Uniform Au@Pt core–shell nanodendrites supported on molybdenum disulfide nanosheets for the methanol oxidation reaction

Abstract

Herein, we presented a facile seeded growth method to prepare high-quality three-dimensional (3D) Au@Pt bimetallic nanodendrite-decorated molybdenum disulfide (MoS₂) nanosheets (Au@Pt/MoS₂). Transmission electron microscopy (TEM) and high-resolution TEM exhibited that Au@Pt core–shell nanostructures were dispersed onto the surface of MoS₂ nanosheets. More importantly, the thickness of the Pt shell of the Au@Pt bimetallic nanodendrites on the surface of the MoS₂ nanosheets could be easily tuned via simply changing the synthesis parameters, such as the concentration of H₂PtCl₆, reaction time and temperature, which greatly influence the catalytic ability of Au@Pt/MoS₂ nanohybrids. Both cyclic voltammetry (CV) and chronoamperometry (CA) demonstrated that the as-prepared Au@Pt/MoS₂ nanohybrids possessed much higher electrocatalytic activity and stability than Pt/MoS₂ or commercial Pt/C catalyst. The peak current mass density of the selected Au@Pt/MoS₂ was 6.24 A mg⁻¹, which was 3389 and 20.3 times those of Pt/C (0.00184 A mg⁻¹) and Pt/MoS₂ (0.307 A mg⁻¹), respectively. The presented method may be a facile approach for the synthesis of MoS₂-supported bimetallic nanocomposites, which is significant for the development of high performance MoS₂-based sensors and catalysts.

---

1. Introduction

The direct methanol fuel cell (DMFC) is regarded as one of the most promising energy sources due to low toxicity, high energy density of methanol, availability at a low price and biological renewability. As we all know, Pt-based nanostructures are considered as the most common and efficient catalysts for the methanol oxidation reaction (MOR).^1–3 However, methanol oxidation on a Pt/C catalyst usually requires high Pt loading to achieve high efficiency. Moreover, Pt/C catalysts easily suffer from poisoning by CO, which limits the MOR kinetics and long-term stability. To improve the electrocatalytic performance of Pt and minimize the usage of Pt, Pt-based bimetallic nanohybrids have attracted more and more attention to replace pure Pt as electrocatalysts during the past decade.^4–9 Among these bimetallic nanohybrids, such as Pd–Pt, Au–Pt, Fe–Pt, Ni–Pt, Ag–Pt and Ru–Pt, Pt-based core–shell nanostructures are particularly interesting because of their excellent catalytic activities.^10–18 The Au@Pt core–shell bimetallic nanohybrid is one of the most studied Pt-based core–shell nanostructures.^14,16,17 Unfortunately, such Au@Pt bimetallic nanostructures usually suffer from heavy aggregation during the synthetic process and reuse in catalytic reactions. Therefore, supporting materials have been introduced into constructing Au@Pt-substrate nanocomposites, which is not only to efficiently solve aggregation but also greatly enhance the performance of the catalyst. For example, Zeng's group successfully synthesized a Au–Pt nanoparticle-dispersed carbon (Au@Pt/C) catalyst, which exhibited excellent electrocatalytic activity toward methanol oxidation.¹⁸ The presence of Au underneath a very thin Pt shell could facilitate the removal of inhibiting CO-like reaction intermediates. Cui et al. employed an under-potential deposition redox replacement technique to synthesize a Au–Pt core–shell catalyst supported on a reduced graphene oxide surface. The prepared Au–Pt/RGO exhibited excellent catalytic activity towards the oxygen reduction reaction and the methanol oxidation reaction.¹⁹

As a graphene analogue, MoS₂ has attracted increasing interest in sensors, catalysis, capacitors, lithium batteries and energy harvesting due to its novel nanoelectronic and optoelectronic properties.^20–31 Like graphene, MoS₂ is also considered as a promising supporting material to stabilize metal nanoparticles (NPs), forming hierarchical nanocomposites. Therefore, it is expected that MoS₂ nanosheets decorated with noble metal nanoparticles (NPs) could potentially be used as novel catalytic nanomaterials. Huang et al. developed the epitaxial growth of Pd, Pt, Au and Ag nanoparticles on the surface of single-layer MoS₂ nanosheets. Among these hybrid nanomaterials, Pt–MoS₂ nanocomposites showed higher catalytic activity toward the hydrogen evolution reaction compared with commercial Pt catalysts.³² Wang's group reported that PdNPs–MoS₂ nanocomposites could significantly enhance catalytic activity toward the methanol oxidation reaction.³³ Considering that single noble metal nanoparticle-decorated MoS₂ had excellent electrocatalytic activity, noble bimetallic nanostructures grown on the surface of MoS₂ nanosheets could possess better electrocatalytic performance. Up to now, there is no report of the synthesis of a Au@Pt/MoS₂ hybrid nanocomposite and the performance of its electrocatalytic activity.

In this paper, we demonstrate for the first time a wet-chemical approach to synthesize high-quality 3D Au@Pt bimetallic nanodendrites supported on MoS₂ nanosheets (Au@Pt/MoS₂). As shown in Fig. 1, gold nanoparticle-decorated MoS₂ nanocomposites were used as nanoseeds to prepare Au@Pt/MoS₂ hybrid nanocomposites. The morphology, structure and composition of the as-prepared Au@Pt/MoS₂ were characterized by TEM, HRTEM, powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy. Interestingly, the thickness of the Pt shell and the catalytic performance of Au@Pt/MoS₂ were easily tuned by altering the concentration of H₂PtCl₆, reaction time and temperature. The as-prepared MoS₂-based substrates possessed synergistic effects of the intrinsic properties of the Au@Pt and MoS₂, making the Au@Pt/MoS₂ nanocomposite exhibit attractive electrocatalytic activity. More importantly, the thicker Pt shell (Au@Pt/MoS₂-2) generated a larger surface area, which exhibited higher electrocatalytic activity toward the MOR than the thinner nanocomposites (Au@Pt/MoS₂-1).

Fig. 1 Schematic illustration for synthesizing Au@Pt/MoS₂ nanocomposites and their application in methanol oxidation reaction.

2. Experimental section

2.1. Reagents and chemicals

N-Butyllithium (n-BuLi, 2.4 M hexane solution) was bought from Amethyst. Gold(III) tetrachloride trihydrate (HAuCl₄·3H₂O, ≥49.0%), hydrogen hexachloroplatinate(IV) (H₂PtCl₆·xH₂O, ≥99.9%), cetyltrimethylammonium bromide (CTAB, 96%), poly(N-vinyl-2-pyrrolidone) (PVP·K30, molecular weight = 30 000–40 000), sodium carboxymethylcellulose (CMC, 800–1200 mPa s), Pt/C (10 wt%) and molybdenum(IV) sulfide powder (<2 μm, 99%) were purchased from Sigma. L-Ascorbic acid (AA, ≥99.7%) and methanol (≥99.7%) were provided by Sinopharm Chemical Reagent Co., Ltd. All chemicals and reagents were directly used without further purification. All solutions were prepared with ultrapure millipore water (18.2 MΩ cm) from a Milli-pore system.

2.2. Apparatus

UV-vis-NIR adsorption spectra were measured on a Shimadzu UV-3600 spectrophotometer. Transmission electron microscopy (TEM) images were taken on a Hitachi H-7500 electron microscope (120 kV) and high-resolution TEM (HRTEM) characterization was performed on a Tecnai G2F20 S-Twin electron microscope (200 kV). Structural analysis of the selected Au@Pt/MoS₂-2 nanocomposite was performed in scanning TEM (STEM) mode on a Philips CM 200 electron microscope (200 kV) equipped with an energy dispersive X-ray spectrometer (EDS). The STEM image was recorded with a high-angle annular dark-field (HAADF) detector. Powder X-ray diffraction (XRD) was performed using a D/max-γB diffractometer. X-ray photoelectron spectroscopy (XPS) was performed using a PHI 5000 Versa Probe with Al Kα as the excitation source. Surface morphology of MoS₂ nanosheets was examined with an atomic force microscope (AFM, Bruker). The loading amounts of dendritic Pt were determined by using inductively coupled plasma mass spectroscopy (ICP-MS, Optima 5300DV, PE).

Electrochemical measurements were carried out by using a CHI-660E Electrochemical Workstation with a three-electrode system (CHI Instruments, USA). The nanocomposite-modified carbon glass electrode (GCE) served as a working electrode. A Pt wire and saturated calomel electrode (SCE) were used as the counter and reference electrode, respectively. Details for preparation of the modified electrodes were provided in the ESI.† All the potentials were reported with respect to the SCE and all electrochemical data were obtained at room temperature.

2.3. Preparation of the MoS₂, Au/MoS₂ and Au@Pt/MoS₂ nanocomposites

MoS₂ nanosheets were prepared according to our previous works.^33–35 The detailed process was listed in the ESI.† The morphology of MoS₂ nanosheets was characterized by TEM. Fig. S1A† showed that the as-prepared MoS₂ nanosheets exhibited a typical layered material with little bending and folding. The thickness of MoS₂ nanosheets was determined by AFM. As shown in Fig. S2,† the average height of the MoS₂ nanosheets was about 1.09 nm, suggesting that the exfoliated MoS₂ nanosheet was a single layer.^36,37

The gold nanoparticle (AuNP)-decorated MoS₂ nanocomposite (Au/MoS₂) was synthesized by an in situ reduction growth method. In a typical synthesis, 4 mL (0.025 mg mL⁻¹) of the MoS₂ nanosheet dispersion was mixed with 400 μL of PVP (5%) under vigorous stirring for 2 min to obtain a stable mixture. Then, 110 μL 10 mM HAuCl₄·3H₂O was dropped into the mixture slowly and stirred vigorously for 20 min. The color of the mixture slowly turned from brown to wine. Finally, the product Au/MoS₂ nanocomposite was stored at 4 °C without further purification. The morphology of Au/MoS₂ was characterized by TEM. Uniform, high-density AuNPs were decorated on the surface of MoS₂ with an average diameter of 15 nm (Fig. S1B†).

In a typical synthesis of the Au@Pt/MoS₂ nanocomposite, 0.3 mL aqueous Au/MoS₂ seed solution was added to 2 mL ultrapure water. Then 0.5 mL 10 mM CTAB solution was mixed with the seed solution for 5 min under vigorous stirring. After that, 1 mL AA (100 mM) was injected quickly into the mixed solution. At intervals of 5 s, 100 μL 5 mM H₂PtCl₆ was added to the solution under stirring. Then, the mixture was heated on a hotplate at approximately 100 °C for 6 min to grow dendritic Pt nanoshells. Finally, the product of Au@Pt/MoS₂ nanocomposite was purified by washing and centrifugation (5000 rpm for 10 min) to remove excess reagent three times with acetone and water.

UV-vis absorption spectra and the color change of the solution have been employed to prove the whole synthesis process. Fig. S3† shows the UV-vis absorption spectra of MoS₂, Au/MoS₂ and Au@Pt/MoS₂ dispersions. Three obvious absorption peaks of MoS₂ were obtained at 255 nm, 304 nm and 400 nm, which were ascribed to exfoliated MoS₂ nanosheets (black line). After the AuNPs grew on the MoS₂ nanosheets, a new absorption peak corresponding to the Au plasma band at around 520 nm emerged (red line).³⁸ For Au@Pt/MoS₂, no obvious new peaks were obtained but the absorbance from 300 nm to 1000 nm noticeably increased, since Au@Pt nanodendrites have a wide absorption range with no distinct absorption peaks in the UV-vis-NIR range (blue line).^33,39,40 Moreover, an obvious color change was observed during the Au/MoS₂ and Au@Pt/MoS₂ synthesis process. The color of the solution changed from brown to wine after HAuCl₄ was added to the MoS₂ solution. During the synthesis of the Au@Pt/MoS₂ nanocomposite, the color of the solution changed from wine to a dark color (Fig. S3,† inset).

3. Results and discussion

3.1. Preparation and characterization of the Au@Pt/MoS₂ nanocomposite

The synthesis process of the Au@Pt/MoS₂ nanocomposite was monitored by TEM. First, the MoS₂ nanosheets decorated with Au@Pt nanodendrites were examined by changing the concentration of H₂PtCl₆ and keeping other conditions unaltered. Interestingly, the morphology of the Au@Pt/MoS₂ nanocomposite could be tuned by varying the concentration of H₂PtCl₆. As shown in Fig. 2A–F, the size of the Au@Pt nanodendrites gradually grew bigger with the concentration of H₂PtCl₆ changing from 0.026 to 0.21 mM. Only few Pt shells were dispersed on the AuNPs with addition of 0.026 mM H₂PtCl₆ (Fig. 2A). When the concentration of H₂PtCl₆ was increased, the Au@Pt grew larger (Fig. 2B and C). When the concentration of H₂PtCl₆ was 0.13 mM, a uniform, high-density Au@Pt/MoS₂ nanocomposite was obtained (Fig. 2D). If the concentration of H₂PtCl₆ increased up to 0.17 mM and 0.21 mM, the thickness of the Pt shell increased a little (Fig. 2E and F). The corresponding particle size distribution of Au@Pt nanodendrites was listed in Fig. S4.† The data also proved that the particle size increased with the concentration of H₂PtCl₆. In order to save the usage of Pt, 0.13 mM H₂PtCl₆ was selected as the optimal concentration.

Fig. 2 TEM images of Au@Pt/MoS₂ synthesized under different concentrations of H₂PtCl₆ (from A to F: 0.026 mM, 0.078 mM, 0.11 mM, 0.13 mM, 0.17 mM and 0.21 mM).

As we know, reaction time usually plays a vital role in nanomaterials’ morphology.^14,16 We further explored the influence of reaction time on the morphologies of Au@Pt/MoS₂ nanohybrids by using 0.13 mM H₂PtCl₆ at 100 °C. As shown in Fig. 3, the thickness of the Pt shell increased with the reaction time in the range from 0 min to 6 min (Fig. 3A–D). When the reaction time was prolonged to 10–15 min, the thickness of the Pt shell was almost unchanged (Fig. 3E and F). These results indicated that the reaction process was fast, and only needed 6 min to form Au@Pt nanodendrites under the appropriate conditions.

Fig. 3 TEM images of Au@Pt/MoS₂ formed under different times (from A to F: 0 min, 2 min, 4 min, 6 min, 10 min and 15 min).

Based on the optimal concentration and time, the reaction temperature was also studied. Fig. 4 shows the TEM images of Au@Pt/MoS₂ nanohybrids at different temperatures. The Pt nanoshell gradually grew thicker as the temperature was increased from 30 °C to 100 °C (Fig. 4A–D). When the temperature was 100 °C, a uniform and well-dispersed Pt nanoshell grew on the surface of the Au nanoparticles (Fig. 4D). If the temperature was over 100 °C, the thickness of the Pt nanoshell still increased (Fig. 4E and F). But it should be pointed out that the stability and dispersibility of the Au@Pt/MoS₂ nanohybrids were worse than that prepared at 100 °C. As shown in Fig. S5,† the Au@Pt/MoS₂ nanocomposite gradually settled to the bottom of the tube after 8 h when it was synthesized at 160 °C. Meanwhile, the as-prepared Au@Pt/MoS₂ at 100 °C was still stable and dispersible. In this work, we chose the best temperature of 100 °C.

Fig. 4 TEM images of Au@Pt/MoS₂ synthesized under different temperatures (from A to F: 30 °C, 60 °C, 80 °C, 100 °C, 120 °C and 160 °C).

The morphology of the Au@Pt/MoS₂ nanocomposite was further characterized by HRTEM. The magnified image revealed that the lattice distances for Au cores and Pt shells were 0.240 nm (image b) and 0.225 nm (image a), respectively, corresponding to the planes of face-centered cubic (fcc) Au and Pt, respectively, which suggested that bimetallic Au@Pt core–shell nanodendrites were successfully synthesized (Fig. 5A).^16,33,41 The HAADF-STEM image further revealed the dendritic structure and the elemental distribution of the nanohybrid (Fig. 5B). The elemental mapping patterns (image a–c) and the line profiles of a single bimetallic nanodendrite (inset image d) further demonstrated the core–shell feature of the Au@Pt nanodendrites. Pt appears to be distributed over the entire surface of the Au core and does not overlap extensively, which agreed with previous reports.^14,17,42

Fig. 5 (A) HRTEM images of the Au@Pt/MoS₂ nanocomposite. (B) HAADF-STEM-EDS elemental mapping images (a–c) and cross-sectional compositional line profiles (d) taken from Au@Pt nanodendrites. The inset shows the corresponding HAADF-STEM image.

Powder X-ray diffraction (XRD) was used to characterize the structure of MoS₂, Au/MoS₂ and Au@Pt/MoS₂. As shown in Fig. S6,† a diffraction peak was located at about 14.40° for the MoS₂ nanosheets, which matched the (001) index of 1T-MoS₂.^25,43 After modification, strong diffraction peaks emerged at 38.5° for the Pt@MoS₂ and 40.0° for the Au@MoS₂ nanocomposite, which can be assigned to the (111) planes of cubic Pt (JCPDS no. 04-0802) and Au (JCPDS no. 04-0784), respectively.^16,17 All strong diffraction peaks of Pt and Au were obtained in the Au@Pt/MoS₂ nanocomposite. The XRD data indicated the successful formation of Au/MoS₂, Pt/MoS₂ and Au@Pt/MoS₂ nanocomposites. XPS was employed to investigate the structure and composition of the Au@Pt/MoS₂ nanocomposite. It had been reported that a trigonal orismatic (2H) and an octahedral (1T) configuration of MoS₂ could coexist during the lithium intercalation–exfoliation process.^33,43–47 As shown in Fig. 6A, the binding energy peaks of the MoS₂ nanosheets were fitted into three groups: (1) two larger peaks located near 232 eV and 229 eV, which correspond to Mo⁴⁺ 3d_3/2 and Mo⁴⁺ 3d_5/2 of 2H-MoS₂, respectively; (2) the doublet peaks located around 231 eV and 228 eV could be assigned to Mo⁴⁺ 3d_3/2 and Mo⁴⁺ 3d_5/2 of 1T-MoS₂, respectively; (3) the peaks of Mo 3d peaks with a higher oxidation state (Mo⁶⁺) located at 235 eV and 231 eV, which may originate from the partial oxidation of Mo atoms at the edges or defects of the MoS₂ nanosheets during chemical exfoliation and preparation of the Au@MoS₂ nanoseeds.^33,48 The binding energies for S 2p_3/2 and S 2p_1/2 were 162.3 and 163.5 eV, respectively (Fig. 5B). Two peaks located at about 87.2 eV and 83.5 eV can be ascribed to Au 4f_5/2 and Au 4f_7/2, respectively (Fig. 6C).²⁵ Peaks at 74.3 eV and 71.0 eV originated from Pt 4f_5/2 and Pt 4f_7/2, respectively (Fig. 6D).¹⁵Fig. 6C and D also suggested the successful synthesis of Au@Pt core–shell nanodendrites. The XPS results further confirmed the coexistence of Au, Pt and MoS₂ in the Au@Pt/MoS₂ nanocomposite, which agreed well with the XRD results.

Fig. 6 High-resolution (A) Mo 3d, (B) S 2s, (C) Au 4f and (D) Pt 3d XPS spectra of the Au@Pt/MoS₂ nanocomposite.

3.2. Electrochemical oxidation of methanol

To select the best catalyst, we explored the activity toward the methanol oxidation reaction of different thicknesses of the Pt shell for Pt@Au/MoS₂ nanocomposites. We selected two typical nanocomposites to evaluate the catalytic performance, a Au@Pt/MoS₂ nanocomposite with a thin Pt shell (Au@Pt/MoS₂-1, Fig. 2B) and a Au@Pt/MoS₂ nanocomposite with a thick Pt shell (Au@Pt/MoS₂-2, Fig. 2D). For comparison, Pt/C (10%) and Pt/MoS₂ were employed to assess the catalytic activity. The synthesis process of Pt/MoS₂ is described in the ESI.† The TEM image of Pt/MoS₂ showed that it possessed a similar structure to Au@Pt/MoS₂ (Fig. S1C†). Fig. 7A shows the CV curves of Pt/C (10%) (black line), Pt/MoS₂ (red line), Au@Pt/MoS₂-1 (blue line) and Au@Pt/MoS₂-2 (green line) in N₂-saturated 0.5 M NaOH solution at 100 mV s⁻¹. Clearly, the hydrogen adsorption–desorption peaks and the Pt oxidation/reduction peaks were well observed for all the catalysts, indicating that the surface composition of the catalysts was Pt. Obviously, the hydrogen adsorption–desorption peaks of Au@Pt/MoS₂-2 were much larger than those of Pt/C, Pt/MoS₂ and Au@Pt/MoS₂-1, indicating that the Au@Pt/MoS₂-2 catalyst had a larger electrochemical surface area (ECSA) and higher catalytic activity than the others. The improved catalytic activity could be ascribed to the 3D Au@Pt nanodendrites and the synergistic effects of Au@Pt and MoS₂ nanosheets.

Fig. 7 (A) Cyclic voltammograms of four catalysts in N₂-saturated 0.5 M NaOH solution. (B) Cyclic voltammograms of four catalysts in 0.5 M NaOH + 1.0 M CH₃OH. Scan rate: 100 mV s⁻¹. (C) Chronoamperometric responses of four catalysts in 0.5 M NaOH + 1.0 M CH₃OH.

Fig. 7B exhibits the electrocatalytic activities of Pt/C (black line), Pt/MoS₂ (red line), Au@Pt/MoS₂-1 (blue line) and Au@Pt/MoS₂-2 (green line) modified GCE in 0.5 M NaOH containing 1.0 M methanol. Clearly, the four catalysts displayed similar electrochemical performances. An oxidation peak was located at about −0.23 V in the forward scan, which was attributed to the direct oxidation of methanol molecules adsorbed on the electrode surface. And the other peak was located at about −0.38 V in the reverse scan, which could be assigned to the removal of carbonaceous species that were not completely oxidized in the forward scan.⁴⁹ The Au/MoS₂ nanocomposite showed no measurable MOR activity under the same experimental conditions (Fig. S7†). Au@Pt/MoS₂-2 showed higher electrocatalytic activity toward methanol, the corresponding mass activity was 6.24 A mg⁻¹, which is 3389, 20.3, and 4.5 times those of Pt/C (0.00184 A mg⁻¹), Pt/MoS₂ (0.307 A mg⁻¹), and Au@Pt/MoS₂-1 (1.39 A mg⁻¹), respectively (the mass concentrations of Pt in the Pt/MoS₂, Au@Pt/MoS₂-1, and Au@Pt/MoS₂-2 were determined by ICP-MS, Table S1†). The mass activity of Au@Pt/MoS₂-2 was comparable to or better than several previous works.^50–52

The onset peak potential of Au@Pt/MoS₂-2 (−0.24 V) was more negative than that of Pt/C (−0.23 V), indicating that Au@Pt/MoS₂-2 had a better tolerance towards CO poisoning. The durability of the four catalysts was also studied through the chronoamperometric measurements at −0.23 V (Fig. 7C). It can be seen that the Au@Pt/MoS₂ catalyst had a much higher initial current than other Pt catalysts. After a sharp drop in the initial period of around 15 s, the currents decay at a much slower speed and then approach a flat line. Both Au@Pt/MoS₂-1 and Au@Pt/MoS₂-2 maintained higher currents within 2000 s of the test than the rest of the catalysts tested. More importantly, the catalyst Au@Pt/MoS₂-2 showed a higher current than that of Au@Pt/MoS₂-1, suggesting that a thicker Pt shell possessed better electrocatalytic activity. The stability of the catalysts was also proved by TEM investigation. Fig. S8† shows that the structures of Pt/MoS₂, Au@Pt-MoS₂-1 and Au@Pt-MoS₂-2 had almost no change after the electrocatalytic process. These results were consistent with the CV measurements, further confirming that the Au@Pt/MoS₂-2 catalyst possessed higher catalytic activity and long-term stability towards the methanol oxidation reaction.

The interfacial processes and kinetics of electrode reactions were studied by the electrochemical impedance spectroscopy (EIS) technique. Fig. S9† exhibits the Nyquist plots for methanol oxidation at different modified electrodes in 0.5 M NaOH containing 1.0 M methanol. The diameter of the charge transfer resistance decreased in the order Pt/C > Pt/MoS₂ > Au@Pt/MoS₂-1 > Au@Pt/MoS₂-2. The lower charge transfer resistance of Au@Pt/MoS₂-2 suggested that this catalyst possessed faster oxidation kinetics, which could be attributed to the prevention of the intermediate adsorption on the catalyst surface.⁵³

4. Conclusions

In summary, dendritic Pt shell and Au core bimetallic heterostructures supported on MoS₂ nanosheets could be easily synthesized by a seeded growth method. The Au@Pt/MoS₂ nanocomposites exhibited higher electrocatalytic activity and long-term durability for methanol oxidation than those of the monometallic Pt catalyst. The improved catalytic performance could be attributed to the large surface area of MoS₂, the unique porous nanostructure of Au@Pt, the high electrocatalytic activity of Pt nanoshells and their excellent synergistic effects. These MoS₂-based nanocomposites possessed high electrocatalytic activity and excellent stability, which could be further employed as a potential nanomaterial in catalytic and fuel cell applications.

Acknowledgements

This work was financially supported by the National Basic Research Program of China (2012CB933301), the National Natural Science Foundation of China (21305070, 21475064), the Natural Science Foundation of Jiangsu Province (BK20130861), the Sci-tech Support Plan of Jiangsu Province (BE2014719), the Ministry of Education of China (20133223120013), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).

Notes and references

1. A. S. Arico, S. Srinivasan and V. Antonucci, Fuel Cells, 2001, 1, 133–161.
2. L. Brandao, D. M. Gattia, R. Marazzi, M. V. Antisari, S. Licoccia, A. D'Epifanio, E. Traversa and A. Mendes, Mater. Sci. Forum, 2010, 638, 1106–1111.
3. M. S. Whittingham and T. Zawodzinski, Chem. Rev., 2004, 104, 4243–4244.
4. J. Y. Cao, M. W. Guo, J. Y. Wu, J. Xu, W. C. Wang and Z. D. Chen, J. Power Sources, 2015, 277, 155–160.
5. B. Lim, M. Jiang, P. H. C. Camargo, E. C. Cho, J. Tao, X. Lu, Y. Zhu and Y. Xia, Science, 2009, 324, 1302–1305.
6. C. M. Sánchez-Sánchez, J. Solla-Gullón, F. J. Vidal-Iglesias, A. Aldaz, V. Montiel and E. Herrero, J. Am. Chem. Soc., 2010, 132, 5622–5624.
7. V. R. Stamenkovic, B. S. Mun, M. Arenz, K. J. J. Mayrhofer, C. A. Lucas, G. Wang, P. N. Ross and N. M. Markovic, Nat. Mater., 2007, 6, 241–247.
8. Y. Yang, Phys. Chem. Chem. Phys., 2009, 11, 9759–9765.
9. D. Zhao and B. Q. Xu, Angew. Chem., Int. Ed., 2006, 118, 5077–5081.
10. S. Alayoglu and B. Eichhorn, J. Am. Chem. Soc., 2008, 130, 17479–17486.
11. E. Lee, J. H. Jang, M. A. Matin and Y. U. Kwon, Ultrason. Sonochem., 2014, 21, 317–323.
12. C. Li and Y. Yamauchi, Phys. Chem. Chem. Phys., 2013, 15, 3490–3496.
13. J. B. Zhu, M. L. Xiao, K. Li, C. P. Liu and W. Xing, Chem. Commun., 2015, 51, 3215–3218.
14. H. Ataee-Esfahani, L. Wang, Y. Nemoto and Y. Yamauchi, Chem. Mater., 2010, 22, 6310–6318.
15. S. J. Guo, S. J. Dong and E. K. Wang, ACS Nano, 2010, 4, 547–555.
16. S. J. Guo, J. Li, S. J. Dong and E. K. Wang, J. Phys. Chem. C, 2010, 114, 15337–15342.
17. Y. Kim, J. W. Hong, Y. W. Lee, M. Kim, D. Kim, W. S. Yun and S. W. Han, Angew. Chem., Int. Ed., 2010, 49, 10197–10201.
18. J. H. Zeng, J. Yang, J. Y. Lee and W. J. Zhou, J. Phys. Chem. B, 2006, 110, 24606–24611.
19. X. Cui, S. Wu, S. Jungwirth, Z. Chen, Z. Wang, L. Wang and Y. Li, Nanotechnology, 2013, 24, 295402.
20. G. S. Bang, K. W. Nam, J. Y. Kim, J. Shin, J. W. Choi and S.-Y. Choi, ACS Appl. Mater. Interfaces, 2014, 6, 7084–7089.
21. R. Ganatra and Q. Zhang, ACS Nano, 2014, 8, 4074–4099.
22. H. Li, J. Wu, Z. Yin and H. Zhang, Acc. Chem. Res., 2014, 47, 1067–1075.
23. H. F. Sun, J. Chao, X. L. Zuo, S. Su, X. F. Liu, L. H. Yuwen, C. H. Fan and L. H. Wang, RSC Adv., 2014, 4, 27625–27629.
24. H. Zhang, ACS Nano, 2015, 9, 9451–9469.
25. C. Tan and H. Zhang, Chem. Soc. Rev., 2015, 44, 2713–2731.
26. X. Huang, C. Tan, Z. Yin and H. Zhang, Adv. Mater., 2014, 26, 2185–2204.
27. X. Huang, Z. Zeng and H. Zhang, Chem. Soc. Rev., 2013, 42, 1934–1946.
28. X. Cao, Y. Shi, W. Shi, X. Rui, Q. Yan, J. Kong and H. Zhang, Small, 2013, 9, 3433–3438.
29. Z. Yin, B. Chen, M. Bosman, X. Cao, J. Chen, B. Zheng and H. Zhang, Small, 2014, 10, 3537–3543.
30. J. Chen, X. J. Wu, L. Yin, B. Li, X. Hong, Z. Fan, B. Chen, X. Can and H. Zhang, Angew. Chem., Int. Ed., 2015, 54, 1210–1214.
31. S. Su, M. Zou, H. Zhao, C. Yuan, Y. Xu, C. Zhang, L. H. Wang, C. H. Fan and L. H. Wang, Nanoscale, 2015, 7, 19129–19135.
32. X. Huang, Z. Zeng, S. Bao, M. Wang, X. Qi, Z. Fan and H. Zhang, Nat. Commun., 2013, 4, 1444.
33. L. Yuwen, F. Xu, B. Xue, Z. Luo, Q. Zhang, B. Bao, S. Su, L. Weng, W. Huang and L. Wang, Nanoscale, 2014, 6, 5762–5769.
34. S. Su, H. F. Sun, F. Xu, L. H. Yuwen and L. H. Wang, Electroanalysis, 2013, 25, 2523–2529.
35. S. Su, C. Zhang, L. Yuwen, J. Chao, X. Zuo, X. Liu, C. Song, C. Fan and L. Wang, ACS Appl. Mater. Interfaces, 2014, 6, 18735–18741.
36. S. S. Chou, M. De, J. Kim, S. Byun, C. Dykstra, J. Yu, J. Huang and V. P. Dravid, J. Am. Chem. Soc., 2013, 135, 4584–4587.
37. J. N. Coleman, M. Lotya, A. O'Neill, S. D. Bergin, P. J. King, U. Khan, K. Young, A. Gaucher, S. De, R. J. Smith, I. V. Shvets, S. K. Arora, G. Stanton, H. Y. Kim, K. Lee, G. T. Kim, G. S. Duesberg, T. Hallam, J. J. Boland, J. J. Wang, J. F. Donegan, J. C. Grunlan, G. Moriarty, A. Shmeliov, R. J. Nicholls, J. M. Perkins, E. M. Grieveson, K. Theuwissen, D. W. McComb, P. D. Nellist and V. Nicolosi, Science, 2011, 331, 568–571.
38. N. R. Jana, L. Gearheart and C. J. Murphy, Langmuir, 2001, 17, 6782–6786.
39. T. Teranishi, M. Hosoe, T. Tanaka and M. Miyake, J. Phys. Chem. B, 1999, 103, 3818–3827.
40. S. Y. Zhao, S. H. Chen, S. Y. Wang, D. G. Li and H. Y. Ma, Langmuir, 2002, 18, 3315–3318.
41. G. Zhang, C. Huang, R. Qin, Z. Shao, D. An, W. Zhang and Y. X. Wang, J. Mater. Chem. A, 2015, 3, 5204–5211.
42. L. Wang and Y. Yamauchi, J. Am. Chem. Soc., 2010, 132(39), 13636–13638.
43. W. Zhou, Z. Yin, Y. Du, X. Huang, Z. Zeng, Z. Fan, H. Liu, J. Wang and H. Zhang, Small, 2013, 9, 140–147.
44. S. Ji, Z. Yang, C. Zhang, Y.-E. Miao, W. W. Tjiu, J. Pan and T. Liu, Microchim. Acta, 2013, 180, 1127–1134.
45. J. Kim, S. Byun, A. J. Smith, J. Yu and J. Huang, J. Phys. Chem. Lett., 2013, 4, 1227–1232.
46. Y. Liu, Y.-X. Yu and W.-D. Zhang, J. Phys. Chem. C, 2013, 117, 12949–12957.
47. Y. Shi, J. K. Huang, L. Jin, Y. T. Hsu, S. F. Yu, L. J. Li and H. Y. Yang, Sci. Rep., 2013, 3, 1839.
48. J. Kim, S. Byun, A. J. Smith, J. Yu and J. Huang, J. Phys. Chem. Lett., 2013, 4, 1227–1232.
49. Y. Chen, J. Yang, Y. Yang, Z. Peng, J. Li, T. Mei, J. Wang, M. Hao, Y. Chen, W. Xiong, L. Zhang and X. Wang, Chem. Commun., 2015, 10, 1039.
50. A. Akinpelu, B. Merzougui, S. Bukola, A.-M. Azad, R. A. Basheer, G. M. Swain, Q. Chang and M. Shao, Electrochim. Acta, 2015, 161, 305–311.
51. C.-S. Chen, F.-M. Pan and H.-J. Yu, Appl. Catal., B, 2011, 104, 382–389.
52. A. Maksic, Z. Rakocevic, M. Smiljanic, M. Nenadovic and S. Strbac, J. Power Sources, 2015, 273, 724–734.
53. A. Dutta and J. Ouyang, ACS Catal., 2015, 5, 1371–1380.

---

Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr06077j

---