CN113241449A

CN113241449A - Co-N-C oxygen reduction catalyst and preparation method and application thereof

Info

Publication number: CN113241449A
Application number: CN202110583252.1A
Authority: CN
Inventors: 刘静; 张明磊; 米立伟; 李善卿; 朱会彬; 石文洁; 延静垒
Original assignee: Zhongyuan University of Technology
Current assignee: Zhongyuan University of Technology
Priority date: 2021-05-27
Filing date: 2021-05-27
Publication date: 2021-08-10

Abstract

The invention belongs to the field of catalysts, relates to the technical field of fuel cells, and particularly relates to a Co-N-C oxygen reduction catalyst, and a preparation method and application thereof. The method comprises the following steps: crushing and sieving peanut shell, soaking the peanut shell in a hydrochloric acid solution, washing the peanut shell with water, centrifuging the peanut shell, and drying the peanut shell to obtain solid powder; adding Co-containing powder to solid powder²⁺The solution is subjected to shake culture, and then is subjected to suction filtration and drying to obtain Co²⁺-peanut shell flour; calcining Co at high temperature in ammonia atmosphere²⁺-peanut shell powder to obtain the Co-N-C oxygen reduction catalyst. The preparation method is simple, low in cost and excellent in performance, is suitable for producing non-noble metal oxygen reduction catalysts of fuel cells on a large scale, and has the potential to be used as fuel cell PtAlternative to/C catalysts.

Description

Co-N-C oxygen reduction catalyst and preparation method and application thereof

Technical Field

The invention belongs to the field of catalysts, relates to the technical field of fuel cells, and particularly relates to a Co-N-C oxygen reduction catalyst, and a preparation method and application thereof.

Background

A fuel cell is a device that directly converts chemical energy into electrical energy. The energy conversion power supply has the outstanding characteristics of high energy conversion efficiency, environmental friendliness, high specific power and specific energy and the like, and is considered to be the most promising chemical power supply for electric automobiles and other civil occasions in the future. Noble metals are usually used as fuel cell cathode catalysts to catalyze oxygen reduction reactions, but the disadvantages of rare reserves, high price, poor stability, low selectivity and the like greatly hinder the scale use of fuel cells. Therefore, the development of inexpensive, sustainable, high-performance non-noble metal oxygen reduction catalysts is of great importance to the commercialization process of fuel cells.

The Co-N-C catalyst has the advantages of high specific surface area, unique electronic structure and property, rich Co-N and C-N catalytic active sites and the like, and is an oxygen reduction catalyst with wide application prospect. However, most of the current synthetic methods are complex in process, expensive in precursor, not suitable for large-scale production, and the final cost of the catalyst is even higher than that of the Pt-based catalyst. Peanuts are important commercial and oil crops. However, at present, most of the peanut shells are used as fuel or directly discarded as waste except that few of the peanut shells are used for feed processing, so that great resource waste is caused, and the sustainable development of the peanut industry is influenced. According to research, natural components such as cellulose, hemicellulose and lignin rich in peanut shells have rich oxygen-containing functional groups, such as carboxyl, phenolic, quinonic and keto groups. These oxygen-containing groups have a strong coordination ability with transition metal ions, such as Co²⁺. Patent CN 201711164119.2 discloses a method for preparing oxygen reduction catalyst material based on modified peanut shells, and the catalyst prepared by the method is prepared byCo(OH)₂And NaH₂PO₂Are inlaid on the surface of peanut shell together, and a plurality of active sites are effectively fixed by skillfully utilizing different gas release principles at different temperatures in the high-temperature calcination process, and the specific surface area of the active sites can reach 366m²g^-1(ii) a Patent CN 201510626107.1 discloses a method for preparing a desulfurization catalyst by using peanut shells, which comprises the steps of soaking the peanut shells by using sodium hydroxide, removing partial impurities, adding sodium abietate, sodium chromate and the like to enlarge pores of the peanut shells, primarily modifying, carbonizing, mixing and stirring the carbonized peanut shells with blast furnace slag powder, sulfuric acid solution, nickel nitrate solution and other substances, and deeply modifying to obtain the desulfurization catalyst, wherein the method mainly aims to improve the desulfurization rate; therefore, the Co-N-C catalyst with high activity is prepared by utilizing the abundant oxygen-containing functional groups in the peanut shell to coordinate with Co ions, so that the cost can be greatly reduced, and the method has important significance for the industrialization of fuel cells.

Disclosure of Invention

The invention provides a Co-N-C oxygen reduction catalyst, a preparation method and application thereof, the preparation method is simple, the specific surface area is large, the performance is excellent, the Co-N-C oxygen reduction catalyst is suitable for producing non-noble metal oxygen reduction catalysts of fuel cells on a large scale, and the Co-N-C oxygen reduction catalyst has important significance for promoting the large-scale application of the fuel cells.

The technical scheme of the invention is realized as follows:

a preparation method of a Co-N-C oxygen reduction catalyst comprises the following steps:

(1) crushing and sieving peanut shell, soaking the peanut shell in a hydrochloric acid solution, washing the peanut shell with water, centrifuging the peanut shell, and drying the peanut shell to obtain solid powder;

(2) adding Co-containing into the solid powder of step (1)²⁺The solution is subjected to shake culture, and then is subjected to suction filtration and drying to obtain Co²⁺-peanut shell flour;

(3) calcining Co in the step (2) at high temperature in ammonia atmosphere²⁺-peanut shell powder to obtain the Co-N-C oxygen reduction catalyst.

The mass ratio of the peanut shell powder to the hydrochloric acid in the step (1) is (1-10): (0.2-2), the concentration of hydrochloric acid is 5% -25%.

The mesh number of the screen in the step (1) is 50-400 meshes, and the drying temperature is 50-100 ℃.

The step (2) contains Co²⁺The solution of (A) is cobalt chloride or cobalt nitrate, the concentration is 20-100 mM, solid powder and Co-containing²⁺The mass ratio of the solution (2) is (5-80): (0.1-10).

The temperature of the shaking culture in the step (2) is 10-50 ℃, 100-500 rpm and the time is 6-24 h; the drying temperature is 50-100 deg.C.

The calcination temperature in the step (3) is 500-1000 ℃, the time is 2-8 h, and the heating rate is 1-10 ℃ for min^-1The flow rate of ammonia gas is 20-200 mL min^-1。

The Co-N-C oxygen reduction catalyst prepared by the method has rich pore structure and the specific surface area is up to 882-² g^-1Meanwhile, the electronic arrangement and charge density of the porous carbon are adjusted by the contained graphite nitrogen and pyridine nitrogen structures, the electrochemical property and conductivity are enhanced, the transmission and migration of charges in the oxygen reduction reaction are accelerated, the oxygen reduction reaction is promoted to carry out a more stable four-electron reaction process, and the Co nanoparticles and the active nitrogen structures form rich Co-N catalytic active sites to promote the oxygen reduction reaction.

The Co-N-C oxygen reduction catalyst is applied to preparing fuel cells.

The preparation principle of the invention is as follows: the carbon with the mesoporous structure is formed by carbonizing the peanut shell powder, the nitrogen element in the ammonia gas generates rich graphite nitrogen and pyridine nitrogen structures in the high-temperature process, the electronic arrangement and the charge density of the porous carbon are adjusted, the electrochemical property and the conductivity are enhanced, the transmission and the migration of charges in the oxygen reduction reaction are accelerated, and the oxygen reduction reaction is promoted to carry out more stable 4e^-Reaction process, Co²⁺Co nano particles are generated by high-temperature thermal reduction and uniformly dispersed in the porous carbon matrix, so that the aggregation and agglomeration of the Co nano particles are reduced, and rich Co-N catalytic active sites are formed with an active nitrogen structure.

The invention has the following beneficial effects:

1. the Co-N-C prepared by the method contains rich Co-N and C-N active sites, and is more fully exposed, so that the Co-N-C (half-wave potential 0.83V) oxygen reduction reaction catalyst shows a half-wave potential higher than that of commercial Pt/C (half-wave potential 0.81V), and has higher oxygen reduction catalytic performance.

2. After the Co-N-C oxygen reduction catalyst prepared by the method is tested for 30000s by timing current, the limit current value is reduced to 73%, and the limit current value of a commercial Pt/C catalyst is reduced to 32%, which shows that the Co-N-C catalyst prepared by the method has better stability compared with the commercial Pt/C catalyst. Meanwhile, the Co-N-C oxygen reduction catalyst prepared by the method has better methanol poisoning resistance compared with a commercial Pt/C catalyst.

3. The peanut shells used in the application have rich sources, low price, simple production process, good consistency of the formed products, small environmental pollution, suitability for large-scale production and hopeful substitution of the noble metal oxygen reduction catalyst for the fuel cell.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 shows the X-ray diffraction pattern of Co-N-C of the present invention and a Co standard card (PDF # 15-0806).

FIG. 2 is a transmission electron microscope and elemental distribution plot of Co-N-C of the present invention.

FIG. 3 is a Raman spectrum of Co-N-C of the present invention and comparative example N-C.

FIG. 4 is an X-ray photoelectron spectrum of Co-N-C of the present invention.

FIG. 5 is a graph of the impedance of Co-N-C of the present invention and comparative example N-C.

FIG. 6 is a nitrogen adsorption/desorption curve of Co-N-C of the present invention and comparative example N-C.

FIG. 7 is a graph showing the oxygen reduction performance of Co-N-C of the present invention, comparative example N-C and commercial Pt/C.

FIG. 8 is a chronoamperometric test at constant potential for Co-N-C of the present invention and commercial Pt/C.

FIG. 9 shows methanol resistance tests of Co-N-C of the present invention and commercial Pt/C.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive effort based on the embodiments of the present invention, are within the scope of the present invention.

Example 1

1. crushing peanut shells, ball-milling the crushed peanut shells into powder, sieving the powder by a 200-mesh sieve, treating the powder for 6 hours at 70 ℃ by using 10% hydrochloric acid solution, washing the treated powder with water, centrifuging the washed powder, and drying the washed powder at 70 ℃ to obtain solid powder.

2. CoCl was added at a concentration of 40 mM₂Shaking the solid obtained in the step 1 for 20 h at 35 ℃ and 200 rpm, and Co²⁺Combining with oxygen-containing functions such as carboxyl, phenolic group, quinonyl and keto group rich in peanut shell powder, filtering, and drying at 80 deg.C to obtain Co²⁺-peanut shell flour.

3. At 900 deg.C (temperature rising rate of 5 deg.C for min)^-1) Ammonia atmosphere (100 mL min)^-1) The obtained Co obtained in the step 2²⁺And (4) calcining the peanut shell powder for 4 hours to obtain the Co-N-C catalyst.

The X-ray diffraction pattern of Co-N-C prepared in this example 1 is shown in FIG. 1, which shows that the three peaks of carbonized peanut shell flour at 44.2 °, 51.5 ° and 75.8 ° correspond to Co⁰The (111), (200), and (220) planes of (A) match those of a standard Co card (PDF # 15-0806), indicating that Co is present²⁺And (4) carrying out high-temperature thermal reduction to generate Co nanoparticles.

The transmission electron microscope and element distribution of Co-N-C prepared in this example are shown in FIG. 2, from which it can be seen that the diameter of Co nanoparticles is about 50-200 nm, and they are uniformly distributed on the surface of the catalyst.

The Raman spectra of Co-N-C prepared in this example and comparative example N-C are shown in FIG. 3, from which it can be seen that I of Co-N-C_D/I_GI with a ratio of 0.97, N-C_D/I_GThe ratio is 0.83, which shows that Co-N-C has higher graphite degree, and the introduction of Co causes more defects in the catalyst, thereby being beneficial to O₂Molecular adsorption, weak O-O bond, faster O₂The molecules are reduced to exhibit excellent oxygen reduction activity.

The X-ray photoelectron spectrum of Co-N-C prepared in this example is shown in FIG. 4. As can be seen from FIG. 4a, C, N and Co are all detected at specific binding energy positions. As can be seen from the spectrum of FIG. 4b C1 s, the peaks at 284.7, 285.3 and 287.0 eV are characteristic peaks of C-C, C-N and C-O, respectively. As can be seen from the spectrum of fig. 4c N1 s, peaks at 397.8, 398.5, 400.4, 401.0 and 403.9 eV respectively correspond to characteristic peaks of pyridine N, Co-N, pyrrole N and graphite N, and abundant graphite N and pyridine N structures can adjust the electronic arrangement and charge density of porous carbon, thereby enhancing the electrochemical properties and conductivity, accelerating the charge transfer and migration in the oxygen reduction reaction, and promoting the oxygen reduction reaction to perform a more stable four-electron reaction process.

Example 2

A Co-N-C oxygen reduction catalyst was prepared in the same manner as in example 1, except that: the result of testing the oxygen reduction performance of the Co-N-C catalyst obtained by sieving the 200 mesh sieve of step 1 with a 100 mesh sieve in 0.1M KOH was comparable to that of the Co-N-C catalyst obtained in example 1.

Example 3

A Co-N-C oxygen reduction catalyst was prepared in the same manner as in example 1, except that: the calcination time 4 h in step 3 was changed to calcination time 3 h, and the obtained Co-N-C catalyst was tested for oxygen reduction performance in 0.1M KOH and the results obtained were comparable to those obtained for the Co-N-C catalyst obtained in example 1.

Example 4

A Co-N-C oxygen reduction catalyst was prepared in the same manner as in example 1, except that: the CoCl of step (a)₂By Co (NO)₃)₂The results obtained when the Co-N-C catalyst obtained was tested for oxygen reduction performance in 0.1M KOH were comparable to the results obtained with the Co-N-C catalyst obtained in example 1.

Example 5

A Co-N-C oxygen reduction catalyst was prepared in the same manner as in example 1, except that: the Co-N-C catalyst obtained by changing the calcination temperature of step 3 from 900 ℃ to 850 ℃ was tested for oxygen reduction performance in 0.1M KOH and the results were comparable to those obtained for the Co-N-C catalyst obtained in example 1.

Example 6

A Co-N-C oxygen reduction catalyst was prepared in the same manner as in example 1, except that: the Co-N-C catalyst obtained by changing the calcination temperature of step 3 from 900 ℃ to 950 ℃ was tested for oxygen reduction performance in 0.1M KOH and the results were comparable to those obtained for the Co-N-C catalyst obtained in example 1.

Comparative example 1

An N-C oxygen reduction catalyst was prepared in the same manner as in example 1, except that: in step 2, CoCl is not added₂The finally obtained sample was labeled as N-C catalyst.

Examples of the effects of the invention

The impedance plots of the Co-N-C prepared in this example and the comparative example N-C are shown in FIG. 5, with a smaller semicircular diameter indicating a lower electron transfer resistance (Rct). Based on an equivalent circuit model, the obtained resistances of Co-N-C and N-C are 41.6 omega and 76.8 omega respectively, which shows that the Co-N-C has better conductivity and is more beneficial to charge transfer, thereby accelerating the occurrence of oxygen reduction reaction.

The nitrogen adsorption and desorption curves of Co-N-C prepared in this example and comparative example N-C are shown in FIG. 6, from which it can be seen that the nitrogen adsorption and desorption isotherms belong to type IV, indicating the existence of the pore structure in the sample, the pore structure in the catalyst can be the diffusion distance of the electrolyte, and from the BET equation, it can be seen that the specific surface areas of the catalyst Co-N-C and comparative example N-C are 882 cm² g^-1And 1028 m²g^-1The high specific surface area can provide a large electrode-electrolyte interface, supporting fuel transport to the catalyst reaction sites, thus resulting in enhanced catalytic activity and long-term stability, and the catalyst prepared by the present application has a slightly smaller specific surface area than the comparative example, but has significantly better catalytic performance than the comparative example due to the presence of rich Co-N and N-C rich active sites.

The oxygen reduction experimental curves for the Co-N-C catalyst prepared in example 1 and the Pt/C catalyst used commercially are shown in FIG. 7. The specific experimental method comprises the following steps: the oxygen reduction experiment curve is measured by a rotating ring disk electrode in a 0.1M KOH solution, the rotating speed of the rotating ring disk electrode is 1600 rpm, and the curve scanning speed is 10 mV s^-1. The control commercially used Pt/C catalyst was a commercial Pt/C catalyst purchased with a hadamard chemical platinum weight percent content of 20%.

Comparing the two curves, it can be seen that the Co-N-C prepared in this example exhibited a half-wave potential of 0.83V, 20 mV higher than the commercial Pt/C catalyst's 0.81V half-wave potential, and 160 mV higher than the comparative N-C's 0.67V half-wave potential in the oxygen reduction experiment. The excellent oxygen reduction catalytic properties of Co-N-C can be attributed to the rich Co-N and N-C rich active sites on the catalyst surface, good electrical conductivity facilitates charge transfer, thereby accelerating the oxygen reduction reaction, large specific surface area, provides a large electrode-electrolyte interface, supports fuel transport to the catalyst reaction sites, and thus results in enhanced catalytic activity and long-term stability.

The experimental curves of the stability tests of the Co-N-C catalyst prepared in example 1 and the Pt/C catalyst used commercially are shown in FIG. 8. The specific experimental method comprises the following steps: the chronoamperometric experimental curve was measured with a rotating disk electrode in 0.1M KOH solution saturated with oxygen at 1600 rpm, a constant potential of 0.7V, a curve sweep rate of 10 mV s-1, and a test time of 30000 s.

Comparing the two curves, it can be seen that the Co-N-C catalyst prepared in this example and the commercial Pt/C catalyst both undergo 0.7V constant potential aging at 30000s, and the reaction current of the Co-N-C oxygen reduction catalyst prepared in this example 1 is 73% of the initial reaction current after 30000s, which is higher than 32% of the commercial Pt/C catalyst, which indicates that the Co-N-C catalyst prepared in this example has better stability than the commercial Pt/C catalyst.

The experimental curves for methanol resistance tests of the Co-N-C catalyst prepared in example 1 and the Pt/C catalyst used commercially are shown in FIG. 9. The specific experimental method comprises the following steps: the oxygen reduction test curve was measured in a 0.1M KOH solution mixed with 0.5M methanol at 1600 rpm with a rotating disk electrode and a curve sweep rate of 10 mV s^-1。

As can be seen from a comparison of the graphs, the Co-N-C oxygen reduction catalyst prepared in this example has excellent methanol poisoning resistance compared to the commercial Pt/C catalyst.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims

1. A preparation method of a Co-N-C oxygen reduction catalyst is characterized by comprising the following steps:

2. The method of claim 1, wherein: the mass ratio of the peanut shell powder to the hydrochloric acid in the step (1) is (1-10): (0.2-2), the concentration of hydrochloric acid is 5% -25%.

3. The method of claim 2, wherein: the mesh number of the screen in the step (1) is 50-400 meshes, and the drying temperature is 50-100 ℃.

4. The method of claim 1, wherein: the step (2) contains Co²⁺The solution of (A) is cobalt chloride or cobalt nitrate, the concentration is 20-100 mM, solid powder and the solution contains Co²⁺The mass ratio of the solution (2) is (5-80): (0.1-10).

5. The method of claim 4, wherein: the temperature of the shaking culture in the step (2) is 10-50 ℃, 100-500 rpm and the time is 6-24 h; the drying temperature is 50-100 deg.C.

6. The method of claim 1, wherein: the calcination temperature in the step (3) is 500-1000 ℃, the time is 2-8 h, and the heating rate is 1-10 ℃ for min^-1The flow rate of ammonia gas is 20-200 mL min^-1。

7. A Co-N-C oxygen reduction catalyst prepared by the process of any one of claims 1 to 6, wherein: the Co-N-C oxygen reduction catalyst has rich pore structure and specific surface area as high as 882 cm² g^-1Meanwhile, the electronic arrangement and charge density of the porous carbon are adjusted by the contained graphite nitrogen and pyridine nitrogen structures, the electrochemical property and conductivity are enhanced, the transmission and migration of charges in the oxygen reduction reaction are accelerated, the oxygen reduction reaction is promoted to carry out a more stable four-electron reaction process, and the Co nanoparticles and the active nitrogen structures form rich Co-N catalytic active sites to promote the oxygen reduction reaction.

8. Use of the Co-N-C oxygen reduction catalyst of claim 7 in the manufacture of a fuel cell.