CN111360279A - A kind of preparation method and application of single-atom copper material - Google Patents

Abstract

The application relates to a method for synthesizing ammonia electrocatalyst by embedding monatomic copper into molecular lattice structure of 3,4,9, 10-pyrenetetracarboxylic dianhydride (PTCDA) as nitrate or nitrite through reduction. The monatomic catalyst can be obtained by a simple electrode in-situ self-reduction deposition method, and has the advantages of simple process, mass preparation, low cost and the like. The insertion of monoatomic copper into PTCDA can couple with carbonyl oxygen in PTCDA molecules, can also cause slow hydrogen evolution reaction kinetics, and copper can also provide proper NO₃ ^‑Reducing the synthetic ammonia site, thereby effectively improving the selectivity of the electrocatalytic synthesis of ammonia.

Description

A kind of preparation method and application of single-atom copper material

technical field

The invention relates to the field of single-atom copper materials, in particular to single-atom catalysts, and more particularly to the preparation and application of an electrocatalyst of single-atom copper materials used in the field of selective ammonia synthesis.

Background technique

The synthesis of ammonia from nitrogen and hydrogen molecules (the Haber-Bosch process) is one of the greatest inventions of the 20th century. Today, this 100-year-old production method is the main source of most of the world's synthetic ammonia, accounting for 90% of annual production. Ammonia and its derivatives (including urea) are important components of fertilizers. It is estimated that without the use of artificial fertilizers in the Haber-Bosch process, global food production could support only a fraction of the world's population today. However, since fossil fuels (mainly natural gas) are the main source of _H2 precursors, continued use of this method in the future will increasingly cause serious environmental problems. Furthermore, the slow kinetics of the reaction between _N and H further _exacerbates the problem. To ensure continued efficient operation of the process, the reaction temperature (500°C) and pressure (>200 atm) must be increased. As a result, this energy-demanding process consumes approximately 2% of the world's total energy supply annually and releases 400 million tons of carbon dioxide annually in order to maintain ammonia production at the levels needed to meet current demand. Therefore, it is of great industrial value to develop a catalytic method that can perform clean, safe and sustainable _NH3 production at atmospheric pressure and room temperature.

In recent years, electrochemical methods have offered hope for the direct conversion of renewable electricity into chemicals and chemical energy carriers. However, electrochemical _N2 reduction to ammonia synthesis has proven to be extremely challenging to achieve in practice, mainly because _N2 is a highly stable (bond energy of 941 kJ mol ⁻¹ ) and non-polarizable molecule. The currently reported NRR yields for ammonia synthesis are two or three orders of magnitude lower than the Haber-Bosch process. The use of alternative nitrogen sources other than _N2 is a possible solution to improve ammonia yield and selectivity. Nitrate anion (NO ³⁻ ) is a potential nitrogen source because the N=O bond has a relatively low dissociation energy (204 kJmol ⁻¹ ) and is abundantly present in agricultural waste resulting from the decomposition of fertilizer bacteria. Therefore, if NO ^3- can selectively reduce NH ₃ under ambient conditions, the green production of NH ₃ can be realized through the process of eliminating water pollution and recycling of waste resources. Most of the electrocatalytic systems reported so far mainly reduce NO ^3- to N ₂ through a five-electron process, and produce almost no NH ₃ . This is because the electrochemical potential for _N2 formation (1.25 V vs. NHE, pH=0) is more positive than that for _NH3 formation (1.20 V). Therefore, the reduction of ^NO3- to _N2 is thermodynamically more favorable than the reduction to _NH3 . In addition, due to the limitation of kinetics, the potential of NO3 ^- reduced synthetic ammonia also mostly occurs in the hydrogen evolution reaction potential region. During the reaction process, the catalyst surface also has the problem of hydrogen evolution competition, which produces a larger amount of H ₂ . This means that these systems also consume excess electron donors for the production of _NH3 , resulting in lower Faradaic efficiencies. Therefore, it is also necessary to design electrocatalysts that selectively generate _NH3 without _H2 .

At present, although heterogeneous catalysts with different sizes and morphologies have been widely reported, these catalyst materials cannot precisely control the active sites, resulting in their inability to effectively improve their selectivity for ammonia synthesis. Single-atom catalysts have attracted extensive attention due to their highly dispersed and precisely tunable active sites. Its preparation methods mainly include mass-selected soft-landing techniques and wet chemical methods (Lei, Y., Mehmood, F., Lee, S., et al.Increased silver activity for direct propyleneepoxidation via subnanometer size effects .Science 2010,328:224-228.Hackett,SF,Brydson,RM,Gass,MH,et al.High-activity,single-site mesoporous Pd/Al ₂ O ₃ catalysts for selective aerobic oxidation of allylicalcohols.Angew.Chem ., Int. Ed. 2007, 46, 8593-8596.). However, these two methods have disadvantages such as complex preparation process, low yield and high consumption, which limit their practical application and promotion.

However, so far, there is no prior art for an efficient single-atom copper material electrocatalyst with good ammonia synthesis selectivity, which is simple in process, can be prepared in large quantities and can be prepared at low cost; the present application aims to solve the above problems.

SUMMARY OF THE INVENTION

The invention aims to overcome the deficiencies of the prior art, and provides a preparation method of a single-atom copper material, a single-atom copper material, and an application of the single-atom copper material.

In order to achieve the above purpose, the present application proposes to embed single-atom copper into the molecular lattice structure of 3,4,9,10-pyrenetetracarboxylic dianhydride (3,4,9,10-perylenetetracarboxylic dianhydride, PTCDA, hereinafter referred to as As PTCDA), a single-atom-containing copper material was further obtained, which was further used as an electrocatalyst for NO3 ^- reduction synthesis of ammonia.

Specifically, in order to achieve the above object, the present invention adopts the following preparation method to obtain a single-atom copper material.

The preparation method comprises the following steps:

Step 1, reducing PTCDA and incorporating hydronium ions into PTCDA;

In step 2, the reduced PTCDA obtained in step 1 is placed in a low-concentration Cu ²⁺ ion solution, preferably, the Cu ²⁺ ion concentration is 0.0001-0.01M, preferably the Cu ²⁺ ion concentration is 0.001-0.01M ;

In the third step, the electrode in-situ self-reduction precipitation reaction occurs on the surface of the PTCDA electrode, Cu ²⁺ replaces the hydronium ion, and a reduction process occurs to obtain a single-atom copper-coupled PTCDA catalyst.

Preferably, in step 1, a three-electrode electrolytic cell is used for activation during the reduction process, and one or more cathode scans are optionally used for the PTCDA electrode, and the three-electrode electrolytic cell is carried out in 1.0 Mol/L HCL.

Preferably, in step 2, the Cu ²⁺ ions are preferably soluble copper salts, preferably copper chloride, copper nitrate, copper sulfate, etc., and the copper ion concentration is preferably 0.001mol/L-0.5mol/ L, the time of the electrode in-situ self-reduction deposition is preferably 50-5000s, preferably 100-2000s, more preferably 500-1000s,

The present application also proposes a single-atom copper material, the single-atom copper material is embedded into the molecular lattice structure of 3,4,9,10-pyrenetetracarboxylic dianhydride by single-atom copper; the single-atom copper material is embedded in the following manner: Step 1 , reducing PTCDA and incorporating hydronium ions into PTCDA;

In step 2, the reduced PTCDA obtained in step 1 is placed in a low-concentration Cu ²⁺ ion solution, preferably, the Cu ²⁺ ion concentration is 0.0001-0.01M, preferably the Cu ²⁺ ion concentration is 0.001-0.01M ;

In the third step, the electrode in-situ self-reduction precipitation reaction occurs on the surface of the PTCDA electrode, Cu ²⁺ replaces the hydronium ion, and a reduction process occurs to obtain a single-atom copper-coupled PTCDA catalyst.

Preferably, the Cu ²⁺ doping time is 0-3600s, the doping amount is 0.096-1.0 mg, preferably 0.096, 0.197, 0.309 mg, and the coating amount of PTCDA on the electrode is 13 mg cm ^-2 ;

The present application also proposes an application of a single-atom copper material, a single-atom copper material, where the single-atom copper is embedded in the molecular lattice structure of 3,4,9,10-pyrenetetracarboxylic dianhydride, and the formed single-atom copper The material is used for ammonia synthesis reaction, preferably ammonia synthesis reaction is ammonia synthesis reaction using nitrate anion as nitrogen source.

Preferably, the single-atom copper is embedded in the molecular lattice structure of 3,4,9,10-pyrene tetracarboxylic dianhydride, which is achieved by the following method: step 1, reducing PTCDA and incorporating hydrated hydrogen into PTCDA ion;

In step 2, the reduced PTCDA obtained in step 1 is placed in a low-concentration Cu ²⁺ ion solution, preferably, the Cu ²⁺ ion concentration is 0.0001-0.01M, preferably the Cu ²⁺ ion concentration is 0.001-0.01M ;

In the third step, the electrode in-situ self-reduction precipitation reaction occurs on the surface of the PTCDA electrode, Cu ²⁺ replaces the hydronium ion, and a reduction process occurs to obtain a single-atom copper-coupled PTCDA catalyst.

Preferably, in the ammonia synthesis reaction, the nitrogen source is nitrate or nitrite, the cathode potential is -0.1- to -1.0V, preferably, the cathode potential is -0.2 to -0.8V, preferably, the cathode potential is -0.3 to -1.0V -0.6, more preferably around -0.4V, the _NH3 yield is 305.7±29.8 μg h ^-1 cm ^-2 , the faradaic yield of _NH3 is 80.0±5.9%, and the overall Faradaic efficiency is 96.0±1.6%.

Beneficial effects of the present invention:

1) The present invention utilizes a simple electrode in-situ self-reduction deposition method to obtain a single-atom copper catalyst (PTCDA/Cu), which overcomes the defects of traditional single-atom catalytic preparation requiring complex preparation technology, low yield, and high cost;

2) And through the unique structure, it has the property of inhibiting the hydrogen evolution reaction, so as to obtain better electrochemical NO3-reduction synthesis ammonia performance;

3) The reaction conditions for ammonia synthesis are mild, and the ammonia yield/Faraday efficiency and total Faradaic efficiency are relatively high.

Description of drawings

Fig. 1 is the CV diagram of the present invention a) PTCDA in 1.0M HCl system;

b) Open circuit potential versus time curve of reduced PTCDA in 0.001M CuSO4 solution _;

Figure 2 is the XRD patterns of PTCDA, reduced PTCDA, PTCDA/Low Cu, PTCDA/Cu and PTCDA/High Cu;

Figure 3 is a) element distribution diagram of PTCDA/Cu, b) XPS spectrum of Cu LMM Auger peak, c) X-ray absorption near-edge structure spectrum, d) extended X-ray absorption fine structure spectrum;

Figure 4 is the LSV curve obtained by testing PTCDA/Cu in 0.1M PBS, 0.1M PBS containing NO ₂ ^- and 0.1M PBS containing NO ₃ ^- ;

Figure 5 is 5a) _NH3 yield and Faradaic efficiency at different potentials; b) total Faradaic efficiency ^of _{both NH3} and NO2- at different potentials;

Figure 6 is a graph comparing the total Faradaic efficiencies of PTCDA/High Cu, PTCDA/Low Cu, Cu foam (equivalent PTCDA loaded on copper foam) and Electrodeposition of Cu (equivalent copper deposited from the same potential range from LSV sweep).

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application will be described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, but not to limit the present application.

1) Preparation of single-atom copper materials.

The inventors studied: First, PTCDA was reduced and incorporated into hydronium ions (H ₃ O ⁺ ). We recorded cyclic voltammetry (CV) curves of PTCDA electrodes in 1.0 M HCl in a three-electrode electrolysis cell. In the first cycle, the cathodic scan showed a reduction peak around −0.62 V (Fig. 1a), corresponding to the reduction reaction of PTCDA and the incorporation of _H3O ⁺ . During the subsequent anodic scan, an oxidation peak at +0.26V was observed. Therefore, the electrode exhibits reversible behavior, but there is a polarization of about 0.88V. This is mainly attributed to the poor electrical conductivity of organic small-molecule materials. After the initial activation, the cathodic scanning of PTCDA was continued to make it finally in the reduced state. It was then placed in a low concentration Cu ²⁺ ion solution (0.001 MCuSO ₄ ). In this system, Cu ²⁺ replaced the hydronium ions on the surface of the PTCDA electrode, and a reduction process occurred.

It can be seen from the XRD pattern in Fig. 2 that after the cathode scanning, the XRD crystal plane of PTCDA is obviously shifted to the right. This is mainly attributed to the reduction of the lattice spacing of PTCDA caused by the insertion of hydronium ions.

Figure 3a is the element distribution diagram of PTCDA/Cu, from which it can be observed that Cu elements are uniformly distributed in PTCDA, confirming that Cu is dispersed and doped in PTCDA molecules.

The XPS spectra, X-ray absorption near-edge structure spectra and extended X-ray absorption fine structure spectra of Cu LMM Auger peaks in Fig. 3b–d confirm the existence of Cu-O-C bonds, indicating that single atoms can be successfully synthesized by the electrode in-situ self-reductive deposition method. Copper-coupled PTCDA catalyst. In this work, three PTCDA/Cu electrodes with different amounts of copper doping (PTCDA/Low Cu: 600 s, PTCDA/Cu: 1200 s, PTCDA/High Cu: 3600 s, PTCDA/High Cu: 3600 s, respectively, are obtained according to the different changes of open circuit potential, Fig. 1b ), and the doping amounts of Cu were 0.096, 0.197, and 0.309 mg, respectively.

2) Ammonia synthesis reaction

The inventors also studied:

First, linear sweep voltammetry (LSV) tests were carried out in electrolytes containing nitrate/nitrite and without nitrate/nitrite to determine the reduction onset potentials of the relevant reactions in this system. Figure 4 shows LSV plots of PTCDA/Cu ⁱⁿ 0.1 M PBS (phosphate buffered saline ₎ , 0.1 M PBS with 500 ppm NO2- ^and 0.1 M PBS with 500 ppm _NO3- . In the blank LSV plot, we observed two characteristic reduction current peaks of pure PTCDA. When more negative potential was applied, no obvious hydrogen evolution current was seen on the surface of PTCDA/Cu, indicating that PTCDA/Cu has poor activity for HER in a wide negative potential range, and this property will be beneficial to improve the subsequent electrolysis. Selectivity of the catalytic ammonia synthesis reaction.

The inventors also investigated the effect of different applied potentials (between -0.1 and -0.6 V vs. RHE) on the electrocatalytic reduction products (ammonium and nitrite) of PTCDA/Cu (0.1 M PBS (pH=7)). Here, nitrite is an intermediate product and ammonium is the final product of electrocatalytic reduction of nitrate.

It can be seen from Fig. 5a that with the increase of cathode potential, the NH ₃ yield gradually increased and reached the maximum value (405.0±31.9 μg h ⁻¹ cm ⁻² ) at −0.5 V vs. RHE. For the Faradaic yield of _NH3 generation, the maximum value of 80-81% can be reached when the applied potential is -0.4V to -0.5V vs. RHE. In addition, according to Figure 5b, PTCDA/Cu can maintain more than 86% total faradaric efficiency in a wide potential range (-0.1V ~ -0.5V vs. RHE), and at -0.3V vs. RHE reached a maximum value of 96.8±2.3%. Combined with the results of ammonia yield, -0.4V vs. RHE is the best reaction potential for this system, the NH ₃ yield is 305.7±29.8μg h ^-1 cm ^-2 , and the Faradaic yield of NH ₃ is 80.0 ±5.9% with an overall Faradaic efficiency of 96.0±1.6%. In addition, both the ammonia yield/Faraday efficiency and the total Faradaic efficiency showed a decreasing trend at −0.6 V vs. RHE, which was mainly attributed to the gradual dominance of the competing hydrogen evolution reaction at high potentials.

3) Effect of Cu doping amount on performance In order to confirm the advantages of PTCDA/Cu with an appropriate amount of Cu doping in improving the efficiency of nitrate reduction for ammonia synthesis, the inventors also studied:

First, a piece of commercial carbon (C cloth) cloth ( ₃ cm × 2 cm) was pretreated with concentrated HNO for 24 h to form carbonyl groups on the surface. Soak the treated carbon cloth in dilute hydrochloric acid solution for 2 to 3 days. After that, it was rinsed several times with deionized water and dried in an oven at 60 °C overnight. The PTCDA powder was mixed with carbon black (Super P) in a mass ratio of 9:1 and milled for about 10 minutes. The mixture was then dispersed in a solvent of tetrahydrofuran (THF) in nafion (5%) in a volume ratio of 9:1 and sonicated for 1 hour in a closed state. It was then uniformly cast onto carbon cloth current collectors and dried under vacuum at ~60°C for 12 hours. The PTCDA loading mass per electrode was -13.0 mg cm ^-2 .

PTCDA/Cu electrodes with different Cu doping amounts can be obtained by a simple electrode in-situ self-reductive deposition method. First, the PTCDA electrode was reduced in a 1.0 M hydrochloric acid system by cyclic voltammetry, during which hydrated ions were inserted into the PTCDA structure (Reduced PTCDA). Subsequently, the electrodes _were transferred into 0.001 M CuSO4 solution. In this environment, since the oxidation potential of PTCDA is greater than the reduction potential of Cu ²⁺ /Cu ⁰ , PTCDA will be gradually oxidized, while Cu ²⁺ will intercalate into PTCDA instead of hydrated ions and be reduced to elemental Cu ⁰ . According to the different changes of open circuit potential with time, three PTCDA/Cu electrodes with different Cu doping amounts (PTCDA/Low Cu: 600s, PTCDA/Cu: 1200s, PTCDA/High Cu: 3600s) were obtained respectively. The impurities were 0.096, 0.197, 0.309 mg, respectively.

The inventors further investigated their properties, testing PTCDA/High Cu, PTCDA/Low Cu, Cu foam (equivalent PTCDA loaded on foamed copper) and Electrodeposition of Cu (equivalent copper deposited from the same potential range according to LSV sweep) Nitrate reduction performance of electrodes for ammonia synthesis. From the comprehensive analysis, all Cu-based electrodes have the performance of electroreduction of nitrate to synthesize ammonia, which reflects that Cu-based catalysts can selectively synthesize ammonia products. However, there is a clear difference in Faradaic efficiency between them. Figure 6 is a comparison chart of their total Faradaic efficiencies, PTCDA/Cu exhibits the highest total Faradaic efficiency value (96.0±1.6%), while the total Faradaic efficiencies of PTCDA/High Cu, PTCDA/Low Cu, Cu foam and Electrodeposition of Cu, respectively were 69.4±9.6%, 78.4±12.7%, 55.2±9.4% and 74.1±12.6%. This result indicates that a moderate amount of Cu-doped PTCDA electrode can achieve higher electrocatalytic nitrate reduction reaction selectivity for ammonia synthesis.

The above-mentioned embodiments are only the preferred exemplary embodiments of the present application, and do not specifically limit the protection scope of the present invention. Any changes made based on the inventive concept of the present invention and based on non-creative work should be It belongs to the protection scope of the present invention.

Claims (10)

1. A monoatomic copper material is composed of pyrenetetracarboxylic dianhydride (PTCDA) and Cu, and is characterized in that: the pyrene tetracarboxylic dianhydride is 3,4,9, 10-pyrene tetracarboxylic dianhydride, and Cu atoms are embedded in the molecular lattice structure of the 3,4,9, 10-pyrene tetracarboxylic dianhydride in the form of single atoms.

2. A preparation method of a monoatomic copper material specifically comprises the following steps:

step one, reducing PTCDA and doping the PTCDA with hydronium ions (H)₃O⁺)；

Step two, placing the reduced PTCDA obtained in the step one in low-concentration Cu²⁺In an ionic solution;

step three, the surface of the PTCDA electrode spontaneously generates an electrode in-situ self-reduction precipitation reaction, and Cu²⁺Replacing hydronium ions and carrying out a reduction process to obtain the monatomic copper-coupled PTCDA catalyst.

3. The method of producing a monoatomic copper material according to claim 2, characterized in that: the Cu²⁺The concentration of the ionic solution is 0.0001-0.01M, preferably Cu²⁺The ion concentration is 0.001-0.01M.

4. The method of producing a monoatomic copper material according to claim 2, characterized in that: cu²⁺The ions are derived from soluble copper salts, preferably copper chloride, nitrate, sulphate.

5. The method of producing a monoatomic copper material according to claim 2, characterized in that: the time for the in-situ self-reduction deposition of the electrode is preferably 50-5000s, preferably 100-2000s, and more preferably 500-1000 s.

6. The method of producing a monoatomic copper material according to claim 2, characterized in that: the Cu doping amount is 0.096-1.0 mg.

7. Use of a monoatomic copper material according to claim 1 or a monoatomic copper material prepared by the method for the preparation of a monoatomic copper material according to claim 2, characterized in that it is used in reactions for the synthesis of ammonia.

8. Use according to claim 7, characterized in that: the nitrogen source for the ammonia synthesis reaction is nitrate or nitrite.

9. Use according to claim 7, characterized in that: the cathodic potential is-0.1 to-1.0V, preferably-0.2 to-0.8V, and preferably-0.3 to-0.6.

10. Use according to claim 7, characterized in that: NH for synthesis of ammonia₃The yield was 305.7. + -. 29.8. mu. g h^-1cm^-2，NH₃The faradaic yield generated is 80.0 +/-5.9%, and the total faradaic efficiency is 96.0 +/-1.6%.

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