Multifunctional electro-catalytic material based on cobalt ferrite nano array and preparation method of multifunctional electro-catalytic material

Abstract

The invention discloses a multifunctional electro-catalytic material based on a cobalt ferrite nano array and a preparation method of the multifunctional electro-catalytic material in the field of electro-catalytic materials. The multifunctional electro-catalytic material is prepared from the following raw materials: a CoFe2O4 nano array substrate, ZIF-67 derived Co-N-C nano cubes and nitrogen-doped carbon nanofiber loaded Fe monatomic. The CoFe2O4 nano array substrate grows on the carbon cloth substrate through a hydrothermal method; the ZIF-67 derived Co-N-C nanocube is prepared by the following steps: stirring Co (NO3) 2.6 H2O and 2-methylimidazole in methanol, dipping a substrate, standing, drying, and calcining at 800-810 DEG C in an Ar atmosphere, thereby obtaining the ZIF-67 derived Co-N-C nanocube. According to the material, the activity and stability of OER, ORR and HER are improved through the synergistic effect of the two modified components, and the material is suitable for the field of clean energy conversion.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrocatalytic materials, and particularly relates to a multifunctional electrocatalytic material based on cobalt ferrite nanometer array and a preparation method thereof. BACKGROUND

[0002] With the continuous growth of global energy demand and the increasingly serious environmental problems, developing efficient and stable electrocatalytic materials has become a core challenge in the field of clean energy technology. Traditional electrocatalytic processes rely on noble metal catalysts (such as platinum, iridium), but their high cost, resource scarcity and insufficient catalytic activity have seriously restricted large-scale application. In recent years, transition metal-based composite materials have attracted widespread attention due to their abundant reserves, adjustable structure and adjustable catalytic activity. Among them, cobalt ferrite materials are considered as a potential non-noble metal electrocatalytic substrate material due to their unique spinel crystal structure, diverse redox active sites and good chemical stability. However, these materials have defects such as low intrinsic active site density, insufficient electron transport efficiency and easy corrosion during long-term use, which make it difficult to meet the efficient and stable requirements of catalytic materials in complex multi-reaction environments (such as oxygen evolution, oxygen reduction and hydrogen evolution reactions).

[0003] Currently, research on improving the performance of cobalt ferrite materials through modification strategies has made some progress, but existing methods still face multiple bottlenecks. Single carbon coating technology can improve the electrical conductivity and enhance the structural stability of the material, but it is difficult to effectively control the distribution of active sites; metal organic framework derived carbon materials can provide rich pore structure, but their adhesion to the substrate is weak, which can easily lead to the shedding of active components. Single atom loading technology can achieve atomic utilization, but the interaction between the carrier and the single atom is insufficient, which can easily cause aggregation, and the preparation process is complex and difficult to scale up. In addition, a single modification strategy can only optimize part of the performance of the material (such as activity or stability), and it is difficult to achieve the synergistic improvement of catalytic efficiency, durability and multi-reaction adaptability, so it is urgent to develop new composite modification methods to break through the limitations of existing technologies.

[0004] In view of the above problems, the present application provides a kind of multifunctional electrocatalytic material design scheme based on cobalt ferrite nano array, and the synergistic system is constructed by introducing two complementary modification components.The scheme takes three-dimensional porous cobalt ferrite nano array as substrate, and the vertically grown nanowire structure not only provides high specific surface area and mechanical stability, but also forms rich edge defects and low coordination active sites.On this basis, Co-N-C nanocubes derived from ZIF-67 are anchored by electrostatic interaction, and the high-density nitrogen-doped carbon network and cobalt monatomic sites can enhance electron transport capacity and expand reaction interface;At the same time, Fe monatomic atoms loaded by nitrogen-doped carbon nanofibers are loaded by electrospinning-carbonization method, and the strong coordination effect between atomically dispersed iron active center and pyrrole nitrogen site effectively reduces the adsorption energy barrier of reaction intermediate state.Two kinds of modified components synergize through different dimensions, which not only solves the performance limitation of single modification strategy, but also significantly improves the catalytic activity and stability through the electronic coupling effect between components, providing a new idea for developing high-performance clean energy conversion materials. SUMMARY

[0005] The present application aims to provide a multifunctional electrocatalytic material based on cobalt ferrite nano array and a preparation method thereof, which solves the problems of insufficient active sites, low electron transport efficiency and poor stability of traditional cobalt ferrite electrocatalytic materials, and single modification strategy cannot simultaneously improve multi-reaction catalytic activity and durability.

[0006] The present application realizes the above-mentioned purpose by the following technical solutions:

[0007] A multifunctional electrocatalytic material based on cobalt ferrite nano array, by mass percentage, the raw materials include:

[0008] CoFe2O4 nano array substrate: 85-93%;

[0009] ZIF-67 derived Co-N-C nanocube: 5-10%;

[0010] Fe monatomic atoms loaded by nitrogen-doped carbon nanofibers: 2-5%;

[0011] The preparation method of the CoFe2O4 nano array substrate includes: A1: placing carbon cloth in a polytetrafluoroethylene inner liner reaction kettle, adding Co(NO3)2·6H2O, Fe(NO3)3·9H2O, NH4F, urea and deionized water, and stirring until completely dissolved;A2: after sealing the reaction kettle, place it in an oven for reaction, naturally cool to 20-25 DEG C, take out the substrate, rinse with deionized water and ethanol in turn, and vacuum dry.

[0012] According to the preferred embodiment of the present application, the suppliers and models of each substance are as follows:

[0013] Carbon cloth: purchased from Suzhou Carbon New Material Technology Co., Ltd., model CF-100 (specification: 1 cm*1 cm*0.3 mm, purity: 99.9% or more, resistivity: 18.2 MΩ*cm or more).

[0014] Polytetrafluoroethylene (PTFE): purchased from Shanghai Sainuo New Material Co., Ltd., model PTFE-600 (dispersion resin, solid content 60%, viscosity: 500 mPa*s or more).

[0015] Reaction kettle: purchased from Nanjing Kexi Experimental Instrument Co., Ltd., model KX-50L (material: polytetrafluoroethylene lining, volume 50 mL, temperature resistance: 260 DEG C or less).

[0016] Oven: purchased from Shanghai Yiheng Scientific Instrument Co., Ltd., model DHG-9070A (electric heating constant temperature air drying oven, temperature range 20-200 DEG C, accuracy: 1 DEG C or less).

[0017] Deionized water: purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., model ultrapure water (resistivity: 18.2 MΩ*cm or more, in line with GB / T 6682-2008 three-grade water standard).

[0018] Ethanol: purchased from Beijing Chemical Plant, model chromatographically pure ethanol (AR grade, purity: 99.7% or more, density: 0.789 g / mL).

[0019] Co(NO3)2*6H2O: purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., model analytical pure (AR grade, molar mass: 291.03 g / mol, purity: 99.0% or more).

[0020] Fe(NO3)3*9H2O: purchased from Beijing Chemical Plant, model analytical pure (AR grade, molar mass: 400.99 g / mol, purity: 99.0% or more).

[0021] NH4F: purchased from Shanghai Shi Si Hui Chemical Co., Ltd., model analytical pure (AR grade, molar mass: 40.46 g / mol, purity: 99.0% or more).

[0022] Urea: purchased from Tianjin Kemeluo Chemical Reagent Co., Ltd., model analytical pure (AR grade, molar mass: 60.06 g / mol, purity: 99.5% or more).

[0023] The preparation of the CoFe2O4 nano array substrate in the application is based on the hydrolysis and polycondensation reaction of metal ions under hydrothermal conditions: the carbon cloth is pretreated as a substrate, Co(NO3)2*6H2O and Fe(NO3)3*9H2O in the reaction kettle provide Co 2+ and Fe 3+ , and NH4F is hydrolyzed to generate F - and OH- The pH of the solution is adjusted to be alkaline, and urea is decomposed to generate NH3 to maintain the alkaline environment, thereby promoting the hydrolysis of Co 2+ and Fe 3+ to generate Co(OH)2 and Fe(OH)3 colloids, and the colloidal particles are aggregated on the carbon cloth surface through hydroxyl bridging (-OH…O-) and electrostatic interaction (surface negative charge), and are hydrothermally crystallized at 120-125℃ for 6-8 hours to form CoFe2O4 nanowire arrays with a spinel structure (diameter 50-200nm, length 1-5μm), and the vertically grown nanowire structure increases the specific surface area and enhances the mechanical stability.

[0024] According to a preferred embodiment of the present application, in step A1, the molar ratio of Co(NO3)2·6H2O, Fe(NO3)3·9H2O, NH4F and urea is 1:1:4:4, and the stirring time is 30-40min.

[0025] According to a preferred embodiment of the present application, in step A2, the temperature of the reaction in the oven is 120-125℃, and the reaction time in the oven is 6-8h; the temperature of vacuum drying is 60-65℃, and the time of vacuum drying is 12-14h.

[0026] The present application also provides a preparation method of the multifunctional electrocatalytic material, and the steps include:

[0027] S1, dissolving Co(NO3)2·6H2O and 2-methylimidazole in methanol to form a solution by stirring;

[0028] S2, immersing the CoFe2O4 nanowire array substrate into the solution, standing at 20-25℃, washing with methanol after centrifugal separation, and vacuum drying to obtain a Co-ZIF-67 / CoFe2O4 intermediate;

[0029] S3, placing the intermediate in a tube furnace, calcining at 800-810℃ under Ar atmosphere, and obtaining a Co-N-C nanocube loaded CoFe2O4 substrate after natural cooling;

[0030] S4, dissolving polyvinylpyrrolidone and FeCl3·6H2O in N,N-dimethylformamide and stirring until completely dissolved;

[0031] S5, loading the solution into a syringe, passing through a needle at a flow rate of 1-1.5mL / h, receiving at a distance of 15-20cm, and applying a high voltage of 15-16kV to obtain a Fe-PVP nanofiber membrane; calcining the fiber membrane at 800-810℃ under Ar atmosphere to obtain an N-CNFs / Fe precursor;

[0032] S6, grinding the N-CNFs / Fe precursor into powder, mixing with Co-N-C / CoFe2O4 substrate which has been ultrasonically dispersed in ethanol at a mass ratio of 1:(5-6), centrifugal separation after ultrasonic treatment, and vacuum drying.

[0033] According to a preferred embodiment of the present application, the suppliers and models of each substance are as follows:

[0034] Co(NO3)2·6H2O: purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., with a model of analytical pure (AR grade, molar mass 291.03 g / mol, purity ≥ 99.0%).

[0035] 2-methylimidazole: purchased from Beijing Chemical Plant, with a model of analytical pure (AR grade, molar mass 96.09 g / mol, purity ≥ 99.0%).

[0036] Methanol: purchased from Tianjin Kermel Chemical Reagent Co., Ltd., with a model of chromatographic pure (HPLC grade, purity ≥ 99.9%, density 0.791 g / mL).

[0037] Tube furnace: purchased from Beijing Zhongke Aobote Technology Co., Ltd., with a model of ZK-80-12 (tube furnace, maximum temperature 1200℃, furnace size Φ80mm×1000mm, heating rate ≤ 10℃ / min).

[0038] Ar (argon): purchased from Beijing Oxygen Factory, with a model of industrial-grade argon (purity ≥ 99.999%, pressure 15 MPa, steel cylinder specification 40L).

[0039] Polyvinylpyrrolidone (PVP): purchased from Shanghai Sihewei Chemical Co., Ltd., with a model of PVP-K90 (molecular weight 1300000, solid content ≥ 99.0%).

[0040] FeCl3·6H2O: purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd., with a model of analytical pure (AR grade, molar mass 270.30 g / mol, purity ≥ 99.0%).

[0041] N,N-dimethylformamide (DMF): purchased from Beijing Chemical Plant, with a model of analytical pure (AR grade, purity ≥ 99.5%, boiling point 153℃).

[0042] Syringe: purchased from Shandong Weigao Group Medical Polymer Products Co., Ltd., with a model of disposable sterile syringe (specification 1 mL, needle inner diameter 0.7-0.8 mm, material polypropylene).

[0043] The loading of ZIF-67 derived Co-N-C nanocubes in the present application is achieved by coordination adsorption and pyrolysis conversion: when Co(NO3)2·6H2O is mixed with 2-methylimidazole (2-MeIm) in methanol, Co 2+ forms a zinc hexacyanocobaltate (II) (ZIF-67) coordination compound with the nitrogen atoms (N3 position) of 2-MeIm, and the Co 2+ in the crystal structure of the compound is combined with the organic ligand (-N=C(CH3)2 - ) through a coordination bond; when the CoFe2O4 nanometer array substrate is immersed in the solution, the hydroxyl (-OH) and carboxyl (-COOH) on the surface of the substrate are negatively charged due to deprotonation, and the positive charge (Co 2+ of ZIF-67 and the polarity of the organic ligand are adsorbed by electrostatic interaction, and after standing for 24-30 hours, the ZIF-67 crystals uniformly coat the surface of the substrate; when calcined under an Ar atmosphere (2-3 ℃ / min to 800-810 ℃, 3-4 h), the organic ligand (containing C, H, N) of ZIF-67 is thermally decomposed into CO2, H2O and small molecule gases, Co 2 is oxidized to Co monatomic or Co-N x site (coordinated with surrounding N atoms), and at the same time, the remaining carbon skeleton is carbonized to form a nitrogen-doped carbon cube (particle size 80-120 nm), which is rich in active nitrogen species such as pyridine nitrogen (-N=) and graphite nitrogen (-C=N-) on the surface, providing carriers for electron transport and active sites.

[0044] The formation of nitrogen-doped carbon nanofiber loaded Fe monatomic in the present application depends on electrospinning and high-temperature carbonization: when polyvinylpyrrolidone (PVP, Mw=1300000) is mixed with FeCl3·6H2O in DMF, Fe 3+ is combined with the carbonyl oxygen (C=O) of PVP through coordination (Fe 3+ -O=C-) to form an Fe-PVP complex solution; during the electrospinning process (flow rate 1-1.5 mL / h, 0.7-0.8 mm needle, 15-20 cm receiving distance, 15-16 kV high voltage), the solution is stretched into a continuous fiber by the electric field, and after the solvent DMF is volatilized, a PVP nanofiber membrane containing Fe 3+ is formed; when calcined under an Ar atmosphere (2-3 ℃ / min to 800-810 ℃, 2-3 h), PVP is thermally decomposed into nitrogen-containing carbon structures (-C-N-, -C=N-), Fe 3+ is reduced to Fe monatomic (by electron transfer or bonding with surrounding N atoms), and is anchored at the pyrrole nitrogen site (-N-H-), forming a stable Fe-N x coordination structure, avoiding the migration and agglomeration of Fe monatomic.

[0045] According to the preferred embodiment of the present application, in step S1, the mass ratio of Co(NO3)2·6H2O and 2-methylimidazole is 1:(4-5), and the stirring time is 30-40 min.

[0046] According to the preferred embodiment of the present application, in step S2, the standing time is 24-30 h, the number of methanol rinsing is 3-4 times, the vacuum drying temperature is 60-65℃, and the vacuum drying time is 12-14 h.

[0047] According to the preferred embodiment of the present application, in step S3, the heating rate is 2-3℃ / min, and the calcination time is 3-4 h.

[0048] According to the preferred embodiment of the present application, in step S4, the mass ratio of polyvinylpyrrolidone and FeCl3·6H2O is (4-5):2, and the stirring time is 12-14 h.

[0049] According to the preferred embodiment of the present application, in step S5, the inner diameter of the needle is 0.7-0.8 mm, the heating rate is 2-3℃ / min, and the calcination time is 2-3 h.

[0050] According to the preferred embodiment of the present application, in step S6, the ultrasonic treatment time is 30-40 min, the vacuum drying temperature is 60-65℃, and the vacuum drying time is 12-14 h.

[0051] The present application has the following beneficial effects:

[0052] The technical effects achieved by the present application mainly lie in the significant improvement in three dimensions of catalytic activity, structural stability and multi-reaction adaptability.

[0053] In terms of catalytic activity, traditional cobalt-iron oxide materials are difficult to efficiently drive multiple types of electrochemical reactions due to low surface active site density and high reaction intermediate state adsorption energy barrier. The present application realizes multi-dimensional strengthening of active sites by constructing a composite structure of "three-dimensional substrate + double modified components". The three-dimensional porous framework of CoFe2O4 nanometer array not only provides high specific surface area and mechanical stability, but also forms initial active centers through edge defects and low coordination sites. Co-N-C nanometer cubes derived from ZIF-67 are anchored on the substrate surface through electrostatic interaction, and the high-density nitrogen-doped carbon network and cobalt single-atom sites further expand the reaction interface and improve the electron transport efficiency. Fe single atoms supported by nitrogen-doped carbon nanofibers are embedded in pyrrole nitrogen sites in an atomic dispersion form, forming a strong coordination environment and effectively reducing the adsorption energy barrier of OH, OOH, H and other intermediates in OER / ORR / HER reactions. The synergistic effect of multiple active centers significantly improves the catalytic efficiency of the material for electrochemical reactions.

[0054] In terms of structural stability, traditional electrocatalytic materials often suffer from severe performance degradation due to easy aggregation of active components and weak binding force between active components and supports. In the present application, the three-dimensional framework of CoFe2O4 nanorarray provides strong mechanical support for the modified components, effectively inhibiting the shedding of active components; ZIF-67 derived Co-N-C nanocubes are tightly combined with the substrate through electrostatic interaction, avoiding peeling caused by external force or changes in electrochemical environment; Fe single atoms are anchored to the pyrrole nitrogen sites of N-CNFs through covalent bonds, forming stable chemical bonds and inhibiting single atom migration and aggregation. Experiments show that the material has an activity decay of less than 5% after 500 hours of continuous electrolysis at a current density of 10 mA / cm 2 , far exceeding the stability level of single cobalt ferrite materials or single modified components, meeting the demand for long service life in practical applications.

[0055] In terms of multi-reaction adaptability, the material of the present application breaks through the limitation of single component only applicable to specific reactions and exhibits high catalytic capacity for OER, ORR and HER in a wide potential window. The synergistic effect of the spinel structure of CoFe2O4 nanorarray and the two modified components enables the material to simultaneously drive OER and HER to proceed efficiently in an alkaline water electrolysis system; in a proton exchange membrane fuel cell, its ORR activity can be comparable to that of a noble metal catalyst; in an anion exchange membrane fuel cell, the material is particularly outstanding in terms of alkali resistance decay characteristics for OER. This multi-reaction adaptability makes it have wide application potential in the field of clean energy conversion and storage (such as water electrolysis, fuel cells and metal-air batteries), providing an effective solution to the catalytic demand of complex electrochemical systems. DETAILED DESCRIPTION

[0056] The following detailed description is only used to further illustrate the present application and cannot be understood as limiting the scope of protection of the present application. Those skilled in the art can make some non-essential improvements and adjustments to the present application based on the above application content.

[0057] I. Example

[0058] Example 1

[0059] Take 10 g of pretreated carbon cloth (10 min ultrasonic cleaning with 6M HCl, rinsed with deionized water and dehydrated with ethanol), place it in a 50 mL polytetrafluoroethylene lined reaction kettle, add 0.145 g of Co(NO3)2·6H2O (0.5 mmol), 0.160 g of Fe(NO3)3·9H2O (0.5 mmol), 0.076 g of NH4F (2 mmol), 0.120 g of urea (2 mmol) and 30 mL of deionized water, and stir for 30 min until completely dissolved. Seal the reaction kettle and place it in a 120°C oven for 6 h. After natural cooling to 25°C, remove the carbon cloth, rinse it with deionized water and ethanol for 3 times respectively, and vacuum dry at 60°C for 12 h to obtain a CoFe2O4 nanowire array substrate (nanowire diameter about 80-150 nm, length about 2-4 μm).

[0060] Dissolve 0.5 g of Co(NO3)2·6H2O (0.0017 mol) and 2 g of 2-methylimidazole (0.018 mol) in 20 mL of methanol, and stir for 30 min to form a uniform solution. Immerse the above CoFe2O4 nanowire array substrate in the solution, and stand at 25°C for 24 h. After centrifugal separation, rinse it with methanol for 3 times, and vacuum dry at 60°C for 12 h to obtain a Co-ZIF-67 / CoFe2O4 intermediate. Place the intermediate in a tube furnace, and calcine it at 800°C for 3 h under Ar atmosphere with a heating rate of 2°C / min. After natural cooling, a Co-N-C nanocube loaded CoFe2O4 substrate (Co-N-C nanocube particle size about 80-120 nm) is obtained.

[0061] Dissolve 0.2 g of polyvinylpyrrolidone (PVP, Mw = 1300000) and 0.08 g of FeCl3·6H2O (0.00029 mol) in 10 mL of N,N-dimethylformamide (DMF), and stir for 12 h until completely dissolved. Load the solution into a syringe, and pass it through a needle with an inner diameter of 0.7 mm at a flow rate of 1 mL / h, with a receiving distance of 15 cm, and apply a high voltage of 15 kV to obtain a Fe-PVP nanofiber membrane. Calcine the fiber membrane at 800°C for 2 h under Ar atmosphere with a heating rate of 2°C / min to remove PVP and carbonize to obtain an N-CNFs / Fe precursor.

[0062] Grind the N-CNFs / Fe precursor into powder, and mix it with the Co-N-C / CoFe2O4 substrate (ultrasonically dispersed in ethanol after ultrasonic dispersion, concentration about 1 mg / mL, take 20 mL) at a mass ratio of 1:5 (10 g of CoFe2O4 substrate, i.e. 2 g), ultrasonic treatment for 30 min, centrifugal separation, and vacuum dry at 60°C for 12 h to obtain a final multifunctional electrocatalytic material.

[0063] Example 2

[0064] The difference from Example 1 is only that the stirring time in step A1 is 40 min; the oven reaction temperature in step A2 is 125℃, and the time is 8h; the standing time in step S2 is 30h, and the methanol flushing is 4 times; the ultrasonic treatment time in step S6 is 40 min. The rest of the parameters are the same as Example 1, and finally CoFe2O4 substrate 10g, Co-N-C nanocubes 0.75g, Fe monatomic 0.3g composite material is obtained.

[0065] Example 3

[0066] The difference from Example 1 is only that the electrospinning flow rate in step S5 is 1.5mL / h, and the needle inner diameter is 0.8mm; the calcination heating rate in step S3 is 3℃ / min, and the time is 4h; the mixing mass ratio in step S6 is 1:6 (i.e. Fe monatomic 0.33g). The rest of the parameters are the same as Example 1, and finally CoFe2O4 substrate 10g, Co-N-C nanocubes 1g, Fe monatomic 0.33g composite material is obtained.

[0067] Comparative Example 1

[0068] Take 10g of pretreated carbon cloth, and prepare CoFe2O4 nanometer array substrate according to steps A1-A2 of Example 1. Take 0.2g of polyvinylpyrrolidone and 0.08g of FeCl3·6H2O dissolved in 10mL of DMF, and prepare Fe-PVP nanofiber membrane according to steps S4-S5 of Example 1. After calcination, N-CNFs / Fe precursor is obtained. Mix N-CNFs / Fe precursor with CoFe2O4 substrate in a mass ratio of 1:5, ultrasonic treatment and drying, to obtain CoFe2O4 substrate 10g, Fe monatomic 0.2g composite material (without Co-N-C component).

[0069] Comparative Example 2

[0070] Take 10g of pretreated carbon cloth, and prepare CoFe2O4 nanometer array substrate according to steps A1-A2 of Example 1. Take 0.5g of Co(NO3)2·6H2O and 2g of 2-methylimidazole dissolved in 20mL of methanol, and prepare Co-ZIF-67 / CoFe2O4 intermediate according to steps S1-S3 of Example 1. After calcination, Co-N-C nanocube loaded CoFe2O4 substrate (Co-N-C nanocube 0.5g) is obtained. Direct vacuum drying of Co-N-C / CoFe2O4 substrate (without mixing Fe monatomic), to obtain CoFe2O4 substrate 10g, Co-N-C nanocube 0.5g composite material (without Fe monatomic component).

[0071] Comparative Example 3

[0072] Take 10 g of pretreated carbon cloth, and prepare CoFe2O4 nanorarray substrate according to steps A1-A2 of Example 1. Take 0.5 g of Co(NO3)2·6H2O and 2 g of 2-methylimidazole, and dissolve them in 20 mL of methanol. Prepare a Co-ZIF-67 / CoFe2O4 intermediate according to steps S1-S3 of Example 1, and obtain a Co-N-C nanocube loaded CCoFe2O4 substrate (single ZIF-67 modification) after calcination.

[0073] II. Performance test

[0074] The materials prepared in Examples 1-3 and Comparative Examples 1-3 above were subjected to performance tests according to the following methods:

[0075] 1. Catalytic activity test (OER / ORR / HER)

[0076] The test was performed using an electrochemical workstation (CHI660E) in a three-electrode system: the working electrode was a glassy carbon electrode (GCE, diameter 3 mm, pretreated: 0.05 μm Al2O3 polishing followed by ultrasonic cleaning), the reference electrode was Ag / AgCl (saturated KCl solution), and the counter electrode was a platinum wire. The electrolyte was 1 M KOH (OER / ORR) and 0.5 M H2SO4 (HER), and the gas atmosphere was high-purity nitrogen (99.999%) or argon (99.999%).

[0077] OER test: 5 μL of catalyst suspension (10 mg / mL, ethanol dispersion) was dropped onto the surface of the GCE, and a uniform film was formed after drying at room temperature. Linear sweep voltammetry (LSV) was performed at a scan rate of 50 mV / s, with a scan range of 0.2-1.8 V vs RHE, and the overpotential (η 2 ) corresponding to the current density of 10 mA / cm 10 ) was recorded.

[0078] ORR test: 5 μL of catalyst suspension was dropped onto the surface of a rotating disk electrode (RDE, Pine Research Instrumentation, rotation speed 1600 rpm), and LSV was performed in 0.1 M KOH solution at a scan rate of 5 mV / s, with a scan range of 0.2-1.2 V vs RHE, and the half-wave potential (E 1 / 2 ) was recorded.

[0079] HER test: 5 μL of catalyst suspension was dropped onto the surface of the GCE, and LSV was performed in 0.5 M H2SO4 solution at a scan rate of 50 mV / s, with a scan range of -0.2-0.8 V vs RHE, and the overpotential (η 2 ) corresponding to the current density of 10 mA / cm 10 ) was recorded.

[0080] 2. Stability test

[0081] Accelerated decay test (ADT): after 500 hours of continuous electrolysis under OER test condition (10 mA / cm 2 ), retest OER overpotential, calculate activity decay rate ((η 500 h-η0h) / η0h x 100%).

[0082] Long-time cycle test: after 2000 cycles of cyclic scanning under HER test condition (10 mA / cm 2 ), test HER overpotential, verify activity retention rate ((η 2000 h-η0h) / η0h x 100%).

[0083] 3. Performance test results:

[0084] Table 1: Performance test results of each example and comparative example

[0085]

[0086] As can be seen from Table 1, through the synergistic effect of the double modification components (Co-N-C nanocubes and Fe single atoms) in Examples 1-3, the problems of insufficient active sites, low electron transport efficiency, poor stability and difficulty in simultaneously improving multi-reaction activity by single modification strategy existing in traditional cobalt ferrite-based electrocatalytic materials are effectively solved. The specific analysis is as follows:

[0087] The traditional cobalt ferrite-based material (such as CoFe2O4) has low intrinsic density of low-coordination metal ions on the surface, which results in insufficient active sites and limited catalytic activity. In Examples 1-3, the Co-N-C nanocubes are anchored on the surface of the CoFe2O4 nanowires through electrostatic interaction, and the high-density nitrogen-doped carbon network (containing pyridine nitrogen and graphite nitrogen) and cobalt single atom sites significantly expand the reaction interface and increase the number of active sites. At the same time, the Fe single atoms are embedded in the pyrrole nitrogen sites of the N-CNFs in the form of atomic dispersion, forming a strong coordination environment and further supplementing the active centers. Experimental data shows that the OER 10 mA / cm2 overpotential (280 mV) of Example 1 is much lower than that of Comparative Example 1 without Co-N-C (310 mV), and the ORR half-wave potential (0.85 V vs RHE) is higher than that of Comparative Example 2 without Fe single atoms (0.82 V), indicating that the synergistic effect of the double modification components significantly improves the active site density and reaction efficiency.

[0088] The traditional materials have high adsorption energy barrier of intermediate states (such as *OH, *OOH, *H) due to the limitation of electronic structure, and low electron transfer efficiency. The nitrogen-doped carbon network of Co-N-C has high conductivity, which can promote the rapid transfer of electrons between the substrate and the active site; the Fe single atom is anchored to the pyrrolic nitrogen site of N-CNFs through covalent bond, forming a stable electronic coupling effect, further reducing the reaction energy barrier. The HER of Example 1 is 10 mA / cm 2 The overpotential (90 mV) is significantly lower than that of Comparative Example 1 (110 mV) without Co-N-C, and the ORR half-wave potential (0.85 V vs RHE) is better than that of Comparative Example 3 (0.83 V) modified by single ZIF-67, verifying the synergistic optimization of the double modified components on the electron transfer efficiency.

[0089] The traditional materials have high adsorption energy barrier of intermediate states (such as *OH, *OOH, *H) due to the limitation of electronic structure, and low electron transfer efficiency. The nitrogen-doped carbon network of Co-N-C has high conductivity, which can promote the rapid transfer of electrons between the substrate and the active site; the Fe single atom is anchored to the pyrrolic nitrogen site of N-CNFs through covalent bond, forming a stable electronic coupling effect, further reducing the reaction energy barrier. The HER of Example 1 is 10 mA / cm

[0090] The traditional materials have high adsorption energy barrier of intermediate states (such as *OH, *OOH, *H) due to the limitation of electronic structure, and low electron transfer efficiency. The nitrogen-doped carbon network of Co-N-C has high conductivity, which can promote the rapid transfer of electrons between the substrate and the active site; the Fe single atom is anchored to the pyrrolic nitrogen site of N-CNFs through covalent bond, forming a stable electronic coupling effect, further reducing the reaction energy barrier. The HER of Example 1 is 10 mA / cm

[0091] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the protection scope of the present application.

Claims

1. A multifunctional electrocatalytic material based on cobalt iron oxide nanoarray, characterized in that: In terms of mass percentage, the raw materials include: CoFe2O4 nanoarray substrate: 85-93%; ZIF-67 derived Co-NC nanocubes: 5-10%; Nitrogen-doped carbon nanofibers loaded with Fe single atoms: 2-5%; The preparation method of the CoFe2O4 nanoarray substrate includes: A1: placing carbon in a polytetrafluoroethylene-lined reactor, adding Co(NO3)2·6H2O, Fe(NO3)3·9H2O, NH4F, urea and deionized water, and stirring until completely dissolved; A2: sealing the reactor and placing it in an oven for reaction, naturally cooling to 20-25°C, taking out the substrate, rinsing it with deionized water and ethanol in turn, and vacuum drying.

2. The multifunctional electrocatalytic material according to claim 1, characterized in that In step A1, the molar ratio of Co(NO3)2·6H2O, Fe(NO3)3·9H2O, NH4F, and urea is 1:1:4:4; and the stirring time is 30-40 min.

3. The multifunctional electrocatalytic material according to claim 1, characterized in that In step A2, the reaction temperature in the oven is 120-125° C., and the reaction time in the oven is 6-8 h; the vacuum drying temperature is 60-65° C., and the vacuum drying time is 12-14 h.

4. A method for preparing a multifunctional electrocatalytic material according to any one of claims 1 to 3, characterized in that the steps include: S1. Dissolve Co(NO3)2·6H2O and 2-methylimidazole in methanol and stir to form a solution; S2, immersing the CoFe2O4 nanoarray substrate in the solution, allowing it to stand at 20-25°C, centrifuging it, rinsing it with methanol, and vacuum drying it to obtain a Co-ZIF-67 / CoFe2O4 intermediate; S3, placing the intermediate in a tube furnace, heating to 800-810°C under Ar atmosphere and calcining, and naturally cooling to obtain Co-NC nanocube-supported CoFe2O4 substrate; S4. Dissolve polyvinylpyrrolidone and FeCl3·6H2O in N,N-dimethylformamide and stir until completely dissolved; S5. The solution is loaded into a syringe and passed through a needle at a flow rate of 1-1.5 mL / h with a receiving distance of 15-20 cm. A high voltage of 15-16 kV is applied to obtain a Fe-PVP nanofiber membrane; the fiber membrane is heated to 800-810 °C in an Ar atmosphere and calcined to obtain an N-CNFs / Fe precursor; S6. Grind the N-CNFs / Fe precursor into powder, mix it with the Co-NC / CoFe2O4 substrate which has been ultrasonically dispersed in ethanol at a mass ratio of 1:(5-6), centrifuge after ultrasonic treatment, and vacuum dry.

5. The method for preparing a multifunctional electrocatalytic material according to claim 4, characterized in that: In step S1, the mass ratio of Co(NO3)2·6H2O and 2-methylimidazole is 1:(4-5); and the stirring time is 30-40 min.

6. The method for preparing a multifunctional electrocatalytic material according to claim 4, characterized in that: In step S2, the standing time is 24-30 hours, the number of methanol washings is 3-4 times, the vacuum drying temperature is 60-65° C., and the vacuum drying time is 12-14 hours.

7. The method for preparing a multifunctional electrocatalytic material according to claim 4, characterized in that: In step S3, the heating rate is 2-3°C / min; and the calcination time is 3-4h.

8. The method for preparing a multifunctional electrocatalytic material according to claim 4, characterized in that: In step S4, the mass ratio of polyvinyl pyrrolidone and FeCl3·6H2O is (4-5):2; and the stirring time is 12-14 hours.

9. The method for preparing a multifunctional electrocatalytic material according to claim 4, wherein: In step S5, the inner diameter of the needle is 0.7-0.8 mm; the heating rate is 2-3° C. / min; and the calcination time is 2-3 h.

10. The method for preparing a multifunctional electrocatalytic material according to claim 4, characterized in that: In step S6, the ultrasonic treatment time is 30-40 minutes; the vacuum drying temperature is 60-65° C., and the vacuum drying time is 12-14 hours.

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