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1、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 near0.93 V and 1.2
2、9 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), respectivel
3、y (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.
4、 Fig. 2a 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 w
5、as further investigated by high resolution transmission electron microscopy (HRTEM). Fig. 2b 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 sing
6、le-crystalline structure. The HRTEM image of a petal marked in Fig. 2b is displayed in Fig. 2c. 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
7、nanoflowers and nanothorn assemblies reported previously 1619,37, the unique characteristic of as-prepared Pt nanoflowers is the formation of high density of atomic steps at the edge of the petals (Fig. 2c), which are crucial for the enhanced activity of Pt nanoflowers toward ethanol electrooxidatio
8、n. The energy dispersive X-ray spectroscopy (EDX) analysis of Pt nanoflowers confirms the presence of only Pt, C and O elements (Fig. 2d), indicating no DESs residue on the surface of Pt nanoflowers. The effect of deposition conditions, namely,the precursor concentration,CV number of cycle, scan rat
9、e 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 wer
10、e formed (Fig. 3a), 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. 3b). Further increasing the H2PtCl6 concentration to 10 mM,the sharp petals started to appear at the edge of the Pt
11、nanoflowers (Fig. 3c). Finally, the perfect Pt nanoflowers with sharp petals were homogeneously formed at the H2PtCl6 concentration of 19.3 mM (Fig. 3d). The concentration dependence of the above Pt nanostructures maybe results from the high viscosity of DESs 25,26, which decreased the mass transpor
12、tation 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 b
13、y 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. 4a and b), which acted as the nuclei for subsequently producing Pt nanoflowers 17,19,38. Since the nucleation pro
14、cess 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. 4c). Further increasing the CV n
15、umber of cycle to 80 cycles,the perfect Pt nanoflowers with sharp petals were formed on the GC substrate (Fig. 3d). When the CV number of cycle was increased to 100 cycles, the aggregation phenomenon of Pt nanoflowers was observed (Fig. 4d). In addition, the scan rate plays important roles in the el
16、ectrodeposition of Pt owing to its possible influence on the anisotropic growth of nanoparticles.At the lower scan rate of 1 mV s1, the rough nanosheets formed on the top of Pt nanostructures (Fig. S2 in supplementary information). Further increasing the scan rate would result in the growth of Pt nanoflowers with sharp petals. It is worthwhile noting thatall electrodeposition processes discussed above were carried outat 80 C, when the
