CN111841549B - Method for preparing nickel-iron hydrotalcite nanosheet graphene electrocatalyst by gel natural diffusion permeation method - Google Patents

Method for preparing nickel-iron hydrotalcite nanosheet graphene electrocatalyst by gel natural diffusion permeation method Download PDF

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CN111841549B
CN111841549B CN202010787881.1A CN202010787881A CN111841549B CN 111841549 B CN111841549 B CN 111841549B CN 202010787881 A CN202010787881 A CN 202010787881A CN 111841549 B CN111841549 B CN 111841549B
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solution
iron hydrotalcite
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CN111841549A (en
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詹天荣
温永红
张朋
王泽琨
陈璐瑶
王磊
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Li Bin
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Qingdao University of Science and Technology
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Abstract

The invention discloses a preparation method and application of a nickel-iron hydrotalcite nanosheet graphene electrocatalyst. Firstly, adding agar powder into water, heating and dissolving, adding graphene oxide into the agar powder, uniformly stirring, adding a metal ion solution into the agar powder, stirring to obtain a uniform solution, quickly transferring the solution into a plastic tube while the solution is hot, and cooling to form gel which is used as an internal reaction medium; the sodium hydroxide solution is used as an external reaction solution, and the product is prepared by natural osmosis reaction at room temperature. The method of gel natural permeation diffusion is adopted, the nickel-iron hydrotalcite nano-sheets with controllable sizes can be grown on the surface of graphene in situ, the size of the obtained nickel-iron hydrotalcite nano-sheets is 500-700 nm, and the obtained nickel-iron hydrotalcite nano-sheets are rectangular or approximately square sheets. The nickel-iron hydrotalcite nanosheet graphene electrocatalyst alkaline electrolyte shows excellent catalytic performance of oxygen evolution reaction.

Description

Method for preparing nickel-iron hydrotalcite nanosheet graphene electrocatalyst by gel natural diffusion permeation method
The technical field is as follows:
the invention relates to a preparation method of a nickel-iron hydrotalcite nanosheet graphene electrocatalyst capable of effectively improving oxygen evolution reaction efficiency, and relates to a catalytic action of the nickel-iron hydrotalcite nanosheet graphene electrocatalyst prepared by the preparation method on an oxygen evolution reaction under an alkaline condition, belonging to the field of electrocatalysis.
Background art:
the electrolysis of water is of great significance to reduce petrochemical energy requirements and protect the environment. However, in acidic and alkaline electrolytes, the electrolyzed water needs to break the O-H bond and release electrons to form O ═ O double bonds, and the kinetic process is very slow, usually requiring a potential higher than 1.23V, i.e. a large overpotential. Therefore, it is desirable to use a high activity catalyst to reduce the overpotential to achieve efficient water splitting. Oxygen Evolution Reaction (OER) is the bottleneck for water decomposition, albeit with noble metal catalysts, such as RuO2And IrO2However, it is expensive, scarce, and requires a large overpotential to drive the OER. Therefore, the development of an efficient, abundant and cheap OER non-noble metal catalyst is one of the subjects of current renewable energy research.
Transition double hydroxides (LDHs) have potential application values due to their compositional diversity and stability. Studies have shown that bimetallic NiFe-LDH has higher catalytic activity and lower overpotential than LDH containing only a single Ni or Fe component. However, the composite material has the defect of poor conductivity, so that the composite material is usually compounded with a conductive carbon material, NiFe-LDH nanosheets show excellent catalytic performance and stability in an oxygen evolution reaction, and the performance of some materials can be even comparable to that of a commercial noble metal catalyst. The surface exposure of the transition metal atoms is very advantageous to accelerate the electron transfer process and the rapid diffusion of the reactants. However, the disadvantages of easy aggregation, poor conductivity and poor stability of hydrotalcite nanosheets limit their applications. In order to overcome the problems, researchers propose that hydrotalcite nanosheets and graphene are compounded so as to fully exert electrocatalytic performance of two components. Graphene has a large specific surface area (theoretically about 2600 m)2G), extremely high conductivity (theoretically about 106S/cm), and can be used as a conduction path for promoting charge transfer and mass transfer in the catalytic reaction process. More importantly, the electrostatic adsorption and accumulation of the positive-charge hydrotalcite nanosheets and the negative-charge graphene (oxide) which are alternately arranged on the molecular scale ensure the structural integrity between the transition metal and the carbon material, and greatly shorten the diffusion distance.
According to the invention, the OER catalyst with excellent catalytic performance is prepared by optimizing the concentration and proportion of nickel-iron ions, the concentration of reduced graphene oxide and the dosage of agar. The preparation method adopts a gel diffusion method to prepare the nickel-iron hydrotalcite ultrathin nanosheet graphene composite, and in a reaction-diffusion (RDF) system, a gel matrix provides a limited reaction space for the formation and growth of the hydrotalcite nanosheets, eliminates convection current destructive to the nanosheet formation process, and slows down the kinetic rate of the nanosheet growth. The method is favorable for clearly researching the in-situ growth process of the hydrotalcite nano-sheets on the surface of the graphene, and provides data support for the basic principle of hydrotalcite nano-sheet formation. The nickel-iron hydrotalcite nanosheet graphene catalyst growing on different layers is subjected to electrochemical performance test, and the influence of different penetration depths on the catalytic performance of the catalyst OER is contrasted. The nickel-iron hydrotalcite nanosheet is combined with reduced graphene oxide (rGO) to prepare a nickel-iron hydrotalcite nanosheet compound growing on the rGO in situ. The related research on the preparation of the nickel-iron hydrotalcite nanosheet graphene electrode by using the permeation diffusion method and the performance of the nickel-iron hydrotalcite nanosheet graphene electrode in catalyzing OER has not been reported.
The invention content is as follows:
aiming at the defects of the prior art and the requirements of research and application in the field, the invention aims to provide a preparation method of a nickel-iron hydrotalcite nanosheet graphene electrocatalyst capable of effectively improving the oxygen evolution reaction efficiency. Firstly, agar is used as a reaction medium, nickel iron ions and graphene are uniformly dispersed in the agar to be used as an internal reaction matrix, a sodium hydroxide solution is used as an osmotic external liquid, and a nickel iron hydrotalcite nanosheet graphene electrocatalyst with controllable morphology and size is prepared by adopting an osmotic diffusion method.
The invention provides a preparation method of a nickel-iron hydrotalcite nanosheet graphene electrocatalyst, which comprises the steps of adding agar powder into water, heating and dissolving, adding graphene oxide into the agar powder, uniformly stirring, adding a metal ion solution into the graphene oxide, stirring to obtain a uniform solution, quickly transferring the solution into a plastic tube while the solution is hot, and cooling to form gel to be used as an internal reaction medium; the method is characterized in that a sodium hydroxide solution is used as an external reaction solution, and the graphene oxide is prepared through natural osmosis reaction at room temperature, wherein graphene oxide is marked as GO, reduced graphene oxide is marked as rGO, nickel-iron hydrotalcite nanosheets are marked as NiFe-LDH, and nickel-iron hydrotalcite nanosheets are marked as NiFe-LDH/rGO. The nickel-iron hydrotalcite nanosheet graphene electrocatalyst is prepared by adopting a permeation natural diffusion method. The method specifically comprises the following steps:
(1) adding 30mL of deionized water into a 50mL single-neck flask, adding a certain amount of agar powder, heating and stirring until the mixture is boiled to ensure that the concentration of the agar powder is 0.5-1.5%, and continuously decocting for 30min to obtain transparent agar sol which is uniformly dispersed;
(2) weighing a certain amount of GO, adding the weighed GO into the decocted thermosol, stirring to uniformly disperse the GO until the content of GO is 0.07-0.13 mg/mL, and pouring the GO into a 50mL beaker; the molar ratio of the components is 1-3: 1 Ni (NO) was weighed3)2·6H2O and Fe (NO)3)3·9H2O, quickly adding the sol containing agar and rGO into the sol containing agar and rGO, stirring to dissolve the sol to form uniform sol, and transferring the sol into a plastic tube while the sol is hot to enable the volume of the sol to reach 2/3 of the plastic tube;
(3) vertically standing until the sol is completely solidified, adding a NaOH solution with the concentration of 42mmol/L from the top end of each plastic tube to fill the plastic tubes, and sealing the plastic tubes by using preservative films; cutting a plastic tube after the natural permeation reaction is carried out for 48h, taking out the gel, keeping the shape intact, discarding 3mm of the top end of each gel, and dividing the gel into an upper section, a middle section and a lower section from top to bottom by taking each 10mm as a unit; and combining the samples in the same section, washing the samples with N, N-dimethylformamide for several times, washing off agar, washing the samples with deionized water and absolute ethyl alcohol for several times, and centrifuging to obtain the nickel-iron hydrotalcite nanosheet graphene electrocatalyst NiFe-LDH/rGO.
Wherein Fe (NO) in step (2) of the preparation method3)3·9H2The adding amount of O is 0.18 mmol; the diameter and the length of the plastic pipe are respectively 12mm and 100 mm; the hydrotalcite nanosheet obtained by the preparation method is rectangular or square, the transverse size of the nanosheet is 500-700 nm, and the nanosheet grows on the surface of the nanosheet in situ by taking reduced graphene oxide as a substrate to form a composite structure.
The nickel-iron hydrotalcite nanosheet graphene electrocatalyst prepared by the preparation method is suitable for catalytic oxygen evolution reaction in alkaline electrolyte, and is applied to the test of the catalytic activity of the oxygen evolution reaction by adding the nickel-iron hydrotalcite nanosheet graphene electrocatalyst into 1mol/L KOH solution to serve as a working electrode, taking a saturated calomel electrode as a reference electrode and taking a platinum sheet as a counter electrode.
Compared with the prior art, the invention has the main beneficial effects and advantages that:
1) the preparation method of the nickel-iron hydrotalcite nanosheet graphene electrocatalyst capable of effectively improving oxygen evolution reaction efficiency overcomes the defects of aggregation, large particle size, wide particle size distribution range, small specific surface area and the like existing in the preparation of nickel-iron hydrotalcite by a traditional coprecipitation method, has the characteristics of uniform particle size, narrow distribution range, large specific surface area, thin lamella and the like, and accordingly improves the electron transport capacity and stability of the catalyst through coordination action at the interface after compounding with rGO.
2) According to the preparation method of the nickel-iron hydrotalcite nanosheet graphene electrocatalyst capable of effectively improving the oxygen evolution reaction efficiency, the hydrotalcite nanosheets prepared by the gel method are controllable in shape and size, uniform in size and beneficial to improvement of catalytic activity due to full exposure of edges.
3) The preparation method of the nickel-iron hydrotalcite nanosheet graphene electrocatalyst capable of effectively improving oxygen evolution reaction efficiency overcomes the defects that pure nickel-iron hydrotalcite nanosheets are easy to stack and poor in stability, and the three-dimensional structure after compounding is beneficial to approaching of electrolyte and releasing of gas.
Description of the drawings:
figure 1 is an XRD diffractogram of the upper, middle and lower trilayer samples of example 1.
FIGS. 2 to 3 are transmission electron micrographs of the upper layer samples obtained in example 1.
FIG. 4 is an OER linear sweep voltammogram of the upper, middle and lower three samples obtained in example 1 in a 1mol/L KOH electrolyte solution at a sweep rate of 5 mV/s.
FIG. 5 is an OER linear sweep voltammogram at a sweep rate of 5mV/s in a 1mol/L KOH electrolyte solution for three samples obtained in example 1, comparative example 1, and comparative example 2.
FIG. 6 is an OER linear sweep voltammogram at a sweep rate of 5mV/s in a 1mol/L KOH electrolyte solution for three samples obtained in example 1, comparative example 3, and comparative example 4.
FIG. 7 is an OER linear sweep voltammogram at a sweep rate of 5mV/s in a 1mol/L KOH electrolyte solution for three samples obtained in example 2, comparative example 5, and comparative example 1.
FIG. 8 is an OER linear sweep voltammogram at a sweep rate of 5mV/s for the samples obtained in example 2, example 3, comparative example 7, comparative example 8, comparative example 9, and comparative example 10 in a 1mol/L KOH electrolyte solution.
FIG. 9 is an OER linear sweep voltammogram of the upper, middle and lower three samples obtained in example 1, example 2 and example 3 in a 1mol/L KOH electrolyte solution at a sweep rate of 5 mV/s.
FIG. 10 is a chronopotentiometric chart of three samples obtained in example 1, example 2 and example 3 in a KOH electrolyte solution of 1mol/L at a current density of 10mA cm-2The test time is 40 h.
The specific implementation mode is as follows:
for a further understanding of the invention, reference will now be made to the following examples and drawings, which are not intended to limit the invention in any way.
Example 1:
1) adding 30mL of deionized water into a 50mL single-neck flask, adding 0.3g of agar to make the content of the agar 1%, heating and stirring until the agar is boiled, and continuing to decoct for 30min to obtain an agar sol solution which is uniformly dispersed and transparent;
2) 104.6mg of Ni (NO) were weighed out3)2·6H2O (0.36mmol) and 72.7mg of Fe (NO)3)3·9H2O(0.18mmol)，Ni(NO3)2And Fe (NO)3)3The molar concentrations of the metal ions are respectively 12mmol/L and 6mmol/L, the total concentration of the metal ions is 18mmol/L, the mixture is put into a small beaker of 50mL, the decocted agar sol is poured into the small beaker while the agar sol is hot, and the mixture is rapidly stirred into a uniform solution. The solution was transferred to a plastic tube while hot, bringing the sol volume to 2/3 of the plastic tube;
3) vertically standing until the sol is completely solidified, adding a NaOH solution with the concentration of 42mmol/L from the top end of each plastic tube to fill the plastic tubes, and sealing the plastic tubes by using preservative films; cutting a plastic tube after the natural permeation reaction is carried out for 48h, taking out the gel, keeping the shape intact, discarding 3mm of the top end of each gel, and dividing the gel into an upper section, a middle section and a lower section from top to bottom by taking each 10mm as a unit; mixing the same-stage samples, washing with N, N-dimethylformamide for several times, washing off agar, washing with deionized water and anhydrous ethanol for several times, centrifuging to obtain 1% Ni of nickel-iron hydrotalcite nanosheet electrocatalyst2Fe-LDH18。
Example 2:
1) referring to the method and preparation conditions in step 1) of example 1, an agar sol having a gel strength of 1% was obtained;
2) referring to the method and preparation conditions in step 2) of example 1, the only difference is that 104.6mg of Ni (NO) was weighed out3)2·6H2O (0.36mmol) and 72.7mg of Fe (NO)3)3·9H2After O (0.18mmol), the total concentration of metal ions is 18mmol/L, and then 2.1mgGO is weighed. Adding GO into the decocted sol, stirring to uniformly disperse the GO, pouring the GO into a beaker containing ferronickel, uniformly stirring, transferring the mixture into a plastic test tube while the mixture is hot to obtain the nickel-iron hydrotalcite nanosheet graphene oxide electrocatalyst which is recorded as 1% Ni2Fe-LDH18/GO。
Example 3:
1) referring to the method and preparation conditions in step 1) of example 1, an agar sol having a gel strength of 1% was obtained;
2) referring to the method and preparation conditions in step 2) of embodiment 2, the only difference is that GO is added into the sol, then heating and decocting are continued for 30min, GO is reduced by a thermal reduction mode to obtain rGO, and the nickel iron hydrotalcite nanosheet reduced graphene oxide electrocatalyst is obtained, which is marked as 1% Ni2Fe-LDH18/rGO。
Comparative example 1:
1) with reference to the method and preparation conditions in step 1) of example 1, the only difference being the amount of agar added, 0.15g of agar being added, giving a sol solution with an agar strength of 0.5%;
2) referring to the method and preparation conditions in step 2) of example 1, obtaining the nickel-iron hydrotalcite nanosheet electrocatalyst, noted as 0.5% Ni2Fe-LDH18；
Comparative example 2:
1) with reference to the method and preparation conditions in step 1) of example 1, the only difference being the amount of agar added, 0.45g of agar being added, giving a sol solution with an agar strength of 1.5%;
2) referring to the method and preparation conditions in step 2) of example 1, obtaining a nickel iron hydrotalcite nanosheet electrocatalyst, noted as 1.5% Ni2Fe-LDH18；
Comparative example 3:
1) with reference to the method and preparation conditions in step 1) of example 1, a sol solution with an agar strength of 1% was obtained;
2) with reference to the process and preparation conditions in step 2) of example 1, the only difference is the concentration of nickel-iron metal ions, Ni (NO)3)2·6H2O and Fe (NO)3)3·9H2The molar weight of O is respectively 0.18mmol and 0.09mmol, the total concentration of metal ions is 9mmol/L, and the nickel iron hydrotalcite nanosheet electrocatalyst is obtained and is marked as 1% of Ni2Fe-LDH9；
Comparative example 4:
1) referring to the method and preparation conditions in step 1) of example 1, a sol solution having an agar strength of 1% was obtained;
2) with reference to the process and preparation conditions in step 2) of example 1, the only difference is the concentration of nickel-iron metal ions, Ni (NO)3)2·6H2O and Fe (NO)3)3·9H2The molar weight of O is respectively 0.72mmol and 0.36mmol, the total concentration of metal ions is 36mmol/L, and the nickel iron hydrotalcite nanosheet electrocatalyst is obtained and marked as 1% of Ni2Fe-LDH36；
Comparative example 5:
1) referring to the method and preparation conditions in step 1) of example 1, a sol solution having an agar strength of 1% was obtained;
2) referring to the method and preparation conditions in step 2) of example 2, the only difference is that the content of GO in the sol is different, and 1.5mg of GO is weighed to obtain the nickel iron hydrotalcite nanosheet graphene oxide electrocatalyst, which is marked as 1% Ni2Fe-LDH18/GO-0.05；
Comparative example 6:
1) referring to the method and preparation conditions in step 1) of example 1, a sol solution having an agar strength of 1% was obtained;
2) referring to the method and preparation conditions in step 2) of example 2, the only difference is that the content of GO in the sol is different, 3.0mgGO is weighed to obtain the nickel iron hydrotalcite nanosheet graphene oxide electrocatalyst, which is marked as 1% Ni2Fe-LDH18/GO-0.10；
Comparative example 7:
1) with reference to the method and preparation conditions in step 1) of example 1, a sol solution with an agar strength of 1% was obtained;
2) referring to the method and preparation conditions in step 2) of example 2, the only difference is that the proportion of Ni-Fe metal ions is different, and Ni (NO) is added under the condition of ensuring that the total metal ion concentration is 12mmol/L3)2·6H2O and Fe (NO)3)3·9H2The molar ratio of O is 3:1, and the nickel-iron hydrotalcite nanosheet graphene oxide electrocatalyst is obtained and is marked as 1% Ni3Fe-LDH12/GO；
Comparative example 8:
1) with reference to the method and preparation conditions in step 1) of example 1, a sol solution with an agar strength of 1% was obtained;
2) referring to the method and preparation conditions in step 2) of example 3, the only difference is that the ratio of nickel-iron metal ions is different, and Ni (NO) is added under the premise of ensuring that the total concentration is 12mmol/L3)2·6H2O and Fe (NO)3)3·9H2The molar ratio of O is 3:1, and the obtained nickel-iron hydrotalcite nanosheet reduced graphene oxide electrocatalyst is marked as 1% Ni3Fe-LDH12/rGO；
Comparative example 9:
1) with reference to the method and preparation conditions in step 1) of example 1, a sol solution with an agar strength of 1% was obtained;
2) referring to the method and preparation conditions in step 2) of example 2, the only difference is that the proportion of Ni-Fe metal ions is different, and Ni (NO) is added under the premise of ensuring that the total concentration is 12mmol/L3)2·6H2O and Fe (NO)3)3·9H2The molar ratio of O is 1:1, and the nickel-iron hydrotalcite nanosheet graphene oxide electrocatalyst is obtained and is marked as 1% NiFe-LDH12/GO；
Comparative example 10:
1) with reference to the method and preparation conditions in step 1) of example 1, a sol solution with an agar strength of 1% was obtained;
2) referring to the method and preparation conditions in step 2) of example 3, the only difference is that the ratio of nickel-iron metal ions is different, and Ni (NO) is added under the premise of ensuring that the total concentration is 12mmol/L3)2·6H2O and Fe (NO)3)3·9H2The molar ratio of O is 1:1, and the nickel-iron hydrotalcite nanosheet reduced graphene oxide electrocatalyst is obtained and recorded as 1% NiFe-LDH12/rGO；
FIG. 1 is the XRD results of the upper, middle and lower three layers of samples of example 1. 1% Ni in the figure2Fe-LDH18-on，1％Ni2Fe-LDH 18-inAnd 1% of Ni2Fe-LDH 18-lowerThree samples all have three characteristic diffraction peaks of hydrotalcite-like 003, 006 and 012 crystal planes at low 2 theta, wherein 1 percent of Ni2Fe-LDH 18-inAnd 1% of Ni2Fe-LDH18-onWith 1% Ni2Fe-LDH 18-lowerCompared with the characteristic peak of the sample, the peak width of the sample is obviously widened, and the strength is obviously weakened, which shows that the nickel-iron hydrotalcite nanosheet of the middle layer prepared by the gel permeation method has lower crystallinity. The width and intensity of the diffraction peaks reflects well the crystallinity of the sample. The diffraction peaks of 110 and 113 were also observed for all three samples at high 2 theta, but 1% Ni was evident2Fe-LDH 18-inAnd 1% of Ni2Fe-LDH 18-onWith 1% Ni2Fe-LDH 18-lowerThe comparison of the characteristic peaks of the samples, that is, the peaks of 110 and 113 are not only overlapped but also weakened in strength and widened in peak width, shows that 1% of Ni in the middle layer prepared by the gel permeation method of the present invention2The Fe-LDH sample has lower crystallinity and thinner lamella.
FIGS. 2 to 3 are scanning electron micrographs of the samples obtained in example 1. The scanning electron microscope image shows that the hydrotalcite nano material of the upper layer sample is in a sheet shape, the size of the sheet is 500-700 nm, and the sheet is rectangular or approximately square. As can be seen from the figure, the edges of the hydrotalcite nanosheets are fully exposed, which facilitates full exposure of the active sites at the edges of the NiFe-LDH. The characterization result shows that the nickel-iron hydrotalcite nanosheet is successfully prepared by the gel permeation method.
FIG. 4 is a linear sweep voltammogram of the top, middle and bottom three samples obtained in example 1 in a 1mol/L KOH electrolyte. As can be seen from the figure, when the molar mass ratio of Ni element to Fe element in the raw materials for preparation is 2:1 and the gel strength is 1%, by examining the OER properties of the upper, middle and lower three samples, the middle sample is 1% Ni2Fe-LDH 18-inThe best OER catalytic performance is obtained mainly because the layer sample is more uniform in size, relatively thinner in thickness and more fully exposed to active sites.
FIG. 5 is a linear sweep voltammogram of three mid-layer samples from example 1, comparative example 1, and comparative example 2 in a 1mol/L KOH electrolyte. As can be seen from the figure, when the molar mass ratio of Ni element to Fe element in the raw materials for preparation was 2:1, it was found by examining the contents of various agar powders that when the agar content was 1% (gel strength was 1%), 1% Ni of the middle layer was obtained2Fe-LDH 18Has the best OER catalytic performance.
FIG. 6 is a linear sweep voltammogram of three middle layer samples from example 1, comparative example 3, and comparative example 4 in a 1mol/L KOH electrolyte. As can be seen from the figure, when the molar mass ratio of Ni element and Fe element in the raw material for preparation is 2:1 and the gel strength is 1%, it was found by examining the total molar concentrations of Ni and Fe metal salts that when the total metal ion concentration is 18mmol/L, 1% Ni of the middle layer was obtained2Fe-LDH18Has the best OER catalytic performance.
FIG. 7 is a linear sweep voltammogram of three middle layer samples from example 2, comparative example 5, and comparative example 6 in a 1mol/L KOH electrolyte. As can be seen from the figure, when the molar mass ratio of Ni element to Fe element in the raw materials for preparation is 2:1, the gel strength is 1%, and the content of GO in the gel is 0.07mg/mL according to different GO contents, the obtained 1% Ni of the middle layer2Fe-LDH18/GO-0.07Has the best OER catalytic performance.
FIG. 8 is a line-scan voltammogram of the middle layer samples obtained in example 2, example 3, comparative example 7, comparative example 8, comparative example/9, and comparative example 10 in a 1mol/L KOH electrolyte. As can be seen from the graph, when the gel strength was 1% and the amount of rGO supported was 0.07mg/mL, the molar mass ratio of Ni and Fe salt was changed to find that the molar ratio of Ni and Fe elements was 2:1, and 1% Ni in the middle layer was obtained2Fe-LDH18the/rGO has the best OER catalytic performance.
FIG. 9 is a linear sweep voltammogram of three middle layer samples obtained in example 1, example 2, and example 3 in a 1mol/L KOH electrolyte. As can be seen from the figure, under the conditions that the molar mass ratio of Ni element to Fe element in the raw materials for preparation was 2:1 and the gel strength was 1%, the gel strength was 1% with respect to Ni2Fe-LDH18、Ni2Fe-LDH18(1%) Ni of samples containing rGO in the gel2Fe-LDH18The best OER catalytic performance of/rGO is fully demonstrated that the existence of rGO improves the conductivity until the Ni is fixed2The Fe-LDH plays a role, so that the excellent OER catalytic performance is presented.
FIG. 10 is a chronopotentiometric chart of the catalysts obtained in examples 1, 2 and 3 in a KOH electrolyte solution of 1mol/L, from which it can be seen that the current density is 10mA cm-2The time-lapse potential curve shows that Ni is removed2Fe-LDH18In addition, both other catalysts maintain an almost constant working potential, e.g. Ni2Fe-LDH181.48V, Ni of/rGO2Fe-LDH181.51V for/GO. Ni2Fe-LDH18The working power of 1.53V is maintained for the first 5hThe working potential of the catalyst is increased with the increase of time, and the catalyst is basically not active after 18 h. This is probably because the hydrotalcite material on the electrode falls off, and the pure nickel iron hydrotalcite nanosheet has poor adhesion and is easy to fall off after undergoing a long-term stability test. And after the LDH nano-sheets compounded with GO/rGO are tested for 40h, the working potential of the LDH nano-sheets is not obviously increased. The results of the chronopotentiometry demonstrated Ni2Fe-LDH18rGO and Ni2Fe-LDH18The durability of the/GO is better than that of Ni2Fe-LDH18Catalysts, which have great potential for use in the electrolysis of water.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and amendments can be made without departing from the principle of the present invention, and these modifications and amendments should also be considered as the protection scope of the present invention.

Claims (3)

1. A preparation method of a nickel-iron hydrotalcite nanosheet graphene electrocatalyst is characterized by comprising the steps of adding agar powder into water, heating and dissolving, adding graphene oxide into the agar powder, uniformly stirring, adding a metal ion solution into the graphene oxide, stirring to obtain a uniform solution, quickly transferring the solution into a plastic pipe while the solution is hot, and cooling to form gel to serve as an internal reaction medium; taking a sodium hydroxide solution as an external reaction solution, and preparing the graphene oxide by natural osmosis reaction at room temperature, wherein the graphene oxide is marked as GO, the reduced graphene oxide is marked as rGO, the nickel iron hydrotalcite nanosheet is marked as NiFe-LDH, and the nickel iron hydrotalcite nanosheet graphene is marked as NiFe-LDH/rGO;
the preparation method of the nickel-iron hydrotalcite nanosheet graphene electrocatalyst is characterized by comprising the following specific steps of:
(1) adding 30mL of deionized water into a 50mL single-neck flask, adding a certain amount of agar powder, heating and stirring until the mixture is boiled to enable the concentration of the agar powder to be 0.5-1.5%, and continuing to decoct for 30min to obtain transparent agar sol which is uniformly dispersed;
(2) weighing a certain amount of GO to be addedStirring the decocted thermosol to uniformly disperse the thermosol to ensure that the GO content is 0.07-0.13 mg/mL, pouring the thermosol into a 50mL beaker, continuously heating and decocting, and reducing GO in a thermal reduction mode to obtain rGO; then, according to the molar ratio of 1-3: 1 ratio of Ni (NO)3)2·6H2O and Fe (NO)3)3·9H2O, quickly adding the sol containing agar and rGO into the sol containing agar and rGO, stirring to dissolve the sol to form uniform sol, and transferring the sol into a plastic tube while the sol is hot to enable the volume of the sol to reach 2/3 of the plastic tube;
(3) vertically standing until the sol is completely solidified, adding a NaOH solution with the concentration of 42mmol/L from the top end of each plastic tube to fill the plastic tubes, and sealing the plastic tubes by using preservative films; cutting a plastic tube after the natural permeation reaction is carried out for 48h, taking out the gel, keeping the shape intact, discarding 3mm of the top end of each gel, and dividing the gel into an upper section, a middle section and a lower section from top to bottom by taking each 10mm as a unit; and combining the samples at the same section, washing the samples with N, N-dimethylformamide for several times, washing off agar, washing the samples with deionized water and absolute ethyl alcohol for several times, and centrifuging to obtain the nickel-iron hydrotalcite nanosheet graphene electrocatalyst NiFe-LDH/rGO.
2. The preparation method of the nickel-iron hydrotalcite nanosheet graphene electrocatalyst according to claim 1, wherein in step (2) of the preparation method, Fe (NO) is used3)3·9H2The addition amount of O is 0.18 mmol; the diameter and the length of the plastic pipe are respectively 12mm and 100 mm; the hydrotalcite nanosheet prepared by the preparation method is rectangular or square, the transverse size of the nanosheet is 500-700 nm, and the nanosheet grows in situ on the surface of the nanosheet by taking reduced graphene oxide as a substrate to form a composite structure.
3. The preparation method of the nickel-iron hydrotalcite nanosheet graphene electrocatalyst according to claims 1 and 2, characterized in that the nickel-iron hydrotalcite nanosheet graphene catalyst obtained by the method is used for alkaline electrolysis water anodic oxygen evolution reaction.
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