Preparation method and application of self-catalytic growth Zn/Co-N-C carbon nanotube oxygen reduction catalyst
Technical Field
The invention belongs to the field of electrochemical energy, and particularly relates to a preparation method and application of an autocatalytically-grown Zn/Co-N-C carbon nanotube oxygen reduction catalyst.
Background
The excessive use of fossil fuels by contemporary society poses serious global pollution and energy crisis, and thus the search for a new generation of renewable clean energy is imminent. Fuel cells, particularly metal-air cells, are considered to be one of the most promising energy conversion devices due to their high energy density and energy conversion efficiency. The development bottleneck of the scale application of the fuel cell is that the kinetic rate of the cathode oxygen reduction reaction is slow, and a noble metal catalyst Pt and the like is usually needed to meet the requirement of large current output. The Pt-based catalyst has problems of high price, low storage capacity, poor cycle stability, etc., and thus there is a need to develop a novel low-Pt or non-Pt high-efficiency oxygen reduction catalyst to promote the development of fuel cells. Through research in recent years, non-noble metal catalysts have been found to be one of the most promising alternatives to Pt. Among them, transition metal-nitrogen-carbon (M-N-C) type catalysts are widely paid attention to by researchers today because of their abundant sources, low cost, and extremely strong electrochemical activity and corrosion resistance in ORR.
The porous carbon-based material derived from metal organic framework Materials (MOFs) has the characteristics of high specific surface, high porosity, high conductivity, high stability, corrosion resistance, adjustable structural function and the like, and has become one of the research hotspots in the field of heterogeneous catalysis at present. The zeolite imidazole ester framework material (ZIFs) is a typical material of MOFs and is an ideal precursor for synthesizing M-N-C catalysts. DFT theoretical calculation shows that due to the synergistic effect between graphitized N in nitrogen-doped carbon nanotubes (N-CNTs) and wrapped metal nanoparticles, the state density around the Fermi level of the nitrogen-doped carbon nanotubes (N-CNTs) is increased, so that the work function is reduced, and the ORR activity is further improved. In addition, due to the unique ultra-large theoretical surface area and the electrical characteristics of high conductivity of the graphene material, the graphene material becomes a preferred carrier for obtaining the high-efficiency energy storage material. Therefore, the MOFs-derived N-CNTs are combined with graphene to construct a three-dimensional carbonaceous polyhedron, so that the synthesis of the efficient ORR catalyst is facilitated. Based on the method, a simple and efficient one-pot synthesis method is designed to realize the construction of the three-dimensional carbonaceous polyhedron cross-linked carbon nanotube structure, and finally the self-catalytic growth Zn/Co-N-C carbon nanotube oxygen reduction catalyst is prepared.
Disclosure of Invention
The invention solves the technical problem of providing a preparation method of an autocatalytically grown Zn/Co-N-C carbon nano tube oxygen reduction catalyst, and firstly, the invention realizes the construction of a three-dimensional carbonaceous polyhedron cross-linked carbon nano tube structure by a simple, convenient and effective one-pot synthesis method. Secondly, the addition of a proper amount of graphene oxide in the preparation process of the invention is beneficial to forming a highly graphitized carbon skeleton, and the electronic conductivity of the target catalyst is improved. Thirdly, the formation of the carbon nano tube in the invention can not only prevent the polyhedron from agglomerating so as to expose more effective active sites, but also provide enough storage space and transportation path for electrolyte ions. Fourthly, the Zn/Co-N-C carbon nano tube oxygen reduction catalyst prepared by the invention can be used as an oxygen reduction catalyst material of a metal-air battery cathode.
The invention adopts the following technical scheme for solving the technical problems, and the preparation method of the self-catalytic growth Zn/Co-N-C carbon nano tube oxygen reduction catalyst is characterized by comprising the following specific processes:
step S1: uniformly dispersing 2-methylimidazole into a methanol solution to obtain a solution A, uniformly dispersing zinc nitrate hexahydrate, cobalt (III) acetylacetonate and graphene oxide into the methanol solution to obtain a solution B, pouring the solution B into the solution A, and stirring and mixing uniformly at normal temperature to obtain a material A;
step S2: centrifuging, washing with methanol and vacuum drying the material A to obtain a material B;
step S3: calcining the material B at high temperature under the protection of inert gas to obtain a material C;
step S4: and (3) soaking the material C in acid, washing for a plurality of times, and drying to obtain the target product Zn/Co-N-C carbon nano tube oxygen reduction catalyst D.
Preferably, the inert gas in step S2 is one or more of nitrogen or argon.
Preferably, the high-temperature calcination in step S3 is performed by first raising the temperature from room temperature to 300 ℃ for 60min through 55min in an inert gas atmosphere, then raising the temperature to 900 ℃ at a rate of 5 ℃/min for 180min, and then naturally cooling to room temperature.
Preferably, the acidic solution in step S4 is a 2M hydrochloric acid solution.
The preparation method of the autocatalytically grown Zn/Co-N-C carbon nanotube oxygen reduction catalyst is characterized by comprising the following specific steps of:
step S1: dispersing 6.5g of 2-methylimidazole into 100mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution A, dispersing 3g of zinc nitrate hexahydrate, 0.514g of cobalt (III) acetylacetonate and 0.2g of graphene oxide into 50mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution B, then quickly pouring the solution B into the solution A, and stirring at normal temperature for 24h to obtain a material A;
step S2: centrifuging the material A at 10000r/min, washing with methanol for three times, and vacuum drying at 80 ℃ for 6h to obtain a material B;
step S3: transferring the material B to a corundum boat, placing the corundum boat in a tube furnace, heating to 300 ℃ from room temperature for 55min in an inert gas atmosphere, keeping for 60min, heating to 900 ℃ at a heating rate of 5 ℃/min, keeping for 180min, and naturally cooling to room temperature to obtain a material C;
step S4: and transferring the material C into a hydrochloric acid solution with the concentration of 2M, soaking for 24h, washing with high-purity water to be neutral, and then placing in a vacuum drying oven to be dried for 12h at the temperature of 80 ℃ to obtain a target product Zn/Co-N-C carbon nano tube oxygen reduction catalyst D.
The invention relates to an application of an autocatalytically grown Zn/Co-N-C carbon nano tube oxygen reduction catalyst as a cathode oxygen reduction catalyst material of a metal-air battery.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the invention realizes the construction of the three-dimensional carbonaceous polyhedron crosslinked carbon nano tube by a simple, convenient and effective one-pot synthesis method, and the special structure can prevent the aggregation and reunion of carbon polyhedrons, is beneficial to the full exposure of active sites, and provides enough storage space and transportation path for electrolyte ions in the ORR process.
2. The addition of a proper amount of graphene oxide in the preparation process is beneficial to constructing a highly graphitized carbon skeleton, accelerating the transfer of electrons and further improving the performance of the oxygen reduction reaction.
3. The oxygen reduction catalyst for the autocatalytically grown Zn/Co-N-C carbon nano tube prepared by the invention is prepared in the alkaline (0.1M KOH) and acidic (0.5M H)2SO4) The electrolyte shows excellent oxygen reduction activity, cycling stability and methanol tolerance. The zinc-air battery cathode material has higher power density and good cycle stability when being applied to the cathode of a zinc-air battery, and provides a basis for the practical application of the zinc-air battery cathode material in the fields of electrochemical energy storage and conversion.
Drawings
FIG. 1 is a scanning electron micrograph of product D4 prepared according to example 4;
FIG. 2 is an X-ray diffraction pattern of products D1-D4 prepared in examples 1-4;
FIG. 3 is a graph showing the nitrogen adsorption and desorption curves of the products D1-D4 prepared in examples 1-4;
FIG. 4 is a Raman spectrum of products D1-D4 prepared in examples 1-4;
FIG. 5 is a full X-ray photoelectron spectroscopy spectrum of products D1-D4 prepared in examples 1-4;
FIG. 6 is a cyclic voltammogram of the products D1-D4 prepared in examples 1-4;
FIG. 7 is a polarization curve of products D1-D4 prepared in examples 1-4;
fig. 8 is a plot of the polarization curve versus the corresponding power density for product D4 prepared in example 4.
Detailed Description
The present invention is described in further detail below with reference to examples, but it should not be construed that the scope of the above subject matter of the present invention is limited to the following examples, and that all the technologies realized based on the above subject matter of the present invention belong to the scope of the present invention.
Example 1
Step S1: dispersing 6.5g of 2-methylimidazole in 100mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution A, dispersing 3g of zinc nitrate hexahydrate in 50mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution B, quickly pouring the solution B into the solution A, and stirring at normal temperature for 24h to obtain a material A1;
step S2: centrifuging the material A1 at 10000r/min, washing with methanol for three times, and vacuum drying at 80 deg.C for 6 hr to obtain material B1;
step S3: transferring the material B2 to a corundum boat, placing the corundum boat in a tube furnace, heating to 300 ℃ from room temperature for 55min in an inert gas atmosphere, keeping the temperature for 60min, heating to 900 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 180min, and naturally cooling to room temperature to obtain a material C1;
step S4: and transferring the material C1 to a hydrochloric acid solution with the concentration of 2M, soaking for 24h, washing with high-purity water to be neutral, and then placing in a vacuum drying oven to be dried for 12h at 80 ℃ to obtain a product D1.
Example 2
Step S1: dispersing 6.5g of 2-methylimidazole in 100mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution A, dispersing 3g of zinc nitrate hexahydrate and 0.2g of graphene oxide in 50mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution B, quickly pouring the solution B into the solution A, and stirring at normal temperature for 24h to obtain a material A2;
step S2: centrifuging the material A2 at 10000r/min, washing with methanol for three times, and vacuum drying at 80 deg.C for 6 hr to obtain material B2;
step S3: transferring the material B2 to a corundum boat, placing the corundum boat in a tube furnace, heating to 300 ℃ from room temperature for 55min in an inert gas atmosphere, keeping the temperature for 60min, heating to 900 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 180min, and naturally cooling to room temperature to obtain a material C2;
step S4: and transferring the material C2 to a hydrochloric acid solution with the concentration of 2M, soaking for 24h, washing with high-purity water to be neutral, and then placing in a vacuum drying oven to be dried for 12h at 80 ℃ to obtain a product D2.
Example 3
Step S1: dispersing 6.5g of 2-methylimidazole in 100mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution A, dispersing 3g of zinc nitrate hexahydrate and 0.514g of cobalt (III) acetylacetonate in 50mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution B, then quickly pouring the solution B into the solution A, and stirring at normal temperature for 24h to obtain a material A3;
step S2: centrifuging the material A3 at 10000r/min, washing with methanol for three times, and vacuum drying at 80 deg.C for 6 hr to obtain material B3;
step S3: transferring the material B3 to a corundum boat, placing the corundum boat in a tube furnace, heating to 300 ℃ from room temperature for 55min in an inert gas atmosphere, keeping the temperature for 60min, heating to 900 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 180min, and naturally cooling to room temperature to obtain a material C3;
step S4: and transferring the material C3 to a hydrochloric acid solution with the concentration of 2M, soaking for 24h, washing with high-purity water to be neutral, and then placing in a vacuum drying oven to be dried for 12h at 80 ℃ to obtain a product D3.
Example 4
Step S1: dispersing 6.5g of 2-methylimidazole into 100mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution A, dispersing 3g of zinc nitrate hexahydrate, 0.514g of cobalt (III) acetylacetonate and 0.2g of graphene oxide into 50mL of methanol, performing ultrasonic treatment for 5min to obtain a uniform solution B, then quickly pouring the solution B into the solution A, and stirring at normal temperature for 24h to obtain a material A4;
step S2: centrifuging the material A4 at 10000r/min, washing with methanol for three times, and vacuum drying at 80 deg.C for 6 hr to obtain material B4;
step S3: transferring the material B4 to a corundum boat, placing the corundum boat in a tube furnace, heating to 300 ℃ from room temperature for 55min in an inert gas atmosphere, keeping the temperature for 60min, heating to 900 ℃ at a heating rate of 5 ℃/min, keeping the temperature for 180min, and naturally cooling to room temperature to obtain a material C4;
step S4: and transferring the material C4 to a hydrochloric acid solution with the concentration of 2M, soaking for 24h, washing with high-purity water to be neutral, and then placing in a vacuum drying oven to be dried for 12h at 80 ℃ to obtain a product D4.
Example 5
Weighing a certain amount of the Zn/Co-N-C carbon nano tube oxygen reduction catalyst D4 product which is ground into powder and grows in an autocatalytic manner by using an electronic balance, uniformly mixing the product with 5wt% of Nafion and high-purity water, and carrying out ultrasonic treatment for several minutes to obtain a uniform ink-shaped dispersion liquid. And (3) using a liquid transfer gun to transfer a proper amount of the ultrasonically-good ink-shaped dispersion liquid to be dropped on the cleaned glassy carbon electrode, and then naturally airing at room temperature to prepare the working electrode. Working electrodes for the D1, D2, D3 products were prepared in the same manner, as were the D4 products for control. All electrochemical tests used a three-electrode system. During Linear Sweep Voltammetry (LSV) testing, glassy carbon is used as a working electrode (diameter is 5 mm), active substances (namely prepared ink-like dispersion liquid) with certain volume and certain concentration are coated on the surface of the working electrode, a mercuric oxide or calomel electrode is used as a reference electrode of alkaline electrolyte and an acid electrolyte respectively, and a platinum sheet (1 cm)2) As counter electrode, the electrolyte is N2/O2Saturated 0.1M KOH solution or 0.5M H2SO4Aqueous solution, the scanning speed during the test is 10mV s-1The rotation speed is 1600rpm, the scanning range is 0V to 1.2V: (vsRHE). In the Cyclic Voltammetry (CV) test, the reference electrode, counter electrode, electrolyte, and test conditions were the same as the above LSV conditions except that the working electrode was a glassy carbon electrode having a diameter of 3mm and coated with a certain volume and a certain concentration of an active material (the above prepared ink dispersion).
Example 6
The self-made zinc-air battery is adopted for performance test, and a Zn sheet is used as an anode to prepare the self-catalystChemically grown Zn/Co-N-C carbon nanotube oxygen reduction catalyst as cathode, 6M KOH and 0.2M Zn (OAc)2The mixed aqueous solution is used as an electrolyte. Generally, a certain amount of the Zn/Co-N-C carbon nano tube oxygen reduction catalyst D4 product which is ground into powder and grows by autocatalysis is weighed by an electronic balance, dispersed in a mixed solution comprising a certain amount of 5wt% Nafion solution, ethanol and 5wt% polytetrafluoroethylene suspension, and subjected to ultrasonic treatment for 1h to obtain a uniform ink-shaped solution. Then, the obtained uniform solution is dropped on the surface of carbon paper and naturally dried, and the catalyst load is ensured to be 2mg cm−2。
While the foregoing embodiments have described the principles, principal features and advantages of the invention, it will be understood by those skilled in the art that the invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, but is susceptible to various changes and modifications without departing from the scope thereof, which fall within the scope of the appended claims.