Three-dimensional network carbon nanofiber loaded iron-based material and application thereof in electro-catalysis of nitrate to synthesize ammonia

Abstract

The invention discloses a three-dimensional network carbon nanofiber loaded iron-based material and application of the three-dimensional network carbon nanofiber loaded iron-based material to ammonia synthesis through electro-catalysis of nitrate radicals, an obtained catalytic system comprises a three-dimensional network carbon nanofiber carrier and uniformly distributed iron nanoparticles, and three-dimensional network carbon nanofibers have ultra-light density and ultra-high specific surface area; and the loaded iron nanoparticles play a role in connecting the carbon nanofibers, so that the electron conduction of the catalytic system is accelerated, and abundant reaction active sites are provided. The invention provides an efficient non-noble metal catalyst for electrocatalytic synthesis of nitrate ammonia, can simultaneously realize super-high yield and Faraday efficiency under large current, and has great significance in promoting development of electrocatalytic synthesis ammonia technology and promoting global nitrogen cycle.

Description

Technical Field

[0001] The invention belongs to the technical field of catalytic materials, and specifically relates to the preparation of an iron-based material supported by three-dimensional carbon nanofibers and its application in electrocatalytic nitrate synthesis of ammonia. Background Art

[0002] As an important chemical product, ammonia is widely used in agriculture, medicine, energy and other fields. First, ammonia is the raw material for the production of chemical fertilizers. It is the large-scale application of chemical fertilizers that has brought huge food production to feed the growing global population. Secondly, ammonia is a precursor for the synthesis of many clinical drugs and is crucial for the research and development of medicines. In addition, ammonia is regarded as a potential carbon-free fuel in the future, which is in line with the environmental protection concept of "carbon peak and carbon neutrality". It has high energy density and storage and transportation advantages brought by easy liquefaction. To date, industrial ammonia synthesis still relies on the Haber-Bosch thermal catalytic process with nitrogen and hydrogen as raw materials under high temperature and high pressure conditions. This process is accompanied by serious fossil fuel consumption, accounting for more than 1% of global fossil energy consumption, and emitting a large amount of greenhouse gas carbon dioxide into the atmosphere. Considering the huge energy and environmental costs of the traditional ammonia synthesis process, it is of great significance to study a more gentle, efficient, green and sustainable ammonia synthesis alternative strategy, and electrocatalytic ammonia synthesis technology has gradually become the focus of attention. This technology is an ideal resource-saving and environmentally friendly method. It uses excess renewable electricity as an energy source to drive the production of ammonia under ambient conditions, which can greatly reduce dependence on fossil fuels and has almost no emissions of greenhouse gases and air pollutants. In addition, nitrate is one of the most widely distributed water pollutants in the world, seriously affecting the ecological environment and threatening human health. On the other hand, the nitrogen-oxygen bond in nitrate (204 kJ·mol -1 ) compared to the nitrogen-nitrogen triple bond in nitrogen (941 kJ·mol -1 ) is more easily broken and activated. Therefore, using nitrate as a raw material for electrocatalytic synthesis of ammonia can not only obtain basic chemical ammonia, but also promote the global nitrogen cycle and help eliminate water pollution. In view of this, electrocatalytic nitrate synthesis of ammonia has important research value and application prospects, and is a major topic in the current field of energy and environmental research.

[0003] In recent years, a variety of metal catalysts for electrocatalytic nitrate synthesis of ammonia have been developed, among which the noble metals Pd and Ru and the non-noble metals Cu and Fe are the main ones. In view of the current research, the electrocatalytic nitrate synthesis of ammonia reaction is restricted by nitrate mass transfer, the number of active sites and electron conduction, and the ammonia yield is still not high, far from the level of industrial application. In addition, the electrocatalytic nitrate synthesis of ammonia reaction is a complex process involving eight electron transfers, which is restricted by competitive hydrogen evolution reactions and other side reactions, resulting in a low Faraday efficiency of ammonia. Therefore, designing highly active, highly selective and low-cost catalysts is the key to promoting the development of electrocatalytic nitrate synthesis of ammonia technology. Summary of the invention

[0004] The present invention provides a three-dimensional mesh carbon nanofiber-loaded iron-based material and a preparation method thereof, aiming to provide a highly active, highly selective and low-cost metal catalyst for the electrocatalytic nitrate synthesis of ammonia reaction, so as to promote the development of electrocatalytic ammonia synthesis technology.

[0005] In order to achieve the purpose, the present invention adopts the following technical scheme:

[0006] The present invention first provides a method for preparing an iron-based material supported by three-dimensional network carbon nanofibers, comprising the following steps: dispersing iron salt in a bacterial cellulose dispersion, rapidly stirring the reaction at room temperature, centrifuging and freeze-drying to obtain dry bacterial cellulose that adsorbs iron ions; placing the bacterial cellulose that adsorbs iron ions in a tubular furnace, and performing high-temperature carbonization in a gas atmosphere to obtain the iron-based material supported by three-dimensional network carbon nanofibers.

[0007] Furthermore, the iron salt is an inorganic salt containing iron, including but not limited to one of inorganic salts such as ferric nitrate, ferric sulfate, and ferric chloride, and the mass ratio of the iron salt to bacterial cellulose is 1-200 mg:400 mg.

[0008] Furthermore, the stirring reaction time is 6 to 48 hours.

[0009] Furthermore, the freeze-drying temperature is -30 to -100°C, the pressure is 0.001 to 10 mbar, and the time is 24 to 96 hours.

[0010] Furthermore, the gas atmosphere is 10% H2 / 90% Ar, and the flow rate is 5-200 sccm.

[0011] Furthermore, the high temperature carbonization conditions are: first, at 1-10°C·min -1 The temperature is heated to 200-500℃ at a rate of 1-20℃·min. -1 Heat to 550-1000°C at a heating rate and keep warm for 1-10 hours.

[0012] The present invention also provides an iron-based material loaded with three-dimensional carbon nanofibers obtained by the above-mentioned preparation method. The material comprises a carrier and a metal component loaded on the surface of the carrier. The carrier is a three-dimensional carbon nanofiber; the metal component is iron nanoparticles; and the iron nanoparticles account for 0.2 to 50% of the total mass of the material.

[0013] The present invention further provides the use of the three-dimensional carbon nanofiber-supported iron-based material as a catalyst in electrocatalytic nitrate synthesis of ammonia.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] The present invention provides a method for preparing a catalyst material for electrocatalytic nitrate synthesis of ammonia, and the obtained catalytic system includes a carbon nanofiber carrier with a three-dimensional network structure and uniformly distributed iron nanoparticles. The three-dimensional network carbon nanofibers have an ultra-light density and an ultra-high specific surface area, which promotes the substrate mass transfer of the catalytic system. The loaded iron nanoparticles play a role in connecting the carbon nanofibers, accelerating the electronic conduction of the catalytic system, and providing abundant reaction active sites. The catalyst prepared by the present invention has high physical and structural stability, and has excellent activity, selectivity and stability in the electrocatalytic nitrate synthesis of ammonia reaction. The Fe@CBC-1 catalyst material prepared in the embodiment has an ammonia yield of 8995840ug·mg at a potential of -0.9V vs.RHE, which is a historical breakthrough. Cat -1 . ·h -1 , and the Faraday efficiency is as high as 98.2%. The present invention provides a highly efficient non-precious metal catalyst for the electrocatalytic nitrate synthesis reaction of ammonia, which can simultaneously achieve ultra-high yield and Faraday efficiency under high current, and is of great significance for promoting the development of electrocatalytic ammonia synthesis technology and promoting the global nitrogen cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 TEM image of the Fe@CBC-1 sample prepared in Example 1.

[0017] Figure 2 This is the XRD pattern of the Fe@CBC-1 sample prepared in Example 1.

[0018] Figure 3 Linear sweep voltammetry curves of the Fe@CBC-1 sample measured in Example 1 in KNO3 and K2SO4 solutions.

[0019] Figure 4 This is the constant potential current density curve of the Fe@CBC-1 sample measured in Example 1.

[0020] Figure 5This is the ammonia production performance diagram of the Fe@CBC-1 sample measured in Example 1, including ammonia yield and Faraday efficiency.

[0021] Figure 6 This is the ammonia production stability cycle diagram of the Fe@CBC-1 sample measured in Example 1.

[0022] Figure 7 This is a diagram showing the nitrate removal effect of the Fe@CBC-1 sample measured in Example 1.

[0023] Figure 8 Linear sweep voltammetry curves of Fe@CBC samples with different iron loadings measured in Example 2.

[0024] Fig. 9 This is the linear sweep voltammetry curve of the Fe@XC72R sample measured in Comparative Example 1. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with specific implementation methods. The given examples are only used to illustrate the present invention and cannot limit the protection scope of the present invention.

[0026] The experimental methods in the following examples, unless otherwise specified, are conventional methods and are performed according to the techniques or conditions described in the literature in the art. The materials, reagents, etc. used in the following examples, unless otherwise specified, can be obtained from commercial sources.

[0027] Example 1

[0028] 1. In this embodiment, the three-dimensional carbon nanofiber-loaded iron-based material is prepared according to the following steps:

[0029] 150 mg of ferric chloride was dispersed in 50 g of bacterial cellulose dispersion with a mass concentration of 0.8%, and stirred rapidly at room temperature for 24 h. After centrifugation, it was freeze-dried at -75 °C and 0.01 mbar for 48 h to obtain dry bacterial cellulose adsorbing iron ions. The treated sample was then placed in a tube furnace with a 10% H2 / 90% Ar atmosphere, with a gas flow rate of 30 sccm and a temperature of 2 °C·min -1 The sample was heated to 360°C at a rate of 1.5°C / min and kept at this temperature for 2 h. -1 The sample was heated to 700℃ at a heating rate of 100℃ and kept warm for 3h to carbonize the bacterial cellulose and convert the adsorbed iron ions into iron nanoparticles. Finally, a three-dimensional network of carbon nanofibers loaded with iron was obtained, which was recorded as Fe@CBC-1. The Fe@CBC-1 sample was systematically characterized by TEM, XRD and other methods.

[0030] Figure 1This is the TEM image of the Fe@CBC-1 sample. It can be seen that Fe@CBC-1 is composed of carbon nanofibers with a three-dimensional network structure and evenly distributed iron nanoparticles, with an ultra-high specific surface area and ultra-light density. Figure 2 This is the XRD spectrum of the Fe@CBC-1 sample. The results show that there is only a diffraction peak of the Fe crystal phase, indicating that there is only one species of elemental Fe in the Fe@CBC-1 sample.

[0031] 2. The catalytic performance of Fe@CBC-1 obtained in this example was tested according to the following steps:

[0032] 3 mg of catalyst was dispersed in 9 mL of ethanol solution containing ~270 uL of Nafion (5 wt%) solution and ultrasonicated for 30 min to form a uniform ink. Then 9 uL of catalyst ink was dropped on a glassy carbon electrode (effective loading area of ​​1 cm 2 , the loading amount is 0.003 mg cm -2 ), and the working electrode is obtained after drying.

[0033] All electrochemical tests were performed in a two-chamber H-type electrolyzer separated by a Nafion 115 proton exchange membrane under ambient conditions. Each compartment contained 35 mL of a mixture of 1 M KNO3 and 0.1 M KOH as the electrolyte. The cathode chamber was heated at 2500 r·min. -1 The magnetic stirring was carried out at a rate of 200 μm, and the test results were recorded by an electrochemical workstation. In a typical three-electrode system, the working electrode with Fe@CBC-1 prepared in this example as the active material was used, and Ag / AgCl (3M KCl) and platinum sheet were used as the reference electrode and counter electrode, respectively. The potential range of 0V to -1.1V vs. RHE was 20mV·s -1 The linear sweep voltammetry curve was recorded at a scan rate of . The constant potential chronoamperometry test was carried out at a constant potential (-0.3V, -0.4V, -0.5V, -0.6V, -0.7V, -0.8V, -0.9V, -1.0V, -1.1V vs. RHE), the test was 10 minutes at each potential, and the electrolyte was collected to quantify the product. The ammonia production stability cycle test was carried out at a constant potential of -0.9V vs. RHE, the number of cycles was 10, and the electrolyte was collected to quantify the product. The nitrate removal test was carried out at a constant potential of -0.9V vs. RHE, the test time was 20h, and the electrolyte and product ammonia after the test were collected to analyze the results.

[0034] Figure 3This is the linear sweep voltammetry curve of Fe@CBC-1 catalyst in KNO3 and K2SO4 solutions (tested in the same way as above, the only difference is that 1M KNO3 in the electrolyte is replaced by 0.5M K2SO4). By comparison, it is found that the current density in KNO3 solution is much greater than that in K2SO4 solution at the same potential, indicating that Fe@CBC-1 catalyst has potential electrocatalytic activity in nitrate synthesis of ammonia within the measured potential range. Figure 4 This is the current density curve of the Fe@CBC-1 catalyst under constant potential chronoamperometry. As the applied potential decreases, the current density of the system increases significantly, reaching a maximum of 430 mA cm at -1.1 V vs. RHE potential. -2 . Figure 5 This is the ammonia production performance diagram of the Fe@CBC-1 catalyst. As the applied potential decreases, the ammonia yield increases continuously and reaches a maximum of 11877320ug·mg at -1.1V vs. RHE potential. Cat -1 ·h -1 ; As the applied potential decreases, the ammonia Faraday efficiency first increases and then decreases, reaching a maximum of 98.2% at a potential of -0.9 V vs. RHE, indicating that Fe@CBC-1 has extremely excellent catalytic activity, far exceeding other electrocatalytic ammonia synthesis catalysts. Figure 6 This is the stability cycle diagram of the Fe@CBC-1 catalyst in ammonia production. During dozens of ammonia production cycle tests, the ammonia yield and Faraday efficiency fluctuated only slightly, and there was no obvious decrease, indicating that Fe@CBC-1 has excellent catalytic stability. Figure 7 The Fe@CBC-1 catalyst was tested for nitrate removal. The results showed that the nitrate removal rate was as high as 99.9%, the ammonia yield was as high as 97.1%, and the yield of ammonium chloride (s) after hydrochloric acid acidification and evaporation crystallization also reached 91.4%, indicating that Fe@CBC-1 has the application prospect of directly converting nitrate in aqueous solution into practical ammonia products.

[0035] Example 2

[0036] 1. In this example, catalyst materials with different iron loadings were prepared according to the same method as in Example 1, except that the mass of ferric chloride added was changed to 50 mg, 15 mg, and 0 mg. The obtained products were respectively recorded as Fe@CBC-2, Fe@CBC-3, and CBC (i.e., pure three-dimensional network carbon nanofiber material without iron nanoparticles).

[0037] 2. In this example, the linear sweep voltammetry curves of Fe@CBC catalyst materials with different iron loadings were recorded according to the same test method as in Example 1.

[0038] Figure 8This is the linear sweep voltammetry curve of Fe@CBC catalyst materials with different iron loadings in KNO3 solution. With the increase of iron content in the catalyst material, the current density increases significantly at the same potential, indicating that the iron content has a great influence on the activity of Fe@CBC catalyst materials in electrocatalytic nitrate synthesis of ammonia, that is, the more iron nanoparticles there are, the higher the activity of the electrocatalytic ammonia synthesis reaction.

[0039] Comparative Example 1

[0040] 1. In this comparative example, commercial carbon XC72R was used as a carrier to prepare Fe@XC72R catalyst comparative material:

[0041] 150 mg of ferric chloride was dispersed in 200 mL of aqueous solution containing 400 mg of commercial carbon XC72R, stirred rapidly at room temperature for 12 h, centrifuged and dried at 80 °C for 12 h to obtain dry commercial carbon XC72R adsorbing iron ions. The treated sample was then placed in a tube furnace in a 10% H2 / 90% Ar atmosphere with a gas flow rate of 30 sccm and a temperature of 2 °C min -1 The sample was heated to 360°C at a rate of 20°C·min -1 The sample was heated to 700 °C at a heating rate and kept warm for 3 h to convert the adsorbed iron ions into iron nanoparticles. Finally, a commercial carbon material loaded with iron nanoparticles was obtained, which was recorded as Fe@XC72R.

[0042] 2. In this comparative example, the linear sweep voltammetry curve of the Fe@XC72R catalyst material was recorded using the same test method as in Example 1.

[0043] Fig. 9 Figure 3 is the linear sweep voltammetry curve of Fe@XC72R and Fe@CBC-1 catalyst materials in KNO3 solution. By comparing the two, it can be seen that the current density of Fe@XC72R catalyst material is much smaller than that of Fe@CBC-1 catalyst material at the same potential, indicating that the electrocatalytic ammonia synthesis activity of Fe@XC72R catalyst material is far inferior to that of Fe@CBC-1 catalyst material prepared by the present invention.

[0044] What is shown above are only several embodiments of the present invention, which are only used to explain the present invention, and do not limit the present invention in any form. Any technician familiar with the profession, without departing from the scope of the technical solution of the present invention, using the technical content provided above to make some changes or improvements are equivalent to equivalent implementation cases and fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a three-dimensional carbon nanofiber-supported iron-based material, It is characterized in that The following steps are involved: The iron salt is dispersed in the bacterial cellulose dispersion, stirred for reaction at room temperature, centrifuged and freeze-dried to obtain bacterial cellulose adsorbing iron ions; the bacterial cellulose adsorbing iron ions is placed in a tubular furnace and subjected to high-temperature carbonization under a gas atmosphere to obtain an iron-based material loaded with three-dimensional network carbon nanofibers.

2. The preparation method according to claim 1, It is characterized in that The iron salt is an inorganic salt containing iron, and the mass ratio of the iron salt to the bacterial cellulose is 1-200 mg:400 mg.

3. The preparation method according to claim 1, It is characterized in that The stirring reaction time is 6 to 48 hours.

4. The preparation method according to claim 1, It is characterized in that The freeze drying process is carried out at a temperature of -30 to -100°C, a pressure of 0.001 to 10 mbar, and a time of 24 to 96 hours.

5. The preparation method according to claim 1, It is characterized in that The gas atmosphere is 10% H 2 / 90% Ar, flow rate is 5~200sccm.

6. The preparation method according to claim 1, It is characterized in that The high temperature carbonization conditions are: first, at 1-10°C·min -1 The temperature is heated to 200-500℃ at a rate of 1-20℃·min. -1 Heat to 550-1000°C at a heating rate and keep warm for 1-10 hours.

7. An iron-based material loaded with three-dimensional carbon nanofibers obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the iron-based material supported by the three-dimensional carbon nanofiber network as claimed in claim 7 as a catalyst in the electrocatalytic synthesis of ammonia from nitrate.

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