CN114808018B - Mono-atom iron doped nitrogen-carbon material, and preparation method and application thereof - Google Patents
Mono-atom iron doped nitrogen-carbon material, and preparation method and application thereof Download PDFInfo
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- 239000003575 carbonaceous material Substances 0.000 title claims abstract description 64
- CKUAXEQHGKSLHN-UHFFFAOYSA-N [C].[N] Chemical compound [C].[N] CKUAXEQHGKSLHN-UHFFFAOYSA-N 0.000 title claims abstract description 57
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims abstract description 50
- 229910052742 iron Inorganic materials 0.000 title claims abstract description 20
- 238000002360 preparation method Methods 0.000 title claims abstract description 20
- 239000003054 catalyst Substances 0.000 claims abstract description 30
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- 238000000034 method Methods 0.000 claims description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 9
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- 239000008367 deionised water Substances 0.000 claims description 9
- 229910021641 deionized water Inorganic materials 0.000 claims description 9
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- 238000005868 electrolysis reaction Methods 0.000 claims description 4
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- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 3
- 229920000557 Nafion® Polymers 0.000 claims description 3
- 239000000463 material Substances 0.000 abstract description 20
- 229910002558 Fe-Nx Inorganic materials 0.000 abstract description 4
- 229910002559 Fe−Nx Inorganic materials 0.000 abstract description 4
- 230000000052 comparative effect Effects 0.000 description 21
- SZQUEWJRBJDHSM-UHFFFAOYSA-N iron(3+);trinitrate;nonahydrate Chemical compound O.O.O.O.O.O.O.O.O.[Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O SZQUEWJRBJDHSM-UHFFFAOYSA-N 0.000 description 9
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- 239000002184 metal Substances 0.000 description 6
- 230000003197 catalytic effect Effects 0.000 description 5
- 239000010902 straw Substances 0.000 description 5
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 4
- 241000209140 Triticum Species 0.000 description 4
- 235000021307 Triticum Nutrition 0.000 description 4
- 238000001354 calcination Methods 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- 238000007792 addition Methods 0.000 description 3
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- 238000003763 carbonization Methods 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 238000000731 high angular annular dark-field scanning transmission electron microscopy Methods 0.000 description 3
- RAXXELZNTBOGNW-UHFFFAOYSA-N imidazole Natural products C1=CNC=N1 RAXXELZNTBOGNW-UHFFFAOYSA-N 0.000 description 3
- NLKNQRATVPKPDG-UHFFFAOYSA-M potassium iodide Chemical compound [K+].[I-] NLKNQRATVPKPDG-UHFFFAOYSA-M 0.000 description 3
- 238000011160 research Methods 0.000 description 3
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- 229910052723 transition metal Inorganic materials 0.000 description 3
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- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
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- 238000011161 development Methods 0.000 description 2
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- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 description 2
- 238000011068 loading method Methods 0.000 description 2
- 239000002070 nanowire Substances 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
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- 238000000197 pyrolysis Methods 0.000 description 2
- 230000027756 respiratory electron transport chain Effects 0.000 description 2
- 238000005245 sintering Methods 0.000 description 2
- LXBGSDVWAMZHDD-UHFFFAOYSA-N 2-methyl-1h-imidazole Chemical compound CC1=NC=CN1 LXBGSDVWAMZHDD-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 229910021577 Iron(II) chloride Inorganic materials 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 238000003917 TEM image Methods 0.000 description 1
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- 229910003481 amorphous carbon Inorganic materials 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
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- 238000010586 diagram Methods 0.000 description 1
- ZOMNIUBKTOKEHS-UHFFFAOYSA-L dimercury dichloride Chemical class Cl[Hg][Hg]Cl ZOMNIUBKTOKEHS-UHFFFAOYSA-L 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 239000010411 electrocatalyst Substances 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
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- 230000002349 favourable effect Effects 0.000 description 1
- 210000003608 fece Anatomy 0.000 description 1
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- 239000005431 greenhouse gas Substances 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 239000000543 intermediate Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- NMCUIPGRVMDVDB-UHFFFAOYSA-L iron dichloride Chemical compound Cl[Fe]Cl NMCUIPGRVMDVDB-UHFFFAOYSA-L 0.000 description 1
- 238000004502 linear sweep voltammetry Methods 0.000 description 1
- 239000010871 livestock manure Substances 0.000 description 1
- 239000008204 material by function Substances 0.000 description 1
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- 238000005259 measurement Methods 0.000 description 1
- 229910001092 metal group alloy Inorganic materials 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 150000002739 metals Chemical class 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 125000000896 monocarboxylic acid group Chemical group 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 150000004690 nonahydrates Chemical class 0.000 description 1
- 238000000643 oven drying Methods 0.000 description 1
- JMANVNJQNLATNU-UHFFFAOYSA-N oxalonitrile Chemical compound N#CC#N JMANVNJQNLATNU-UHFFFAOYSA-N 0.000 description 1
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- 230000000737 periodic effect Effects 0.000 description 1
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- 238000010298 pulverizing process Methods 0.000 description 1
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- 238000007086 side reaction Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000010802 sludge Substances 0.000 description 1
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- 239000013154 zeolitic imidazolate framework-8 Substances 0.000 description 1
- MFLKDEMTKSVIBK-UHFFFAOYSA-N zinc;2-methylimidazol-3-ide Chemical compound [Zn+2].CC1=NC=C[N-]1.CC1=NC=C[N-]1 MFLKDEMTKSVIBK-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
- C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
- C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
- C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
- 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
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
- C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
- C25B1/01—Products
- C25B1/23—Carbon monoxide or syngas
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Inorganic Chemistry (AREA)
- Catalysts (AREA)
Abstract
The invention discloses a single-atom iron doped nitrogen-carbon material, and a preparation method and application thereof, wherein the preparation method comprises the following steps: mixing ferric salt, biochar and water, drying to form solid, heating the solid to 300-650 ℃ in an inert gas or nitrogen environment, keeping the temperature for 1-3 h, heating to 900-1100 ℃ and keeping the temperature for 1-2 h, and cooling to room temperature to obtain the nitrogen-carbon material. The nitrogen-carbon material is used as a catalyst to perform electrocatalytic reduction on CO 2 in 0.1M KHCO 3 electrolyte, the Tafel slope is 70mv dec ‑1, the active center Fe-Nx is formed and the porous structure of the material is adopted, so that the catalyst reaches 93% at FECO under the lower overpotential of-0.6V; has good material stability.
Description
Technical Field
The invention belongs to the technical field of environmental functional materials, and particularly relates to a single-atom iron-doped nitrogen-carbon material, and a preparation method and application thereof.
Background
With the increasing severity of environmental problems caused by greenhouse gases and the reduction of non-renewable energy reserves such as fossil energy, the capture and utilization of carbon dioxide are of great importance, and development of efficient technologies for converting carbon dioxide into valuable chemical energy for utilization is urgently needed. The electrocatalytic reduction method reduces CO 2 into a value-added product under the action of the power-on energy, has the advantages of simple operation, controllable reaction conditions and the like, and the power required by the electrocatalytic process can be provided by renewable energy sources such as solar energy, wind energy and the like, so that the green sustainable development is realized. However, the high bond energy of c=o (750 kJ mol -1) means that a high overpotential is required to activate the CO 2 molecule. Therefore, an effective electrocatalyst is a necessary condition to improve the performance of the electrocatalytic CO 2 RR.
In the past studies, researchers have developed a series of catalysts for electrocatalytic reduction of CO 2, such as elemental metals, metal oxides, metal alloys, carbon-based materials, N-doped carbon-based materials, etc., but the catalytic effect of the catalysts is not ideal, and the proposal of single-atom catalysts has been attracting extensive research interest. The monoatomic metal has higher surface energy, and the monoatomic catalyst has the characteristics of high selectivity, high stability, repeated recycling and the like. Sui and the like research that noble metal silver (Ag) is loaded on the surface of a nitrogen-doped carbon material, and the prepared monoatomic Ag-N 3/PCNC can convert CO 2 into CO under a lower overpotential, has higher CO Faraday Efficiency (FECO), but has the problems of high price, limited resources, poor stability and the like, and greatly restricts large-scale commercial application.
Currently, catalysts of M-N-C structure have been proposed to increase the activity of monoatomic transition metals (M) by doping of N and support of carbon material (C). Fe-N-C catalyst has excellent performance in numerous transition metal catalysts, zong Ziao and the like disclose a preparation method of Fe-N-C nanowire catalyst (Zong Ziao, fan Chuanbin, huang Guimei, pang Yaqin, binmussel east, wei Lianggu and the like; a preparation method of Fe-N-C nanowire catalyst, 202111262456.1), however, raw materials for preparing Fe-N-C comprise Zn (NO 3)2·nH2O、FeCl2·mH2 O, 2-methylimidazole, potassium iodide and methanol, slow dropwise adding, stirring, separating and the like involved in the preparation step are used for obtaining a Fe-doped ZIF-8 precursor, and then calcining to obtain a Fe-N-C structural material; likewise, wang Jide and the like disclose an Fe-N co-doped carbon nano catalytic material (Wang Jide, feng Chao, guo Yuan, xie Yuehong, zhang Li, chen Tingxiang and the like) (2020) for improving the electrocatalytic oxygen reduction performance; CN 111082084A), wherein the involved Fe@N-C structural material requires a complex coordination function of Fe@N-C imidazole or a Fe-N-C structural material to be successfully prepared by using a complex coordination method for preparing Fe@N-C material, and the same kind of Fe@N-C structural material is required for the current complex oxygen-C coordination method.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a preparation method of a single-atom iron-doped nitrogen-carbon material.
It is another object of the present invention to provide a monoatomic iron-doped nitrogen-carbon material obtained by the above preparation method.
It is another object of the present invention to provide the use of the above-described nitrogen-carbon material as a catalyst for improving the faraday efficiency of CO in the electrocatalytic reduction of CO 2.
The aim of the invention is achieved by the following technical scheme.
A preparation method of a monoatomic iron-doped nitrogen-carbon material comprises the following steps: mixing ferric salt, biochar and water, drying at 10-105 ℃ until solid is formed, heating the solid to 300-650 ℃ and keeping the temperature for 1-3 h under the environment of inert gas or nitrogen, heating to 900-1100 ℃ and keeping the temperature for 1-2 h, and cooling to room temperature to obtain a nitrogen-carbon material, wherein the ratio of the ferric salt to the biochar to the water is (0.001-0.01) in parts by weight: 1:15.
In the technical scheme, the temperature rising rate of the solid to 300-650 ℃ is 2-10 ℃/min.
In the technical proposal, the temperature rising rate of rising to 900-1100 ℃ is 2-15 ℃/min.
In the technical scheme, the ratio of iron, biochar and water in the ferric salt is (0.002-0.009) according to the parts by weight: 1:15, preferably (0.003 to 0.008): 1:15, more preferably (0.004 to 0.006): 1:15.
The nitrogen-carbon material obtained by the preparation method.
The nitrogen-carbon material is applied to improving the Faraday efficiency of CO 2 in electrocatalytic reduction as a catalyst.
In the technical scheme, the highest CO Faraday efficiency is 93%.
In the technical scheme, the method for electrocatalytic reduction of CO 2 by taking the nitrogen-carbon material as a catalyst comprises the following steps of: uniformly mixing 5-7 parts by weight of catalyst, 190-210 parts by volume of deionized water, 360-380 parts by volume of absolute ethyl alcohol and 20-40 parts by volume of 5% Nafion solution to obtain a solution, dripping the solution on the surface of carbon cloth, drying the solution to serve as a working electrode, putting the working electrode, a reference electrode and a counter electrode into electrolyte for electrolysis, wherein the overpotential is-0.3V to-1.1V, the electrolyte is a mixture of water and KHCO 3, the concentration of KHCO 3 in the electrolyte is 0.1-0.3M, the volume unit of the parts is mu L, and the unit of the mass unit is mg.
In the above technical scheme, the overpotential is-0.4V to-0.8V, preferably-0.5V to-0.7V.
In the technical scheme, the concentration of KHCO 3 in the electrolyte is 0.1-0.15M.
According to the invention, the N-enriched biochar and the transition metal directly form a coordination bond to construct an Fe-Nx active center, so that the catalyst capable of effectively improving the reduction efficiency of CO 2 is prepared.
The single-atom iron doped nitrogen-carbon material is successfully prepared by the impregnation and calcination method, the preparation method is simple, and the raw material cost is low. The nitrogen-carbon material is used as a catalyst to perform electrocatalytic reduction on CO 2 in 0.1M KHCO 3 electrolyte, the Tafel slope is 70mv dec -1, the active center Fe-Nx is formed and the porous structure of the material is adopted, so that the catalyst reaches 93% at FECO under the condition of low overpotential-0.6V (RHE); has good material stability.
Drawings
FIG. 1 is XRD of the nitrogen-carbon material obtained in example 1 and comparative example 1;
FIG. 2 is a diagram showing SEM, EDS, TEM and HAADF-STEM of the nitrogen-carbon material, wherein a is SEM of the nitrogen-carbon material obtained in comparative example 1, b is SEM of the nitrogen-carbon material obtained in example 1, c is EDS of the nitrogen-carbon material obtained in example 1, d is TEM of the nitrogen-carbon material obtained in example 1, and e is HAADF-STEM of the nitrogen-carbon material obtained in example 1;
FIG. 3a is FECO of examples 6-8 and comparative example 2 electrocatalytically reducing CO 2;
FIG. 3b is FEH 2 of examples 6-8 and comparative example 2 electrocatalytically reducing CO 2;
FIG. 4a is FECO of examples 6, 9, 10 and comparative example 2 for electrocatalytically reducing CO 2;
FIG. 4b is FEH 2 of examples 6, 9, 10 and comparative example 2 for electrocatalytically reducing CO 2;
FIG. 5a is FECO of examples 6, 11 and 12 electrocatalytically reducing CO 2;
FIG. 5b is FEH 2 of examples 6,11 and 12 electrocatalytically reducing CO 2;
FIG. 6a is a graph showing the linear voltammetric properties of the single-atom iron-doped nitrogen-carbon materials obtained in examples 1-3 for electrocatalytic reduction of CO 2;
FIG. 6b is a graph showing the linear voltammetric properties of the single-atom iron-doped nitrogen-carbon materials obtained in examples 1, 4 and 5 for electrocatalytic reduction of CO 2;
Fig. 6c shows Tafel slopes of the monatomic iron doped nitrogen-carbon material obtained in example 1 and the nitrogen-carbon material obtained in comparative example 1.
Detailed Description
The technical scheme of the invention is further described below with reference to specific embodiments.
The raw materials of the biochar can be straw, wood dust, animal manure, sludge and the like. The raw material of the biochar in the following examples is wheat straw. The method for preparing the biochar comprises the following steps: drying and pulverizing wheat straw to particle size below 5mm, weighing 20g of pulverized wheat straw in a ceramic crucible, placing into a baking oven (DGG-9023A, shanghai Simpson laboratory apparatus Co., ltd., china), and oven drying at 80deg.C for 24 hr. Placing the dried wheat straw into a ceramic crucible, covering, and placing into an atmosphere box (SQFL-1200, shanghai rectangular crystal, china) for 2h of pyrolysis at 500 ℃ under the lower limit of oxygen. After the pyrolysis is finished, the biochar is obtained and sealed for standby.
Example 1
A preparation method of a monoatomic iron-doped nitrogen-carbon material (Fe-N-C) comprises the following steps: mixing ferric nitrate (ferric salt) nonahydrate, biochar and deionized water, drying at 80 ℃ for 24 hours to form solid, heating the solid to 550 ℃ at a speed of 6 ℃/min in a vacuum atmosphere furnace under the nitrogen environment, keeping the temperature for 2 hours, heating to 900 ℃ at a speed of 2 ℃/min, keeping the temperature for 1 hour, and cooling to room temperature of 20-25 ℃ to obtain the nitrogen-carbon material, wherein the ratio of the iron, the biochar and water in the ferric nitrate nonahydrate is 0.005:1:15 in parts by weight.
Example 2
A preparation method of a monoatomic iron-doped nitrogen-carbon material (Fe-N-C) comprises the following steps: mixing ferric nitrate nonahydrate, biochar and deionized water, drying at 80 ℃ for 24 hours to form solid, heating the solid to 550 ℃ at a speed of 6 ℃/min in a vacuum atmosphere furnace under the nitrogen environment, keeping the temperature for 2 hours, heating to 1000 ℃ at a speed of 2 ℃/min, keeping the temperature for 1 hour, and cooling to room temperature of 20-25 ℃ to obtain the nitrogen-carbon material, wherein the ratio of the iron, the biochar and water in the ferric nitrate nonahydrate is 0.005:1:15 in parts by weight.
Example 3
A preparation method of a monoatomic iron-doped nitrogen-carbon material (Fe-N-C) comprises the following steps: mixing ferric nitrate nonahydrate, biochar and deionized water, drying at 80 ℃ for 24 hours to form solid, heating the solid to 550 ℃ at a speed of 6 ℃/min in a vacuum atmosphere furnace under the nitrogen environment, keeping the temperature for 2 hours, heating to 1100 ℃ at a speed of 2 ℃/min, keeping the temperature for 1 hour, and cooling to room temperature of 20-25 ℃ to obtain the nitrogen-carbon material, wherein the ratio of the iron, the biochar and water in the ferric nitrate nonahydrate is 0.005:1:15 in parts by weight.
Example 4
A preparation method of a monoatomic iron-doped nitrogen-carbon material (Fe-N-C) comprises the following steps: mixing ferric nitrate nonahydrate, biochar and deionized water, drying at 80 ℃ for 24 hours to form solid, heating the solid to 550 ℃ at a speed of 6 ℃/min in a vacuum atmosphere furnace under the nitrogen environment, keeping the temperature for 2 hours, heating to 900 ℃ at a speed of 2 ℃/min, keeping the temperature for 1 hour, and cooling to room temperature of 20-25 ℃ to obtain the nitrogen-carbon material, wherein the ratio of the iron, the biochar and water in the ferric nitrate nonahydrate is 0.001:1:15 in parts by weight.
Example 5
A preparation method of a monoatomic iron-doped nitrogen-carbon material (Fe-N-C) comprises the following steps: mixing ferric nitrate nonahydrate, biochar and deionized water, drying at 80 ℃ for 24 hours to form solid, heating the solid to 550 ℃ at a speed of 6 ℃/min in a vacuum atmosphere furnace under the nitrogen environment, keeping the temperature for 2 hours, heating to 900 ℃ at a speed of 2 ℃/min, keeping the temperature for 1 hour, and cooling to room temperature of 20-25 ℃ to obtain the nitrogen-carbon material, wherein the ratio of the iron, the biochar and water in the ferric nitrate nonahydrate is 0.01:1:15 in parts by weight.
Comparative example 1
A method for preparing a nitrogen-carbon material, comprising: mixing biochar and deionized water, drying at 80 ℃ for 24 hours to form solid, heating the solid to 550 ℃ at a speed of 6 ℃/min and keeping the temperature for 2 hours in a vacuum atmosphere furnace, heating to 900 ℃ at a speed of 2 ℃/min and keeping the temperature for 1 hour, and cooling to room temperature of 20-25 ℃ to obtain the nitrogen-carbon material, wherein the ratio of the biochar to the water is 1:15 in parts by weight.
As shown in FIG. 1, the XRD patterns of the nitrogen-carbon material obtained in example 1 had two distinct peaks at 25.9℃and 42.9℃corresponding to the graphitic carbon of the (002) and (100) planes, respectively. Furthermore, no other distinct peaks were detected in the XRD pattern, which means that Fe atoms may appear in amorphous phase, atomic form or embedded in the N-C framework. The calcined carbon-based material had some degree of graphitization, and it is noted that the nitrogen-carbon material obtained in example 1 had one more graphitic carbon peak (100) at 42.9 ° than the nitrogen-carbon material obtained in comparative example 1, probably due to the effect of iron doping on the natural periodic arrangement of the carbon matrix. The degree of graphitization also affects the conductivity of the material.
As shown in fig. 2, it can be observed from fig. 2 that the surface of the nitrogen-carbon material obtained in comparative example 1 has a similar spherical structure (a of fig. 2), which is probably due to the fact that at the end of calcination, the pores of the material surface are closed by sintering, and thus the material surface assumes an approximately spherical structure. The nitrogen-carbon material obtained in example 1 (b of fig. 2) has a rich porous structure as compared with the nitrogen-carbon material obtained in comparative example 1. This is probably due to the addition of metallic iron during calcination, which changes the original morphology of the material, reducing the grain size and order of the carbon material. The corresponding EDS (C of fig. 2) results show that Fe, C and N are uniformly dispersed throughout the material surface, no bright aggregation sites are observed, demonstrating that no metal clusters are formed during Fe doping. The TEM image showed the amorphous carbon appearance of the nitrogen-carbon material obtained in example 1, as shown in fig. 2 d, no significant black shadow aggregation was observed, which demonstrates that the Fe-doped material can be uniformly dispersed on the carbon-based material surface or incorporated into the carbon-nitrogen skeleton, and no clusters were formed on the carbon-based material. In addition, bright spots of high density were observed in the HAADF-STEM image (e of fig. 2), and these bright spots illustrate the presence of monoatomic Fe.
One of the nitrogen-carbon materials obtained in examples 1 to 5 and comparative document 1 was used as a catalyst to perform electrocatalytic reduction of CO 2, and the method of electrocatalytic reduction of CO 2 was as follows: 6mg of catalyst, 200. Mu.L of deionized water, 370. Mu.L of absolute ethyl alcohol and 30. Mu.L of 5% Nafion solution (Tianjin river Tian chemical engineering Co., ltd.) are weighed, mixed, sonicated for 4 hours to obtain a solution, 600. Mu.L of the solution is dropwise added on the surface of 1cm x 1cm carbon cloth, and naturally air-dried, so that the catalyst is loaded on the surface of the carbon cloth to serve as a working electrode, and a Saturated Calomel Electrode (SCE) and a graphite electrode (both purchased from Camad Tianjin chemical engineering Co., ltd.) are respectively used as a reference electrode and a counter electrode. The electrolysis process was carried out from-0.3V (RHE) to-1.1V (RHE) in an electrolyte solution, which is a mixture of water and KHCO 3, wherein the concentration of KHCO 3 is C M, and the values of the catalyst and C used are shown in the following table.
| Examples | Catalyst | C |
| Example 6 | Example 1 | 0.1 |
| Example 7 | Example 2 | 0.1 |
| Example 8 | Example 3 | 0.1 |
| Example 9 | Example 4 | 0.1 |
| Example 10 | Example 5 | 0.1 |
| Comparative example 2 | Comparative example 1 | 0.1 |
| Example 11 | Example 1 | 0.2 |
| Example 12 | Example 1 | 0.3 |
As can be seen from the results of the electrocatalytic reduction of CO 2 in comparative examples 6-8 and comparative example 2, the formation rate of CO (namely, the CO Faraday efficiency and FE CO) of the reduction product of CO 2 at the optimal overpotential of-0.6V (RHE) is reduced from 93% to 54% (FIG. 3 a), and the formation rate of H 2 (namely, the H 2 Faraday efficiency and FE H2) of the by-product generated by the electrolysis of H 2 O in examples 6-8 and comparative example 2 is increased from 7% to 62% (FIG. 3 b), which means that the nitrogen-carbon material obtained by 900 ℃ in example 6 is more favorable for reducing CO 2 to CO and reducing side reactions with water. The carbonization temperature is increased, the coking degree of the surface of the material is serious, the abundant pore structure is destroyed, and metal atoms are gathered on the surface of the material, so that the catalytic efficiency of the catalyst is reduced. This result also confirms that 900℃in example 1 is the optimal carbonization temperature.
As is evident from the results of the electrocatalytic reduction of CO 2 in comparative examples 6, 9, 10 and comparative example 2, the maximum FECO position for the three metal additions was-0.6V (RHE), but the FE CO of example 6 was highest (FIG. 4 a) and the corresponding FE H2 was lowest (FIG. 4 b) throughout the overpotential window. This is because the composition of the active center Fe-Nx is reduced when the Fe loading ratio is low, and the expected catalytic effect is not achieved; when the loading content of Fe is high, the metal atoms are gathered on the surface of the material due to the fact that Fe monoatoms have high specific surface energy, and the catalytic efficiency of the catalyst is reduced under both conditions. This also demonstrates that the electrocatalytic activity of the electrocatalytic reduction of CO 2 is best when the mass ratio of iron, biochar and water is 0.005:1:15, which is the optimal Fe addition for catalyst preparation.
As can be seen from the results of comparative examples 6, 11, 12 electrocatalytic reduction of CO 2, FE CO in the high potential region is significantly reduced (fig. 5 a) with an increase in electrolyte concentration, while the corresponding FE H2 is increased (fig. 5 b), possibly because with an increase in KHCO 3 concentration, other ions adsorb to the working electrode surface, and with an increase in potential, CO 2 is hindered from binding to protons, resulting in a decrease in FE CO. It was found by research that the 0.1M aqueous KHCO 3 solution showed less hydrogen evolution reaction than the other concentrations of electrolyte. Therefore, 0.1M KHCO 3 aqueous solution is most desirable as an electrolyte.
In order to investigate the conductivity of the catalyst, linear voltammetric characteristic measurements were performed on the nitrogen-carbon materials obtained in examples 1 to 3 and examples 4 to 5. The Linear Sweep Voltammetry (LSV) results are shown in fig. 6a and 6 b). As shown in fig. 6a, the conductivity of the monatomic iron-doped nitrogen-carbon material gradually decreased from example 1 to example 3 as the carbonization temperature increased, representing a decrease in maximum current density from 11 to 8.3mA cm -2, probably due to the decrease in the degree of densification of the monatomic iron-doped nitrogen-carbon material sintering with increasing temperature. The conductivities of the different iron mass percentages in the reaction are shown in fig. 6 b. With the mass ratio of iron, biochar and water from 0.001:1:15 (example 4) to 0.005:1:15 (example 1) the conductivity of the monatomic iron doped carbon nitride material gradually increased, exhibiting a maximum current density rise from 8.1 to 11mA cm -2. And when the mass ratio of iron, biochar and water is increased to 0.01:1:15 (example 5) there was no significant increase in conductivity of the nitrogen carbon material (maximum current density increased from 11 to 11.7mA cm -2).
The Tafel slope may describe the first electron transfer rate, the smaller the slope, the faster the initial electron transfer rate of CO 2. As shown in fig. 6c, the result shows that example 1 has a linear interval between 0.56V and 0.6V, the Tafel slope is 68mV dec -1, which is less than 13368mV dec -1 of comparative example 1, indicating that formation of related intermediates such as x COOH has higher kinetic rates when the overpotential is moderately increased.
The foregoing has described exemplary embodiments of the invention, it being understood that any simple variations, modifications, or other equivalent arrangements which would not unduly obscure the invention may be made by those skilled in the art without departing from the spirit of the invention.
Claims (7)
1. The application of a single-atom iron doped nitrogen-carbon material as a catalyst in improving the CO Faraday efficiency of electrocatalytic reduction of CO 2 is characterized in that the preparation method of the nitrogen-carbon material comprises the following steps: mixing ferric salt, biochar and water, drying at 10-105 ℃ until solid is formed, heating the solid to 300-650 ℃ and keeping the temperature for 1-3 h under the environment of inert gas or nitrogen, heating to 900-1100 ℃ and keeping the temperature for 1-2 h, and cooling to room temperature to obtain a nitrogen-carbon material, wherein the ratio of the ferric salt to the biochar to the water is (0.004-0.006) in parts by weight: 1:15.
2. Use according to claim 1, characterized in that the temperature rise rate of the solid to 300-650 ℃ is 2-10 ℃/min.
3. Use according to claim 2, characterized in that the rate of temperature rise to 900-1100 ℃ is 2-15 ℃/min.
4. The use according to claim 1, characterized in that the CO faraday efficiency is at most 93%.
5. The use according to claim 1, wherein the electrocatalytic reduction of CO 2 with a nitrogen carbon material as catalyst is: uniformly mixing 5-7 parts by weight of catalyst, 190-210 parts by volume of deionized water, 360-380 parts by volume of absolute ethyl alcohol and 20-40 parts by volume of 5% Nafion solution to obtain a solution, dripping the solution on the surface of carbon cloth, drying the solution to serve as a working electrode, putting the working electrode, a reference electrode and a counter electrode into electrolyte for electrolysis, wherein the overpotential is-0.4V to-0.8V, the electrolyte is a mixture of water and KHCO 3, the concentration of KHCO 3 in the electrolyte is 0.1-0.3M, the volume unit of the parts is mu L, the unit of the parts by weight is mg, and the overpotential is relative to RHE.
6. The use according to claim 5, wherein the electrolyte is a mixture of water and KHCO 3, and the concentration of KHCO 3 in the electrolyte is 0.1 to 0.15M.
7. The method according to claim 5, wherein the overpotential is from-0.5V to-0.7V.
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