CN1972739A - Carbon nanotube pastes and methods of use - Google Patents

Abstract

Dispersable pastes comprising single-walled carbon nanotubes (SWNT) in water or in an organic solvent are prepared. The method of preparing the dispersable pastes comprises in general the following steps: a) removal of the catalyst used during the synthesis of SWNT; b) while the SWNT are still wet, addition of the appropriate amount of solvent, in a solvent/SWNT ratio which preferably varies between 30:1 and 100:1, depending on the desired viscosity of the paste; and c) high-energy horn sonication with a dismembrator probe. The resulting pastes are suitable for easy redispersion in solvents and incorporation in various matrices such as polymers. They are also suitable to be impregnated with metal precursors such as noble metal compounds for example, Pt. Appropriate drying and thermal treatments of the impregnated material produce metal-SWNT composites in which small metal clusters can be uniformly dispersed over the nanotube surface. These metal-SWNT composites may find applications as catalysts as well as electrodes for fuel cells, batteries, and capacitors.

Description

Carbon nanotube pastes and using method

Background of invention

Because the discovery of SWCN (SWNT), the application study of these unique material is increased fast.The a large amount of possible commerce of multiple SWNT sill coupling are used, and comprise polymer composites, Field Emission Display, capacitor and thermal management materials.Therefore, propose a large amount of different technology and made the SWNT sill.The current needs of these materials relate generally to research activities.Several Factors causes the observed delay of these activities being transferred to commercial application from the laboratory.At first, in this production phase, the expensive quantity that can be used for extensive development that limited of SWNT.Secondly, the processing that SWNT is intrinsic and disperse difficulty in these materials to make them in useful matrix, be combined into challenge.The incompatibility of SWNT and most of typical solvent has limited their effective processing and extensive use, because when placing water or most of organic solvent, nanotube settles out from suspension usually fast, even after strong ultrasonic processing.The 3rd, because the outstanding performance of CNT every day all occurs many new application, and every kind of application may all require different processing and dispersion process.Interesting is, although the performance of having only very small amount of nanotube just can be enough to be greatly improved in some applications, in other was used, the SWNT concentration of use may need high a lot.

Though independent SWNT has the ideal structure of sharp outline, they finish into the rope of different size, depend on the concrete synthetic and processing method that the manufacturer selects.Almost there is not the commercial sources of SWNT that their product can be used with various forms.For example, changed into the soot of the change of granularity that comprises the variable concentrations residual catalyst by commerce by the SWNT of arc discharge and laser ablation production.In other cases, SWNT is changed into suspension in liquid medium by commerce.First kind of effort of dissolving nanotube utilizes the possibility that shortens SWNT in the concentrated sulfuric acid-nitrate mixture by acid attack.But these rodent processing are indicated in and introduce bigger defective and the common unwanted amorphous carbon of quantity among the SWNT.Other products is introduced and to be helped the external elements that disperse.They comprise the chemical modification of nanotube and use wetting agent such as surfactant.

The most influential functionizing method is the method for exploitation such as Haddon.Wherein nanotube is dissolved in chloroform, benzene, toluene or other organic solvent in oxidation and after subsequently with thionyl chloride and octadecyl amine derivative.Another optional method utilizes the partial oxidation of SWNT, then sidewall and fluorine, alkane, diazol reaction or by ionic functionalization.The major defect of these methods is to make inevitably nanotube prototype structure and chemical composition distortion.

Other team have selected to adhere to soluble polymer to SWNT by the whole bag of tricks.For example, O ' Connell etc. has developed SWNT and has combined with straight chain polymer such as the non-covalent of polyvinylpyrrolidone and poly styrene sulfonate.The close interaction that produces between polymer and SWNT causes the suspending power of nanotube in water to increase.Zyvex has developed similar approach, but in this case, proposes as these inventors, and functionalized not relating to is aggregated the nanotube that thing wraps up, but the non-covalent bond between conjugated polymer and nanotube.The interaction that proposes between polymer backbone and the nanotube is because pi-pi bond closes.Although as if this specific solubilising effective to the deliquescent raising of nanotube, in order to disperse at least 30 minutes time of these material requires again, and can use " selection " organic solvent of limited quantity.

Surfactant also has been widely used in obtaining dense nanotube suspension.Thoroughgoing and painstaking work in each university has confirmed that the different surfaces activating agent is disperseing the validity in the single wall nano tube material.There is a large amount of the report to use the especially publication of lauryl sodium sulfate, neopelex and TRITON X.But,, therefore remove surfactant and just be a problem very much from nanotube because the strong Van der Waals between the hydrophobic end of nanotube surface and surfactant molecule interacts.In addition, the Cmax of acquisition SWNT is very low in these suspension.

People such as Smalley have proposed to use alewife as redispersible SWNT product.This product is by process for producing in liquid peracid such as oleum (high-concentration sulfuric acid) and other corrosive liquids.The major defect of this method is to need to handle harmful liquid.In addition, this aggregation can not form in anhydrous medium, and product of the present invention can prepare in aqueous medium or non-aqueous media, and is as described in greater detail below.

Obviously, producing the method for easy molten SWNT will be favourable greatly to the application and development of SWNT sill.Drawn the present invention for this reason.

The accompanying drawing summary

Fig. 1 is the TEM figure of Pt/SWNT sample, Pt heap(ed) capacity=10wt%.Sample (A) is by Pt tetramine precursor preparation, and sample (B) is by Pt chlordene precursor preparation.

Fig. 2 is the TEM microphoto by the Pt/SWNT sample of chloroplatinic acid salt preparation.Pt heap(ed) capacity=30wt%.(the relict catalyst form that the bulky grain among the figure is produced corresponding to SWNT).

Fig. 3 is by the TEM microphoto of the Pt/SWNT sample of chloroplatinic acid salt preparation under pH=8, Pt heap(ed) capacity=10wt%.

Fig. 4 is that 2%SWNT sticks with paste in 25 ℃ of following aqueous mediums viscosity is to shear rate.Go up and measure at 25mm cone and plate (cone angle=1 °).

Fig. 5 is that 2%SWNT sticks with paste in 25 ℃ of following aqueous mediums shear stress is to shear rate; Stress is spared change=0-600Pa; Total time=60 second (1 second at interval).

Fig. 6 be various SWNT stick with paste in 25 ℃ of following aqueous mediums viscosity to shear rate, go up and measure at 25mm cone and plate (cone angle=1 °).

Fig. 7 is that 2.7%SWNT sticks with paste in 25 ℃ of following aqueous mediums shearing is to shear rate; Equilibrium mode, Stress Control.

Fig. 8 is for showing the figure of ultrasonic processing time to the relation of the absorptivity of the freeze-drying SWNT of wet SWNT paste and non-paste.

Detailed Description Of The Invention

The present invention uses more available form with commerce the method and composition that has overcome existing treatment S WNT and the method defective of SWNT is provided is provided.Especially the present invention considers that SWNT concentration reaches and surpass the disperseed SWNT paste of 3wt%.This SWNT sticks with paste can be by long time stored, and then disperse and be incorporated in other system such as polymer, organic solution, the aqueous solution and the electrode.This SWNT sticks with paste (being also referred to as SWNT gel, SWNT dispersion or CNT dispersion herein) and comprises the unit for uniform suspension of SWCN in water or other solvent, it need not be by the chemical modification of nanotube, also need not add additive or external chemical agents and just can keep stablizing (do not precipitate or be separated).

In one embodiment, the present invention includes novel disperseed SWNT and stick with paste, it is included in the SWCN of water middle and high concentration.In water and with tubaeform broken instrument (dismembrator) ultrasonic processing mixture under high-energy and frequency, prepare the SWNT paste by introducing SWCN.Supersaturation occurs and form the SWNT paste up to handling to the SWCN of purifying by introducing water by high-energy ultrasonic.For one group of given preparation condition, the primary quantity that concentration that SWNT sticks with paste and viscosity depend on SWNT, initial water volume and ultrasonic processing time and the energy that adds.Use the less ultrasonic processing time and the higher initial adding water yield to form rarer paste (lower viscosity).The SWNT that produces sticks with paste can introduce CNT in other system such as polymer solution, surfactant solution or organic solvent, because the dispersiveness that nanotube is stuck with paste increases.

Have high viscosity because SWNT sticks with paste, so it is easy to handle and processing.The present invention can also form the SWNT paste in as isopropyl alcohol at other organic solvent such as dimethylbenzene, chlorobenzene, acetone, N-methyl pyrrolidone (NMP), dichloro-benzenes and alcohol.

The new SWNT of the present invention sticks with paste and shows a large amount of significant advantage that surpass other SWNT form.For example:

1.SWNT it is stable that paste is passed when storing in time.Even do not stir place several weeks after, do not observe yet and be separated.

Has even composition 2.SWNT stick with paste.

Need less energy consumption and time 3.SWNT stick with paste disperseing again in surfactant or organic solvent.Because hydrone is around bundle, therefore this material can easily be incorporated in the wet system.

4. compare with the drying nano pipe, the surface area that SWNT increased during SWNT stuck with paste is more suitable in the crucial application of exposed surface area it.

5. when the introducing nanotube is in water-soluble system, can avoid the use of toxic organic solvent such as toluene, THF or DMF.

6. handling a small amount of SWNT (milligram or following) no longer is much problems.

7. can apply SWNT with the form (lacquer shape) of viscous crude China ink sticks with paste as the coating on the plane surface.

8. because the high viscosity that SWNT sticks with paste, can avoid transporting with processing procedure in overflow.

In second kind of embodiment of the present invention, can use SWNT to stick with paste as the precursor of producing metal/SWNT composite.For example, the property list of SWNT reveals the great potential that improves the fuel cell electrode performance.Nanotube can be stablized high Pt dispersion (or other metal), increases the electronic conductivity in the electrode, improves the gas transmission in the electrode reaction layer and reduces ionomeric peroxide attack.

Although used multinomial technology to deposit the Pt particle in the past on CNT, method is simple and efficient as described herein for existing method neither one.Previously used method applies prior oxidation for utilizing nitric acid or similar oxidant to nanotube.For example, the method for people such as Lordi exploitation relies in rare ethylene glycol surface oxidation SWCN before the backflow Pt mineralization Pt particle.Similarly, used before the ion-exchange that is operated in the Pt ion that people such as Li describes and passed through HNO ₃/ H ₂SO ₄Erosion is to the chemical modification of multi-walled carbon nano-tubes.But well-known, acid attack causes the destruction of nanotube, begins from the tip and produces amorphous carbon.In addition, the technology instruction used of people such as Li deviates from the present invention.In the method that people such as Li describe, the scope of the pH of use makes surface charge have identical symbol with the electric charge of metal precursor ions.Although irrelevant with the preparation of fuel-cell catalyst, the interesting method of people such as Govindaraj exploitation utilizes vacuum vapor deposition Pt salt to insert the Pt nano wire in the SWNT capillary.The complexity of this method is that high vacuum atmosphere and Pt salt decompose required very high-temperature.

Therefore, with respect to previously presented other Pt-SWNT deposition, the present invention shows significant advantage.Most important advantage do not need to be the chemical modification (for example functionalized) of nanotube, therefore, has avoided unnecessary nanotube to destroy.Simultaneously, reduced time and the effort that long nanotube pre-treatment step consumes.

Embodiment

By embodiment each embodiment of summarizing is above described in more detail below.But the present invention is not restricted to embodiment provided by the invention.The following examples provide and have pasted the details that is equipped with, and have illustrated that wherein this material shows the application type of clear superiority than other SWNT material forms.By catalysis process (CoMoCAT ^TMSynthetic) obtain SWNT material used among the embodiment provided herein, catalysis process is developed by us, and produce high SWNT and form selectivity, it uses Co-Mo catalyst (illustrate that in for example United States Patent (USP) 6333016 and United States Patent (USP) 6413487 specially wherein each of introducing is as a reference in full for this paper).The carbon product that obtains in this method depends on Co: Mo than and prior to the catalyst treatment of nanotube growth.Adjusting these parameters allows the form and the corresponding nano tube structure of active catalyst bunch are carried out meticulous control.The nanotube that uses in the present embodiment has the average diameter of 0.8nm.But the present invention is not restricted to nanotube that use forms by this method or the nanotube with this average diameter.

In fluidized-bed reactor, on silicon dioxide carried bimetallic CoMo catalyst, carry out CoMoCAT ^TMSynthetic, by cobalt nitrate and ammonium heptamolybdate precursor preparation.Total metal heap(ed) capacity in the catalyst is 2wt%, Co: the Mo mol ratio is 1: 3.Before being exposed to the CO charging, at gas H ₂Heatable catalyst to 500 ℃ in the stream is heated to 850 ℃ again in the He that flows.In pure CO stream, under the 5atm gross pressure, carry out the CO disproportionated reaction then.The SWNT of growth keeps mixing with dead catalyst by this method, comprises silica supports and Co and Mo species.Remove silica and metal by two kinds of different purification process.

In order to determine of the influence of different purification process to the SWNT surface chemistry, remove at silica and to use in the process and compare two kinds of diverse ways, a kind of is alkaline, a kind of is acid.Before removing silica, raw material is placed in the baking oven under 250 ℃ 10 hours is retained in Co and Mo species in the product with oxidation, in hydrochloric acid (38% is pure), bathe ultrasonic processing then and remove metal oxide.Thorough rinsing solid material returns to neutrality up to testing pH with the pH test paper in nanopure water then.In case metal is removed, just remove silica supports by using acidity or basic treatment to dissolve.Under first kind of situation, grind composite and also join hydrofluoric acid (～33% is pure), ultra sonic bath (Cole Parmer, 168W, 50-60KHz) in 3 hours.Return to neutrality by removing hydrofluoric acid up to pH with the nanopure water cyclic washing.Similarly, in alkaline method, placed the second reply condensation material contact 10M NaOH 3 hours.Equally, use rinsing several times up to reaching neutral pH.

Embodiment 1: the preparation method that can disperse SWNT to stick with paste in the aqueous medium:

In glass container, reclaim the SWNT of purifying according to the method described above, be still wetly simultaneously, and add other deionized water.Then solution is applied the ultrasonic processing of very high-octane loudspeaker (using Fisher 550 Sonic Dismembrator) preset time.In this embodiment, the ultrasonic processing time is 1min, but is obtaining similar result in 10 seconds to 5 minutes time range.The best ultrasonic processing time is depended on the total amount of processed material, and can determine by the viscosity of observing slurry.Loudspeaker ultrasonic processor optimized frequency is 20KHz at least, and operates in the ceiling capacity scope of 60W-600W.The toughness (it also may be described to cream or slurry) that suspension black is stuck with paste is given in the combination that high-energy ultrasonic is handled and solution heats up.The ultrasonic processing method of this method before at least one importance is different from promptly is to be had wet condition by the SWNT of ultrasonic processing before the ultrasonic processing procedure of beginning.

Embodiment 2: the preparation method that can disperse SWNT to stick with paste in the organic media:

In glass container, reclaim the SWNT of purifying according to the method described above, be still simultaneously wet, and by with the organic solvent filtration washing up to removing residual water fully.The SWNT-solvent paste that obtains is transferred in the glass container, to wherein adding additional organic solvents, be provided at 100: 1-30: the SWNT/ ratio of solvent in 1 scope.Behind said process, apply the ultrasonic processing of high energy loudspeaker, up to forming thick paste.In this embodiment, nanotube bundle by organic solvent molecule rather than water ring around, this makes this paste be easy to be distributed in any organic media again.

Embodiment 3:Pt/SWNT Preparation of catalysts method:

The PZC of nanotube (point of zero electric charge) changes with purification process.When the pH of surrounding medium is lower than PZC, considers on nanotube surface, to take place proton and absorb the variation of soluble PZC.On the contrary, when pH is higher than PZC, the release of proton from the surface takes place.On the contrary, when pH is higher than PZC, the release of proton from the surface takes place.If further increase OH ^-Concentration, then produce negative electrical charge from the teeth outwards.According to the electric charge of the metal precursor ions of being paid close attention to, adjust pH on nanotube surface, to produce the electric charge of contrary sign.Then, the aqueous solution that in gel, adds metal precursor.Because the electrostatic attraction between charged nanotube and the precursor ion, metal absorbs on the nanotube surface rapidly.Ultrasonic then processing mixture makes the surface area maximum to open bundle, and makes the metal ion diffusion and deposit on the nanotube walls acquisition preferred metal dispersion.

Use wet SWNT to stick with paste and use Pt precursor impregnated carrier material, this is different from the Pt Preparation of Catalyst that metal precursor wherein is added into the typical carbon load on the dried carrier.The paste of preferred freeze-drying metal impregnation anhydrates to remove then.Freeze-drying process is also referred to as desivac, forms by removing to anhydrate in two steps from product, at first by distillation, then by desorb.Because freeze-drying process, the surface area that SWNT sticks with paste is saved.Change drying under environmental condition into if SWNT sticks with paste, then surface area is lost, and dry material is difficult to disperse again.Carry out freeze-drying process in freeze-drying apparatus, freeze-drying apparatus is made up of condenser, cooling system and the vavuum pump of the moisture that the hothouse with temperature control bottle, capture remove from product.

Behind drying material, the Pt/SWNT product that calcining obtains is handled under hydrogen stream then the Pt particle is reduced into metallic state with the decomposing metal precursor.Use an advantage of this dipping method (pasting use Pt precursor over) to be, compare, can obtain the dispersiveness of higher surface area and Geng Gao with any other method for preparing catalyst at nanotube.

In this particular example, the preparation concentrations of nanotubes is that the SWNT of the specified quantitative of about 10-30mg SWNT/ml water sticks with paste, and comprises the various batch of materials of 20mg SWNT at least so that have.Adjust the pH to 3 or 8 of every batch of material, depend on Pt precursor (H ₂PtCl ₆(chloroplatinic acid) and Pt (NH ₃) ₄(NO ₃) ₂(platinum nitrate four ammoniums)).In case adjust pH, just in nanotube is stuck with paste, add the Pt precursor aqueous solution of certain volume.The volume of the Pt solution that calculate to add is to provide 10 and the Pt content of 30wt% respectively.Under high-frequency and energy, use the ultrasonic processing mixture of the broken instrument of loudspeaker then.Behind ion exchange process, freeze-drying sample at first, and in air 300 ℃ of calcinings 2 hours down.At last at H ₂In at 120 ℃ of following reduction Pt oxides 1 hour.

As shown below, obtained to have deposit herein than the as many as 30wt%Pt of polymolecularity.The spectrum analysis of X-ray photoelectric is used for the surface concentration of the Pt of quantitative deposition on SWNT, the i.e. result of specific dipping method.The percentage of the Pt that exists on the SWNT surface is consistent well with the total amount of the Pt that is incorporated into mixture, means that the Pt of entire quantity is deposited on the nanotube.

X-radiation absorption fine-structure distribution (EXAFS) the results are shown in the table 1.Obtain the low ligancy (N) of the Pt-Pt key of SWNT paste electrode support.But, when on dry SWNT, depositing Pt by conventional initial wetting method, N _Pt-ptIncrease greatly.Therefore, the new method of using this paper to consider, the dipping of Pt will be more effective to higher dispersiveness.

Pt introducing method/carrier	Pt heap(ed) capacity (wt%)	R()	N pt-pt	σ 2( 2)
					Ion-exchange/SWNT sticks with paste initial wetting/dry powder	10 (amine precursors) 30 (amine precursor), 10 (amine precursors) 10 (amine precursor)	2.77 2.79 2.77 2.80	5.85 7.78 4.40 8.01	0.0036 0.0027 0.0039 0.0027

Table 1. is by the structural parameters (interatomic distance, R, ligancy, the N that load on the Pt particle on the SWNT of EXAFS assay determination _Pt-ptAnd the Debye-Waller factor, σ ²).

Fig. 1 and 2 has shown the TEM microphoto of the SWNT behind the deposition Pt particle.Final material comprises the heap(ed) capacity of 10wt% and 30wt% respectively, all has polymolecularity under two kinds of situations.Under the situation of Fig. 1, observe little particle to 1-2nm.In addition, the particle of the about 5-10nm of size is dispersed on the original nanotube.Fig. 2 shows that even the Pt heap(ed) capacity of 30wt%, it is very little that granularity still keeps, and dispersiveness is still very high.

Can to control improving one's methods of Pt particle dispersiveness by the pH that suitably adjusts medium in order confirming the invention provides, to have estimated the influence of before adding precursor, putting upside down pH.By this comparison, confirmed clearly that when nanotube surface shows the electric charge identical with Pt salt precursor repelling effect takes place, and this causes the bigger Pt particle size and the dispersiveness of poor (low).Low Pt dispersiveness is unfavorable for effective running of fuel cell electrode, causes low Pt utilization rate and has increased the cost of electrode.

As shown in Figure 3.The remarkable increase of granularity occurs in carries out PtCl under alkaline pH ₆ ^2-Deposition after, obviously surpass the PZC of nanotube.In addition, also find not exist the zone of Pt particle.

Embodiment 4: the preparation of fuel cell electrode:

Can realize the preparation of the fuel cell electrode stuck with paste based on Pt/SWNT by at least two kinds of optional methods that this paper discusses.In first method, paste dipping Pt at SWNT according to the method for describing among the top embodiment 3.Freeze-drying has the gained catalyst material of viscous crude China ink denseness to preserve high surface area.The material that calcining and reduction obtain is to obtain the Pt particle of high dispersive on the SWNT carrier.Membrane cell (PEM type) is preceding in that it is attached to, the Pt/SWNT solid that must resuspension obtains.Can obtain the Pt/SWNT catalyst suspension by mixing dry substance and NMP (N-N-methyl-2-2-pyrrolidone N-).

In order to obtain high operating efficiency, favorable mechanical need be arranged between catalyst material and film and electrically contact.In order to shift thin catalyst layer to film, can use " applique " method.Applique is the catalyst layer on substrate such as TEFLON.In this preparation method, the suspension that will comprise Pt/SWNT catalyst, ionomer such as NAFION and TEFLON is coated onto on the TEFLON substrate equably and stays slowly dry.After regulating membrane stage, arrive above it decal transfer and hot pressing between metallic plate.Peel off the TEFLON lining at last, catalyst layer remains fixed on the film simultaneously.The operating parameter of the preconditioning of the concentration of NAFION and TEFLON, applied pressure and film for using the known method of those of ordinary skills to optimize in the mixture at every kind of concrete catalyst material.Three-phase boundary (being also referred to as TPB) is the recombination site of generating electrodes reaction.The characteristic of this position is determined by catalyst structure.Therefore TPB length determined electro catalytic activity, and can be optimised by control metal granularity, metal heap(ed) capacity and ionomer quantity.

Ionomer is generally the dissolved form of dielectric film, adds or do not add adhesive such as TEFLON.By add ionomer on catalyst, electric charge shifts the interface and can extend in the electrode structure from the film surface.Perhaps, on film, directly introduce catalyst/ionomer mixture by " brushing " or " spraying " method.The deposition of ionomer on catalyst comes from slurry compositions.In this suspension, ionomer can just form aggregation, and its size and pattern have determined ionomeric thickness and three-dimensional structure on the catalyst.This structure is imported into from the metal surface proton and gaseous reactant and has been spread out of material impact.The diffusion of proton conduction and reactant and the product ionomer layer by covering metallic particles sometimes can determine the overall fuel cell performance.

In the second approach, paste dipping Pt at SWNT according to the method described above, this generation has the Pt/SWNT suspension of viscous crude China ink denseness.Opposite with first method, in the second approach, the viscous crude China ink is directly brushed on TEFLON substrate and NAFION ionomer and the TEFLON, carrying out the applique preparation method identical with first method, but without dry and Pt reduction step.Therefore, have to behind heat-press step process N-process, on applique, carry out the decomposition and the reduction step of Pt precursor.If in air, under enough temperature (for example 150 ℃), carry out hot pressing, then in this step, can finish the decomposition of Pt precursor.Subsequently, need in hydrogen stream, (for example about 135 ℃) handle sample to realize the Pt reduction.

In other embodiments, for example, also can in sticking with paste, SWNT add other metal such as Pd, Ru, Ni and Li, to form other metal/SWNT catalyst or composition by suitable metal precursor.

Embodiment 5: the viscosity measurement that dispersible SWNT sticks with paste in aqueous medium:

Prepare the concentration of CNT in water according to the method for describing among the embodiment 1 and change to a series of SWNT pastes of 2.7% from 1.4%.In glass container, reclaim SWNT, when still wetting, add other deionized water, obtain required concentrations of nanotubes according to the said method purifying.Then solution is applied the ultrasonic processing of very high-octane loudspeaker (use Fisher550SonicDismembrator) a few minutes up to reaching preferred paste denseness.

The rheology that 2%SWNT sticks with paste

2%SWNT several milliliters of 25 ℃ of BrookfieldR/S CPS P1 Rheometer tests of using down to have cone and plate (25mm diameter, 1 ° of cone angle) sticks with paste.Use is given birth to test result from the even sell of one's property of 0 to 600Pa stress.In 60 seconds with at interval read off in 1 second.For repeatability is carried out eight tests altogether.Fig. 4 has shown as the viscosity of shear rate function and shear stress.Notice interestingly, 2% nanotube content (98%) water only during SWNT sticks with paste, the increase that causes 40000 times of water viscosity in the low shear rate zone is (at 10s ^-1Down～40000cp).Curve shape demonstrates typical non newtonian and cuts rare behavior, and promptly viscosity reduces when shear rate increases.In addition, according to the observation under constant shear rate, SWNT sticks with paste and manifests slight thixotropy, and promptly viscosity is relevant with the time.Shear stress is provided among Fig. 5 the data and curves of shear rate.SWNT sticks with paste and follows Herschel-Bulkley (HB) model, and promptly the Bingham model is at the variant of plastic fluid.The Bingham plastic features is that shear rate is 0 o'clock non-0 shear strain.The Herschel-Bulkley model combines the influence of Bingham and power law behavior in the fluid, shown in equation (1):

τ＝τ ₀+A·γ ^b(1)

τ wherein ₀Be the HB yield stress, A is the HB plastic viscosity, and b is the HB yield index.As τ＜τ ₀The time, material keeps rigidity.For τ＞τ ₀, material flows as the power law fluid.The Bingham fluid shows the value of b=1.The fitting parameter that obtains by model is provided in the table 2.In this case, b=0.72 (b＜1), it departs from typical B ingham plastics, and corresponding to cutting rare Herschel-Bulkley model.This SWNT sticks with paste and be similar to various medium-viscosity food (sauce, salad dressing) and personal care product's (washing lotion) on rheology, and this makes it become the suitable material that is used for various application such as coating and lacquer.

1.4%, 2% and the comparison of the rheological behavior stuck with paste of 2.7%SWNT

Use several milliliters every kind paste of rheometer test same as described above down at 25 ℃.Under the equilibrium mode of proof stress, produce test result.According to the quantity of available sample, carry out the test several times of same sample for repeatability.Fig. 6 has compared three kinds of viscosity that different SWNT stick with paste under the shear rate influence.According to expectation arrives, and the viscosity of paste increases with the concentration of nanotube.Be important to note that, change, significant viscosity takes place change that this shows that this characterization technique is very responsive to little variation for very little concentrations of nanotubes.For example, get three kinds of pastes at 5000s ^-1Following viscosity number.1.4%, the 2% and 2.7% η value of sticking with paste is respectively 40cp, 80cp and 150cp.And the viscosity of paste reduces with shear rate, shows rare behavior of cutting.

Also obtain the value of the shear stress of various SWNT pastes to shear rate.For example, find the 2.7% yield stress (τ that sticks with paste ₀) be 576.27Pa, the shape of curve turns out to be the Herschel-Bulkley behavior from Fig. 7.Regression parameter is A=0.173 and b=0.674 (b＜1).When the concentration of nanotube reduced, the yield stress that SWNT sticks with paste reduced with denseness.Therefore, the τ that these SWNT stick with paste in the aqueous medium ₀Value from about 100 to 600Pa.

τ 0(Pa)	A(Pa·s)	b
			184.74	0.4553	0.7244

* regression parameter: B=0.9928, S=5.27

Table 2. has the analysis result according to the Herschel-Bulkley model of the SWNT paste of 2% nanotube in aqueous medium.

In one embodiment, SWNT sticks with paste has the viscosity of 0.001Pa.s-1000Pa.s, and wherein range of shear rate is 1000/s-10000/s, and concentrations of nanotubes is 0.1wt%-3wt%.In another embodiment, SWNT sticks with paste has the viscosity of 0.1Pa.s-10Pa.s, and wherein range of shear rate is 1000/s-4000/s, and concentrations of nanotubes is 1wt%-3wt%.

To be it be dissolved in the water after ultrasonic processing a few minutes one of the most remarkable characteristic that SWNT of the present invention sticks with paste (gel) easily.Fig. 8 has compared the speed of measuring by optical absorption by under the 800nm wavelength of disperseing again of having been stuck with paste by the dispersion again and the SWNT of the present invention of the non-paste sample of the nanotube of freeze-drying.Along with the existence that is dispersed in the nanotube in the water, absorbing increases.The difference that absorption gathers way is significant.In 2 minutes of ultrasonic treatment S WNT paste, because the big nanotube dispersion that SWNT sticks with paste, absorptivity has been that freeze-drying SWNT sample ultrasonic is handled the absorptivity that obtains after 25 minutes.Shorten to reach and specify the ultrasonic processing time of nanotube dispersion not only aspect operating time and the cost economic advantages being arranged, but also reduced may damage that in the high-energy ultrasonic processing procedure, cause nanotube by violent mechanical oscillation.

In one embodiment, the method that the present invention includes production CNT dispersion that this paper considers, comprise step: provide a certain amount of SWCN with wet condition, combination SWCN and solvent form nanotube-solvent mixture, and ultrasonic processing nanotube-solvent mixture comprises the supersaturation mixture of nanotube and solvent up to the mixture of ultrasonic processing under high frequency, this supersaturation mixture comprises the CNT dispersion, and wherein the CNT dispersion has the viscosity thicker than the nanotube-solvent mixture before the ultrasonic processing.High frequency can be 20KHz at least.Solvent can be for example water or organic solvent.The viscosity of CNT dispersion can be for example 0.001Pa.s-1000Pa.s, or 0.1Pa.s-10Pa.s.The present invention also comprises by the CNT dispersion of any one production of these methods and/or comprise the carbon nanotube product of CNT dispersion as herein described after the CNT dispersion is by freeze-drying.

The present invention also comprises the method that the metal-carbon nanotube is stuck with paste of producing, comprise and provide be dispersed in the SWCN in the solvent and have the CNT dispersion of sticking with paste the class denseness a certain amount of comprising, combination and mixing CNT dispersion and metal precursor solutions form nanotube-metal precursor mixture, with ultrasonic processing nanotube-metal precursor mixture with the metal ion diffusion that strengthens metal precursor with absorb on the CNT, form the metal-carbon nanotube and stick with paste.In the method, metal precursor can comprise at least a in for example platinum, palladium, ruthenium, nickel or the lithium.This method can comprise the additional step that freeze-drying metal-carbon nanotube is stuck with paste.This method can comprise the step of the metal-carbon nanotube paste of calcining freeze-drying.The pH that this method can comprise the nanotube of adjusting the CNT dispersion is to have the step with the electric charge of the opposite charge of the metal ion of metal precursor solutions.This method can comprise the additional step of the metal ion of reducing metal precursor.The present invention can comprise the metal carbon nanotube paste of any method production that shows by this paper.The present invention can comprise the fuel cell electrode that contains the metal-carbon nanotube paste of producing by any method shown in this article.Fuel cell electrode can comprise for example being the metal precursor of the precursor of platinum, palladium, ruthenium, nickel or lithium.

The present invention can comprise the method for producing the Pt-carbon nanotube pastes, comprise step: provide be dispersed in the SWCN in the solvent and have the CNT dispersion of sticking with paste the class denseness a certain amount of comprising, combination and mixing CNT dispersion and Pt precursor solution form nanotube-Pt precursor mixture, with ultrasonic processing nanotube-Pt precursor mixture with the Pt ions diffusion that strengthens the Pt precursor with absorb on the CNT, form the Pt-carbon nanotube pastes.This method can comprise the additional step of freeze-drying Pt-carbon nanotube pastes.This method can comprise the step of the Pt-carbon nanotube pastes of calcining freeze-drying.The pH that this method can comprise the nanotube of adjusting the CNT dispersion is to have the step with the electric charge of the opposite charge of the Pt ion of Pt precursor solution.This method can comprise reduces the additional step of Pt ion of carbon nanotube pastes.The present invention can comprise the Pt carbon nanotube pastes of any method production that shows by this paper.The present invention can comprise the fuel cell electrode that contains the Pt-carbon nanotube pastes of producing by any method shown in this article.

The present invention also comprises comprising and is dispersed in the SWCN in the solvent and has the CNT dispersion of sticking with paste the class denseness, during wherein when the combination of CNT dispersion and surfactant solution and with the ultrasonic processing of the ultrasonic device of the loudspeaker of 500-750W, after the ultrasonic processing in 5 minutes, the heavy suspension of SWCN in surfactant solution is provided, described heavy suspension is 50% of the heavy suspension of maximum obtainable SWCN in surfactant solution, wherein measures heavy suspension by the optical absorption under the 800-900nm wavelength.

The present invention also comprises the method that SWCN heavy suspension is provided, comprise providing to contain and be dispersed in the SWCN in the solvent and have the CNT dispersion of sticking with paste the class denseness, combination CNT dispersion and surfactant solution prepare nanotube-surfactant mixture, with the ultrasonic processing nanotube-surfactant mixture of the ultrasonic device of loudspeaker with 500-750W, wherein after ultrasonic processing in 5 minutes, the heavy suspension of SWCN in nanotube-surfactant mixture has the maximum of SWCN in nanotube-surfactant mixture can obtain at least 50% of heavy suspension, wherein measures the heavy suspension of SWCN by the optical absorption under the 800-900nm wavelength.

The present invention is not restricted to the scope of specific embodiments described herein, because this class embodiment is intended to one aspect of the present invention only is described, the embodiment of equivalence all within the scope of the invention on any function.In fact, except this paper show and describe those, the various changes of the inventive method are tangible to those technical staff in the above-mentioned specification field.

This paper specially be incorporated herein in full in list of references, patent or the publication of being quoted each as a reference.

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Claims (32)

1. method of producing the CNT dispersion comprises:

A certain amount of SWCN with wet condition is provided;

Make up this SWCN and solvent and form nanotube-solvent mixture; With

This nanotube-solvent mixture of ultrasonic processing comprises the supersaturation mixture of nanotube and solvent up to the mixture of ultrasonic processing under high frequency, this supersaturation mixture comprises the CNT dispersion, and wherein the CNT dispersion has the viscosity thicker than the nanotube-solvent mixture before the ultrasonic processing.

2. the process of claim 1 wherein that high frequency is 20KHz at least.

3. the process of claim 1 wherein that solvent is a water.

4. the process of claim 1 wherein that solvent is an organic solvent.

5. the process of claim 1 wherein that the viscosity of CNT dispersion is 0.001Pa.s-1000Pa.s.

6. pass through the CNT dispersion of the method production of claim 1.

7. the CNT dispersion of claim 6 has the viscosity of 0.1Pa.s-10Pa.s.

8. pass through the CNT dispersion of the method production of claim 3.

9. the CNT dispersion of claim 8 has the viscosity of 0.1Pa.s-10Pa.s.

10. pass through the CNT dispersion of the method production of claim 4.

11. the CNT dispersion of claim 10 has the viscosity of 0.1Pa.s-10Pa.s.

12. a carbon nanotube product comprises the CNT dispersion of the claim 1 after the CNT dispersion is by freeze-drying.

13. produce the method that the metal-carbon nanotube is stuck with paste, comprising for one kind:

Provide be dispersed in the SWCN in the solvent and have the CNT dispersion of sticking with paste the class denseness a certain amount of comprising, combination and mixing CNT dispersion and metal precursor solutions form nanotube-metal precursor mixture; With

Ultrasonic processing nanotube-metal precursor mixture spreads with the metal ion that strengthens metal precursor and absorbs on the CNT, forms the metal-carbon nanotube and sticks with paste.

14. the method for claim 13, wherein metal precursor comprises at least a in platinum, palladium, ruthenium, nickel or the lithium.

15. the method for claim 13 comprises the additional step that freeze-drying metal-carbon nanotube is stuck with paste.

16. the method for claim 15 comprises the step that the metal-carbon nanotube of calcining freeze-drying is stuck with paste.

17. the method for claim 13, the pH that comprises the nanotube of adjusting the CNT dispersion is to have the step with the electric charge of the opposite charge of the metal ion of metal precursor solutions.

18. the method for claim 13 comprises the additional step of the metal ion of reducing metal precursor.

19. stick with paste by the metal carbon nanotube that the method for claim 13 is produced.

20. the method for claim 13, wherein the CNT dispersion is the CNT dispersion of claim 1.

21. a fuel cell electrode comprises the metal carbon nanotube paste of producing by the method for claim 13.

22. the fuel cell electrode of claim 21, wherein metal precursor is the precursor of platinum, palladium, ruthenium, nickel or lithium.

23. a method of producing the Pt-carbon nanotube pastes comprises:

Provide be dispersed in the SWCN in the solvent and have the CNT dispersion of sticking with paste the class denseness a certain amount of comprising, combination and mixing CNT dispersion and Pt precursor solution form nanotube-Pt precursor mixture; With

Ultrasonic processing nanotube-Pt precursor mixture is with the Pt ions diffusion that strengthens the Pt precursor and absorb on the CNT, forms the Pt-carbon nanotube pastes.

24. the method for claim 23 comprises the additional step of freeze-drying Pt-carbon nanotube pastes.

25. the method for claim 24 comprises the step of the Pt-carbon nanotube pastes of calcining freeze-drying.

26. the method for claim 23, the pH that comprises the nanotube of adjusting the CNT dispersion is to have the step with the electric charge of the opposite charge of the Pt ion of Pt precursor solution.

27. the method for claim 23 comprises and reduces the additional step of Pt ion of carbon nanotube pastes.

28. the method for claim 23, wherein the CNT dispersion is the CNT dispersion of claim 1.

29. pass through the Pt carbon nanotube pastes that the method for claim 23 is produced.

30. a fuel cell electrode comprises the Pt-carbon nanotube pastes of producing by the method for claim 23.

31. a CNT dispersion comprises:

Be dispersed in the SWCN in the solvent, and have and stick with paste the class denseness, during wherein when the combination of CNT dispersion and surfactant solution and with the ultrasonic processing of the ultrasonic device of the loudspeaker of 500-750W, after the ultrasonic processing in 5 minutes, the heavy suspension of SWCN in surfactant solution is provided, described heavy suspension is that the maximum of SWCN in surfactant solution can obtain at least 50% of heavy suspension, wherein measures heavy suspension by the optical absorption under the 800-900nm wavelength.

32. the method that SWCN heavy suspension is provided comprises:

Provide to contain and be dispersed in the SWCN in the solvent and have the CNT dispersion of sticking with paste the class denseness;

Combination CNT dispersion and surfactant solution prepare nanotube-surfactant mixture; With

With the ultrasonic processing nanotube-surfactant mixture of the ultrasonic device of the loudspeaker of 500-750W, wherein after ultrasonic processing in 5 minutes, the heavy suspension of SWCN in nanotube-surfactant mixture is that the maximum of SWCN in nanotube-surfactant mixture can obtain at least 50% of heavy suspension, wherein measures the heavy suspension of SWCN by the optical absorption under the 800-900nm wavelength.

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