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2021-02-10 03:13
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2021年2月10日发(作者:时间不长)


3.



Results and discussion


Cyclic voltammogram (CV) of Pt electrodeposition on GC


electrode in 19.3 mM H2PtCl6/DESs solution at 80


?


C is shown in


Fig.


1


.


From


this


figure,


in


the


negative- going


potential


scan,it


can be clearly observed that two current peaks of reduction


occurred


at


near


?


0.93


V


and


?


1.29


V


(vs.


Pt),


in


comparison


with


the voltammogram (inset of


Fig. 1


) recorded on the same GC


substrate in DESs. X-ray photoelectron spectra (XPS) results


demonstrated


that


these


two


reduction


peaks


are


corresponding


to


the electrochemical reduction of Pt(IV) to Pt(II) and Pt(II) to


Pt(0), respectively (


Fig. S1 and Table S1 in supplementary


information


). This is consistent with the electrodeposition


behaviors of Pt in hydrophilic 1-n-butyl-3-methylimidazolium


tetrafluoroborate (BMIMBF4) and hydrophobic


1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6)


room- temperature ionic liquids


[36]


.



Fig. 2


a displays the typical SEM image of Pt nanoflowers


electrodeposited


on


GC


by


using


CV


method


in


19.3


mM


H2PtCl6/DESs


solution at 80


?


C. It can be seen that the Pt nanoflowers with


sharp


petals


were


homogeneously


formed,


and


their


size


was


about


200 nm. The crystal structure of Pt nanoflowers was further


investigated


by


high


resolution


transmission


electron


microscopy


(HRTEM).


Fig. 2


b shows the TEM image of a single Pt nanoflower,


and the inset is the corresponding selected area electron


diffraction (SAED) pattern, which indicates that the petals of


as- prepared


nanoflowers


possess


the


single-crystalline


structure.


The


HRTEM


image


of


a


petal


marked


in


Fig.


2


b


is


displayed


in


Fig.


2


c. The continuous fringe pattern further verifies the single


crystalline property of the petal. The lattice spacing of 0.23


nm agrees with the distancebetween two


{


1 1 1


}


planes of Pt. As


compared to other Pt nanoflowers and nanothorn assemblies


reported previously


[16



19 ,37]


, the unique characteristic of


as-prepared Pt nanoflowers is the formation of high density of


atomic


steps


at


the


edge


of


the


petals


(


Fig.


2


c),


which


are


crucial


for the enhanced activity of Pt nanoflowers toward ethanol


electrooxidation.


The


energy


dispersive


X-ray


spectroscopy


(EDX)


analysis of Pt nanoflowers confirms the presence of only Pt, C


and


O


elements


(


Fig.


2


d),


indicating


no


DESs


residue


on


the


surface


of Pt nanoflowers.


The effect of deposition conditions, namely,the precursor


concentration,CV number of cycle, scan rate and temperature on


the


size


and


morphology


of


Pt


nanostructures


electrodeposited


in


DESs


was


examined.


Fig.


3


shows


the


SEM


images


of


Pt


nanostructures


prepared


by


using


the


different


concentrations


of


H2PtCl6.


We


can


see that, at the H2PtCl6 concentration of 1.93 mM, the


quasispherical


Pt


NPs


were


formed


(


Fig.


3


a),


and


their


size


ranged


from 45 to 95 nm. When the H2PtCl6 concentration was 5 mM, the


flowerlike Pt NPs without sharp petals and several cubic Pt NPs


appeared


(


Fig.


3


b).


Further


increasing


the


H2PtCl6


concentration


to 10 mM,the sharp petals started to appear at the edge of the


Pt


nanoflowers


(


Fig.


3


c).


Finally,


the


perfect


Pt


nanoflowers


with


sharp petals were homogeneously formed at the H2PtCl6


concentration


of


19.3


mM


(


Fig.


3


d).


The


concentration


dependence


of the above Pt nanostructures maybe results from the high


viscosity of DESs


[25,26]


, which decreased the mass


transportation of reactive species in DESs, leading to the


difficult formation of Pt nanoflowers with sharp petals at the


lower H2PtCl6 concentration.


Among all deposition conditions, the CV number of cycle


exerts a leading influence on the process of particle growth.


Different Pt nanostructures generated by various CV number of


cycle were obtained, as shown in


Fig. 4


. Some irregular


quasi- spherical nanoparticles with low surface coverage were


produced in the lower CV number of cycle (


Fig. 4


a and b), which


acted as the nuclei for subsequently producing Pt nanoflowers


[17,19,38]


. Since the nucleation process is relatively slow and


irreversible, newly deposited Pt favors growing on the small Pt


cores


instead


of


generating


more


new


nuclei


[39]


.


Increasing


the


CV number of cycle would result in complex monodisperse


nanoflowers with more sharp petals and larger size (


Fig. 4


c).


Further


increasing


the


CV


number


of


cycle


to


80


cycles,the


perfect


Pt nanoflowers with sharp petals were formed on the GC substrate


(


Fig.


3


d).


When


the


CV


number


of


cycle


was


increased


to


100


cycles,


the aggregation phenomenon of Pt nanoflowers was observed (


Fig.


4


d). In addition, the scan rate plays important roles in the


electrodeposition of Pt owing to its possible influence on the


anisotropic growth of the lower scan rate of 1

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