CN117446920A - Two-dimensional nano-sheet heterojunction electrocatalyst and preparation method and application thereof - Google Patents

Two-dimensional nano-sheet heterojunction electrocatalyst and preparation method and application thereof Download PDF

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CN117446920A
CN117446920A CN202311457341.7A CN202311457341A CN117446920A CN 117446920 A CN117446920 A CN 117446920A CN 202311457341 A CN202311457341 A CN 202311457341A CN 117446920 A CN117446920 A CN 117446920A
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ldh
cofe
electrocatalyst
nico
nano
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闫明磊
刘文纲
张俊杰
任俣骁
孙一淞
赵洋
曾赟
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Sichuan Agricultural University
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Sichuan Agricultural University
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    • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
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    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
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    • C02F1/46—Treatment of water, waste water, or sewage by electrochemical methods
    • C02F1/461—Treatment of water, waste water, or sewage by electrochemical methods by electrolysis
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Abstract

The invention discloses a two-dimensional nano-sheet heterojunction electrocatalyst and a preparation method and application thereof, and belongs to the technical field of catalysts. The two-dimensional nano-sheet heterojunction electrocatalyst comprises a matrix CoFe-LDH nano-sheet and a NiCo-LDH nano-sheet loaded on the CoFe-LDH. The catalyst is of a three-dimensional hierarchical structure composed of two-dimensional nano sheets, has high specific surface area, can provide rich catalytic active sites, has hydrophilic characteristic, and is beneficial to the diffusion of electrolyte ions; in addition, the heterojunction formed by two different nano sheets causes charge redistribution at the interface, and the d-band center moves upwards, so that the adsorption and desorption of intermediate species are facilitated, and the catalytic reaction is promoted; and the 2D/2D heterojunction with surface contact can obviously shorten the transmission distance of charges, effectively increase the transmission channel of the charges and improve the catalytic effect to a certain extent.

Description

Two-dimensional nano-sheet heterojunction electrocatalyst and preparation method and application thereof
Technical Field
The invention relates to the technical field of catalysts, in particular to a two-dimensional nano-sheet heterojunction electrocatalyst and a preparation method and application thereof.
Background
With the development of human society, there is an increasing demand for fossil fuels such as petroleum, natural gas, coal, etc. among non-renewable resources. Excessive use of fossil fuels will increase greenhouse gas emissions and ultimately lead to serious environmental pollution. In view of the problem, the advanced clean energy production technology can continuously improve energy efficiency, can solve the problems related to environmental pollution, is an effective method for realizing sustainable development of human society, and is characterized by hydrogen (H) 2 ) Because of its high energy density and zero environmental pollution, is considered to be the most promising green energy carrier for fossil fuel replacement. Hydrogen can be produced by a variety of methods, among which fossil fuels and the like release toxic gases into the environment, and thus the produced hydrogen is impure and the harmful gases easily pollute the environment, and electrochemical water decomposition is considered as one of the cleanest hydrogen production methods. Electrochemical water splitting involves two half reactions: cathodic Hydrogen Evolution Reaction (HER) Oxygen Evolution Reaction (OER) of the anode. The theoretical potential required for electrochemical water splitting is 1.23V. However, due to the presence of impedance and slow kinetics of OER, the decomposition voltage of the electrolyzed water is typically above 1.8V, which results in higher energy consumption. In order to reduce the high energy consumption generated during OER, some researchers use other heatThe more mechanically facile half-reactions replace OER, mainly: urea oxidation, ethanolamine oxidation, glycerol oxidation, and the like. Among them, urea Oxidation (UOR) has been attracting attention because of its low theoretical potential (0.37V) requirement, urea (CO (NH) 2 ) 2 ) Is an organic compound containing a large amount of hydrogen elements (6.67%), and is a good carrier for developing and utilizing hydrogen energy in the future; on the other hand, urea has high solubility in water, high stability at room temperature and normal pressure, low cost, no toxicity, nonflammability and convenient storage and transportation. Urea is mostly present in industrial wastewater and animal urine, and it is reported that more than 80% of wastewater per year is directly discharged into the natural environment, which poses serious threat to the environment, because urea decomposition in nature generates compounds containing ammonia and nitrate, which can pose serious harm to the environment and human health. The urea in the urea-rich wastewater can be converted into nitrogen and carbon dioxide through the electrolysis process, and the process not only can purify the urea-rich wastewater, but also can realize low-energy-consumption hydrogen production, thereby being an efficient and clean preparation technology. However, the urea electrolysis process is a six-electron transfer process, and the reaction kinetics are slow, so that a high-efficiency electrocatalyst is required to improve the reaction efficiency.
At present, noble metal catalysts, although exhibiting high activity, have limited industrial applications due to their scarcity and high cost. Recent researches show that the layered double hydroxide has adjustable morphology and electronic structure, shows higher catalytic activity in alkaline electrolyte, and is one of the best choices for replacing noble metal catalysts. In recent years, research on nickel-based catalysts for electrolytic urea-assisted hydrogen production has also increased, and chinese patent document CN110327942a discloses a foam nickel-supported MoS for use as an electrolytic urea-assisted hydrogen production 2 /Ni 3 S 2 The preparation of NiFe-LDH/NF catalyst includes the steps of using foamed nickel as substrate and nickel source, synthesizing MoS at 180-220 deg.c under hydrothermal condition 2 /Ni 3 S 2 Firstly, introducing nickel-iron double-layer hydroxide into a nano rod array of NF (nano-porous membrane)/nano rod array at 120-160 ℃ under hydrothermal condition to finally form a lamellar micron flower-like MoS 2 /Ni 3 S 2 NiFe-LDH/NF material, the heteroThe mass junction consists of a one-dimensional nano rod (1D) and a two-dimensional nano sheet (2D), but has the problems of longer charge transmission distance and fewer charge transmission channels, so that the electrocatalytic activity is lower; in addition, moS 2 /Ni 3 S 2 The preparation process of the NiFe-LDH/NF needs a two-step hydrothermal method, is complex in process and long in time consumption, and limits large-scale industrial production.
Based on this, there is a need for an electrocatalyst having excellent electrocatalyst properties and low production costs.
Disclosure of Invention
In order to solve the problem that the existing electrocatalyst has lower catalytic activity when the urea is subjected to electrocatalytic degradation to assist in hydrogen production, one of the purposes of the invention is to provide a two-dimensional nanosheet heterojunction electrocatalyst.
The technical scheme for solving the technical problems is as follows:
a two-dimensional nano-sheet heterojunction electrocatalyst comprises a substrate CoFe-LDH nano-sheet and a NiCo-LDH nano-sheet loaded on the CoFe-LDH nano-sheet.
The beneficial effects of the invention are as follows: the electrocatalyst is of a three-dimensional hierarchical structure consisting of two-dimensional nano sheets, has high specific surface area, can provide rich catalytic active sites, has the characteristic of hydrophilic property, and is beneficial to the diffusion of electrolyte ions; in addition, the heterojunction formed by two different two-dimensional nano sheets leads to charge redistribution at the interface, and the d-band center moves upwards, so that the adsorption and desorption of intermediate species are facilitated, and the catalytic reaction is promoted; and the 2D/2D heterojunction with surface contact can obviously shorten the transmission distance of charges, effectively increase the transmission channel of the charges and improve the catalytic effect to a certain extent.
Based on the technical scheme, the invention can also be improved as follows:
further, the catalyst also comprises a carrier, wherein the CoFe-LDH nano sheet is grown on the carrier in situ, and the carrier is foam nickel.
The beneficial effects of adopting the further technical scheme are as follows: the three-dimensional porous structure of the foam nickel is favorable for the infiltration of electrolyte, and improves the conductivity of the electrocatalyst to a certain extent.
The second purpose of the invention is to provide a preparation method of the two-dimensional nano-sheet heterojunction electrocatalyst, which comprises the following steps:
step 1, cobalt salt, ferric salt, urea and NH 4 F, after being dissolved in deionized water, carrying out a high-temperature hydrothermal reaction with the pretreated carrier in a reaction kettle, and after the reaction is finished, preparing an intermediate of the CoFe-LDH nanosheet loaded on the carrier;
step 2, respectively taking an intermediate, a platinum wire and Saturated Calomel (SCE) as a working electrode, a counter electrode and a reference electrode, and taking a solution containing Ni and Co as electrolyte to carry out electrodeposition to prepare a two-dimensional nano-sheet heterojunction electrocatalyst CoFe-LDH/NiCo-LDH/NF;
preferably, the pretreated carrier in the invention is pretreated foam nickel, wherein the preparation of the pretreated foam nickel is as follows: respectively carrying out ultrasonic treatment on the foam nickel in 2M HCl, acetone, deionized water and ethanol for 30min, then drying the foam nickel in a vacuum drying oven at 60 ℃ for 12h, and cooling the foam nickel to room temperature to obtain pretreated foam nickel; the pretreated foam nickel is favorable for the in-situ growth of CoFe-LDH on the foam nickel, and the conductivity of the catalyst can be improved to a certain extent.
Further, the cobalt salt is Co (NO 3 ) 2 ·6H 2 O, iron salt is Fe (NO) 3 ) 3 ·9H 2 O; cobalt salt, iron salt, urea and NH in step 1 4 The molar ratio of F is 0.5:0.5:10:4 to 1:0.5:14:4; preferably cobalt salts, iron salts, urea and NH 4 F in a molar ratio of 0.5:0.5:10:4.
Further, the high-temperature hydrothermal reaction conditions in the step 1 are as follows: preserving heat for 4-8 hours at 100-140 ℃; preferably, the conditions of the hydrothermal reaction are: preserving the heat for 6 hours at 120 ℃.
Further, ni (NO) 3 ) 2 ·6H 2 O and Co (NO) 3 ) 2 ·6H 2 O, ni (NO) in electrolyte 3 ) 2 ·6H 2 O and Co (NO) 3 ) 2 ·6H 2 The molar concentration of O is 0.01-0.03 mmol/mL; preferably, ni (NO 3 ) 2 ·6H 2 O and Co (NO) 3 ) 2 ·6H 2 The molar concentration of O was 0.02mmol/mL.
Further, the conditions of electrodeposition in step 2 are: performing electrodeposition for 50-400 s under the voltage of-1V; preferably, the conditions for electrodeposition are that electrodeposition is carried out at a voltage of-1V for 200s.
The invention further aims to provide the application of the two-dimensional nano-sheet heterojunction electrocatalyst in catalyzing and degrading urea, waste water containing urea and hydrogen production assisted by electrocatalytic degradation of urea.
The invention has the following beneficial effects:
1. the two-dimensional nano-sheet heterojunction electrocatalyst is prepared by combining a hydrothermal method and an electrodeposition method, the time required by electrodeposition is 400s at the longest, and the preparation efficiency of the two-dimensional nano-sheet heterojunction electrocatalyst is improved; therefore, the preparation method has the characteristics of simple and convenient operation, less time consumption and low energy consumption.
2. According to the invention, fe, co and Ni are selected as metal elements for preparing the CoFe-LDH nano sheet and the NiCo-LDH nano sheet, and a d electron layer of Fe, co and Ni transition metal easily loses electrons or abstracts electrons, so that the catalyst has stronger oxidation-reduction performance and higher activity in electrocatalytic reaction; in addition, coFe-LDH and NiCo-LDH are common double metal hydroxides in electrocatalysis, and the effect of '1+1 > 2' can be achieved by forming a heterostructure by the CoFe-LDH and the NiCo-LDH.
Meanwhile, the Fe, co and Ni transition metals have the characteristics of low price and rich reserves, and the cost is greatly reduced.
3. The two-dimensional nano-sheet heterojunction electrocatalyst prepared by the method has high specific surface area and rich active sites; meanwhile, the three-dimensional porous structure of the carrier foam nickel is favorable for infiltration of electrolyte, and the conductivity of the electrocatalyst is improved. The built-in electric field of the heterogeneous interface causes charge redistribution, regulates and controls the electronic structure of the electrocatalyst, is beneficial to the adsorption and desorption of intermediate species, and promotes the catalytic reaction.
4. The electrocatalyst prepared by the invention shows excellent electrocatalytic urea oxidation activity between 1M KOH and 0.5M urea10mA/cm in the electrolyte of (C) 2 The potential at the current density was only 1.35V vs. RHE (reversible hydrogen electrode), and the catalytic activity was hardly attenuated after continuous cycle for 100 hours at the current density, showing excellent electrochemical stability.
In addition, in order to simulate the practical application of the electrolytic urea, the human urine containing 1M KOH is used as electrolyte, and the electric catalyst in the invention can reach 10mA/cm only by 1.39V potential 2 Shows potential for purifying urea-rich wastewater.
Drawings
FIG. 1 is a Scanning Electron Microscope (SEM) image of CoFe-LDH electrocatalyst and CoFe-LDH/NiCo-LDH electrocatalyst; wherein a is an SEM image of the CoFe-LDH electrocatalyst and b is an SEM image of the CoFe-LDH/NiCo-LDH/NF electrocatalyst;
FIG. 2 is a Transmission Electron Microscope (TEM) image of a CoFe-LDH/NiCo-LDH electrocatalyst; wherein, a is a transmission electron microscope image of the CoFe-LDH/NiCo-LDH electrocatalyst under the scale of 50 nm; FIG. b is a High Resolution Transmission Electron Microscopy (HRTEM) of a CoFe-LDH/NiCo-LDH electrocatalyst at a scale of 5 nm; FIG. c is a plot of the corresponding CoFe-LDH after Fourier transformation in the dashed area in FIG. b; FIG. d is a plot of the corresponding NiCo-LDH after Fourier transformation in the dashed area in FIG. b;
FIG. 3 is an X-ray diffraction (XRD) pattern of Nickel Foam (NF), coFe-LDH electrocatalyst, coFe-LDH/NiCo-LDH electrocatalyst, and NiCo-LDH electrocatalyst;
FIG. 4 is an X-ray photoelectron spectroscopy (XPS) of a CoFe-LDH/NiCo-LDH electrocatalyst;
FIG. 5 is RuO 2 Linear sweep voltammograms for (ruthenium oxide) electrocatalysts, coFe-LDH/NiCo-LDH electrocatalysts and NiCo-LDH electrocatalysts;
FIG. 6 is RuO 2 Tafel slope (Tafel) plots for CoFe-LDH electrocatalyst, coFe-LDH/NiCo-LDH electrocatalyst and NiCo-LDH electrocatalyst;
FIG. 7 is an alternating current impedance spectroscopy (EIS) plot of CoFe-LDH electrocatalyst, coFe-LDH/NiCo-LDH electrocatalyst and NiCo-LDH electrocatalyst;
FIG. 8 shows CoFe-LDH/NiCo-LDH at 10mA/cm 2 A timing voltage plot at current density of (2);
FIG. 9 is RuO 2 Linear sweep voltammograms of the Pt/C urea full cell, coFe-LDH urea full cell, coFe-LDH/NiCo-LDH urea full cell, and NiCo-LDH urea full cell;
FIG. 10 is a graph of Linear Sweep Voltammograms (LSV) of a CoFe-LDH/NiCo-LDH urea full cell with human urine containing 1M KOH as electrolyte;
FIG. 11 is a graph of the timing voltage of a CoFe-LDH/NiCo-LDH urea full cell in human urine containing 1M KOH as electrolyte.
Detailed Description
The principles and features of the present invention are described below with reference to the drawings, the examples are illustrated for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
Example 1
The preparation method of the two-dimensional nano-sheet heterojunction electrocatalyst comprises the following steps:
step 1, respectively ultrasonically cleaning foam nickel (2 cm multiplied by 4 cm) with dilute hydrochloric acid (2M), acetone, deionized water and ethanol for 30min, drying in a vacuum drying oven at 60 ℃ for 12h, and cooling to room temperature for later use;
step 2, 0.5mmol Co (NO 3 ) 2 ·6H 2 O (cobalt nitrate), 0.5mmol Fe (NO) 3 ) 3 ·9H 2 O (ferric nitrate), 10mmol urea and 4mmol NH 4 F (ammonium fluoride) is dissolved in 30mL of water solution, and mixed solution I is formed after stirring for 3 hours;
pouring the mixed solution I into a 50mL reaction kettle, then placing the foam nickel (2 cm multiplied by 4 cm) pretreated in the step 1 into the reaction kettle, preserving heat for 6 hours at 120 ℃, cooling to room temperature, respectively cleaning with deionized water and ethanol for three times, and drying in a vacuum drying oven at 60 ℃ for 12 hours to obtain CoFe-LDH/NF;
step 4, 4mmol Ni (NO) 3 ) 2 ·6H 2 O (Nickel nitrate) and 4mmol Co (NO) 3 ) 2 ·6H 2 O is dissolved in 200mL of deionized water to form a mixed solution II;
step 5, taking 25mL of the mixed solution II obtained in the step 4 as an electrolyte, and then taking the CoFe-LDH/NF (1 cm multiplied by 2 cm), the platinum wire and the Saturated Calomel (SCE) obtained in the step 3 as a working electrode, a counter electrode and a reference electrode respectively, and preparing the CoFe-LDH/NiCo-LDH/NF two-dimensional nano-sheet heterojunction electrocatalyst by using a three-electrode system through an electrodeposition method, wherein the electrodeposition conditions are as follows: electrodeposition was performed at a voltage of-1V for 200s; and after the electrodeposition is finished, washing the CoFe-LDH/NiCo-LDH/NF two-dimensional nano-sheet heterojunction electrocatalyst obtained by the electrodeposition with deionized water and ethanol for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 12 hours.
Example 2
The preparation method of the two-dimensional nano-sheet heterojunction electrocatalyst comprises the following steps:
step 1, respectively ultrasonically cleaning foam nickel (2 cm multiplied by 4 cm) with dilute hydrochloric acid (2M), acetone, deionized water and ethanol for 30min, drying in a vacuum drying oven at 60 ℃ for 12h, and cooling to room temperature for later use;
step 2, 0.7mmol Co (NO 3 ) 2 ·6H 2 O (cobalt nitrate), 0.5mmol Fe (NO) 3 ) 3 ·9H 2 O (ferric nitrate), 11mmol urea and 4mmol NH 4 F (ammonium fluoride) is dissolved in 30mL of water solution, and mixed solution I is formed after stirring for 3 hours;
pouring the mixed solution I into a 50mL reaction kettle, then placing the foam nickel (2 cm multiplied by 4 cm) pretreated in the step 1 into the reaction kettle, preserving heat for 8 hours at 100 ℃, cooling to room temperature, respectively cleaning with deionized water and ethanol for three times, and drying in a vacuum drying oven at 60 ℃ for 12 hours to obtain CoFe-LDH/NF;
step 4, 2mmol Ni (NO 3 ) 2 ·6H 2 O (Nickel nitrate) and 2mmol Co (NO) 3 ) 2 ·6H 2 O is dissolved in 200mL of deionized water to form a mixed solution II;
step 5, taking 25mL of the mixed solution II obtained in the step 4 as an electrolyte, and then taking the CoFe-LDH/NF (1 cm multiplied by 2 cm), the platinum wire and the Saturated Calomel (SCE) obtained in the step 3 as a working electrode, a counter electrode and a reference electrode respectively, and preparing the CoFe-LDH/NiCo-LDH/NF two-dimensional nano-sheet heterojunction electrocatalyst by using a three-electrode system through an electrodeposition method, wherein the electrodeposition conditions are as follows: electrodepositing at a voltage of-1V for 50s; and after the electrodeposition is finished, washing the CoFe-LDH/NiCo-LDH/NF two-dimensional nano-sheet heterojunction electrocatalyst obtained by the electrodeposition with deionized water and ethanol for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 12 hours.
Example 3
The preparation method of the two-dimensional nano-sheet heterojunction electrocatalyst comprises the following steps:
step 1, respectively ultrasonically cleaning foam nickel (2 cm multiplied by 4 cm) with dilute hydrochloric acid (2M), acetone, deionized water and ethanol for 30min, drying in a vacuum drying oven at 60 ℃ for 12h, and cooling to room temperature for later use;
step 2, 1mmol Co (NO 3 ) 2 ·6H 2 O (cobalt nitrate), 0.5mmol Fe (NO) 3 ) 3 ·9H 2 O (ferric nitrate), 14mmol urea and 4mmol NH 4 F (ammonium fluoride) is dissolved in 30mL of water solution, and mixed solution I is formed after stirring for 3 hours;
pouring the mixed solution I into a 50mL reaction kettle, then placing the foam nickel (2 cm multiplied by 4 cm) pretreated in the step 1 into the reaction kettle, preserving heat for 4 hours at 140 ℃, cooling to room temperature, respectively cleaning with deionized water and ethanol for three times, and drying in a vacuum drying oven at 60 ℃ for 12 hours to obtain CoFe-LDH/NF;
step 4, 6mmol Ni (NO 3 ) 2 ·6H 2 O (Nickel nitrate) and 6mmol Co (NO) 3 ) 2 ·6H 2 O is dissolved in 200mL of deionized water to form a mixed solution II;
step 5, taking 25mL of the mixed solution II obtained in the step 4 as an electrolyte, and then taking the CoFe-LDH/NF (1 cm multiplied by 2 cm), the platinum wire and the Saturated Calomel (SCE) obtained in the step 3 as a working electrode, a counter electrode and a reference electrode respectively, and preparing the CoFe-LDH/NiCo-LDH/NF two-dimensional nano-sheet heterojunction electrocatalyst by using a three-electrode system through an electrodeposition method, wherein the electrodeposition conditions are as follows: electrodeposition was performed at a voltage of-1V for 400s; and after the electrodeposition is finished, washing the CoFe-LDH/NiCo-LDH/NF two-dimensional nano-sheet heterojunction electrocatalyst obtained by the electrodeposition with deionized water and ethanol for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 12 hours.
Comparative example 1
The preparation method of the NiCo-LDH/NF nano-sheet electrocatalyst comprises the following steps:
step 1, 4mmol Ni (NO 3 ) 2 ·6H 2 O (Nickel nitrate) and 4mmol Co (NO) 3 ) 2 ·6H 2 O is dissolved in 200mL of deionized water to form a mixed solution;
step 2, taking 25mL of the mixed solution in the step 1 as an electrolyte, and then taking blank NF (1 cm multiplied by 2 cm), a platinum wire and Saturated Calomel (SCE) as a working electrode, a counter electrode and a reference electrode respectively, and preparing the NiCo-LDH/NF nano-sheet catalyst by using a three-electrode system through an electrodeposition method, wherein the electrodeposition conditions are as follows: electrodeposition was performed at a voltage of-1V for 200s; and after the electrodeposition is finished, cleaning the NiCo-LDH/NF nano-sheet electrocatalyst obtained by the electrodeposition with deionized water and ethanol for three times respectively, and drying in a vacuum drying oven at 60 ℃ for 12 hours.
Test analysis:
(one), structure characterization
1. SEM test analysis was performed on the CoFe-LDH/NiCo-LDH/NF electrocatalyst prepared in example 1 and the CoFe-LDH/NF electrocatalyst prepared in comparative example 1, the test results of which are shown in detail in FIG. 1, wherein graph a in FIG. 1 is an SEM image of the CoFe-LDH electrocatalyst and graph b in FIG. 1 is an SEM image of the CoFe-LDH/NiCo-LDH/NF electrocatalyst.
As can be seen from fig. 1, coFe-LDH nanoplatelets are distributed staggeredly on nickel foam, while ultrathin NiCo-LDH nanoplatelets are attached to CoFe-LDH matrix, and the two nanoplatelets are interlaced with each other to form a three-dimensional hierarchical structure, have a high specific surface area, and provide a large number of active sites.
2. The morphology of the CoFe-LDH/NiCo-LDH/NF electrocatalyst prepared in example 1 was observed with a high resolution transmission electron microscope, and the results are detailed in FIG. 2. As can be seen from graph a in fig. 2, the CoFe-LDH/NiCo-LDH exhibits a nanoplatelet morphology; HRTEM results show that the CoFe-LDH/NiCo-LDH/NF electrocatalyst consists of two phases of CoFe-LDH and NiCo-LDH (see b diagram in detail), wherein 0.26nm interplanar spacing corresponds to the (012) crystal plane of CoFe-LDH nanoplatelets (see c diagram in detail) and 0.19nm interplanar spacing corresponds to the (018) crystal plane of NiCo-LDH nanoplatelets (see d diagram in detail).
3. XRD test analysis was performed on CoFe-LDH/NF electrocatalyst, niCo-LDH/NF electrocatalyst and CoFe-LDH/NiCo-LDH/NF electrocatalyst, and the test results are shown in FIG. 3.
As can be seen from fig. 3, the foam nickel substrate (NF) has very strong diffraction peaks; however, since the amount of NiCo-LDH nanoplatelets produced by electrodeposition is small, no diffraction peak of NiCo-LDH can be seen in XRD, and diffraction peaks of three crystal planes (003), (006) and (012) can be clearly seen for CoFe-LDH. For CoFe-LDH/NiCo-LDH, the diffraction peaks of two phases of CoFe-LDH and NiCo-LDH are contained, so that the two-dimensional nano-sheet heterojunction electrocatalyst of CoFe-LDH/NiCo-LDH is successfully prepared by combining with FIG. 2.
4. XPS test analysis was performed on CoFe-LDH/NiCo-LDH/NF electrocatalyst, and the results are detailed in FIG. 4. As can be seen from FIG. 4, the CoFe-LDH/NiCo-LDH/NF electrocatalyst prepared in the present invention contains Co, fe, ni, O element.
(II) Performance test
The performance of the electrocatalyst and the assembled battery thereof is tested by adopting an Shanghai Chenhua electrochemical workstation (CHI 760E); when the CoFe-LDH electrocatalyst, the CoFe-LDH/NiCo-LDH electrocatalyst and the NiCo-LDH electrocatalyst are tested, the electrocatalyst loaded on foam nickel (1 cm multiplied by 1 cm) is directly used as a working electrode, and Hg/HgO and a graphite rod are respectively used as a reference electrode and a counter electrode.
For RuO 2 When testing, ruO 2 And the Pt/C electrode adopts a coating method, and comprises the following specific steps: ruO is to be made into 2 (or Pt/C), acetylene black and polyvinylidene fluoride (PVDF) are mixed according to the mass ratio of 8:1:1, and then a proper amount of N-methyl is addedPyrrolidinone (NMP) was ground to a slurry and coated at 1cm 2 Is then dried in vacuo at 100℃for 12h.
In the test, 1M KOH+0.5M urea was used as the electrolyte. Before the overpotential is tested, the method comprises the steps of activating for 20 circles by using a Cyclic Voltammetry (CV) at a scanning speed of 50mV/s, obtaining a polarization curve by using a linear sweep voltammetry after an equal CV curve is stabilized, wherein the voltage window of UOR is 0-0.8V (vs Hg/HgO), and the scanning speed is 5mV s -1 According to Nernst equation (E RHE = E Saturated calomel + 0.0591 ×ph+0.098) the potential is iR corrected and converted to a Reversible Hydrogen Electrode (RHE).
In addition, the frequency range of the alternating current impedance spectroscopy (EIS) test is 100 kHz-0.01 Hz, and the bias voltage is 5mV; stability testing uses Chronopotentiometry (CP).
1、RuO 2 The results of voltammetric tests performed on electrocatalysts, coFe-LDH/NiCo-LDH electrocatalysts and NiCo-LDH electrocatalysts are detailed in FIG. 5.
As can be seen from FIG. 5, the temperature was set at 10mA/cm 2 RuO at current density of (c) 2 The potentials of CoFe-LDH, coFe-LDH/NiCo-LDH and NiCo-LDH are respectively: 1.41V, 1.37V, 1.35V, and 1.39V, wherein the potential of the CoFe-LDH/NiCo-LDH is the smallest (1.35V), i.e., the CoFe-LDH/NiCo-LDH in the present invention drives the electrocatalytic urea degradation reaction to occur upon application of a smaller potential. Namely, the CoFe-LDH/NiCo-LDH in the present invention has the best electrocatalytic urea oxidation performance in an electrolyte of 1M KOH and 0.5M urea.
2、RuO 2 The results of tafel tests performed on electrocatalysts, coFe-LDH/NiCo-LDH electrocatalysts and NiCo-LDH electrocatalysts are detailed in fig. 6.
As can be seen from FIG. 6, ruO 2 The potentials of the electrocatalyst, coFe-LDH/NiCo-LDH electrocatalyst and NiCo-LDH electrocatalyst are respectively: 164mV dec -1 、54mV dec -1 、42mV dec -1 And 110mV dec -1 Wherein the potential of the CoFe-LDH/NiCo-LDH is at a minimum (42 mV dec -1 ) Description of CoFe-LDH/NiCo-LDH electrocatalyst at 1M KThe electrolyte of OH and 0.5M urea has the fastest catalytic reaction kinetics.
3. The results of the ac impedance spectroscopy measurements performed on the CoFe-LDH electrocatalyst, coFe-LDH/NiCo-LDH electrocatalyst and NiCo-LDH electrocatalyst are detailed in fig. 7, wherein the semicircle represents the charge transfer impedance.
As can be seen from fig. 7, the (alternating current impedance spectrum) EIS semicircle of the CoFe-LDH/NiCo-LDH electrocatalyst is smallest, indicating that the CoFe-LDH/NiCo-LDH electrocatalyst has the smallest charge transfer impedance during the electrochemical reaction and the optimal electrode reaction kinetics.
4. The stability of CoFe-LDH/NiCo-LDH is tested by adopting a chronopotentiometric method, and the test conditions are as follows: 10mA/cm 2 The results of the tests at the current density of (2) for electrocatalytic urea oxidation for 100h are shown in FIG. 8.
As can be seen from fig. 8, the activity of the CoFe-LDH/NiCo-LDH electrocatalyst of the invention is hardly attenuated after 100h of electrocatalytic urea oxidation, indicating that the CoFe-LDH/NiCo-LDH has excellent electrochemical stability.
5. Voltammetric tests are carried out on the CoFe-LDH-CoFe-LDH urea full electrolytic cell, the CoFe-LDH/NiCo-LDH-CoFe-LDH/NiCo-LDH urea full electrolytic cell and the NiCo-LDH-NiCo-LDH urea full electrolytic cell, and the test results are shown in figure 9.
As can be seen from FIG. 9, the CoFe-LDH-CoFe-LDH urea total electrolytic cell, the CoFe-LDH/NiCo-LDH-CoFe-LDH/NiCo-LDH urea total electrolytic cell and the NiCo-LDH-NiCo-LDH are 10mA/cm 2 The decomposition voltages of the urea full electrolytic cell at the current density are 1.59V, 1.54V and 1.60V respectively, which shows that the urea full electrolytic cell consisting of CoFe-LDH/NiCo-LDH has the minimum decomposition voltage and is combined with noble metal RuO 2 The decomposition voltage (1.53V) of the Pt/C electrolytic cell is very close; the CoFe-LDH/NiCo-LDH electrocatalyst has excellent electrocatalytic urea oxidation performance.
6. The voltammetric test is carried out on a urea full electrolytic cell composed of CoFe-LDH/NiCo-LDH, and when the test is carried out, human urine with 1M KOH is used as electrolyte, and the test result is shown in figure 10.
As can be seen from FIG. 10, the temperature is 10mA/cm 2 The decomposition voltage at the current density of (2) is 1.55V, which is close to 1.54V in 1M KOH and 0.5M urea electrolyte, which shows that the CoFe-LDH/NiCo-LDH electrocatalyst has good practical application effect.
7. The stability of the urea full electrolytic cell composed of CoFe-LDH/NiCo-LDH is tested by adopting a chronopotentiometry, and the test result is shown in figure 11; human urine containing 1M KOH was used as electrolyte for the test.
As can be seen from FIG. 11, the temperature is 50mA/cm 2 After the electrocatalytic urea is oxidized for 60 hours under the current density, the activity of the electrocatalytic catalyst is little, which shows that CoFe-LDH/NiCo-LDH has good electrochemical stability in human urine containing 1M KOH as electrolyte, and the aim of producing hydrogen by full electrolysis of urea with low energy consumption can be fulfilled.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the precise form disclosed, and any such modifications, equivalents, and alternatives falling within the spirit and scope of the invention are intended to be included within the scope of the invention.

Claims (8)

1. The two-dimensional nano-sheet heterojunction electrocatalyst is characterized by comprising a substrate CoFe-LDH nano-sheet and NiCo-LDH nano-sheets supported on the CoFe-LDH nano-sheet.
2. The two-dimensional nano-sheet heterojunction electrocatalyst of claim 1, further comprising a support on which the CoFe-LDH nano-sheets are grown in situ, the support being nickel foam.
3. The method for preparing the two-dimensional nano-sheet heterojunction electrocatalyst according to claim 1 or 2, comprising the steps of:
step 1, cobalt salt, ferric salt, urea and NH 4 F, after being dissolved in deionized water, carrying out a high-temperature hydrothermal reaction with the pretreated carrier in a reaction kettle, and after the reaction is finished, preparing an intermediate of the CoFe-LDH nanosheet loaded on the carrier;
and step 2, respectively taking an intermediate, a platinum wire and saturated calomel as a working electrode, a counter electrode and a reference electrode, and taking a solution containing Ni and Co as electrolyte to carry out electrodeposition so as to prepare the two-dimensional nano-sheet heterojunction electrocatalyst CoFe-LDH/NiCo-LDH/NF.
4. A method according to claim 3, wherein the cobalt salt is Co (NO 3 ) 2 ·6H 2 O, the ferric salt is Fe (NO) 3 ) 3 ·9H 2 O；
Cobalt salt, ferric salt, urea and NH in the step 1 4 The molar ratio of F is 0.5:0.5:10:4 to 1:0.5:14:4.
5. The method according to claim 3, wherein the conditions for the hydrothermal reaction in step 1 are: preserving heat for 4-8 hours at 100-140 ℃.
6. The method according to claim 3, wherein the electrolyte comprises Ni (NO 3 ) 2 ·6H 2 O and Co (NO) 3 ) 2 ·6H 2 O, ni (NO) 3 ) 2 ·6H 2 O and Co (NO) 3 ) 2 ·6H 2 The molar concentration of O is 0.01-0.03 mmol/mL.
7. A method according to claim 3, wherein the conditions for electrodeposition in step 2 are: and (5) performing electrodeposition for 50-400 s under the voltage of-1V.
8. Use of the two-dimensional nano-sheet heterojunction electrocatalyst of claim 1 or 2 for catalytic degradation of urea, urea-containing wastewater, and electrocatalytically degrading urea-assisted hydrogen production.
CN202311457341.7A 2023-11-03 2023-11-03 Two-dimensional nano-sheet heterojunction electrocatalyst and preparation method and application thereof Pending CN117446920A (en)

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