Nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia and preparation method thereof

Abstract

The present invention discloses a nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia and a preparation method thereof, which belongs to the field of nanomaterial technology; the nanoporous intermetallic compound catalyst prepared by the present invention has a bicontinuous nanoporous structure, wherein the intermetallic compound is specifically a copper-zinc intermetallic compound; the prepared catalyst shows great potential in energy and environmental fields such as nitrogen oxide reduction synthesis of ammonia, wastewater treatment and energy storage. At the same time, a preparation method of the above catalyst is further proposed, which has a simple preparation process, low cost and environmental friendliness, high nitrogen oxide conversion rate, and is suitable for large-scale industrial promotion and application.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and in particular to a nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia and a preparation method thereof. Background Art

[0002] Ammonia (NH3), one of the most important chemicals in the world, is mainly produced by the Haber-Bosch process, which accounts for 1-2% of global energy consumption and 1-2% of carbon dioxide emissions. As an alternative route, the synthesis of ammonia by electrochemical reduction of nitrogen oxides is gaining increasing attention. Among them, nitrogen oxides are a pollutant widely present in industrial waste gas / water, liquid nuclear waste, livestock excrement and fertilizers, which seriously threatens human health. Therefore, using renewable electricity under ambient conditions to directly convert toxic and harmful nitrogen oxides into valuable products NH3 through electrochemical reduction reactions is an attractive strategy to produce clean hydrogen carriers while controlling pollution sources.

[0003] Although significant progress has been made in the development of electrocatalysts in recent years, the direct electrosynthesis of ammonia with high selectivity remains a huge scientific challenge. Therefore, it is very necessary to rationally design electrocatalysts with high density of active sites and high selectivity. Based on the above, the present invention proposes a nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia and a preparation method thereof. Summary of the invention

[0004] The object of the present invention is to provide a nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia and a preparation method thereof to solve the problems raised in the background technology.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia, wherein the intermetallic compound is specifically a copper-zinc intermetallic compound, including but not limited to CuZn5, CuZn4, Cu5Zn8, CuZn; the nanoporous intermetallic compound catalyst has a bicontinuous nanoporous structure.

[0007] Preferably, the porosity of the catalyst is 20-80%, preferably 40-70%; the pore size is 2-200 mm, preferably 2-50 mm.

[0008] A method for preparing a nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia comprises the following steps:

[0009] S1, mixing pure copper and pure zinc in a certain proportion, and then performing arc melting to prepare a copper-zinc precursor alloy ingot;

[0010] S2, remelting the alloy ingot by melt spinning technology, and rapidly quenching it on the surface of a high-speed rotating copper roller to obtain a copper-zinc precursor alloy strip;

[0011] S3. In a 1 mol / L KOH solution, the copper-zinc precursor alloy strip is electrochemically dealloyed and phase-transformed using a constant potential to obtain a nanoporous intermetallic compound catalyst.

[0012] Preferably, the molar ratio of copper to zinc in S1 is 4:30:70:96, preferably 6:20:80:94.

[0013] Preferably, the rotation speed of the copper roller in S2 is 500 5000 r / min, preferably 1000 3000 r / min.

[0014] Preferably, in S3, a three-electrode system is used for electrochemical dealloying phase transition, with Hg / HgO electrode as reference electrode, platinum sheet as counter electrode, alloy strip as working electrode, voltage of 1.4-0.3V vs.Hg / HgO, and dealloying time of 1 to 6 hours.

[0015] Preferably, during the preparation process, the nitrogen source used is nitrogen oxides, including but not limited to NO, nitrite, and nitrate.

[0016] Compared with the prior art, the present invention proposes a nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia and a preparation method thereof, which has the following beneficial effects:

[0017] The present invention provides a nanoporous intermetallic compound catalyst for electrochemical synthesis of ammonia and a preparation method thereof. The catalyst of the bicontinuous nanoporous copper-zinc intermetallic compound is prepared by adopting electrochemical dealloying phase transformation. The present invention achieves high NH3 Faraday efficiency, high ammonia yield and energy conversion efficiency in a wide nitrite concentration range. Under membrane electrode assembly conditions, it can -2 The conversion of low-concentration nitrite to ammonia was achieved for 220 hours under the conditions of NH3, with a stable NH3 Faradaic efficiency of about 80% and a nitrite removal rate close to 100%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 XRD patterns of np / CuZn5, np / CuZn4, np / Cu5Zn8 and np / CuZn catalysts synthesized by electrochemical dealloying phase transition method in Example 1-2 of the present invention;

[0019] Figure 2The SEM images of np / CuZn4, np / Cu5Zn8 and np / CuZn catalysts synthesized by the electrochemical dealloying phase transition method in Examples 1-2 of the present invention;

[0020] Figure 3 The SEM-EDS images of np / CuZn4, np / Cu5Zn8 and np / CuZn catalysts synthesized by the electrochemical dealloying phase transition method in Example 1-2 of the present invention;

[0021] Figure 4 The performance of the np / CuZn catalyst in Example 3 of the present invention at different nitrite concentrations was evaluated. The np / CuZn catalyst exhibited excellent ammonia synthesis activity in the nitrite concentration range of 0.1mmol / L-1mol / L. When the nitrite concentration was ≥1mmol / L, the NH3 Faraday efficiency exceeded 90%;

[0022] Figure 5 The results of the Faradaic efficiency, yield and energy conversion efficiency of the electroreduction of nitrite to ammonia by np / CuZn catalyst under the condition of 10 mmol / L nitrite concentration in Example 3 of the present invention are shown. In the wide potential range of -0.2--0.8 V vs. RHE, the Faradaic efficiency of NH3 exceeds 95%, and the yield reaches 2.48 mg h -1 mg cat. -1 , energy conversion efficiency is as high as 59.1%;

[0023] Figure 6 The results of the Faradaic efficiency, yield and energy conversion efficiency of the electroreduction of nitrite to ammonia by np / CuZn4 and np / Cu5Zn8 catalysts under the condition of 10 mmol / L nitrite concentration in Example 3 of the present invention;

[0024] Figure 7 In Example 4 of the present invention, under the membrane electrode assembly conditions, the np / CuZn catalyst can -2 The conversion of nitrite to ammonia was achieved in 220 hours under the conditions of NH3 Faradaic efficiency of about 80% and nitrite removal rate close to 100%;

[0025] Figure 8 The results are the yield and Faraday efficiency of synthesizing ammonia by electroreduction of nitrate with np / CuZn catalyst under the condition of 10 mmol / L nitrate concentration in Example 5 of the present invention. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] Embodiment 1:

[0028] This example provides a method for preparing np / CuZn4 and np / CuZn5 catalysts, comprising the following steps:

[0029] S1. Pure copper and pure zinc are mixed in a ratio of 6:94 at%, and then arc smelted to prepare Cu6Zn 94 Alloy ingot.

[0030] S2, using melt spinning technology to remelt the alloy ingot, and quickly quenching it on the surface of a high-speed rotating copper roller to obtain Cu6Zn 94 Precursor alloy strips.

[0031] S3. In the three-electrode system of the electrochemical workstation, electrochemical etching was performed with a accurately calibrated Hg / HgO electrode as the reference electrode, a platinum sheet as the counter electrode, an alloy strip as the working electrode, and 1 mol / L potassium hydroxide as the electrolyte. Etching was performed at a voltage of -1.32 V vs Hg / HgO for 6.0 h (the current was reduced to 10 5 A) to obtain np / CuZn5 strips. Etching at -1.26 V vs Hg / HgO for 3.2 h (current dropped to 10 5 A) np / CuZn4 strips were obtained.

[0032] Embodiment 2:

[0033] Based on Example 1, but different in that, this example provides a method for preparing np / Cu5Zn8 and np / CuZn catalysts, comprising the following steps:

[0034] S1. Pure copper and pure zinc are mixed in a ratio of 15:85 at%, and then arc smelted to prepare Cu 15 Zn 85 Alloy ingot.

[0035] S2, remelt the alloy ingot using melt spinning technology, and quickly quench it on the surface of a high-speed rotating copper roller to obtain Cu 15 Zn 85 Precursor alloy strips.

[0036] S3. In the three-electrode system of the electrochemical workstation, electrochemical etching was performed using a calibrated Hg / HgO electrode as the reference electrode, a platinum sheet as the counter electrode, an alloy strip as the working electrode, and 1 mol / L potassium hydroxide as the electrolyte. 15 Zn 85 The alloy strip was etched at a corrosion voltage of -1.15 V vs Hg / HgO for 4.0 h (the corrosion current dropped to 10 5A) to obtain np / Cu5Zn8 strips. Etched at a corrosion voltage of -0.95V vs Hg / HgO for 3.0h (corrosion current dropped to 10 5 A) np / CuZn strips were obtained.

[0037] Based on Examples 1-2, the morphology of np / CuZn5, np / CuZn4, np / Cu5Zn8 and np / CuZn catalysts synthesized by electrochemical dealloying phase inversion method was characterized. Figure 1-3 As shown, Figure 1 The XRD patterns of np / CuZn5, np / CuZn4, np / Cu5Zn8 and np / CuZn catalysts synthesized by electrochemical dealloying phase inversion method are shown; Figure 2 The SEM images of np / CuZn4, np / Cu5Zn8 and np / CuZn catalysts synthesized by electrochemical dealloying phase inversion method are shown; Figure 3 The SEM-EDS images of np / CuZn4, np / Cu5Zn8 and np / CuZn catalysts synthesized by electrochemical dealloying phase inversion method are shown.

[0038] Embodiment 3:

[0039] Based on Example 1-2, but different in that the electrocatalytic reduction of nitrite to synthesize ammonia is as follows:

[0040] The test used a three-electrode system, with nanoporous intermetallic compounds as the working electrode, accurately calibrated Ag / AgCl as the reference electrode, and platinum as the counter electrode. The electrolytic cell used was an H-type electrolytic cell, with a mixed solution of 0.2 mol / L potassium bicarbonate and potassium nitrite (0.1 mmol / L-1 mol / L) as the electrolyte.

[0041] Based on the above conditions, the reaction results are as follows Figure 4 As shown, Figure 4 The performance evaluation of np / CuZn catalyst under different nitrite concentrations was demonstrated, and np / CuZn catalyst showed excellent ammonia synthesis activity in the nitrite concentration range of 0.1mmol / L-1mol / L. When the nitrite concentration was ≥1mmol / L, the NH3 Faradaic efficiency exceeded 90%.

[0042] Embodiment 4:

[0043] Based on Example 1-3, but different in that, under the membrane electrode assembly conditions, the electrocatalytic reduction of nitrite to synthesize ammonia reaction is:

[0044] The test used a two-electrode system. The experimental device consisted of a customized membrane electrode electrolyzer (0.5 cm -2), nanoporous intermetallic compound strips (cathode), proton exchange membrane (Nafion117) and IrO2-Ti mesh (cathode), with a mixed solution of 0.2 mol / L potassium bicarbonate and 10 mmol / L potassium nitrite as the electrolyte, and the electrolyte volume is 2.5 liters.

[0045] Based on the above conditions, the reaction results are as follows Figure 5 As shown, Figure 7 The np / CuZn catalyst was shown to be able to generate a high current density of 500 mA cm under membrane electrode assembly conditions. -2 Under the conditions of 220 hours, the conversion of nitrite to ammonia was achieved, the NH3 Faradaic efficiency was about 80%, and the nitrite removal rate was close to 100%.

[0046] Embodiment 5,

[0047] Based on Example 1-4, but different in that the electrocatalytic reduction of nitrate to synthesize ammonia reaction is:

[0048] The test used a three-electrode system, with a nanoporous intermetallic compound as the working electrode, a precisely calibrated Ag / AgCl electrode as the reference electrode, and a platinum sheet as the counter electrode. The electrolytic cell used was an H-type electrolytic cell, with a mixed solution of 0.2 mol / L potassium bicarbonate and 10 mmol / L potassium nitrate as the electrolyte.

[0049] Based on the above conditions, the reaction results are as follows Figure 5-8 As shown, Figure 5 The Faradaic efficiency, yield and energy conversion efficiency of the electroreduction of nitrite to ammonia over the np / CuZn catalyst under the condition of 10 mmol / L nitrite concentration are shown. In the wide potential range of -0.2--0.8 V vs. RHE, the Faradaic efficiency of NH3 exceeds 95% and the yield reaches 2.48 mg h - 1 mg cat. -1 , the energy conversion efficiency is as high as 59.1%. Figure 6 The Faradaic efficiency, yield and energy conversion efficiency of np / CuZn4 and np / Cu5Zn8 catalysts for electroreduction of nitrite to ammonia under 10mmol / L nitrite concentration conditions are shown. Figure 7 The np / CuZn catalyst was shown to be able to generate a high current density of 500 mA cm -2 Under the conditions of 220 hours, the conversion of nitrite to ammonia was achieved, the NH3 Faradaic efficiency was about 80%, and the nitrite removal rate was close to 100%. Figure 8 The yield and Faradaic efficiency of ammonia synthesis by electroreduction of nitrate over np / CuZn catalyst under 10 mmol / L nitrate concentration conditions are shown.

[0050] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a nanoporous intermetallic compound catalyst for electrochemical ammonia synthesis, characterized in that: The intermetallic compound is specifically a copper-zinc intermetallic compound, including any one of CuZn5, CuZn4, Cu5Zn8, and CuZn; the nanoporous intermetallic compound catalyst has a bicontinuous nanoporous structure; The preparation method comprises the following steps: S1, mixing pure copper and pure zinc in a certain proportion, and then performing arc melting to prepare a copper-zinc precursor alloy ingot; S2, remelting the alloy ingot by melt spinning technology, and rapidly quenching it on the surface of a high-speed rotating copper roller to obtain a copper-zinc precursor alloy strip; S3. In 1 mol / L KOH solution, the copper-zinc precursor alloy strips were electrochemically dealloyed and phase-transformed using a constant potential to obtain a nanoporous intermetallic compound catalyst.

2. The preparation method according to claim 1, characterized in that: The porosity of the catalyst is 20-80%, and the pore diameter is 2-200 mm.

3. The preparation method according to claim 2, characterized in that: The catalyst has a porosity of 40-70% and a pore diameter of 2-50 mm.

4. The preparation method according to claim 1, characterized in that: The molar ratio of copper to zinc content in S1 is 4-30: 70-96.

5. The preparation method according to claim 1, characterized in that: The molar ratio of copper to zinc content in S1 is 6-20: 80-94.

6. The preparation method according to claim 1, characterized in that: The rotation speed of the copper roller in S2 is 500~5000 r / min.

7. The preparation method according to claim 1, characterized in that: The rotation speed of the copper roller in S2 is 1000~3000 r / min.

8. The preparation method according to claim 1, characterized in that: In S3, a three-electrode system was used for electrochemical dealloying phase transition, with Hg / HgO electrode as reference electrode, platinum sheet as counter electrode, alloy strip as working electrode, and control voltage as V vs. Hg / HgO, dealloying time is 1~6 h.

9. The preparation method according to claim 1, characterized in that: During the preparation process, the nitrogen source used is nitrogen oxide, including any one of NO, nitrite and nitrate.

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