CN109926083B - Bimetallic Fe-Co nitride electrocatalyst and preparation method and application thereof - Google Patents
Bimetallic Fe-Co nitride electrocatalyst and preparation method and application thereof Download PDFInfo
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/36—Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
Abstract
The invention discloses a bimetallic Fe-Co nitride electrocatalyst and a preparation method and application thereof, wherein the preparation method comprises the following steps: firstly, precursor solution A containing soluble Fe salt and Co salt and excessive NaBH4The reducing solution B is slowly mixed and stirred in inert gas for reaction; and then purifying and drying the catalyst, and carrying out heating and nitriding treatment in ammonia gas to obtain the bimetallic Fe-Co nitride electrocatalyst. The preparation method has the advantages of simplicity, safety, easy regulation and control of metal proportion, no adverse impurity influence and the like, the element percentage of N in the prepared Fe-Co nitride electrocatalyst is 5.46-10.01%, the bimetallic Fe-Co nitride electrocatalyst is applied to the catalysis of oxygen precipitation reaction, the activity of the catalysis of the oxygen precipitation reaction is good and exceeds that of IrO2The standard catalyst obviously improves the catalytic performance of the oxygen precipitation reaction relative to single metal, and the stability is obviously improved.
Description
Technical Field
The invention relates to the technical field of electrocatalysis, in particular to a bimetallic Fe-Co nitride electrocatalyst and a preparation method and application thereof.
Background
Human development brings with it increasingly more environmental problems and energy crisis, and the exploration and development of sustainable clean energy is undoubtedly one of the major problems we face in the twenty-first century. In the storage and conversion of renewable energy, the oxygen evolution reaction is one of the keys of the water-oxygen conversion process. Because four electron transfers are involved, the kinetic process of the oxygen evolution reaction is slow, and the conversion efficiency of related energy devices is greatly restricted. The oxygen evolution catalyst with high efficiency, stability and low cost can effectively reduce the overpotential of the oxygen evolution reaction, and is a breakthrough for improving the storage and conversion efficiency of renewable energy.
Transition metal nitrides are known as "quasi-platinum catalysts" due to their unique electronic structure and excellent electrocatalytic properties. On one hand, the transition metal nitride expands the crystal lattice due to the introduction of nitrogen atoms, the metal atom spacing and the crystal lattice constant are increased, the interaction between metal atoms is weakened, and meanwhile, the formation of a metal-nitrogen bond causes the contraction of a d band and the rearrangement of state density near a Fermi level, so that the metal nitride has an electronic structure similar to noble metal platinum, and has good electrocatalytic performance; on the other hand, as the radius of the nitrogen atoms is smaller, the nitrogen atoms are embedded in the metal gaps, so that the structure of the metal atoms is rearranged to keep a close-packed or near-close-packed structure, and the metal nitride has good electronic conductivity; meanwhile, the transition metal nitride has excellent physical and chemical properties such as high melting point, high hardness, high conductivity, high temperature chemical stability, high corrosion resistance and the like, so that the transition metal nitride has higher intrinsic catalytic activity and wider electrocatalysis application prospect compared with metal or alloy.
Bimetallic nitrides have been found to exhibit superior electrocatalytic properties compared to monometallic nitrides. Chen et al obtain carbon material loaded bimetallic nitride nanosheet NiMoN by nitriding ammonia gas at high temperature of 700 DEG CxThe catalytic performance of the catalyst/C is obviously superior to that of MoNx(Angewandte Chemie International Edition,2012,51: 6131-. Cao et al prepared a lamellar Co composed of octahedrons and dihedral prisms by a two-step solid phase reaction0.6Mo1.4N2The result of the electrocatalytic hydrogen evolution test shows that Co0.6Mo1.4N2Has higher electrocatalytic hydrogen evolution performance than MoN in both acidic and alkaline environments (Journal of the American Chemical Society,2013,135: 19186-. The Chinese invention patent 201810405656.X discloses a composite cobalt-vanadium nitride nanowire electrocatalyst, which is prepared by taking cobalt, vanadium metal salt and urea as raw materials, water as a solvent and carbon cloth as a substrate, performing hydrothermal reaction to obtain a precursor, placing the precursor in a glucose solution with a certain concentration, and finally calcining in an ammonia atmosphere. Chinese patent 201810361941.6 publicationFirstly, synthesizing a cobalt-phosphorus-molybdenum polyacid ion crystal compound, then doping electrostatic spinning with polyacrylonitrile, and synthesizing the nitrogen-cobalt-molybdenum-containing carbon nanofiber by roasting, wherein the carbon nanofiber has good electrocatalytic hydrogen evolution reaction activity under both acid and alkaline conditions. At present, metal nitrides are widely used as a high-efficiency hydrogen evolution reaction catalyst, but the research on the metal nitrides as an oxygen evolution reaction catalyst is less.
Disclosure of Invention
The invention aims to provide a bimetallic Fe-Co nitride electrocatalyst and a preparation method and application thereof, wherein NaBH is adopted in the method4The method for preparing the bimetallic Fe-Co nitride by combining direct liquid-phase reduction with an ammonia nitriding treatment method is simple, does not need to additionally add a surfactant, has high product purity, is suitable for large-scale production, and shows excellent oxygen evolution catalytic activity and stability in an alkaline medium.
In order to achieve the above object, the present invention provides a bimetallic Fe-Co nitride electrocatalyst, wherein the elemental percentage of N in the bimetallic Fe-Co nitride electrocatalyst is 5.46 to 10.01%, and the bimetallic Fe-Co nitride electrocatalyst has Co according to XRD characterization5.47N、Co7Fe3And Fe4Characteristic peak of N.
As a preferred embodiment, when the bimetallic Fe-Co nitride electrocatalyst has an elemental molar ratio of n (Fe) to n (Co) of 1:4, the TEM is characterized by a cotton-like morphology.
The invention also provides a preparation method of the bimetallic Fe-Co nitride electrocatalyst, which is characterized by comprising the following steps:
1) preparing a reaction solution: weighing soluble Fe salt and soluble Co salt, dissolving in water to prepare metal precursor solution A, and weighing NaBH4Dissolving in water to prepare a reducing solution B;
2) liquid-phase reaction: dropwise adding the reducing solution B into the metal precursor solution A under the conditions of inert gas protection and stirring, continuously stirring and reacting for 0.5-2 h to obtain a black mixture, and then sequentially purifying and drying the black mixture to obtain solid powder;
3) nitriding treatment: the solid powder is placed in a tube furnace in NH3And carrying out nitriding treatment in the atmosphere, and cooling to obtain the bimetallic Fe-Co nitride electrocatalyst.
Preferably, in step 1), the soluble Co salt is selected from CoCl2.6H2O、Co(NO3).6H2O or Co (OAc)2.4H2One or more of O;
the soluble Fe salt is selected from FeCl3.6H2O、Fe(NO3)3.6H2O or Fe (SO)4)2.7H2One or more of O.
Preferably, the soluble Fe salt and the soluble Co salt are fed according to the element molar ratio of n (Fe) to n (Co) of 1: 6-2: 1.
Most preferably, the soluble Fe and Co salts are dosed in an elemental molar ratio of n (Fe) to n (Co) of 1: 4.
As a preferred embodiment, the NaBH4The molar amount of the reducing solution B is 4.2 to 5.6 times of the total molar amount of the elements n (Fe) and n (Co), and the molar concentration of the reducing solution B is 0.22 to 0.52 mol/L.
Preferably, the protective inert gas is Ar gas or N2Gas; the stirring reaction temperature is 20-35 ℃, and the stirring speed is 700-900 r/min.
Preferably, in the step 2), the purification treatment specifically includes firstly performing centrifugation treatment, and then washing with distilled water for 3-5 times; the drying treatment adopts a vacuum drying mode, the temperature of the vacuum drying is 60-80 ℃, and the time is 8-12 hours.
As a preferred embodiment, in the step 3), the nitriding treatment specifically includes: at NH3And heating to 400-750 ℃ at a heating rate of 5-8 ℃/min in the atmosphere, preserving the heat for 2-5 h, and naturally cooling to obtain the bimetallic Fe-Co nitride electrocatalyst.
The invention also provides an application of the bimetallic Fe-Co nitride electrocatalyst, which is characterized in that the bimetallic Fe-Co nitride electrocatalyst is used for oxygen precipitation reaction, and the method for the oxygen precipitation reaction comprises the following steps: the method comprises the steps of ultrasonically dispersing a bimetallic Fe-Co nitride electrocatalyst into a mixed solution of isopropanol and a perfluorinated resin solution (Nafion) according to a volume ratio of 100-150: 1 to form catalyst ink, uniformly coating the catalyst ink on the surface of a glassy carbon electrode, drying at room temperature to form a catalyst layer film, taking the glassy carbon electrode coated with the catalyst film as a working electrode, and finally placing the working electrode in an alkaline solution, taking a Pt sheet as a counter electrode and taking Hg/HgO as a reference electrode.
Compared with the prior art, the invention has the following advantages:
first, the invention uses NaBH4The method for preparing the bimetallic Fe-Co nitride by combining direct liquid-phase reduction with an ammonia nitriding treatment method is simple, a surfactant is not required to be additionally added, the metal proportion is easy to regulate and control, the obtained product has high purity, harmful gas is not generated in the preparation process, the environmental pollution is small, and the safety coefficient is high.
Second, NaBH of the invention4Part of NaBH in liquid phase reduction method4The metaboric acid, alkali and hydrogen are generated through hydrolysis, wherein the metaboric acid has a certain protection effect on the formation of nano particles, and a part of metaboric acid directly participates in the reduction of metal ions to generate active metal or low-valence oxide particles thereof, so that the process operation is rapid and convenient, and can be carried out at normal temperature. Because the metal particles or the low-valence oxides generated by reduction are easier to form metal nitride through ammonia nitridation compared with metal salts or stable oxides, the high-temperature operation of ammonia nitridation at the later stage is avoided, and the process is safer.
Thirdly, the bimetallic Fe-Co nitride electrocatalyst generates metal nitride by ammonia nitridation treatment, and the catalyst keeps a nano structure, so that the bimetallic Fe-Co nitride electrocatalyst has higher N content and specific surface area; due to the electronic regulation of the second transition metal, the mono-metal nitrides such as CoN are significantly improvedxOr FeNxThe catalytic oxygen precipitation reaction performance and the stability are obviously improved.
Drawings
FIG. 1 (a) shows Fe-Co (1:3) N prepared in example 2xXRD spectrum of electrocatalyst; (b) Fe-Co (1:5) N prepared for example 3xXRD spectrum of electrocatalyst; (c) Fe-Co (1:4) N prepared for example 7xXRD spectrum of electrocatalyst; (d) monometallic CoN prepared for comparative example 1xXRD spectrum of electrocatalyst;
FIG. 2 shows Fe-Co (1:4) N prepared in example 7xTEM images of the electrocatalyst at 200nm (a) and 50nm scale (b), respectively;
FIG. 3(a) shows different ratios of bimetallic Fe-CoN prepared in examples 1, 2, 3, 4, 5, 6 and 7xAnd IrO2OER polarization curves of the catalysts are compared; (b) nitriding Fe-Co (1:4) N at different temperatures for the samples obtained in examples 7, 8 and 9xAnd IrO2OER polarization curves of the catalysts are compared; (c) the best bimetallic nitride catalyst made in example 7, Fe-Co (1:4) NxSingle metal CoN prepared in comparative example 1xAnd IrO2OER polarization curves of the catalysts are compared;
FIG. 4(a) shows the best catalyst made in example 7, Fe-Co (1:4) NxAnd the single metal CoN prepared in comparative examplexComparing polarization curves of the electrocatalyst before and after 1000 cycles of cyclic voltammetry scanning; (b) the best catalyst for the preparation of example 7 is Fe-Co (1:4) NxAnd the single metal CoN prepared in comparative examplexI-t curves of the electrocatalysts are compared.
Detailed Description
The invention is described in further detail below with reference to the figures and the specific embodiments.
Example 1: Fe-Co (2:1) NxPreparation of electrocatalysts
Weighing 1.65mmol Co (NO)3)2.6H2O、3.31mmol Fe(NO3)3.9H2Dissolving O in 20ml of deionized water to prepare a metal precursor solution A; 26mmol excess NaBH was weighed4Dissolving in 150ml deionized water to prepare a reducing solution B (the molar concentration is 0.17 mol/L); under the conditions of room temperature, magnetic stirring at 900 revolutions per minute and Ar gas protection, dropwise adding the solution B into the metal precursor solution A, and continuously stirring for reaction for 2 hours to obtain blackMixing; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 60 deg.C for 12 hr to obtain solid powder; putting the solid powder into a tube furnace NH3Heating to 500 deg.C at a heating rate of 8 deg.C/min under atmosphere, maintaining for 2h, and cooling to obtain bimetallic Fe-Co nitride electrocatalyst, denoted as Fe-Co (2:1) NxAn electrocatalyst.
For the bimetallic Fe-Co (2:1) N prepared in example 1xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (2:1) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the glassy carbon electrode with the surface coated with the catalyst film to be tested is taken as a working electrode (the coating amount of the catalyst is 255 mug/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, the reference electrode is placed in a salt bridge, the tip of a lujin capillary tube at one end of the salt bridge is close to a working electrode, and the catalytic activity of the catalyst on oxygen precipitation reaction is tested in oxygen-saturated electrolyte at the scanning speed of 10mV/s and the electrode rotating speed of 1600 rpm. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Example 2: Fe-Co (1:3) NxPreparation of electrocatalysts
Weigh 4.59mmol of Co (NO)3)2.6H2O、1.53mmol Fe(NO3)3.9H2Dissolving O in 30ml of deionized water to prepare a metal precursor solution A; then 26mmol of excess NaBH was weighed4Dissolving in 100ml deionized water to prepare a reducing solution B (the molar concentration is 0.26 mol/L); dropwise adding the solution B into the metal precursor solution A at room temperature under the conditions of 700 revolutions per minute of magnetic stirring and Ar gas protection, and continuously stirring and reacting for 1h to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 60 deg.C for 12 hr to obtain solid powder; putting the solid powder into a tube furnace NH3Heating to 500 ℃ at a heating rate of 5 ℃/min under the atmosphereKeeping the temperature for 2h, and cooling to obtain the bimetallic Fe-Co nitride electrocatalyst which is marked as Fe-Co (1:3) NxAn electrocatalyst.
For the Fe-Co (1:3) N prepared in this examplexXRD characterization was performed and the results are shown in FIG. 1 a. As can be seen from the figure, Fe-Co (1:3) N prepared in this examplexMain characteristic peak of electrocatalyst and Co5.47N(PDF No.41-0943)、Fe4N (PDF No.06-0627) and Co7Fe3The characteristic peaks of (PDF No.50-0795) correspond to each other, indicating that they are a mixed phase of the above three substances (ACS Sustainable chem. Eng.,2018,6, 11457-11465; Electrochimica Acta,2017,258, 51-60).
For the bimetallic Fe-Co (1:3) N prepared in example 2xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (1:3) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the glassy carbon electrode with the surface coated with the catalyst film to be tested is taken as a working electrode (the coating amount of the catalyst is 255 mug/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, the reference electrode is placed in a salt bridge, the tip of a lujin capillary tube at one end of the salt bridge is close to a working electrode, and the catalytic activity of the catalyst on oxygen precipitation reaction is tested in oxygen-saturated electrolyte at the scanning speed of 10mV/s and the electrode rotating speed of 1600 rpm. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Example 3: Fe-Co (1:5) NxPreparation of the catalyst
Weigh 4.59mmol of Co (NO)3)2.6H2O、0.92mmol Fe(NO3)3.9H2Dissolving O in 40ml of deionized water to prepare a metal precursor solution A; then 26mmol of excess NaBH was weighed4Dissolving in 50ml deionized water to obtain reducing solution B (with a molar concentration of 0.52 mol/L); magnetic stirring at 900 rpm and N at room temperature2Gas protectionUnder the condition, dropwise adding the solution B into the metal precursor solution A, and continuously stirring for reaction for 0.5h to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 80 deg.C for 8 hr to obtain solid powder; putting the solid powder into a tube furnace NH3Heating to 500 deg.C at a heating rate of 5 deg.C/min under atmosphere, maintaining for 2h, and cooling to obtain bimetallic Fe-Co nitride electrocatalyst, denoted as Fe-Co (1:5) NxAn electrocatalyst.
For the Fe-Co (1:5) N prepared in this examplexXRD characterization was performed and the results are shown in FIG. 1 b. As can be seen from the figure, Fe-Co (1:5) N prepared in this examplexMain characteristic peak of electrocatalyst and Co5.47N(PDF No.41-0943)、Fe4N (PDF No.06-0627) and Co7Fe3The characteristic peaks of (PDF No.50-0795) correspond to each other, indicating that they are a mixed phase of the above three substances (ACS Sustainable chem. Eng.,2018,6, 11457-11465; Electrochimica Acta,2017,258, 51-60). For the Fe-Co (1:5) N prepared in this examplexEDX compositional analysis was performed with the elemental percentages of N, Fe, Co being 9.98%, 15.53% and 74.49%, respectively.
For the bimetallic Fe-Co (1:5) N prepared in example 3xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (1:5) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the glassy carbon electrode with the surface coated with the catalyst film to be tested is taken as a working electrode (the coating amount of the catalyst is 255 mug/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, the reference electrode is placed in a salt bridge, the tip of a lujin capillary tube at one end of the salt bridge is close to a working electrode, and the catalytic activity of the catalyst on oxygen precipitation reaction is tested in oxygen-saturated electrolyte at the scanning speed of 10mV/s and the electrode rotating speed of 1600 rpm. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Practice ofExample 4: Fe-Co (1:6) NxPreparation of the electrocatalyst:
weigh 4.59moml of Co (NO)3)2.6H2O、0.76mmol Fe(NO3)3.9H2Dissolving O in 40ml of deionized water to prepare a metal precursor solution A; 26mmol excess NaBH was weighed4Dissolving in 120ml deionized water to prepare a reducing solution B (the molar concentration is 0.22 mol/L); magnetic stirring at room temperature at 700 rpm and N2Under the condition of gas protection, dropwise adding the solution B into the metal precursor solution A, and continuously stirring for reaction for 2 hours to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 60 deg.C for 12 hr to obtain solid powder; putting the solid powder into a tube furnace NH3Heating to 500 deg.C at a heating rate of 8 deg.C/min under atmosphere, maintaining for 2h, and cooling to obtain bimetallic Fe-Co nitride electrocatalyst, denoted as Fe-Co (1:6) NxAn electrocatalyst.
For the Fe-Co (1:6) N prepared in this examplexEDX compositional analysis was performed with the elemental percentages of N, Fe, Co being 10.01%, 12.90% and 77.09%, respectively.
For the bimetallic Fe-Co (1:6) N prepared in example 4xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (1:6) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the glassy carbon electrode with the surface coated with the catalyst film to be tested is taken as a working electrode (the coating amount of the catalyst is 255 mug/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, the reference electrode is placed in a salt bridge, the tip of a lujin capillary tube at one end of the salt bridge is close to a working electrode, and the catalytic activity of the catalyst on oxygen precipitation reaction is tested in oxygen-saturated electrolyte at the scanning speed of 10mV/s and the electrode rotating speed of 1600 rpm. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Examples5: preparation of Fe-Co (1:1.4) N from nitrate precursorxElectro-catalyst
Weigh 4.59mmol of Co (NO)3)2.6H2O、3.30mmol Fe(NO3)3.9H2Dissolving O in 40ml of deionized water to prepare a metal precursor solution A; weighing 40mmol of excessive NaBH4Dissolving in 150ml deionized water to prepare a reducing solution B (the molar concentration is 0.27 mol/L); dropwise adding the solution B into the metal precursor solution A at room temperature under the conditions of 700 revolutions per minute of magnetic stirring and Ar gas protection, and continuously stirring for reaction for 2 hours to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 60 deg.C for 12 hr to obtain solid powder; putting the solid powder into a tube furnace NH3Heating to 500 deg.C at a heating rate of 8 deg.C/min under atmosphere, maintaining for 2h, and cooling to obtain bimetallic Fe-Co nitride electrocatalyst, denoted as Fe-Co (1:1.4) NxAn electrocatalyst.
For the Fe-Co (1:1.4) N prepared in this examplexEDX compositional analysis was performed with elemental percentages of N, Fe, and Co of 5.46%, 40.24%, and 54.30%, respectively.
For the bimetallic Fe-Co (1:1.4) N prepared in example 5xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (1:1.4) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the glassy carbon electrode with the surface coated with the catalyst film to be tested is taken as a working electrode (the coating amount of the catalyst is 255 mug/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, the reference electrode is placed in a salt bridge, the tip of a lujin capillary tube at one end of the salt bridge is close to a working electrode, and the catalytic activity of the catalyst on oxygen precipitation reaction is tested in oxygen-saturated electrolyte at the scanning speed of 10mV/s and the electrode rotating speed of 1600 rpm. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Example 6: preparation of Fe-Co (1:1.4) N from acetate precursorxElectro-catalyst
Reference was made to the preparation of the catalyst of example 1, except that 6.83mmol of Co (CH) was weighed3COO)2.4H2O、4.88mmol Fe(CH3COO)2.4H2Dissolving O in 40ml of deionized water to prepare a metal precursor solution A; weighing 66mmol of excessive NaBH4Dissolving in 150ml deionized water to prepare a reducing solution B (the molar concentration is 0.44 mol/L); dropwise adding the solution B into the metal precursor solution A at room temperature under the conditions of magnetic stirring at 900 revolutions per minute and Ar gas protection, and continuously stirring for reaction for 2 hours to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 60 deg.C for 12 hr to obtain solid powder; putting the solid powder into a tube furnace NH3Heating to 500 deg.C at a heating rate of 8 deg.C/min under atmosphere, maintaining for 2h, and cooling to obtain bimetallic Fe-Co nitride electrocatalyst, denoted as Fe-Co (1:1.4) NxAn electrocatalyst.
For the bimetallic Fe-Co (1:1.4) N prepared in example 6xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (1:1.4) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the glassy carbon electrode with the surface coated with the catalyst film to be tested is taken as a working electrode (the coating amount of the catalyst is 255 mug/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, the reference electrode is placed in a salt bridge, the tip of a lujin capillary tube at one end of the salt bridge is close to a working electrode, and the catalytic activity of the catalyst on oxygen precipitation reaction is tested in oxygen-saturated electrolyte at the scanning speed of 10mV/s and the electrode rotating speed of 1600 rpm. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Example 7: preparation of Fe-Co (1:4) N by ammonia treatment at 500 DEG CxElectro-catalyst
Reference was made to the preparation of the catalyst of example 1, except that 4.59mmol of Co (NO) was weighed3)2.6H2O、1.15mmol Fe(NO3)3.9H2Dissolving O in 40ml of deionized water to prepare a metal precursor solution A; then 26mmol of excess NaBH was weighed4Dissolving in 120ml deionized water to prepare a reducing solution B (the molar concentration is 0.22 mol/L); dropwise adding the solution B into the metal precursor solution A at room temperature under the conditions of 700 revolutions per minute of magnetic stirring and Ar gas protection, and continuously stirring and reacting for 1h to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 80 deg.C for 8 hr to obtain solid powder; putting the solid powder into a tube furnace NH3Heating to 500 deg.C at a heating rate of 8 deg.C/min under atmosphere, maintaining for 2h, and cooling to obtain bimetallic Fe-Co nitride electrocatalyst, denoted as Fe-Co (1:4) NxAn electrocatalyst.
For the Fe-Co (1:4) N prepared in this examplexXRD characterization was performed and the results are shown in FIG. 1 c. As can be seen from the figure, Fe-Co (1:4) N prepared in this examplexMain characteristic peak of electrocatalyst and Co5.47N(PDF No.41-0943)、Fe4N (PDF No.06-0627) and Co7Fe3The characteristic peaks of (PDF No.50-0795) correspond to each other, indicating that they are a mixed phase of the above three substances (ACS Sustainable chem. Eng.,2018,6, 11457-11465; Electrochimica Acta,2017,258, 51-60). TEM observation of Fe-Co (1:4) N prepared in this examplexThe results are shown in fig. 2, and the sample shows a cotton ball shape. For the Fe-Co (1:4) N prepared in this examplexEDX compositional analysis was performed, with the elemental percentages of N, Fe, and Co being 9.71%, 17.89%, and 72.39%, respectively.
For the bimetallic Fe-Co (1:4) N prepared in example 7xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (1:4) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the catalyst layer film is respectively coated on the surfacesThe glassy carbon electrode coated with the catalyst film to be measured is used as a working electrode (the catalyst coating amount is 255 mug/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, the reference electrode is placed in a salt bridge, the tip of a lujin capillary tube at one end of the salt bridge is close to a working electrode, and the catalytic activity of the catalyst on oxygen precipitation reaction is tested in oxygen-saturated electrolyte at the scanning speed of 10mV/s and the electrode rotating speed of 1600 rpm. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Example 8: preparation of Fe-Co (1:4) N by ammonia treatment at 400 DEG CxElectro-catalyst
Reference was made to the preparation of the catalyst of example 1, except that 4.59mmol of Co (NO) was weighed3)2.6H2O、1.15mmol Fe(NO3)3.9H2Dissolving O in 40ml of deionized water to prepare a metal precursor solution A; then 26mmol of excess NaBH was weighed4Dissolving in 120ml deionized water to prepare a reducing solution B (the molar concentration is 0.22 mol/L); dropwise adding the solution B into the metal precursor solution A at room temperature under the conditions of 700 revolutions per minute of magnetic stirring and Ar gas protection, and continuously stirring and reacting for 1h to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 80 deg.C for 8 hr to obtain solid powder; putting the solid powder into a tube furnace NH3Heating to 400 ℃ at a heating rate of 8 ℃/min under the atmosphere, preserving heat for 2h, and cooling to obtain the bimetallic Fe-Co nitride electrocatalyst, which is marked as Fe-Co (1:4) NxAn electrocatalyst.
For the bimetallic Fe-Co (1:4) N prepared in example 8xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (1:4) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the glassy carbon electrode with the surface coated with the catalyst film to be tested is taken as a working electrode (the coating amount of the catalyst is 255 mug/cm)2) The platinum sheet is a counter electrode and HgO is greater than or equal toTaking an Hg electrode as a reference electrode, taking 0.1mol/L potassium hydroxide solution as electrolyte, placing the reference electrode in a salt bridge, enabling the tip of a Rujin capillary at one end of the salt bridge to be close to a working electrode, and testing the catalytic activity of the catalyst on oxygen precipitation reaction at the scanning speed of 10mV/s and the electrode rotating speed of 1600rpm in oxygen-saturated electrolyte. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Example 9: preparation of Fe-Co (1:4) N by ammonia gas treatment at 750 DEG CxElectro-catalyst
Reference was made to the preparation and testing of the catalyst of example 1, except that 4.59mmol Co (NO) was weighed3)2.6H2O、1.15mmol Fe(NO3)3.9H2Dissolving O in 40ml of deionized water to prepare a metal precursor solution A; then 26mmol of excess NaBH was weighed4Dissolving in 120ml deionized water to prepare a reducing solution B (the molar concentration is 0.22 mol/L); dropwise adding the solution B into the metal precursor solution A at room temperature under the conditions of 700 revolutions per minute of magnetic stirring and Ar gas protection, and continuously stirring and reacting for 1h to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 80 deg.C for 8 hr to obtain solid powder; adding solid powder into NH3Heating to 750 deg.C at a heating rate of 8 deg.C/min under atmosphere, calcining for 2 hr, and cooling to obtain bimetallic Fe-Co nitride electrocatalyst (Fe-Co (1:4) N)xA catalyst.
For the bimetallic Fe-Co (1:4) N prepared in example 9xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg of Fe-Co (1:4) NxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the glassy carbon electrode with the surface coated with the catalyst film to be tested is taken as a working electrode (the coating amount of the catalyst is 255 mug/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, and the reference electrode is placed in a salt bridge to ensure that the salt bridge is formedThe tip of the luggin capillary at one end is close to the working electrode, and the catalytic activity of the catalyst on the oxygen evolution reaction is tested at the scanning speed of 10mV/s and the electrode rotating speed of 1600rpm in the oxygen saturated electrolyte. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Comparative example 1: single metal CoNxPreparation of the electrocatalyst:
weigh 4.59mmol of Co (NO)3)2.6H2Dissolving O in 30ml of deionized water to prepare a metal precursor solution A; then 26mmol of NaBH was weighed4Dissolving in 120ml deionized water to prepare a reducing solution B (the molar concentration is 0.22 mol/L); dropwise adding the solution B into the metal precursor solution A at room temperature under the conditions of 700 revolutions per minute of magnetic stirring and Ar gas protection, and continuously stirring and reacting for 1h to obtain a black mixture; centrifuging the obtained mixture, washing with deionized water, and vacuum drying at 60 deg.C for 12 hr to obtain solid powder; adding solid powder into NH3Heating to 500 ℃ at a heating rate of 8 ℃/min under the atmosphere, continuously calcining for 2h, and cooling to obtain the monometal CoNxAn electrocatalyst.
For the single metal CoN prepared in comparative example 1xThe electrocatalyst was XRD characterised and the results are shown in figure 1 d. As can be seen from the figure, the single-metal CoN obtained in comparative example 1xThe electrocatalyst being of Co5.47N (PDF No.41-0943) and Co2N (PDF No.65-1458) (ACS Sustainable chem. Eng.,2018,6, 11457-11465; Electrochimica Acta,2017,258, 51-60). For CoN prepared in comparative example 1xEDX compositional analysis was performed with elemental percentages of N and Co of 8.12% and 23.07%, respectively (the remainder being residual C in the sample and substrate).
For the monometallic CoN prepared in comparative example 1xThe catalytic performance of the electrocatalyst is tested by the following specific method:
5mg CoNxThe electrocatalyst is ultrasonically dispersed in 1mL of isopropanol and Nafion mixed solution (the volume ratio of the isopropanol to the Nafion is 100:1) to form catalyst ink with the concentration of 5mg/mL, the catalyst ink is uniformly coated on the surface of the glassy carbon electrode, a catalyst layer film is formed by drying at room temperature, and then the surfaces of the catalyst layer film are respectively coated with the catalyst inkThe glassy carbon electrode of the catalyst film to be measured is used as a working electrode (the coating amount of the catalyst is 255 mu g/cm)2) The platinum sheet is used as a counter electrode, the HgO/Hg electrode is used as a reference electrode, 0.1mol/L potassium hydroxide solution is used as electrolyte, the reference electrode is placed in a salt bridge, the tip of a lujin capillary tube at one end of the salt bridge is close to a working electrode, and the catalytic activity of the catalyst on oxygen precipitation reaction is tested in oxygen-saturated electrolyte at the scanning speed of 10mV/s and the electrode rotating speed of 1600 rpm. The test temperature is room temperature and is in contact with IrO2And (5) comparing the catalysts.
Effect example 1:
different proportions of bimetallic Fe-CoN prepared in examples 1, 2, 3, 4, 5, 6, 7, 8 and 9x、IrO2Catalyst and comparative example 1 an Oxygen Evolution (OER) performance test was performed. FIG. 3(a) shows different ratios of bimetallic Fe-CoN prepared in examples 1, 2, 3, 4, 5, 6 and 7xAnd IrO2OER polarization curves of the catalysts are compared; FIG. 3(b) is a graph showing different temperature nitriding treatments of Fe-Co (1:4) N obtained in examples 7, 8 and 9xAnd IrO2OER polarization curves of the catalysts are compared; FIG. 3(c) is a diagram of the best bimetallic nitride catalyst made in example 7, Fe-Co (1:4) NxSingle metal CoN prepared in comparative example 1xAnd IrO2OER polarization curves of the catalysts are compared;
as can be seen from FIG. 3(a), except for Fe-Co (2:1) N prepared in example 1xExcept that the activity of (2) is low, the current density is 10mA/cm2At an overpotential of the double metal nitride Fe-Co (1:4) N obtained in example 7xMinimum (420mV)<Fe-Co (1:6) N obtained in example 4x(432mV)<IrO2Catalyst (440mV)<Fe-Co (1:5) N obtained in example 3x(442 mV). apprxeq.Fe-Co (1:3) N obtained in example 2x(445mV)<Fe-Co (1:1.4) N obtained in examples 5 and 6x(462mV) for Fe-Co (1:4) NxCatalyst in same series bimetal Fe-CoNxThe activity of catalyzing oxygen precipitation reaction in the catalyst is optimal;
as shown in FIG. 3(b), example 7 was nitrided at 500 ℃ to produce Fe-Co (1:4) NxThe activity of the catalyst is slightly higher than that of example 8 (nitriding treatment at 400 ℃) and is obviously higher than that of example 9 (nitriding treatment at 750 ℃), in the prior artPrepared Fe-Co (1:4) NxCatalyst, which shows that the optimum temperature for the nitriding treatment is 500 ℃, and the activity of the catalyst obtained by the nitriding treatment at 400-500 ℃ is higher than that of IrO2。
As can be seen from FIG. 3(c), Fe-Co (1:4) N was prepared in example 7xThe activity of the catalyst is obviously higher than that of single-metal CoNx(overpotential 450mV) and noble metal IrO2Catalyst (overpotential 440 mV). The activity is improved mainly by the bigold Fe-Co (1:4) NxThe addition of Fe in the catalyst causes a catalytic synergistic effect.
Effect example 2:
the best catalyst made in example 7, Fe-Co (1:4) N, FIG. 4(a), was tested for i-t performance using example 7 and comparative example 1xAnd the single metal CoN prepared in the comparative examplexComparing polarization curves before and after the catalyst is subjected to 1000 cycles of cyclic voltammetry scanning; FIG. 4(b) shows the best catalyst made in example 7, Fe-Co (1:4) NxAnd the single metal CoN prepared in the comparative examplexI-t curves of the catalysts were compared.
From FIG. 4(a), which is a comparison of the polarization curves of the two catalysts after 1000 cycles of cyclic voltammetry scan and before 1000 cycles of scan, it was found that the activity of the two catalysts did not change much, wherein Fe-Co (1:4) NxThe activity of the catalyst is slightly increased compared with that before the stability test, and is probably caused by partial oxidation of the bimetallic alloy in the catalyst under an oxygen evolution environment; CoN of comparative examplexThe activity of the catalyst is slightly reduced, which shows that the introduction of the second metal Fe can improve the catalytic stability.
FIG. 4(b) is a graph comparing the i-t curves at a potential of 1.58V for two catalysts, and it can be seen that Fe-Co (1:4) N prepared in example 7xThe current density after 4h can be maintained at 18.2% of the initial value, while the CoN prepared in the comparative examplexThe catalyst maintained 9.0% of the initial value, and it can be seen that the addition of the second metal significantly improved the stability of the metal nitride catalyst.
The above embodiments are merely illustrative of the technical solutions and features of the present invention, and the purpose thereof is to better enable those skilled in the art to practice the invention, and it is not intended to limit the scope of the invention, and all equivalent changes and modifications made according to the spirit of the present invention are within the scope of the present invention, wherein the prior art is not described in detail.
Claims (10)
1. The bimetallic Fe-Co nitride electrocatalyst is characterized in that the element percentage of N in the bimetallic Fe-Co nitride electrocatalyst is 5.46-10.01%, and the bimetallic Fe-Co nitride electrocatalyst has Co through XRD (X-ray diffraction) characterization5.47N、Co7Fe3And Fe4A characteristic peak of N;
the bimetallic Fe-Co nitride electrocatalyst is prepared by the following method:
1) preparing a reaction solution: weighing soluble Fe salt and soluble Co salt, dissolving in water to prepare metal precursor solution A, and weighing NaBH4Dissolving in water to prepare a reducing solution B;
2) liquid-phase reaction: dropwise adding the reducing solution B into the metal precursor solution A under the conditions of inert gas protection and stirring, continuously stirring and reacting for 0.5-2 h to obtain a black mixture, and then sequentially purifying and drying the black mixture to obtain solid powder;
3) nitriding treatment: the solid powder is placed in a tube furnace in NH3And carrying out nitriding treatment in the atmosphere, and cooling to obtain the bimetallic Fe-Co nitride electrocatalyst.
2. The bimetallic Fe-Co nitride electrocatalyst according to claim 1, characterized by TEM as characterized by cotton-like morphology when the molar ratio of elements n (Fe) to n (Co) of the bimetallic Fe-Co nitride electrocatalyst is 1: 4.
3. A method for preparing the bimetallic Fe-Co nitride electrocatalyst according to claim 1 or 2, characterized by comprising the steps of:
1) preparing a reaction solution: weighing soluble Fe salt and soluble Co salt, dissolving in water to prepare metal precursor solution A, and weighing NaBH4Dissolving in water to prepare a reducing solution B;
2) liquid-phase reaction: dropwise adding the reducing solution B into the metal precursor solution A under the conditions of inert gas protection and stirring, continuously stirring and reacting for 0.5-2 h to obtain a black mixture, and then sequentially purifying and drying the black mixture to obtain solid powder;
3) nitriding treatment: the solid powder is placed in a tube furnace in NH3And carrying out nitriding treatment in the atmosphere, and cooling to obtain the bimetallic Fe-Co nitride electrocatalyst.
4. The method of preparing a bimetallic Fe-Co nitride electrocatalyst according to claim 3, characterized in that in step 1) the soluble Co salt is selected from CoCl2.6H2O、Co(NO3).6H2O or Co (OAc)2.4H2One or more of O;
the soluble Fe salt is selected from FeCl3.6H2O、Fe(NO3)3.6H2O or Fe (SO)4)2.7H2One or more of O.
5. The method for preparing a bimetallic Fe-Co nitride electrocatalyst according to claim 3, wherein in step 1), soluble Fe salt and soluble Co salt are fed according to the element molar ratio of n (Fe) to n (Co) of 1: 6-2: 1.
6. The method for preparing a bimetallic Fe-Co nitride electrocatalyst according to claim 3, characterized in that in step 1), NaBH is used4The molar amount of the reducing solution B is 4.2 to 5.6 times of the total molar amount of the elements n (Fe) and n (Co), and the molar concentration of the reducing solution B is 0.22 to 0.52 mol/L.
7. The method for preparing a bimetallic Fe-Co nitride electrocatalyst according to claim 3, wherein in the step 2), the protective inert gas is Ar gas or N2Gas; the stirring reaction temperature is 20-35 ℃, and the stirring speed is 700-900 r/min.
8. The method for preparing the bimetallic Fe-Co nitride electrocatalyst according to claim 3, wherein in the step 2), the purification treatment is centrifugal treatment and then distilled water washing for 3-5 times; the drying treatment adopts a vacuum drying mode, the temperature of the vacuum drying is 60-80 ℃, and the time is 8-12 hours.
9. The method for preparing a bimetallic Fe-Co nitride electrocatalyst according to claim 3, wherein in the step 3), the nitriding treatment is specifically: at NH3And heating to 400-750 ℃ at a heating rate of 5-8 ℃/min in the atmosphere, preserving the heat for 2-5 h, and naturally cooling to obtain the bimetallic Fe-Co nitride electrocatalyst.
10. Use of a bimetallic Fe-Co nitride electrocatalyst according to claim 1 or 2, characterised in that it is used for oxygen evolution reactions, the method for oxygen evolution reaction comprising the steps of: the method comprises the steps of ultrasonically dispersing a bimetallic Fe-Co nitride electrocatalyst into a mixed solution of isopropanol and Nafion according to a volume ratio of 100-150: 1 to form catalyst ink, uniformly coating the catalyst ink on the surface of a glassy carbon electrode, drying at room temperature to form a catalyst layer film, taking the glassy carbon electrode coated with the catalyst film as a working electrode, and finally placing the working electrode in an alkaline solution, taking a Pt sheet as a counter electrode and taking Hg/HgO as a reference electrode.
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