Oxygen reduction catalyst for constructing local "alkaline-like" microenvironment and preparation method and application thereof

Abstract

The embodiment of the application relates to an oxygen reduction catalyst for constructing a local alkaline-like microenvironment and a preparation method and application thereof, and belongs to the technical field of material synthesis. The preparation method of the oxygen reduction catalyst for constructing a local alkaline-like microenvironment comprises the following steps: (1) loading Fe on a core MOF material to obtain a core Fe / MOF material, and then constructing metal atoms M with water activation capacity in-situ on a shell MOF material by an epitaxial growth method to obtain a core-shell Fe / MOF@M / MOF precursor material, and Fe and M are limited in the core and the shell respectively; (2) performing in-situ carbon conversion on the Fe / MOF@M / MOF precursor material by pyrolysis to obtain a FeNC@MNC oxygen reduction catalyst for constructing a local alkaline-like microenvironment in natural seawater. The catalyst with water activation capacity provided in the embodiment overcomes the challenges of low ion conductivity and chloride adsorption in natural seawater, enhances the stability and activity of the catalyst in seawater, and realizes efficient and stable oxygen reduction.

Description

TECHNICAL FIELD

[0001] The embodiment of the present application relates to the technical field of material synthesis, in particular to an oxygen reduction catalyst for constructing a local "alkaline-like" microenvironment and a preparation method and application thereof. BACKGROUND

[0002] The seawater metal-air battery is a new type of battery device directly using natural seawater as an electrolyte, taking common metals such as zinc, magnesium and aluminum as an anode, and taking an oxygen reduction electrocatalyst as a cathode. The seawater metal-air battery has the advantages of high theoretical energy density, safe use, low price, and abundant resources of the positive electrode metal. Therefore, the seawater metal-air battery has a broad application prospect in ocean observation equipment, island power supply and small underwater vehicles.

[0003] The oxygen reduction reaction is the core reaction of the seawater metal-air battery, which determines the efficiency and output power of the seawater metal-air battery device during use. Pt-based catalysts are the most effective oxygen reduction catalysts, but their high cost, low reserves and poor durability restrict their large-scale application in seawater metal-air batteries. Fe single-atom catalysts are considered to be one of the most effective catalysts in oxygen reduction reactions due to their high atomic utilization, explicit and uniform active sites, and unique electronic structure. Moreover, Fe single-atom catalysts are low in price. However, in the natural seawater system, the low ionic conductivity of the seawater leads to slow oxygen reduction reaction of the seawater metal-air battery. In addition, the Fe single-atom catalysts are affected by chloride ion adsorption, which leads to a decrease in the stability and activity of the catalysts. Therefore, it is urgent to develop a synthesis strategy for an oxygen reduction catalyst for constructing a local "alkaline-like" microenvironment to achieve efficient and stable oxygen reduction in natural seawater. SUMMARY

[0004] Therefore, the embodiment of the present application provides an oxygen reduction catalyst for constructing a local "alkaline-like" microenvironment and a preparation method and application thereof. The oxygen reduction catalyst overcomes the challenges of low ionic conductivity and chloride ion adsorption in natural seawater, enhances the stability and activity of the catalyst in seawater, improves the efficiency and output power of the seawater metal-air battery, achieves efficient and stable oxygen reduction, promotes the practical development of the seawater metal-air battery, and can effectively overcome the defects of the prior art.

[0005] The first aspect of the embodiment of the present application provides a preparation method of an oxygen reduction catalyst for constructing a local "alkaline-like" microenvironment, comprising the following steps:

[0006] (1) Fe is loaded on a core MOF material to obtain a core Fe / MOF material, and then metal atoms M with water activation ability are constructed in situ on a shell MOF material by an epitaxial growth method to obtain a Fe / MOF@M / MOF precursor material with a core-shell structure, and Fe and M are limited in the core and the shell, respectively;

[0007] (2) in-situ carbon conversion of the Fe / MOF@M / MOF precursor material by pyrolysis to obtain the FeNC@MNC oxygen reduction catalyst for constructing a local "alkaline-like" microenvironment in natural seawater.

[0008] In some embodiments that can include the above embodiments, in step (1), the metal atom M having water activation ability is at least one of Cu, Ni, and Zn. Cu is more preferred in view of its stronger water activation ability, but other metals having water activation ability are also suitable for the present application.

[0009] In some embodiments that can include the above embodiments, in step (2), the pyrolysis temperature is 800-1000°C, and the pyrolysis time is 1-4h, preferably 1-3h.

[0010] In some embodiments that can include the above embodiments, in step (1), the MOF material in the core Fe / MOF material and the shell M / MOF material is ZIF-8.

[0011] During pyrolysis, Fe and Cu are respectively in-situ confined in the core-shell double-layer carbon carrier, migration of Fe and Cu is inhibited, and an oxygen reduction catalyst with Fe single atoms in the core layer having oxygen reduction activity and Cu single atoms in the shell layer having water activation ability is formed.

[0012] In some embodiments that can include the above embodiments, the preparation process of the core Fe / MOF material is as follows:

[0013] Zn(NO3)2·6H2O and Fe(C5H7O2)3 were dissolved in methanol, ultrasonically dispersed, and denoted as solution A; C4H6N2 was dissolved in methanol and denoted as solution B; solution A was slowly poured into solution B, slowly stirred, and after the reaction was completed, the precipitate was collected by centrifugation, washed with methanol several times by centrifugation, and vacuum dried overnight to obtain the core Fe / MOF material.

[0014] In some embodiments that can include the above embodiments, the preparation process of the Fe / MOF@M / MOF precursor material having a core-shell structure is as follows:

[0015] The core Fe / MOF material is dispersed in methanol, denoted as solution C; Cu(C5H7O2)2 is dissolved in methanol and ultrasonically dispersed, denoted as solution D; C4H6N2 is dissolved in methanol, denoted as solution E; solution D and solution E are slowly poured into solution C respectively, and slowly stirred, denoted as solution F; Zn(NO3)2·6H2O is dissolved in methanol and ultrasonically dispersed, denoted as solution G; solution G is added to solution F, and slowly stirred, after the reaction is completed, the precipitate is collected by centrifugation, washed with methanol several times by centrifugation, and dried in vacuum overnight to obtain a Fe / MOF@M / MOF precursor material with a core-shell structure.

[0016] In some embodiments which can include the above-mentioned embodiments, in step (1), the mass ratio of the Fe, the core MOF material, the M and the shell MOF material is 5:30:1:10. By controlling the thickness of the shell MOF material, the optimal performance is screened.

[0017] The second aspect of the embodiments of the present application further provides an oxygen reduction catalyst for constructing a local 'alkaline-like' microenvironment, which is prepared by the above-mentioned method.

[0018] The third aspect of the embodiments of the present application further provides the application of the above-mentioned oxygen reduction catalyst for constructing a local 'alkaline-like' microenvironment in a seawater metal-air battery.

[0019] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0020] The core of the present application is to synthesize a catalyst with water activation ability, thereby constructing a local 'alkaline-like' microenvironment, overcoming the challenges of low ionic conductivity and chloride adsorption of natural seawater, enhancing the stability and activity of the catalyst in seawater, realizing efficient and stable oxygen reduction, and promoting the practical development of seawater metal-air batteries. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0022] Figure 1 The synthesis flow chart of the core-shell FeNC@CuNC catalyst for constructing a local 'alkaline-like' microenvironment of the present application;

[0023] Figure 2 The X-ray diffraction pattern of the core-shell FeNC@CuNC catalyst synthesized in Embodiment 1 of the present application;

[0024] Figure 3 TEM image of core-shell FeNC@CuNC catalyst synthesized in Example 1 of the present application;

[0025] Figure 4 Spherical aberration image of core-shell FeNC@CuNC catalyst synthesized in Example 1 of the present application;

[0026] Figure 5 Oxygen reduction reaction catalytic performance chart of core-shell FeNC@CuNC catalyst synthesized in Example 1 of the present application and catalyst in Comparative Example 1-2 and commercial Pt / C. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0028] The experimental methods used in the embodiments of the present application are all conventional methods unless otherwise specified.

[0029] In the following examples and comparative examples, all raw materials can be obtained by commercial purchase or conventional methods unless otherwise specified.

[0030] The present application provides a synthesis method of an oxygen reduction catalyst for constructing a local "alkaline-like" microenvironment. First, a core layer MOF precursor loaded with Fe monatomic atoms is synthesized. Then, metal atoms with water activation capacity are loaded on the shell layer MOF by epitaxial growth method. Finally, a core-shell FeNC@CuNC catalyst for constructing a local "alkaline-like" microenvironment can be obtained by high-temperature in-situ carbon conversion (after pyrolysis, Fe and Cu are limited in the core layer NC carrier and the shell layer NC carrier, respectively, and NC is nitrogen-doped carbon. The dimethyl imidazole added during the synthesis of ZIF-8 provides nitrogen and carbon elements, which are converted into nitrogen-doped carbon carrier after high-temperature pyrolysis).

[0031] Among them, "metal atoms with water activation capacity" can be selected according to actual needs, which is not limited to Cu atoms selected in the following embodiments. Moreover, based on the synthesis method proposed in the present application, a person skilled in the art can select different reagents and method steps according to actual needs, which is not limited to the specific reagents and condition parameters used in the following embodiments.

[0032] Wherein: the construction of local "alkaline-like" micro-environment means that the O-H bond of water molecules is broken to form active OH by the metal with the ability to activate water - And Fe single atom site pairs OH - has strong adsorption capacity, thus it can construct a "alkaline-like" local micro-environment around the Fe single atom active center.

[0033] Example 1: Synthesis method of core-shell FeNC@CuNC catalyst

[0034] I. Synthesis method of core-shell Fe / MOF@Cu / MOF precursor

[0035] i. Synthesis of core layer Fe / MOF precursor

[0036] Take 1.16g of Zn(NO3)2·6H2O and 0.2g of Fe(C5H7O2)3 and dissolve them in 50mL of methanol, ultrasonic for 10min, marked as solution A. Take 1.314g of C4H6N2 and dissolve it in 50mL of methanol, marked as solution B. Then slowly pour solution A into solution B, slowly stir for 12h. After the reaction, centrifuge at 9000rpm to collect the precipitate, wash with methanol for 3 times, and the obtained product is dried under vacuum overnight to obtain a light yellow solid, which is the core layer Fe / MOF.

[0037] ii. Synthesis of core-shell Fe / MOF@Cu / MOF precursor

[0038] Take 200mg of Fe / MOF and disperse it in 50mL of methanol, marked as solution C. Take 0.1g of Cu(C5H7O2)2 and add it to 50mL of methanol, ultrasonic for 10min to disperse it uniformly, marked as solution D. Take 0.657g of C4H6N2 and add it to 20mL of methanol to dissolve, marked as solution E. Then, slowly pour solutions D and E into C, slowly stir for 12h, marked as solution F. Then take 0.58g of Zn(NO3)2·6H2O and add it to 20mL of methanol, ultrasonic for 10min, marked as solution G. Then add solution G to solution F, slowly stir for 6h. After the reaction, centrifuge at 9000rpm to collect the precipitate, wash with methanol for 3 times, and the obtained product is dried under vacuum overnight to obtain a light yellow solid, which is the core-shell Fe / MOF@Cu / MOF precursor.

[0039] II. Synthesis method of core-shell FeNC@CuNC catalyst

[0040] The core-shell Fe / MOF@Cu / MOF precursor is placed in a tube furnace and pyrolyzed at 900℃ for 2 hours under Ar atmosphere to obtain the core-shell FeNC@CuNC catalyst. The synthesis flow chart of the core-shell FeNC@CuNC catalyst for constructing a local "alkaline-like" microenvironment is shown in Figure 1 .

[0041] Figure 2 The X-ray diffraction pattern of the core-shell FeNC@CuNC catalyst synthesized in the present embodiment is shown in Figure 3 The TEM image of the core-shell FeNC@CuNC catalyst synthesized in the present embodiment is shown in the present embodiment. The FeNC@CuNC catalyst synthesized in the present embodiment has no metal particles, and in addition, a core-shell structure can be observed.

[0042] The spherical aberration image of the FeNC@CuNC catalyst is shown in Figure 4 The red boxed position can find dispersed metal atoms, and it can be considered that the metal exists in the form of single atoms.

[0043] The oxygen reduction reaction catalytic performance of the prepared catalyst was tested by cyclic voltammetry scanning in oxygen-saturated natural seawater at a scanning speed of 5mV / s and an electrode rotation speed of 1600r / min. As shown in Figure 5 , the prepared core-shell FeNC@CuNC catalyst exhibits good oxygen reduction reaction catalytic performance.

[0044] Example 2

[0045] The synthesis provided in the present embodiment can refer to Example 1, and the difference is that the metal atom M having the ability to activate water is Ni.

[0046] Example 3

[0047] The synthesis provided in the present embodiment can refer to Example 1, and the difference is that the metal atom M having the ability to activate water is Zn.

[0048] Comparative Example 1: Synthesis method of core-shell FeNC@NC catalyst

[0049] I. Synthesis method of core-shell Fe / MOF@MOF

[0050] i. Synthesis of core layer Fe / MOF precursor

[0051] Take 1.16 g of Zn(NO3)2·6H2O and 0.2 g of Fe(C5H7O2)3 and dissolve them in 50 mL of methanol, ultrasonic for 10 min, and mark it as solution A. Take 1.314 g of C4H6N2 and dissolve it in 50 mL of methanol, and mark it as solution B. Then slowly pour solution A into solution B, and slowly stir for 12 h. After the reaction is completed, centrifugally collect the precipitate at 9000 rpm, wash it with methanol for 3 times, and dry the obtained product under vacuum overnight to obtain a light yellow solid, which is the core layer Fe / MOF.

[0052] ii. Synthesis of core-shell Fe / MOF@MOF precursor

[0053] Take 200 mg of Fe / MOF and disperse it in 50 mL of methanol, and mark it as solution C. Take 0 g of Cu(C5H7O2)2 and add it to 50 mL of methanol, ultrasonic for 10 min, and mark it as solution D. Take 0.657 g of C4H6N2 and add it to 20 mL of methanol to dissolve, and mark it as solution E. Then, slowly pour solutions D and E into C respectively, and slowly stir for 12 h, and mark it as solution F. Then take 0.58 g of Zn(NO3)2·6H2O and add it to 20 mL of methanol, ultrasonic for 10 min, and mark it as solution G. Then add solution G to solution F, and slowly stir for 6 h. After the reaction is completed, centrifugally collect the precipitate at 9000 rpm, wash it with methanol for 3 times, and dry the obtained product under vacuum overnight to obtain a light yellow solid, which is the core-shell Fe / MOF@MOF precursor.

[0054] II. Synthesis method of core-shell FeNC@NC catalyst

[0055] Place the core-shell Fe / MOF@MOF precursor in a tube furnace, pyrolyze it at 900°C for 2 hours under Ar atmosphere, and obtain the core-shell FeNC@NC catalyst.

[0056] Comparative example 2: synthesis method of core-shell NC@CuNC catalyst

[0057] I. Synthesis method of core-shell MOF@Cu / MOF

[0058] i. Synthesis of core layer MOF precursor

[0059] Take 1.16 g of Zn(NO3)2·6H2O and 0 g of Fe(C5H7O2)3 and dissolve them in 50 mL of methanol, ultrasonic for 10 min, and mark it as solution A. Take 1.314 g of C4H6N2 and dissolve it in 50 mL of methanol, and mark it as solution B. Then slowly pour solution A into solution B, and slowly stir for 12 h. After the reaction is completed, centrifugally collect the precipitate at 9000 rpm, wash it with methanol for 3 times, and dry the obtained product under vacuum overnight to obtain a light yellow solid, which is the core layer MOF.

[0060] ii. Synthesis of core-shell MOF@Cu / MOF precursor

[0061] Take 200 mg of the core layer MOF and disperse it in 50 mL of methanol, and mark it as solution C. Take 0.1 g of Cu(C5H7O2)2 and add it to 50 mL of methanol, and ultrasonically disperse the mixture for 10 minutes to make it uniformly dispersed, and mark it as solution D. Take 0.657 g of C4H6N2 and add it to 20 mL of methanol to dissolve it, and mark it as solution E. Then, slowly pour solutions D and E into solution C respectively, and slowly stir for 12 h, and mark it as solution F. Then, take 0.58 g of Zn(NO3)2·6H2O and add it to 20 mL of methanol, and ultrasonically disperse it for 10 min, and mark it as solution G. Then, add solution G to solution F, and slowly stir for 6 h. After the reaction is completed, centrifuge the precipitate at 9000 rpm, and wash it with methanol for 3 times, and dry the obtained product under vacuum overnight to obtain a light yellow solid, which is the core-shell MOF@Cu / MOF precursor.

[0062] II. Synthesis method of core-shell NC@CuNC catalyst

[0063] Place the core-shell MOF@Cu / MOF precursor in a tube furnace, and pyrolyze it at 900℃ for 2 hours under an Ar atmosphere to obtain the core-shell NC@CuNC catalyst.

[0064] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing an oxygen reduction catalyst for constructing a localized "alkaline-like" microenvironment, characterized in that: The following steps are involved: (1) Fe is loaded on the core MOF material to obtain the core Fe / MOF material. Then, the metal atom M with the ability to activate water is in situ constructed on the shell MOF material through epitaxial growth to obtain the core-shell structure Fe / MOF@M / MOF precursor material, in which Fe and M are confined in the core and shell, respectively. (2) The Fe / MOF@M / MOF precursor material was subjected to in situ carbon conversion by pyrolysis to obtain the FeNC@MNC oxygen reduction catalyst that constructed a local "alkaline-like" microenvironment in natural seawater; The metal atom M having the ability to activate water is Cu; In step (1), the MOF materials in the core Fe / MOF material and the shell M / MOF material are both ZIF-8; the preparation process of the core Fe / MOF material is as follows: Zn(NO3)2·6H2O and Fe(C5H7O2)3 are dissolved in methanol and ultrasonically dispersed, which is recorded as solution A; C4H6N2 is dissolved in methanol, which is recorded as solution B; solution A is slowly poured into solution B and slowly stirred. After the reaction is completed, the precipitate is collected by centrifugation, washed several times with methanol by centrifugation, and vacuum dried overnight to obtain the core Fe / MOF material; The preparation process of the Fe / MOF@M / MOF precursor material with a core-shell structure is as follows: the core Fe / MOF material is dispersed in methanol, which is recorded as solution C; Cu(C5H7O2)2 is dissolved in methanol and ultrasonically dispersed, which is recorded as solution D; C4H6N2 is dissolved in methanol, which is recorded as solution E; solution D and solution E are slowly poured into solution C respectively, and slowly stirred, which is recorded as solution F; Zn(NO3)2·6H2O is dissolved in methanol and ultrasonically dispersed, which is recorded as solution G; Solution G was added to solution F and stirred slowly. After the reaction was completed, the precipitate was collected by centrifugation, washed several times with methanol, and vacuum dried overnight to obtain a Fe / MOF@M / MOF precursor material with a core-shell structure.

2. The method for preparing an oxygen reduction catalyst for constructing a localized "alkaline-like" microenvironment according to claim 1, characterized in that: In step (2), the pyrolysis temperature is 800-1000°C, and the pyrolysis time is 1-4 hours.

3. The method for preparing an oxygen reduction catalyst for constructing a localized "alkaline-like" microenvironment according to claim 1, characterized in that: In step (1), the mass ratio of Fe, core MOF material, M and shell MOF material is 5:30:1:

10.

4. An oxygen reduction catalyst for constructing a localized "alkaline-like" microenvironment, characterized in that: An oxygen reduction catalyst for constructing a localized "alkaline-like" microenvironment prepared by the method described in any one of claims 1 to 3.

5. Use of the oxygen reduction catalyst for constructing a localized "alkaline-like" microenvironment as claimed in claim 4 in seawater metal-air batteries.

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