CN109926084B - Oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs (metal-organic frameworks) and preparation method thereof - Google Patents
Oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs (metal-organic frameworks) and preparation method thereof Download PDFInfo
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Abstract
The invention discloses an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs and a preparation method thereof. The method comprehensively considers two important factors which influence the material performance, namely the distribution of active sites and a catalysis mechanism, so that the optimal Zn/Co/Fe ratio in a precursor is obtained through optimal design by taking the optimal catalytic oxygen reduction/oxygen evolution reaction efficiency of the material as a design principle, and the catalyst has the optimal catalytic performance. The invention can prepare the catalytic material which has high-efficiency oxygen reduction and oxygen evolution performances, high specific surface area, abundant micropores, uniform dispersion of reaction active sites and far lower cost than commercial noble metal catalysts.
Description
Technical Field
The invention belongs to the technical field of catalyst materials, and particularly relates to an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs and a preparation method thereof.
Background
In recent years, with the rapid development of electrochemical-electric energy conversion devices such as fuel cells, zinc-air cells, electrolyzed water and the like, people realize the conversion of energy with high efficiency, order, cleanness and no pollution. The Oxygen Reduction Reaction (ORR) and the Oxygen Evolution Reaction (OER) are part of the key reactions involved in this type of electrochemical-electrical energy conversion device. However, the kinetics of ORR and OER reactions are slow, which greatly reduces the energy conversion efficiency, and usually requires additional catalysts to accelerateAnd (3) carrying out the reaction. The commercial catalysts currently used are mainly Pt/C, RuO2And IrO2And the like, but the commercial application of the device is greatly limited by the rare resource, high price and poor stability of the noble metal. Therefore, the development of a high-efficiency and cheap non-noble metal catalyst is of great significance for promoting the commercial application of the electrochemical-electric energy conversion technology.
The MOFs-derived carbon-based non-noble metal material shows wide application potential in the fields of gas capture, catalysts, energy storage and the like by virtue of the advantages of various structures, high specific surface area, porosity and the like. In addition, the structure of the carbon-based non-noble metal material derived from the MOFs can be regulated and designed, more active sites can be exposed by the catalyst, the accessibility of reactants is enhanced, and rapid mass transfer and electron transfer are realized.
However, in practice, it has been found that the catalytic activity of the material is seriously impaired by the problems of uneven dispersion and easy loss of active sites in the catalyst. To solve these problems, researchers at home and abroad have made many studies. The BMZIF-derived porous carbon material combines the advantages of both ZIF-8 (large specific Surface Area) and ZIF-67 (uniformly distributed Co-N-C Active sites), and shows excellent ORR activity. Recently, Rowei team at Wuhan university is reported in the literature "Reduced Graphene Oxide-Wrapped Co9-xFexS8The method comprises the steps of carrying out a semi-vulcanization and high-temperature sintering treatment process on a ZIF-67 precursor to obtain Co coated with graphene9-xFexS8the/Co, Fe-N-C composite material has excellent ORR/OER dual-functional activity by skillfully concentrating ORR and OER double-active sites in one monomer, wherein the half-wave potential of the ORR is 0.84V, and the overpotential of the OER is 0.29V (at 10mA cm)-2At (c).
In recent years, MOFs-derived carbon-based non-noble metal catalytic materials have made breakthrough research progress and are expected to become powerful candidates for replacing traditional noble metal catalysts, but the problems of complex preparation process, unstable catalytic activity and the like still exist, and how to overcome the difficulties and obtain the continuous, efficient and cheap non-noble metal catalyst is a challenge to be faced by scientific researchers.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs and a preparation method thereof, wherein the material has the characteristics of high efficiency and low cost of catalytic oxygen reduction (ORR)/Oxygen Evolution (OER) reaction, so that the high-efficiency conversion of chemical energy-electric energy is realized.
In order to achieve the purpose, the invention adopts the technical scheme that:
the oxygen reduction/oxygen evolution bifunctional catalytic material based on multi-metal MOFs derivation comprises a carbon-nitrogen matrix, and is formed by sintering a vulcanized precursor, wherein elements in the precursor are Zn, Co and Fe, the molar ratio of Zn to Co is 0.1-10, the molar ratio of Co to Fe is 10-100, and the molar ratio of S to the sum of Zn, Co and Fe in the precursor is 0.5-2.
The invention also provides a preparation method of the oxygen reduction/oxygen evolution bifunctional catalytic material derived based on the multi-metal MOFs, which comprises the following steps:
(1) uniformly mixing zinc salt, cobalt salt, ferric salt and 2-methylimidazole, and putting the mixture into a methanol solution for coprecipitation reaction;
(2) centrifugally cleaning the reaction precipitate obtained in the step (1) by using water and absolute ethyl alcohol, and drying to obtain precursor powder;
(3) putting the precursor powder into an absolute ethyl alcohol solution, uniformly stirring, adding a vulcanizing agent, stirring and heating to carry out a vulcanization reaction;
(4) centrifugally cleaning the vulcanized reactant in the step (3) by using water and absolute ethyl alcohol, and drying to obtain vulcanized powder;
(5) placing the vulcanized powder in a high-temperature tube furnace, and sintering and heat-treating under the protection of inert gas;
(6) and (3) soaking the heat-treated material in HCL solution, removing redundant metal to obtain the final composite material, namely the oxygen reduction/oxygen evolution dual-functional catalytic material derived based on the multi-metal MOFs.
The zinc salt, the cobalt salt and the iron salt are all nitrate or sulfate, and the vulcanizing agent is thioacetamide, sodium sulfide or thiourea.
The reaction time of the coprecipitation reaction in the step (1) is 20-24 hours.
In the step (2) and the step (4), centrifugal cleaning is carried out for three times, the rotating speed of a centrifugal machine is 9000r/min, and drying conditions are that drying is carried out for 24 hours at 60 ℃ in a vacuum drying oven.
The temperature of the sulfurization reaction in the step (3) is 85-90 ℃, and the reaction time is 1 hour.
In the step (5), the sintering temperature is 700-1200 ℃, the time is 3 hours, and the protective gas is argon or nitrogen.
The soaking time in the step (6) is 12-24 hours.
The molar ratio of the total amount of the zinc salt, the cobalt salt and the ferric salt to the 2-methylimidazole is 1:4, the mass ratio of the precursor powder to the vulcanizing agent is 1: 2.
the molar ratio of Zn to Co in the precursor powder is 0.1-10, the molar ratio of Co to Fe is 10-100, and the molar ratio of S to the sum of Zn, Co and Fe in the vulcanized reactant is 0.5-2.
PVP powder with a K value of 90 is also added in the step (1).
Compared with the prior art, the preparation method of the oxygen reduction/oxygen evolution bifunctional catalytic material based on the derivative of the multi-metal MOFs (metal organic framework) firstly synthesizes a Zn/Co/Fe multi-metal ZIF precursor by a room temperature coprecipitation method, and secondly synthesizes an ORR active site (Co/Fe-N-C) and an Oxygen Evolution Reaction (OER) active site (Co/Fe-S) on a single material by a vulcanization and sintering treatment process, thereby obtaining the bifunctional oxygen reduction (ORR)/Oxygen Evolution (OER) electrocatalyst with low cost and performance comparable to that of a commercial catalyst. Most of Zn added in the precursor is volatilized to leave vacancies after subsequent sintering treatment, and the vacancies can effectively avoid the agglomeration of Co-N-C active sites, so that the Co-N-C active sites are dispersed more uniformly. The method comprehensively considers two important factors which influence the material performance, namely the distribution of active sites and a catalytic mechanism, takes the optimal catalytic oxygen reduction/oxygen evolution reaction efficiency of the material as a design principle, and further researches the molar ratio of Zn, Co and Fe to obtain the optimal structure (the specific surface area and the porosity of the material can be enhanced) and the high-efficiency catalytic performance matched with the optimal structure. In addition, under the synergistic effect of Zn-Co-Fe, many irregular carbon nanotubes are derived from the surface of the carbon body of the material, and the carbon nanotubes and the metal sulfide on the surface can provide abundant mesopores, increase the specific surface area of the material, and effectively promote the adsorption and desorption of oxygen and the transfer of electrons in the catalysis process. The catalytic material obtained by the method has large specific surface area and high porosity, shows high-efficiency oxygen reduction (ORR)/Oxygen Evolution (OER) dual-functional catalytic activity, has far better cost and stability than commercial noble metal catalysts, and has great application prospects in the fields of electro-catalysis and energy conversion.
The invention can prepare the catalytic material which has high-efficiency oxygen reduction and oxygen evolution performances, high specific surface area, abundant micropores, uniform dispersion of reaction active sites and far lower cost than commercial noble metal catalysts.
Drawings
FIG. 1 is a schematic diagram of the preparation process of the catalyst of the present invention.
FIG. 2 is a schematic diagram of a typical MS-Co/Fe @ NC-3:2-900 catalyst and its precursor microstructure in the present invention, wherein (a) is the appearance of the precursor corresponding to MS-Co/Fe @ NC-3: 2-900; (b) is a schematic diagram of the appearance of the precursor after further vulcanization; (c) is a shape schematic diagram of a final catalyst MS-Co/Fe @ NC-3:2-900 obtained after vulcanization and high-temperature sintering; (d) is the complete shape of the MS-Co/Fe @ NC-3:2-900 catalyst under high multiplying power; (e) is the EDS analysis of elements existing in the MS-Co/Fe @ NC-3:2-900 catalyst, and sequentially comprises the following steps: C. n, O, S, Co, Zn and Fe.
FIG. 3 is a graph of oxygen reduction/evolution performance of the catalyst according to the present invention at different Zn/Co/Fe ratios, wherein (a) is the ORR curve of the catalyst at different Zn/Co/Fe ratios obtained in a 0.1M KOH solution under saturated oxygen; (b) the OER curves of the catalysts at different Zn/Co/Fe ratios obtained in 0.1M KOH solution under saturated oxygen are shown.
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the drawings and examples.
Example 1
As shown in FIG. 1, a preparation method of an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs comprises the following steps:
(1) preparing a precursor: first, 9.6mmol of Zn (NO) was weighed3)2·6H2O, 2.4mmol of Co (NO)3)2·6H2O and 0.24mmol of FeSO4·7H2The O mixture was dissolved in 125mL of methanol and stirred well to obtain solution A. Then, 48mmol of 2-methylimidazole was weighed out and dissolved in 45mL of methanol, and the solution B was obtained by stirring uniformly. And slowly pouring the solution A into the solution B, stirring the mixed solution at room temperature for 25min, and carrying out room-temperature coprecipitation reaction for 24 hours to obtain a precursor product. Finally, centrifugally cleaning the obtained product with absolute ethyl alcohol and deionized water for three times respectively, and placing the product in a vacuum drying oven for drying at 60 ℃ for 24 hours, and marking as Zn0.8Co0.2Fe0.02ZIF (Zn/Co/Fe molar ratio 4:1:0.1), i.e. precursor powder.
(2) And (3) vulcanization: first, 1g of the prepared precursor powder was weighed out and dissolved in 250mL of absolute ethanol to form solution C. Next, 0.5g of Na was weighed2S was dissolved in 50mL of absolute ethanol to form solution D. Then, the two were mixed well, heated to 85 ℃ and stirred for 30 min. And finally, centrifugally cleaning the obtained precipitate with absolute ethyl alcohol and deionized water for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 24 hours for later use.
(3) And (3) sintering: weighing a proper amount of the vulcanized product, placing the vulcanized product in a tube furnace, and keeping the temperature of 900 ℃ for 3 hours under the protection of nitrogen to obtain a sintered product.
(4) Acid washing: and (3) soaking the sintered product in 0.1M HCL for 6 hours, removing unreacted metal, centrifugally cleaning the product three times by using deionized water, and drying the product for 24 hours at 60 ℃ in a vacuum drying oven to obtain a final sample, wherein the final sample is recorded as: MS-Co/Fe @ NC-4: 1-900.
And (3) measuring results: the specific surface area of the catalyst is 389.32m2(ii)/g, ORR onset potential 0.994V, half-wave potential 0.865V, already surpassing commercial 20% Pt/C; at a current density of 10mA/cm2There is a lower OER over-potential (0.48V) with performance approaching that of commercial IrO2Catalyst (0.41V), see figure 3 and table 1 for details.
Example 2
As shown in FIG. 1, a preparation method of an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs comprises the following steps:
(1) preparing a precursor: first, 7.2mmol of Zn (NO) was weighed3)2·6H2O, 4.8mmol of Co (NO)3)2·6H2O and 0.48mmol of FeSO4·7H2The O mixture was dissolved in 125mL of methanol and stirred well to obtain solution A. Then, 48mmol of 2-methylimidazole was weighed out and dissolved in 45mL of methanol, and the solution B was obtained by stirring uniformly. And slowly pouring the solution A into the solution B, stirring the mixed solution at room temperature for 25min, and carrying out room-temperature coprecipitation reaction for 24 hours to obtain a precursor product. Finally, centrifugally cleaning the obtained product with absolute ethyl alcohol and deionized water for three times respectively, and placing the product in a vacuum drying oven for drying at 60 ℃ for 24 hours, and marking as Zn0.6Co0.4Fe0.04ZIF (Zn/Co/Fe molar ratio 3:2:0.2), i.e. precursor powder.
(2) And (3) vulcanization: first, 1g of the prepared precursor was weighed and dissolved in 250mL of absolute ethanol to form solution C. Next, 0.5g of Na was weighed2S was dissolved in 50mL of absolute ethanol to form solution D. Then, the two were mixed well, heated to 85 ℃ and stirred for 30 min. And finally, centrifugally cleaning the obtained precipitate with absolute ethyl alcohol and deionized water for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 24 hours for later use.
(3) And (3) sintering: weighing a proper amount of the vulcanized product, placing the vulcanized product in a tube furnace, and keeping the temperature of 900 ℃ for 3 hours under the protection of nitrogen to obtain a sintered product.
(4) Acid washing: and (3) soaking the sintered product in 0.1M HCL for 6 hours, removing unreacted metal, centrifugally cleaning the product three times by using deionized water, and drying the product for 24 hours at 60 ℃ in a vacuum drying oven to obtain a final sample, wherein the final sample is recorded as: MS-Co/Fe @ NC-3: 2-900. Referring to fig. 2, the morphology of the precursor is shown in fig. 2(a), the morphology of the precursor after further sulfidation is shown in fig. 2(b), the morphology of the final catalyst MS-Co/Fe @ NC-3:2-900 after sulfidation and high-temperature sintering is shown in fig. 2(c), fig. 2(d) is the complete morphology at high rate, and EDS analysis is performed on the elements present therein, as shown in fig. 2(d), in sequence: C. n, O, S, Co, Zn and Fe.
And (3) measuring results: the specific surface area of the catalyst is 395.02m2(ii)/g, ORR onset potential 1.004V, half-wave potential 0.874V, already surpassing commercial 20% Pt/C; at a current density of 10mA/cm2There is a lower OER over-potential (0.41V) which is comparable to commercial IrO2Catalyst (0.41V), see figure 3 and table 1 for details.
Example 3
As shown in FIG. 1, a preparation method of an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs comprises the following steps:
(1) preparing a precursor: first, 6.0mmol of Zn (NO) was weighed3)2·6H2O, 6.0mmol of Co (NO)3)2·6H2O and 0.6mmol of FeSO4·7H2The O mixture was dissolved in 125mL of methanol and stirred well to obtain solution A. Then, 48mmol of 2-methylimidazole was weighed out and dissolved in 45mL of methanol, and the solution B was obtained by stirring uniformly. And slowly pouring the solution A into the solution B, stirring the mixed solution at room temperature for 25min, and carrying out room-temperature coprecipitation reaction for 24 hours to obtain a precursor product. Finally, centrifugally cleaning the obtained product with absolute ethyl alcohol and deionized water for three times respectively, and placing the product in a vacuum drying oven for drying at 60 ℃ for 24 hours, and marking as Zn0.5Co0.5Fe0.05ZIF (Zn/Co/Fe molar ratio 1:1:0.1), i.e. precursor powder.
(2) And (3) vulcanization: first, 1g of the prepared precursor was weighed and dissolved in 250mL of absolute ethanol to form solution C. Next, 0.5g of Na was weighed2S was dissolved in 50mL of absolute ethanol to form solution D. Then, mixing the twoHomogenizing, heating to 85 deg.C and stirring for 30 min. And finally, centrifugally cleaning the obtained precipitate with absolute ethyl alcohol and deionized water for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 24 hours for later use.
(3) And (3) sintering: weighing a proper amount of the vulcanized product, placing the vulcanized product in a tube furnace, and keeping the temperature of 900 ℃ for 3 hours under the protection of nitrogen to obtain a sintered product.
(4) Acid washing: and (3) soaking the sintered product in 0.1M HCL for 6 hours, removing unreacted metal, centrifugally cleaning the product three times by using deionized water, and drying the product for 24 hours at 60 ℃ in a vacuum drying oven to obtain a final sample, wherein the final sample is recorded as: MS-Co/Fe @ NC-1: 1-900.
And (3) measuring results: the specific surface area of the catalyst is 381.63m2(ii)/g, ORR onset potential 1.001V, half-wave potential 0.856V, near commercial 20% Pt/C; at a current density of 10mA/cm2The OER overpotential is 0.52V, and the performance is slightly inferior to that of commercial IrO2Catalyst (0.41V), see figure 3 and table 1 for details.
Example 4
As shown in FIG. 1, a preparation method of an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs comprises the following steps:
(1) preparing a precursor: first, 2.4mmol of Zn (NO) was weighed3)2·6H2O, 9.6mmol of Co (NO)3)2·6H2O and 0.96mmol of FeSO4·7H2The O mixture was dissolved in 125mL of methanol and stirred well to obtain solution A. Then, 48mmol of 2-methylimidazole was weighed out and dissolved in 45mL of methanol, and the solution B was obtained by stirring uniformly. And slowly pouring the solution A into the solution B, stirring the mixed solution at room temperature for 25min, and carrying out room-temperature coprecipitation reaction for 24 hours to obtain a precursor product. Finally, centrifugally cleaning the obtained product with absolute ethyl alcohol and deionized water for three times respectively, and placing the product in a vacuum drying oven for drying at 60 ℃ for 24 hours, and marking as Zn0.2Co0.8Fe0.08ZIF (Zn/Co/Fe molar ratio 1:4:0.4), i.e. precursor powder.
(2) And (3) vulcanization: first, 1g of the prepared precursor was weighed and dissolved in 250mL of absolute ethanol to form solution C. It is composed of0.5g of Na was weighed out2S was dissolved in 50mL of absolute ethanol to form solution D. Then, the two were mixed well, heated to 85 ℃ and stirred for 30 min. And finally, centrifugally cleaning the obtained precipitate with absolute ethyl alcohol and deionized water for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 24 hours for later use.
(3) And (3) sintering: weighing a proper amount of the vulcanized product, placing the vulcanized product in a tube furnace, and keeping the temperature of 900 ℃ for 3 hours under the protection of nitrogen to obtain a sintered product.
(4) Acid washing: and (3) soaking the sintered product in 0.1M HCL for 6 hours, removing unreacted metal, centrifugally cleaning the product three times by using deionized water, and drying the product for 24 hours at 60 ℃ in a vacuum drying oven to obtain a final sample, wherein the final sample is recorded as: MS-Co/Fe @ NC-1: 4-900.
And (3) measuring results: the specific surface area of the catalyst is 347.64m2(ii)/g, ORR onset potential 1.02V, half-wave potential 0.841V, near commercial 20% Pt/C; at a current density of 10mA/cm2The OER overpotential is 0.52V, and the performance is slightly inferior to that of commercial IrO2Catalyst (0.41V), see figure 3 and table 1 for details.
Example 5
As shown in FIG. 1, a preparation method of an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs comprises the following steps:
(1) preparing a precursor: first, 12mmol of Co (NO) was weighed3)2·6H2O and 1.2mmol of FeSO4·7H2The O mixture was dissolved in 125mL of methanol and stirred well to obtain solution A. Then, 48mmol of 2-methylimidazole was weighed out and dissolved in 45mL of methanol, and the solution B was obtained by stirring uniformly. And slowly pouring the solution A into the solution B, stirring the mixed solution at room temperature for 25min, and carrying out room-temperature coprecipitation reaction for 24 hours to obtain a precursor product. And finally, centrifugally cleaning the obtained product by using absolute ethyl alcohol and deionized water for three times, placing the product in a vacuum drying oven for drying at 60 ℃ for 24 hours, and marking the product as CoFe-ZIF (prepared by single ZIF-67, free of Zn and with the Co/Fe molar ratio of 1:0.1), namely precursor powder.
(2) And (3) vulcanization: firstly, 1g of prepared precursor is weighed and dissolved in 250mL of absolute ethyl alcohol,forming solution C. Next, 0.5g of Na was weighed2S was dissolved in 50mL of absolute ethanol to form solution D. Then, the two were mixed well, heated to 85 ℃ and stirred for 30 min. And finally, centrifugally cleaning the obtained precipitate with absolute ethyl alcohol and deionized water for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 24 hours for later use.
(3) And (3) sintering: weighing a proper amount of the vulcanized product, placing the vulcanized product in a tube furnace, and keeping the temperature of 900 ℃ for 3 hours under the protection of nitrogen to obtain a sintered product.
(4) Acid washing: and (3) soaking the sintered product in 0.1M HCL for 6 hours, removing unreacted metal, centrifugally cleaning the product three times by using deionized water, and drying the product for 24 hours at 60 ℃ in a vacuum drying oven to obtain a final sample, wherein the final sample is recorded as: MS-Co/Fe @ NC-0-900.
And (3) measuring results: the specific surface area of the catalyst is 136.97m2The ORR initial potential is 0.882V, the half-wave potential is 0.79V, which is far lower than the commercial 20% Pt/C; at a current density of 10mA/cm2The OER over potential is 0.61V, and the performance is obviously lower than that of commercial IrO2Catalyst (0.41V), see table 1 for details.
Example 6
As shown in FIG. 1, a preparation method of an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs comprises the following steps:
(1) preparing a precursor: first, 7.2mmol of Zn (NO) was weighed3)2·6H2O and 4.8mmol of Co (NO)3)2·6H2The O mixture was dissolved in 125mL of methanol and stirred well to obtain solution A. Then, 48mmol of 2-methylimidazole was weighed out and dissolved in 45mL of methanol, and the solution B was obtained by stirring uniformly. And slowly pouring the solution A into the solution B, stirring the mixed solution at room temperature for 25min, and carrying out room-temperature coprecipitation reaction for 24 hours to obtain a precursor product. Finally, centrifugally cleaning the obtained product with absolute ethyl alcohol and deionized water for three times respectively, and placing the product in a vacuum drying oven for drying at 60 ℃ for 24 hours, and marking as Zn0.6Co0.4ZIF (Zn/Co molar ratio of 3:2, Fe free), i.e. precursor powder.
(2) And (3) vulcanization: first, 1g of the preparedThe precursor was dissolved in 250mL of absolute ethanol to form solution C. Next, 0.5g of Na was weighed2S was dissolved in 50mL of absolute ethanol to form solution D. Then, the two were mixed well, heated to 85 ℃ and stirred for 30 min. And finally, centrifugally cleaning the obtained precipitate with absolute ethyl alcohol and deionized water for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 24 hours for later use.
(3) And (3) sintering: weighing a proper amount of the vulcanized product, placing the vulcanized product in a tube furnace, and keeping the temperature of 900 ℃ for 3 hours under the protection of nitrogen to obtain a sintered product.
(4) Acid washing: and (3) soaking the sintered product in 0.1M HCL for 6 hours, removing unreacted metal, centrifugally cleaning the product three times by using deionized water, and drying the product for 24 hours at 60 ℃ in a vacuum drying oven to obtain a final sample, wherein the final sample is recorded as: MS-Co @ NC-3: 2-900.
And (3) measuring results: the specific surface area of the catalyst is 385.44m2The ORR initial potential is 0.998V, the half-wave potential is 0.864V, and the ORR initial potential is close to the commercial 20% Pt/C; at a current density of 10mA/cm2There is a lower OER over-potential (0.46V) which is lower than commercial IrO2Catalyst (0.41V), see table 1 for details.
Example 7
As shown in FIG. 1, a preparation method of an oxygen reduction/oxygen evolution bifunctional catalytic material derived based on multi-metal MOFs comprises the following steps:
(1) preparing a precursor: first, 7.2mmol of Zn (NO) was weighed3)2·6H2O, 4.8mmol of Co (NO)3)2·6H2O and 0.48mmol of FeSO4·7H2The O mixture was dissolved in 125mL of methanol and stirred well to obtain solution A. Then, 48mmol of 2-methylimidazole was weighed out and dissolved in 45mL of methanol, and the solution B was obtained by stirring uniformly. And slowly pouring the solution A into the solution B, stirring the mixed solution at room temperature for 25min, and carrying out room-temperature coprecipitation reaction for 24 hours to obtain a precursor product. Finally, centrifugally cleaning the obtained product with absolute ethyl alcohol and deionized water for three times respectively, and placing the product in a vacuum drying oven for drying at 60 ℃ for 24 hours, and marking as Zn0.6Co0.4Fe0.04ZIF (Zn/Co/Fe mol)The ratio is 3:2:0.2), i.e. precursor powder.
(2) And (3) vulcanization: first, 1g of the prepared precursor was weighed and dissolved in 250mL of absolute ethanol to form solution C. Next, 0.5g of Na was weighed2S was dissolved in 50mL of absolute ethanol to form solution D. Then, the two were mixed well, heated to 85 ℃ and stirred for 30 min. And finally, centrifugally cleaning the obtained precipitate with absolute ethyl alcohol and deionized water for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 24 hours for later use.
(3) And (3) sintering: and (3) placing a proper amount of the vulcanized product in a tube furnace, and respectively keeping the vulcanized product at 700 ℃, 800 ℃, 1000 ℃ and 1100 ℃ for 3 hours under the protection of nitrogen to obtain a sintered product.
4) Acid washing: and (3) sequentially placing the sintered product in 0.1M HCL for soaking for 6 hours, removing unreacted metal, centrifugally cleaning the product for three times by using deionized water, placing the product in a vacuum drying oven for drying for 24 hours at the temperature of 60 ℃, and obtaining a final sample, wherein the final sample is sequentially recorded as: MS-Co/Fe @ NC-3:2-700, MS-Co/Fe @ NC-3:2-800, MS-Co/Fe @ NC-3:2-1000, and MS-Co/Fe @ NC-3: 2-1100.
The measurement results show that: the temperature is low, Zn in the material can exist in a large amount and cover active sites, the original structure of the MOFs can be damaged due to the overhigh temperature, the structure of the material is changed, and the active sites are lost in a large amount. The optimum temperature is 900 ℃ and the corresponding catalytic activity is also optimum, as detailed in table 1.
TABLE 1 oxygen reduction/evolution Performance of different types of catalysts
(Note: all the above catalysts OER overpotentials were at a current density of 10mA cm-2Measured here)
The measurement methods are all electrochemical general methods, and the measurement conditions can adopt: oxygen reduction (ORR) and Oxygen Evolution (OER) catalytic performance tests were conducted in 0.1M KOH solution under saturated oxygen,adopting a standard three-electrode system (platinum wire is a counter electrode, silver/silver chloride is a reference electrode, 5mmGC is a working electrode), the LSV sweep rate is 5mV s-1。
Referring to FIG. 3, it can be seen from FIG. 3(a) ORR plots of the catalysts at different Zn/Co/Fe ratios in 0.1M KOH solution under saturated oxygen: of the five catalysts comprising commercial platinum carbon, the catalyst MS-Co/Fe @ NC-3:2-900 exhibited an optimum ORR performance at a half-wave potential of 0.874V, even exceeding that of the commercial 20% Pt/C catalyst (0.86V), when the Zn/Co/Fe molar ratio was 3:2: 0.2.
From FIG. 3(b) OER plots of the catalysts at different Zn/Co/Fe ratios obtained in 0.1M KOH solution under saturated oxygen: of the six catalysts comprising commercial iridium dioxide and platinum carbon, catalyst MS-Co/Fe @ NC-3:2-900 exhibited an optimum OER performance, i.e., at a current density of 10mA cm-2At an overpotential of 0.41V, very close to that of a commercial iridium dioxide catalyst (current density of 10mA cm)-2At an overpotential of 0.41V).
Claims (10)
1. The preparation method of the oxygen reduction/oxygen evolution bifunctional catalytic material based on multi-metal MOFs derivation comprises a carbon-nitrogen matrix and is formed by sintering a vulcanized precursor, and is characterized by comprising the following steps:
(1) uniformly mixing zinc salt, cobalt salt, ferric salt and 2-methylimidazole, and putting the mixture into a methanol solution for coprecipitation reaction;
(2) centrifugally cleaning the reaction precipitate obtained in the step (1) by using water and absolute ethyl alcohol, and drying to obtain precursor powder, wherein elements in the precursor are Zn, Co and Fe, the molar ratio of Zn to Co is 0.1-10, the molar ratio of Co to Fe is 10-100, and the molar ratio of S to the sum of Zn, Co and Fe in the precursor is 0.5-2;
(3) putting the precursor powder into an absolute ethyl alcohol solution, uniformly stirring, adding a vulcanizing agent, stirring and heating to carry out a vulcanization reaction;
(4) centrifugally cleaning the vulcanized reactant in the step (3) by using water and absolute ethyl alcohol, and drying to obtain vulcanized powder;
(5) placing the vulcanized powder in a high-temperature tube furnace, and sintering and heat-treating under the protection of inert gas;
(6) and (3) soaking the heat-treated material in HCL solution, removing redundant metal to obtain the final composite material, namely the oxygen reduction/oxygen evolution dual-functional catalytic material derived based on the multi-metal MOFs.
2. The preparation method of the oxygen reduction/oxygen evolution bifunctional catalytic material derived from multi-metal MOFs according to claim 1, wherein the zinc salt, cobalt salt and iron salt are all nitrates or sulfates, and the vulcanizing agent is thioacetamide, sodium sulfide or thiourea.
3. The preparation method of the oxygen reduction/oxygen evolution bifunctional catalytic material derived from the polymetallic MOFs according to claim 1, wherein the reaction time of the coprecipitation reaction in the step (1) is 20-24 hours, the temperature of the sulfurization reaction in the step (3) is 85-90 ℃, and the reaction time is 1 hour.
4. The preparation method of the oxygen reduction/oxygen evolution bifunctional catalytic material derived from the polymetallic MOFs according to claim 1, wherein in the step (2) and the step (4), centrifugal cleaning is performed for three times, the rotating speed of a centrifugal machine is 9000r/min, and drying is performed for 24 hours at 60 ℃ in a vacuum drying oven.
5. The preparation method of the oxygen reduction/oxygen evolution bifunctional catalytic material derived from the polymetallic MOFs according to claim 1, wherein the sintering temperature in the step (5) is 700-1200 ℃, the sintering time is 3 hours, and the protective gas is argon or nitrogen.
6. The process for preparing an oxygen reduction/evolution bifunctional catalytic material derived from multimetallic MOFs according to claim 1, wherein the soaking time in step (6) is 12-24 hours.
7. The process for the preparation of the oxygen reduction/evolution bifunctional catalytic material derived from multimetallic MOFs according to claim 1, wherein the molar ratio of the total amount of said zinc salt, cobalt salt and iron salt to 2-methylimidazole is 1:4, the mass ratio of the precursor powder to the vulcanizing agent is 1: 2.
8. the preparation method of the oxygen reduction/oxygen evolution bifunctional catalytic material derived based on the multi-metal MOFs according to claim 1, wherein the molar ratio of Zn to Co in the precursor powder is 0.1-10, the molar ratio of Co to Fe is 10-100, and the molar ratio of S to the sum of Zn, Co and Fe in the vulcanized reactant is 0.5-2.
9. The method for preparing the oxygen reduction/evolution bifunctional catalytic material derived from polymetallic MOFs according to claim 1, wherein PVP powder with a K value of 90 is further added in the step (1).
10. The oxygen reduction/oxygen evolution bifunctional catalytic material derived from multimetallic MOFs prepared by the method for preparing oxygen reduction/oxygen evolution bifunctional catalytic material derived from multimetallic MOFs as claimed in claim 1.
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