissolving by ultrasonication to form a uniform mixed solution;

[0011] Add sodium nitrate to the mixed solution and stir at room temperature to obtain a uniform mixed solution;

[0012] Add hydrochloric acid solution dropwise to the mixed solution, transfer to a polytetrafluoroethylene-lined autoclave, and perform hydrothermal reaction;

[0013] After the reaction was completed, the mixture was cooled to room temperature, and the resulting precipitate was centrifuged, washed with ethanol and ultrapure water, and dried in vacuo;

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

[0015] As a preferred embodiment of the preparation method of the present invention, the organic solvent comprises ethanol.

[0016] As a preferred embodiment of the preparation method of the present invention, 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 embodiment of the preparation method of the present invention, the molar concentration of the hydrochloric acid is 0.09M.

[0018] As a preferred embodiment of the preparation method of the present invention, the molar ratio of ferric chloride to sodium nitrate is 12:1.

[0019] As a preferred embodiment of the preparation method of the present invention, the stirring time at room temperature is 30 to 60 minutes.

[0020] As a preferred embodiment of the preparation method of the present invention, the hydrothermal reaction has a reaction temperature of 100-120° C. and a reaction time of 3 hours.

[0021] As a preferred embodiment of the preparation method of the present invention, the vacuum drying is carried out at a temperature of 60° C. and a time of 12 h.

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

[0023] Another object of the present invention is to overcome the deficiencies in the prior art and provide a catalyst for use in electrochemical synthesis of ammonia.

[0024] Beneficial effects of the present invention:

[0025] (1) The present invention uses Co-doped FeOOH catalyst to improve the electrochemical ammonia synthesis performance. The iron-based catalyst FeOOH exhibits certain electrochemical ammonia synthesis performance in the electrochemical ammonia synthesis. The strong synergistic effect of Co and FeOOH loading improves the activity, selectivity and stability of the electrochemical ammonia synthesis of Co / FeOOH, increasing the ammonia yield from 15.9 μg·h -1 mg -1 cat Increased to 28.2 μg·h -1 mg -1 cat .

[0026] (2) The Co element doped in the present invention can improve the electronic conductivity and enhance the conductivity of the catalyst, which is beneficial to the improvement of the catalyst performance 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 catalyzing NRR, thereby enhancing the activity; at the same time, since the doping of Co causes the FeOOH lattice to expand, the utilization rate of FeOOH is improved, N2 has more active sites, the adsorption process is accelerated, and the catalytic reaction is more likely to occur.

[0027] (3) The present invention achieves the best ammonia catalytic effect by adding different Co input amounts without destroying FeOOH; the present invention proposes for the first time a catalyst suitable for high-performance electrochemical synthesis of ammonia, and preferably selects 6% Co / FeOOH to achieve the best ammonia catalytic effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0029] Figure 1 This is the electrochemical ammonia synthesis performance diagram of the FeOOH sample prepared in Example 1 of the present invention.

[0030] Figure 2 This is the electrochemical ammonia synthesis performance diagram of the 2% Co-FeOOH sample prepared in Example 2 of the present invention.

[0031] Figure 3 This is the electrochemical ammonia synthesis performance diagram of the 4% Co-FeOOH sample prepared in Example 3 of the present invention.

[0032] Figure 4This is the electrochemical ammonia synthesis performance diagram of the 6% Co-FeOOH sample prepared in Example 4 of the present invention.

[0033] Figure 5 This is a graph showing the ammonia production performance of all samples prepared in the present invention at an applied voltage of -0.9 V (vs. Ag / AgCl).

[0034] Figure 6 1 and 2 are XRD patterns of FeOOH doped with Co in different proportions prepared in Examples 1, 5 and 6 of the present invention. DETAILED DESCRIPTION

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the embodiments of the specification.

[0036] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0037] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0038] Performance evaluation of electrochemical ammonia synthesis in the embodiment of the present invention:

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

[0040] All electrochemical tests were performed using an electrochemical workstation (CH Instruments, 760E) at room temperature and pressure to perform electrochemical synthesis of ammonia. The electrolytic cell was a double-chamber sealed H-type electrolytic cell separated by a Nafion-117 membrane (DuPont). 45 mL of 0.1 mol·L -1 Na2SO4 electrolyte;

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

[0042] To ensure the gas saturation of the electrolyte, high-purity nitrogen or argon was added at a rate of 20 mL min -1 The rate of 2.5 % was continuously passed into the cathode of the electrolytic cell 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 chronoamperometric test (it) was performed under the condition of applying the optimal voltage while nitrogen was passed through, and the concentration of ammonia in the product was detected using the indophenol blue method;

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

[0046] The calculated ammonia production rate was used as an indicator 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, and mix and dissolve by ultrasonication to form a uniform mixed solution;

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

[0051] The solution was placed on a magnetic stirrer for stirring under heating in a water bath;

[0052] The mixed solution was transferred to a stainless steel high-pressure reactor containing polytetrafluoroethylene and reacted at 120°C for 3 h.

[0053] After the reaction is completed, the mixture is cooled to room temperature, and the resulting precipitate is centrifuged several times with ethanol and ultrapure water, washed, and vacuum dried to obtain the product FeOOH catalyst.

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

[0055] Electrochemical test calculations show that the FeOOH used has a certain electrochemical ammonia synthesis activity, and its ammonia generation rate is 15.90 μg·h -1 mg -1 cat .

[0056] Example 2

[0057] 2% Co-FeOOH catalyst preparation method:

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

[0059] (1) Dissolve 12 mmol of ferric nitrate nonahydrate, 0.24 mmol of cobalt chloride hexahydrate, and 1 mmol of sodium nitrate in 100 mL of ethanol, and mix and dissolve by ultrasonication to form a uniform mixed solution;

[0060] (2) The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave and reacted in an oven at 120°C for 3 h.

[0061] (3) After the reaction was completed, the reactor was cooled to room temperature and the obtained precipitate was washed three times by centrifugation with ethanol and deionized water.

[0062] (4) Drying in a vacuum oven at 60 °C for 12 h yields a yellow product, namely, the Co-doped FeOOH catalyst;

[0063] After the above catalyst was prepared into a working electrode for electrochemical ammonia synthesis test, it was found that the 2% Co-FeOOH catalyst had good electrochemical ammonia synthesis performance, and the ammonia synthesis rate was 21.00 μg·h -1 mg -1 cat , the catalytic performance is higher than that of FeOOH.

[0064] Example 3

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

[0066] The same synthesis method was used as in Example 2, the amount of cobalt chloride hexahydrate added was 0.48 mmol, and other factors remained unchanged. The final product was named 4% Co-FeOOH.

[0067] After the above catalyst was prepared into a working electrode for electrochemical ammonia synthesis test, Figure 3 The performance diagram shows that the 4% Co-FeOOH catalyst has good electrochemical ammonia synthesis performance, and the ammonia synthesis rate is 22.80 μg·h -1 mg -1 cat , the catalytic performance is higher than that of FeOOH.

[0068] Example 4

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

[0070] The same synthesis method was used as in Example 2, the amount of cobalt chloride hexahydrate added was 0.72 mmol, and other factors remained unchanged. The final product was named 6% Co-FeOOH.

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

[0072] Example 5

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

[0074] The same synthesis method was used as in Example 2, the amount of cobalt chloride hexahydrate added was 0.96 mmol, and other factors remained unchanged. The final product was named 8% Co-FeOOH.

[0075] from Figure 6 XRD showed that 8% Co-FeOOH was successfully synthesized.

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

[0077] Example 6

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

[0079] The same synthesis method was used as in Example 2, the amount of cobalt chloride hexahydrate added was 1.2 mmol, and other factors remained unchanged. The final product was named 10% Co-FeOOH.

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

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

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

[0083] The electrochemical synthesis ammonia performance diagram of FeOOH, 2% Co-FeOOH, and 6% Co-FeOOH samples prepared in Examples 1, 2, and 4 of the present invention is shown in FIG. Figure 1 , Figure 2 , Figure 4 , 6% Co-FeOOH is preferred to achieve the best ammonia catalytic effect.

[0084] The performance regularity diagram of all samples prepared in the present invention is shown in Figure 5 ;

[0085] Depend on Figure 5 It can be seen that different Co input amounts do affect the performance of the catalyst, which can be attributed to the following reasons: as the Co input amount increases, when Co ions enter the FeOOH lattice, the FeOOH lattice is distorted, oxygen vacancies increase, and the chemical properties and electronic structure of the Co-FeOOH sample also change accordingly; Co doping will lead to poor crystallinity of the crystal, and the growth of FeOOH grains will be inhibited, while smaller grains are conducive to improving the dispersion of the crystal, exposing more active sites, and improving the activity of the catalyst. It can be seen that the appropriate amount of Co doping will increase the oxygen vacancies on the catalyst surface, thereby improving the catalytic performance.

[0086] Comparative Example 1

[0087] 2% La-FeOOH catalyst preparation method:

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

[0089] (2) 12 mmol of ferric nitrate nonahydrate, 0.24 mmol of lanthanum nitrate, 7.5 mmol of ammonium fluoride and 18 mmol of urea were dissolved in 100 mL of ethanol and mixed and dissolved by ultrasonication to form a uniform mixed solution;

[0090] (2) The mixed solution was transferred to a polytetrafluoroethylene-lined autoclave and reacted in an oven at 90°C for 36 h.

[0091] (3) After the reaction was completed, the reactor was cooled to room temperature and the obtained precipitate was washed three times by centrifugation with ethanol and deionized water.

[0092] (4) drying in a vacuum drying oven at 60° C. for 12 h to obtain the product, i.e., La-doped FeOOH catalyst;

[0093] After the above catalyst was prepared into a working electrode for electrochemical ammonia synthesis test, it was found that the ammonia synthesis rate of 2% La-FeOOH catalyst was 7.64 μg·h -1 mg -1 cat , which is lower than FeOOH’s 15.90 μg·h -1 mg -1 cat .

[0094] Comparative Example 2

[0095] 4% La-FeOOH catalyst preparation method:

[0096] The same synthesis method was used as in Comparative Example 1, 0.48 mmol of lanthanum nitrate was added, and the molar ratio of La / Fe was controlled to be 4%.

[0097] After the above catalyst was prepared into a working electrode for electrochemical ammonia synthesis test, it was found that the ammonia synthesis rate of 4% La-FeOOH catalyst was 9.37 μg·h -1 mg -1 cat , which is lower than FeOOH’s 15.90 μg·h -1 mg -1 cat .

[0098] Comparative Example 3

[0099] 6% La-FeOOH catalyst preparation method:

[0100] The same synthesis method was used as in Comparative Example 1, 0.72 mmol of lanthanum nitrate was added, and the molar ratio of La / Fe was controlled to be 6%.

[0101] After the above catalyst was prepared into a working electrode for electrochemical ammonia synthesis test, it was found that the ammonia synthesis rate of 6% La-FeOOH catalyst was 11.03 μg·h -1 mg -1 cat , which is lower than FeOOH’s 15.90 μg·h -1 mg -1 cat .

[0102] The present invention uses Co-doped FeOOH as an electrochemical catalyst for the first time to improve the performance of electrochemical ammonia synthesis. It not only retains the original structure of FeOOH, but also successfully dopes Co onto the FeOOH carrier. Iron oxyhydroxide, one of the typical structural materials of transition metal-based catalysts, has shown certain electrochemical ammonia synthesis performance in electrochemical ammonia synthesis. The interaction between Co and FeOOH improves the activity and selectivity of Co-FeOOH electrochemical ammonia synthesis, increasing the ammonia yield from 15.90 μg·h -1 mg -1 cat Increased to 28.20 μg·h -1 mg -1 cat .

[0103] Meanwhile, in the preparation method of the high-performance electrochemical ammonia synthesis catalyst of the present invention, washing with ethanol and deionized water, centrifuging in a centrifuge, and then vacuum drying at 60° C. to remove residual organic solvent makes the measured performance more accurate.

[0104] The electrochemical synthesis of ammonia is considered to be the most promising method. Compared with the high-temperature and high-pressure Haber-Bosch method, it can reduce energy consumption by 20%, and the reaction is not limited by thermodynamics. Theoretically, the single-pass hydrogen conversion rate can reach 100%. In particular, the electrocatalytic nitrogen reduction reaction (NRR) of ammonia using nitrogen and water as raw materials at low temperature and normal pressure has mild reaction conditions and readily available raw materials, which transcends the demand for hydrogen production from fossil fuels and is expected to become a green synthetic ammonia technology with sustainable development in the future.

[0105] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention 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 invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the present invention.

Claims

1. A method for preparing a Co-doped FeOOH catalyst, characterized in that: include, Adding ferric chloride and cobalt chloride hexahydrate into an organic solvent, mixing and dissolving by ultrasonication to form a uniform mixed solution; Add sodium nitrate to the mixed solution and stir at room temperature to obtain a uniform mixed solution; Add hydrochloric acid solution dropwise to the mixed solution, transfer to a polytetrafluoroethylene-lined autoclave, and perform hydrothermal reaction; After the reaction was completed, the mixture was cooled to room temperature, and the resulting precipitate was centrifuged, washed with ethanol and ultrapure water, and dried in vacuo; The product obtained after drying was cooled to room temperature to obtain the product Co-doped FeOOH catalyst.

2. The preparation method according to claim 1, characterized in that: The organic solvent includes ethanol.

3. The preparation method according to claim 1 or 2, characterized in that: The molar ratio of cobalt to iron in the Co-doped FeOOH catalyst is x%, wherein x=0, 2, 4, 6, 8, 10.

4. The preparation method according to claim 3, characterized in that: The molar concentration of the hydrochloric acid is 0.09M.

5. The preparation method according to claim 1 or 4, characterized in that: The molar ratio of the ferric chloride to the sodium nitrate is 12:

1.

6. The preparation method according to claim 1, characterized in that: The stirring time at room temperature is 30 to 60 minutes.

7. The preparation method according to claim 1, characterized in that: The hydrothermal reaction has a reaction temperature of 100-120° C. and a reaction time of 3 hours.

8. The preparation method according to claim 7, characterized in that: The vacuum drying is carried out at a temperature of 60° C. and a time of 12 hours.

9. The Co-doped FeOOH catalyst prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the Co-doped FeOOH catalyst as claimed in claim 9 in electrochemical synthesis of ammonia.

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