CN112458483B

CN112458483B - Preparation method of NiFe LDH @ Super-P composite electro-catalytic material

Info

Publication number: CN112458483B
Application number: CN202011455086.9A
Authority: CN
Inventors: 李芳菲; 任丽; 薛兵; 王嘉琦; 夏茂盛; 雒锋
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2020-12-10
Filing date: 2020-12-10
Publication date: 2022-01-07
Anticipated expiration: 2040-12-10
Also published as: CN112458483A

Abstract

The invention relates to a preparation method of a NiFe LDH @ Super-P composite electro-catalytic material, and belongs to the technical field of catalysis of electrolytic water oxygen evolution reaction. The invention fully utilizes the excellent catalytic activity of the electrolytic water oxygen evolution reaction of the NiFe LDH and the good conductivity of the Super-P, prepares the NiFe LDH precursor at a lower temperature by hydrothermal in advance to ensure nucleation, then adds the Super-P for secondary hydrothermal, and then carries out heat treatment under atmosphere protection to prepare the composite electro-catalytic material. The method can expose more active sites of the NiFe LDH, improve the electron transfer rate by utilizing the high conductivity of the Super-P, effectively overcome the problem of poor conductivity of the NiFe LDH, and enhance the catalytic activity and stability of the composite electro-catalytic material. The method has the advantages of low raw material cost, low equipment requirement, environmental friendliness and high repeatability, and the obtained composite electro-catalysis material has high crystallization degree, large specific surface area and strong shape controllability, is an ideal catalyst for the electrolysis water oxygen evolution reaction and is expected to be applied to industry.

Description

Preparation method of NiFe LDH @ Super-P composite electro-catalytic material

Technical Field

The invention belongs to the field of new energy material technology and electrochemical catalysis, and particularly relates to a preparation method of a NiFe LDH @ Super-P composite electro-catalytic material.

Background

The problems of environmental pollution and energy shortage are increasingly outstanding, and the problems are urgently needed to be solved. In particular, hydrogen gas has been considered as the most promising new energy source to replace conventional fossil fuels due to its high energy density and environmental friendliness. Recently, electrocatalytic water splitting has been considered as a simple and effective oneA large-scale clean hydrogen production technology. However, due to its slow kinetics of the half-reaction Oxygen Evolution Reaction (OER), the overall efficiency of water splitting is greatly reduced. Therefore, the OER reaction occurring at the anode is considered to be the rate determining step of water electrolysis. Therefore, there is a strong need for a high-performance electrocatalyst to accelerate the OER at a lower overpotential (η) to improve the energy conversion efficiency. At present, noble metal based materials (IrO)₂And RuO₂) Are the most widely used OER catalysts today, but their large-scale use is limited due to the high cost associated with their scarcity. Therefore, it is of great importance to develop non-noble metal-based electrocatalysts having excellent OER performance and stability.

Layered Double Hydroxides (LDHs) are a class of two-dimensional (2D) materials, such as NiCo LDH, CoMn LDH, ZnCo LDH, NiFe LDH and NiCr LDH, that have received much attention due to their high earth abundance and excellent OER performance. NiFe LDHs are reported to be the most catalytically active OER catalysts compared to other transition bimetallic LDHs, especially in alkaline environments. The layered structure of NiFe LDH itself makes it have a large specific surface area and exposes more active sites, thus greatly improving catalytic activity. However, the nano-sized NiFe LDH easily forms aggregates, so that the specific surface area and the number of exposed active sites are reduced, thereby degrading the catalytic performance. In addition, NiFe LDH itself has poor conductivity, which is not favorable for electron transfer, resulting in a decrease in catalytic activity. The mechanical mixing of the catalyst and the conductive material has been studied before, but the simple physical contact is difficult to realize the function of enhancing the electronic conduction, so that the increase of the conductivity is very limited, and the problem that the nano-particles are easy to agglomerate is not solved.

In the prior art, high-conductivity carbon materials such as carbon nanotubes, graphene and carbon cloth are used as substrates to support NiFe LDH nanosheets, so that the problems of agglomeration and poor conductivity are solved. In general, compounding with a conductive substrate can improve catalyst dispersibility and conductivity. [ CN105618060A ] introduces a non-metal bifunctional oxygen catalyst of graphene/nickel-iron hydrotalcite and a preparation method thereof. Firstly, assembling the nickel-iron hydrotalcite on graphene by using micelle as a template under a hydrothermal condition, and then reducing by a hydration trap to obtain the graphene/nickel-iron hydrotalcite spherical nano composite. The spherical porous shape formed by the method increases the specific surface area, but the method uses an organic template and a reducing agent, introduces a plurality of impurity ions into the original system to influence ion transmission, is not beneficial to the oxygen evolution reaction, and has high hydrothermal treatment temperature, long time and larger energy consumption. [ CN110247072A ] introduces a NiFe-LDH @ CNT nano material and a preparation method thereof, and NiFe-LDH nano sheets which are uniformly grown on a carbon nano tube substrate are obtained. However, the method not only needs to add a surfactant, but also uses sulfuric acid and nitric acid for CNT treatment, uses a strong reducing agent sodium borohydride solution for redox reaction, and has complex preparation method and higher safety requirements on experimental equipment and experimental environment. [ CN109811365A ] introduces a ferronickel-based nanosheet array based on carbon cloth growth and a preparation method thereof, wherein a NiFe LDH nanosheet array (NiFe LDH NSAs/CC) grows on a carbon cloth substrate through a hydrothermal method, the preparation method is simple, but the interface combination of the NiFe LDH nanosheet array and the carbon cloth is weak, and the high-proportion load is difficult to realize.

In order to solve the problems, the invention adopts another material as a substrate, namely conductive carbon black Super-P, which is small-particle conductive carbon black with high purity and excellent conductivity, and can obviously reduce the resistance by compounding with the conductive carbon black Super-P. Compared with the carbon material, the Super-P has simple manufacturing process and larger specific surface area, is beneficial to the adsorption of electrolyte and improves the ionic conductivity; the active material is dispersed around the active material by primary aggregates with the particle size of 150-200nm to form a branched chain structure, and the chain conductive structure is beneficial to improving the electronic conductivity of the material. Compared with the carbon material, the Super-P is cheaper and has more reliable performance, but until now, no report is found about the research on the preparation of the NiFe LDH-based composite electrolysis water oxygen evolution reaction catalyst by using the Super-P as a conductive substrate.

The NiFe LDH nano-sheets are loaded on the carbon conductive substrate, if a hydrothermal method is directly adopted to directly contact a carbon material with a nickel source and an iron source, the nucleation process and the crystallinity of the NiFe LDH are easily influenced, the problem of uneven distribution of ferronickel is easily caused, and the problems of agglomeration of the nano-sheets and low fixation firmness can not be well solved. Aiming at the problems, the invention provides a method for preparing a high-activity NiFe LDH @ Super-P composite electro-catalytic material by step-by-step hydrothermal method assisted with low-temperature heat treatment. Firstly, obtaining a NiFe LDH precursor through a first hydrothermal treatment, and ensuring the normal nucleation process of high-activity NiFe LDH; and then adding Super-P for secondary hydrothermal treatment to realize in-situ uniform growth of the NiFe LDH active precursor which takes nucleation first on the Super-P conductive substrate, wherein the process can remarkably promote the full contact of the NiFe LDH and the Super-P in a three-dimensional space, thereby not only greatly increasing the loading capacity, but also realizing efficient transfer of electrons between the NiFe LDH and the Super-P, and further remarkably improving the conductivity and OER catalytic activity of the electro-catalytic material. In order to further enhance the interface bonding effect between the electrode material and the electrode material, after the two hydrothermal processes, the heat treatment method of atmosphere protection is continuously utilized to enhance the bonding between the electrode material and the electrode material, so that the environmental pollution caused by the solution reduction method and the adverse effect of impurity ions on the OER performance of the electrode material are avoided.

Disclosure of Invention

The invention aims to solve the problems that NiFe LDH nano sheets are easy to agglomerate, poor in self conductivity and weak in binding effect with a conductive substrate interface, and provides a preparation method of a NiFe LDH @ Super-P composite electro-catalytic material. The electrocatalyst prepared by the method has the advantages of large amount of catalytic active sites, good conductivity, strong interface binding effect and the like by in-situ growth of NiFe LDH on a Super-P substrate, and can greatly reduce overpotential and obviously improve the electrolytic water oxygen evolution reaction efficiency. The invention adopts a two-step hydrothermal method and a heat treatment method to prepare the composite catalytic material, and the method has the advantages of strong practicability, less used chemical reagents, low cost and convenient popularization and use.

The purpose of the invention is realized by the following technical scheme:

(1) weighing a certain amount of Ni (NO)₃)₂·6H₂O、Fe(NO₃)₃·9H₂O、CO(NH₂)₂And NH₄Dissolving F in deionized water with a certain volume, stirring for 0.5-1h by using a magnetic stirrer to fully dissolve the F, transferring the mixed solution into a closed reaction kettle, carrying out first hydrothermal treatment at the temperature of 100-140 ℃ for 1-3h, naturally cooling to room temperature after the reaction is finished, and transferring all reactants into a beaker to enable the Ni (NO) to be reserved₃)₂·6H₂O and Fe (NO)₃)₃·9H₂Molar ratio of O in the range of 3:1 to 1:1, Ni (NO)₃)₂·6H₂The molar concentration of O is in the range of 0.036-0.1mol/L, and CO (NH)₂)₂The molar concentration range in the first hydrothermal system is 0.64-1.92mol/L, NH₄The molar concentration of F in the primary hydrothermal system is in the range of 0.1-0.3 mol/L.

(2) Weighing 0.1-0.3g of Super-P, adding the Super-P into the slurry obtained in the step (1), stirring the mixture for 0.5-1h by using a magnetic stirrer to fully dissolve the mixture, then transferring the mixture into a closed reaction kettle again, carrying out second hydrothermal treatment for 10-16h at the temperature of 140 ℃ and 100 ℃, naturally cooling the mixture to room temperature after the reaction is finished, then carrying out centrifugal washing by using deionized water, drying the centrifugal product for 12-24h at the temperature of 60-80 ℃, and grinding the centrifugal product to obtain the composite powder material.

(3) And (3) carrying out heat treatment on the composite powder material obtained in the step (2) at the temperature of 300-450 ℃ in a nitrogen atmosphere for 2-3h to obtain the NiFe LDH @ Super-P composite electro-catalytic material.

Has the advantages that:

compared with the prior art, the high-conductivity Super-P material is used as the substrate, and the conductivity of the NiFe LDH @ Super-P composite electrocatalyst and the interface combination effect between the host and the guest are obviously enhanced through a two-step hydrothermal method and heat treatment. The composite catalytic material fully utilizes the lamellar structure of NiFe LDH and the high conductivity of Super-P, and does not need additional mechanical mixing of conductive agents such as carbon black and the like. Carrying out primary hydrothermal treatment to form a NiFe LDH high-activity precursor, and then adding Super-P for secondary hydrothermal treatment to enable the NiFe LDH to grow on the Super-P in situ, so that more active sites can be exposed; subsequent heat treatment enhances the interfacial bonding of the two, resulting in more efficient electron transfer and enhanced conductivity. Electrochemical tests show that the impedance is reduced from 14-18 omega to 6-9 omega at 10 mA-cm^-2The overpotential is reduced by at least 20mV, the OER reaction activity is obviously improved, the cycle stability is very excellent, the original appearance can be basically maintained after the OER reaction is carried out for 20 hours, and the material is one of ideal catalytic materials for the electrolytic water oxygen evolution reaction.

The method has the advantages that the required equipment is simple, the price of the Super-P is low compared with that of other carbon materials, and a surfactant, a reducing agent and the like are not required to be additionally added in the preparation process, so that the production cost is reduced on one hand, and impurity ions are not introduced to influence the performance of the catalyst on the other hand.

Drawings

FIG. 1 is an X-ray diffraction pattern of the NiFe LDH @ Super-P composite electro-catalytic material in the methods of examples 1 and 2 of the invention.

Detailed Description

The present invention is described in further detail below with reference to specific embodiments and drawings, it being understood that the specific embodiments described herein are merely illustrative and explanatory of the invention and are not restrictive thereof.

Example 1

Weighing 6mmol Ni (NO)₃)₂·6H₂O、3mmol Fe(NO₃)₃·9H₂O、128mmol CO(NH₂)₂And 20mmol NH₄Dissolving F in 100mL of deionized water, stirring for 0.5h by using a magnetic stirrer to fully dissolve the F, transferring the mixed solution into a closed reaction kettle, carrying out hydrothermal treatment for 2h at 100 ℃, naturally cooling to room temperature after the reaction is finished, transferring all the products into a beaker, adding 0.22g of Super-P into the beaker, stirring for 0.5h by using the magnetic stirrer to uniformly mix the Super-P, transferring the mixture into the closed reaction kettle again, carrying out hydrothermal treatment for 12h at 100 ℃, naturally cooling to room temperature after the reaction is finished, carrying out centrifugal washing for 5 times by using deionized water, drying the centrifugal product for 12h at 60 ℃, grinding to obtain a composite powder material, and finally carrying out the thermal treatment on the composite powder material for 2h at 400 ℃ in a nitrogen atmosphere to obtain the NiFe LDH @ Super-P composite electrocatalytic material. The phase structure of the material can be seen in fig. 1, with 2 peaks at 20.5 ° and 43.4 ° assigned to the Super-P substrate; in addition, at 11.8 °, 23.4 °, 34.4 °, 39.0 ° and 60.1 °Correspond to the (003), (006), (012), (015) and (110) planes of the NiFe LDH structure, respectively. The material has good electrochemical activity as an OER reaction catalyst, and has the electrochemical activity of 10 mA-cm according to a linear sweep voltammetry test^-2The overpotential of the current density is only 206mV, which is reduced by 28mV compared with pure phase NiFe LDH; in the chronopotentiometric stability test, at 10mA · cm^-2Can stably work for more than 20 hours under the current density; the electrochemical impedance is 7 omega, and the initial polarization curve of the electrochemical impedance is basically overlapped with the polarization curve after 2000 cycles of CV cycle, so that the material is an efficient OER catalytic material with good stability.

Example 2

3.6mmol of Ni (NO) are weighed₃)₂·6H₂O、1.2mmol Fe(NO₃)₃·9H₂O、64mmol CO(NH₂)₂And 10mmol NH₄Dissolving F in 100mL of deionized water, stirring for 0.5h by using a magnetic stirrer to fully dissolve the solution, transferring the mixed solution into a closed reaction kettle, performing hydrothermal treatment for 3h at 120 ℃, naturally cooling to room temperature after the reaction is finished, transferring all the products into a beaker, adding 0.1g of Super-P into the beaker, stirring for 1h by using the magnetic stirrer to uniformly mix the mixture, transferring the mixture into the closed reaction kettle again, performing hydrothermal treatment for 16h at 110 ℃, naturally cooling to room temperature after the reaction is finished, performing centrifugal washing for 5 times by using deionized water, drying the centrifugal product for 16h at 70 ℃, grinding to obtain a composite powder material, and performing thermal treatment on the composite powder material for 3h at 300 ℃ in a nitrogen atmosphere to obtain the NiFe @ LDH Super-P composite electrocatalyst. At 10mA cm^-2At a current density of 224mV, the electrochemical impedance is 9 Ω, and the initial polarization curve substantially coincides with the polarization curve after 2000 cycles of CV.

Example 3

Weighing 10mmol Ni (NO)₃)₂·6H₂O、4mmol Fe(NO₃)₃·9H₂O、192mmol CO(NH₂)₂And 30mmol NH₄Dissolving F in 100mL deionized water, stirring with magnetic stirrer for 0.5 hr to dissolve completely, transferring the mixed solution to a sealed containerCarrying out hydrothermal treatment for 1h at 140 ℃ in a reaction kettle, naturally cooling to room temperature after the reaction is finished, completely transferring the product into a beaker, adding 0.3g of Super-P into the beaker, stirring for 0.5h by using a magnetic stirrer, fully and uniformly mixing, transferring into a closed reaction kettle again, carrying out hydrothermal treatment for 10h at 140 ℃, naturally cooling to room temperature after the reaction is finished, centrifugally washing for 5 times by using deionized water, drying the centrifugal product for 12h at 80 ℃, grinding to obtain a composite powder material, and carrying out thermal treatment on the composite powder material for 2h at 450 ℃ in a nitrogen atmosphere to obtain the NiFe LDH @ Super-P composite electrocatalyst. At 10mA cm^-2Has an overpotential of 213mV and an electrochemical impedance of 6 Ω, and the initial polarization curve substantially coincides with the polarization curve after 1500 CV cycles.

Example 4

Weighing 5.4mmol Ni (NO)₃)₂·6H₂O、5.4mmol Fe(NO₃)₃·9H₂O、136mmol CO(NH₂)₂And 24mmol NH₄Dissolving F in 100mL of deionized water, stirring for 0.5h by using a magnetic stirrer to fully dissolve the solution, transferring the mixed solution into a closed reaction kettle, carrying out hydrothermal treatment for 1.5h at 120 ℃, naturally cooling to room temperature after the reaction is finished, transferring all the products into a beaker, adding 0.15g of Super-P into the beaker, stirring for 0.5h by using the magnetic stirrer to uniformly mix the Super-P, transferring the mixture into the closed reaction kettle again, carrying out hydrothermal treatment for 14h at 120 ℃, naturally cooling to room temperature after the reaction is finished, carrying out centrifugal washing for 5 times by using deionized water, drying the centrifugal product for 24h at 60 ℃, grinding to obtain a composite LDH powder material, and carrying out thermal treatment on the composite powder material for 2.5h at 400 ℃ in a nitrogen atmosphere to obtain the NiFe @ Super-P composite electrocatalyst. At 10mA cm^-2At a current density of 219mV, an electrochemical impedance of 8 Ω, and an initial polarization curve substantially coinciding with the polarization curve after 1500 CV cycles.

Example 5

Preparation of pure phase NiFe LDH, 6mmol Ni (NO) was first weighed₃)₂·6H₂O、3mmol Fe(NO₃)₃·9H₂O、128mmol CO(NH₂)₂And 20mmol NH₄Dissolving F in 100mL of deionized water, stirring for 0.5h by using a magnetic stirrer to fully dissolve the F, transferring the mixed solution into a closed reaction kettle, carrying out hydrothermal treatment for 12h at 100 ℃, naturally cooling to room temperature after the reaction is finished, then carrying out centrifugal washing for 5 times by using the deionized water, drying the centrifugal product for 12h at 60 ℃, and grinding to obtain the pure-phase NiFe LDH electrocatalyst. At 10mA cm^-2At a current density of 248mV and an electrochemical impedance of 16. omega. in a chronopotentiometric stability test at 10mA cm^-2Can stably work for more than 20h under the current density of the (A), and the initial polarization curve of the (A) basically coincides with the polarization curve after 1500 CV cycles.

The working electrode surface modification method comprises the following steps:

first, Al having a particle size of 0.5 μm is used₂O₃Grinding a glassy carbon electrode with the diameter of 3mm, weighing 5mg of the catalyst material in the embodiment into a penicillin bottle, adding 1ml of ethanol, performing ultrasonic treatment for 30 minutes, adding 50 mu l of 5 wt% naphthol solution, performing ultrasonic treatment for 30 minutes, dropping 1 mu l of ink onto the glassy carbon electrode by using a liquid transfer gun, naturally drying at room temperature, repeatedly dropping for 5 times, and performing mass loading of 0.34 mg-cm^-2And carrying out electrochemical performance test after the film is completely dried.

The electrochemical performance test was performed on Shanghai Hua CHI 660E workstation, and a three-electrode system was used, the working electrode was the above surface-modified glassy carbon electrode, the counter electrode was platinum mesh, the reference electrode was Hg/HgO electrode, and the electrolyte was 1M KOH solution. Linear sweep voltammetry test (LSV): the scanning rate is 10 mV.s^-1Voltage range 0.2-0.8V vs. RHE;

timing potential test: the fixed current density is 10mA cm^-2。

Electrochemical impedance test (EIS): frequency range of 0.01Hz-10⁶Hz, amplitude 5mV, DC voltage conditions to maintain open circuit voltage.

Cyclic voltammetry test (CV): the test voltage range is 0.1-0.7V vs. RHE, and the scanning speed is 100mV s^-1。

Claims

1. A preparation method of a NiFe LDH @ Super-P composite electro-catalytic material is characterized by comprising the following specific steps:

(1) weighing a certain amount of Ni (NO)₃)₂·6H₂O、Fe(NO₃)₃·9H₂O、CO(NH₂)₂And NH₄Dissolving F in deionized water with a certain volume, stirring until the F is fully dissolved, transferring the solution into a closed reaction kettle, carrying out first hydrothermal treatment for 1-3h at the temperature of 100-; ni (NO)₃)₂·6H₂O and Fe (NO)₃)₃·9H₂The molar ratio of O is in the range of 3:1 to 1:1, CO (NH)₂)₂The molar concentration range in the first hydrothermal system is 0.64-1.92mol/L, NH₄The molar concentration range of F in the primary hydrothermal system is 0.1-0.3 mol/L;

(2) weighing 0.1-0.3g of Super-P, adding into the slurry obtained in the step (1), stirring and mixing uniformly, performing secondary hydrothermal treatment at the temperature of 100-140 ℃ for 10-16h, naturally cooling to room temperature after the reaction is finished, performing solid-liquid separation, centrifugally washing for several times, drying and grinding to obtain a composite powder material;

(3) and (3) carrying out heat treatment on the composite powder material obtained in the step (2) for 2-3h at the temperature of 300-450 ℃ in a nitrogen atmosphere to obtain the NiFe LDH @ Super-P composite electro-catalytic material.