A kind of MWCNT@Cu composite catalyst and its preparation method and applicationTechnical field
The invention belongs to electrochemical applications technical fields, and in particular to a kind of MWCNT@Cu composite catalyst and its preparation sideMethod and application.
Background technique
It is that acquisition hydrocarbon products one is important and environmentally friendly by electrochemically reducing carbon dioxide on copper electrodeMethod.It is interesting that copper be it is currently the only known, can be used as catalyst and these products played with the gold of catalytic actionBelong to, other metals cannot be used for identical reaction process.The activity and selectivity of this reaction is highly dependent on such as surfaceActive site, the factors such as mass transfer related with copper electrode size, form, porosity.By to monocrystalline crystal and nanometer materialPotential reaction mechanism may be better understood in the system research of material.However, the optimization of selectivity of product is still one severeChallenge.
In reduction CO2During, the reactivity and selectivity of copper electrode are strongly depend on crystal orientation, wherein Cu(111) be conducive to CO2It is reduced into CH4, Cu(100) be conducive to CO2It is reduced into C2H4.It is different with bulk phase catalyst, it receivesMeter level catalyst has biggish specific surface area, higher low the advantages that matching bit density and higher catalytic activity.For havingThe Cu of nano shape, it has been found that size is lower than the nano particle (NP) of 5nm, for the catalytic electrolysis reduction activation of carbon dioxideIt greatly increases, however due to increasing H using hydrocarbon selective depression as cost2Precipitation and CO formation.And sizeBiggish nano particle then observes that the selectivity of hydrocarbon is considerably higher.In the linear copper oxide catalyst of nanometer,Due to the influence of shape effect and pH value, to CH4Strong inhibition selectivity is shown, to C2H4And C2H6Selectivity increasedAdd.Cu(100) the Cu medium crystalline substance blocked is conducive to C2H4Generation.In polycrystalline copper film electroreduction carbon dioxide process, ethaneAlso it is accredited as secondary product.Result of study shows that the Cu nanometer foam with nanoscale hole, catalysis primary product haveHCOOH, H2And CO, in addition there are minimal amount of (< 2%) C3H6, CH4, C2H4And C2H6, this is also attributable to active material selectivityLimitation.In fact, the reactant diffusion of intermediate materials and again absorption are moderate phenomenon, in research nanometer rulerIt is needed when very little electrode system by research multistep reaction, with the selectivity of the different products of determination.In the reduction of carbon dioxideCheng Zhong leads to CH due to increasing a possibility that adsorbing again among CO when copper ion spacing reduces4And C2H4The selectivity of testIt increased.When studying nano-scale composite catalyzing system, it is necessary to fully consider above-mentioned factor.To have bigger serface,CO2Electroreduction activity Cu material will be a kind of very potential developing direction in conjunction with conductive carbon electrode supporter.Therefore, there is research to coat Cu on Vulcan carbon, graphene oxide and unjustified multi-walled carbon nanotube (MWCNT) respectively to receiveRice grain (NPs), to study its catalytic performance.In these researchs, largely, due to Cu nano particle (NPs) rulerVery little and preparation means differences, so as to cause the difference of the selectivity of catalysate.
It therefore, can send out a kind of when being catalyzed carbon dioxide reduction with preferable hydrocarbon selectivity and catalytic activityCopper catalyst has important research significance and application value.
Summary of the invention
It is an object of the invention to overcome in the prior art carbon dioxide reduction catalyst catalytic activity it is bad, nytronThe defect and deficiency of object poor selectivity provide a kind of MWCNT@Cu composite catalyst and its preparation method and application.Benefit of the inventionUse with nano-scale dimension, bigger serface carbon electrode as carrier, i.e., directly growth is independent on vitreous carbon, vertical arrangementMulti-walled carbon nanotube, and deposit one layer of thin polycrystalline copper on it and be used as shell, it is final to obtain the MWCNT@being arranged verticallyCu array.MWCNT@Cu composite catalyst provided by the invention can be used for being catalyzed reduction carbon dioxide, and there is preferable catalysis to liveProperty and hydrocarbon selectivity.
Another object of the present invention is to provide the preparation methods of above-mentioned MWCNT@Cu composite catalyst.
Another object of the present invention is to provide above-mentioned MWCNT@Cu composite catalysts in catalysis CO2Application in reduction.
For achieving the above object, the present invention adopts the following technical scheme:
A kind of MWCNT Cu composite catalyst, including grown on vitreous carbon multi-walled carbon nanotube that is independent, being vertically arranged andThe polycrystalline copper that magnetron sputtering deposits on the multi-walled carbon nanotube；The diameter of the multi-walled carbon nanotube is 10~300nm, lengthFor 100~5000nm, the distance between managing in array of multi-walled carbon nanotubes is 50nm or more.
Vitreous carbon and carbon nanotube are the carbon materials in terms of being widely used in electrochemical applications.Wherein vitreous carbon is a kind of heavyIt wants and efficient inert electrode material, is used usually as catalyst carrier.Carbon nanotube is a kind of nanoscale carbon material, toolThere are unique electronic property and excellent thermal stability, mechanical stability and chemical stability.By vitreous carbon and carbon nanotubeCombine, i.e., directly grow the multi-walled carbon nanotube of independent vertical arrangement on vitreous carbon, multi-wall carbon nano-tube can be obtainedThe full carbon electrode of pipe/glass carbon structure, this electrode can be used as further electrochemical applications.The present invention passes through on vitreous carbonThe multi-walled carbon nanotube for growing independent vertical arrangement ensure that the well-ordered of multi-walled carbon nanotube, it is ensured that charge transferHomogeneity；Meanwhile multi-walled carbon nanotube conductivity also with higher and chemical stability.The present invention is also by multi wall carbonOne layer of thin polycrystalline copper of nanotube surface sputtering sedimentation is used as shell, the final MWCNT@Cu array for obtaining vertical arrangementIn CO2Electric reduction catalyst.
Specifically, we can obtain higher current density and CH compared with plate copper catalyst4Selectivity.ThisOutside, the interval that is directly grown on glass carbon by Direct current plasma enhanced chemical vapour deposition DC-PECVD, vertical arrangementCarbon nanotube, it is ensured that its excellent conductivity, and as other carbon-carbon/carbon-copper composite materials, do not need adhesive.SeparatelyOne crucial benefit is vertical arrangement, it has the peak structure for increasing electric field, to surpass needed for reducing drive responsePotential.Finally, after CO extraction, the composition very close ideal " hydrogen alkane " composition, this be a kind of cleaning burning hydrogen/Natural gas mixture has the advantage for improving engine efficiency and reduced NOx emission.It means that our catalyst canFor electroreduction CO2To prepare hydrogen alkane.
The length of multi-walled carbon nanotube can be from 100nm to 5 μm.Shorter MWCNT is embedded in copper, and longer multi wall carbon is receivedThe coating of mitron the obstruction lower part MWCNT and glass carbon carrier.Void space between individual multi-walled carbon nanotube is 50nm or more(open end) greatly, advantageously forms sheet material.
In the present invention, the shell thickness of polycrystalline copper can be adjusted by the parameter of sputtering, and shell thickness is simultaneouslyDensity and length depending on multi-walled carbon nanotube.
Preferably, the diameter of the multi-walled carbon nanotube is 50~200nm, and length is 100~500nm, multi-wall carbon nano-tubeThe distance between pipe is 50~200nm in pipe array.
The preparation method of above-mentioned MWCNT@Cu composite catalyst, includes the following steps:
S1: by the method for Direct current plasma enhanced chemical vapour deposition, the orderly multi wall carbon of growth of vertical on vitreous carbonNano-tube array；
S2: copper sputtering sedimentation array of multi-walled carbon nanotubes surface described in S1 obtained using magnetron sputtering technique describedMWCNT@Cu composite catalyst.
In the present invention, the carbon of diameter a certain uniform diameters in 10~300nm can be used in array of multi-walled carbon nanotubesThe carbon nanotube of random size in the range also can be used in nanotube.Enhance chemical vapor deposition by direct-current plasmaLong-pending method is difficult to prepare smaller or bigger multi-walled carbon nanotube.The length of carbon nanotube passes through control growth time controlBetween 100~5000nm.Length of carbon nanotube is too short to be completely covered by polycrystalline copper, too long, be difficult in carbon nanotube lower partDivide uniformly coating Shell Materials.The distance between every carbon nanotube is maintained at 50nm or bigger, to ensure that one can be formedA grid.
Preferably, the array of multi-walled carbon nanotubes is placed in the position perpendicular to sputtering target in S2.
Sample is relative to sputtering target vertical alignment to eliminate shadow effect.
Preferably, make copper deposition by the way of direct current, exchange or radio-frequency sputtering in S2.
Preferably, the condition sputtered in S2 are as follows: sputtering pressure is 0.1 ~ 10Pa, and the gas of sputtering is inert gas argon.
Above-mentioned MWCNT@Cu composite catalyst is in catalysis CO2Application in reduction is also within the scope of the present invention.
Preferably, the CO2The product of reduction is hydrocarbon.
It is further preferable that the CO2The product of reduction is CO, CH4Or C2H6One or more of.With prior art phaseThan, the invention has the following beneficial effects:
The present invention ensure that multi-walled carbon nanotube by growing the multi-walled carbon nanotube of independent vertical arrangement on vitreous carbonIt is well-ordered, it is ensured that the homogeneity of charge transfer；Meanwhile multi-walled carbon nanotube conductivity also with higher and chemical stabilizationProperty.The present invention is also by the way that in one layer of thin polycrystalline copper of multi-wall carbon nano-tube pipe surface sputtering sedimentation, as shell, final acquisition is verticalThe MWCNT@Cu array of arrangement.MWCNT@Cu composite catalyst provided by the invention can be used for being catalyzed reduction carbon dioxide, toolThere are preferable catalytic activity and hydrocarbon selectivity.
Detailed description of the invention
Fig. 1 is Cu gusts of MWCNT@after (A) MWCNT and (B) sputtering sedimentation that the individual vertical that embodiment 1 provides arrangesThe scanning electron microscope (SEM) photograph of column；
Fig. 2 is to utilize DC-PECVD, the schematic diagram for the multi-walled carbon nanotube process that growth of vertical arranges on vitreous carbon；
Fig. 3 is to sputter Cu on the array of multi-walled carbon nanotubes surface of individual vertical arrangement on vitreous carbon, and deposition forms MWCNT@The schematic diagram of Cu composite catalyst；
Fig. 4 is the flow chart that MWCNT Cu elctro-catalyst is prepared by MWCNT array；
Fig. 5 be different materials linear polarisation curves (sweep speed be 2 mV/s-1)；
Fig. 6 be different materials current efficiency, wherein a) be MWCNT@Cu array of the vitreous carbon as carrier, MWCNT array,The current density of polycrystalline Cu film and original glass carbon (GC)；B) MWCNT array；It c) is copper film；D) it is produced for MWCNT@Cu arrayObject.
Specific embodiment
Below with reference to embodiment, the present invention is further explained.These embodiments are merely to illustrate the present invention rather than limitationThe scope of the present invention.Test method without specific conditions in lower example embodiment usually according to this field normal condition or is pressedThe condition suggested according to manufacturer；Used raw material, reagent etc., unless otherwise specified, being can be from the business such as conventional marketThe raw materials and reagents that approach obtains.The variation for any unsubstantiality that those skilled in the art is done on the basis of the present inventionAnd replacement belongs to scope of the present invention.
Embodiment 1
The present embodiment provides a kind of MWCNT Cu composite catalysts, including growing multi wall that is independent, being vertically arranged on vitreous carbonCarbon nanotube and the polycrystalline copper that magnetron sputtering deposits on the multi-walled carbon nanotube.
The MWCNT@Cu composite catalyst is prepared via a method which to obtain (such as Fig. 2 ~ 4).
S1: by the method for Direct current plasma enhanced chemical vapour deposition, orderly more of growth of vertical on vitreous carbonCarbon nanotube array (growth schematic diagram such as Fig. 2)；The electron microscope of the multi-walled carbon nanotube battle array such as Figure 1A；
S2: copper sputtering sedimentation described in S1 array of multi-walled carbon nanotubes surface (such as Fig. 3) is obtained using magnetron sputtering techniqueThe MWCNT@Cu composite catalyst.Electron microscope such as Figure 1B of the MWCNT@Cu composite catalyst.
Specifically, the diameter control of multi-walled carbon nanotube is in the range of 10 ~ 300nm in S1, by controlling growth time,The multi-walled carbon nanotube that length is 500nm is obtained, meanwhile, the control of the distance between pipe is in 50nm or more.
In S2, such as Fig. 4, array of multi-walled carbon nanotubes is placed in the position of vertical copper target, avoids that yin occurs in sputtering processShadow effect.Argon gas is passed through as protective gas, the length by controlling sputtering time controls the thickness of layers of copper, and sputtering terminates, obtainsTo MWCNT@Cu composite catalyst.
The performance of MWCNT@Cu composite catalyst provided in this embodiment is tested.
Such as Fig. 5, (sputtered on the MWCNTs@Cu composite catalyst, vitreous carbon on vitreous carbon identical negative for different materialsThe Cu film of load, the MWCNTs and glass carbon source materials that equal length, vertical arrangement are grown on vitreous carbon) linear polarization it is bentLine.Each dotted line is the take-off potential obtained by linear extrapolation.In Fig. 5 it is found that current potential needed for MWCNT@Cu is minimum.ThisIt is that its electric field expection can increase than plate material due to the one-dimensional material with sharp spike, for driving phase same electric fieldReaction needs less application potential.
Such as Fig. 6, the current efficiency of different materials.As can be known from Fig. 6, compared with the Cu film of plane sputtering, MWCNTs@CuOverall current density increase above 100%(Fig. 6 a), CH4The significant increase of selectivity, and the H from water electrolysis2By-product is reduced(Fig. 6 c and 6d).As reference, Fig. 6 b is the selectivity of original MWCNT product, it can be seen that no any hydrocarbon products generate.
In addition, can get 66 % CH when separating CO from the catalysate of MWCNT@Cu4With 34 % H2Gaseous mixture.For the composition very close to the ideal composition of " hydrogen alkane ", " hydrogen alkane " is a kind of hydrogen/natural gas mixtureCleaning burning, have very high engine efficiency and extremely low NOx emission.Therefore, when isolating CO from our productAfterwards, it can be used as " hydrogen alkane " use.
Above-described specific embodiment has carried out further the purpose of the present invention, technical scheme and beneficial effectsIt is described in detail, it should be understood that being not intended to limit the present invention the foregoing is merely a specific embodiment of the inventionProtection scope, all within the spirits and principles of the present invention, any modification, equivalent substitution, improvement and etc. done should all includeWithin protection scope of the present invention.