WO2019109212A1

WO2019109212A1 - Metal-nitrogen carbon material with metal dispersed on an atomic scale, preparation method therefor and use thereof

Info

Publication number: WO2019109212A1
Application number: PCT/CN2017/114469
Authority: WO
Inventors: 孙晓明; 张国新; 贾茵
Original assignee: 北京化工大学
Priority date: 2017-12-04
Filing date: 2017-12-04
Publication date: 2019-06-13

Abstract

Disclosed is a metal-nitrogen carbon material precursor with the metal dispersed on an atomic scale, wherein the content of N is 25 wt%-35 wt% and the content of metal is 0.1 wt%-1.3 wt%, based on the total weight of the metal-nitrogen carbon material precursor, wherein the metal is one or more of transition metals or noble metals. The precursor is formed by self-polymerization of a formamide solution of a metal salt. The metal-nitrogen carbon material with the metal dispersed on an atomic scale is obtained by high-temperature roasting of the precursor in an inert atmosphere, wherein the content of N is 4 wt%-7 wt% and the content of metal is 0.3 wt%-8 wt%, based on the total weight of the metal-nitrogen carbon material. The precursor and metal-nitrogen carbon material can both be used as an electrochemical catalyst. The preparation method is simple, easy to operate, and cost-effective, and has a high preparation efficiency for the metal-nitrogen carbon material with dispersion on an atomic scale.

Description

Metal-nitrogen carbon material with atomic dispersion of metal, preparation method and use thereof

Technical field

The invention belongs to the field of novel material preparation, in particular to a metal-nitrogen carbon material in which a metal is atomically dispersed, a preparation method thereof and use thereof.

Background technique

Atomic-scale dispersed metal nitrogen-carbon composites are used in many important electrochemical reactions such as oxygen reduction and oxygen evolution due to their excellent catalytic performance, high utilization of metal components, high anti-pollution and high failure. Reaction, hydrogen evolution reaction, carbon dioxide reduction reaction. There are two classical preparation methods: the first one is to mechanically mix metal salts with nitrogen sources and carbon sources. After high temperature roasting, strong acid is used to remove the aggregated particles of the metal, and the strong coordination of nitrogen with transition metals is utilized. The effect is that a small amount of atomic-level dispersed transition metal component can be retained during the acid treatment. The second is that the metal organic skeleton carbon material (MOF) can be used to uniformly chelate the characteristics of the transition metal component, and the MOF having a special element combination and content can be obtained to some extent to obtain a nitrogen-carbon material with atomic-level dispersion of the metal component. . For example, the use of bimetallic ZnCo-MOF, subjected to high temperature roasting, can utilize the effect of Zn on the surrounding Co at high temperatures, greatly reducing the migration of the catalytic component Co, and producing a composite material of monoatomic Co-NC. The composite exhibits excellent catalysis in the oxygen reduction reaction and has the same performance as the noble metal Pt carbon catalyst output. In general, the first preparation method obtains atomic-level dispersed metal nitrogen-carbon composites with extremely low efficiency, which relies heavily on pre-treatment and requires strict post-treatment to ensure that particulate metal components are removed and atomic grade metals. The retention of the components, and the acid elution rate is greater than 50%, the content of the atomically dispersed metal component remaining in the metal-nitrogen carbon material is extremely low, usually not more than 1% by weight. The efficiency of preparing the atomic grade metal nitrogen carbon material by the second material is much higher than that of the first preparation method, and the content of the atomic grade dispersed metal component remaining in the metal-nitrogen carbon material can be increased to 1.4 wt% to 5 wt%. It is very difficult to increase it, but it is also difficult to use it for a wide range of industrial production because of its expensive and toxic nature.

Therefore, there is still a need for atomic-scale dispersed metal nitrocarbon materials having higher metal contents and better preparation methods thereof.

Summary of the invention

A first aspect of the invention provides a metal-nitrocarburethane precursor having a metal atomically dispersed, wherein the N content is 25-35 wt% and the metal content is 0.1- based on the total weight of the metal-nitrocarburethane precursor. 1.3 wt%, wherein the metal is one or more of a transition metal or a noble metal.

A second aspect of the present invention provides a method for preparing a metal-nitrogen carbon material precursor in which the above metal is atomically dispersed, comprising the steps of:

A. Dissolving a metal salt in formamide to prepare a solution of a metal salt in formamide, wherein the metal is a transition metal or One or more of precious metals;

B. The metal salt solution of the metal salt is reacted at 120-300 ° C for 0.5 to 49 hours, so that the formamide therein is self-polymerized, and the solid-liquid separation is carried out after the reaction to obtain a metal-nitrogen-carbon material precursor in which the metal is atomically dispersed. body.

A third aspect of the present invention provides a metal-nitrogen carbon material in which a metal is atomically dispersed, wherein an N content is 4 to 7 wt% and a metal content is 0.3 to 8 wt% based on the total weight of the metal-nitrogen carbon material; The metal is one or more of a transition metal or a noble metal.

Preferably, the metal-nitrogen-carbon material in which the metal is atomically dispersed has a metal content of 5 to 8 wt%, more preferably a metal content of 6 to 8 wt%,

Preferably, the metal-nitrocarburethane material composite has substantially the balance of carbon in addition to the metal element and the nitrogen element. "Basically" means that more than 99% of the balance is carbon, but there may be some impurities that are inevitably brought in during the preparation process.

Preferably, the metal is one or more of a transition metal or a noble metal such as zinc, cobalt, iron, nickel, copper, manganese, chromium, tungsten, molybdenum, vanadium, niobium, tantalum or the like.

The nitrogen-carbon material is a product obtained by calcining a formamide self-polymer under an inert atmosphere at 500 to 1000 °C.

It has been found through experiments that the metal and the nitrogen-carbon material are chemically bonded, which is manifested in the fact that after the acid-washing of the composite material, the elution rate of the metal therein is less than 6.4%. The pickling means that the metal-nitrogen carbon material composite is immersed for a sufficient time with a non-oxidizing strong acid such as dilute sulfuric acid, hydrochloric acid, hydrofluoric acid or the like which can dissolve the metal or an oxide of the metal. Pickling is an effective method for testing free metals and metal oxides. If free metals or metal oxides are present, they are dissolved by these non-oxidizing strong acids. The ratio of the amount of dissolved metal to the total amount of metal is defined as metal. Elution rate. By detecting the elution rate of the metal after pickling, it can be judged whether or not the metal is bonded to the nitrogen-carbon material by chemical bonding. In the present invention, the metal pickling elution rate is less than 6.4%, indicating that most of the metals are not present in the free elemental state and the oxide form, but are combined with the nitrogen-carbon material by chemical bonds.

A fourth aspect of the invention provides the method for preparing a metal-nitrogen carbon material according to the third aspect, comprising the steps of:

A, a metal salt is dissolved in formamide to prepare a solution of a metal salt in formamide, wherein the metal is one or more of a transition metal or a noble metal;

B. The metal salt solution of the metal salt is reacted at 120-300 ° C for 0.5 to 49 hours, so that the formamide therein is self-polymerized, and the solid-liquid separation is carried out after the reaction to obtain a metal-nitrogen-carbon material precursor in which the metal is atomically dispersed. body;

C. The foregoing precursor is calcined at 500-1000 ° C for 0.5 to 30 hours under an inert atmosphere to obtain the metal-nitrogen carbon material.

In the above step A, the concentration of the metal salt in the formamide solution is not higher than the saturated solubility of the metal salt in the formamide. Preferably, the formamide solution of the metal salt is subjected to effective mixing after dissolution. Effective mixing means include but not limited For manual oscillation, mechanical oscillation, ultrasonic, stirring, etc. More preferably, in step A, some zinc salt may be further dissolved in the formamide solution of the target metal salt to increase the content of the target metal component in the final metal-nitrocarbon material composite.

In the above step B, the formamide will self-polymerize to form a nitrogen-doped carbon material, and at the same time, the nitrogen element on the formamide will preferentially chelate the metal cation, so that the metal ions are distributed in the atomic-level dispersed state. Miscellaneous carbon material. The process of self-polymerization of metalformamide and metal ion bonding with its self-polymer is complicated. It is presumed that the process may be as follows: the molecular formula of formamide is HCONH2, which has only four elements of carbon, nitrogen, hydrogen and oxygen, and dehydration occurs during self-polymerization. And removing most of the hydrogen and oxygen elements to obtain a nitrogen-doped carbon material, wherein the nitrogen content is about 25-35 wt%, and wherein the metal ions are dispersed at the atomic level and doped with the chemical bond with the nitrogen Bonding of carbon materials. After the end of step B, the product can be optionally separated from the reaction liquid by an effective means, and the solid product is dried.

In the above step C, after calcination under an inert atmosphere, the product of the step B removes all of the hydrogen element and a part of the nitrogen element, leaving only nitrogen, carbon and metal elements, and the metal of the third aspect of the invention is obtained. Nitrogen carbon material. In the case where a zinc salt is added in the step A, it is necessary to make the calcination temperature in the step C higher than 700 ° C, more preferably higher than the boiling point of 908 ° C in the zinc. And because the metal in the present invention is atomically dispersed and chemically bonded to the nitrogen carbon material, the metal-nitrogen carbon material which is embodied in the third aspect of the invention is characterized in that the nitrogen content is extremely high and can reach 4- 7wt%, and the metal is atomically dispersed and the content is extremely high, and can reach 0.3-8wt%; preferably, the metal content is 5-8wt%, more preferably 6-8wt%, and the metal pickling elution rate is lower than 6.4. %.

A fifth aspect of the invention relates to the use of the metal-nitrocarburethane precursor or metal-nitrogen carbon material as an electrochemical reaction catalyst. Preferably, the electrochemical reaction comprises an oxygen reduction reaction, an oxygen evolution reaction, a hydrogen evolution reaction or a carbon dioxide reduction reaction. Of course, the invention may also have other uses that are yet to be developed.

The beneficial effects of the invention:

A. The metal-nitrogen carbon precursor obtained by the present invention has a nitrogen content of 25 to 35 wt%, and such a high nitrogen content is difficult to achieve by doping nitrogen into the carbon material by other methods, and further, since the metal cation is Chelating with nitrogen, the high content of nitrogen ensures that more metals can be chelated, laying the foundation for subsequent metal content enhancement. As mentioned later, the metal-nitrogen carbon material obtained by calcining the metal-nitrogen carbon material precursor at a high temperature will have a much higher metal content than other methods for preparing a metal nitrogen-carbon composite (for example, the method described in the background section). The metal content that can be achieved.

B. The metal-nitrogen carbon material obtained by the invention has strong stability. The nitrogen-carbon material itself is highly stable since it has undergone the high-temperature calcination process of step C. And because the metal is chemically bonded to the nitrogen-carbon material, the metal is also highly stable, as shown by its elution rate after pickling is less than 6.4%. Moreover, in the present invention, the metal is in an atomic-scale dispersed state. Considering that the metal component is a core functional component of many catalysts, and generally the higher the metal content, the better the metal dispersion, the better the catalytic effect. Therefore, the metal component having such a high loading amount, which is atomically dispersed and highly stable, has laid the invention. The possibility of materials being used as catalysts in various chemical reactions. The latter examples show that the materials of the present invention are useful as excellent electrochemical reaction catalysts. In addition, the metal-nitrogen carbon material precursor of the present invention can also be used as an electrochemical reaction catalyst, but since the precursor can be dissolved by a high concentration of strong acid and strong alkali, it can only be applied to an electrolyte without using a high concentration of strong acid. The occasion of strong alkali.

C. The preparation method of the invention has the advantages of low cost, low toxicity, simple and easy reaction operation, and suitable for industrial expansion, and the atomic-level dispersed metal nitrogen carbon material has high preparation efficiency, and the preparation method is not limited to the type and valence of the metal. The preparation strategy of the present invention is also highly feasible for the preparation of a combined nitrogen-carbon material of a multi-metal component, and can be used to study the synergistic effect of a multi-atomic dispersed metal component on electrochemical catalysis.

D. In the present invention, by adding a soluble zinc salt in the step A and calcining at a temperature higher than 700 ° C in the step C, the metal content of the finished product obtained by adding no soluble zinc salt under the same conditions is more. High and can achieve a higher dispersion of the remaining metals. This phenomenon is surprising, and there is no particularly reasonable explanation for this applicant. It is speculated that it may be because during the reaction of step B, zinc promotes more chelation of metal with N atoms, and zinc and other metals After sequestration to the N atoms at intervals, and then evaporating off the zinc at a high temperature, the dispersion of the remaining metals is improved.

DRAWINGS

1 is a transmission electron microscope (TEM) characterization image of a metal-nitrogen carbon precursor prepared in Examples 1-14 of the present invention, and no metal element or metal oxide particles were observed.

2 is a dark field scanning transmission electron microscope (STEM) characterization image of a metal-nitrogen carbon precursor prepared in Examples 1-14 of the present invention, and the metal is monoatomic dispersed and dispersed in density. Higher.

3 is an X-ray diffraction (XRD) pattern of a metal-nitrogen carbon precursor prepared in Examples 1-14 of the present invention, and the spectrum shows that there are no obvious metal elements, metal oxides and the like.

4 is a transmission electron microscope (TEM) characterization image of a metal-nitrogen carbon material according to Examples 15-17 of the present invention.

5 is a dark field scanning transmission electron microscope (STEM) characterization image of the metal-nitrogen carbon material according to Embodiment 15-17 of the present invention. It can be seen from the image that the metal is in a monoatomic state and the dispersion density is high. .

Fig. 6 is an X-ray diffraction (XRD) pattern of the metal-nitrogen carbon material according to Example 15-17 of the present invention, and the spectrum shows a metal-free element, a metal oxide or the like.

Figure 7 is a transmission electron microscope (TEM) characterization image of the metal-nitrogen carbon material prepared in Examples 1A-14A of the present invention, and no metal element or metal oxide particles were observed.

8 is a dark field scanning transmission electron microscope (STEM) characterization image of the metal-nitrogen carbon material prepared in Example 1A-14A of the present invention. It can be seen from the image that the metal is in a monoatomic state with a high dispersion density. .

Figure 9 is an X-ray diffraction (XRD) pattern of the metal-nitrogen carbon material prepared in Example 1A-14A of the present invention, and the spectrum shows no significant metal element, metal oxide or the like.

Detailed ways

The following examples are provided to illustrate the invention, which are intended to be illustrative and not restrictive.

Example 1-12

According to the following Table 1, a certain amount of metal salt was dissolved in 30 mL of formamide, ultrasonically dispersed to be transparent, and then placed in a volume of 40.0 mL of a Teflon reactor at the reaction temperature shown in Table 1. React with time. After the reaction is completed, the temperature is naturally lowered, the solid-liquid mixture is taken out, the solid-liquid separation is carried out by centrifugation, and the solid is dried in an oven at 60 ° C to collect a dry powder, which is a metal-nitrogen carbon material precursor in which the metal is atomically dispersed. The precursors shown in Examples 1-14 were subjected to measurement of nitrogen content and metal content and pickling elution rate, wherein the metal elution rate was determined after soaking the target product with 1 mol/L of dilute sulfuric acid for 2 hours. Shown in Table 1.

Then, each precursor was calcined under the argon atmosphere at the calcination temperature and time shown in Table 1, to obtain a target product, that is, a metal-nitrogen carbon material in which the metal was atomically dispersed, which were numbered as Examples 1A-14A and implemented. Example 15-17. Elemental analysis of the target product revealed that it consisted essentially of only nitrogen, carbon and metals. The data of the nitrogen content, the metal content, and the metal elution rate after pickling of the target product are also listed in Table 1.

Table 1

The above Example 15 is compared with Example 1A, Example 16 and Example 11A, and Example 17 and Example 12A, and it is also apparent that when a zinc salt is additionally added to the metal salt solution of the metal salt and in the step C, Calcination above 700 °C can significantly increase the metal content in the final product after calcination, and the metal acid elution rate of the calcined product is also lower than that in the absence of zinc salt, indicating that the zinc salt promotes more The metal is directly complexed with N and the metal is more dispersed.

Application effect example

The products obtained in Examples 1-14 and Examples 1A-14A and Examples 15-17 were used for electrocatalytic oxygen reduction (ORR), oxygen evolution (OER) and hydrogen evolution (HER), respectively. The initial potential and the half-wave potential were compared with a commercial Pt/C catalyst (platinum content of 20% by weight) and Ir/C catalyst (Ir content of 20% by weight), and the results are shown in Table 2 below.

Table 2

Note: Oxygen reduction test conditions: test linear sweep voltammetry curve in 0.1mol/L KOH solution, oxygen saturation, 1600rpm, sweep speed 5mV/s; oxygen precipitation test conditions: in 0.1mol/L KOH solution, The linear sweep voltammetry curve was tested at a speed of 1600 rpm and a sweep rate of 5 mV/s. The hydrogen evolution reaction test conditions were tested in a 0.5 mol/L H ₂ SO ₄ solution at a rotational speed of 1600 rpm and a sweep rate of 5 mV/s. An curve.

It can be seen from Table 2 that the metal in the present invention is a metal-nitrogen carbon precursor which is atomically dispersed, and has a certain catalytic effect on the electrocatalytic oxygen reduction reaction, the oxygen evolution reaction and the hydrogen evolution reaction, but the metal after calcination A metal-nitrogen-carbon material dispersed in an atomic order, which has a better catalytic effect, which is reflected in the fact that in their oxygen reduction reaction and hydrogen evolution reaction, the initial reaction potential is higher, the half-wave potential is higher, and oxygen is precipitated. The initial potential and half-wave potential are lower in the reaction, and its catalytic effect is equivalent to or even superior to current commercial Pt/C catalysts and commercial Ir/C catalysts. However, the present invention utilizes a less expensive transition metal as an active component and has a higher metal utilization efficiency, and thus is more cost effective than a commercial Pt/C catalyst and a commercial Ir/C catalyst.

In the above embodiment, the metal component may also be ruthenium chloride, tin chloride, palladium chloride or the like, which will not be enumerated here. Rather, the above-described embodiments are merely illustrative of the invention, and are not intended to limit the scope of the embodiments.

Claims

A metal-nitrogen carbon material precursor in which a metal is atomically dispersed, wherein an N content is 25-35 wt% and a metal content is 0.1-1.3 wt% based on the total weight of the metal-nitrocarburethane material precursor. Wherein the metal is one or more of a transition metal or a noble metal.
A method for preparing a metal-nitrogen carbon material precursor in which a metal is atomically dispersed, characterized in that it comprises the following steps:

A, a metal salt is dissolved in formamide to prepare a solution of a metal salt in formamide, wherein the metal is one or more of a transition metal or a noble metal;

B. The metal salt solution of the metal salt is reacted at 120-300 ° C for 0.5 to 49 hours, so that the formamide therein is self-polymerized, and the solid-liquid separation is carried out after the reaction to obtain a metal-nitrogen-carbon material precursor in which the metal is atomically dispersed. body.
A metal-nitrogen carbon material in which a metal is atomically dispersed, wherein a N content is 4 to 7 wt% and a metal content is 0.3 to 8 wt% based on the total weight of the metal-nitrogen carbon material; preferably, a metal The content is 5-8 wt%, wherein the metal is one or more of a transition metal or a noble metal.
The metal-nitrocarburethane material according to claim 3, wherein the metal-nitrogen carbon material has a balance of carbon other than the metal element and the nitrogen element.
The metal-nitrocarburethane material according to claim 3, wherein the nitrogen-carbon material is a product obtained by calcining a formamide self-polymer at 500 to 1000 ° C under an inert atmosphere.
The metal-nitrocarburethane material according to claim 3, wherein the metal and the nitrogen-carbon material are chemically bonded such that the elution rate of the metal in the composite after pickling is less than 6.4%. .
A method for preparing a metal-nitrogen carbon material in which a metal is atomically dispersed, comprising the steps of:

A, a metal salt is dissolved in formamide to prepare a solution of a metal salt in formamide, wherein the metal is one or more of a transition metal or a noble metal;

B. The metal salt solution of the metal salt is reacted at 120-300 ° C for 0.5 to 49 hours, so that the formamide therein is self-polymerized, and the solid-liquid separation is carried out after the reaction to obtain a metal-nitrogen-carbon material precursor in which the metal is atomically dispersed. body;

C. The foregoing precursor is calcined at 500-1000 ° C for 0.5 to 30 hours under an inert atmosphere to obtain the metal-nitrogen carbon material.
The method for preparing a metal-nitrogen carbon material according to claim 7, wherein the metal salt has a concentration of a formamide solution of not higher than a saturated solubility of the metal salt in formamide.
The method for producing a metal-nitrogen carbon material according to claim 5, wherein a zinc salt is additionally added to the metal amide solution of the metal salt in the step A, and is not lower than 700 ° C in the step C. The temperature is calcined.
The use of the metal-nitrogen carbon precursor precursor in which the metal is atomically dispersed according to claim 1 or the metal-nitrogen carbon material according to claim 3 is used as an electrochemical reaction catalyst, wherein the electrochemical reaction comprises oxygen Reduction reaction, oxygen evolution reaction, hydrogen evolution reaction or carbon dioxide reduction reaction.