CN115074756B - Bimetal doped porous carbon nanofiber catalyst and preparation method and application thereof - Google Patents
Bimetal doped porous carbon nanofiber catalyst and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a bimetal doped porous carbon nanofiber catalyst and a preparation method and application thereof, wherein the method comprises the following steps: sequentially mixing polyacrylonitrile, N-N dimethylformamide, znO, cobalt nitrate hexahydrate and lithium carbonate, and fully stirring to obtain a spinning precursor solution; carrying out electrostatic spinning on the spinning precursor solution to obtain a cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane; performing pre-oxidation treatment on the nanofiber membrane in an air atmosphere to obtain a pre-oxidized nanofiber membrane; and (3) placing the pre-oxidized nanofiber membrane in an inert atmosphere for carbonization treatment, and cooling to room temperature to obtain the bimetal doped porous carbon nanofiber catalyst. The preparation method provided by the invention is simple, the cost of raw materials is low, the reaction condition is mild, the large-scale production is convenient, the catalyst has excellent performance on electrochemical reduction of nitrate, the ammonia generation rate is higher than that of an industrial method, and the catalyst has guiding significance on industrial use of electrochemical reduction of nitrate.
Description
Technical Field
The invention relates to the field of electrochemical bimetal doped porous carbon nanofiber catalyst preparation, in particular to a bimetal doped porous carbon nanofiber catalyst and a preparation method and application thereof.
Background
Ammonia (NH) 3 ) Is the most basic chemical raw material, is not only an indispensable chemical for preparing fertilizers, medicines, dyes and the like, but also is considered as an important energy storage medium and a carbon-free energy carrier. Currently, NH is industrially synthesized 3 The Haber-Bosch (Haber-Bosch) process is still used, which is required to be carried out under severe operating conditions, i.e., at high temperatures (400-500 ℃), high pressures (200-350 atm) and heterogeneous iron-based catalysts. NH synthesis due to its large annual output and energy loss processes 3 Industry accounts for 1-2% of the total energy consumption worldwide, and carbon dioxide (CO) is discharged 2 ) The amount is about 2% of the total greenhouse gases. In recent years, electrocatalytic nitrogen (N 2 ) Reduction Reactions (NRR) have attracted attention in the ammonia synthesis industry, but are limited in industrial applications due to their high energy consumption, low reaction rates, selectivity and faraday efficiency. Electrochemical reduction of Nitrate (NO) 3 - ) Is NH 3 Compared with the Haber-Bosch process and the NRR, the method is more energy-saving, has wide nitrate sources in nature, and has great significance in solving two major problems of energy and environment by converting nitrate into ammonia through electrocatalytic reaction.
In recent years, due to high preparation cost of noble metal catalysts, reports of replacing noble metal catalysts with non-noble metal catalysts are increasing, but due to generally lower current density of the non-noble metal catalysts and poorer selectivity of ammonia, competing hydrogen evolution reactions exist, and raw material cost of some non-noble metal catalysts is higher, the preparation process is complex, and large-scale production and application to industry are difficult to realize.
Accordingly, the prior art is still in need of improvement and development.
Disclosure of Invention
In view of the shortcomings of the prior art, the invention aims to provide a bimetal doped porous carbon nanofiber catalyst and a preparation method and application thereof, and aims to solve the problems that the current density of a non-noble metal catalyst in the existing electrochemical reduction nitrate catalyst is low, the selectivity of ammonia is poor, and hydrogen evolution reaction competes and large-scale preparation cannot be performed.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a method for preparing a bimetal doped porous carbon nanofiber catalyst, which comprises the following steps:
sequentially mixing polyacrylonitrile, N-N dimethylformamide, znO, cobalt nitrate hexahydrate and lithium carbonate, and fully stirring to obtain a spinning precursor solution;
carrying out electrostatic spinning on the spinning precursor solution to obtain a cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane;
performing pre-oxidation treatment on the cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane in an air atmosphere to obtain a pre-oxidized nanofiber membrane;
and (3) placing the pre-oxidized nanofiber membrane in an inert atmosphere for carbonization treatment, and cooling to room temperature to obtain the bimetal doped porous carbon nanofiber catalyst.
The preparation method of the bimetal doped porous carbon nanofiber catalyst comprises the following steps of: and dissolving zinc acetate dihydrate in deionized water to obtain zinc acetate solution, dissolving triethanolamine in deionized water to obtain triethanolamine solution, dripping the zinc acetate solution into the triethanolamine solution, fully stirring, and performing ultrasonic treatment, standing, centrifugation, washing and drying to obtain ZnO.
The preparation method of the bimetal doped porous carbon nanofiber catalyst comprises the steps of preparing ZnO, wherein the stirring speed is 400-600rpm, the stirring time is 5-10min, the temperature is 20-50 ℃, the ultrasonic time is 10-50min, the standing time is 10-20h, the centrifugation speed is 8000-10000rpm, the drying temperature is 50-70 ℃, the activating temperature is 400-600 ℃ and the time is 1-3h.
The preparation method of the bimetal doped porous carbon nanofiber catalyst comprises the following steps of sequentially mixing polyacrylonitrile, N-N dimethylformamide, znO, cobalt nitrate hexahydrate and lithium carbonate:
N-N dimethylformamide, polyacrylonitrile, znO, cobalt nitrate hexahydrate, lithium carbonate at 95:8:8:0.3: the mass ratio of 0.3 was mixed in order.
In the preparation method of the bimetal doped porous carbon nanofiber catalyst, in the step of fully stirring to obtain a spinning precursor solution, the stirring speed is 400-600rpm, the stirring time is 12-15h, and the temperature is 20-60 ℃.
The preparation method of the bimetal doped porous carbon nanofiber catalyst comprises the following steps of: a metal needle with the inner diameter of 0.5-1.5mm is used as a spray head, the vertical distance from the spray head to a receiver is 10-30cm, the spinning voltage is 15-25KV, the feeding rate is 0.5-1mL/h, the spinning temperature is 30-50 ℃, and the air relative humidity is 10-90RH%.
The preparation method of the bimetal doped porous carbon nanofiber catalyst comprises the following steps of: heating to 200-250deg.C at a rate of 1-5deg.C/min, and maintaining for 1-2h.
The preparation method of the bimetal doped porous carbon nanofiber catalyst comprises the following steps of: heating to 700-1000deg.C at a rate of 1-10deg.C/min, and maintaining for 1-3h.
A bimetal doped porous carbon nanofiber catalyst prepared by the method for preparing the bimetal doped porous carbon nanofiber catalyst according to any one of the above schemes, wherein the method comprises the following steps: porous carbon nanofiber membranes and cobalt lithium nanoclusters supported on the carbon nanofiber membranes.
Use of a bimetallic doped porous carbon nanofiber catalyst according to the above scheme for electrochemical nitrate reduction.
Beneficial effectsThe effect is as follows: the invention discloses a bimetal doped porous carbon nanofiber catalyst and a preparation method and application thereof, wherein the method comprises the following steps: sequentially mixing polyacrylonitrile, N-N dimethylformamide, znO, cobalt nitrate hexahydrate and lithium carbonate, and fully stirring to obtain a spinning precursor solution; carrying out electrostatic spinning on the spinning precursor solution to obtain a cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane; performing pre-oxidation treatment on the cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane in an air atmosphere to obtain a pre-oxidized nanofiber membrane; and (3) placing the pre-oxidized nanofiber membrane in an inert atmosphere for carbonization treatment, and cooling to room temperature to obtain the bimetal doped porous carbon nanofiber catalyst. The preparation method disclosed by the invention is simple, low in raw material cost, mild in reaction condition and convenient for large-scale production. Cobalt ions in the catalyst have electron-deficient structures, and lithium ions adsorbed on the surface of the catalyst can effectively inhibit competing hydrogen evolution reactions and improve the selectivity of the catalyst, and in addition, the porous structure of the surface of the catalyst increases the active surface area of the catalyst. Owing to the synergistic effect of cobalt and lithium ion and relatively large specific surface area, the catalyst has excellent electrochemical reduction performance, and the Faraday efficiency of ammonia can reach 66.1% at-0.82V Vs RHE potential and reach 431.9mmol g cat -1 h -1 The ammonia formation rate of (2) is about 2.1 times the ammonia conversion of the Haber-Bosch reaction. The ammonia generation rate is higher than that of the industrial method, and the method has guiding significance for the industrial use of the electrochemical reduction of nitrate.
Drawings
FIG. 1 is a flow chart of a preferred embodiment of a method for preparing a bimetallic doped porous carbon nanofiber catalyst according to the present invention.
Fig. 2 is a TEM image of the bimetal doped porous carbon nanofiber catalyst of example 1 in the present invention.
Fig. 3 is a TEM image of the bimetal doped porous carbon nanofiber catalyst of example 3 in the present invention.
Fig. 4 is an XRD pattern of the bimetal doped porous carbon nanofiber catalysts of examples 1 to 3 in the present invention.
FIG. 5 is an XPS plot of the bimetallic doped porous carbon nanofiber catalysts of examples 1-2 in the present invention.
FIG. 6 shows the bimetallic doped porous carbon nanofiber catalyst of examples 1-2 of the present invention with 0.5M KNO 3 0.5M Na of (2) 2 SO 4 The Faraday efficiency of ammonia production when the electrolysis is carried out for 1h under different potentials.
FIG. 7 shows the bimetallic doped porous carbon nanofiber catalyst of example 1 of the present invention with 0.5M KNO added 3 0.5M Na of (2) 2 SO 4 0.5M Na 2 SO 4 Linear Sweep Voltammetry (LSV) plot.
FIG. 8 shows a bimetallic doped porous carbon nanofiber catalyst of example 2 of the present invention with 0.5M KNO added 3 0.5M Na of (2) 2 SO 4 0.5M Na 2 SO 4 Linear Sweep Voltammetry (LSV) plot.
FIG. 9 shows the bimetallic doped porous carbon nanofiber catalyst of example 3 of the present invention with 0.5M KNO added 3 0.5M Na of (2) 2 SO 4 0.5M Na 2 SO 4 Linear Sweep Voltammetry (LSV) plot.
Detailed Description
The invention provides a bimetal doped porous carbon nanofiber catalyst and a preparation method and application thereof, and the invention is further described in detail below in order to make the purposes, technical schemes and effects of the invention clearer and more definite. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
The invention provides a preparation method of a bimetal doped porous carbon nanofiber catalyst, which comprises the following steps:
preparing a spinning precursor solution;
the spinning precursor solution is used for preparing the nanofiber membrane by electrostatic spinning;
pre-oxidizing the prepared nanofiber membrane;
and (3) performing high-temperature carbonization treatment on the pre-oxidized nanofiber membrane.
Specifically, referring to fig. 1, fig. 1 is a flowchart of a preferred embodiment of a preparation method of a bimetal doped porous carbon nanofiber catalyst provided by the present invention, as shown in fig. 1, which includes the steps of:
s100, preparing a spinning precursor solution: sequentially mixing polyacrylonitrile, N-N dimethylformamide, znO, cobalt nitrate hexahydrate and lithium carbonate, and fully stirring to obtain a spinning precursor solution;
s200, electrostatic spinning: carrying out electrostatic spinning on the spinning precursor solution to obtain a cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane;
s300, pre-oxidation treatment: performing pre-oxidation treatment on the cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane in an air atmosphere to obtain a pre-oxidized nanofiber membrane;
s400, high-temperature carbonization treatment: and (3) placing the pre-oxidized nanofiber membrane in an inert atmosphere for carbonization treatment, and cooling to room temperature to obtain the bimetal doped porous carbon nanofiber catalyst.
According to the invention, polyacrylonitrile, znO, cobalt nitrate hexahydrate and lithium carbonate are sequentially dissolved in an N-N Dimethylformamide (DMF) solvent to prepare a spinning precursor solution, and then an electrostatic spinning technology is adopted to obtain the bimetal doped porous carbon nanofiber catalyst through electrostatic spinning, pre-oxidation treatment and high-temperature carbonization treatment, and the bimetal doped porous carbon nanofiber catalyst prepared by the method has certain mechanical strength, can be used for electrochemical nitrate reduction, and has the following advantages:
(1) The preparation method of the bimetal doped porous carbon nanofiber catalyst is simple, the raw material cost is low, the reaction condition is mild, and the catalyst can be produced in a large scale;
(2) The cobalt doped nanocluster of the bimetal doped porous carbon nanofiber catalyst can be used as an active site for electrocatalytic nitrate radical reduction;
(3) The lithium doped nanocluster of the bimetal doped porous carbon nanofiber catalyst has a good adsorption effect on nitrate enriched on the surface of the catalyst, and is catalytically reduced to ammonia;
(4) The prepared bimetal doped porous carbon nanofiber catalyst has excellent mechanical properties;
(5) The surface of the bimetal doped porous carbon nanofiber catalyst contains abundant porous structures and has large specific surface area;
(6) The prepared bimetal doped porous carbon nanofiber catalyst has wide application prospect in the field of electrochemical nitrate radical reduction catalysts.
The mechanism of the present invention is described in detail below: the nanofiber membrane prepared by electrostatic spinning is subjected to pre-oxidation treatment, so that the density of the nanofiber membrane can be increased, the rigidity performance of the fiber is properly enhanced, the nanofiber structure is not easy to break and is more stable through carbonization treatment, and meanwhile, znO is easy to volatilize in a high-temperature environment, so that rich holes can be formed on the surface of the nanofiber membrane.
In this embodiment, the preparation method of ZnO includes the steps of: and dissolving zinc acetate dihydrate in deionized water to obtain zinc acetate solution, dissolving triethanolamine in deionized water to obtain triethanolamine solution, dripping the zinc acetate solution into the triethanolamine solution, fully stirring, and performing ultrasonic treatment, standing, centrifugation, washing and drying to obtain ZnO.
In some preferred embodiments, it is desirable to activate the ZnO in a muffle furnace prior to preparing the spinning precursor solution.
In some embodiments, in the preparation step of ZnO, the stirring is at a speed of 400-600rpm, the stirring is for a time of 5-10min, the temperature is 20-50 ℃, the sonication time is 10-50min, the standing time is 10-20h, the centrifugation speed is 8000-10000rpm, the drying temperature is 50-70 ℃, and the activation temperature is 400-600 ℃ for a time of 1-3h.
In this embodiment, the step of sequentially mixing polyacrylonitrile, N-N dimethylformamide, znO, cobalt nitrate hexahydrate, and lithium carbonate specifically includes:
N-N dimethylformamide, polyacrylonitrile, znO, cobalt nitrate hexahydrate, lithium carbonate at 95:8:8:0.3: and the mass ratio of 0.3 is sequentially mixed, and the fiber with uniform diameter is formed in the electrostatic spinning process.
Specifically, adding N-N dimethylformamide into polyacrylonitrile, and magnetically stirring to obtain a viscous transparent solution; then ZnO is added and magnetically stirred to obtain a viscous milky white solution; continuously adding cobalt nitrate hexahydrate, and magnetically stirring to obtain a viscous purple solution; and continuously adding lithium carbonate, and magnetically stirring to obtain spinning precursor solution.
In some embodiments, in the step of sufficiently stirring to obtain the spinning precursor solution, the stirring speed is 400-600rpm, the stirring time is 12-15h, and the temperature is 20-60 ℃, under the condition that the spinning precursor solution is easy to obtain and uniformly disperse.
In this embodiment, the process parameters of the electrospinning are as follows: the metal needle with the inner diameter of 0.5-1.5mm is used as a spray head, the vertical distance from the spray head to a receiver is 10-30cm, the spinning voltage is 15-25KV, the feeding rate is 0.5-1mL/h, the spinning temperature is 30-50 ℃, the air relative humidity is 10-90RH%, and the obtained fiber diameter distribution can be uniform by selecting the parameters.
In some embodiments, the step of pre-oxidizing treatment specifically includes: heating to 200-250 ℃ at the speed of 1-5 ℃/min, and then preserving heat for 1-2h, so that the rigidity performance of the nanofiber membrane can be enhanced through pre-oxidation treatment, and the nanofiber membrane is not easy to break in the high-temperature calcination process.
In some embodiments, the step of carbonizing specifically includes: heating to 700-1000 ℃ at a speed of 1-10 ℃/min, and then preserving the temperature for 1-3 hours, wherein the inert atmosphere for carbonization treatment is preferably high-purity argon or nitrogen with the purity of more than or equal to 99.99%.
The present invention also provides a bimetal doped porous carbon nanofiber catalyst prepared by the preparation method of the bimetal doped porous carbon nanofiber catalyst according to any one of the above schemes, which comprises: porous carbon nanofiber membranes and cobalt lithium nanoclusters supported on the carbon nanofiber membranes.
The bimetal doped porous carbon nanofiber catalyst prepared by the invention mainly provides electrochemical activity by two factors: the synergy of the cobalt lithium nanoclusters and the porous structure. Wherein, cobalt ions have electron-deficient structure, which can provide active sites to increase current density; the lithium ions can effectively inhibit hydrogen evolution reaction, nitrate radical is enriched on the surface of the catalyst, and the selectivity of the product is improved; the porous structure is beneficial to increasing the specific surface area of the reaction and improving the reactivity.
The invention also provides an application of the bimetal doped porous carbon nanofiber catalyst in electrochemical nitrate radical reduction.
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The nitrogen used in the embodiment is high-purity nitrogen with the purity more than or equal to 99.99 percent; other chemical reagents used, unless otherwise specified, are commercially available.
Example 1
10mLN-N dimethylformamide is added into 0.8g of polyacrylonitrile, and the mixture is magnetically stirred for 5 hours to obtain a viscous transparent solution; then 0.8g ZnO is added and magnetically stirred for 12 hours to obtain a viscous milky white solution; continuously adding 0.03g of cobalt nitrate hexahydrate, and magnetically stirring for 5 hours to obtain a viscous purple solution; and then adding 0.03g of lithium carbonate, and magnetically stirring for 12 hours to obtain a spinning precursor solution. Carrying out electrostatic spinning on the obtained spinning precursor solution, and collecting a cobalt acid/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane; the electrostatic spinning parameters are as follows: a metal needle with the inner diameter of 0.8mm is used as a spray head, the spinning voltage is 21KV, the vertical distance between the needle and a receiver is 15cm, the feeding speed is 0.7mL/h, the spinning temperature is 30 ℃, the air relative humidity is 20RH%, and a circular roller aluminum foil receives spinning fibers. Placing the cobalt nitrate hexahydrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane obtained in the previous step in a muffle furnace, heating to 220 ℃ at a speed of 1 ℃/min under the air atmosphere, and then preserving heat for 1h, and performing pre-oxidation treatment to obtain a pre-oxidized nanofiber membrane; and (3) placing the pre-oxidized nanofiber membrane obtained in the previous step in a tube furnace, heating to 900 ℃ at a speed of 5 ℃/min under the protection of nitrogen atmosphere, preserving heat for 2 hours, carbonizing, and cooling to room temperature to obtain the bimetal doped porous carbon nanofiber catalyst after carbonization.
Ammonia was produced by electrochemical reduction of nitrate using the catalyst material produced in example 1.
Ethanol and 2wt.% Nafion 117 membrane solution were first mixed in a volume ratio of 980:20, adding 1mg of the bimetal doped porous carbon nanofiber catalyst into 100 mu LNafion diluent, uniformly dispersing by ultrasonic, uniformly dripping the dispersion on 0.5cm carbon paper washed by 1mol/L hydrochloric acid, ethanol and deionized water by using a 10 mu L pipette, and drying the working electrode by using an infrared lamp. An Ag/AgCl electrode is used as a reference electrode, and a Pt electrode is used as an auxiliary electrode; the cathode chamber of the H tank is provided with a working electrode and a reference electrode, argon is introduced to remove oxygen, the anode chamber is provided with an auxiliary electrode, and the two electrode chambers are separated by an anion exchange membrane FAB-PK-130. Respectively with 0.5MKNO 3 0.5M Na of (2) 2 SO 4 Aqueous solution and 0.5M Na 2 SO 4 The aqueous solution was used as an electrolyte, and the test was performed at room temperature under normal pressure.
Example 2
10mLN-N dimethylformamide is added into 0.8g of polyacrylonitrile, and the mixture is magnetically stirred for 5 hours to obtain a viscous transparent solution; then 0.8g ZnO is added and magnetically stirred for 12 hours to obtain a viscous milky white solution; 0.03g of cobalt nitrate hexahydrate is continuously added, and the mixture is magnetically stirred for 12 hours to obtain a spinning precursor solution. Carrying out electrostatic spinning on the obtained spinning precursor solution, and collecting a cobalt nitrate hexahydrate/ZnO/polyacrylonitrile nanofiber membrane; the electrostatic spinning parameters are as follows: a metal needle with the inner diameter of 0.8mm is used as a spray head, the spinning voltage is 21KV, the vertical distance between the needle and a receiver is 15cm, the feeding speed is 0.7mL/h, the spinning temperature is 30 ℃, the air relative humidity is 20RH%, and a circular roller aluminum foil receives spinning fibers. Placing the cobalt hexahydrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane obtained in the previous step in a muffle furnace, heating to 220 ℃ at a speed of 1 ℃/min under the air atmosphere, and then preserving heat for 1h, and performing pre-oxidation treatment to obtain a pre-oxidized nanofiber membrane; and (3) placing the pre-oxidized nanofiber membrane obtained in the previous step in a tube furnace, heating to 900 ℃ at a speed of 5 ℃/min under the protection of nitrogen atmosphere, preserving heat for 2 hours, carbonizing, and cooling to room temperature to obtain the carbonized cobalt metal doped porous carbon nanofiber catalyst.
Ammonia was produced by electrochemical reduction of nitrate using the catalyst material produced in example 2.
Ethanol and 2wt.% Nafion 117 membrane solution were first mixed in a volume ratio of 980:20, adding 1mg of cobalt metal doped porous carbon nanofiber catalyst into 100 mu LNafion diluent, uniformly dispersing by ultrasonic, uniformly dripping the dispersion on 0.5cm carbon paper washed by 1mol/L hydrochloric acid, ethanol and deionized water by using a 10 mu L pipette, and drying the working electrode by using an infrared lamp. An Ag/AgCl electrode is used as a reference electrode, and a Pt electrode is used as an auxiliary electrode; the cathode chamber of the H tank is provided with a working electrode and a reference electrode, argon is introduced to remove oxygen, the anode chamber is provided with an auxiliary electrode, and the two electrode chambers are separated by an anion exchange membrane FAB-PK-130. Respectively with 0.5MKNO 3 0.5M Na of (2) 2 SO 4 Aqueous solution and 0.5M Na 2 SO 4 The aqueous solution was used as an electrolyte, and the test was performed at room temperature under normal pressure.
Example 3
10mLN-N dimethylformamide is added into 0.8g of polyacrylonitrile, and the mixture is magnetically stirred for 5 hours to obtain a viscous transparent solution; then 0.03g of cobalt nitrate hexahydrate is added, and the mixture is magnetically stirred for 12 hours to obtain spinning precursor solution. Carrying out electrostatic spinning on the obtained spinning precursor solution, and collecting a cobalt nitrate hexahydrate/polyacrylonitrile nanofiber membrane; the electrostatic spinning parameters are as follows: a metal needle with the inner diameter of 0.8mm is used as a spray head, the spinning voltage is 21KV, the vertical distance between the needle and a receiver is 15cm, the feeding speed is 0.7mL/h, the spinning temperature is 30 ℃, the air relative humidity is 20RH%, and a circular roller aluminum foil receives spinning fibers. Placing the cobalt nitrate hexahydrate// polyacrylonitrile nanofiber membrane obtained in the previous step in a muffle furnace, heating to 220 ℃ at a speed of 1 ℃/min under the air atmosphere, and then preserving heat for 1h, and performing pre-oxidation treatment to obtain a pre-oxidized nanofiber membrane; and (3) placing the pre-oxidized nanofiber membrane obtained in the previous step in a tube furnace, heating to 900 ℃ at a speed of 5 ℃/min under the protection of nitrogen atmosphere, preserving heat for 2 hours, carbonizing, and cooling to room temperature to obtain the carbonized cobalt metal doped carbon nanofiber catalyst.
Ammonia was produced by electrochemical reduction of nitrate using the catalyst material produced in example 3.
Ethanol and 2wt.% Nafion 117 membrane solution were first mixed in a volume ratio of 980:20, adding 1mg of cobalt metal doped carbon nanofiber catalyst into 100 mu LNafion diluent, uniformly dispersing by ultrasonic, uniformly dripping the dispersion on 0.5cm carbon paper washed by 1mol/L hydrochloric acid, ethanol and deionized water by using a 10 mu L pipette, and drying the working electrode by using an infrared lamp. An Ag/AgCl electrode is used as a reference electrode, and a Pt electrode is used as an auxiliary electrode; the cathode chamber of the H tank is provided with a working electrode and a reference electrode, argon is introduced to remove oxygen, the anode chamber is provided with an auxiliary electrode, and the two electrode chambers are separated by an anion exchange membrane FAB-PK-130. Respectively with 0.5MKNO 3 0.5M Na of (2) 2 SO 4 Aqueous solution and 0.5M Na 2 SO 4 The aqueous solution was used as an electrolyte, and the test was performed at room temperature under normal pressure.
The test results of the above examples are shown in fig. 2-9.
FIG. 2 is a TEM image of the bimetallic doped porous carbon nanofiber catalyst of example 1 of the present invention, as shown in FIG. 2, the surface of the catalyst of example 1 is distributed with more holes, and the diameter of the holes is about 150nm; similar to the ZnO diameter.
Fig. 3 is a TEM image of the bimetallic doped porous carbon nanofiber catalyst of example 3 of the present invention, as shown in fig. 3, the catalyst surface of example 3 is smooth without obvious pores.
FIG. 4 shows XRD patterns of the bimetallic doped porous carbon nanofiber catalysts of examples 1 to 3 according to the present invention, and as shown in FIG. 4, the catalysts of examples 1 to 3 have only two peaks at 24.1 and 44.1℃corresponding to the (002) and (100) crystal planes of carbon, respectively, except that there are no other distinct peaks. The above characterization initially demonstrates that the cobalt lithium elements supported in examples 1-3 exist in nanocluster form.
FIG. 5 is an XPS plot of the bimetallic doped porous carbon nanofiber catalysts of examples 1-2 of the present invention, as shown in FIG. 5, the catalyst of example 1 had a peak at 55.05eV, whereas the catalyst of example 2 had no peak, indicating that example 2 had no lithium ion.
FIG. 6 is a graph showing the Faraday efficiency of the bimetallic doped porous carbon nanofiber catalysts of examples 1-2 in the invention when electrolyzed for 1h at different potentials in 0.5M Na2SO4 of 0.5M KNO3, wherein the Faraday efficiency of the catalyst of example 1 is always kept above 55% in the potential interval of 0.79-0.89V Vs RHE, and the maximum Faraday efficiency of ammonia is 66.1% at the potential of-0.82V Vs RHE, and the ammonia generation rate of 431.9mmol g cat-1h-1 is superior to that of the catalyst of example 2, as shown in FIG. 6. After the lithium ions are added, the capability of enriching nitrate on the surface of the catalyst can be promoted, the nitrate can be converted into ammonia, and the product selectivity of the catalyst can be improved.
FIG. 7 shows a bimetallic doped porous carbon nanofiber catalyst of example 1 of the present invention at 0.5M KNO 3 0.5M Na of (2) 2 SO 4 0.5M Na 2 SO 4 LSV graph in aqueous solution electrochemical test was performed in electrochemical test System (CHI 760E,CH Instrument Inc), test apparatus was H tank, catalyst-loaded carbon paper as working electrode, platinum electrode as auxiliary electrode, ag/AgCl as reference electrode, as shown in FIG. 7, current density of 404.6mA/cm was reached in example 1 2 The current density of the hydrogen evolution reaction is 179.8mA/cm 2 . The current density of example 1 is superior to examples 2 to 3, and the hydrogen evolution reaction can be suppressed more remarkably. The addition of lithium ions into the catalyst can promote the synergistic effect of cobalt and lithium and improve the current density.
FIG. 8 is a double embodiment 2 of the present inventionMetal doped porous carbon nanofiber catalyst with KNO of 0.5M 3 0.5M Na of (2) 2 SO 4 0.5M Na 2 SO 4 LSV graph in aqueous solution electrochemical test was performed in electrochemical test System (CHI 760E,CH Instrument Inc), test apparatus was H tank, catalyst-loaded carbon paper as working electrode, platinum electrode as auxiliary electrode, ag/AgCl as reference electrode, as shown in FIG. 8, current density of 304.5mA/cm was reached in example 2 2 The current density of the hydrogen evolution reaction is 251.3mA/cm 2 . The current density of example 2 is intermediate between examples 1 and 3, indicating that the addition of ZnO increases the catalyst surface area, helping to increase the active surface area of the catalyst, increasing the current density.
FIG. 9 shows a bimetallic doped porous carbon nanofiber catalyst of example 3 of the present invention at 0.5M KNO 3 0.5M Na of (2) 2 SO 4 0.5M Na 2 SO 4 LSV graph in aqueous solution electrochemical test was performed in electrochemical test System (CHI 760E,CH Instrument Inc), test apparatus was H tank, catalyst-loaded carbon paper as working electrode, platinum electrode as auxiliary electrode, ag/AgCl as reference electrode, as shown in FIG. 9, current density of 270.5mA/cm was reached in example 3 2 The current density of the hydrogen evolution reaction is 196.1mA/cm 2 。
In summary, the invention discloses a bimetal doped porous carbon nanofiber catalyst, and a preparation method and application thereof, wherein the method comprises the following steps: sequentially mixing polyacrylonitrile, N-N dimethylformamide, znO, cobalt nitrate hexahydrate and lithium carbonate, and fully stirring to obtain a spinning precursor solution; carrying out electrostatic spinning on the spinning precursor solution to obtain a cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane; performing pre-oxidation treatment on the cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane in an air atmosphere to obtain a pre-oxidized nanofiber membrane; and (3) placing the pre-oxidized nanofiber membrane in an inert atmosphere for carbonization treatment, and cooling to room temperature to obtain the bimetal doped porous carbon nanofiber catalyst. The preparation method disclosed by the invention is simple, low in raw material cost, mild in reaction condition and convenient for large-scale production. Catalytic reactionThe cobalt ions in the catalyst have electron-deficient structures, and the lithium ions adsorbed on the surface of the catalyst can effectively inhibit competing hydrogen evolution reaction and improve the selectivity of the catalyst, and in addition, the porous structure of the surface of the catalyst increases the active surface area of the catalyst. Owing to the synergistic effect of cobalt and lithium ion and relatively large specific surface area, the catalyst has excellent electrochemical reduction performance, and the Faraday efficiency of ammonia can reach 66.1% at-0.82V Vs RHE potential and reach 431.9mmol g cat -1 h -1 The ammonia generation rate is about 2.1 times of the ammonia conversion rate of the Haber-Bosch reaction, and the ammonia generation rate is higher than that of the industrial method, thereby having guiding significance for the industrial use of the electrochemical reduction of nitrate.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; while the invention has been described in detail with reference to the foregoing embodiments, it will be appreciated by those skilled in the art that variations may be made in the techniques described in the foregoing embodiments, or equivalents may be substituted for elements thereof; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (6)
1. A method for preparing a bimetal doped porous carbon nanofiber catalyst, which comprises the following steps:
N-N dimethylformamide, polyacrylonitrile, znO, cobalt nitrate hexahydrate, lithium carbonate at 95:8:8:0.3: mixing the materials in a mass ratio of 0.3 in sequence, and fully stirring to obtain spinning precursor solution;
carrying out electrostatic spinning on the spinning precursor solution to obtain a cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane; the technological parameters of the electrostatic spinning are as follows: a metal needle with the inner diameter of 0.5-1.5mm is adopted as a spray head, the vertical distance from the spray head to a receiver is 10-30cm, the spinning voltage is 15-25KV, the feeding rate is 0.5-1mL/h, the spinning temperature is 30-50 ℃, and the air relative humidity is 10-90RH%;
performing pre-oxidation treatment on the cobalt nitrate/lithium carbonate/ZnO/polyacrylonitrile nanofiber membrane in an air atmosphere to obtain a pre-oxidized nanofiber membrane; the pre-oxidation treatment comprises the following steps: heating to 200-250deg.C at a rate of 1-5deg.C/min, and maintaining for 1-2h;
the pre-oxidized nanofiber membrane is placed in inert atmosphere for carbonization treatment, and cooled to room temperature, so that the bimetal doped porous carbon nanofiber catalyst is obtained; the carbonization treatment specifically comprises the following steps: heating to 700-1000deg.C at a rate of 1-10deg.C/min, and maintaining for 1-3h.
2. The method for preparing a bimetal doped porous carbon nanofiber catalyst according to claim 1, wherein the method for preparing ZnO comprises the steps of: and dissolving zinc acetate dihydrate in deionized water to obtain zinc acetate solution, dissolving triethanolamine in deionized water to obtain triethanolamine solution, dripping the zinc acetate solution into the triethanolamine solution, fully stirring, and performing ultrasonic treatment, standing, centrifugation, washing and drying to obtain ZnO.
3. The method for preparing a bimetal doped porous carbon nanofiber catalyst according to claim 2, wherein in the preparation step of ZnO, the stirring speed is 400-600rpm, the stirring time is 5-10min, the temperature is 20-50 ℃, the ultrasonic time is 10-50min, the standing time is 10-20h, the centrifugation speed is 8000-10000rpm, and the drying temperature is 50-70 ℃; the ZnO needs to be subjected to activation treatment in a muffle furnace before preparing the spinning precursor solution, wherein the activation temperature is 400-600 ℃ and the activation time is 1-3h.
4. The method for preparing a bimetal doped porous carbon nanofiber catalyst according to claim 1, wherein in the step of fully stirring to obtain a spinning precursor solution, the stirring speed is 400-600rpm, the stirring time is 12-15h, and the temperature is 20-60 ℃.
5. A bimetal doped porous carbon nanofiber catalyst prepared by the method for preparing the bimetal doped porous carbon nanofiber catalyst according to any one of claims 1 to 4, comprising: porous carbon nanofiber membranes and cobalt lithium nanoclusters supported on the carbon nanofiber membranes.
6. Use of a bimetallic doped porous carbon nanofiber catalyst according to claim 5 for electrochemical reduction of nitrate to ammonia.
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