3D-printed synthetic ammonia iron-based electrode catalysts, preparation and use thereof

Abstract

The application discloses a 3D-printed iron-based electrode catalyst and a preparation and application thereof, and relates to the technical field of catalysts.The 3D-printed iron-based electrode catalyst is prepared by using 3D printing technology and a thermal oxidation method to modify an iron-based high-temperature alloy powder, and the catalyst has a honeycomb structure formed by three layers of regular hexagons.The regular hexagons are connected by a rod-shaped iron-based alloy and a spherical iron-based alloy.The catalyst is beneficial to the uniform and dynamic distribution of electrolyte on the positive and negative surfaces of the electrode, and can maximize the use of the reaction surface of the electrode catalyst, and the integrated electrode catalyst has the advantages of stable reaction current and difficulty in falling off and dissolving out, and the thermal oxidation method can effectively inhibit the hydrogen evolution reaction of the electrode catalyst in the electrocatalytic ammonia synthesis reaction, so that the selectivity of ammonia synthesis is improved, and the yield of ammonia synthesis is high.The catalyst preparation method is simple, the catalyst is easy to form, and the catalyst has a good industrial application prospect.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysis, and particularly relates to a 3D-printed iron-based electrode catalyst and a preparation method and application thereof in electrocatalytic reduction of nitrate to ammonia. BACKGROUND

[0002] Ammonia is widely used in the fields of fertilizer, chemical industry, pharmaceuticals and energy storage, etc. At present, it is considered as a good carrier for the next generation of renewable energy due to its high energy density (4.32 kWh L -1 ), strong hydrogen storage capacity (17.6%) and low carbon emission, and plays a key role in the development of human society. The traditional Haber-Bosch process in industry is to reduce N2 to NH3 by using ruthenium-based catalysts under harsh reaction conditions (15-25 MPa, 300-550 ℃), which consumes a large amount of energy and inevitably causes a large amount of CO2 emission and other problems. Therefore, electrocatalytic synthesis of ammonia is considered as one of the best ways for energy saving and emission reduction in the future.

[0003] At present, the efficiency of electrocatalytic synthesis of ammonia from nitrogen is still far lower than that of the traditional H-B process, and a long way needs to be taken for large-scale application. Compared with nitrogen, nitrate has high solubility in water, and the energy barrier (204 kJ mol -1 ) required for breaking the N-O bond is lower, and the reaction is easier to proceed. Therefore, electrocatalytic reduction of nitrate to ammonia (NO3 - RR) is considered as a relatively ideal strategy, which can realize environmental friendliness and renewable energy.

[0004] In recent years, with the rapid development of 3D printing technology, its application in the field of electrocatalytic synthesis of ammonia has also increased. Some researchers have constructed a grid-type structure electrode catalyst for the reduction of nitrate to ammonia, and the yield of the reduction of nitrate to ammonia reached 383 μg h -1 cm -2 , and the faradic efficiency reached 37%. This self-supporting electrode catalyst has the advantages of stable current conduction and non-falling of surface catalyst. However, the grid-type structure still has the disadvantages of high powder consumption, relatively poor performance and faradic efficiency, and therefore a new electrode structure needs to be improved to improve the performance. SUMMARY

[0005] The present application provides a 3D-printed iron-based electrode catalyst for synthesis of ammonia and a preparation method and application thereof, which has a unique electrode morphology structure, is beneficial to uniform coverage of electrolyte on the electrode surface, and has good nitrate reduction activity.

[0006] To achieve the above object, the application adopts the following technical scheme:

[0007] A 3D-printed iron-based electrode catalyst is prepared by using a 3D printing technology of laser melting (SLM) combined with a surface modification technology of thermal oxidation, with an iron-based high-temperature alloy powder as a raw material.

[0008] Further, the catalyst is a honeycomb structure composed of three layers of regular hexagonal connections; the regular hexagons are connected by a rod-shaped iron-based alloy and a spherical iron-based alloy.

[0009] Further, the side length of the regular hexagon is 4±0.1 mm; the pipe diameter of the rod-shaped iron-based alloy is 0.8±0.1 mm; and the diameter of the spherical iron-based alloy is 1.2±0.1 mm.

[0010] Further, the iron-based high-temperature alloy powder is a 316L stainless steel powder.

[0011] The preparation method of the iron-based electrode catalyst comprises the following steps:

[0012] 1) using computer-aided design software to design and build a digital model of the required iron-based electrode catalyst;

[0013] 2) using an iron-based high-temperature alloy powder as a raw material, using a 3D printer for laser printing;

[0014] 3) cutting the sample obtained in step 2) and sequentially washing with anhydrous ethanol and water, then immersing in a hydrochloric acid solution, rinsing with water, and drying;

[0015] 4) performing thermal oxidation surface modification on the sample obtained in step 3) to obtain the iron-based electrode catalyst.

[0016] Further, the setting parameters for the laser printing in step 2) are: laser scanning speed 300 m / s, laser power 10 W, and scanning filling strategy is strip filling.

[0017] Further, the concentration of the hydrochloric acid solution used in step 3) is 0.09~0.11 M.

[0018] Further, the soaking time in step 3) is 5~6 h.

[0019] Further, the temperature for thermal oxidation surface modification in step 4) is 400~600 ℃, and the time is 11~12 h.

[0020] The 3D-printed iron-based electrode catalyst can be used for electrocatalytic reduction of nitrate to ammonia.

[0021] Further, the application method is specifically to construct a three-electrode electrochemical workstation by taking the iron-based electrode catalyst as a working electrode, a platinum sheet as a counter electrode, an Ag / AgCl electrode as a reference electrode, and a mixed solution containing 500 ppm KNO3+0.1 M K2SO4 as an electrolyte, so as to realize the electrocatalytic preparation of ammonia. The optimal reaction potential is-0.8 V~ -0.9 V.

[0022] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0023] 1、The iron-based electrode catalyst prepared by the 3D printing of the present application has a planar honeycomb structure, and the honeycomb structure has the characteristics of porosity and macroporosity, which is beneficial to the uniform and dynamic distribution of the electrolyte on the front and back surfaces of the electrode, so that the electrolyte and the catalyst can react more fully, and the reaction efficiency is greatly improved. Compared with other electrode catalysts of the prior art, the present application has better ammonia synthesis performance.

[0024] 2、The electrode catalyst prepared by the thermal oxidation technology of the present application can greatly reduce the hydrogen evolution reaction (HER) while ensuring the stability of the ammonia synthesis performance, thereby improving the selectivity of ammonia synthesis.

[0025] 3、The honeycomb structure involved in the present application requires less raw material powder and has lower manufacturing cost compared with other structures, and the obtained catalyst has good mechanical properties and can adapt to various reaction environments.

[0026] 4、Compared with the traditional catalyst preparation process, the preparation process of the 3D printed electrode catalyst of the present application does not require binders, conductive agents, current collectors and the like, and can be directly used as an electrode.

[0027] 5、Compared with the traditional powder catalyst, the integrated electrode catalyst obtained by the present application has the advantages of stable reaction current and not easy to fall off, and can make the conduction of current more stable.

[0028] 6、The catalyst preparation process of the present application is simple, the raw material powder used is 316L powder, which has the characteristics of low preparation cost and high reuse rate; and in the 3D printing process, the printing precision can reach 0.1 mm by adjusting the printing parameters, so that the required morphology can be accurately printed. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is the digital model graph (a) and the entity graph (b) of the iron-based electrode catalyst in Example 1.

[0030] Figure 2 It is the X-ray powder diffraction pattern of the iron-based electrode catalyst prepared in Example 1.

[0031] Figure 3Linear sweep voltammogram of the iron-based electrode catalyst prepared for Example 1 in the electrocatalytic ammonia synthesis reaction.

[0032] Figure 4 Catalytic efficiency of the iron-based electrode catalyst prepared for Example 1 in the electrocatalytic ammonia synthesis reaction.

[0033] Figure 5 Catalytic efficiency of the iron-based electrode catalyst prepared for Example 2 in the electrocatalytic ammonia synthesis reaction.

[0034] Figure 6 Catalytic efficiency of the iron-based electrode catalyst prepared for Example 3 in the electrocatalytic ammonia synthesis reaction.

[0035] Figure 7 Comparison of catalytic efficiency of the iron-based electrode catalyst prepared for Comparative Example 1 and the iron-based electrode catalyst prepared for Example in the electrocatalytic ammonia synthesis reaction.

[0036] Figure 8 Digital model of the iron-based electrode catalyst composed of different number of regular hexagons in Comparative Example 2.

[0037] Figure 9 Comparison of catalytic efficiency of the iron-based electrode catalyst composed of different number of regular hexagons in Comparative Example 2 in the electrocatalytic ammonia synthesis reaction.

[0038] Figure 10 Digital model of the iron-based electrode catalyst with different number of layers in Comparative Example 3.

[0039] Figure 11 Comparison of catalytic efficiency of the iron-based electrode catalyst with different number of layers prepared for Comparative Example 3 in the electrocatalytic ammonia synthesis reaction.

[0040] Figure 12 Digital model of the iron-based electrode catalyst with different morphology in Comparative Example 4.

[0041] Figure 13 Comparison of catalytic efficiency of the iron-based electrode catalyst with different morphology prepared for Comparative Example 4 in the electrocatalytic ammonia synthesis reaction.

[0042] Figure 14 Structure schematic of the grid-type iron-based electrode catalyst prepared in Comparative Example 5.

[0043] Figure 15 Catalytic efficiency of the grid-type iron-based electrode catalyst prepared for Comparative Example 5 in the electrocatalytic ammonia synthesis reaction. DETAILED DESCRIPTION

[0044] A 3D-printed iron-based electrode catalyst, the preparation of which comprises the following steps:

[0045] 1) using computer-aided design software to design and construct a digital model of the desired iron-based electrode catalyst;

[0046] 2) using 316L stainless steel powder as raw material, laser printing is carried out by using a 3D printer; the setting parameters of laser printing are: laser scanning rate 300 m / s, laser power 10 W, and scanning filling strategy is strip filling.

[0047] 3) the sample obtained in step 2) is cut and then washed with anhydrous ethanol and water, and then immersed in a 0.09-0.11 M hydrochloric acid solution for 5-6 h, then washed with water and dried;

[0048] 4) the sample obtained in step 3) is subjected to thermal oxidation surface modification at 400-600 ℃ for 11-12 h to obtain the iron-based electrode catalyst.

[0049] The catalyst is a honeycomb structure composed of three layers of regular hexagons connected; the regular hexagons are connected by rod-shaped iron-based alloy and spherical iron-based alloy. The side length of the regular hexagon is 4±0.1 mm; the tube diameter of the rod-shaped iron-based alloy is 0.8±0.1 mm; the diameter of the spherical iron-based alloy is 1.2±0.1 mm.

[0050] In order to make the content of the application more convenient to understand, the technical solutions of the application will be further described below in combination with specific embodiments, but the application is not limited thereto.

[0051] In the following examples, the materials, electrodes, etc. can be obtained from commercial channels unless otherwise specified.

[0052] The alloy used in the examples and comparative examples is 316L powder, and its component composition is shown in Table 1 (counted by mass percentage):

[0053] Table 1

[0054]

[0055] Example 1

[0056] 1) using solidworks software for auxiliary design, constructing a digital model and digital task (digital task includes scanning rate, scanning path, laser power, etc.); as Figure 1 As can be seen in a) of the foregoing, the digital model is a honeycomb structure composed of three layers of regular hexagons connected, the first layer and the third layer are two connected regular hexagons, the second layer is a regular hexagon for connecting the first layer and the third layer, and the side length of each regular hexagon is 4 mm; each regular hexagon is connected by a ball and a rod, and the tube diameter of the rod is 0.8 mm and the diameter of the ball is 1.2 mm.

[0057] 2) Using 316L powder as raw material, the laser scanning rate was set to 300 m / s, the laser power to 10 W, and the scanning and filling strategy to be strip filling. Laser printing was performed using a 3D printer.

[0058] 3) Use a CNC machine tool to cut the printed sample from the substrate in step 2). Then, clean the cut sample with anhydrous ethanol and ultrapure water by ultrasonication for 30 min each, soak it in 0.1 M HCl solution for 6 h, rinse it with ultrapure water, and place it in a vacuum drying oven to dry at 50 ℃ for 6 h.

[0059] 4) Fix the dried sample from step 3) with copper wire, making it upright in the crucible, and then calcine it in a muffle furnace. The calcine temperature was 500 °C, the heating rate was 5 °C / min, and the calcine time was 12 h. The resulting iron-based electrode catalyst is shown in [reference needed]. Figure 1 (b) Its X-ray powder diffraction pattern is shown in Figure 1. Figure 2 .

[0060] The prepared iron-based electrode was used in the electrocatalytic ammonia synthesis reaction. The test system employed a typical three-electrode system: the prepared electrode catalyst was used as the working electrode, a platinum sheet as the counter electrode, and a saturated Ag / AgCl electrode as the reference electrode. Before the reaction, Ar was bubbled into an electrolyte containing 500 ppm KNO3 + 0.1 M K2SO4 for 30 min to ensure that the electrolyte at the cathode was saturated with Ar. In the linear voltammetry scan, the scan voltage range was selected as 0 to -1.0 V vs. RHE. The results are shown in [Figure number missing]. Figure 3 .from Figure 3 It can be seen that the obtained iron-based electrode catalyst achieved a higher current density in an electrolyte containing 500 ppm KNO3.

[0061] To prove that this phenomenon is caused by the electrocatalytic reduction of nitrate, further experiments were conducted using an H-type reactor under ambient conditions to react aqueous NO3. - RR test. The chronoamperometry with a reaction voltage of -0.5 to -1.1 V vs. RHE was used to determine the nitrate reduction performance. The results are shown in [Figure number missing]. Figure 4 .from Figure 4 It can be seen that, under the catalytic action of the electrode catalyst, when the applied voltage is -0.9 V vs. RHE, 652 μg·h can be achieved. -1 ·cm -2 The ammonia yield and Faraday efficiency were 54%.

[0062] Example 2

[0063] The calcination temperature in step 4) is adjusted to 400 ℃, and other operations are the same as in Example 1 to prepare an iron-based electrode catalyst.

[0064] The prepared iron-based electrode catalyst is tested by chronoamperometry with a reaction voltage of -0.5 to -1.1 V vs. RHE to determine the nitrate reduction performance, and the results are shown in Figure 5 From Figure 5 it can be seen that, under the catalysis of the electrode catalyst, the ammonia yield of 582 μg·h -1 ·cm -2 and the Faraday efficiency of 60% can be achieved when the applied voltage is -0.9 V vs. RHE.

[0065] Example 3

[0066] The calcination temperature in step 4) is adjusted to 600 ℃, and other operations are the same as in Example 1 to prepare an iron-based electrode catalyst.

[0067] The prepared iron-based electrode catalyst is tested by chronoamperometry with a reaction voltage of -0.5 to -1.1 V vs. RHE to determine the nitrate reduction performance, and the results are shown in Figure 6 From Figure 6 it can be seen that, under the catalysis of the electrode catalyst, the ammonia yield of 628 μg·h -1 ·cm -2 and the Faraday efficiency of 53% can be achieved when the applied voltage is -0.9 V vs. RHE.

[0068] Comparative Example 1

[0069] Step 4) is not calcined, and the calcination temperature is adjusted to 300 ℃ or 700 ℃, and other operations are the same as in Example 1 to prepare corresponding iron-based electrode catalysts.

[0070] The prepared iron-based electrode catalyst is tested by chronoamperometry with a reaction voltage of -0.5 to -1.1 V vs. RHE to determine the nitrate reduction performance, and the results are shown in Figure 7 From Figure 7 it can be seen that, under the catalysis of the electrode catalyst, the ammonia yield of 183 μg·h -1 ·cm -2 can be achieved for the fresh uncalcined sample when the applied voltage is -0.9 V vs. RHE, the ammonia yield of 356 μg·h -1 ·cm -2 for the sample calcined at 300 ℃, and the ammonia yield of 153 μg·h -1 ·cm -2, which are all lower than that of Example 1. This result shows that the Fe2O3 covering the surface of the electrode catalyst after the calcination process covers the active sites of the HER reaction, making the NO3 - The selectivity of the reaction of RR is improved; but when the calcination temperature is further increased to above 600℃, too much oxide is accumulated on the surface, which makes the electrode conductivity worse, thus the yield decreases.

[0071] Comparative Example 2

[0072] Referring to the method described in Example 1, iron-based electrode catalysts with different numbers of regular hexagons as shown in Figure 8 were prepared respectively.

[0073] The prepared iron-based electrode catalysts were tested by chronoamperometry with a reaction voltage of-0.9 V vs. RHE to determine the nitrate reduction performance, and the results are shown in Figure 9 . It can be seen from Figure 9 that under the catalysis of the electrode catalyst, the yield of the double torus is the highest, reaching 492 μg·h -1 ·cm -2 . It can be seen from the results that as the number of toruses increases, the ammonia yield shows a decreasing trend, so the number of single-layer toruses is 1-2.

[0074] Comparative Example 3

[0075] Referring to the method described in Example 1, iron-based electrode catalysts with different numbers of layers as shown in Figure 10 were prepared respectively.

[0076] The prepared iron-based electrode catalysts were tested by chronoamperometry with a reaction voltage of-0.9 V vs. RHE to determine the nitrate reduction performance, and the results are shown in Figure 11 . It can be seen from Figure 11 that under the catalysis of the electrode catalyst, when the applied voltage is-0.9 V vs. RHE, the ammonia yields of the single-layer and the three-layer are 492 μg·h -1 ·cm -2 and 390 μg·h -1 ·cm -2 respectively, which are all lower than that of the double-layer, 652 μg·h -1 ·cm -2 , so the number of layers should not be too many.

[0077] Comparative Example 4

[0078] Referring to the method described in Example 1, iron-based electrode catalysts with three-prism, tubular and spherical structures as shown in Figure 12 were prepared respectively.

[0079] The prepared iron-based electrode catalyst was tested by chronoamperometry with a reaction voltage of-0.9 V vs. RHE to determine the nitrate reduction performance, and the results are shown in Table 1. Figure 13 As can be seen from Table 1, Figure 13 the synthesis ammonia yield of the reaction using the iron-based electrode catalyst with other morphologies as the working electrode is lower than that of Example 1. This is because the simple macroporous structure of Example 1 is beneficial to the electrolyte covering the electrode surface, making the reaction more complete.

[0080] Comparative Example 5

[0081] Referring to the patent CN 116479443A, an iron-based electrode catalyst with a grid type as shown in Figure 14 was prepared.

[0082] The prepared iron-based electrode catalyst was tested by chronoamperometry with a reaction voltage of-0.9 V vs. RHE to determine the nitrate reduction performance, and the results are shown in Table 1. Figure 15 As can be seen from Table 1, Figure 15 under the catalysis of the electrode catalyst, the grid type iron-based electrode catalyst can only reach an ammonia yield of 383 μg·h -1 ·cm -2 and a faradic efficiency of 37% when the voltage is-0.9 V vs. RHE, which is far lower than the ammonia yield of 652 μg·h -1 ·cm -2 and the faradic efficiency of 54% achieved by Example 1. This is because the grid structure is not conducive to the flow of electrolyte in the H-type cell due to its sharp corner structure, while the honeycomb structure has larger pore structure and smoother corner structure, which is more conducive to the dynamic distribution of electrolyte on the electrode surface; and thanks to the ball and stick structure, the longer residence time of electrolyte on the electrode surface due to the greater roughness makes the reaction more efficient, thus greatly improving the catalytic performance.

[0083] In summary, the present application takes advantage of the additive manufacturing of 3D printing technology to construct a honeycomb electrode morphology, which is beneficial to the uniform and dynamic distribution of electrolyte on the front and back surfaces of the electrode, not only maximizing the use of the reaction surface of the electrode catalyst, but also having the advantages of stable reaction current and not easy to fall off and dissolve, etc. Combined with the heat oxidation method for modifying the surface of the electrode catalyst, the modified electrode catalyst can effectively inhibit the hydrogen evolution reaction in the electrocatalytic synthesis of ammonia reaction by using the oxides generated on the surface after heat oxidation, thereby improving the selectivity of ammonia synthesis, and thus showing a strong ammonia synthesis yield. At the same time, the catalyst preparation method provided by the present application is relatively simple, and the catalyst is easy to shape, which has a good industrial application prospect.

[0084] The above merely describes preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the present application should be included in the scope of the present application.

Claims

1. A 3D-printed iron-based electrode catalyst, characterized in that, The iron-based high-temperature alloy powder is used as raw material, and the 3D printing technology is combined with the surface modification technology of thermal oxidation to prepare the iron-based electrode catalyst; the catalyst is a honeycomb structure composed of three layers of coplanar connected regular hexagons; the regular hexagons are connected by rod-shaped iron-based alloy and spherical iron-based alloy.

2. The iron-based electrode catalyst according to claim 1, characterized in that, The iron-based high-temperature alloy powder is 316L stainless steel powder.

3. The iron-based electrode catalyst according to claim 1, characterized in that, The side length of the regular hexagon is 4±0.1 mm; the pipe diameter of the rod-shaped iron-based alloy is 0.8±0.1 mm; and the diameter of the spherical iron-based alloy is 1.2±0.1 mm.

4. A method of preparing a 3D-printed iron-based electrode catalyst as claimed in claim 1, characterized in that, The method comprises the following steps: 1) using computer-aided design software to design and build a digital model of the required iron-based electrode catalyst; 2) using iron-based high-temperature alloy powder as raw material, laser printing is carried out by using a 3D printer; 3) the sample obtained in step 2) is cut and then washed with anhydrous ethanol and water in sequence, then soaked in a hydrochloric acid solution, washed with water, and dried; 4) the sample obtained in step 3) is subjected to thermal oxidation surface modification to obtain the iron-based electrode catalyst.

5. The method of producing a 3D-printed iron-based electrode catalyst according to claim 4, characterized in that, The setting parameters of the laser printing in step 2) are: laser scanning speed 300 m / s, laser power 10 W, and scanning filling strategy is strip filling.

6. The method of producing a 3D-printed iron-based electrode catalyst according to claim 4, characterized in that, The concentration of the hydrochloric acid solution used in step 3) is 0.09-0.11 M.

7. The method of producing a 3D-printed iron-based electrode catalyst according to claim 4, characterized in that, The soaking time in step 3) is 5-6 h.

8. The method of producing a 3D-printed iron-based electrode catalyst according to claim 4, characterized in that, The temperature for thermal oxidation surface modification in step 4) is 400-600 ℃, and the time is 11-12 h.

9. The application of the 3D printed iron-based electrode catalyst of claim 1 in the electrocatalytic reduction of nitrate to produce ammonia.

10. Use according to claim 9, characterized in that, The three-electrode electrochemical workstation is constructed by using the iron-based electrode catalyst as the working electrode, platinum sheet as the counter electrode, Ag / AgCl electrode as the reference electrode, and a mixed solution containing 500 ppm KNO3+0.1 M K2SO4 as the electrolyte, so as to realize the electrocatalytic preparation of ammonia.

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