Method for preparing low-coordination environment single-atom-based nano-reactor for electrocatalytic reduction of co2 and use thereof

Abstract

The application relates to a preparation method and application of a low-coordination environment single-atom-based nano reactor for electrocatalytic CO2 reduction. The steps are as follows: (1) using tetraethyl orthosilicate under alkaline conditions, self-grown silica small balls are used as hard templates; a transition metal phthalocyanine ethanol solution is added, and a SiO2@MPc suspension is formed through an electrostatic self-assembly method; (2) adding hydrochloric acid dopamine into the SiO2@MPc suspension to form a SiO2@MPc@PDA sample; through high-temperature carbonization, a SiO2@I-MSA@NHCRs composite material is obtained; through acid / alkali solution etching, the SiO2 small balls are removed, and finally, the I-MSA / NHCRs nano reactor material is obtained. The application can optimize the activity and selectivity of the catalytic material in the process of electrocatalytic CO2 reduction.

Description

TECHNICAL FIELD

[0001] The present application relates to the preparation of a catalytic material for the electrocatalytic reduction of CO2 to CO, in particular to a preparation method and use of a low coordination environment single atom-based nano-reactor for electrocatalytic CO2 reduction. BACKGROUND

[0002] With the production and life of human beings, a large amount of carbon dioxide (CO2) is discharged into the air, causing global greenhouse effect, triggering a series of environmental problems: food safety is reduced, a large number of species are extinct, freshwater competition pressure is intensified, and ecological cycle is destroyed, etc. Therefore, it is urgent to develop an effective CO2 utilization technology. As a new CO2 resource technology, electrocatalytic CO2 reduction (CO2RR) involves mild reaction conditions, simple operation, and controllable reaction steps, and has attracted widespread attention. However, due to its chemical inertness and limited solubility of CO2 in electrolyte solution, electrocatalytic CO2 reduction technology is still limited by slow reaction kinetics and the existence of competing reaction-hydrogen evolution reaction (HER), resulting in low selectivity and activity of CO2 reduction products. To solve this thorny problem and improve the selectivity and activity of single product of electrocatalytic CO2 reduction, developing specific electrocatalytic CO2 reduction catalysts has become an effective research approach.

[0003] Currently, the catalytic materials for electrocatalytic CO2 reduction are mostly concentrated on noble metals such as gold and silver. The reduction product, carbon monoxide (CO), can be easily separated from the reaction phase, saving separation cost. At the same time, CO can be used as an important raw material for Fischer-Tropsch process to produce higher value-added fuels or chemicals. However, the scarcity of noble metals such as gold and silver limits their industrial application prospects. At the same time, electrocatalytic processes are also accompanied by low product selectivity, high overpotential, and low activity. For example, CN104846393A uses a silver-containing electrode as the cathode, and the selectivity of electrocatalytic CO2→CO is <90%, and the test potential is >1.70 V. As a competitive candidate, atomic dispersed metal catalysts composed of transition metals such as nickel have the advantages of clear active site structure, high atomic utilization rate, stable metal-support strong interaction, and modifiable coordination environment, and also combine the advantages of heterogeneous and homogeneous catalysts, and have been widely studied and rapidly developed in the field of electrocatalytic CO2 reduction. How to optimize the 3d orbit of transition metal, control the coordination environment of metal single atom, and optimize the local micro-reaction environment of the site, so as to improve the activity and selectivity of electrocatalytic CO2→CO, and meet the needs of industrial application, is a technical problem that needs to be solved at present. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a preparation method of a low-coordination environment single-atom-based nano reactor for electrocatalytic CO2 reduction, which can optimize the activity and selectivity of catalytic materials in the process of electrocatalytic CO2 reduction.

[0005] The technical solution provided by the present application is:

[0006] The preparation method of the low-coordination environment single-atom-based nano reactor for electrocatalytic CO2 reduction provided by the present application has the following specific steps:

[0007] (1) Under alkaline conditions, tetraethyl orthosilicate is used to self-generate silica (SiO2) small balls, which are used as a hard template, that is, tetraethyl orthosilicate is added to a mixed solution of ethanol, deionized water and ammonia water, and the size of the nano reactor substrate is controlled; a transition metal phthalocyanine (MPc) ethanol solution is added, and by means of electrostatic self-assembly, the negative (-) charge on the surface of the silica ball attracts the transition metal phthalocyanine (MPc) with a positive (+) charge center to the surface of the silica ball, forming a SiO2@MPc suspension;

[0008] (2) Hydrochloric acid dopamine (DA) is added to the SiO2@MPc suspension, and under alkaline conditions, DA is used to grow and polymerize, thereby wrapping the SiO2@MPc to form a SiO2@MPc@PDA sample; then through high-temperature carbonization, single atoms are inlaid in the ball, obtaining a SiO2@I-MSA@NHCRs composite material; and then through acid / alkali solution etching, the SiO2 small balls are removed, and finally the I-MSA / NHCRs nano reactor material is obtained.

[0009] In the present application, hydrochloric acid dopamine is used as a carbon source and a nitrogen source, and metal phthalocyanine (MPc) is used as a precursor of a single-atom site. By controlling the micro-reaction environment, carbonization temperature and carbonization atmosphere, a single-atom nano reactor material with a hollow carbon ball special structure is synthesized by using SiO2 as a template. The preparation method of the present application can use different types of phthalocyanines, such as nickel phthalocyanine (NiPc), iron phthalocyanine (FePc) and cobalt phthalocyanine (CoPc), so as to obtain a specific type of metal single-atom catalytic material. The key to obtaining a low-coordination environment nano reactor material in the present application is: 1) selection of a single-atom metal precursor, and the large ring structure of the metal phthalocyanine will inhibit the hydrolysis of the central metal, thereby ensuring the uniformity of the subsequent generation of a single-atom coordination environment; 2) setting of a multi-stage carbonization program, including carbonization time, temperature rising program and other technical parameters. At the same time, the ratio of tetraethyl orthosilicate / deionized water / ethanol / ammonia water is changed, thereby affecting the size of the SiO2 ball, and finally affecting the size of the nano reactor, the specific surface area and the pore of the material, thereby affecting the mass transfer of CO2 in the material, and finally affecting the catalytic performance of the material.

[0010] Preferably, in step (1), the total amount of the added ingredients is 5-8 parts of tetraethyl orthosilicate, 180-300 parts of anhydrous ethanol, 30-40 parts of deionized water, and 4-6 parts of ammonia water, in terms of volume fraction; the amount of the transition metal phthalocyanine is 10-15 mg / 100 mL of anhydrous ethanol.

[0011] Preferably, in step (1), the transition metal phthalocyanine macrocyclic molecule is one of nickel phthalocyanine (NiPc), iron phthalocyanine (FePc), and cobalt phthalocyanine (CoPc), and the metal phthalocyanine macrocyclic molecule can inhibit the hydrolysis of metal ions under alkaline conditions; the metal phthalocyanine molecule is dissolved in part of the total amount of anhydrous ethanol in advance, ultrasonically treated for 30-60 min to form a homogeneous solution, and then added dropwise into the SiO2 suspension; the components are reacted under alkaline conditions for 1-2 h, and then ultrasonically treated for 5-30 min to achieve uniform dispersion of the SiO2 beads and form the SiO2@MPc suspension.

[0012] Preferably, in step (2), dopamine hydrochloride (DA) is polymerized and grown under alkaline conditions, and is dissolved in a mixed solution containing ethanol and deionized water (1:1) in advance to obtain a DA / ethanol / deionized water mixed solution. The mixed solution is quickly added to the SiO2@MPc mixed solution to cause the DA molecules to undergo a polymerization reaction.

[0013] Preferably, in step (2), the mixed solution is stirred for 12-15 h, collected by high-speed centrifugation (5000-9000 rpm), and washed with ethanol and deionized water 1-2 times before high-temperature carbonization to remove unreacted small molecules.

[0014] Preferably, in step (2), the high-temperature carbonization step is divided into two steps. In the first step, the surface polymerized molecules are first preheated to stabilize them: the temperature is increased from room temperature to 300-400 ℃ at a rate of 1-2 ℃ / min, and the heat treatment time is 2-4 h. In the second step, the stable carbon layer is obtained at a high temperature: the carbonization temperature is controlled at 800-900 ℃, the temperature is increased at a rate of 5-10 ℃ / min, and the heat treatment time is 2-4 h. The inert gas is one of nitrogen, argon, and helium, and the flow rate is controlled at 2-5 mL / min. This step strengthens the formation of single-atom carbon-nitrogen structures and completes the anchoring of the metal inside the hollow carbon sphere. The inert gas not only ensures an inert environment and improves the stability of the high-temperature reaction environment, but also provides a constant environment for high-temperature carbonization of the sample.

[0015] Preferably, in step (2), the etching solution is an acidic solution selected from hydrogen fluoride solution with a concentration of 2-4 mol / L and a treatment time of 24-30 h, and an alkaline solution selected from one of NaOH and KOH with a concentration of 2-4 mol / L and an etching temperature of 80 ℃ and a time of 24-30 h.

[0016] The application also provides a use of the low-coordination environment single-atom-based nano-reactor material as a cathode in electrocatalytic CO2 reduction.

[0017] The method for using the low-coordination environment single-atom-based nano-reactor material of the application is as follows: the I-M SA / NHCRs nano-reactor material obtained in the above steps is used to prepare a cathode, a Pt electrode is used as a counter electrode, an Ag / AgCl electrode is used as a reference electrode, a CO2-saturated aqueous salt solution is used as an electrolyte, and an electrocatalytic reduction process of CO2 to CO is carried out in a “H-type” electrolytic cell.

[0018] Preferably, the electrode carrier of the cathode prepared from the I-M SA / NHCRs nano-reactor material is one of carbon paper, carbon felt, carbon cloth or carbon fiber, which can meet the requirements of uniform dispersion of the electrode material and good electrical conductivity, and the test does not participate in the electrocatalytic reaction.

[0019] Preferably, the method for preparing the cathode from the I-M SA / NHCRs nano-reactor material is as follows: the I-M SA / NHCRs nano-reactor material is added into a certain volume of ethanol, mixed with a commercial perfluorinated acid resin Nafion solution (1 wt%-10 wt%), and ultrasonically treated to obtain a homogeneous electrode ink in the bulk phase. The electrode ink is coated on the surface of the electrode carrier and dried to obtain the cathode.

[0020] Preferably, the loading amount of the low-coordination single-atom nano-reactor material on the electrode is 0.1-1 mg cm −2 .

[0021] Preferably, the material prepared in the application is first tested for performance in an H-type electrolytic cell by a three-electrode system, the products of the cathode and the anode are separated by a proton exchange membrane, and the electrode loaded with the material is the cathode for the reaction.

[0022] Preferably, the CO2-saturated aqueous salt solution is one of NaHCO3, KHCO3, KCl and K2SO4 electrolyte.

[0023] The application adopts the above technical solution, and compared with the prior art, the technical progress achieved is as follows:

[0024] (1) The inner-embedded single-atom hollow nano-reactor material prepared in the application has accelerated CO2 mass transfer kinetics, promotes the contact between the active sites and the reaction components, and improves the catalytic performance, compared with the single-atom catalyst with an internal solid structure.

[0025] (2) The nano-reactor material prepared by the application has low coordination characteristics of metal sites, which helps to optimize the metal d orbit, promote the activation of CO2 molecules to COOH, and improve the electrocatalytic activity of CO2 to CO.

[0026] (3) The single-atom-based nano-reactor material prepared by the application has excellent selectivity for electrocatalytic CO2 to CO. In the H-type electrolytic cell, the optimal component of the low-coordination single-atom nano-reactor material can not only electrocatalyze CO2 to CO with high selectivity (the highest Faraday efficiency of CO can reach > 94%), but also achieve atomic dispersion of metal sites, greatly improve the atomic utilization rate, and save costs. In the flow cell test, the highest industrial current density can reach ≥ 200 mA cm −2 , and the highest Faraday efficiency of CO can reach > 90% in the constant current test range of 25-150 mA cm −2 . BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The left picture is a scanning electron microscope (SEM) picture of the I-Ni SA / NHCRs in the material of Example 1, and the right picture is a transmission electron microscope (TEM) picture, with a scale of 100 nm and 200 nm, respectively.

[0028] Figure 2 The picture is a high-angle annular dark-field transmission electron microscope (HADDF-TEM) picture of the I-Ni SA / NHCRs in the material of Example 1, with a scale of 5 nm.

[0029] Figure 3 The picture is a TEM picture of the Ni-NC in the material of Comparative Example 1, with a scale of 200 nm.

[0030] Figure 4 The picture is a synchrotron radiation data chart of the I-Ni SA / NHCRs in the material of Example 1 and a standard sample.

[0031] Figure 5 The picture is a current density chart and a Faraday efficiency chart of the I-Ni SA / NHCRs in the material of Example 1 and the Ni-NC in the material of Comparative Example 1.

[0032] Figure 6 The picture is a stability test chart of the I-Ni SA / NHCRs in the material of Example 1.

[0033] Figure 7 The picture is a flow cell test performance chart of the I-Ni SA / NHCRs in the material of Example 1.

[0034] Figure 8Scanning electron micrograph of I-Ni SA / NHCRs-1 in Example 2 material.

[0035] Figure 9 Transmission electron micrographs of a) I-Co SA / NHCRs and b) I-Fe SA / NHCRs in Example 3, 4 materials.

[0036] Figure 10 Current density and Faraday efficiency plots of I-Co SA / NHCRs in Example 3 material.

[0037] Figure 11 Current density and Faraday efficiency plots of I-Fe SA / NHCRs in Example 4 material. DETAILED DESCRIPTION Example One:

[0038] Into a 250 mL single neck flask, 30 mL of deionized water and 4 mL of ammonia water (25-28%) and 100 mL of ethanol were added and stirred for 0.5 h to obtain a uniform solution. Subsequently, 5 mL of TEOS was added to the above mixed solution, stirred for 1 h, and then ultrasonicated for 5 min to obtain a uniform silica sphere (SiO2) suspension. 12 mg of NiPc was added to 80 mL of ethanol and ultrasonicated for 30 min to obtain a NiPc-ethanol suspension. The NiPc-ethanol suspension was added dropwise to the SiO2 suspension, and the positively charged center Ni(2+) was attracted to the negatively charged surface of SiO2, and was adsorbed on the surface of SiO2 by electrostatic interaction. After the addition was completed, it was stirred vigorously for another 0.5 h to obtain a SiO2@NiPc-mixed solution. 0.5 g of dopamine hydrochloride was dissolved in 10 mL of a solution of ethanol and water (1:1), and was added to the SiO2@NiPc-mixed solution and reacted for 12 h. The dopamine molecules polymerized to form polydopamine under alkaline conditions, which was coated on the surface of SiO2@NiPc spheres to form polydopamine (PDA). The above sample was collected by centrifuge at 7000 rpm for 3 min to obtain SiO2@NiPc@PDA. The obtained sample was placed in a tube furnace, first at 400 °C for 2 h, then programmed to 800 °C for 3 h, and then naturally cooled to room temperature to obtain SiO2@I-Ni SA@NHCRs. The obtained sample was treated with 4 mol / L KOH at 80 °C for 24 h to remove the SiO2 beads. Then it was washed with deionized water for 30 times and dried at 60 °C, and finally the low coordination intercalated single atom nickel-based nanoreactor material—I-Ni SA / NHCRs was obtained.

[0039] H-type electrolyzer performance test: 3 mg of the obtained I-Ni SA / NHCRs were added into 3 mL of ethanol containing 30 μL of Nafion (5 wt%) and sonicated for 1 h to form catalyst ink. The obtained ink was coated on a commercial carbon paper with a size of 3 cm´1 cm and a coating area of 0.5 cm 2 ´2 with a catalyst loading of 1 mg cm −2 . The obtained electrode was dried at room temperature to form an electrode. The obtained electrode was used as the working electrode, the Ag / AgCl electrode as the reference electrode, and the Pt electrode as the counter electrode. All the test potentials were converted to the reversible hydrogen electrode (RHE). The linear sweep voltammetry (LSV) was performed in the range of −0.2 ~ −1.2 V vs. RHE at a scan rate of 5 mV s −1 . The test potentials were −0.4, −0.5, −0.55, −0.6, −0.7, −0.75, −0.8, −0.85, −0.9, and −1.0 V vs. RHE, and the products were monitored by online gas chromatography.

[0040] Flow cell performance test: 3 mg of I-Ni SA / NHCRs were added into 3 mL of ethanol containing 50 μL of Nafion solution (5 wt%) and sonicated for 1 h to form catalyst ink, which was then sprayed onto a commercial gas diffusion layer using an airbrush to make a cathode gas diffusion electrode with a loading of 1 mg / cm 2 , and dried at 50 °C. A Pt foil was used as the anode electrode, and an Ag / AgCl electrode (3.5 M KCl) was chosen as the reference electrode. An anion membrane was used to separate the cathode and anode compartments. The flow rate of CO2 (99.999%) gas was controlled by a mass flow controller at 20 sccm. The gas product content was collected at 1200 s under continuous constant current test. Example Two:

[0041] Into a 250 mL single neck flask, 40 mL of deionized water and 6 mL of ammonia water (25-28%) and 120 mL of ethanol were added and stirred for 0.5 h to obtain a homogeneous solution. Subsequently, 8 mL of TEOS was added to the above mixed solution, stirred for 1 h, and then ultrasonicated for 5 min to obtain a homogeneous silica sphere (Si02) suspension. 15 mg of NiPc was added to 80 mL of ethanol and ultrasonicated for 30 min to obtain a NiPc-ethanol suspension. The NiPc-ethanol suspension was added dropwise to the Si02 suspension, and the positively charged center Ni(2+) was attracted to the negatively charged surface of Si02, adsorbed on the surface of Si02 by electrostatic interaction. After the addition was completed, it was stirred vigorously for 0.5 h to obtain a Si02@NiPc-mixed solution. 1 g of dopamine hydrochloride was dissolved in 10 mL of a mixed solution of ethanol and water (1:1), and added to the Si02@NiPc-mixed solution, and reacted for 12 h. The dopamine molecules polymerize to form polydopamine under alkaline conditions, which is coated on the surface of Si02@NiPc spheres to form polydopamine (PDA). The above sample was collected by centrifuge at 7000 rpm for 3 min to obtain Si02@NiPc@PDA. The obtained sample was placed in a tube furnace, kept at 300 °C for 4 h, then programmed to 900 °C for 2 h, and then naturally cooled to room temperature to obtain Si02@I-Ni SA@NHCRs-1. The obtained sample was placed in 2 mol / L KOH at 80 °C for 30 h to remove the Si02 beads. The obtained sample was washed with deionized water for 30 times, and then dried at 60 °C to obtain the low coordination intercalated single atom nickel-based nanoreactor material I-Ni SA / NHCRs-1.

[0042] Comparative Example 1:

[0043] Into a 250 mL single neck flask, 30 mL of deionized water and 5 mL of ammonia water (25-28%) and 100 mL of ethanol were added and stirred for 1.5 h to obtain a homogeneous solution. 12 mg of NiPc was added to 80 mL of ethanol and ultrasonicated for 30 min to obtain a NiPc-ethanol suspension. The NiPc-ethanol suspension was added dropwise to the above mixed solution, and after the addition was completed, it was stirred vigorously for 0.5 h. 0.5 g of dopamine hydrochloride was dissolved in 10 mL of a solution of ethanol and water (1:1), and added to the NiPc-mixed solution, and reacted for 12 h. The above sample was collected by centrifuge at 7000 rpm for 3 h to obtain a NiPc@PDA sample. The obtained sample was placed in a tube furnace, kept at 400 °C for 2 h, then programmed to 800 °C for 3 h, and then naturally cooled to room temperature to obtain a Ni-NC sample.

[0044] H-type electrolyzer performance test: the preparation of Ni-NC electrode ink in Comparative Example 1 and the material performance test method are the same as in Example 1, wherein the loading amount of the Ni-NC catalyst is 1 mg cm -2 .

[0045] As shown in Figure 1 , the I-Ni SA / NHCRs catalyst of Example 1 is an internal hollow structure.

[0046] Figure 2 In the middle, there are obvious bright spots, indicating that the metal is at the atomic level, proving the successful preparation of single-atom Ni.

[0047] As shown in Figure 3 , the Ni-NC sample in Comparative Example 1 is a solid structure.

[0048] Figure 4 The a figure in is the X-ray absorption near-edge absorption spectrum of different samples, and from the figure, it can be seen that compared with the standard NiPc and Ni foil, the near-edge absorption curve of I-Ni SA / NHCRs is similar to that of NiPc. The b figure is the Fourier transform extended X-ray absorption structure diagram of the sample, and the c figure is the fitting curve diagram. From the analysis of b and c, it can be seen that the coordination configuration of Ni in I-Ni SA / NHCRs is Ni-C3N1 structure. The d figure is a comparison of the theoretical spectrum and the experimental spectrum, and the inset is the spatial configuration of the Ni-C3N1 structure.

[0049] As shown in Figure 5 a, under the condition that the test potential is-0.2 ~-1.2 V (vs. RHE), the current density of I-Ni SA / NHCRs prepared in Example 1 is obviously higher than that of Ni-NC prepared in Comparative Example 1, indicating that the hollow structure is more conducive to the electrocatalytic reduction of CO2, and the optimization of the microenvironment of the active site is very important for the improvement of the catalytic performance. As shown in Figure 5 b, within the test potential range of-0.2 ~-1.2 V (vs. RHE), the selectivity of I-Ni SA / NHCRs prepared in Example 1 to CO is obviously higher than that of Ni-NC to CO, indicating that I-Ni SA / NHCRs has higher selectivity to product CO.

[0050] Figure 6 I-Ni SA / NHCRs prepared in Example 1 is used as a cathode catalyst in an H-type electrolyzer, and under the test condition of-0.8 V (vs. RHE), the stability test diagram for 13 h, in this process, the FE CO changes little (94.85%~91.44%)

[0051] As shown in Figure 7As shown in Figure a, under test potentials of −0.2 to −1.2 V (vs. RHE), the I-NiSA / NHCRs nanoreactor material prepared in Example 1, used as the cathode, achieved a current density (≥200 mA cm⁻¹) under flow cell test conditions that meets the requirements for commercial applications. −2 ), and in the range of 25~150 mA cm. −2 Within the constant current testing range, the Faraday efficiency of CO is >90% ( Figure 7 b).

[0052] like Figure 8 As shown, the I-Ni SA / NHCRs-1 nanoreactor in Example 2 has an internal hollow structure. Example 3:

[0053] 30 mL of deionized water, 5 mL of ammonia (25-28%), and 100 mL of ethanol were added to a 250 mL single-necked flask and stirred for 0.5 h to obtain a homogeneous solution. Then, 5 mL of TEOS was added to the mixture, stirred for 1 h, and sonicated for 5 min to obtain a homogeneous silica sphere (SiO2) suspension. 12 mg of CoPc was added to 80 mL of ethanol and sonicated for 30 min to obtain a CoPc-ethanol suspension. The CoPc-ethanol suspension was added dropwise to the SiO2 suspension. The positively charged Co(2+) ions were attracted to the negatively charged surface of SiO2 and adsorbed onto the SiO2 surface through electrostatic interaction. After the addition was complete, the mixture was stirred vigorously for 0.5 h to obtain a SiO2@CoPc mixed solution. 0.5 g of dopamine hydrochloride was dissolved in 10 mL of ethanol and water (1:1) and added to the SiO2@CoPc mixed solution, and the reaction was allowed to proceed for 12 h. Dopamine molecules polymerize under alkaline conditions to form polydopamine, which coats the surface of SiO2@CoPc spheres, forming polydopamine (PDA). The sample was collected by centrifuging at 7000 rpm for 3 minutes to obtain SiO2@CoPc@PDA. The obtained sample was placed in a tube furnace and initially held at 400 °C for 2 h, then programmed to 800 °C and held for 3 h, before naturally cooling to room temperature to obtain SiO2@I-Co SA@NHCRs. The obtained sample was heat-treated with 4 mol / L KOH at 80 °C for 24 h to remove the SiO2 microspheres. After washing 30 times with deionized water, the sample was dried at 60 °C to finally obtain the low-coordinated, internally embedded single-atom cobalt-based nanoreactor material—I-Co SA / NHCRs.

[0054] like Figure 9 As shown in a, the I-Co SA / NHCRs catalyst in this embodiment has an internal hollow structure. Example 4:

[0055] Into a 250 mL single neck flask, 30 mL of deionized water and 5 mL of ammonia water (25-28%) and 100 mL of ethanol were added, stirred for 0.5 h to obtain a uniform solution. Subsequently, 5 mL of TEOS was added to the above mixed solution, stirred for 1 h, and then ultrasonicated for 5 min to obtain a uniform silica sphere (SiO2) suspension. 12 mg of FePc was added to 80 mL of ethanol and ultrasonicated for 30 min to obtain a FePc-ethanol suspension. The FePc-ethanol suspension was added dropwise to the SiO2 suspension, and the positively charged center Fe(2+) was attracted to the negatively charged surface of SiO2, and was adsorbed on the surface of SiO2 by electrostatic interaction. After the addition was completed, it was stirred vigorously for 0.5 h to obtain a SiO2@FePc-mixed solution. 0.5 g of dopamine hydrochloride was dissolved in 10 mL of a solution of ethanol and water (1:1), and was added to the SiO2@FePc-mixed solution and reacted for 12 h. The dopamine molecules polymerized to form polydopamine under alkaline conditions, which was coated on the surface of SiO2@FePc spheres to form polydopamine (PDA). The above sample was collected by centrifugation at 7000 rpm for 3 min to obtain SiO2@FePc@PDA. The obtained sample was placed in a tube furnace, first at 400 ℃ for 2 h, then programmed to 800 ℃ for 3 h, and then naturally cooled to room temperature to obtain SiO2@I-Fe SA@NHCRs. The obtained sample was treated with 4 mol / L KOH at 80 ℃ for 24 h to remove the SiO2 beads. The obtained sample was washed with deionized water for 30 times and dried at 60 ℃ to finally obtain the low coordination intercalated single atom iron-based nanoreactor material—I-Fe SA / NHCRs.

[0056] As shown in Figure 9 b, the I-Fe SA / NHCRs catalyst of the present embodiment has an internal hollow structure.

[0057] The preparation of the I-Co SA / NHCRs and I-Fe SA / NHCRs electrode ink in Examples 3 and 4 and the material performance test method are the same as those in Example 1.

[0058] As shown in Figure 10 a, under the test potential of -0.2 ~ -1.2 V (vs. RHE), the I-Co SA / NHCRs prepared in Example 3 showed obvious activity for electrochemical CO2 reduction. As shown in Figure 10 b, under the application of -0.7 V (vs. RHE), the selectivity to CO reached a maximum value of 72.91%, and the current change curve corresponding to different constant voltage tests was as shown in Figure 10c.

[0059] As Figure 11 a, the I-Fe SA / NHCRs prepared in Example 4 showed obvious electrocatalytic activity for CO2 reduction under the test potential of -0.2 ~ -1.2 V (vs. RHE), and the total current density reached ~29 mA cm-2at -1.2 V (vs. RHE). -2 As Figure 11 b, the selectivity to CO reached the maximum value of 73.41% at the applied potential of -0.5 V (vs. RHE), and the current change curves corresponding to different constant voltage tests are shown in Figure 11 c.

[0060] It should be understood, moreover, that it is not necessarily limited to particular embodiments described, as such may vary. It is intended that the application shall only be limited by the scope of the appended claims, regardless of whether they issued in the same patent family as the present application.

Claims

1. A method for the preparation of low-coordination environment single-atom based nano-reactors for electrocatalytic CO2 reduction, characterized by: The specific steps are as follows, (1) using tetraethyl orthosilicate under alkaline conditions, self-growth into silica small ball, with it as a hard template, namely adding tetraethyl orthosilicate in the mixed solution of ethanol, deionized water, ammonia, controlling the size of the nano reactor base; adding transition metal phthalocyanine ethanol solution, through the method of electrostatic self-assembly, using the negative charge on the surface of the silica ball, attracting the transition metal phthalocyanine with positive charge center on the surface of the silica ball, forming SiO2@MPc suspension; (2) adding hydrochloric acid dopamine to the SiO2@MPc suspension, using hydrochloric acid dopamine to grow under alkaline conditions, so as to wrap SiO2@MPc, forming SiO2@MPc@PDA sample; then through high temperature carbonization, realizing that a single atom is inlaid in the ball, obtaining SiO2@I-MSA@NHCRs composite material; then through acid / alkaline solution etching, removing the SiO2 small ball, finally obtaining I-MSA / NHCRs nano reactor; The high temperature carbonization step is divided into two steps, the first step, preheating to stabilize the surface polymer molecules: the temperature is increased from room temperature to 300~400 ℃, the temperature rising program is 1~2 ℃ / min, and the heat treatment time is 2~4 h; the second step, high temperature to obtain stable carbon layer: the carbonization temperature is controlled at 800~900 ℃, the temperature rising program is 5~10 ℃ / min, and the heat treatment time is 2~4 h; the inert gas is one of nitrogen, argon and helium, and the flow rate is controlled at 2~5 mL / min.

2. The method for the preparation of low coordination environment single atom based nano-reactors for electro-catalytic CO2 reduction according to claim 1, characterized in that: In step (1), the total amount of added ingredients is calculated by volume fraction, tetraethyl orthosilicate is 5~8 parts, ethanol is 180~300 parts, deionized water is 30~40 parts, and ammonia is 4~6 parts; the amount of transition metal phthalocyanine is 10~15 mg per 100 mL of ethanol.

3. The method for the preparation of low coordination environment single atom based nano-reactors for electro-catalytic CO2 reduction according to claim 2, characterized in that: In step (1), the transition metal phthalocyanine macrocyclic molecule is one of nickel phthalocyanine, iron phthalocyanine and cobalt phthalocyanine; the metal phthalocyanine molecules are dissolved in part of the total amount of anhydrous ethanol in advance, ultrasonic treatment for 30~60 min to form a homogeneous solution, and then added dropwise into the SiO2 suspension; each component reacts under alkaline conditions for 1~2 h, then ultrasonic treatment for 5 min~30 min to realize uniform dispersion of SiO2 small ball, forming SiO2@MPc suspension.

4. The method for the preparation of low-coordination environment single-atom based nano-reactors for electrocatalytic CO2 reduction according to claim 2 or 3, characterized in that: In step (2), hydrochloric acid dopamine is dissolved in a mixed solution containing ethanol:deionized water=1:1 by volume ratio to obtain a DA / ethanol / deionized water mixed solution; the mixed solution is quickly added to the SiO2@MPc mixed solution to make the DA molecules polymerize.

5. The method for the preparation of low-coordination environment single-atom based nano-reactors for electrocatalytic CO2 reduction according to claim 2 or 3, characterized in that: In step (2), the mixed solution is stirred and reacted, centrifuged and collected, and washed with ethanol and deionized water before high temperature carbonization to remove unreacted small molecules.

6. The method for the preparation of low coordination environment single atom based nano-reactors for electro-catalytic CO2 reduction according to claim 2 or 3, characterized in that: In step (2), the etching solution: the acid solution is selected from hydrogen fluoride solution with a concentration of 2-4 mol / L, and the treatment time is 24-30 h; the alkaline solution is one of NaOH and KOH with a concentration of 2-4 mol / L, and the etching temperature is 80 ℃, and the time is 24-30 h.

7. A method of using a low coordination environment single atom based nano reactor, characterized by: The low coordination environment single atom based nano reactor of claim 1 is made into a cathode for electrocatalytic CO2 reduction reaction.

8. The method of using a low coordination environment single atom based nano reactor of claim 7, wherein: The I-M SA / NHCRs nano reactor material obtained in the above step is made into a cathode for the reaction of electrocatalytic CO2 reduction to prepare CO in a "H-type" electrolytic cell, with a Pt electrode as a counter electrode, an Ag / AgCl electrode as a reference electrode, and a CO2 saturated aqueous salt solution as an electrolyte, to perform the process of electrocatalytic reduction of CO2 to CO. ​ 9. The method of using a low coordination environment single atom based nano reactor of claim 7, wherein: The cathode is prepared by using I-M SA / NHCRs nano-reactor material, and the electrode carrier is one of carbon paper, carbon felt, carbon cloth or carbon fiber; the method for preparing the cathode is as follows: I-M SA / NHCRs nano-reactor material is added into a certain volume of ethanol, mixed with 1-10 wt% of Nafion solution, and ultrasonically treated to obtain a homogeneous electrode ink; the electrode ink is coated on the surface of the electrode carrier, and dried to obtain the cathode; the loading amount of the low-coordination monatomic nano-reactor material on the electrode is 0.1-1 mg cm −2 . ​

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