CN110808381B

CN110808381B - Composite catalyst for oxygen reduction reaction in alkaline medium and preparation method thereof

Info

Publication number: CN110808381B
Application number: CN201911118659.6A
Authority: CN
Inventors: 庄仲滨; 许志远; 朱威
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2019-11-15
Filing date: 2019-11-15
Publication date: 2021-07-16
Anticipated expiration: 2039-11-15
Also published as: CN110808381A

Abstract

The invention discloses a composite catalyst for oxygen reduction reaction in an alkaline medium and a synthesis method thereof. According to the invention, the novel oxygen reduction nano-catalyst is obtained by preparing the copper-silver-manganese ternary metal composite nano-particles, and the novel oxygen reduction nano-catalyst shows good catalytic performance in alkaline electrolyte.

Description

Composite catalyst for oxygen reduction reaction in alkaline medium and preparation method thereof

Technical Field

The invention belongs to the technical field of oxygen reduction electrocatalyst preparation, and particularly relates to a composite catalyst for oxygen reduction reaction in an alkaline medium and a preparation method thereof.

Background

The low-temperature hydrogen fuel cell is one of key technologies for transferring fossil energy to hydrogen energy. These batteries will provide a highly efficient power source for pollution-free vehicles to replace conventional internal combustion engines. However, the main reason for limiting commercialization is because current cell catalyst systems, particularly cathode oxygen reduction catalysts, rely heavily on the noble metal Pt, which results in high cost of the fuel cell system and cannot be reduced by economies of scale. The development of a cathode catalyst free of platinum group metals is very important for hydrogen-oxygen fuel cells. Since the dissolution and corrosion phenomena of non-noble metal catalysts in acidic environments are very severe in proton membrane exchange fuel cells, it is quite difficult to develop catalysts based on non-noble metals. In contrast, in a relatively benign alkaline environment, the hydroxide exchange membrane fuel cell may use more economical bipolar plates and inexpensive catalysts that are completely free of Pt group elements, which has attracted the interest of researchers. Due to the development of several excellent hydroxide exchange membranes, significant progress has been made in recent years in improving the performance and stability of alkaline membrane fuel cells.

Currently, Pt group element-free cathode oxygen reduction catalysts used in alkaline membrane fuel cells mainly include Ag-based catalysts, transition metal oxides, metal-aza-carbon materials, and the like. At present, the Ag-based catalyst is expected to replace Pt, and the device efficiency is far higher than that of other catalysts without Pt group elements. Considering that the cost of Ag-based catalysts is still not negligible (the price of silver is 1/50 for platinum), the size of the metal particles of Ag-based catalysts should also be guaranteed on the nanometer scale to ensure the utilization efficiency of Ag atoms, providing the best catalytic performance with the minimum amount of Ag used. However, as Ag particles are reduced in size to the nanometer scale, these nanoparticles tend to aggregate, primarily due to the lowering of the work function of the metal surface and the negative shift in the standard oxidation electrode potential of Ag as the particles reach the nanometer scale.

Disclosure of Invention

The invention aims to provide a novel composite catalyst for oxygen reduction reaction in an alkaline medium and a preparation method thereof, and solves the problems of low oxygen reduction electrocatalytic activity and low electrochemical stability of the existing silver-based nano catalyst.

The invention provides a composite catalyst for an oxygen reduction reaction in an alkaline medium, which comprises silver-manganese-copper ternary metal composite particles.

In some embodiments, the composite catalyst includes an outer layer based on silver and manganese and an inner core based on copper.

In some embodiments, the outer layer is comprised of silver manganese and the inner core is comprised of copper silver.

In some embodiments, the composite catalyst is a core-shell structure, the shell is distributed on at least part of the surface of the core, the core is mainly composed of copper, and the shell is mainly composed of silver and manganese.

In some embodiments, the atomic ratio of the silver element in the composite catalyst ranges from 23% to 75%, the atomic ratio of the manganese element ranges from 2% to 25%, and the atomic ratio of the copper element ranges from 23% to 75%.

In some embodiments, the composite catalyst has an average particle size in the range of 2 to 50 nm.

In some embodiments, the composite catalyst includes a support material and silver-manganese-copper ternary metal composite particles distributed on the surface of the support material.

In some embodiments, the support material comprises a one-, two-, or three-dimensional structure of a carbon material or a metal oxide material.

The invention also provides a synthetic method of the composite catalyst, which comprises the following steps: forming a first precursor solution comprising at least a copper source; forming a second precursor solution comprising at least a silver source and a manganese source; heating the first precursor solution to a first temperature, and maintaining the first temperature for a first reaction time to form a first reaction solution in which copper-containing nanoparticles are dispersed; adjusting the first reaction solution to a second temperature, adding the second precursor solution, and maintaining the second reaction time to form a second reaction solution in which the silver-manganese-copper ternary metal composite particles are dispersed; and separating and purifying the second reaction solution to obtain the composite catalyst.

In some embodiments, the first temperature ranges from 180 ℃ to 280 ℃ and the first reaction time ranges from 0.5 to 4 hours, and the second temperature ranges from 180 ℃ to 240 ℃ and the second reaction time ranges from 1 to 6 hours.

The invention combines copper, silver and manganese in a certain way to obtain a novel oxygen reduction nano catalyst. Compared with the traditional silver-based oxygen reduction catalyst, the novel composite catalyst provided by the invention has the advantages that the electrocatalytic performance and the electrochemical stability of the oxygen reduction reaction are obviously improved.

Drawings

FIG. 1 is an XRD pattern of Cu-Ag-Mn composite metal nanoparticles obtained in example 1 of the present invention;

FIG. 2 is a TEM image of the Cu-Ag-Mn composite metal nanoparticles of the present invention obtained from example 1;

FIG. 3 is a TEM image of silver-manganese-copper composite metal nanoparticles obtained from example 2 according to the present invention;

FIG. 4 is a TEM image of the carbon-supported copper-silver-manganese composite metal nanoparticles obtained in example 1;

FIG. 5 is a polarization curve of oxygen reduction test of the catalysts obtained in example 1, example 2 and comparative example 1;

FIG. 6 is an oxygen reduction accelerated aging test curve for the copper silver manganese on carbon composite catalyst of example 1;

FIG. 7 is an oxygen reduction accelerated aging test curve for the silver nanoparticle catalyst of comparative example 1;

FIG. 8 is a TEM image of the composite catalyst obtained in example 1 after 30K cycles of accelerated aging test;

FIG. 9 is a TEM image of the catalyst obtained in comparative example 1 after 5K cycles of accelerated aging test;

FIG. 10 is a high magnification TEM contrast of the composite catalyst of example 1 with elemental copper, elemental silver;

FIG. 11 is a STEM-EELS line scan of Cu @ Ag-Mn NPs of the catalysts from example 1 after accelerated aging test with inset showing the scanned nanoparticles.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

It is to be noted that, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The invention provides a composite catalyst for oxygen reduction reaction in an alkaline medium, which comprises silver-manganese-copper ternary metal composite particles. Preferably, the composite catalyst comprises an outer layer mainly containing silver and manganese and an inner core mainly containing copper. In some embodiments, the outer layer is comprised of silver manganese and the inner core is comprised of copper silver. The composite catalyst can also be in a core-shell structure, at least part of the surface of the core is distributed with a shell, the core takes copper as the main element, and the shell takes silver and manganese as the main element. In some embodiments, the composite catalyst of the present invention comprises an alloy of at least one of silver manganese, manganin, silver copper, silver manganin.

In some embodiments, the atomic ratio of the silver element in the composite catalyst ranges from 23% to 75%, the atomic ratio of the manganese element ranges from 2% to 25%, and the atomic ratio of the copper element ranges from 23% to 75%. In some preferred embodiments, the atomic proportion of the silver element in the composite catalyst ranges from 40% to 70%, the atomic proportion of the manganese element ranges from 5% to 15%, and the atomic proportion of the copper element ranges from 25% to 55%.

In some embodiments, the composite catalyst has an average particle size in the range of 2 to 50 nm. The preferable average particle size range is 5 to 20 nm. The particle size range of the composite catalyst in the invention is controlled by different synthesis conditions, and the particle size distribution of the composite catalyst synthesized under the same synthesis conditions or in the same batch is uniform, as shown in fig. 2 or fig. 3. In some embodiments, the composite catalyst synthesized under the same synthesis conditions or in the same batch has a proportion of particles within a range of 10% from the average particle diameter of 70% or more, preferably 80% or more.

In some embodiments, the composite catalyst includes a support material and silver-manganese-copper ternary metal composite particles distributed on the surface of the support material. The support material comprises a one-, two-or three-dimensional structure of a carbon material or a metal oxide material. In some embodiments, the support material is Vulcan XC-72, BP2000, acetylene black, carbon nanotubes, graphite, graphitized carbon, graphene, Al₂O₃And manganese oxide, or a mixture of two or more thereof.

The invention also provides a synthetic method of the composite catalyst, which comprises the following steps: forming a first precursor solution comprising at least a copper source; forming a second precursor solution comprising at least a silver source and a manganese source; heating the first precursor solution to a first temperature, and maintaining the first temperature for a first reaction time to form a first reaction solution in which copper-containing nanoparticles are dispersed; and adjusting the first reaction liquid to a second temperature, adding a second precursor solution, and maintaining the second reaction time to form a second reaction liquid in which the silver-manganese-copper ternary metal composite particles are dispersed. The first precursor solution, the second precursor solution, the first reaction liquid and the second reaction liquid are all formed in an oxygen-removing environment. Separating and purifying the second reaction solution, and loading the catalyst particles obtained by separation and purification on a carrier material to form the composite catalyst.

In some embodiments, a copper source is dissolved into a first solvent to form a first precursor solution; and dissolving the silver source and the manganese source into a second solvent to form a second precursor solution. Both the first solvent and the second solvent may be organic or aqueous phases. Preferably, the first solvent and the second solvent are amine-based organic phases. More preferably, the first solvent and the second solvent are amine-based organic reagents including an amino group and not less than 8 carbon atoms. In some embodiments, the first solvent and the second solvent are selected from the group consisting of oleylamine, dodecylamine, tetradecylamine, and like saturated or unsaturated amine reagents.

In some embodiments, the silver source includes, but is not limited to, one or more of silver nitrate, silver acetate, silver acetylacetonate, and silver trifluoroacetate. Manganese sources include, but are not limited to, one or more of manganese nitrate, manganese carbonyl, potassium permanganate. Copper sources include, but are not limited to, one or more of copper acetylacetonate, copper sulfate, copper nitrate, copper acetate, cuprous acetate.

In some embodiments, the silver-manganese-copper composite catalyst is synthesized by the following steps:

A) adding copper acetylacetonate as copper source into a certain quantity of oleylamine in N₂Under protection, heating oleylamine to 180-280 deg.C, and keepingAfter 0.5-2 hours, cooling to 180-240 ℃, injecting oleylamine in which a certain amount of silver nitrate and manganese nitrate are dissolved in advance into a reaction system, and keeping the temperature at 180-240 ℃ for 1-6 hours to obtain the copper-silver-manganese core-shell metal nanoparticles with the particle size of 2-50 nm.

B) The prepared metal nanoparticles are mixed with a certain amount (volume ratio 1: 1) dispersing isopropanol and ethanol, repeating centrifugal separation for 2 times, and dispersing in cyclohexane;

C) and (2) dropwise adding the metal nanoparticles dispersed in the cyclohexane into the cyclohexane in which a certain amount of activated carbon powder is dissolved, stirring to load the metal nanoparticles on the activated carbon, then carrying out suction filtration and washing by using absolute ethyl alcohol, and drying to obtain the corresponding carbon-supported metal catalyst.

Qualitative analysis was performed on the prepared product using Shimadu XRD-6000 type powder X-ray diffractometer, qualitative analysis was performed on the prepared product using Thermo-Fisher ICPS-6300 type inductively coupled plasma emission spectrometer, sample morphology analysis was performed using JEM-2100 type transmission electron microscope, and rotating disk test was performed on the corresponding electrocatalyst using CHI760E electrochemical workstation.

The following is further illustrated with reference to specific examples.

Example 1

A preparation method of a silver-manganese-copper composite catalyst comprises the following steps:

1. 170mg of copper acetylacetonate were added to 10ml of oleylamine and N was passed through the mixture at room temperature₂And removing dissolved oxygen in oleylamine for 30 min. Then, oleylamine was heated to 220 ℃ and held for 2 hours, then, cooled to 200 ℃ and 2ml of oleylamine in which 110mg of silver nitrate and 20. mu.l of a 50% manganese nitrate solution were dissolved in advance was injected into the reaction system and held at 200 ℃ for 4 hours. The system was kept under stirring and under inert gas blanket throughout the reaction.

2. 30ml (volume ratio 1: 1) of isopropanol and ethanol are added into the oleylamine after the reaction is finished, and centrifugal separation is carried out at 10000rpm for 3 min. The supernatant was decanted and the pellet redispersed in 30ml (1: 1 by volume) of isopropanol and ethanol and the centrifugation process repeated once. The precipitate obtained is redispersed in 30ml of cyclohexane.

3. 150mg of activated carbon powder (Volcan XC-72) was added to 150ml of cyclohexane and ultrasonically dispersed for 30 min. And (3) dropwise adding the nano particles prepared in the step (2) into cyclohexane in which activated carbon powder is dispersed, and stirring for 5 hours to load the metal nano particles on the activated carbon. And then, carrying out suction filtration and washing by using absolute ethyl alcohol, and standing and drying in an oven at the temperature of 60 ℃ to obtain the carbon-supported copper-silver-manganese composite metal nanoparticle catalyst which is marked as Cu @ Ag-Mn-1.

And (3) taking 2mg of the carbon-supported copper-silver-manganese composite metal nanoparticle catalyst prepared in the step (3) and 10 mu l of 5 wt% Nafion solution, adding into a mixed solvent of 790 mu l of absolute ethyl alcohol and 200 mu l of deionized water, and carrying out ultrasonic dispersion for 2 hours. And obtaining the uniformly dispersed carbon-supported silver-manganese catalyst ink.

20 μ l of the ink was applied in portions (5 μ l each, 4 times) to a glassy carbon electrode, and then the oxygen reduction activity was measured by rotating a disk electrode. The electrolyte was 0.1M oxygen saturated KOH solution and the rotating disk was rotated at 1600 rpm.

Through the characterization, the XRD pattern of the carbon-supported copper-silver-manganese composite catalyst in figure 1 shows that the copper-silver-manganese composite catalyst mainly shows the structure of CuAg alloy. The characteristic diffraction peak positions of silver are shifted to different degrees, because the interplanar spacing of the silver is changed to a certain degree after the Cu atoms enter. From the ICP-ACE results, the actual atomic ratios of copper, silver and manganese were found to be 53 at%, 40 at% and 7 at%, respectively. From the TEM images of the silver-manganese nanoparticles in fig. 2 and the carbon-supported copper-silver-manganese catalyst in fig. 4, it can be seen that the particle size of the copper-silver-manganese nanoparticles is about 13nm and is uniformly distributed on the surface of the carbon carrier.

As can be seen from fig. 10, the composite catalyst of example 1 basically has an outer layer and an inner core structure, the outer layer is mainly composed of silver and manganese elements, and the inner core is mainly composed of copper elements.

Example 2

with 10ml of trioctylamine as solvent, 123mg of cuprous acetate and 139mg of n-tetradecylphosphonic acid are added, and the solution is stirred under inert gas and heated to 105 ℃ to ensure that all solids are dissolved. Then rapidly heated to 180 c and held at this temperature for 30 minutes. The reaction mixture was then heated to 270 ℃ and held at this temperature for a further 30 minutes. Thereafter, the temperature was lowered to 200 ℃ and 2ml oleylamine in which 110mg of silver nitrate and 20. mu.l of a 50% manganese nitrate solution were dissolved in advance was injected into the reaction system, and the temperature was maintained at 180 ℃ for 4 hours. The system was kept under stirring and under inert gas blanket throughout the reaction.

The other steps are the same as in example 1. The prepared carbon-supported composite metal catalyst is marked as Cu @ Ag-Mn-2.

The Cu @ Ag-Mn-2 nanoparticles in FIG. 3 are characterized by a uniform particle size distribution of about 7 nm. The atomic percentages of copper, silver and manganese are respectively 55 at%, 39 at% and 6 at%.

Example 3

85mg of copper acetylacetonate are added to 10ml of oleylamine and N is introduced at room temperature₂And removing dissolved oxygen in oleylamine for 30 min. Then, oleylamine was heated to 220 ℃ and held for 2 hours, then, cooled to 200 ℃ and 2ml of oleylamine in which 110mg of silver nitrate and 20. mu.l of a 50% manganese nitrate solution were dissolved in advance was injected into the reaction system and held at 200 ℃ for 4 hours. The system was kept under stirring and under inert gas blanket throughout the reaction.

The other steps are the same as in example 1. The prepared carbon-supported composite metal catalyst is marked as Cu @ Ag-Mn-3.

The characteristics show that the atomic proportions of copper, silver and manganese in the Cu @ Ag-Mn-3 nano particles are respectively 25 at%, 64 at% and 11 at%.

Example 4

170mg of copper acetylacetonate were added to 10ml of oleylamine and N was passed through the mixture at room temperature₂And removing dissolved oxygen in oleylamine for 30 min. Then, oleylamine was heated to 220 ℃ and held for 2 hours, then, cooled to 180 ℃, and 2ml of oleylamine, in which 110mg of silver nitrate and 20. mu.l of a 50% manganese nitrate solution were dissolved in advance, was injected into the reaction system and held at 180 ℃ for 4 hours. The system was kept under stirring and under inert gas blanket throughout the reaction.

The other steps are the same as in example 1. The prepared carbon-supported composite metal catalyst is marked as Cu @ Ag-Mn-4.

The characteristics show that the atomic proportions of copper, silver and manganese in the Cu @ Ag-Mn-3 nano particles are respectively 60 at%, 34 at% and 6 at%.

Comparative example 1

A preparation method of a silver nanoparticle catalyst comprises the following steps:

taking 110mg AgNO₃Dissolved in 10ml of oleylamine, after which the solution was charged into a 50ml three-necked flask and N was passed through the flask at room temperature₂And keeping for 30min, and removing oxygen dissolved in the oleylamine. Then heated to 200 ℃ for 4 hours. The other steps are the same as in example 1.

As can be seen from fig. 5, compared with the carbon-supported nano silver catalyst, the oxygen reduction electrocatalytic activity of the carbon-supported copper-silver-manganese composite catalyst is greatly improved.

As can be seen from fig. 6 and 7, the carbon-supported copper-silver-manganese composite catalyst of the present invention still maintains high catalytic activity after 30K aging tests, and is substantially unchanged, whereas the silver particle catalyst of comparative example 1 has a significant drop in half-wave potential and limiting current after 5000 aging tests. It can also be seen from fig. 8 and 9 that the catalyst particles of the present invention remained uniformly distributed after 30K aging tests, whereas the silver particles of comparative example 1 had significantly agglomerated after 5000 aging tests. It can also be seen from fig. 11 that the catalyst particles of the present invention still maintain the composition of copper, silver and manganese after aging testing. It can be shown that the stability of the composite catalyst of the present invention is significantly improved.

In conclusion, the novel composite nano material is obtained by combining copper, silver and manganese elements and controlling the structure, can be applied to an alkaline medium oxygen reduction reaction catalyst, and remarkably improves the catalytic activity and the stability.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The composite catalyst for the oxygen reduction reaction in the alkaline medium is characterized by comprising silver-manganese-copper ternary metal composite particles, and the synthetic method of the composite catalyst comprises the following steps:

forming a first precursor solution comprising at least a copper source;

forming a second precursor solution comprising at least a silver source and a manganese source;

heating the first precursor solution to a first temperature, and maintaining the first reaction time to form a first reaction solution dispersed with copper-containing nanoparticles, wherein the first temperature range is 180-280 ℃, and the first reaction time is 0.5-4 hours;

adjusting the first reaction liquid to a second temperature, adding the second precursor solution, and maintaining the second reaction time to form a second reaction liquid dispersed with silver-manganese-copper ternary metal composite particles, wherein the second temperature range is 180-240 ℃, and the second reaction time is 1-6 hours;

and separating and purifying the second reaction solution to obtain the composite catalyst.

2. The composite catalyst according to claim 1, wherein the composite catalyst comprises an outer layer based on silver and manganese and an inner core based on copper.

3. The composite catalyst of claim 2 wherein the outer layer is comprised of silver manganese and the inner core is comprised of copper silver.

4. The composite catalyst according to claim 2, wherein the composite catalyst is of a core-shell structure, the shell is distributed on at least part of the surface of the core, the core is mainly composed of copper, and the shell is mainly composed of silver and manganese.

5. The composite catalyst of any one of claims 1-4, wherein the atomic ratio of silver is in the range of 23% to 75%, the atomic ratio of manganese is in the range of 2% to 25%, and the atomic ratio of copper is in the range of 23% to 75%.

6. The composite catalyst according to any one of claims 1 to 4, wherein the composite catalyst has an average particle diameter in the range of 2 to 50 nm.

7. The composite catalyst according to any one of claims 1 to 4, wherein the composite catalyst comprises a support material and silver-manganese-copper ternary metal composite particles distributed on the surface of the support material.

8. The composite catalyst according to claim 7, wherein the support material comprises a one-, two-or three-dimensional structure of carbon material or metal oxide material.

9. The method for synthesizing the composite catalyst is characterized by comprising the following steps of:

forming a first precursor solution comprising at least a copper source;