A nanosheet electrocatalyst, preparation method and application thereof

Abstract

The present invention discloses a nano-sheet electrocatalyst, a preparation method and an application thereof in electrocatalytic nitrite reduction to synthesize ammonia. The preparation method of the electrocatalyst comprises the following steps: (1) cutting a foam metal to a fixed size and then placing it in a porcelain boat; (2) placing the porcelain boat containing the foam metal in a muffle furnace, setting a heating rate, a heating temperature and a heat preservation time program, and taking it out after the temperature is cooled to room temperature with the furnace to obtain a catalyst precursor CoO x ; (3) placing the obtained catalyst precursor in a standard three-electrode system containing potassium hydroxide solution, and reducing it by constant potential method for a certain period of time to obtain a nanosheet OD-Co electrocatalyst. The present invention can develop a revolutionary technology that can simultaneously treat pollutants and produce high value-added products, and take into account energy saving, environmental protection and stability, and provides a new strategy, which can not only promote energy utilization and improve the overall reaction rate, but also turn waste into treasure and harvest value-added products.

Description

Technical Field

[0001] The invention belongs to the technical field of electrocatalytic ammonia synthesis, and specifically relates to a method for preparing a nano-sheet OD-Co electrocatalyst and application thereof in electrocatalytic nitrite reduction to synthesize ammonia. Background Art

[0002] Ammonia is an important chemical raw material in modern society. In addition, as a hydrogen energy carrier, ammonia has a greater volumetric hydrogen carrying capacity than liquid hydrogen, and there is no carbon element in ammonia molecules. Therefore, it is urgent to develop revolutionary synthetic ammonia technology to achieve an efficient and green ammonia production process under mild conditions.

[0003] At the same time, due to the sharp increase in human activities (such as the treatment of three wastes in modern industrial production processes), nitrates / nitrites have accumulated in large quantities, becoming the main nitrogen-containing pollutants in rivers, lakes and groundwater, which provides opportunities for nitrate / nitrite reduction to synthesize ammonia. However, traditional thermal catalytic methods mainly rely on hydrogen generated by steam reforming under high temperature conditions. This process not only significantly increases energy and capital consumption, but also its environmental impact cannot be ignored. However, the use of renewable energy-driven electrocatalytic conversion technology to achieve the conversion of nitrates / nitrites to ammonia does not require the introduction of additional hydrogen. More importantly, the bond energy of nitrates / nitrites is as high as 941 kJmol -1 The bond energy of nitrogen is only 204 kJ mol -1 / 298 kJ mol -1 , making it easier to undergo reduction reactions, making it a more attractive raw material for synthesizing ammonia. Therefore, from the dual perspectives of energy conservation and environmental protection, synthesizing ammonia by reducing nitrate / nitrite-containing pollutants through electrocatalytic technology is undoubtedly a very promising alternative. At the same time, this production model provides a practical solution for the manufacture of nitrogen fertilizers and nitrogen-containing chemicals, further promoting the closed-loop realization of the nitrogen cycle and promoting the sustainable use of resources. Summary of the invention

[0004] In order to solve the problems that the competitive hydrogen evolution reaction in the existing electrocatalytic nitrite to ammonia reaction leads to the kinetic sluggishness of nitrite reduction, the high reaction energy barrier limits its catalytic reaction activity and the formation of by-products and has a certain influence on its Faraday efficiency and selectivity, the present invention provides a nano-sheet OD-Co electrocatalyst, a preparation method and its application in electrocatalytic nitrite reduction, aiming to improve the performance of cathode electrocatalytic nitrite to ammonia synthesis.

[0005] The scheme adopted by the present invention is as follows:

[0006] A method for preparing a nano-sheet OD-Co electrocatalyst comprises the following steps:

[0007] (1) Cut the foam metal into a fixed size and place it in a porcelain boat.

[0008] (2) Place the porcelain boat containing the foam metal into the muffle furnace, set the heating rate, heating temperature and holding time program, and take it out after the temperature cools down to room temperature with the furnace to obtain the catalyst precursor CoO x .

[0009] (3) The obtained catalyst precursor was placed in a standard three-electrode system containing potassium hydroxide solution, and a black nanosheet OD-Co electrocatalyst was obtained after a certain period of reduction by constant potential method.

[0010] Furthermore, the foam metal in step (1) is foamed cobalt.

[0011] Furthermore, the specifications of the foam metal in step (1) are 0.5 cm×0.75 cm×0.5 mm.

[0012] Furthermore, the heating rate in step (2) is 3-8 °C min -1 .

[0013] Furthermore, the heating temperature in step (2) is 500-700°C.

[0014] Furthermore, the insulation time in step (2) is 2-3 h.

[0015] Furthermore, the volume of the potassium hydroxide solution in step (3) is 40 mL and the concentration is 1 mol L -1 , pH value is 14.

[0016] Furthermore, in the standard three-electrode system described in step (3), the cathode electrode is a catalyst precursor, the anode is Pt, and the reference electrode is Hg / HgO.

[0017] Furthermore, the constant potential in step (3) is -1.0-0.7 V RHE .

[0018] Furthermore, the constant potential reduction time in step (3) is 0.5-12 h.

[0019] The present invention also provides an application of a nanosheet electrocatalyst in electrocatalytic nitrite reduction to synthesize ammonia, comprising the following steps:

[0020] a. The electrocatalytic system was constructed using a three-electrode system, with Pt as the anode, OD-Co as the cathode, and Hg / HgO as the reference electrode.

[0021] b. The anolyte solution is potassium hydroxide solution, and the cathode electrolyte solution is alkaline nitrite solution.

[0022] c. The three-electrode system is connected to an external voltage for electrocatalytic nitrite reduction.

[0023] Furthermore, the pH value of the alkaline nitrite solution in step (b) is 14, and the nitrite concentration is 0-0.2 mol L -1 , volume is 40 mL.

[0024] Furthermore, in step (c), the external voltage of the three-electrode system is -1.0-+ 0.8 V RHE .

[0025] Compared with the prior art, the present invention has the following technical advantages:

[0026] The cathode nitrite reduction electrochemical cycle reaction designed by the present invention is a technological breakthrough that combines innovation and practicality. It deepens our understanding and application of catalyst changes in electrochemical reactions. The core of this cycle mechanism lies in the cathode reaction path of the designed electrocatalytic material. This cycle cleverly utilizes the continuous change of cobalt (Co) elements between different valence states, realizing the conversion of Co (Co) from a low oxidation state to a high oxidation state. δ+ , where 0<δ<1) to high oxidation state Co (Co Ⅱ / Ⅲ , that is, the cyclic and continuous transformation of the mixed state of active high-valent cobalt ions.

[0027] Specifically, by carefully controlling the structure and properties of the electrode materials, the electrocatalyst of the present invention can RHE ) can drive nitrite (NO 2 - ) The reduction reaction produces 10 mA cm -2 The reduction current density is 2.33°, which is a significant advantage in energy efficiency compared to most traditional catalysts. At the same time, the low overpotential reaction means a significant reduction in energy input during the reduction process, which is of great significance for promoting green and sustainable chemical reaction processes.

[0028] In addition, the constructed Co δ+ With Co Ⅱ / Ⅲ The rapid and reversible cycle conversion between the catalyst and the reaction ensures the continuity and efficiency of the reaction. This design not only enhances the stability of the catalyst and prolongs its reaction life, but also greatly improves the overall reaction rate, laying a solid foundation for industrial application.

[0029] In terms of environmental protection, the present invention provides a new way to efficiently treat nitrite pollution in water bodies. As a common environmental pollutant, the effective removal of nitrite is crucial to protecting water resources and maintaining ecological balance. The electrochemical cycle reaction of the present invention converts harmful nitrite into high-value-added chemicals (ammonia) while realizing the resource utilization of pollutants, truly achieving "turning waste into treasure".

[0030] Furthermore, from the perspective of energy and economy, the application of the present invention not only promotes the effective use of renewable energy (such as solar energy, wind energy, etc.) in the field of electrochemical synthesis, but also reduces the dependence on traditional energy, reduces production costs, and improves economic benefits. At the same time, ammonia is an important basic substance for synthetic fertilizers, chemical raw materials, etc., and its efficient and environmentally friendly production method is of great significance for promoting the sustainable development of agriculture, chemical industry and other industries.

[0031] In summary, the cathode nitrite reduction electrochemical cycle reaction designed in the present invention has not only achieved significant progress in technology, injected new vitality into the field of electrocatalysis, but also demonstrated great potential and value in multiple dimensions such as environmental protection, energy utilization and economic benefits, providing a practical solution to the current environmental and energy problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0033] Figure 1 The foamed cobalt prepared in Example 1 of the present invention ( Figure 1 (a)), CoO x ( Figure 1 (b) in), OD-Co( Figure 1 (c) in), OD-Co -reduction ( Figure 1 Scanning electron micrograph of (d).

[0034] Figure 2 The foamed cobalt, CoO prepared in Example 1 of the present invention x 、OD-Co、OD-Co -reduction X-ray diffraction pattern of .

[0035] Figure 3 It is the technical roadmap of cathode nitrite reduction driven by OD-Co catalyst of the present invention.

[0036] Figure 4 The Pt-driven anode oxygen production reaction and the prepared cobalt foam, OD-Co, OD-Co -reductionLinear sweep voltammogram of the driven cathode nitrite.

[0037] Figure 5 The Pt-driven anode oxygen production reaction and the prepared foamed cobalt and CoO x 、OD-Co、OD-Co -reduction Catalyst driven cathode nitrite to ammonia synthesis performance and ammonia synthesis Faraday efficiency diagram.

[0038] Figure 6 The Pt-driven anode oxygen production reaction and the prepared foamed cobalt and CoO x 、OD-Co、OD-Co -reduction Current diagram of catalyst-driven cathode nitrite synthesis of ammonia.

[0039] Figure 7 This is a Faraday efficiency-time diagram of a long-term test of nitrite reduction to ammonia synthesis driven by the OD-Co prepared in the present invention. DETAILED DESCRIPTION

[0040] The present invention is described in detail below in conjunction with specific embodiments. x 、OD-Co、OD-Co -reduction Comparison of catalyst-driven electrocatalytic cathode nitrite reduction to ammonia reaction. Figure 3 is a schematic diagram of the basic electrocatalytic system. Figure 3 changes based on the .

[0041] Example 1.

[0042] A method for preparing a nano-sheet OD-Co electrocatalyst comprises the following steps:

[0043] Cut the cobalt foam into 0.5 cm × 0.75 cm × 0.5 mm, place it in a porcelain boat, and then place the porcelain boat in the center of the muffle furnace heating area. Set the heating rate to 5 °C min -1 ; Set the heating temperature to 600℃; set the holding time to 3 h, and take it out after the temperature cools down to room temperature to obtain the catalyst precursor CoO x The obtained catalyst precursor was placed in a standard three-electrode system containing potassium hydroxide solution and the RHE Black nanosheet-like OD-Co electrocatalyst was obtained after reduction for 3 h.

[0044] Scanning electron microscopy analysis of the OD-Co electrocatalyst prepared in Example 1 revealed that the OD-Co exhibited a nanosheet-like structure ( Figure 1 ).

[0045] Figure 2 The X-ray diffraction (XRD) results show that the foamed cobalt and CoO prepared in Example 1 x 、OD-Co、OD-Co -reduction The electrocatalysts can be indexed as standard PDF (89-4308; 71-0816, 71-4749; 80-1537, 89-4308, 80-1537; 71-4651).

[0046] The OD-Co was used as an electrocatalyst to construct a traditional three-electrode system. The cathode was the OD-Co, the cathode electrode was Pt, and the reference electrode was Hg / HgO, which was placed at the cathode. The anolyte composition was 40 mL of 1 mol L -1 The pH of the solution was 14 and the cathode electrolyte was 40 mL of 1 mol L -1 KOH solution containing 0.2 mol L -1 of nitrite and carried out electrochemical catalytic test.

[0047] Linear sweep voltammetry curve ( Figure 4 ) showed that the OD-Co catalyst exhibited excellent performance in driving the reduction of nitrite to synthesize ammonia at -0.03 V RHE 300 mA cm-2 was achieved at an extremely low potential -2 Compared with most of the current catalytic materials, this catalyst can greatly reduce the energy input for ammonia synthesis and improve energy utilization. RHE In the case of 25 h of testing, the system maintained an average of 1.97 A cm -2 The ammonia synthesis current density, the high ammonia synthesis Faraday efficiency of 97.8% and the -2 h -1 The high ammonia synthesis rate of the catalyst proves the long-term stability of the cathode nitrous acid reduction to synthesize ammonia. Figure 7 shown.

[0048] Example 2.

[0049] The OD-Co and Pt prepared in Example 1 were used as electrocatalysts to construct a traditional three-electrode system. The anode was Pt (counter electrode), the cathode was OD-Co (working electrode), and the reference electrode was Hg / HgO, which was placed at the cathode. The anolyte composition was 40 mL of 1 mol L -1 The cathode electrolyte was 40 mL of 1 mol L -1 KOH solution containing 0.2 mol L -1of nitrite and carried out electrochemical catalytic test.

[0050] Figure 4 The linear voltammetric curves show that the OD-Co catalyst exhibits the best electrocatalytic nitrite reduction performance. RHE When the electrocatalytic nitrite reduction rate to ammonia is 13.29 mmol cm -2 h -1 The Faradaic efficiency of synthetic ammonia is 100%, and the partial current density of synthetic ammonia is 2.21 A cm -2 ( Figure 5 and Figure 6 ).

[0051] Example 3.

[0052] The cobalt foam and Pt prepared in Example 1 were used as electrocatalysts to construct a traditional three-electrode system. The anode was Pt (counter electrode), the cathode was cobalt foam (working electrode), and the reference electrode was Hg / HgO, which was placed at the cathode. The anode electrolyte consisted of 40 mL of 1 mol L -1 The cathode electrolyte was 40 mL of 1 mol L -1 KOH solution containing 0.2 mol L -1 of nitrite and carried out electrochemical catalytic test.

[0053] Figure 4 The linear voltammetric curve shows that the foamed cobalt catalyst exhibits poor electrocatalytic nitrite reduction performance. RHE When the electrocatalytic nitrite reduction rate to ammonia is 9.67 mmol cm -2 h -1 The Faradaic efficiency of synthetic ammonia is 91.73%, and the partial current density of synthetic ammonia is 1.43 A cm -2 ( Figure 5 and Figure 6 ).

[0054] Example 4.

[0055] The OD-Co prepared in Example 1 -reduction The anode is Pt (counter electrode), the cathode electrode is OD-Co-hydrogen argon reduction (working electrode), and the reference electrode is Hg / HgO, which is placed at the cathode; the anode electrolyte is composed of 40 mL of 1 mol L -1 The cathode electrolyte was 40 mL of 1 mol L -1KOH solution containing 0.2 mol L -1 of nitrite and carried out electrochemical catalytic test.

[0056] Figure 4 The linear voltammetric curve shows that OD-Co -reduction The catalyst exhibited the worst electrocatalytic nitrite reduction performance. When the voltage was -0.7 V RHE When the electrocatalytic nitrite reduction rate to ammonia is 8.82 mmol cm -2 h -1 , the Faradaic efficiency is 89.85%, and the partial current density of synthetic ammonia is 1.27 A cm -2 ( Figure 5 and Figure 6 ).

[0057] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modification, equivalent substitution and improvement made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a nanosheet electrocatalyst, characterized in that: The following steps are involved: (1) Cut the foam metal into a fixed size and then place it in a porcelain boat; (2) Place the porcelain boat containing the foam metal into the muffle furnace, set the heating rate, heating temperature and holding time program, and take it out after the temperature cools down to room temperature with the furnace to obtain the catalyst precursor CoO x ; (3) The obtained catalyst precursor is placed in a standard three-electrode system containing a potassium hydroxide solution, and a black nanosheet OD-Co electrocatalyst is obtained after a certain period of reduction by a constant potential method; The foam metal in step (1) is foam cobalt, and the foam metal is cut to a fixed size of 0.5×0.75 cm 2 ; The heating rate in step (2) is 3-8 ℃ min -1 , heating temperature is 500-700 ℃, holding time is 2-5 h; The volume of the potassium hydroxide solution in step (3) is 40 mL and the concentration is 1 mol L -1 , pH value is 14; The cathode electrode of the standard three-electrode system in step (3) is a catalyst precursor, the anode is Pt, and the reference electrode is Hg / HgO; The constant potential relative to the reversible hydrogen electrode in step (3) is -1.0-0.7 V, and the constant potential reduction time is 0.5-12 h.

2. A nanosheet electrocatalyst prepared according to the method of claim 1.

3. Use of the nanosheet electrocatalyst according to claim 2 in electrocatalytic nitrite reduction to synthesize ammonia, characterized in that: The following steps are involved: a. The electrocatalytic system was constructed using a three-electrode system, with Pt as the anode, OD-Co as the cathode, and Hg / HgO as the reference electrode; b. The anolyte is composed of potassium hydroxide solution, and the catholyte is composed of alkaline nitrite solution; c. The three-electrode system is connected to an external voltage for electrocatalytic nitrite reduction.

4. The use of the nanosheet electrocatalyst according to claim 3 in electrocatalytic nitrite reduction, characterized in that: The pH value of the alkaline nitrite solution in step (b) is 14, and the nitrite concentration is 0-0.2 mol L -1 , volume is 40 mL.

5. The use of the nanosheet electrocatalyst according to claim 3 in electrocatalytic nitrite reduction, characterized in that: In step (c), the external voltage of the three-electrode system is –1.0-+ 0.8 V. RHE .

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