CN113611881B - Atomic-level dispersed Fe/nitrogen-doped mesoporous carbon spheres and preparation method and application thereof - Google Patents
Atomic-level dispersed Fe/nitrogen-doped mesoporous carbon spheres and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a method for preparing an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalytic material (N-MCS-Fe) by self-assembling a block copolymer template agent and a nitrogen-containing carbon source precursor in a high-temperature hydrothermal process to obtain a nitrogen-doped mesoporous polymer sphere, adsorbing transition metal ions by a wet chemical impregnation method strategy, and combining with a programmable high-temperature carbonization process. The atomic-level dispersed N-MCS-Fe catalyst obtained by the method has the advantages of high specific surface area, uniform pore size distribution and excellent conductivity, and shows excellent oxygen reduction electrocatalytic performance and stability in alkaline seawater. In addition, the material is used as an air electrode to be assembled in an alkaline seawater zinc-air battery, and the open-circuit voltage and the power density are higher. The preparation method of the catalyst has the advantages of simple process, convenient operation, low cost and excellent seawater corrosion resistance, and has certain guiding significance for developing a novel seawater zinc-air battery cathode oxygen reduction electrocatalyst.
Description
Technical Field
The invention belongs to the field of electrochemical energy materials, and particularly relates to an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere and a preparation method and application thereof.
Background
In recent years, with environmental pollution caused by fossil energy consumption and carbon emission, the concepts of green, low carbon and sustainable development become global consensus, and the main subjects of China and even the world are to improve the utilization rate of energy and develop alternative energy. The development of new and effective energy storage technologies to maximize the use of renewable energy sources is currently favored by a wide range of researchers. Among them, water-based metal-air batteries (zinc-air batteries, ZABs) are considered to be the most promising energy storage devices because they can use naturally abundant low-cost active materials and have a high theoretical energy density. Typical zinc-air batteries mainly use zinc as an anode, an air electrode as a cathode, and an alkaline aqueous solution as an electrolyte, and currently, the most widely used ZABs alkaline electrolyte is mainly prepared from high-purity deionized water (fresh water), high-concentration alkali and zinc salt.
The reaction principle of the zinc-air battery is mainly as follows:
the general reaction formula is as follows: 2Zn + O 2 →2ZnO
Cathode: o is 2 +2H 2 O+4e - →4OH -
Anode: zn +2OH – →ZnO+H 2 O+2e -
The cathode mainly generates oxygen reduction reaction related to a multi-electron reaction process, the dynamics is slow, and the power density and the conversion efficiency of the zinc-air battery are limited, so that the commercialization promotion process is stopped. Therefore, it is urgently needed to develop a novel oxygen reduction electrocatalyst to greatly improve the oxygen reduction reaction rate, and the current commonly used commercial electrocatalyst is still a noble metal Pt/C catalyst, but the Pt element has the defects of resource scarcity, high price, easy poisoning and the like, and the large-scale use of the Pt element is limited. In order to greatly improve the power density of the zinc-air battery and reduce the research and development cost, the mass production of key materials such as the electrocatalyst and the like needs to be realized as soon as possible, the consumption of platinum in the electrocatalyst needs to be reduced, and the catalytic activity and stability of the catalyst are ensured, so that the method has very important significance for promoting the commercialization process of the zinc-air battery.
In the last decade, transition metal-based and carbon-based materials, which are abundant and inexpensive, have attracted considerable attention from researchers. Wherein the single-atom transition metal-nitrogen-carbon catalyst (M-N-C) becomes a research hotspot in the field of oxygen reduction catalysts. The monatomic M-N-C catalyst is a novel efficient electrocatalyst which combines isolated single metal atoms with coordination atoms such as C, N, O, S and the like on a carrier, thereby realizing the spatial isolation and uniform dispersion of the metal atoms. Zhang et al (Nature Chemistry, 2011,3(8),634 + 641) was first introduced in 2011The concept of the monatomic catalyst, and the synthesis of the platinum monatomic catalyst fixed on the iron oxide, has been found to have very high reactivity and stability in the field of catalytic oxidation of CO. Since the catalyst has the advantages of nearly 100% of atom utilization rate, high reaction activity, selectivity, stability and the like, the monatomic catalyst is rapidly developed in the field of electrocatalysis. For example, the leidona topic group (angelw. chem. int. ed.,2017,56(24),6937-6941) reports a monatomic Fe and N co-doped carbon skeleton formed by heat-treating a Fe-modified zeolite imidazolate skeleton (ZIF), which has excellent activity and stability in an alkaline environment. Wang et al (Small,2021,17(6), e2006178) developed a dual-anchoring method to synthesize an atomic-level Fe-loaded N-doped porous carbon catalyst (FeNC-D0.5), i.e. the space-limited domain effect of silicon dioxide and the coordination of diethylenetriaminepentaacetic acid (DTPA) are utilized to prevent the aggregation of Fe and obtain high-density Fe-N 4 An active center. The structure has proper hydrophobicity and larger specific surface area, so that the prepared atomic-scale FeNC-D0.5 has excellent oxygen reduction catalytic performance. Fen with atomic level dispersion by Kuang et al (Nano Energy, 2020,71,104547.) 4 The site is anchored on a three-dimensional ordered microporous mesoporous-macroporous nitrogen-doped carbon skeleton (3DOM Fe-N-C). Benefiting from highly dispersed FeN 4 The synergistic effect of the active center and the three-dimensional ordered porous structure, 3DOM Fe-N-C-900 shows excellent ORR activity and excellent stability in both alkaline medium and acidic medium. In addition, the 3DOM-Fe-N-C-900 catalyst is used as a cathode catalytic material to be applied to the alkaline zinc-air battery, and 235 mW cm of carbon is obtained -2 High power density of 768.3mAh g -1 High specific capacity of (2). It is worth noting that these catalysts are mainly applied to the zinc-air battery assembled after high-purity deionized water (fresh water) is prepared into strong alkaline electrolyte, but the fresh water resource on earth is increasingly scarce, the pollution is serious and uneven, and large-scale fresh water consumption brings heavy environmental pressure. As is known, seawater resources have the advantages of high natural abundance (about 96.5% of total water resources of the earth), low cost and the like, and have great potential for replacing fresh water in the field of electrochemical energy. Especially for zinc oxideFor the gas battery, the seawater is used as the electrolyte, so that various economic and social advantages are brought, the development cost of the electrolyte and the battery is reduced, and the competition of human activities on the consumption of limited fresh water resources is relieved. More importantly, the electrolyte based on seawater can greatly expand the application of the zinc-air battery in islands and coastal areas with shortage of fresh water resources. However, alkaline seawater zinc-air cells have the following challenges for catalyst design: (1) seawater has high salinity, and contains sodium ion and chloride ion, and minority cation and anion such as Mg 2+ ， Ca 2+ ，K + ，SO 4 2- ，HCO 3 - Etc., which accelerate corrosion of the catalyst, resulting in poor stability. (2) The chloride ions are used as main dissolved components in seawater to hinder the adsorption behavior of oxygen-containing intermediates on active sites in the ORR process of the cathode oxygen reduction reaction, so that the catalytic activity is greatly reduced, and the power density of the zinc-air battery is further reduced. So far, there is no report about the application of the monatomic M-N-C catalytic material in the alkaline seawater zinc-air battery.
Disclosure of Invention
Aiming at the problems, the invention provides a preparation method and application of an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere. The invention increases the effective utilization rate and the external stability of the intrinsic active sites by reasonably designing the novel high-efficiency cathode oxygen reduction electrocatalyst, can realize the practical application in the assembly of the zinc-air battery by the strong alkaline seawater electrolyte, and is very important for clean and sustainable energy storage by utilizing natural resources.
In order to solve the technical problems, the invention adopts the technical scheme that:
in a first aspect, the invention provides an atomically dispersed Fe/nitrogen-doped mesoporous carbon sphere, wherein the diameter of the Fe/nitrogen-doped mesoporous carbon sphere is 50-100nm, the pore diameter is 3-5nm, the mass fraction of Fe is 1-2.5%, and the atomic coverage of Fe is about 0.2-0.5 atom per square nanometer.
In an optimized embodiment, the diameter of the Fe/nitrogen-doped mesoporous carbon sphere is 60nm, the pore diameter is 3.9nm, the mass fraction of Fe is 2.02%, and the Fe atomic coverage rate is 0.38 atoms per square nanometer.
The atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon spheres with the specifications have larger specific surface area and a large number of mesopores, and the mesoporous structure can prevent ions in a solution from corroding active center M-Nx sites, so that high-efficiency oxygen reduction catalytic activity and stability are realized, and the mesoporous carbon spheres have potential application value in alkaline seawater zinc-air batteries.
In a second aspect, the invention provides a preparation method of an atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon sphere, comprising the following steps:
(a) a hydrothermal process: dissolving Pluronic F127 in deionized water to obtain a solution A, dissolving 3-aminophenol in deionized water to obtain a solution B, dissolving hexamethylenetetramine in deionized water to obtain a solution C, mixing the solution A, the solution B and the solution C, stirring for 5-15min, transferring into a polytetrafluoroethylene reaction kettle, placing in an oven for reaction at 80-150 ℃ for 12-48h, centrifuging, washing with deionized water, and vacuum-drying the collected product at 25-100 ℃ to obtain a final product, namely a mesoporous polymer sphere NPS;
(b) preparation of a Fe-loaded nitrogen-doped mesoporous polymer sphere precursor NPS-Fe: adding the mesoporous polymer ball NPS into deionized water, stirring and ultrasonically treating, dripping potassium ferricyanide solution, stirring for 8-24h, centrifuging, washing with deionized water, and vacuum drying at 25-100 ℃ for 8-36h to obtain a precursor NPS-Fe.
(c) And (3) calcining: and (c) placing a proper amount of the precursor in the step (b) into a tube furnace, carrying out temperature programmed heating to 600-1000 ℃ at the heating rate of 1-10 ℃/min under the protection of nitrogen atmosphere, carrying out heat preservation for 1-3h, and naturally cooling to room temperature to obtain the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst N-MCS-Fe-X (X represents the calcination temperature).
In some embodiments, the specific steps are as follows:
(a) a hydrothermal process: dissolving Pluronic F127 in deionized water to obtain a solution A, dissolving 3-aminophenol in deionized water to obtain a solution B, dissolving hexamethylenetetramine in deionized water to obtain a solution C, mixing the solution A, the solution B and the solution C, stirring for 5-15min, transferring into a polytetrafluoroethylene reaction kettle, placing in an oven for reaction at 100 ℃ for 24h, centrifuging, washing with deionized water, and vacuum-drying the collected product at 50 ℃ to obtain a final product, namely a mesoporous polymer sphere NPS;
(b) preparation of a Fe-loaded nitrogen-doped mesoporous polymer sphere precursor NPS-Fe: adding the mesoporous polymer ball NPS into deionized water, stirring and ultrasonically treating, dripping potassium ferricyanide solution, stirring for 12 hours, centrifuging, washing with the deionized water, and vacuum-drying for 24 hours at 50 ℃ to obtain a precursor NPS-Fe.
(c) And (3) calcining: and (c) placing a proper amount of the precursor in the step (b) into a tube furnace, carrying out temperature programmed heating to 850-900 ℃ at the heating rate of 1-4 ℃/min under the protection of nitrogen atmosphere, carrying out heat preservation for 3h, and naturally cooling to room temperature to obtain the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst N-MCS-Fe-X.
Preferably, the mass ratio of Pluronic F127 to deionized water in step (a) is 1:46-50, the mass ratio of 3-aminophenol to deionized water is 1:88-94, and the mass ratio of hexamethylenetetramine to deionized water is 1: 88-94.
Preferably, the mass ratio of the mesoporous polymer spheres to the deionized water in the step (b) is 1:1-2, and the mass ratio of the potassium ferricyanide to the mesoporous polymer spheres is 1: 27-30.
Preferably, the temperature rise rate in step (c) is 2 ℃/min, up to 900 ℃.
In a third aspect, the invention provides an application of an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere in a zinc-air battery. The strong-alkaline electrolyte of the zinc-air battery is not prepared from fresh water, but is prepared from seawater to prepare a strong-alkaline (6M KOH) electrolyte. However, the components in the seawater are complex, the electrolyte ions are of various types, the corrosion of the electrocatalyst can be accelerated, the oxygen reduction reaction is hindered, the catalytic activity and the stability of the zinc-air battery are poor, and the zinc-air battery belongs to the blank field of the existing alkaline seawater zinc-air battery.
Further, a using method of fixing the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon spheres on a carbon paper electrode as an air cathode catalyst in a zinc-air battery, specifically, ultrasonically dispersing the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst in a Nafion mixed solution to obtain 10mg/mL ink dispersion, uniformly dripping the ink dispersion on the carbon paper electrode by using a micro syringe, and baking under an infrared lamp, wherein the Nafion mixed solution is a solution of DMF (dimethyl formamide)/isopropanol (isopropanol)/Nafion (Nafion) with a volume ratio of 4:0.5-1.5: 0.05-0.15.
Compared with the prior art, the invention has the beneficial effects that:
(1) the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst provided by the invention has concentrated particle size distribution, is expected to realize stable mass production, and has stable performance when being applied to a seawater zinc-air battery.
(2) The atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst provided by the invention has good Fe atom dispersibility, promotes the adsorption of oxygen molecules in the oxygen reduction reaction process, reduces the overpotential of the oxygen reduction reaction, can rapidly realize high-efficiency oxygen reduction performance in an alkaline seawater environment, and shows excellent electrochemical stability: has superior half-wave potential and current density than commercial Pt/C electrocatalysts; and has good stability under long-term cycling tests.
(3) The invention adopts the nitrogen-doped mesoporous carbon spheres as the load matrix, and the nitrogen-doped mesoporous carbon spheres have the advantages of good conductivity, larger pore volume, higher specific surface area and the like. The nitrogen-containing functional groups derived from the triblock copolymer Pluronic F127, triaminophenol and hexamethylenetetramine are advantageous for anchoring and promoting uniform dispersion of Fe atoms, thereby preventing agglomeration and migration of Fe atoms during pyrolysis.
(4) The invention takes the Fe/nitrogen-doped mesoporous carbon sphere catalyst applied to atomic-scale dispersion as an air cathode, alkaline seawater as electrolyte and a zinc sheet as an anode to assemble the alkaline seawater zinc-air battery device, and the alkaline seawater zinc-air battery shows very high power density and open-circuit voltage: has superior power density and open circuit voltage to alkaline seawater zinc-air cell devices assembled when commercial Pt/C electrocatalyst is used as air electrode, and has very superior stability.
(5) The invention provides an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst, wherein the mass fraction of Fe is 2.02%, and the mass fraction of Pt in commercial Pt/C is 20%. The raw materials adopted in the preparation method are abundant in reserves, relatively low in price and simple in preparation process, and the obtained atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst has oxygen reduction catalytic performance equivalent to that of commercial Pt/C, shows excellent activity in an alkaline seawater zinc-air battery, and is very important for clean and sustainable energy storage by utilizing natural resources.
Drawings
FIG. 1 is a TEM image and a high resolution transmission HRTEM image (a-c) of an atomic-scale dispersed Fe/N-doped mesoporous carbon sphere; HAADF-STEM image and C, N of the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon spheres and Fe distribution image (d-g);
FIG. 2 is an XRD image of an atomically dispersed Fe/nitrogen doped mesoporous carbon sphere catalyst;
FIG. 3 is N of an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst 2 Adsorption and desorption curve graphs and aperture distribution graphs;
FIG. 4 is a LSV graph of atomically dispersed Fe/nitrogen doped mesoporous carbon spheres and a commercial Pt/C catalyst in alkaline seawater (0.1M KOH in seawater);
FIG. 5 is a comparison graph of open circuit voltages of an alkaline seawater zinc-air cell assembled by using atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon spheres as an air electrode and an alkaline seawater zinc-air cell assembled by using a commercial Pt/C catalyst as an air electrode;
FIG. 6 is a graph comparing the power density of an alkaline seawater zinc-air cell assembled by using an atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon sphere as an air electrode and an alkaline seawater zinc-air cell assembled by using a commercial Pt/C catalyst as an air electrode;
fig. 7 is a graph comparing the stability of an alkaline seawater zinc-air cell assembled by using an atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon sphere as an air electrode with that of an alkaline seawater zinc-air cell assembled by using a commercial Pt/C catalyst as an air electrode.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the present invention is not limited to the examples.
Example 1 preparation of Nitrogen-doped mesoporous carbon sphere nanomaterial (N-MCS-900)
In order to compare the performance difference between the nitrogen-doped mesoporous carbon sphere oxygen reduction electrocatalyst without supported atomic-level dispersed Fe and the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst, firstly, a nitrogen-doped mesoporous carbon sphere (N-MCS) is prepared, and the specific preparation method comprises the following steps:
(a) a hydrothermal process: synthesis of nitrogen-doped mesoporous polymer spheres (NPS): pluronic F127, 3-aminophenol and HMT are respectively used as a template, a carbon source and a nitrogen source, and a soft template method is adopted to synthesize the nitrogen-doped mesoporous polymer spheres. The specific operation is as follows: dissolving 0.625g F127 in 30mL of deionized water, and fully stirring to obtain a uniform solution A; adding 0.327g of 3-aminophenol into 30mL of deionized water, and uniformly stirring to obtain a solution B; 0.280g HMT was added to 20mL deionized water and stirred well to homogeneity and was designated as solution C. And (3) quickly pouring the solution B and the solution C into the solution A in sequence under the stirring state of the solution A, and continuously stirring for about 10min to obtain a mixed solution uniformly. And then, transferring the mixed solution into a polytetrafluoroethylene reaction kettle, placing the reaction kettle in an oven at 100 ℃ for 24 hours, centrifuging, washing with deionized water for three times, and drying the collected product at 50 ℃ in vacuum to obtain a final product NPS.
(b) And (3) calcining: placing the ceramic boat containing the nitrogen-doped mesoporous polymer sphere precursor NPS in a programmable atmosphere tube furnace, and carrying out temperature programming to 900 ℃ at the speed of 2 ℃/min under the condition of N 2 Calcining at high temperature in the atmosphere, preserving the heat for 3 hours, and naturally cooling to room temperature to obtain the nitrogen-doped mesoporous carbon sphere nano material (N-MCS-900).
Example 2 preparation of an atomically dispersed Fe/nitrogen doped mesoporous carbon sphere catalyst (N-MCS-Fe-900)
A preparation method of an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst nano material comprises the following steps:
(a) a hydrothermal process: synthesis of nitrogen-doped mesoporous polymer spheres (NPS): pluronic F127, 3-aminophenol and HMT are respectively used as a template, a nitrogen source and a carbon source, and a soft template method is adopted to synthesize the nitrogen-doped mesoporous polymer spheres. The specific operation is as follows: dissolving 0.625g F127 in 30mL of deionized water, and fully stirring to obtain a uniform solution A; adding 0.327g of 3-aminophenol into 30mL of deionized water, and uniformly stirring to obtain a solution B; 0.280g HMT was added to 20mL deionized water and stirred well to homogeneity and was designated as solution C. And (3) quickly pouring the solution B and the solution C into the solution A in sequence under the stirring state of the solution A, and continuously stirring for about 10min to obtain a mixed solution uniformly. And then, transferring the mixed solution into a polytetrafluoroethylene reaction kettle, placing the reaction kettle in an oven at 100 ℃ for 24 hours, centrifuging, washing with deionized water for three times, and drying the collected product at 50 ℃ in vacuum to obtain a final product NPS.
(b) Preparation of Fe-loaded nitrogen-doped mesoporous polymer sphere precursor (NPS-Fe): adding 24mg of mesoporous polymer spheres into 36mL of deionized water, and stirring and ultrasonically treating to obtain a uniform suspension. The stirring was continued, and the concentration was 1.65mg mL -1 500. mu.L of potassium ferricyanide (K) 3 [Fe(CN) 6 ]) The solution was slowly dropped into the above solution. After stirring at room temperature for 12h, centrifugation, washing with deionized water at least three times and vacuum drying at 50 ℃ for 24h gave the precursor (NPS-Fe).
(c) And (3) calcining: and (c) placing a proper amount of the precursor in the step (b) into a tube furnace, carrying out programmed heating to 900 ℃ at a heating rate of 2 ℃/min under the protection of nitrogen atmosphere, carrying out heat preservation for 3h, and naturally cooling to room temperature to obtain the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst (N-MCS-Fe-900).
Example 3 method for modifying glassy carbon electrode by using atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst
Ultrasonically dispersing the prepared atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst (N-MCS-Fe-900) in a Nafion mixed solution to obtain 2mg/mL ink dispersion liquid, uniformly dripping the Nafion mixed solution into a glassy carbon electrode by using a micro-syringe, and baking under an infrared lamp to obtain the catalyst modified glassy carbon electrode, wherein the volume ratio of the DMF to the isopropanol to the Nafion mixed solution is 4:0.5-1.5: 0.05-0.15.
Example 4 test of performance of oxygen reduction catalytic reaction of glassy carbon electrode modified by atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst
In 0.1M KOH electrolyte prepared from seawater, a three-electrode system is adopted to carry out electrochemical test on the catalyst, a glassy carbon electrode modified by an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst is used as a working electrode, a saturated Ag/AgCl electrode is used as a reference electrode, a Pt wire is used as a counter electrode, and an Shanghai Hua CHI-842D electrochemical workstation and a Japanese ALS RRDE-3A rotary disc device are adopted to carry out oxygen reduction catalytic reaction performance test on the glassy carbon electrode modified by the catalyst. The oxygen reduction catalytic activity was tested in 0.1M KOH solution prepared from natural seawater of Qingdao under oxygen saturation.
The specific operation is as follows: at the constant temperature of 25 ℃, introducing oxygen into 0.1M KOH electrolyte prepared from Qingdao natural seawater for about 60min in advance to saturate the oxygen in the solution, and then scanning an oxygen reduction polarization curve from high potential 0.2V to low potential-0.8V at a scanning rate of 10 mV/s. The glassy carbon electrode modified by the nitrogen-doped mesoporous carbon sphere catalyst or the glassy carbon electrode modified by the atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst, which is obtained by the invention, is placed in a 0.1M KOH solution prepared from oxygen-saturated Qingdao natural seawater to perform a cathodic oxygen reduction reaction test, and the activity parameters for representing the oxygen reduction reaction comprise the initial potential, half-wave potential and limiting current density of the oxygen reduction reaction.
Example 5 alkaline seawater Zinc air cell Assembly and testing
Polished zinc foil was used as anode with catalyst layer (1mg cm) -2 ) The hydrophobic carbon paper of (a) is used as an air cathode. In the alkaline seawater zinc-air battery, 6.0M KOH solution prepared from Qingdao seawater is used as electrolyte, and the activity of the zinc-air battery is evaluated by measuring an LSV polarization curve on a CHI-760E electrochemical workstation at room temperature at a sweep rate of 10mV s -1 . Constant current charge and discharge stability is measured at 10mAcm by LAND test system -2 At room temperature. For comparison, a commercial Pt/C catalyst (0.5mg cm) was used -2 ) An alkaline seawater zinc-air battery was assembled as an air electrode, and its activity and stability were tested.
Example 6 Fe Mass fraction test in atomically dispersed Fe/Nitrogen doped mesoporous carbon spheres
Firstly, performing acid dissolution digestion on an atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst sample prepared in example 2, then fixing the volume to 20mL by using a 5% nitric acid solution, filtering, diluting 10mL of solution to 100mL, and performing ICP-OES: the Agilent 725 instrument test of Agilent company of America shows that the Fe mass fraction in the N-MCS-Fe-900 catalyst is 2.02%.
The invention also detects the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon spheres as shown in figures 1-7.
FIG. 1 is a Transmission Electron Microscope (TEM) used for characterizing the morphology of the catalyst, and as can be seen from a, b and c in FIG. 1, the catalyst N-MCS-Fe-900 presents an obvious cellular mesoporous spherical morphology, the size of the spheres is uniform, the average particle size is about 50-100nm, and the spheres have a plurality of pore structures, which is beneficial to mass transfer and oxygen diffusion. From the High Resolution Transmission Electron Microscope (HRTEM) image (d in FIG. 1), it can be found that the catalyst N-MCS-Fe-900 is composed of disordered carbon having a large number of pores, and no significant iron-based nanoparticles are found. The elemental mapping of energy dispersive X-ray spectroscopy (EDS, e-g in fig. 1) confirms the uniform distribution of iron and nitrogen atoms on the mesoporous carbon spheres.
N-MCS-Fe-900 in FIG. 2 shows the same XRD diffraction peaks as N-MCS-900, with two broad peaks in the range of 20-30 ° and 40-50 ° assigned to (002) and (101) mirror planes, respectively, of graphitic carbon, and no other crystalline diffraction peaks are observed in the XRD pattern, indicating the absence of crystalline Fe particles in the catalyst, indicating that Fe may be present in the catalyst in atomic form.
FIG. 3 by N 2 And (3) carrying out further characterization and analysis on the pore structure of the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst by an adsorption-desorption isotherm test. N is a radical of hydrogen 2 The adsorption-desorption isotherm exhibited a typical type IV curve (b in fig. 3), indicating that the catalyst contained a large amount of mesoporous structure, and the pore size distribution results showed that the mesoporous size in N-MCS-Fe-900 was mainly concentrated at about 3.9 nm. The specific surface area of the catalyst N-MCS-Fe-900 is 574.3m 2 g -1 507.2m higher than pure N-MCS-900 2 g -1 。
FIG. 4 is an evaluation of the electrocatalytic oxygen reduction performance of different catalysts in 0.1M KOH electrolyte prepared from Qingdao natural seawater. At O 2 In saturated electrolyte, Linear Sweep Voltammetry (LSV) curve shows that the Fe/nitrogen doped mesoporous carbon is dispersed at atomic levelThe half-wave potential of the spherical catalyst is 0.905V, and the limiting current density is 4.6mAcm -2 Exceeds the half-wave potential (0.875V) and the limiting current density (4.7 mAcm) of the commercial Pt/C catalyst -2 ) The method shows that the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst can realize rapid oxygen adsorption and reduction processes in an alkaline seawater environment, and shows excellent electrochemical performance.
The atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon spheres in FIG. 5 exhibited excellent open circuit voltage (1.45V) in alkaline seawater zinc-air cells, close to commercial Pt/C (1.47V).
FIG. 6 atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon spheres exhibit power densities exceeding commercial Pt/C catalysts in alkaline seawater zinc-air cells (the power density of the atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon spheres is 176mW cm) -2 Commercial Pt/C power density of 143mW cm -2 )。
Fig. 7 shows that the atomic-level dispersed Fe/nitrogen-doped mesoporous carbon spheres have excellent stability in the alkaline seawater zinc-air battery, are superior to the alkaline seawater zinc-air battery assembled by a commercial Pt/C catalyst, and show a certain commercial application prospect.
By combining the above embodiments and test results, the atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst provided by the invention has uniform diameter and pore size distribution, and has superior oxygen reduction catalytic activity and stability to commercial Pt/C catalysts. In addition, the preparation process is simple, the mass fraction of metal in the obtained atomic-level dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst is far lower than the Pt content in a commercial Pt/C catalyst, so that the preparation and application costs of the catalyst are greatly reduced, and the catalyst has an immeasurable promoting effect on the popularization and application of a zinc-air battery. In addition, in the assembled alkaline seawater zinc-air battery, the alkaline seawater zinc-air battery with the atomic-scale dispersed Fe/nitrogen-doped mesoporous carbon sphere catalyst as the air electrode shows excellent activity and stability, the open-circuit voltage is comparable to that of the alkaline seawater zinc-air battery with the commercial Pt/C catalyst as the air electrode, and the power density and the stability of the battery are superior to those of the zinc-air battery with the commercial Pt/C catalyst as the air electrode.
While there have been shown and described what are at present considered the fundamental principles of the invention, its essential features and advantages, it will be understood by those skilled in the art that the invention is not limited by the embodiments described above, which are merely illustrative of the principles of the invention, but various changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.
Claims (7)
1. The nitrogen-doped mesoporous carbon spheres loaded with the atomic-level dispersed Fe are used as an air cathode catalyst of a zinc-air battery, and an electrolyte of the zinc-air battery is alkaline seawater, and are characterized in that the diameter of the nitrogen-doped mesoporous carbon spheres loaded with the atomic-level dispersed Fe is 50-100nm, the pore diameter is 3-5nm, the mass fraction of the Fe is 1-2.5%, and the atomic coverage rate of the Fe is 0.2-0.5 atom per square nanometer.
2. The nitrogen-doped mesoporous carbon sphere carrying atomic-level dispersed Fe as claimed in claim 1, wherein the diameter of the nitrogen-doped mesoporous carbon sphere carrying atomic-level dispersed Fe is 60nm, the pore diameter is 3.9nm, the Fe mass fraction of the nitrogen-doped mesoporous carbon sphere carrying atomic-level dispersed Fe is 2.02%, and the Fe atomic coverage is 0.38 atoms per square nanometer.
3. The nitrogen-doped mesoporous carbon spheres carrying the atomically dispersed Fe as claimed in claim 1, wherein the nitrogen-doped mesoporous carbon spheres carrying the atomically dispersed Fe are ultrasonically dispersed in a Nafion mixed solution to obtain an ink dispersion liquid of 10mg/mL, the ink dispersion liquid is uniformly dripped onto a hydrophobic carbon paper electrode by a micro-injector, and the hydrophobic carbon paper electrode is baked under an infrared lamp to prepare an air cathode;
the Nafion mixed solution is a solution of DMF, isopropanol and Nafion in a volume ratio of 4:0.5-1.5: 0.05-0.15.
4. The method for preparing the nitrogen-doped mesoporous carbon spheres carrying the Fe dispersed at atomic level according to any one of claims 1 to 3, wherein the method comprises the following steps:
(a) a hydrothermal process: dissolving Pluronic F127 in deionized water to obtain a solution A, dissolving 3-aminophenol in deionized water to obtain a solution B, dissolving hexamethylenetetramine in deionized water to obtain a solution C, mixing the solution A, the solution B and the solution C, stirring for 5-15min, transferring into a polytetrafluoroethylene reaction kettle, placing in an oven for reaction at 80-150 ℃ for 12-48h, centrifuging, washing with deionized water, and vacuum-drying the collected product at 25-100 ℃ to obtain a final product, namely a mesoporous polymer sphere NPS;
(b) preparation of a Fe-loaded nitrogen-doped mesoporous polymer sphere precursor NPS-Fe: adding a mesoporous polymer ball NPS into deionized water, stirring and ultrasonically treating, dripping a potassium ferricyanide solution, stirring for 8-24h, centrifuging, washing with deionized water, and vacuum-drying at 25-100 ℃ for 8-36h to obtain a precursor NPS-Fe;
(c) and (3) calcining: and (c) placing a proper amount of the precursor in the step (b) into a tube furnace, carrying out temperature programmed heating to 600-1000 ℃ at the heating rate of 1-10 ℃/min under the protection of nitrogen atmosphere, carrying out heat preservation for 3h, and naturally cooling to room temperature to obtain the N-MCS-Fe-X loaded with the atomic-level dispersed Fe nitrogen-doped mesoporous carbon sphere catalyst, wherein X represents the calcination temperature.
5. The method for preparing the nitrogen-doped mesoporous carbon spheres loaded with the atomically dispersed Fe as claimed in claim 4, wherein in the step (a), the mass ratio of Pluronic F127 to deionized water in the solution A is 1: 46-50; in the solution B, the mass ratio of the 3-aminophenol to the deionized water is 1: 88-94; in the solution C, the mass ratio of hexamethylene tetramine to deionized water is 1: 88-94.
6. The method of claim 4, wherein the mass ratio of the mesoporous polymer spheres to the deionized water in the step (b) is 1:1-2, and the mass ratio of the potassium ferricyanide to the mesoporous polymer spheres is 1: 27-30.
7. The method for preparing nitrogen-doped mesoporous carbon spheres carrying Fe dispersed at atomic level according to claim 4, wherein the temperature rise rate in the step (c) is 2 ℃/min and the temperature rises to 900 ℃.
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