Hydroxystannate perovskite electrocatalyst Cu1-xCoxSn (OH) 6 as well as preparation method and application thereof

Abstract

The invention discloses a hydroxystannate perovskite type electrocatalyst Cu < 1-x > CoxSn (OH) 6 and a preparation method and application thereof, and the preparation method comprises the following steps: dissolving stannate in deionized water to obtain a stannate solution; soluble copper salt and cobalt salt are dissolved in deionized water, and a copper-cobalt mixed solution is obtained; and directly mixing and stirring the stannate solution and the copper-cobalt mixed solution to react to generate a precipitate, and carrying out solid-liquid separation and freeze drying to obtain the Cu1-xCoxSn (OH) 6 which is used for preparing ammonia by reducing nitrate through electro-catalysis. The hydroxystannate perovskite type electrocatalyst is in a nano cubic particle morphology, has rich reaction sites, when the electrocatalyst is used for electrocatalytic reduction of nitrate radicals, the ammonia productivity is higher than 1 mmol cm <-2 > h <-1 >, the ammonia production Faraday efficiency is kept at 90% or above, and the electrocatalyst has excellent ammonia production Faraday efficiency and ammonia yield.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrocatalytic materials, and particularly relates to a hydroxy stannate perovskite electrocatalyst Cu 1-x Co x Sn(OH)6 and its preparation method and application. Background Art

[0002] Nitrate anions (NO3 - ) widely exist in industrial and agricultural wastewater, posing a threat to human health and ecological balance.

[0003] Traditionally, the conversion and removal of NO3 - mainly proceed in two directions: (1) reduction to nitrogen gas (N2) through the denitrification process in wastewater treatment plants; (2) reduction to ammonia (NH3) through nitrate / nitrite reductases secreted by microorganisms (such as Shewanella oneidensis cytochrome c nitrite reductase). Among them, the reduction of NO3 - to NH3 is more concerned from an industrial perspective because NH3 is a very important industrial chemical, widely used in the synthesis of drugs, fertilizers, dyes, plastics, etc., and is also used as a hydrogen storage / release carrier for carbon-free hydrogen carriers. However, to date, the industrial synthesis of NH3 severely depends on the unsustainable and eco-unfriendly Haber-Bosch route, which requires harsh conditions of high temperature (400 - 600 °C) and high pressure (200 - 3~50 atm), and the source of hydrogen as a raw material severely depends on fossil energy. In fact, the total amount of carbon dioxide generated during the Haber-Bosch process accounts for about 1.2% of the global annual carbon dioxide emissions.

[0004] By utilizing denitrifying microorganisms in the natural environment to biocatalytically reduce NO3 - in wastewater to NH3 (referred to as bio-NRA) under mild environmental conditions is an emerging, sustainable and environmentally friendly technology that can convert refractory nitrate pollutants into high-value products. These high-value products can then obtain precipitates of NH3 through physicochemical methods such as ion exchange adsorption and struvite precipitation and be used for further industrial applications. However, the biocatalytic system of bio-NRA has a long reaction time and a low NH3 yield, far from that of the Haber-Bosch route and difficult to meet the actual industrial demands. In addition, bio-NRA is very sensitive to the environment of the wastewater to be treated. For example, the concentration of NO3 - in mining wastewater is high (exceeding 2500 mg L -1Moreover, the low organic matter content limits the reproduction and growth of microorganisms. Therefore, to fill the gap between the limitations of natural biocatalysis and the high demand for environmental remediation, scientists have begun to introduce the functions of microbial enzymes into easily batch-prepared synthetic chemical materials and use renewable electric energy for reduction drive to achieve low-carbon, environmentally friendly, and efficient nitrate reduction to ammonia.

[0005] In bio-NRA, nitrate reductase accepts electrons from quinone to reduce NO3 - to NO2 - , and the generated NO2 - is further converted to NH3 by nitrite reductase (NIR). Among various NIRs, the copper-type NIR (Cu-NIR) widely present in rhizobia has been extensively studied by scientists. Cu-NIR consists of a trimeric protein composed of 3 identical subunits, and there are two types of copper atoms in each enzyme monomer, serving as the electron donor center (T1Cu) and the catalytic center (T2Cu), respectively. Its mechanism of action is that *NO2 - (where * represents the adsorbed substance) binds to T2Cu in a bidentate form through two oxygen atoms, electrons are transferred from T1Cu to T2Cu, and the oxidation state of T2Cu decreases from (II) to (I), promoting *NO2 - to bind to T2Cu in a bridging nitro-binding form. At the same time, aspartic acid beside T2Cu provides a proton for one of the oxygen atoms in NO2 - , causing the N-O bond to elongate and resulting in the cleavage of the N-O bond.

[0006] Although Cu-NIR has a unique composition structure and excellent catalytic activity, its Faraday efficiency for ammonia production is about 70%, and the ammonia production rate is lower than 1 mmol cm -2 h -1 . Although in the prior art, many researchers have modified Cu-NIR and increased the Faraday efficiency of nitrate reduction to ammonia to more than 90%, however, the ammonia production rate still cannot meet the requirements of practical applications. SUMMARY OF THE INVENTION

[0007] To solve the problems existing in the prior art, the purpose of the present invention is to provide a hydroxy stannate perovskite-type electrocatalyst Cu 1-x Co x Sn(OH)6 and its preparation method and application in electrocatalytic reduction of nitrate. This hydroxy stannate perovskite-type electrocatalyst has a nano-cubic particle morphology and has abundant reaction sites. When used for electrocatalytic reduction of nitrate, the ammonia production rate is higher than 1 mmol cm -2 h -1 , and the Faraday efficiency of ammonia production remains above 90%, having excellent Faraday efficiency and ammonia production rate of ammonia.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solutions:

[0009] A preparation method of a hydroxy stannate perovskite-type electrocatalyst Cu 1-x Co x Sn(OH)6. Dissolve the stannate in deionized water to obtain a stannate solution; dissolve the soluble copper salt and cobalt salt in deionized water to obtain a copper-cobalt mixed solution; then directly mix and stir the stannate solution and the copper-cobalt mixed solution to produce a precipitate, and obtain Cu 1-x Co x Sn(OH)6 after solid-liquid separation and freeze-drying, where x = 0.15 - 0.3.

[0010] Preferably, x = 0.2.

[0011] Preferably, the stannate is sodium stannate, and the concentration of the stannate solution is 10 - 50 g / L.

[0012] Preferably, the soluble copper salt and cobalt salt are selected from one of their respective nitrates, sulfates, acetates, and chlorides, and the concentrations of the soluble copper salt and cobalt salt in the copper-cobalt mixed solution are both 10 - 50 g / L.

[0013] Preferably, the conditions for the stirring reaction are: the speed is 600 - 900 r / min, the temperature is 5 - 40 °C, and the time is not less than 3 h.

[0014] Preferably, the temperature of the freeze-drying is -30 - -70 °C, and the pressure is 8 - 50 Pa.

[0015] The present invention also provides the hydroxy stannate perovskite-type electrocatalyst Cu 1-x Co x Sn(OH)6 prepared by the above preparation method.

[0016] The present invention also provides the application of the above hydroxy stannate perovskite-type electrocatalyst Cu 1-x Co x Sn(OH)6, which is used for electrocatalytic reduction of nitrate to ammonia.

[0017] Advantages of the present invention:

[0018] The hydroxy stannate perovskite-type electrocatalyst of the present invention has a nano-cubic particle morphology and has abundant reaction sites. When used for electrocatalytic reduction of nitrate, in the wide potential range of -0.8 - -1.0 V vs. RHE, its ammonia production Faraday efficiency can be maintained above 90%, and at the same time, in the wide range of 40 - 200 mmol L -1 of the wide NO3 -Within the concentration range, the ammonia production Faraday efficiency at -0.8V vs. RHE also remains above 90%, which can adapt to a variety of wastewater environment systems, and the ammonia production rate is higher than 1 mmol cm -2 h -1 , maintaining good NO3 - recovery ability. Description of the Drawings

[0019] Figure 1 SEM image of Cu 0.8 Co 0.2 Sn(OH)6 prepared in Example 2.

[0020] Figure 2 XRD pattern of Cu 0.8 Co 0.2 Sn(OH)6 prepared in Example 2.

[0021] Figure 3 Electrochemical water splitting performance and electrochemical nitrate reduction performance diagrams of Cu 0.8 Co 0.2 Sn(OH)6 prepared in Example 2.

[0022] Figure 4 Electrocatalytic hydrogen production performance diagrams of the catalysts prepared in Examples 1-2 and Comparative Examples 1-4. Detailed Embodiments

[0023] The technical solutions of the present invention will be described below through specific examples, but the technical solutions of the present invention are not limited to specific examples.

[0024] Performance Test:

[0025] (1) Reagent Preparation:

[0026] A. Preparation of nitrate reduction electrolyte: Weigh 6.601 g of KOH solid and place it in a beaker, then add water to dissolve it. After the solution temperature drops to room temperature, transfer it to a 1000 mL flask and make up the volume to obtain 100 mmol L -1 KOH solution. Weigh 5.055 g of KNO3 and 6.601 g of KOH in a beaker, add water to dissolve them. After the solution temperature drops to room temperature, transfer it to a 1000 mL flask and make up the volume to obtain 100 mmol L -1 KNO3 and 100 mmol L -1 KOH mixed solution. Weigh 10.110 g of KNO3 and 6.601 g of KOH in a beaker, add water to dissolve them. After the solution temperature drops to room temperature, transfer it to a 1000 mL flask and make up the volume to obtain 200 mmol L - 1 KNO3 and 100 mmol L-1 A mixed solution of KOH. Similarly, by adjusting the ratio, 100 mmol / L -1 KOH and 20, 40, 60, 80, 300, 400, 500, 1000 mmol / L -1 A mixed solution of KNO3.

[0027] (2) Specific test conditions:

[0028] A. All the electrochemical tests of the present invention were carried out on a Biologic electrochemical workstation in an H-type electrolytic cell using a three-electrode system. The carbon paper electrode loaded with the catalyst was used as the working electrode, the platinum sheet was used as the counter electrode, and the mercury / mercurous chloride electrode (filled with 1 mol / L -1 KCl solution) was used as the reference electrode. With a scanning rate of 5 mV / s -1 , an electrochemical linear voltammogram was obtained in the H-type electrolytic cell (working electrode area: 1.0*1.0 cm 2 ). An aqueous solution of 0.1 mol / L KOH with different potassium nitrate concentrations (20 and 200 mmol / L-1) was used as the electrolyte, and a constant voltage electrocatalytic reduction experiment for nitrate reduction was carried out in the H-type electrolytic cell (working electrode area: 1.0*1.0 cm 2 ).

[0029] B. Each catalyst was ultrasonically dispersed in a solvent containing a binder (225 μL anhydrous ethanol: 225 μL deionized water: 50 μL 5% Nafion solution) to form a uniform ink (10 mg / mL -1 ). 40 μL of the ink was evenly loaded on a clean carbon paper. The carbon paper electrode loaded with the above catalyst, the platinum electrode, and the mercury / mercurous chloride electrode were used as the working electrode, the counter electrode, and the reference electrode respectively. In the H-type electrolytic cell, an aqueous solution of 0.1 mol / L -1 KOH containing 200 mmol / L -1 concentration of potassium nitrate was used as the electrolyte to obtain a linear voltammogram at a scanning rate of 5 mV / s -1 . Before all electrochemical tests, argon was blown through until saturation to remove the dissolved oxygen in the electrolyte.

[0030] C. The stability test of the catalyst was carried out in an H-type electrolytic cell. The carbon paper electrode loaded with the Cu 0.8 Co 0.2 Sn(OH) 6-δ catalyst was used as the working electrode, the platinum sheet was used as the counter electrode, and the mercury / mercurous chloride electrode (filled with 1 mol / L -1 KCl solution) was used as the reference electrode. In 100 mmol / L -1 KNO3 + 1 mol / L -1In an electrolyte of KOH, potentiostatic electrolytic reduction was carried out at a potential of -0.8 V vs. RHE for 10 hours. The anode and cathode chambers were separated by a Nafion 117 membrane.

[0031] Comparative Example 1

[0032] Dissolve 2.0 g of sodium stannate trihydrate in 100 ml of deionized water to obtain a stannate solution of 75 mmol L -1 Dissolve 1.9 g of copper sulfate pentahydrate in 100 ml of deionized water to obtain a copper salt solution of 75 mmol L -1 Pour the above copper sulfate solution into the above stannate solution, stir the above mixed solution at 20 °C for 3 h, wash it 5 times with deionized water, and vacuum freeze-dry it at -56 °C to obtain a solid powder CuSn(OH)6.

[0033] For the electrocatalytic nitrate reduction to ammonia performance test of the above sample under constant pressure, the ammonia production rate and Faraday efficiency are shown in Figure 4 The ammonia production rate is 0.66 mmol h -1 mg cat -1 The corresponding Faraday efficiency is 39.4%.

[0034] Comparative Example 2

[0035] Dissolve 2.0 g of sodium stannate trihydrate in 100 ml of deionized water to obtain a stannate solution of 75 mmol L -1 Dissolve 2.2 g of cobalt nitrate hexahydrate in 100 ml of deionized water to obtain a cobalt salt solution of 75 mmol L -1 Pour the above cobalt nitrate solution into the above stannate solution, stir the above mixed solution at 20 °C for 3 h, wash it 5 times with deionized water, and vacuum freeze-dry it at -56 °C to obtain a solid powder CoSn(OH)6.

[0036] For the electrocatalytic nitrate reduction to ammonia performance test of the above sample under constant pressure, the ammonia production rate and Faraday efficiency are shown in Figure 4 The ammonia production rate is 0.87 mmol h -1 mg cat -1 The corresponding Faraday efficiency is 90.6%.

[0037] Example 1

[0038] Dissolve 2.0 g of sodium stannate trihydrate in 100 ml of deionized water to obtain a stannate solution of 75 mmol L -1The stannate solution was prepared by dissolving copper sulfate pentahydrate and cobalt nitrate hexahydrate in 100 ml of deionized water. The mass was adjusted so that the sum of the amounts of the copper salt and the cobalt salt was equal to the amount of the stannate, and the molar ratio of Cu / Co was 7:3. The above mixed solution was stirred at 20 °C for 3 h, washed 5 times with deionized water respectively, and vacuum freeze-dried at -56 °C to obtain the solid powder Cu 0.7 Co 0.3 Sn(OH)6.

[0039] For the electrocatalytic nitrate reduction to ammonia performance test of the above sample under constant pressure, the ammonia production rate and Faraday efficiency are shown in Figure 4 , and the ammonia production rate is 1.36 mmol h -1 mg cat -1 , corresponding to a Faraday efficiency of 94.3%.

[0040] Example 2

[0041] Dissolve 2.0 g of sodium stannate trihydrate in 100 ml of deionized water to obtain a 75 mmol L -1 stannate solution. Dissolve copper sulfate pentahydrate and cobalt nitrate hexahydrate in 100 ml of deionized water. Adjust the mass so that the sum of the amounts of the copper salt and the cobalt salt is equal to the amount of the stannate, and the molar ratio of Cu / Co is 8:2. The above mixed solution was stirred at 20 °C for 3 h, washed 5 times with deionized water respectively, and vacuum freeze-dried at -56 °C to obtain the solid powder Cu 0.8 Co 0.2 Sn(OH)6.

[0042] For the morphological analysis of the prepared Cu 0.8 Co 0.2 Sn(OH)6 sample, the scanning electron microscope (SEM) image is shown in Figure 1 . It can be seen from Figure 1 that the above sample has a nano-cubic particle morphology with abundant reaction sites.

[0043] For the phase composition analysis of the above sample, the X-ray diffraction pattern is as shown in Figure 2 . It can be observed from Figure 2 the characteristic diffraction peaks of CuSn(OH)6 and CoSn(OH)6, and the characteristic diffraction peaks of Cu 0.8 Co 0.2 Sn(OH)6 are obtained by superimposing the characteristic diffraction peaks of CuSn(OH)6 and CoSn(OH)6, indicating the coexistence of two phases in the catalyst.

[0044] For the electrochemical water splitting performance and electrochemical nitrate reduction performance tests of the above sample, the linear voltammogram is shown in Figure 3。It is observed that Figure 3 Cu 0.8 Co 0.2 The current density of electrocatalytic nitrate reduction of Sn(OH)6 is much higher than that of electrochemical water splitting, indicating its excellent electrocatalytic nitrate reduction performance.

[0045] For the electrocatalytic nitrate reduction to ammonia performance test of the above samples under constant pressure, the ammonia production rate and Faraday efficiency are shown in Figure 4 , and the ammonia production rate is 1.60 mmol h -1 mg cat -1 , corresponding to a Faraday efficiency of 91.4%.

[0046] Comparative Example 3

[0047] Dissolve 2.0 g of sodium stannate trihydrate in 100 ml of deionized water to obtain a stannate solution of 75 mmol L -1 . Dissolve copper sulfate pentahydrate and cobalt nitrate hexahydrate in 100 ml of deionized water, and adjust their masses so that the sum of the amounts of substance of copper salt and cobalt salt is equal to the amount of substance of stannate, and the molar ratio of Cu / Co is 9:1. Stir the above mixed solution at 20 °C for 3 h, wash it 5 times with deionized water respectively, and vacuum freeze-dry it at -56 °C to obtain the solid powder Cu 0.9 Co 0.1 Sn(OH)6.

[0048] For the electrocatalytic nitrate reduction to ammonia performance test of the above samples under constant pressure, the ammonia production rate and Faraday efficiency are shown in Figure 4 , and the ammonia production rate is 1.35 mmol h -1 mg cat -1 , corresponding to a Faraday efficiency of 77.0%.

[0049] Comparative Example 4

[0050] Mechanically mix the CuSn(OH)6 prepared in the above Comparative Example 1 and CoSn(OH)6 prepared in Comparative Example 2 in a molar ratio of 8:2, and mix them thoroughly in a mortar to obtain the solid powder mech-Cu 0.8 Co 0.2 Sn(OH)6.

[0051] For the electrocatalytic nitrate reduction to ammonia performance test of the above samples under constant pressure, the ammonia production rate and Faraday efficiency are shown in Figure 4 , and the ammonia production rate is 0.90 mmol h -1 mg cat -1 , corresponding to a Faraday efficiency of 50.7%.

Claims

1. A preparation method of a hydroxy stannate perovskite type electrocatalyst Cu 1-x Co x Sn(OH)6, characterized in that: Dissolve stannate in deionized water to obtain a stannate solution; dissolve soluble copper salt and cobalt salt in deionized water to obtain a copper-cobalt mixed solution; then directly mix and stir the stannate solution and the copper-cobalt mixed solution to produce a precipitate, and after solid-liquid separation and freeze-drying, Cu 1-x Co x Sn(OH)6 is obtained, where x = 0.15 - 0.

3.

2. The preparation method according to claim 1, characterized in that: x＝0.2。 3. The preparation method according to claim 1 or 2, characterized in that: The stannate is sodium stannate, and the concentration of the stannate solution is 10-50 g / L.

4. The preparation method according to claim 1 or 2, characterized in that: The soluble copper salt and cobalt salt are selected from one of their respective nitrates, sulfates, acetates, and chlorides, and the concentrations of the soluble copper salt and cobalt salt in the copper-cobalt mixed solution are both 10-50 g / L.

5. The preparation method according to claim 1 or 2, characterized in that: The conditions for the stirring reaction are: the speed is 600-900 r / min, the temperature is 5-40 °C, and the time is not less than 3 h.

6. The preparation method according to claim 1 or 2, characterized in that: The temperature of the freeze-drying is -30 to -70 °C, and the pressure is 8-50 Pa.

7. Hydroxy stannate perovskite electrocatalyst Cu prepared by the preparation method according to any one of claims 1-6 1-x Co x Sn(OH)6.

8. Use of the hydroxy stannate perovskite electrocatalyst Cu 1-x Co x Sn(OH)6, characterized in that: It is used for electrocatalytic reduction of nitrate to ammonia.

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