CN113529108A - For reducing CO2Preparation method and application of composite electrocatalyst - Google Patents

Abstract

For reducing CO₂Relates to the preparation method and the application of the composite electrocatalyst, and relates to the reduction of CO₂The technical field adopts a mixed ligand strategy to synthesize the PCN-224 (Zn) with a microporous structure and a bimetallic porphyrin center_xFe_y) Precursor is decomposed at high temperature to create micropores in the sublimation process of Zn so as to promote Fe²⁺Central transformation to atomic-scale Fe-N_nThe Kirkendall effect is simultaneously utilized to obtain Fe_y-an N-C composite electrocatalyst. Mixing Fe_ythe-N-C composite electrocatalyst is coated and modified on the surface of the carbon paper electrode and is used for reducing CO₂The working electrode fully exerts the structural advantages thereof and shows high-efficiency CO conversion₂For CO performance and long-range stability.

Description

For reducing CO2Preparation method and application of composite electrocatalyst

Technical Field

The invention relates to the reduction of CO₂Technical field, in particular reusable Fe_y-N-C cathode material preparation technology.

Background

CO₂Has caused a number of environmental problems worldwide, the electrocatalytic reduction of CO₂（CO₂RR) is a countermeasure with attention prospect and feasibility in the aspects of environmental protection, energy storage and the likeBut not shown. However, CO₂RR still faces a plurality of challenges, the reaction mechanism is complex, the overpotential is high, the competition of Hydrogen Evolution Reaction (HER) and the catalyst deactivation are all used for restricting CO₂The RR factor.

Heteroatom doped carbon materials have been widely used for CO in recent years₂Research on RR, particularly emerging metal atom-doped carbon catalysts. Carbon-supported transition metal-nitrogen structures (M-N, e.g. Fe-N, Co-N, Ni-N) with unsaturated coordination to CO₂Exhibit higher activity. Pyrolysis is the most direct method for preparing M-N-C materials, but during pyrolysis of organic precursors at high temperatures, partial fusion and aggregation of carbon-based catalysts inevitably occurs due to newly formed C-C and C-N bonds. Thus, a large number of active sites are unevenly distributed and enclosed in the internal carbon matrix, making it difficult for the reactants to access the M-N sites. In order to solve this problem, it is critical to synthesize a metal and nitrogen-co-doped carbon catalyst having a hierarchical pore structure and a high specific surface area. Patent document CN2019107757689 discloses excellent CO of Co-N-C material₂RR Performance, its CO Faraday Efficiency (FE)_CO) Can reach 93 percent. Peter Bogdannoff et al (Stephen Paul, YL Kao, LM Ni, et al. influx of the metal center in M-N-C catalysts on the CO₂ reduction reaction on gas diffusion electrodes[J]ACS Catal. 2021, 11, 5850-5864) discusses electrocatalytic reduction of CO by series of M-N-C materials₂Activity, FE of the Fe-N-C and Ni-N-C catalysts_COCan be maintained at more than 80 percent, and can effectively inhibit HER competitive reaction. Liu Lian Cheng et al (ZP Chen, XX Zhang, W Liu, et al, animation growth to boost the CO₂ electroreduction current density of M–N/C single-atom catalysts to the industrial application level[J]Energy environ. Sci., 2021, 14, 2349-₂The current density of RR is improved to the industrial application level, wherein the CO partial current density of the Ni-N-C catalyst is up to 450 mA cm⁻². Nevertheless, the content of M-N sites currently available for effective catalysis is rather limited and there is deactivation of most catalystsAnd the phenomenon is difficult to recycle.

Disclosure of Invention

The first purpose of the invention is to provide a method for electrocatalytic reduction of CO₂Preparation of CO and Fe with long-range stability_yA preparation method of the (E) -N-C composite electrocatalyst.

The invention comprises the following steps:

1) mixing Fe-TCPP, Zn-TCPP and ZrCl₄Uniformly ultrasonically stirring benzoic acid, acetic acid and DMF (dimethyl formamide) to perform hydrothermal reaction till the end, cooling to room temperature, washing with DMF and acetone respectively, and centrifugally drying to obtain PCN-224 (Zn)_xFe_y) A precursor; x is 0.2-0.8, and y is 0.2-0.8;

2) mixing PCN-224 (Zn)_xFe_y) Placing the precursor in N₂Pyrolyzing at 1000 deg.C for 1 hr in atmosphere, and cleaning with HF to remove ZrO₂Then washing with deionized water and ethanol, centrifuging and drying to obtain Fe_y-an N-C composite electrocatalyst.

The invention adopts a mixed ligand strategy to synthesize the PCN-224 (Zn) with a microporous structure and a bimetallic porphyrin center_xFe_y) Precursor is decomposed at high temperature to create micropores in the sublimation process of Zn so as to promote Fe²⁺Central transformation to atomic-scale Fe-N_nThe sites simultaneously utilize the Kirkendall effect to obtain the highly dispersed mesoporous Fe in the carbon matrix_y-N-C derivatives, i.e. Fe_y-an N-C composite electrocatalyst.

The Fe_y-N-C composite electrocatalyst at 0.1M KHCO₃CO in solution₂RR all showed>80% FE_COThe successful preparation of the composite electrocatalyst solves the problem of deactivation of most catalysts, and realizes the high-efficiency utilization of the M-N-C catalyst.

Furthermore, the mixing mass ratio of the Fe-TCPP to the Zn-TCPP is 0.8: 0.2-0.2: 0.8. Since iron in the precursor is easy to aggregate to form iron nanoparticles during pyrolysis, and the iron nanoparticles promote hydrogen evolution reaction, the content of iron needs to be controlled under the above mixing ratio condition to realize full utilization of iron atoms.

Pyrolytic Fe_yN-C follow the labeling method in the precursor. The precursor is cubic and has high stability and specific surface area.

The mixing mass ratio of the Fe-TCPP to the Zn-TCPP is 0.5: 0.5, x is 0.5, and y is 0.5. When x: y = 0.5: 0.5, Fe obtained_0.5-N-C has a FE of 93%_COAnd only 6% of the electrolyte is reduced after 6 times of circulating electrolysis.

Another object of the present invention is Fe obtained by the above process_y-use of an N-C composite electrocatalyst.

Mixing Fe_ythe-N-C composite electrocatalyst is coated and modified on the surface of the carbon paper electrode and is used for reducing CO₂The working electrode of (1).

Mixing Fe_ythe-N-C composite electrocatalyst is mixed with Nafion, Isopropanol (IPA) and water to form a slurry mixture, then the slurry mixture is coated on the surface of the carbon paper electrode, and then the carbon paper electrode is dried.

Said Fe_yThe loading amount of the-N-C composite electrocatalyst on the surface of the carbon paper electrode is 2.5 mg/cm²。2.5 mg/cm²The minimum loading of the catalyst on the carbon paper is uniform.

The process of the invention is characterized in that:

1) with PCN-224 (Zn)_xFe_y) As a precursor, a large number of mesopores are generated in the thermally derived carbon skeleton. Meanwhile, a large number of micropores are left in the process of reducing Zn at high temperature, so that the aggregation of Fe nano particles is avoided, and Fe is promoted²⁺Central transformation to atomic-scale Fe-N_nThe sites are uniformly distributed in the carbon matrix, and the selectivity of CO is improved.

2）Fe_ythe-N-C shows excellent stability, still shows higher catalytic activity after 6 times of repeated electrolysis, and realizes efficient recycling of the catalyst.

3) The carbon paper has stable electrochemical performance, high specific surface area, low price and easy obtainment, and is used as a substrate electrode material, so that the preparation cost is greatly reduced.

The invention avoids the aggregation of Fe nano particles and successfully obtains the high-density monatomic Fe-N with a hierarchical pore structure_nFe with uniformly distributed active sites_y-N-C material, fully taking advantage of its structure, exhibiting high efficiency in converting CO₂The catalyst is recycled for CO performance and long-range stability, and the defect that the traditional catalyst is difficult to recycle is overcome.

Drawings

FIG. 1 shows PCN-224 (Zn) prepared in examples 1 to 5_xFe_y) Nitrogen adsorption and desorption curve diagram of the precursor.

FIG. 2 shows PCN-224 (Zn) prepared in examples 1 to 5_xFe_y) Pore size distribution of the precursor.

FIG. 3 shows Fe prepared in examples 1 to 5_yNitrogen desorption profile of N-C catalyst.

FIG. 4 shows Fe prepared in examples 1 to 5_yPore size distribution of N-C catalyst.

FIG. 5 shows Fe prepared in example 1 of the present invention₀TEM photographs of the N-C composite electrocatalyst.

FIG. 6 shows Fe prepared in example 2 of the present invention_0.2TEM photographs of the N-C composite electrocatalyst.

FIG. 7 shows Fe prepared in example 3 of the present invention_0.5TEM photographs of the N-C composite electrocatalyst.

FIG. 8 shows Fe prepared in example 4 of the present invention_0.8TEM photographs of the N-C composite electrocatalyst.

FIG. 9 shows Fe prepared in example 5 of the present invention_1.0TEM photograph of the N-C nano-composite electrocatalyst.

FIG. 10 shows Fe prepared in example 3 of the present invention_0.5HRTEM (a) (b) (C) and HRTEM-Mapping (d) of the N-C composite electrocatalyst.

FIG. 11 shows Fe prepared in examples 1 to 5_y-Linear Sweep Voltammogram (LSV) of the N-C composite electrocatalyst.

FIG. 12 is a graph of the Faraday efficiency of CO obtained by electrolysis of the composite electrocatalysts prepared in examples 1-5 at-1.2V vs. Ag/AgCl potential for 2 h.

FIG. 13 is Fe prepared in example 3 of the present invention_0.5An efficiency diagram of the-N-C composite electrocatalyst at-1.2V vs. Ag/AgCl for 12 h of electrolysis.

FIG. 14 is Fe prepared in example 3 of the present invention_0.5-an efficiency diagram of 6 cycles of Ag/AgCl cyclic electrolysis of N-C composite electrocatalyst at-1.2V vs.

Detailed Description

Firstly, preparing a composite electrocatalyst:

example 1

Fe-TCPP (0 mg), Zn-TCPP (40 mg), ZrCl by a mixed ligand strategy₄(120 mg), benzoic acid (1.2 g), 0.5 mL acetic acid and 7.5 mL DMF, and stirring the mixture evenly by ultrasound, and then placing the mixture in a reaction kettle for reaction at a constant temperature. After the reaction is finished, cooling to room temperature, washing for 3 times by using DMF and acetone respectively, and centrifugally drying to obtain a purple solid product PCN-224 (Zn)₁Fe₀) And (3) precursor.

Fe-TCPP and Zn-TCPP ligands were synthesized according to the procedures reported in the literature (DW Feng, WC Chung, ZW Wei, et al, Construction of ultrastable porphyrin Zr metal-organic frame work through linker evaluation [ J]J Am Chem Soc, 2013, 135, 17105-17110.). Putting the precursor into a tube furnace for pyrolysis, and cleaning a sample by HF to remove ZrO₂Then respectively washing with deionized water and ethanol, centrifugally collecting samples, and drying to obtain Fe₀-an N-C composite electrocatalyst.

Preparing an electrode: weighing a certain amount of Fe₀-N-C composite electrocatalyst dispersed in a catalyst composed of (C) 400μL H₂O、200 μL Nafion solution (mass fraction 5%) and 400μIn a mixed solution formed by L IPA (isopropyl alcohol), carrying out ultrasonic treatment and then stirring for 12 hours to obtain a suspension; uniformly brushing the obtained suspension on a carbon paper electrode, and air-drying at room temperature to obtain Fe₀-an N-C catalyst modified working electrode.

Example 2

Fe-TCPP (8 mg), Zn-TCPP (32 mg), ZrCl by a mixed ligand strategy₄(120 mg), benzoic acid (1.2 g), 0.5 mL of acetic acid and7.5 mL of DMF is subjected to ultrasonic treatment and is stirred uniformly, and then the mixture is placed in a reaction kettle for constant-temperature reaction. After the reaction is finished, cooling to room temperature, washing for 3 times by using DMF and acetone respectively, and centrifugally drying to obtain a purple solid product PCN-224 (Zn)_0.8Fe_0.2) And (3) precursor.

Putting the precursor into a tube furnace for pyrolysis, and cleaning a sample by HF to remove ZrO₂Then respectively washing with deionized water and ethanol, centrifugally collecting samples, and drying to obtain Fe_0.2-an N-C composite electrocatalyst.

Preparing an electrode: weighing a certain amount of Fe_0.2-N-C composite electrocatalyst dispersed in a catalyst composed of (C) 400μL H₂O、200 μL Nafion solution (mass fraction 5%) and 400μCarrying out ultrasonic treatment on a mixed solution formed by L IPA (isopropyl alcohol), and stirring for 12 hours to obtain a suspension; uniformly brushing the obtained suspension on a carbon paper electrode, and air-drying at room temperature to obtain Fe_0.2-an N-C catalyst modified working electrode.

Example 3

Fe-TCPP (20 mg), Zn-TCPP (20 mg), ZrCl by a mixed ligand strategy₄(120 mg), benzoic acid (1.2 g), 0.5 mL acetic acid and 7.5 mL DMF, and stirring the mixture evenly by ultrasound, and then placing the mixture in a reaction kettle for reaction at a constant temperature. After the reaction is finished, cooling to room temperature, washing for 3 times by using DMF and acetone respectively, and centrifugally drying to obtain a purple solid product PCN-224 (Zn)_0.5Fe_0.5) And (3) precursor.

Putting the precursor into a tube furnace for pyrolysis, and cleaning a sample by HF to remove ZrO₂Then respectively washing with deionized water and ethanol, centrifugally collecting samples, and drying to obtain Fe_0.5-an N-C composite electrocatalyst.

Preparing an electrode: weighing a certain amount of Fe_0.5-N-C composite electrocatalyst dispersed in a catalyst composed of (C) 400μL H₂O、200 μL Nafion solution (mass fraction 5%) and 400μA mixed solution of L IPA (isopropyl alcohol) was ultrasonically treated, and then stirred for 12 hours to obtain a suspension. Uniformly brushing the obtained suspension on a carbon paper electrode, and air-drying at room temperature to obtain Fe_0.5-an N-C catalyst modified working electrode.

Example 4

Fe-TCPP (32 mg), Zn-TCPP (8 mg), ZrCl by a mixed ligand strategy₄(120 mg), benzoic acid (1.2 g), 0.5 mL acetic acid and 7.5 mL DMF, and stirring the mixture evenly by ultrasound, and then placing the mixture in a reaction kettle for reaction at a constant temperature. After the reaction is finished, cooling to room temperature, washing for 3 times by using DMF and acetone respectively, and centrifugally drying to obtain a purple solid product PCN-224 (Zn)_0.2Fe_0.8) And (3) precursor.

Putting the precursor into a tube furnace for pyrolysis, and cleaning a sample by HF to remove ZrO₂Then respectively washing with deionized water and ethanol, centrifugally collecting samples, and drying to obtain Fe_0.8-an N-C composite electrocatalyst.

Preparing an electrode: weighing a certain amount of Fe_0.8-N-C composite electrocatalyst dispersed in a catalyst composed of (C) 400μL H₂O、200 μL Nafion solution (mass fraction 5%) and 400μThe mixture solution of L IPA (isopropyl alcohol) was sonicated and stirred for 12 hours to obtain a suspension. Uniformly brushing the obtained suspension on a carbon paper electrode, and air-drying at room temperature to obtain Fe_0.8-an N-C catalyst modified working electrode.

Example 5

Fe-TCPP (40 mg), Zn-TCPP (0 mg), ZrCl by a mixed ligand strategy₄(120 mg), benzoic acid (1.2 g), 0.5 mL acetic acid and 7.5 mL DMF, and stirring the mixture evenly by ultrasound, and then placing the mixture in a reaction kettle for reaction at a constant temperature. After the reaction is finished, cooling to room temperature, washing for 3 times by using DMF and acetone respectively, and centrifugally drying to obtain a purple solid product PCN-224 (Zn)₀Fe₁) And (3) precursor.

Putting the precursor into a tube furnace for pyrolysis, and cleaning a sample by HF to remove ZrO₂Then respectively washing with deionized water and ethanol, centrifugally collecting samples, and drying to obtain Fe₁-an N-C composite electrocatalyst.

Preparing an electrode: weighing a certain amount of Fe₁-N-C composite electrocatalyst dispersed in a catalyst composed of (C) 400μL H₂O、200 μL Nafion solution (mass fraction 5%) and 400μL IPA (isopropyl alcohol) formIn the prepared mixed solution, stirring for 12 hours after ultrasonic treatment to obtain a suspension; uniformly brushing the obtained suspension on a carbon paper electrode, and air-drying at room temperature to obtain Fe₁-an N-C catalyst modified working electrode.

Product Properties

FIGS. 1 and 2 are N for precursors prepared in examples 1 to 5 at 77K, respectively₂The absorption and desorption test curve graph and the pore size distribution graph are shown as typical type I isotherms, and the pore size distribution condition of the material is obtained by applying a Density Function Theory (DFT) model, and shows two micropores of 1.3 nm and 1.6 nm.

TABLE 1N of the precursors₂Test result comparison table for adsorption and desorption

As can be seen from the table: PCN-224 (Zn) synthesized by mixed ligand method_0.8Fe_0.2)、PCN−224(Zn_0.5Fe_0.5) And PCN-224 (Zn)_0.2Fe_0.8) The precursors all show higher specific surface area (BET)>1700 m²Per g) and total pore volume (V)>1 cm³/g)。

BET of the precursor after pyrolysis is obviously reduced, and Fe obtained after pyrolysis is shown in figures 3 and 4_yN of-N-C₂An adsorption-desorption curve and an aperture distribution diagram,P/P ₀ the hysteresis ring appearing at 0.4-0.9 represents the mesoporous structure of the material.

TABLE 2 Fe_yN of-N-C material₂Test result comparison table for adsorption and desorption

Analysis of the data from the table shows PCN-224 (Zn) by the bimetal center_0.8Fe_0.2)、PCN−224(Zn_0.5Fe_0.5) And PCN-224 (Zn)_0.2Fe_0.8) Fe obtained by precursor pyrolysis_y-N-C (y =0.2,0.5,0.8) materials all have a high specific surface area (BET)>290 m²Per g) and pore volume (V)>0.24 cm³/g), especially in the mesopore volume part, because the introduction of iron ions not only facilitates the formation of the mesopore structure, but also triggers the Kirkendall effect during pyrolysis, resulting in the generation of larger voids inside the carbon-based derivative. Thus Fe_0.5-N-C showed the highest specific surface area (411 m)²In g) and considerable total pore volume (0.332 cm)³(iv)/g); however, as the Fe content is further increased, aggregation of Fe nanoparticles occurs after pyrolysis, resulting in a decrease in specific surface area, such as Fe_0.8-N-C and Fe_1.0N-C, the BET and pore volume of which show a decreasing trend.

As can be seen from fig. 5 to 9: the electrocatalysts prepared in examples 1-5 all maintain the cubic morphology of the precursor, wherein no aggregation of Fe nanoparticles is observed on the surfaces of the electrocatalysts prepared in examples 2 and 3. Meanwhile, it can be observed that the surface of the samples of the electrocatalysts prepared in examples 4 and 5 had a large amount of aggregation of Fe nanoparticles of about 40 nm with the increase of Fe content.

HRTEM of the electrocatalyst prepared in example 3 is shown in FIG. 10, indicating Fe_0.5Monoatomic Fe-N of-N-C electrocatalyst_nThe active sites are evenly distributed.

TABLE 3 Fe_yPercentage of different N types (%)

Sample (I)	Total nitrogen content	Pyridine-nitrogen/total nitrogen content	Fe−NnTotal nitrogen content	Pyrrole/total nitrogen content	graphite-nitrogen/Total Nitrogen content	NO/Total Nitrogen content Measurement of
							Fe0.2-N-C-224	2.54	18.46	13.08	24.83	35.15	8.47
Fe0.5-N-C-224	2.42	18.34	18.35	29.97	18.36	14.98

XPS analysis from table 3 shows: increase of Fe-N by introduction of Fe_nThe content of active sites further illustrates the content of Fe in the precursor to Fe-N thereof_nThe control of the active site is of crucial importance, among others Fe_0.5Fe-N in-N-C materials_nThe content is as high as 0.44.

Two, electrocatalytic reduction of CO to composite electrocatalyst₂And (3) testing the performance:

1. modifying the carbon paper electrode:

firstly 400 mu L of H₂O, Nafion 200. mu.L at a concentration of 5 wt% and IPA (isopropyl alcohol) 400. mu.L were mixed to form a mixed solution, and then 10mg of Fe was added_yMixing the-N-C composite electrocatalyst with the mixed solution to form a slurry-like mixture. Coating the slurry mixture on the surface of carbon paper electrode, and air drying at room temperature to obtain Fe_y-an N-C modified carbon paper electrode.

2. Assembling:

in H-type cells, with Fe_ythe-N-C modified carbon paper electrode is used as a working electrode (cathode), a platinum sheet is used as a counter electrode, an Ag/AgCl electrode is used as a reference electrode, and CO is used₂Gas saturated 0.1M KHCO₃For the electrolytes, Linear Sweep Voltammetric (LSV) and potentiostatic electrolysis tests were carried out, and the products were qualitatively and quantitatively analyzed by means of gas chromatography.

3. Test results and analysis:

LSV testing of the catalysts prepared in examples 1-5 is shown in FIG. 11, Fe₀-N-C composite electrocatalyst and Fe₁-N-C composite electrocatalysts exhibiting lower current densities, Fe obtained from the pyrolysis of bimetallic-centered precursors_y-N-C (y =0.2,0.5,0.8) material exhibits significantly improved current density and more positive onset potential, with Fe prepared in example 3_0.5the-N-C composite electrocatalyst has the highest current density.

Fe prepared in example 3_0.5the-N-C composite electrocatalyst has the highest selectivity for CO in a wider potential range. FIG. 12 is a graph of the faradaic efficiency of CO obtained by electrolysis of the composite electrocatalyst prepared in examples 1-5 at-1.2V vs. Ag/AgCl potential for 2 h, where Fe_0.5-N-C composite electrocatalyst with 93% FE_COFE of several other composite electrocatalysts_COAll are kept at about 80%.

Selection of Fe prepared in example 3_0.5The stability test was performed at-1.2V vs. Ag/AgCl potential for the example of-N-C composite electrocatalyst, and FIG. 13 shows that the current density reached plateau in a short time and remained for 12 h. Effect of electrolysis time on the Faraday efficiency of the product Fe at a potential of-1.2V is shown in the bar graph in FIG. 13_0.5FE of-N-C composite electrocatalyst_COThe maintenance is 90%, which shows that the composite electrocatalyst has good long-range stability.

Fe prepared as in example 3_0.5-N-C complexThe electrocatalysts were synthesized for example and tested for cyclability as shown in FIG. 14. The same electrode is electrolyzed circularly for 6 times and then FE is added_COOnly 6% reduction, showing excellent recyclability.

Claims (6)

1. For reducing CO₂The preparation method of the composite electrocatalyst is characterized by comprising the following steps:

1) mixing Fe-TCPP, Zn-TCPP and ZrCl₄Uniformly ultrasonically stirring benzoic acid, acetic acid and DMF (dimethyl formamide) to perform hydrothermal reaction till the end, cooling to room temperature, washing with DMF and acetone respectively, and centrifugally drying to obtain PCN-224 (Zn)_xFe_y) A precursor; x is 0.2-0.8, and y is 0.2-0.8;

2) mixing PCN-224 (Zn)_xFe_y) Placing the precursor in N₂Pyrolyzing at 1000 deg.C for 1 hr in atmosphere, and cleaning with HF to remove ZrO₂Then washing with deionized water and ethanol, centrifuging and drying to obtain Fe_y-an N-C composite electrocatalyst.

2. The method according to claim 1, wherein the mixing mass ratio of Fe-TCPP to Zn-TCPP is 0.8: 0.2 to 0.2: 0.8.

3. The method according to claim 2, wherein the mixing mass ratio of Fe-TCPP to Zn-TCPP is 0.5: 0.5, x is 0.5, and y is 0.5.

4. Fe obtained by the production method according to claim 1_y-use of an N-C composite electrocatalyst characterized in that: mixing Fe_ythe-N-C composite electrocatalyst is coated and modified on the surface of the carbon paper electrode and is used for reducing CO₂The working electrode of (1).

5. Use according to claim 4, characterized in that: mixing Fe_yMixing the-N-C composite electrocatalyst with Nafion, isopropanol and water to form a uniform slurry mixture, and coating the mixture on the surface of a carbon paper electrodeAnd then dried.

6. Use according to claim 4 or 5, characterized in that: said Fe_yThe loading amount of the-N-C composite electrocatalyst on the surface of the carbon paper electrode is 2.5 mg/cm²。

Images