CN111360279A

CN111360279A - Preparation method and application of monoatomic copper material

Info

Publication number: CN111360279A
Application number: CN202010204906.0A
Authority: CN
Inventors: 王海辉; 陈高锋
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2020-03-22
Filing date: 2020-03-22
Publication date: 2020-07-03

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

Preparation method and application of monoatomic copper material

Technical Field

The invention relates to the field of monoatomic copper materials, in particular to a monoatomic catalyst, and more particularly relates to preparation and application of an electrocatalyst of a monoatomic copper material applied to the field of selective ammonia synthesis.

Background

The synthesis of ammonia from nitrogen and hydrogen molecules (Haber-Bosch process) is one of the most prominent inventions in the 20 th century. Today, this production process, which has a history of over 100 years, is the major source of synthetic ammonia in most of the world, accounting for 90% of the annual production. Ammonia and its derivatives (including urine)Element) is an important component of fertilizers. It is estimated that global food production can only support a small portion of today's world population without the use of artificial fertilizers in the Haber-Bosch process. However, since fossil fuels (mainly natural gas) are H₂The main source of precursors, if the process is continued to be used in the future, will increasingly pose serious environmental problems. Furthermore, N₂And H₂The slow kinetics of the reaction further exacerbates this problem. To ensure a continuous and efficient operation of the process, the reaction temperature (500 ℃) and pressure (C) must be increased>200 atm). This energy demanding process therefore consumes approximately 2% of the world's total energy supply annually and releases 4 billion tons of carbon dioxide annually in order to maintain ammonia production at the levels required to meet current demand. Therefore, a process has been developed which can be carried out at atmospheric pressure and room temperature and which enables clean, safe and sustainable production of NH₃The catalytic method of (A) is of great industrial value.

In recent years, electrochemical methods have provided promise for the direct conversion of renewable electricity to chemicals and chemical energy carriers. However electrochemical N₂The reductive synthesis of ammonia has proven to be extremely challenging to achieve in practice, primarily because of N₂Is highly stable (the bond energy is 941kJ mol)^-1) And non-polarizable molecules. The presently reported yields of NRR synthetic ammonia are two to three orders of magnitude lower than the Haber-Bosch process. Using other than N₂Alternative nitrogen sources beyond this are one possible approach to enhance the yield and selectivity of synthetic ammonia. Nitrate anion (NO)^3-) Is a potential nitrogen source because the N ═ O bond has a relatively low dissociation energy (204 kJmol)^-1) And are present in large amounts in agricultural waste produced by the bacterial breakdown of fertilizers. Thus, if NO can be converted under ambient conditions^3-Selective reduction of NH₃NH can be realized through the process of eliminating water body pollution and recycling waste resources₃Green production. Most of the electro-catalytic systems reported so far convert NO by a five-electron process^3-Reduction to N mainly₂And hardly generates NH₃. This is because N is formed₂Electrochemical potential of (1.25V vs. nhe, pH 0) to NH₃The resulting potential (1.20V) is more positive. Thus, NO^3-Reduction to N₂Thermodynamically specific reduction to NH₃Is more advantageous. In addition, NO due to kinetic limitations^3-The potential of the reduced synthetic ammonia is also in a region of a potential for hydrogen evolution reaction in many cases. During the reaction, the surface of the catalyst also has the problem of hydrogen evolution competing reaction, and a larger amount of H is generated₂. This means that these systems also consume excess electron donor for the production of NH₃Resulting in lower faraday efficiency. Thus, the design selectively generates NH₃Without generating H₂The electrocatalyst is also necessary.

At present, although heterogeneous catalysts with different sizes and morphologies have been widely reported, these catalyst materials cannot precisely control active sites, so that the selectivity of synthetic ammonia cannot be effectively improved. Monatomic catalysts have been of great interest because of their highly dispersed, precisely controllable active sites. The preparation method mainly comprises mass-selected soft-mapping technologies and wet-chemical methods (Lei, Y., Mehmod, F., Lee, S., et Al, incorporated silver activity for direct propylene amplification video sub-meter activity, science 2010,328:224-228.Hackett, S.F., Brydson, R.M., Gass, M.H., et Al, high-activity, single-site mesoporous Pd/Al₂O₃catalysts for selective aerobic oxidation of allylic alcohols, Angew. chem., int. Ed.2007,46, 8593-. However, the two methods have the disadvantages of complex preparation process, low yield, high consumption and the like, so that the practical application and popularization of the method are limited.

However, the prior art of the high-efficiency monatomic copper material electrocatalyst with good synthetic ammonia selectivity, which has simple process, can be prepared in large scale and at low cost, does not exist so far; the present application aims to solve the above problems.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a preparation method of a monoatomic copper material, the monoatomic copper material and application of the monoatomic copper material.

In order to achieve the above object, the present application proposes to embed monoatomic copper into a molecular lattice structure of 3,4,9, 10-pyrenetetracarboxylic dianhydride (3,4,9, 10-rylenetetracarboxylic dianhydride, PTCDA, hereinafter, abbreviated as PTCDA), to obtain a monoatomic copper material, and to use the monoatomic copper material as NO^3-And (3) reducing and synthesizing the ammonia electrocatalyst.

Specifically, in order to achieve the above object, the present invention obtains a monoatomic copper material by the following preparation method.

The preparation method comprises the following steps:

step one, reducing PTCDA and doping hydronium ions into the PTCDA;

step two, placing the reduced PTCDA obtained in the step one in low-concentration Cu²⁺In ionic solution, preferably Cu²⁺Ion concentration of 0.0001-0.01M, preferably Cu²⁺The ion concentration is 0.001-0.01M;

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.

Preferably, in step one, the reduction process is activated using a three-electrode cell, optionally with one or more cathodic scans of the PTCDA electrode, in 1.0Mol/L HCL.

Preferably, in step two, the Cu²⁺The ion is preferably soluble copper salt, preferably copper chloride, copper nitrate, copper sulfate and the like, the concentration of the copper ion is preferably 0.001mol/L-0.5mol/L, the time of the in-situ self-reduction deposition of the electrode is preferably 50-5000s, preferably 100-2000s, more preferably 500-1000s,

the application also provides a monoatomic copper material, wherein the monoatomic copper material is embedded into a 3,4,9, 10-pyrenetetracarboxylic dianhydride molecular lattice structure by monoatomic copper; it is embedded in the following way: step one, reducing PTCDA and doping hydronium ions into the PTCDA;

step two, placing the reduced PTCDA obtained in the step one at low concentrationCu²⁺In ionic solution, preferably Cu²⁺Ion concentration of 0.0001-0.01M, preferably Cu²⁺The ion concentration is 0.001-0.01M;

Preferably, Cu²⁺The doping time is 0-3600s, the doping amount is 0.096-1.0mg, preferably 0.096, 0.197 and 0.309mg, and the coating amount of PTCDA on the electrode is 13mg cm^-2；

The application also provides an application of the monoatomic copper material, wherein the monoatomic copper is embedded into a molecular lattice structure of 3,4,9, 10-pyrenetetracarboxylic dianhydride, and the formed monoatomic copper material is used for ammonia synthesis reaction, preferably the ammonia synthesis reaction is ammonia synthesis reaction which takes nitrate anions as nitrogen sources.

Preferably, the monoatomic copper is embedded into a molecular lattice structure of the 3,4,9, 10-pyrenetetracarboxylic dianhydride, and the method is implemented as follows: step one, reducing PTCDA and doping hydronium ions into the PTCDA;

Preferably, the nitrogen source is nitrate or nitrite and the cathodic potential is-0.1 to-1.0V, preferably-0.2 to-0.8V, preferably-0.3 to-0.6, more preferably-0.4V, NH in the ammonia synthesis reaction₃The 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%.

The invention has the beneficial effects that:

1) the invention utilizes a simple electrode in-situ self-reduction deposition method to obtain the monatomic copper catalyst (PTCDA/Cu), thereby overcoming the defects of complex preparation process, low yield, high cost and the like of the traditional monatomic catalytic preparation;

2) and the unique structure has the property of inhibiting hydrogen evolution reaction, thereby obtaining better performance of synthesizing ammonia by electrochemical NO3 reduction;

3) the reaction conditions for synthesizing ammonia are mild, and the method has higher time ammonia yield/Faraday efficiency and total Faraday efficiency.

Drawings

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

b) reduced PTCDA at 0.001M CuSO₄Open circuit potential in solution versus time;

FIG. 2 is an XRD pattern of PTCDA, reduced PTCDA, PTCDA/Low Cu, PTCDA/Cu and PTCDA/High Cu;

FIG. 3 is a PTCDA/Cu a) elemental profile, b) XPS spectra of Cu LMM Auger peaks, c) X-ray absorption near-edge structure spectra, d) extended X-ray absorption fine structure spectra;

FIG. 4 shows PTCDA/Cu in 0.1M PBS containing NO₂ ^-0.1M PBS and containing NO₃ ^-The obtained LSV curve is tested in 0.1M PBS;

FIG. 5 is 5a) NH at different potentials₃Yield and faraday efficiency; b) NH at different potentials₃And NO₂ ^-The total faradaic efficiency of the two;

FIG. 6 is a graph comparing the total Faraday efficiencies of PTCDA/High Cu, PTCDA/Low Cu, Cu foam (equal amount of PTCDA loaded on foam copper) and Electrodisplacement of Cu (equal amount of copper deposited according to the same potential range of LSV scans).

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

1) Preparation of monoatomic copper material.

The inventor researches: PTCDA is first reduced and incorporated with hydronium ion (H)₃O⁺). We recorded the Cyclic Voltammogram (CV) of PTCDA electrodes at 1.0M HCl in a three electrode cell. In the first cycle, the cathodic scan showed a reduction peak around-0.62V (FIG. 1a), corresponding to the reduction of PTCDA and H₃O⁺The doping process of (1). During the subsequent anode scan, an oxidation peak at +0.26V was observed. Thus, the electrode exhibited reversible behavior, but there was a polarization of about 0.88V. This is mainly due to the poor conductivity of small organic molecule materials. After the initial activation, the cathode scan of PTCDA was continued to be finally in the reduced state. Then it is placed in low concentration Cu²⁺Ionic solution (0.001 MCuSO)₄) In (1). In this system, Cu self-generated on the surface of the PTCDA electrode²⁺Displaces hydronium ions and a reduction process takes place.

From the XRD pattern of FIG. 2, it can be seen that the XRD crystal plane of PTCDA is shifted to the right significantly after cathode scanning. This is mainly due to the insertion of hydronium ions causing the lattice spacing of PTCDA to decrease.

Fig. 3a is an elemental distribution diagram of PTCDA/Cu, from which it can be observed that the Cu element is uniformly distributed in PTCDA, confirming that Cu is dispersedly 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 of FIGS. 3b-d confirm the presence of Cu-O-C bonds, indicating that the monatomic copper-coupled PTCDA catalyst can be successfully synthesized by the electrode in-situ self-reduction deposition method. According to the change of the open-circuit potential along with the change of time, three PTCDA/Cu electrodes (PTCDA/Low Cu: 600s, PTCDA/Cu: 1200s and PTCDA/High Cu: 3600s, shown in figure 1b) with different copper doping amounts are respectively obtained, and the doping amounts of Cu are respectively 0.096 mg, 0.197 mg and 0.309 mg.

2) Synthetic ammonia reaction

The inventors also studied:

firstly, nitrate/nitrite-containing and nitrate-freeLinear Sweep Voltammetry (LSV) tests were performed in a nitrite electrolyte to determine the reduction initiation potential of the relevant reactions in the system. FIG. 4 shows 0.1M PBS (phosphate buffered saline), containing 500ppm NO₂ ^-0.1M PBS and containing 500ppm NO₃ ^-LSV profile of PTCDA/Cu in 0.1M PBS. In the blank LSV plot, we observed two characteristic reduction current peaks of pure PTCDA. When more negative potential is applied, no obvious hydrogen evolution current is seen on the surface of PTCDA/Cu, which shows that the PTCDA/Cu has poor activity on HER in a wider negative potential range, and the property is favorable for improving the selectivity of the subsequent electrocatalytic ammonia synthesis reaction.

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

As can be seen from FIG. 5a, NH increases with increasing cathode potential₃The yield increased gradually and reached a maximum at-0.5V vs. RHE (405.0. + -. 31.9. mu. g h)^-1cm^-2). For NH₃The faradaic yield of the produced faradaic can reach a maximum value of 80-81% when the applied potential is-0.4V to-0.5 Vvs. Furthermore, as can be seen from FIG. 5b, PTCDA/Cu can maintain a total faraday efficiency (total faraday efficiency) of 86% or more over a wide potential range (-0.1V to-0.5V vs. RHE), and reaches a maximum of 96.8 + -2.3% at-0.3V vs. RHE. RHE is the optimum reaction applied potential for the system, NH, in combination with ammonia yield results₃The 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%. In addition, both the ammonia yield/faradaic efficiency and the overall faradaic efficiency show a tendency to decrease at-0.6V vs. rhe, mainly due to the progressive dominance of the hydrogen evolution competition reaction at high potential.

3) Influence of Cu doping amount on performance to confirm the advantage of PTCDA/Cu with proper Cu doping amount in improving the efficiency of synthesizing ammonia by reducing nitrate, the inventor also researches:

first, a piece of commercial carbon (C cloth) (3cm × 2cm) was treated with concentrated HNO₃Pretreatment for 24 hours led to the formation of carbonyl groups on the surface. And soaking the treated carbon cloth in a dilute hydrochloric acid solution for 2-3 days. Thereafter, it was rinsed several times with deionized water and dried in an oven at 60 ℃ overnight. PTCDA powder was mixed with carbon black (Super P) at 9: 1, and grinding for about 10 minutes. The mixture was then dispersed in Tetrahydrofuran (THF) in nafion (5%) at a volume ratio of 9: 1 for 1 hour under sealed ultrasound. It was then cast uniformly onto a carbon cloth current collector and dried under vacuum at-60 ℃ for 12 hours. 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-reduction deposition method. The PTCDA electrode was first Reduced by cyclic voltammetry in a 1.0M hydrochloric acid system, during which hydrated ions would be inserted into the PTCDA structure (Reduced PTCDA). Subsequently, the electrode was transferred to 0.001M CuSO₄In solution. In this environment, the oxidation potential of PTCDA is larger than that of Cu²⁺/Cu⁰The PTCDA will be gradually oxidized, while the Cu²⁺Substitutional hydrated ions are intercalated into PTCDA and reduced to elemental Cu⁰. Three PTCDA/Cu electrodes (PTCDA/Low Cu: 600s, PTCDA/Cu: 1200s and PTCDA/High Cu: 3600s) with different Cu doping amounts are respectively obtained according to the change of the open-circuit potential along with the time, and the Cu doping amounts are respectively 0.096, 0.197 and 0.309 mg.

The inventors further investigated their performance and tested the nitrate reduction ammonia synthesis performance of PTCDA/High Cu, PTCDA/Low Cu, Cu foam (equal amount of PTCDA loaded on foam copper) and electrochemical position of Cu (equal amount of copper deposited according to the same potential range of LSV scan) electrodes. The comprehensive analysis shows that all Cu-based electrodes have the performance of electroreduction of nitrate to synthesize ammonia, and the Cu-based catalyst can selectively synthesize ammonia products. However, there is a clear difference in faradaic efficiency between them. FIG. 6 is a graph comparing their total Faraday efficiencies, PTCDA/Cu exhibiting the highest values of total Faraday efficiency (96.0 + -1.6%), while PTCDA/High Cu, PTCDA/Low Cu, Cu foam and electrodeposionof Cu have total Faraday efficiencies of 69.4 + -9.6%, 78.4 + -12.7%, 55.2 + -9.4% and 74.1 + -12.6%, respectively. This result indicates that a proper amount of Cu-doped PTCDA electrode can obtain higher reaction selectivity of synthesizing ammonia by electrocatalytic nitrate reduction.

The above-mentioned embodiments are only preferred illustrative embodiments of the present application, and do not specifically limit the scope of the present invention, but all the inventive concepts adopting the present invention and any changes made on the basis of non-inventive efforts shall fall within the scope of the present invention.

Claims

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;

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%.