CN113106470B - Vanadium-doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction and preparation method thereof - Google Patents
Vanadium-doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction and preparation method thereof Download PDFInfo
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- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 title claims abstract description 117
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 title claims abstract description 84
- 239000004408 titanium dioxide Substances 0.000 title claims abstract description 55
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 53
- 229910021389 graphene Inorganic materials 0.000 title claims abstract description 51
- 229910052757 nitrogen Inorganic materials 0.000 title claims abstract description 42
- 239000010411 electrocatalyst Substances 0.000 title claims abstract description 25
- 238000002360 preparation method Methods 0.000 title claims description 11
- 229910052720 vanadium Inorganic materials 0.000 claims abstract description 23
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 claims abstract description 23
- GNTDGMZSJNCJKK-UHFFFAOYSA-N divanadium pentaoxide Chemical compound O=[V](=O)O[V](=O)=O GNTDGMZSJNCJKK-UHFFFAOYSA-N 0.000 claims abstract description 14
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 10
- 238000010438 heat treatment Methods 0.000 claims description 32
- 239000000463 material Substances 0.000 claims description 28
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 claims description 20
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 18
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 17
- 239000003054 catalyst Substances 0.000 claims description 15
- 238000006243 chemical reaction Methods 0.000 claims description 10
- 239000011889 copper foil Substances 0.000 claims description 10
- 238000003756 stirring Methods 0.000 claims description 10
- 238000001035 drying Methods 0.000 claims description 9
- 238000001816 cooling Methods 0.000 claims description 8
- 229910052802 copper Inorganic materials 0.000 claims description 8
- 239000010949 copper Substances 0.000 claims description 8
- 239000002243 precursor Substances 0.000 claims description 8
- 239000000047 product Substances 0.000 claims description 8
- 238000001291 vacuum drying Methods 0.000 claims description 8
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 7
- 229910052739 hydrogen Inorganic materials 0.000 claims description 7
- 239000001257 hydrogen Substances 0.000 claims description 7
- YHWCPXVTRSHPNY-UHFFFAOYSA-N butan-1-olate;titanium(4+) Chemical compound [Ti+4].CCCC[O-].CCCC[O-].CCCC[O-].CCCC[O-] YHWCPXVTRSHPNY-UHFFFAOYSA-N 0.000 claims description 6
- 238000001354 calcination Methods 0.000 claims description 6
- 239000010453 quartz Substances 0.000 claims description 6
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 claims description 6
- 239000012085 test solution Substances 0.000 claims description 5
- 239000002131 composite material Substances 0.000 claims description 4
- 239000008367 deionised water Substances 0.000 claims description 4
- 229910021641 deionized water Inorganic materials 0.000 claims description 4
- 235000019441 ethanol Nutrition 0.000 claims description 4
- 238000001914 filtration Methods 0.000 claims description 4
- 238000010304 firing Methods 0.000 claims description 4
- 238000000227 grinding Methods 0.000 claims description 4
- 238000003760 magnetic stirring Methods 0.000 claims description 4
- 239000012299 nitrogen atmosphere Substances 0.000 claims description 4
- 239000012265 solid product Substances 0.000 claims description 4
- 238000009210 therapy by ultrasound Methods 0.000 claims description 4
- 238000001132 ultrasonic dispersion Methods 0.000 claims description 4
- 238000005406 washing Methods 0.000 claims description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 4
- 238000011049 filling Methods 0.000 claims description 2
- 239000007788 liquid Substances 0.000 claims description 2
- 230000015572 biosynthetic process Effects 0.000 abstract description 4
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- 238000005234 chemical deposition Methods 0.000 abstract 1
- 239000012808 vapor phase Substances 0.000 abstract 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 60
- 229910021529 ammonia Inorganic materials 0.000 description 26
- 238000006722 reduction reaction Methods 0.000 description 17
- 230000000052 comparative effect Effects 0.000 description 15
- PCKPVGOLPKLUHR-UHFFFAOYSA-N indoxyl Chemical group C1=CC=C2C(O)=CNC2=C1 PCKPVGOLPKLUHR-UHFFFAOYSA-N 0.000 description 10
- 238000004519 manufacturing process Methods 0.000 description 9
- 239000003792 electrolyte Substances 0.000 description 7
- 238000010531 catalytic reduction reaction Methods 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 4
- 238000000862 absorption spectrum Methods 0.000 description 4
- 239000007789 gas Substances 0.000 description 4
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000002835 absorbance Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000007772 electrode material Substances 0.000 description 3
- 239000002105 nanoparticle Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonia chloride Chemical compound [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 2
- 229910052580 B4C Inorganic materials 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 229920000557 Nafion® Polymers 0.000 description 2
- 238000001237 Raman spectrum Methods 0.000 description 2
- 229910021607 Silver chloride Inorganic materials 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 229910052796 boron Inorganic materials 0.000 description 2
- INAHAJYZKVIDIZ-UHFFFAOYSA-N boron carbide Chemical compound B12B3B4C32B41 INAHAJYZKVIDIZ-UHFFFAOYSA-N 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 239000001569 carbon dioxide Substances 0.000 description 2
- 229910002092 carbon dioxide Inorganic materials 0.000 description 2
- 230000003197 catalytic effect Effects 0.000 description 2
- 238000012512 characterization method Methods 0.000 description 2
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- 239000002135 nanosheet Substances 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 239000002096 quantum dot Substances 0.000 description 2
- YGSDEFSMJLZEOE-UHFFFAOYSA-N salicylic acid Chemical compound OC(=O)C1=CC=CC=C1O YGSDEFSMJLZEOE-UHFFFAOYSA-N 0.000 description 2
- HKZLPVFGJNLROG-UHFFFAOYSA-M silver monochloride Chemical compound [Cl-].[Ag+] HKZLPVFGJNLROG-UHFFFAOYSA-M 0.000 description 2
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical class [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 description 1
- 239000005708 Sodium hypochlorite Substances 0.000 description 1
- CVTZKFWZDBJAHE-UHFFFAOYSA-N [N].N Chemical compound [N].N CVTZKFWZDBJAHE-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 238000012271 agricultural production Methods 0.000 description 1
- 235000019270 ammonium chloride Nutrition 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000006555 catalytic reaction Methods 0.000 description 1
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- 150000001875 compounds Chemical class 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- XEYBHCRIKKKOSS-UHFFFAOYSA-N disodium;azanylidyneoxidanium;iron(2+);pentacyanide Chemical compound [Na+].[Na+].[Fe+2].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].[O+]#N XEYBHCRIKKKOSS-UHFFFAOYSA-N 0.000 description 1
- 238000003487 electrochemical reaction Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 239000004744 fabric Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 239000005431 greenhouse gas Substances 0.000 description 1
- 238000003837 high-temperature calcination Methods 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 238000011031 large-scale manufacturing process Methods 0.000 description 1
- 238000012417 linear regression Methods 0.000 description 1
- 238000011068 loading method Methods 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 239000011943 nanocatalyst Substances 0.000 description 1
- 150000002829 nitrogen Chemical class 0.000 description 1
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 239000013384 organic framework Substances 0.000 description 1
- FJKROLUGYXJWQN-UHFFFAOYSA-N papa-hydroxy-benzoic acid Natural products OC(=O)C1=CC=C(O)C=C1 FJKROLUGYXJWQN-UHFFFAOYSA-N 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 231100000614 poison Toxicity 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 229960004889 salicylic acid Drugs 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 239000001509 sodium citrate Substances 0.000 description 1
- NLJMYIDDQXHKNR-UHFFFAOYSA-K sodium citrate Chemical compound O.O.[Na+].[Na+].[Na+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NLJMYIDDQXHKNR-UHFFFAOYSA-K 0.000 description 1
- SUKJFIGYRHOWBL-UHFFFAOYSA-N sodium hypochlorite Chemical compound [Na+].Cl[O-] SUKJFIGYRHOWBL-UHFFFAOYSA-N 0.000 description 1
- 229940083618 sodium nitroprusside Drugs 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000002798 spectrophotometry method Methods 0.000 description 1
- 238000010186 staining Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 150000003464 sulfur compounds Chemical class 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 1
- 239000003440 toxic substance Substances 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
- C25B1/00—Electrolytic production of inorganic compounds or non-metals
Abstract
The invention discloses a vanadium doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction, which is prepared by dissolving vanadium pentoxide with sulfuric acid, participating in titanium dioxide synthesis with the dissolved vanadium solution, preparing graphene by a vapor phase chemical deposition method and compositing the graphene with vanadium doped titanium dioxide.
Description
Technical Field
The invention relates to the technical field of nitrogen reduction, in particular to a vanadium-doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction and a preparation method thereof.
Background
Ammonia is one of the most basic chemical raw materials in modern industry and agricultural production, and plays a vital role in the aspects of human production, living and the like. The industrial ammonia is prepared by combining nitrogen and hydrogen under the conditions of high temperature and high pressure and the presence of a catalyst by a Haber method, namely, the mixed gas consisting of the nitrogen and the hydrogen is the raw material gas of the synthetic ammonia. However, since the raw gas from the fuel industry contains sulfur compounds and oxides of carbon, which are toxic substances for the catalyst for synthesizing ammonia, a purification treatment is necessary before the synthesis of ammonia; and it also emits a large amount of carbon dioxide greenhouse gases in the case of consuming a large amount of energy to synthesize ammonia. Therefore, in order to solve the current serious energy and environmental problems, the search for sustainable alternative technology for producing ammonia by the Haber method industry has been attracting attention.
In recent years, electrocatalytic reduction of nitrogen is considered to be an eco-friendly and sustainable process that can directly convert nitrogen into ammonia with a catalyst under normal temperature and pressure conditions and achieve zero emission of carbon dioxide. CN110479379a discloses a covalent organic framework material catalyst based on Ru nano particles, a preparation method and application thereof, which uses high temperature calcination treatment to mix the prepared organic framework carrier powder with ruthenium metal salt and calcine again at high temperature, finally prepares an electrocatalyst of the covalent organic framework material loaded with Ru nano particles, but because the electrocatalyst is expensive in raw material, high in energy consumption and the like, the electrocatalyst is not suitable for industrial production and application in practice, and the catalyst is doped with only a small amount of Ru nano particles, so that the ammonia conversion efficiency of the material is not ideal. CN110028961B discloses a preparation method of boron carbide nano-sheet/boron doped graphene quantum dot and application of the preparation method in electro-reduction ammonia production, which compounds the boron carbide nano-sheet with boron doped graphene quantum dot which is mechanically stripped for many times to improve the activity of electro-catalytic nitrogen reduction, but the size of the graphene compounded by the method is very small and the synthesis is not easy to control, which results in difficult realization of large-scale production in industrial application. Based on this, it would be of great importance to design and develop a non-noble metal nitrogen reduction electrocatalyst with high activity.
Disclosure of Invention
The invention mainly aims to solve the problems and provides a vanadium-doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction and a preparation method thereof. The technical scheme adopted by the invention is as follows:
(1) Under magnetic stirring, dissolving vanadium pentoxide in hot sulfuric acid solution at 45-60 ℃, uniformly stirring, adjusting the pH to 1-2, then slowly adding tetrabutyl titanate under rapid stirring to obtain vanadium-doped titanium dioxide precursor, and then transferring the vanadium-doped titanium dioxide precursor into an oil bath kettle for heating to further promote the growth of titanium dioxide; after the reaction is finished, washing, filtering and vacuum drying the prepared solid product to obtain a vanadium-doped titanium dioxide material;
(2) Sequentially carrying out ultrasonic treatment on 1cm 2 of copper sheets by using ethanol and deionized water, drying, putting the dried copper sheets into a quartz boat, calcining in a tube furnace filled with nitrogen, closing the nitrogen, filling methane, and keeping the temperature for 30min; after the reaction is finished, closing methane and a power supply, cooling in flowing nitrogen atmosphere to obtain graphene deposited on the copper foil, and separating the graphene from the copper foil;
(3) Dispersing the graphene prepared in the step (2) into absolute ethyl alcohol, then adding the vanadium-doped titanium dioxide prepared in the step (1), performing ultrasonic dispersion for 20min, then transferring into a magnetic stirrer, and stirring for 1h; repeating the steps 1-3 times, and transferring the test solution into a vacuum drying oven for drying; and then placing the dried product in the central position of a tubular furnace after idle firing at 200 ℃ for 0.5-1h, introducing nitrogen to presintere for 20-30min, then introducing hydrogen to calcine, taking out the product after heating is finished and cooling to room temperature, and grinding and finely crushing to obtain the vanadium doped titanium dioxide material of the composite graphene.
Preferably, the molar ratio of vanadium pentoxide to tetrabutyl titanate in step (1) is (0.001-0.043): 1.
Preferably, the heating in the step (1) is heating at 180-200 ℃ for 6-12h.
Preferably, the calcination in the step (2) is to heat up to 1000 ℃ at a heating rate of 5 ℃/min and to heat at a constant temperature, wherein the flow rate of nitrogen is (100-200) mL/min; the methane flow rate is (10-20) mL/min.
Preferably, the mass ratio of the graphene to the vanadium-doped titanium dioxide in the step (3) is (0.01-0.1): 1.
Preferably, the drying temperature in step (3) is 60-80 ℃.
Preferably, the calcination in the step (3) is to heat up to 420-600 ℃ at a heating rate of 2 ℃/min, and then heat for 1-3 hours at constant temperature.
In the present invention, the separation of graphene from the copper foil may be performed by a method in the prior art, for example, a method described in patent application publication No. CN108439375A, to separate graphene from the copper foil.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
(1) The invention provides a vanadium doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction and a preparation method thereof, wherein vanadium is introduced into titanium dioxide by using an in-situ doping technology, high-quality and high-purity graphene is prepared by a chemical vapor deposition method, and finally the vanadium doped titanium dioxide/graphene electrocatalyst and the graphene electrocatalyst are compounded together by heat treatment.
(2) The work provides a nano catalyst which has great development potential and rich resources for electrochemical synthesis of ammonia, the catalyst successfully dopes vanadium into titanium dioxide, and vanadium with smaller atomic radius is utilized to rearrange the electronic structure of titanium oxide; the vanadium-doped titanium dioxide and the graphene are compounded later, so that the conductivity of the material is improved, the electron transmission efficiency in the electrochemical reaction process is accelerated, and the catalytic activity of the catalyst on electrochemical nitrogen reduction reaction is further enhanced.
Drawings
FIG. 1 is a Raman spectrum of the materials prepared in example 1 and comparative examples 1-2.
FIG. 2 (a) is a graph showing the current density of the electrode material prepared in example 1 over time at different potentials over 2 h; FIG. 2 (b) is an ultraviolet visible absorption spectrum corresponding to electrolytes at different potentials after staining with indoxyl indicator; FIG. 2 (c) is a graph of the UV-visible absorption spectrum of ammonia obtained at different potentials after indoxyl determination; FIG. 2 (d) is a calibration graph of the concentration of ammonia gas generated using indoxyl blue spectrophotometry.
FIG. 3 is a graph showing the ammonia production performance of the material prepared in example 1 in electrochemical catalytic reduction reactions at different potentials.
FIG. 4 is a graph showing the ammonia production performance of the materials prepared in example 1 and comparative examples 1-2 in electrochemical catalytic reduction at a potential of-0.5V.
Detailed Description
In order that the inventive aspects, features, and advantages of the present invention may be further understood, they are described by way of the following examples and comparative examples.
Example 1
The embodiment 1 of the invention provides a vanadium-doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction and a preparation method thereof, and the specific steps are as follows:
(1) Under magnetic stirring, 0.7mmol of vanadium pentoxide is dissolved in 50mL of hot sulfuric acid solution at 50 ℃, uniformly stirred and pH value is adjusted to 2; slowly adding 0.02mol of tetrabutyl titanate under rapid stirring to obtain vanadium-doped titanium dioxide precursor, transferring the vanadium-doped titanium dioxide precursor into an oil bath, and heating at 180 ℃ for 12 hours to further promote the growth of titanium dioxide; after the reaction is finished, washing, filtering and vacuum drying the prepared solid product to obtain a vanadium-doped titanium dioxide material;
(2) Sequentially carrying out ultrasonic treatment on a 1cm 2 copper sheet by using ethanol and deionized water, drying, putting the dried copper sheet into a quartz boat, placing the quartz boat into the central position of a tubular furnace, then introducing nitrogen at a rate of 150mL/min, heating to 1000 ℃ at a heating rate of 5 ℃/min, heating at a constant temperature for 30min, closing the nitrogen, introducing methane at a rate of 15mL/min, and keeping at a constant temperature for 30min; after the reaction is finished, closing methane and a power supply, cooling in flowing nitrogen atmosphere to obtain graphene deposited on the copper foil, and separating the graphene from the copper foil;
(3) Dispersing 60mg of graphene prepared in the step (2) into 100mL of absolute ethyl alcohol, then adding 1g of vanadium-doped titanium dioxide prepared in the step (1), performing ultrasonic dispersion for 20min, then transferring into a magnetic stirrer, and stirring for 1h; repeating the steps for 3 times, transferring the test solution into a vacuum drying oven, and heating for 6 hours at 80 ℃; and then placing the dried product in the central position of a tube furnace after idle firing at 200 ℃ for 1h, introducing nitrogen for presintering for 20min, then introducing hydrogen instead, heating to 500 ℃ at a heating rate of 2 ℃/min, heating at constant temperature for 3h, taking out the product after heating is finished and cooling to room temperature, and grinding and crushing to obtain the vanadium doped titanium dioxide material of the composite graphene.
Example 2
The embodiment 2 of the invention provides a vanadium-doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction and a preparation method thereof, and the specific steps are as follows:
(1) Under magnetic stirring, 0.5mmol of vanadium pentoxide is dissolved in 50mL of hot sulfuric acid solution at 50 ℃, uniformly stirred and pH value is adjusted to 2; slowly adding 0.02mol of tetrabutyl titanate under rapid stirring to obtain vanadium-doped titanium dioxide precursor, transferring the vanadium-doped titanium dioxide precursor into an oil bath, and heating at 180 ℃ for 12 hours to further promote the growth of titanium dioxide; after the reaction is finished, washing, filtering and vacuum drying the prepared solid product to obtain a vanadium-doped titanium dioxide material;
(2) Sequentially carrying out ultrasonic treatment on a 1cm 2 copper sheet by using ethanol and deionized water, drying, putting the dried copper sheet into a quartz boat, placing the quartz boat into the central position of a tubular furnace, then introducing nitrogen at a rate of 150mL/min, heating to 1000 ℃ at a heating rate of 5 ℃/min, heating at a constant temperature for 30min, closing the nitrogen, introducing methane at a rate of 15mL/min, and keeping at a constant temperature for 30min; after the reaction is finished, closing methane and a power supply, cooling in flowing nitrogen atmosphere to obtain graphene deposited on the copper foil, and separating the graphene from the copper foil;
(3) Dispersing 25mg of graphene prepared in the step (2) into 100mL of absolute ethyl alcohol, then adding 1g of vanadium-doped titanium dioxide prepared in the step (1), performing ultrasonic dispersion for 20min, then transferring into a magnetic stirrer, and stirring for 1h; repeating the steps for 3 times, transferring the test solution into a vacuum drying oven, and heating for 6 hours at 80 ℃; and then placing the dried product in the central position of a tube furnace after idle firing at 200 ℃ for 1h, introducing nitrogen for presintering for 20min, then introducing hydrogen instead, heating to 500 ℃ at a heating rate of 2 ℃/min, heating at constant temperature for 3h, taking out the product after heating is finished and cooling to room temperature, and grinding and crushing to obtain the vanadium doped titanium dioxide material of the composite graphene.
Comparative example 1
The comparative example 1 of the present invention differs from example 1 in that it is not composited with graphene, i.e., only one vanadium-doped titanium dioxide material was prepared.
Comparative example 2
The comparative example 2 differs from example 1 in that it is not complexed with graphene and is not vanadium doped, i.e. only one titania material is prepared.
1. Characterization analysis of materials
FIG. 1 shows the Raman spectra of the materials prepared in example 1 and comparative examples 1-2. As can be seen from fig. 1, the material prepared in example 1 shows typical D and G peaks near 1300cm -1 and 1580cm -1, which is attributable to the incorporation of graphene, and the diffraction peaks of titanium dioxide are weakened or even masked due to the too great intensities of D and G peaks. Whereas the materials prepared in comparative examples 1 and 2, which were not composited with graphene, had 4 similar titanium dioxide characteristic peaks, and the two were only slightly different in peak positions, probably due to the too small vanadium doping amount of the material prepared in comparative example 1. And it was also found that the diffraction peak of the material prepared in comparative example 1 had a significant blue shift in the peak position compared to comparative example 2, which was attributable to the increase in vibration energy due to vanadium-doped titanium dioxide, and thus the shift in the characteristic peak of titanium dioxide.
2. Electrochemical nitrogen reduction ammonia production experiment
The experimental device is carried out in a two-chamber electrolytic cell filled with 0.1mol/L hydrochloric acid liquid of saturated nitrogen, wherein a Nafion 117 membrane separates a cathode chamber from an anode chamber, an air inlet and an air outlet are also arranged in the cathode chamber, the air inlet of the cathode chamber is connected with a nitrogen introducing device, and the air outlet of the cathode is connected with a gas collecting device. Dispersing 5mg of catalyst material prepared by the technical scheme into a mixed solution of 1mL of absolute ethyl alcohol and 5% Nafion, and then coating 0.02mL of catalyst slurry onto 1cm 2 of carbon cloth and drying to serve as a working electrode for standby; then the working electrode and the silver/silver chloride reference electrode are placed in the cathode chamber electrolyte, the platinum sheet counter electrode is placed in the anode chamber electrolyte, then the three electrodes are connected through a lead, electrochemical catalytic reduction reaction is respectively carried out under the potential of-0.4V, -0.45V, -0.5V, -0.55V, -0.6V through an electrochemical workstation (the working voltage is set to-1V to 0.1V, the scanning speed is set to 10 mV/s), and finally the collected ammonia gas is collected and detected through the outlet of the cathode chamber. And the potential of the present invention has been calibrated to the reversible hydrogen electrode potential RHE; e (vs. rhe) =e (vs. ag/AgCl) +0.059×ph+0.197V, the current density of which can be normalized to geometric surface area, as shown in particular in fig. 2.
FIG. 2 (a) shows a current density curve of the electrode material prepared in example 1 over time at a potential of from-0.4 to-0.6V over 2 hours; fig. 2 (b) shows the uv-visible absorption spectra of the electrolyte corresponding to different potentials, which was stained with indoxyl indicator. As can be seen from fig. 2 (b), the highest characteristic peak of uv absorption of the electrolyte at different potentials appears at-0.50V, which suggests that the electrode material tested under-0.50V conditions may have the best electrochemical performance.
(1) Determination of Ammonia gas
The ammonia gas produced by electrochemical nitrogen reduction of the catalyst of example 1 was measured spectrophotometrically by indoxyl blue method, and the specific procedure is as follows: 2mL of electrolyte was obtained from the cathode chamber and mixed with 2mL of 1mol/L sodium hydroxide solution containing 5% salicylic acid, 5% sodium citrate; then 1mL,0.05mol/L sodium hypochlorite and 0.2mL,1mol/L sodium nitroprusside were added to the above solution for 2 hours; finally, measuring the absorbance of the test solution at 655nm wavelength by using an ultraviolet-visible absorption spectrum (figure 2 c); the concentration-absorbance curve of ammonia was then calibrated using standard ammonium chloride solution (fig. 2 d). A fitted curve of absorbance values versus ammonia concentration can be obtained with a linear equation of y=0.846 x-0.067 and r 2 =0.998.
(2) Calculation of Ammonia yield
The ammonia production was calculated using the following equation: [ NH 3]＝V×[NH3 ]/(m x t). Wherein [ NH 3 ] can calculate the measured ammonia concentration through a linear regression equation, V is the volume of the cathode reaction electrolyte, t is the applied potential time, and m is the catalyst loading.
FIG. 3 shows the yield of ammonia gas under electrochemical catalytic reduction of the catalyst of example 1 at-0.4V, -0.45V, -0.5V, -0.55V, -0.6V potentials, respectively, wherein the concentration of ammonia gas collected at the corresponding potentials is 0.12. Mu.g/h, 0.15. Mu.g/h, 0.18. Mu.g/h, 0.16. Mu.g/h, 0.15. Mu.g/h (both valid digits are reserved); it is further possible to obtain an ammonia amount of 18. Mu.g/h, 22.5. Mu.g/h, 27. Mu.g/h, 24. Mu.g/h, 22.5. Mu.g/h, respectively, per unit mass of the catalyst in the catalytic system under electrochemical catalytic reduction at-0.4V, -0.45V, -0.55V, -0.6V potential. It was found that the catalyst gave maximum ammonia production (27. Mu.g/h) at-0.50V, which is consistent with the UV analysis spectral characterization of FIG. 2 (b). In order to further characterize the excellent electrochemical reduction nitrogen ammonia production performance of the materials, the materials prepared in comparative examples 1-2 were also subjected to electrochemical reduction nitrogen catalytic reaction, the experimental procedure was the same as in example 1, and the yield of ammonia gas under electrochemical catalytic reduction reaction at-0.5V was compared, and the specific data are shown in FIG. 4.
As can be seen from FIG. 4, the vanadium doped titanium dioxide electrocatalyst prepared in comparative example 1 has a relatively small ammonia production (12.3. Mu.g/h) compared to the vanadium doped titanium dioxide/graphene electrocatalyst prepared in example 1, whereas the titanium dioxide electrocatalyst prepared in comparative example 2 only produces a small amount of ammonia (1.65. Mu.g/h). This further illustrates that vanadium doped titania and graphene complexing significantly improves the activity of electrocatalytic ammonia reduction to produce ammonia.
The various materials listed in the present invention, as well as the values of the upper and lower intervals of the various materials of the present invention, and the values of the upper and lower intervals of the process parameters (e.g., temperature, time, etc.), are all capable of carrying out the present invention, and examples are not meant to be limiting. While the invention has been described with respect to the preferred embodiments, it will be understood that the invention is not limited thereto, but is capable of modification and variation without departing from the spirit of the invention. Such modifications and variations are also considered to be a departure from the scope of the invention.
Claims (8)
1. The preparation method of the vanadium-doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction is characterized by comprising the following steps of:
(1) Under magnetic stirring, dissolving vanadium pentoxide in hot sulfuric acid liquid at 45-60 ℃, uniformly stirring, adjusting the pH to 1-2, then slowly adding tetrabutyl titanate under rapid stirring to obtain vanadium-doped titanium dioxide precursor, and then transferring the vanadium-doped titanium dioxide precursor into an oil bath kettle for heating to further promote the growth of titanium dioxide; after the reaction is finished, washing, filtering and vacuum drying the prepared solid product to obtain a vanadium-doped titanium dioxide material;
(2) Sequentially carrying out ultrasonic treatment on 1cm 2 of copper sheets by using ethanol and deionized water, drying, putting the dried copper sheets into a quartz boat, calcining in a tube furnace filled with nitrogen, closing the nitrogen, filling methane, and keeping the temperature for 30min; after the reaction is finished, closing methane and a power supply, cooling in flowing nitrogen atmosphere to obtain graphene deposited on the copper foil, and separating the graphene from the copper foil;
(3) Dispersing the graphene prepared in the step (2) into absolute ethyl alcohol, adding the vanadium-doped titanium dioxide prepared in the step (1), performing ultrasonic dispersion for 20min, transferring into a magnetic stirrer, stirring for 1h, repeating for 1-3 times, and transferring the test solution into a vacuum drying oven for drying; then placing the dried product in the central position of a tubular furnace after idle firing for 0.5-1 h at 200 ℃, introducing nitrogen to presintere for 20-30 min, then introducing hydrogen to calcine instead, taking out the product after heating is finished and cooling to room temperature, and grinding and finely crushing to obtain the vanadium-doped titanium dioxide material of the composite graphene; the mass ratio of the graphene to the vanadium-doped titanium dioxide is (0.01-0.1): 1; the calcination is to heat up to 420-600 ℃ at a heating rate of 2 ℃/min, and then heat for 1-3 h at constant temperature.
2. The method for preparing the vanadium doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction according to claim 1, wherein the molar ratio of vanadium pentoxide to tetrabutyl titanate in step (1) is (0.001-0.043): 1.
3. The method for preparing the vanadium doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction according to claim 1, wherein the heating in step (1) is performed at 180-200 ℃ for 6-12 hours.
4. The method for preparing the vanadium doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction according to claim 1, wherein the calcining in step (2) is performed by heating to 1000 ℃ at a heating rate of 5 ℃/min and heating at a constant temperature.
5. The method for preparing the vanadium doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction according to claim 1, wherein the flow rate of nitrogen in step (2) is (100-200) mL/min.
6. The method for preparing the vanadium doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction according to claim 1, wherein the methane flow rate in step (2) is (10-20) mL/min.
7. The method for preparing the vanadium doped titanium dioxide/graphene electrocatalyst suitable for electrochemical nitrogen reduction according to claim 1, wherein the drying temperature in step (3) is 60-80 ℃.
8. A vanadium doped titania/graphene electrocatalyst suitable for electrochemical nitrogen reduction, characterised in that the catalyst has been prepared by a method according to any one of claims 1 to 7.
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