Ionic liquid-mediated synthesis of unique PtPd bimetallic particles with tiny subunits for efficient electrocatalytic and catalytic applications

Abstract

Ionic liquids provide chemists with a versatile platform and many opportunities for constructing various interesting inorganic materials. Here, an ionic liquid-mediated synthesis route is proposed for the controlled synthesis of PtPd bimetallic particles. The synthesized PtPd particles have unique three dimensional nanostructures (3D) constructed by nanoparticle subunits. For the 3D nanostructures, the primary PtPd particles form aggregates with the characteristic of interparticle porosity. Among others, the Pt₁Pd₁ bimetallic particles exhibit superior electrocatalytic activity toward oxidation of methanol in an alkaline medium than the commercial state-of-the-art Johnson-Matthey platinum black catalyst (Hispec™ 1000). Furthermore, the catalytic activity towards p-nitrophenol reduction indicates that the synthesized Pt₁Pd₃ particles exhibit the highest catalytic activity in comparison with the studied various PtPd bimetallic particles, the monometallic Pt and the monometallic Pd particles. This study may pave the way for the efficient synthesis of three dimensional bimetallic nanostructures for improved catalytic applications.

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Introduction

Size, morphology and composition are the vital factors in determining optical, electronic, magnetic and catalytic properties of noble metal nanocrystals.^1–4 Bimetallic particles usually exhibit improved properties in electronics, catalysis, and electrocatalysis in comparison with the monometallic counterparts due to the synergistic effect of elements.^5–10 Among the studied bimetallic particles, PtPd bimetallic particles are particularly attractive for catalyzing multiple reactions as a result of the presence of the powerful catalytic components of Pt and Pd.^11–14 For example, PtPd nanostructures have exhibited promising catalytic capability toward the methanol oxidation reaction due to the synergism between Pt and Pd.^15,16 Until now, various PtPd nanostructures, including nanodendrites,^17,18 tetrahedrons,¹⁹ nanotubes,²⁰ triangular nanoplates²¹ and nanocubes²² have been prepared by different synthesis routes. Upon the open literatures, the synthesis of PtPd particles with three dimension (3D) nanostructures is still challenging. In comparison with other kinds of nanostructures, 3D nanostructures with nanoparticle subunits not only possess high surface area but also avoid the aggregation-resulted deactivation encountered by most of the nanoparticle catalysts. Therefore, the synthesis of PtPd particles with 3D nanostructure is highly demanded in consideration that such structure might be promising candidate for the catalytic applications.

Recently, ionic liquids have attracted great attention for the synthesis of inorganic particles due to their unique chemical and physical properties such as high solubilizing power and low vapor pressure.^23–27 Specifically, inorganic synthesis in ionic liquids occasionally leads to materials that are difficult to achieve by using other synthesis routes.^28,29 In the previous reported researches, ionic liquids have already been used as an environmental benign solvent, as a crystal growth modifier, or as an reactant precursor for the fabrication of inorganics.^30–35 The reported works have demonstrated that ionic liquids can provide the chemists with a versatile platform for constructing various inorganic materials.³⁶ The ionic liquids thus add great values to the inorganic materials community.

In our recent work, we reported a facile route for the synthesis of AuPd and AuPt bimetallic particles with the assistance of the imidazolium-based ionic liquids.^37,38 The successful synthesis of these bimetallic particles indicates ionic liquid-assisted route might be very promising for fabrication of efficient bimetallic catalysts. However, our previous synthesized AuPd and AuPt particles are in micrometer scale. This is because the short carbon chain in the studied ionic liquids cannot have a better modification for the formation of small particles. In order to synthesize bimetallic particles with small size, it is of great interest to perform the synthesis with ionic liquid possessing long carbon chain in the cation. Herein, we report on the synthesis of PtPd bimetallic particles with the assistance of the ionic liquid 1-decyl-3-methyl imidazolium chloride (DMIMCl) which possesses long carbon chain. Interestingly, primary PtPd particles form aggregates with the characteristic of interparticle porosity, resulting in small 3D PtPd particles with tiny nanoparticles as the subunits. The PtPd particles exhibit excellent electrocatalytic and catalytic activities toward methanol electro-oxidation and p-nitrophenol reduction.

Experimental section

Materials

Na₂PtCl₆·6H₂O, K₂PdCl₄ and NaBH₄ were purchased from Aladdin Industrial Corporation. 1-Decyl-3-methyl imidazolium chloride (DMIMCl) was purchased from Lanzhou Greenchem ILS, LICP, CAS, China. Johnson-Matthey platinum black catalyst (Hispec™ 1000) was purchased from Alfa Aesar. Nafion solution was purchased from Sigma-Aldrich. All the regents were used without further purification.

Synthesis

In a typical synthesis of Pt₁Pd₁ particles, an aqueous solution of K₂PdCl₄/Na₂PtCl₆·6H₂O mixture in a molar ratio of 1 : 1 (5 mL, the total metal salt concentration is 2.96 mM) was first prepared. Then, 1-decyl-3-methylimidazolium chloride (DMIMCl) was added into the above solution to result in 200 mM DMIMCl. Then, NaBH₄ was added with shaking to result in 200 mM solution. After this, the solution was kept at room temperature for 2 h. Finally, the products were centrifuged and washed with water and ethanol for several times. The procedure for synthesis of other metal particles at various Na₂PtCl₆·6H₂O/K₂PdCl₄ molar ratios (1 : 0 for Pt, 3 : 1 for Pt₃Pd₁, 1 : 3 for Pt₁Pd₃, and 0 : 1 for Pd) is similar to the above while the total metal salt concentration is the same.

Characterization

X-Ray diffraction was performed using a Rigaku Dmax-rc X-ray diffractometer with Ni-filtered Cu Kα (λ = 1.5418 Å) radiation. Transmission electron microscopy (TEM) was performed using a JEM 1400 TEM operating at 120 kV. HAADF-STEM-EDS mapping and HRTEM characterization were performed with a JEM-2100F. For the measurement of particle size, over 100 particles were counted according to the TEM images. The compositions of the bimetallic particles were determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES, VISTAMPX). The alloy sample was added in aqua regia and then the solution was ultrasonicated for enough time to ensure complete dissolution of the precious metals. Finally, the solution was further diluted to concentrations in the range of ca.100 ppm for ICP-AES analysis.

Electrocatalytic activity

Electrocatalytic experiments were performed on an electrochemical workstation (CHI model 660C). The conventional three electrode test cell contained a glassy carbon electrode (GCE, diameter: 3 mm) as working electrode, a Pt wire as counter electrode, and a saturated calomel electrode (SCE) as reference electrode. 5 μL aqueous solution (2 mg mL⁻¹) of PtPd bimetallic particles, Pt, Pd and Johnson-Matthey platinum black was dropped onto the surface of the GCE, respectively. After the solution was dried, 5 μL of Nafion solution (0.2 wt%) was added. The GCE was dried naturally before use. The cyclic voltammograms (CVs) for methanol oxidation was performed in 1 M CH₃OH + 1 M KOH solution with the potential scanned from −0.8 V to 0.4 V at a scan rate 50 mV s⁻¹. The chronoamperometry (CA) curves were recorded at −0.2 V in 1 M CH₃OH + 1 M KOH solution for 10 000 s to investigate the stability of the electrocatalysts.

Catalytic reduction of p-nitrophenol

The catalytic reduction reaction was occurred in a standard quartz cell with a 1 cm path length. NaBH₄ (255 μL of a 53 mM aqueous solution) was mixed together with p-nitrophenol (3 mL of a 0.09 mM aqueous solution) in the quartz cell. After addition of metal particles (40 μL of a 2 mg mL⁻¹ aqueous solution), the successive absorption spectra were recorded by a U-4100 spectrophotometer at room temperature.

Results and discussion

Fig. 1a and b shows typical low magnification TEM images of the synthesized Pt₁Pd₁ sample. From Fig. 1a and b, it is found that particles with the size of 58 ± 15 nm form. Close view of the high magnification TEM images for these particles, it shows that each of these particles is indeed composed of very small nanoparticles as shown in Fig. 1c and d. The size of the very small nanoparticles is about 3.1 ± 0.5 nm. It is clear that primary Pt₁Pd₁ particles form aggregates with the characteristic of interparticle porosity. Therefore, 3D Pt₁Pd₁ nanostructures with tiny nanoparticles as the subunits are successfully synthesized through the present synthesis route. Electron diffraction (ED) for the tiny nanoparticles is not possible as they are either too small to generate sufficient diffraction contrast or they could not be separated from one another. The ED pattern for the synthesized nanostructure displays rings (the insert in Fig. 1c), which are usually assigned to polycrystalline habit.³⁹ However, the typical HRTEM image of the tiny nanoparticle subunit demonstrates its single-crystalline nature (Fig. 1e), in which the d spacing (0.22 nm) for adjacent lattice fringes corresponds to (111) lattice planes of face-centered-cubic (fcc) PtPd alloy. Fig. 1f shows the XRD patterns of the as-prepared various PtPd particles, Pt particles and Pd particles. All the particles show four diffraction peaks corresponding to (111), (200), (220) and (311) of the fcc structure, respectively. This further indicates the synthesized particles are a single phase with fcc crystal structure. The atomic ratios of Pt to Pd for Pt₁Pd₃, Pt₁Pd₁, and Pt₃Pd₁ are determined to be 1 : 2.62, 1.12 : 1, and 3.33 : 1 by ICP-AES, which is almost identical to the feed ratio of metal salts. This indicates the complete reduction of the reaction due to the addition of excess NaBH₄. The elemental distribution of Pt and Pd on the Pd₁Pd₁ particles is further characterized by elemental mapping. Fig. 1g–i shows the high-angle annular dark-field scanning TEM (HAADF-STEM) and the element mapping of the sample. The uniform color distribution verifies the homogenous distribution of Pt and Pd in the particle, indicating that the as-prepared particle is an alloy structure. The Pt and Pd have extremely high lattice match (99.23%)⁴⁰ and similar redox potential ([PdCl₄]²⁻/Pd: 0.755 V versus SHE, [PtCl₆]²⁻/Pt: 0.591 V versus SHE),¹⁶ therefore the successful formation of alloy structure could be easily understood.

Fig. 1 (a and b) Low magnification TEM images of Pt₁Pd₁ particles, (c) high magnification TEM image of Pt₁Pd₁ particles, (d) high magnification TEM image of the edge part of Pt₁Pd₁ particles, (e) the corresponding HRTEM image, (f) XRD patterns of as-prepared Pt, Pt₁Pd₃, Pt₁Pd₁, Pt₃Pd₁, Pd particles, (g) HAADF-STEM image, and (h–j) EDS mapping images of Pt₁Pd₁ bimetallic particles (h: Pt green, i: Pd red, j: overlap image of Pt and Pd).

In order to understand whether the present DMIMCl ionic liquid plays a unique role for the formation of these 3D nanostructured particles with tiny nanoparticles as the subunits, the controlled synthesis without DMIMCl ionic liquid is performed with the synthesis condition similar to that of Pt₁Pd₁. Fig. 2a–c show the low and high magnification TEM images of the Pt₁Pd₁ particles synthesized without DMIMCl. It is found that particles with the size of 7.4 ± 1.3 nm form. The corresponding HRTEM image is shown in Fig. 2d. Based on the images in Fig. 2c and d, it is clear that these particles are not composed of nanoparticle subunits. Therefore these particles are not in 3D nanostructure shape. For a better comparison of the size of the Pt₁Pd₁ particles synthesized without and with DMIMCl, the corresponding size distribution histograms are shown in Fig. 2e and f. For the Pt₁Pd₁ particles synthesized without DMIMCl ionic liquid, the size distribution in Fig. 2e is obtained by direct counting of the particles because there are no subunits for the particles. For the Pt₁Pd₁ particles synthesized with DMIMCl, the size distribution in Fig. 2f is obtained by counting the subunits of the particles. From Fig. 2e and f, it is clear that the size of the Pt₁Pd₁ particles synthesized without DMIMCl is much larger than that of the Pt₁Pd₁ nanoparticle subunits within the 3D particles synthesized with DMIMCl ionic liquid. Therefore, it is clear that the DMIMCl ionic liquid plays an important role for the formation of the as-prepared 3D nanostructured particles with the tiny nanosubunits. In principle, the crystal growth process consists of nucleation and growth, which are influenced by the intrinsic crystal structure and the external conditions including the kinetic energy barrier, temperature, time, capping molecules, and so forth.⁴¹ The initial formed nuclei can further growth by consuming the reactants or the metastable primary particles. The growth by consuming metastable primary particles is mainly related to the well-known Ostwald ripening process which is usually apparent in high temperature synthesis. In our case, the synthesis is performed at room temperature, therefore the further growth of the particles could be attributed to the depletion of the reactant salts. During the synthesis with DMIMCl, many alloy nuclei form quickly after the addition of NaBH₄ to the metal precursor solution. Because of the molecular structure of DMIMCl has a long carbon chain, it has a better stabilization for the particle formation, which could inhibit the further growth of the nuclei, resulting in very small nanoparticles. Compared with larger particles synthesized without DMIMCl, these very small nanoparticles are easily fused and aggregated for the formation of 3D nanostructures in consideration that small nanoparticles possess higher surface energies. Besides, it is known that 1,3-dialkylimidazolium ionic liquids can form a polymeric supramolecular structure.^42,43 It is therefore reasonable to assume that the organized structure of the ionic liquid may have a template effect, which further helps the formation of the 3D nanostructures for the Pt₁Pd₁ particles synthesized with DMIMCl. Moreover, the inherent nature of the Pt and Pd component in the PtPd bimetallic particles might also be helpful for the cooperative formation of these interesting particles in the present of the ionic liquid. As a result, the 3D nanostructure with tiny nanoparticle subunits could be successfully formed with the assistance of DMIMCl ionic liquid.

Fig. 2 (a–c) Low and high magnification TEM images of Pt₁Pd₁ particles synthesized without the assistance of DMIMCl ionic liquid. (d) The corresponding HRTEM image. (e) Particle size distribution of Pt₁Pd₁ particles synthesized without the assistance of DMIMCl ionic liquid. (f) Particle size distribution of the nanoparticle subunits within the 3D Pt₁Pd₁ particles synthesized with the assistance of DMIMCl ionic liquid.

The morphologies of PtPd bimetallic particles with controlled composition are also characterized by TEM. For comparison, the monometallic Pt and Pd are also synthesized. Fig. 3 shows TEM images of samples obtained at various metal precursor molar ratios. For pure Pt, individual spherical nanoparticles with size of 3.8 ± 0.5 nm form (Fig. 3a). For the Pt₃Pd₁ as shown in Fig. 3b and c, it is found that nanoparticle-constructed 3D nanostructure forms, which is similar to Pt₁Pd₁ in Fig. 1. The size of the nanoparticle subunit is 3.0 ± 0.4 nm. However, individual spherical nanoparticles without 3D nanostructure form for the Pt₁Pd₃, in which the size of the nanoparticles is 3.3 ± 0.4 nm as shown in Fig. 3d and e. In principle, the crystal growth process is influenced by the intrinsic crystal structure and the external conditions. In comparison with the external conditions, the intrinsic crystal structure might also play an important role for the formation of specific morphologies. For example, the well-known soft template of cetyltrimethylammonium bromide (CTAB) can result in different morphologies for various kinds of inorganic particles, which implies that the intrinsic crystal structure play an important role for the formation of various nanostructured-particles. For the nanoparticle synthesis in ionic liquid, the intrinsic crystal structure also play an important role for the formation of different morphologies. For example, the ionic liquid tetrabutylammonium hydroxide (TBAH) can result in the formation of hollow ZnO mesocrystals with tube-like morphology while Ni(OH)₂ and Co(OH)₂ nanoplates are formed in TBAH.^23,39 Therefore, the formation of the present individual spherical Pt₁Pd₃ particles could be attributed to their crystal structure in which the distribution of Pt and Pd atoms on the surfaces of the crystal largely changes the surface energies. In this case, the template effect of the ionic liquid does not work sufficient for the formation of the 3D Pt₁Pd₃ nanostructure. For pure Pd, individual spherical nanoparticles still form with the size of 4.1 ± 0.5 nm (Fig. 3f). Thus, the morphology of the PtPd bimetallic particles synthesized by the present ionic liquid route could be well controlled, which is largely dependent on their compositions. This is similar to our previous reported AuPd and AuPt bimetallic particles in which the morphologies are mainly determined by the composition of the metal components,^37,38 demonstrating the important role of the inherent nature of the Pt and Pd component for the formation of the various particles.

Fig. 3 TEM images of the synthesized various PtPd bimetallic particles, pure Pt particles and pure Pd particles: (a) Pt, (b and c) Pt₃Pd₁, (d and e) Pt₁Pd₃, (f) Pd.

Because of the unique nanostructures of the as-prepared PtPd particles, the synthesized PdPt particles were further characterized by their composition-dependent electroactivities. The electrocatalytic performance of the PtPd particles toward a methanol oxidation reaction was tested in the 1 M CH₃OH and 1 M KOH solution at a scan rate of 50 mV s⁻¹. For comparison, the electrocatalytic performances of the commercial state-of-the-art Johnson-Matthey platinum black catalyst (Hispec™ 1000), the as-prepared pure Pt and pure Pd were also tested. For the practical applications of the catalysts, the mass-normalized electroactivities are the most important criterion for judging the activities, therefore the total metal (Pt and Pd) loaded on the GCE is controlled at the same. Fig. 4a shows the cyclic voltammograms (CVs) of methanol oxidation with the various catalysts in a 1 M CH₃OH and 1 M KOH aqueous solution. The current densities are normalized to the total metal mass that loaded on GCE. Characteristic anodic peaks in the forward and reverse sweeps associated with methanol oxidation are observed. The peak current densities are 0.38, 0.40, 0.64, 0.29, 0.23 and 0.53 A mg⁻¹ for Pt, Pt₃Pd₁, Pt₁Pd₁, Pt₁Pd₃, Pd and commercial Pt black catalyst, respectively. Among the studied catalysts, the Pt₁Pd₁ exhibits the highest mass-normalized current density for the methanol oxidation. The onset potentials (E_onset) for methanol oxidation are −0.727, −0.553, −0.661, −0.758, −0.786 and −0.718 V for Pt, Pt₃Pd₁, Pt₁Pd₁, Pt₁Pd₃, Pd and commercial Pt black catalyst, respectively. The corresponding forward peak potential (E_f) for methanol oxidation is −0.186, −0.236, −0.223, −0.146, −0.201 and −0.159 V for Pt, Pt₃Pd₁, Pt₁Pd₁, Pt₁Pd₃, Pd and commercial Pt black catalyst, respectively. Although the commercial Pt black catalyst has a lower E_onset than that of the Pt₁Pd₁, the E_f of commercial Pt black catalyst is much higher than that of the Pt₁Pd₁. Therefore, it is clear that the Pt₁Pd₁ bimetallic particles have superior electrocatalytic properties toward methanol oxidation than others, which is attributed to the electronic coupling between Pt and Pd metals being optimized at the atomic percentage of Pt is ca. 50%. The differences in electrocatalytic activity of the various PtPd bimetallic particles can be attributed to their different morphology, composition and surface structure. It is known that the methanol oxidation reaction is structure-sensitive. Therefore, the change in the surface atom arrangements (the distribution of the atoms on the crystal surface) of bimetallic PtPd nanocrystals could easily result in the changes of activities for methanol oxidation even though the catalysts have similar shape and size.¹³ The value of I_f/I_b (in which I_f and I_b are the forward and backward peak current densities, respectively) is usually used to evaluate the CO poison tolerance of Pt based catalysts in the methanol oxidation reaction.¹⁶ From Fig. 4a, the calculated value of I_f/I_b for 3D Pt₁Pd₁ and commercial Pt black catalyst is 5.2 and 2.8, respectively, demonstrating the superior poison tolerance of Pt₁Pd₁. The electrochemical stability of Pt₁Pd₁ and commercial Pt black catalysts for methanol oxidation is also investigated by chronoamperometry (CA) experiment for 10 000 s (Fig. 4b). It is seen that the current decay of Pt₁Pd₁ particles is much slower, indicating their better electrochemical stability and electrocatalytic activity toward methanol oxidation. Pd is much cheaper than Pt, therefore one can expect that the present synthesized Pt₁Pd₁ catalyst might have promising applications in the fuel cell field.

Fig. 4 (a) Cyclic voltammograms (CVs) of the as-prepared Pt, Pt₃Pd₁, Pt₁Pd₁, Pt₁Pd₃ and Pd and commercial Pt black in 1 M CH₃OH and 1 M KOH solution, scan rate: 50 mV s⁻¹. (b) Chronoamperometric curves of the catalysts in 1 M CH₃OH and 1 M KOH solution at −0.2 V.

One of the important applications of the metal particles is to catalyze some reactions that are otherwise unfeasible.⁴⁴ p-Nitrophenol is a well-known pollutant with high toxicity and poor biological degradability. The hydrogenation of p-nitrophenol to p-aminophenol is very useful because of the important applications of p-aminophenol as an analgesic and antipyretic drug.⁴⁵ Without metal catalyst, the reduction of p-nitrophenol to p-aminophenol using aqueous NaBH₄ is negligible since the reaction is kinetically restricted in the absence of a catalyst.⁴⁶ The composition-dependent catalytic performance of the as-synthesized PtPd particles towards the reduction of p-nitrophenol by NaBH₄ is thus investigated. Fig. 5a shows the UV-vis spectra of p-nitrophenol aqueous solution in the absence and presence of NaBH₄. The solution is pale yellow color with the UV-vis absorption peak at about 316 nm in the absence of NaBH₄. Once adding NaBH₄, the color of the solution becomes yellow with the absorption peak shifting from 316 nm to 399 nm, indicating the formation of p-nitrophenolate ions. Fig. 5b shows the time-dependent UV-vis spectra of the p-nitrophenol solution with NaBH₄, demonstrating the negligible changes without metal catalysts. Fig. 5c shows the typical time-dependent UV-vis spectra of the p-nitrophenol solution with NaBH₄ after the addition of Pt₁Pd₁ particles. It is found that the peak at 399 nm decreases rapidly with time, accompanying a color change to colorless finally. This indicates the effective catalytic property of the particles towards the reduction of p-nitrophenol. Since the concentration of NaBH₄ in the system is in largely excess in comparison with that of p-nitrophenol, the concentration of BH₄⁻ can be regarded as constant during the reaction. Accordingly, pseudo-first-order kinetics could be used to evaluate the apparent kinetic reaction rate constant of the reaction. Based on the UV-vis spectra, the relationship between lnC_t/C₀ and the reaction time for the synthesized Pt, Pt₁Pd₃, Pt₁Pd₁, Pt₃Pd₁ and Pd catalysts is shown in Fig. 5d. The calculated apparent kinetic reaction rate constant for the synthesized Pt, Pt₁Pd₃, Pt₁Pd₁, Pt₃Pd₁ and Pd catalysts is 0.0196, 0.1386, 0.1192, 0.1128 and 0.0829 min⁻¹, respectively. It is clear that the PtPd bimetallic catalysts have a higher catalytic activity in comparison with Pt and Pd catalysts, indicating the important synergistic effect of Pt and Pd species. Among the studied metal catalysts, the synthesized Pt₁Pd₃ particles show the highest catalytic activity for the reduction of p-nitrophenol. The calculated mass-normalized kinetic reaction rate constant of the Pt₁Pd₃ is 1.7325 mg⁻¹ min⁻¹, which is much higher than the reported Pt/γ-alumina (0.064 mg⁻¹ min⁻¹)⁴⁷ and Pt_1.4Pd₁ (0.6 mg⁻¹ min⁻¹)⁴⁵ catalysts. Thus, such PtPd bimetallic catalyst might be very useful towards the important reduction reaction of p-nitrophenol.

Fig. 5 (a) UV-Vis spectra of p-nitrophenol in water before and after the addition of NaBH₄. (b) Time-dependent UV-vis absorption spectra of reduction of the p-nitrophenol solution by NaBH₄ without metal catalysts. (c) The typical successive absorption spectra of the p-nitrophenol solution with NaBH₄ after the addition of Pt₁Pd₁ particles. (d) Plots of ln(C_t/C₀) versus time for the synthesized Pt, Pt₃Pd₁, Pt₁Pd₁, Pt₁Pd₃ and Pd.

Conclusions

In this work, a facile ionic liquid-based route is proposed for the synthesis of various PtPd bimetallic particles. In order to synthesize bimetallic particles with small size, the ionic liquid possessing long carbon chain in the cation is explored in the present study. 3D PtPd bimetallic nanostructure with tiny nanoparticles as the subunits can be successfully synthesized with the assistance of ionic liquid 1-decyl-3-methyl imidazolium chloride. The detailed structure of the synthesized 3D PtPd particles shows that primary PtPd particles form aggregates with the characteristic of interparticle porosity. The as-prepared Pt₁Pd₁ bimetallic particles exhibit excellent electrocatalytic activity toward oxidation of methanol due to their unique structure and the synergistic effect of elements. The catalytic activity of the synthesized bimetallic particles towards p-nitrophenol reduction shows that the PtPd bimetallic catalysts have a higher catalytic activity in comparison with monometallic Pt and monometallic Pd catalysts. Among the studied catalysts, the Pt₁Pd₃ particles exhibit highest catalytic activity towards p-nitrophenol reduction. The present contribution may provide a simple and efficient approach for the chemists to fabricate 3D nanostructured bimetals with interesting catalytic activities.

Acknowledgements

This work is supported by National Natural Science Foundation of China (Grant No. 21173127), and the Fundamental Research Funds of Shandong University (Grant No. 2015JC003).

References

1. K. Zhang, X. Hu, J. Liu, J. Yin, S. Hou, T. Wen, W. He, Y. Ji, Y. Guo, Q. Wang and X. Wu, Langmuir, 2011, 27, 2796.
2. J. N. Anker, W. P. Hall, O. Lyandres, N. C. Shah, J. Zhao and R. P. van Duyne, Nat. Mater., 2008, 7, 442.
3. S. E. Skrabalak, J. Chen, Y. Sun, X. Lu, L. Au, C. M. Cobley and Y. Xia, Acc. Chem. Res., 2008, 41, 1587.
4. X. Zhao, M. Yin, L. Ma, L. Liang, C. Liu, J. Liao, T. Lu and W. Xing, Energy Environ. Sci., 2011, 4, 2736.
5. Y. Wu, S. F. Cai, D. S. Wang, W. He and Y. D. Li, J. Am. Chem. Soc., 2012, 134, 8975.
6. B. Y. Xia, H. B. Wu, X. Wang and X. W. Lou, J. Am. Chem. Soc., 2012, 134, 13934.
7. J. W. Hong, D. H. Kim, Y. W. Lee, M. J. Kim, S. W. Kang and S. W. Han, Angew. Chem., Int. Ed., 2011, 50, 8876.
8. Q. Yuan, D. B. Huang, H. H. Wang, Z. Y. Zhou and Q. Wang, CrystEngComm, 2014, 16, 2560.
9. Z. Zhang, Y. Yang, F. Nosheen, P. Wang, J. Zhang, J. Zhuang and X. Wang, Small, 2013, 9, 3063.
10. Q. Liu, Z. Yan, N. L. Henderson, J. C. Dauer, D. W. Goodman, J. D. Batteas and R. E. Schaak, J. Am. Chem. Soc., 2009, 131, 5720.
11. Y. Liu, M. Chi, V. Mazumder, K. L. More, S. Soled, J. D. Henao and S. Sun, Chem. Mater., 2011, 23, 4199.
12. C. Zhu, S. Guo and S. Dong, Chem.–Eur. J., 2013, 19, 1104.
13. D. Huang, Q. Yuan, H. Wang and Z. Zhou, Chem. Commun., 2014, 50, 13551.
14. J. Lv, J. Zheng, S. Li, L. Chen, A. Wang and J. Feng, J. Mater. Chem. A, 2014, 2, 4384.
15. Y. Kim, Y. W. Lee, M. Kim and S. W. Han, Chem.–Eur. J., 2014, 20, 7901.
16. H. Ataee-Esfahani, M. Imura and Y. Yamauchi, Angew. Chem., Int. Ed., 2013, 52, 13611.
17. Z. M. Peng and H. Yang, J. Am. Chem. Soc., 2009, 131, 7542.
18. B. Lim, M. J. Jiang, P. H. C. Camargo, E. C. Cho, J. Tao, X. M. Lu, Y. M. Zhu and Y. N. Xia, Science, 2009, 324, 1302.
19. A. X. Yin, X. Q. Min, Y. W. Zhang and C. H. Yan, J. Am. Chem. Soc., 2011, 133, 3816.
20. Z. Huang, H. Zhou, F. Sun, C. Fu, F. Zeng, T. Li and Y. Kuang, Chem.–Eur. J., 2013, 19, 13720.
21. B. Lim, J. Wang, P. H. C. Camargo, C. M. Cobley, M. J. Kim and Y. Xia, Angew. Chem., Int. Ed., 2009, 48, 6304.
22. H. Zhang, M. Jin, J. Wang, W. Li, P. H. C. Camargo, M. J. Kim, D. Yang, Z. Xie and Y. Xia, J. Am. Chem. Soc., 2011, 133, 6078.
23. Z. Li, A. Geßner, J. Richters, J. Kalden, T. Voss, C. Kubel and A. Taubert, Adv. Mater., 2008, 20, 1279.
24. J. Lian, X. Duan, J. Ma, P. Peng, T. Kim and W. J. Zheng, ACS Nano, 2009, 3, 3749.
25. K. Richter, A. Birkner and A. V. Mudring, Angew. Chem., Int. Ed., 2010, 49, 2431.
26. Z. Ma, J. H. Yu and S. Dai, Adv. Mater., 2010, 22, 261.
27. M. Antonietti, D. Kuang, B. Smarsly and Y. Zhou, Angew. Chem., Int. Ed., 2004, 43, 4988.
28. A. Taubert and Z. Li, Dalton Trans., 2007, 723.
29. E. R. Parnham and R. E. Morris, Acc. Chem. Res., 2007, 40, 1005.
30. H. Kaper, F. Endres, I. Djerdj, M. Antonietti, B. Smarsly, J. Maier and Y. S. Hu, Small, 2007, 3, 1753.
31. Y. Zhu, W. Wang, R. Qi and X. Hu, Angew. Chem., Int. Ed., 2004, 43, 1410.
32. H. Wender, P. Migowski, A. F. Feil, L. F. de Oliveira, M. H. G. Prechtl, R. Giovanna Machado, S. R. Teixeira and J. Dupont, Phys. Chem. Chem. Phys., 2011, 13, 13552.
33. Y. J. Zhao, J. L. Zhang, B. X. Han, J. L. Song, J. S. Li and Q. A. Wang, Angew. Chem., Int. Ed., 2011, 50, 636.
34. P. F. Zhang, J. Y. Yuan, F. Tim-Patrick, M. Antonietti, H. R. Li and Y. Wang, Angew. Chem., Int. Ed., 2013, 52, 6028.
35. Y. Qin, Y. Song, N. Sun, N. Zhao, M. Li and L. Qi, Chem. Mater., 2008, 20, 3965.
36. E. Ahmed, J. Breternitz, M. Friedrich Groh and M. Ruck, CrystEngComm, 2012, 14, 4874.
37. Z. Li, R. Li, T. Mu and Y. Luan, Chem.–Eur. J., 2013, 19, 6005.
38. Z. Li and Q. Niu, ACS Sustainable Chem. Eng., 2014, 2, 533.
39. Z. Li, P. Rabu, P. Strauch, A. Mantion and A. Taubert, Chem.–Eur. J., 2008, 14, 8409.
40. Z. M. Peng and H. Yang, J. Am. Chem. Soc., 2009, 131, 7542.
41. S. M. Lee, S. N. Cho and J. W. Cheon, Adv. Mater., 2003, 15, 441.
42. Z. Li, A. Friedrich and A. Taubert, J. Mater. Chem., 2008, 18, 1008.
43. J. Dupont, J. Braz. Chem. Soc., 2004, 15, 341.
44. J. Liu, G. Qin, P. Raveendran and Y. Ikushima, Chem.–Eur. J., 2006, 12, 2131.
45. Y. Shen, Y. Sun, L. Zhou, Y. Li and E. S. Yeung, J. Mater. Chem. A, 2014, 2, 2977.
46. G. Fu, L. Ding, Y. Chen, J. Lin, Y. Tang and T. Lu, CrystEngComm, 2014, 16, 1606.
47. A. Dandapat, D. Jana and G. de, ACS Appl. Mater. Interfaces, 2009, 1, 833.

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