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Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction
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Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction Xuexiang Weng a, Yan Liu a, Ke-Ke Wang a, Jiu-Ju Feng a, Junhua Yuan a, Ai-Jun Wang a,*, Quan-Qing Xu b,** a College of Chemistry and Life Science, College of Geography and Environmental Science, Zhejiang Normal University, Jinhua 321004, China b Faculty of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650050, China
article info
abstract
Article history:
Herein, well-dispersed porous AuPt alloy nanodendrites (AuPt NDs) were facilely synthe-
Received 22 May 2016
sized by a single-step seedless approach by using 5-aminouracil-6-carboxylic acid (AUCA)
Received in revised form
as the capping agent and weak stabilizer. The architectures showed large electrochemi-
15 July 2016
cally active surface area (29.67 m2 g1), and enhanced catalytic performances for oxygen
Accepted 18 July 2016
reduction reaction (ORR) and hydrogen evolution reaction (HER) both in acid and alkaline
Available online xxx
media. Specifically, the mass activity and specific activity of the as-made catalyst were 31.55 mA mg1 and 2.65 mA cm2 (0.1 M HClO4), 29.49 mA mg1 and 2.5 mA cm2 (0.1 M
Keywords:
KOH) for ORR, respectively, along with a notably low Tafel slope of 34 mV dec1
Nanodendrites
(0.5 M H2SO4) and 55 mV dec1 (0.1 M KOH) towards HER. This synthetic approach can be
Alloy
explored to fabricate other catalysts with improved catalytic performances in fuel cells and
5-Aminouracil-6-carboxylic acid
renewable energy.
Oxygen reduction reaction
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Hydrogen evolution reaction
Introduction As well known, Pt-based nanocatalysts are essential for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in renewable energy and fuel cells [1e3]. However, the high cost of Pt and the sluggish ORR kinetics on Pt surface [4] have limited their wide applications [5,6], albeit
with the slight small hydrogen absorption energy and minimum overpotential [7]. Alloying Pt with another metal (M ¼ Pd, Ni, Fe, Au, etc.) is practical to solve these problems [8]. Researchers have constructed many Pt-based bimetallic nanocatalysts to improve the catalytic performances [9e12]. Dominguez-Crespo's group synthesized PtNi nanoparticles with enhanced catalytic activity for hydrogen evolution reaction (HER) [13]. Choi et al. synthesized urchin-like PtNi alloy nanocrystals by a
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (A.-J. Wang), [email protected] (Q.-Q. Xu). http://dx.doi.org/10.1016/j.ijhydene.2016.07.160 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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controlled one-pot method for oxygen reduction reaction (ORR) [14]. Raoof and coworkers fabricated CuPt bimetallic nanoparticles by the galvanic replacement of Cu nanoparticles with Pt for HER [15]. Among Pt-based bimetallic nanocatalysts, AuPt nanocrystals have drawn significant attention because of the unique function of Au [16]. According to the previous literature, the incorporation of Au into Pt catalysts can profoundly enhance the catalytic activity and stability [17,18]. Also, Au can effectively stabilize Pt catalysts, because Au can modify the electronic structure of Pt and reduce the respective d-band center [19,20]. Moreover, the morphologies of nanocatalysts have influence on the catalytic activity [21]. Recently, three-dimensional (3D) dendrite-like nanomaterials are widely investigated because of their large surface areas, providing more active sites available for reactants during ORR [22,23]. Hence, it is important to synthesize porous nanocrystals for the enhanced catalytic behaviors [24]. Wang's group synthesized porous dendritic NiPt nanoparticles for ORR [25]. Li and coworkers constructed Au nanodendrites on graphene oxide nanosheets for ORR [26]. Kim et al. fabricated size-controlled Pt dendrites for ORR [27]. It is interesting and challenging for simple preparation of dendrite-like nanocrystals for ORR and HER under mild conditions. 5-Aminouracil-6-carboxylic acid (AUCA, as described in Fig. S1, Supporting Information, SI) is commonly used to inhibit the metabolic process of the cardioprotective drug dexrazoxane [28]. Herein, with the assistance of AUCA, we facilely synthesized uniform bimetallic AuPt alloy nanodendrites (AuPt NDs) by a single-step seedless aqueous approach. The catalytic properties of AuPt NDs were tested by using ORR and HER as two model systems.
Experimental Preparation of AuPt NDs For the preparation of AuPt NDs, 0.648 mL of H2PtCl6 (38.62 mM), 1.029 mL of HAuCl4 (24.3 mM) and 0.0428 g of AUCA (dissolved by 0.5 mL of 1 M NaOH solution) were put into 5 mL of polyvinylpyrrolidone (PVP) with the concentration of 0.5 wt% under stirring at room temperature. The mixture was diluted to 10 mL. Afterwards, 100 mL of hydrazine hydrate solution (16.5 M) was dropwise put into the system and reacted for 10 min. The resulting solution was centrifuged and the precipitates were obtained by completely washing several times to remove the excess PVP. Finally, the product was dried in vacuum at 60 C for further characterization. For comparison, Au1Pt3 and Au3Pt1 nanocrystals, and Pt nanospheres (NSs) were prepared by changing the ratios of HAuCl4 and H2PtCl6 while the other experiments were kept unchanged.
Electrochemical experiments All the electrochemical measurements were conducted on a conventional three-electrode system [29]. For preparation of AuPt NDs modified electrode, 1 mg of AuPt NDs was firstly put
into 1 mL of water by ultrasonication (1 mg mL1) to form a homogeneous suspension. Next, 6 mL of the suspension and 4 mL of Nafion solution (0.05 wt%) was orderly dropped on the clean glassy carbon electrode (GCE) and then dried in air. For comparison, Au1Pt3, Au3Pt1, Pt NSs, Pt black and Pt/C (20 wt%) catalysts modified electrodes were prepared using the same method. More details of the experimental sections were provided in Supporting Information (SI).
Results and discussion Physical characterization The morphology and size of the as-obtained AuPt NDs were examined by transmission electron microscopy (TEM) images (Fig. 1AeC). As displayed in Fig. 1A and B, the lowmagnification TEM images reveal that the product contains many uniformly well-dispersed dendrites with the mean size of 35.45 nm. Each nanodendrite is consisted of many smaller grains, showing the interconnected porous nanostructures. High-resolution TEM (HRTEM, Fig. 1C) image reveals the welldefined fringes with the d-spacing distances of 0.226 (a), 0.225 (b), and 0.224 nm (c). These values are smaller than that of the face-centered cubic (fcc) Au (0.235 nm), but are very close to that of Pt (0.226 nm) [30], indicating the formation of AuPt alloy [31]. Furthermore, the selected-area electron diffraction (SAED) pattern of one nanodendrite implies their polycrystalline nature (Fig. 1D). The high-angle annular dark-field scanning TEM (HAADFSTEM), energy-dispersive X-ray spectroscopy (EDS) mapping, and EDS line scanning profiles manifest the elemental distribution of AuPt NDs (Fig. 2) [32]. As shown in Fig. 2AeD, Au and Pt are evenly distributed among the whole nanodendrite, which reflects the formation of AuPt alloy [33]. The EDS line scanning profiles (Fig. 2E) show the coexistence of Pt and Au elements, proving their homogeneous distribution of AuPt NDs. According to the EDS analysis, the atomic ratio of Au to Pt is estimated to be 0.79. Additionally, C and Cu elements are also found in the product, which are originated from the copper grid (Fig. 2F). Fig. 3 shows the TEM images of Au1Pt3, Au3Pt1 and Pt nanocrystals synthesized by regulating the molar ratios of HAuCl4 and H2PtCl6. It clearly indicates that the nanocrystals are aggregated together (Fig. 3A and C) and sphere-like Pt nanocrystals are obtained with the relative smooth surface and the size of about 109.2 nm (Fig. 3E and F). These reveal the important role of Au in the process to form the nanodendrites. The asprepared AuPt NDs may have improved electrochemical activity owing to their porous dendrite-like nanocrystals [34]. X-ray diffraction (XRD, Fig. 4) spectra were provided to inspect the crystal structure of AuPt NDs. Apparently, the representative diffraction peaks of AuPt NDs are matched perfectly with those of the fcc structures (2q ¼ 39.15 , 45.51 , 66.75 , and 79.75 , corresponding to the (111), (200), (220), and (311) planes, respectively). Furthermore, the above-mentioned peaks locate between monometallic Au and Pt [35]. It is worthy to note that the intensity ratio of the (111) planes relative to the (200), (220) and (311) planes are about 3.10, 4.57, and 5.54,
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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Fig. 1 e (A) Low-, (B) medium-, and (C) high-resolution TEM images of AuPt NDs obtained in the presence of 25 mM AUCA. (D) The corresponding SAED pattern. Inset in (A) shows the particle-size distribution.
respectively, which are much higher than those of bulk Pt and Au [36]. These results strongly demonstrate the preferential crystal growth along the (111) directions in the synthetic process, as supported by the HR-TEM analysis [37]. X-ray photoelectron spectroscopy (XPS) measurements were conducted to analyze the chemical composition and electronic structure of AuPt nanocrystals [38]. As clearly described by Fig. 5A, the peak position of Pt is blue-shifted with the content of Au increased, while Au is red-shifted (Fig. 5B). These phenomena indicate the changes of the electronic structure, the intra- and inter-atomic charges transfer between Au and Pt in AuPt nanocrystals, which are previously reported by the literature [39,40]. The modified electronic structure by alloying Pt with Au has some effects on the electrocatalytic performances of ORR and HER [41,42]. Besides, the atomic ratios of Pt/Au are estimated to be 1.26:1, 2.97:1, and 1:3.05 for Au1Pt1, Au1Pt3 and Au3Pt1, which are in good consistent with the EDS data (Figs. 2F and 3B, D). Fig. 5C and D show the valence states of Pt 4f and Au 4f in AuPt NDs. Obviously, Au0 is the main species, as manifested by the high-resolution Au 4f XPS spectrum, in which Au 4f5/2 and Au 4f7/2 bands are located at 83.95 and 87.62 eV, respectively (Fig. 5C). As described in Fig. 5D, Pt 4f signals are divided into two components, a lower binding energy band (Pt 4f7/2) and a higher one (Pt 4f5/2). The binding energies at 74.22 and 70.89 eV are assigned to Pt 4f5/2 and Pt 4f7/2 of metallic Pt0, and the peaks at 75.02 eV and 71.83 eV come from Pt 4f5/2 and Pt 4f7/2 of Pt2þ. Notably, Pt0 is the primary species in AuPt NDs. These facts manifest the efficient reduction of the precursors 2 (AuCl 4 and PtCl6 ) [43].
Formation mechanism It is well known that AUCA molecules have some positively charged groups, such as amino and imino groups (Fig. S1, SI)
which have strong electrostatic adsorption with negatively 2 charged groups (i.e., AuCl 4 and PtCl6 ) [44]. Fig. 6 shows the effects of the AUCA concentrations on the formation of AuPt NDs. Apparently, the addition of 5 mM AUCA (Fig. 6A) induces the formation of irregular solid nanoparticles with rather large diameter (83.9 nm). And the solid particles become smaller with rough surfaces by increasing the AUCA concentrations up to 10 mM (Fig. 6B). The solid particles become smaller when the AUCA concentration achieves 20 mM (Fig. 6C). And well-dispersed dendrites with an average diameter of 36.5 nm show up by further increasing the concentration of AUCA to 25 mM (Fig. 1A). Alternatively, with the excessive of AUCA (50 mM), the products become relatively small and inhomogeneous (Fig. 6D). These observations strongly demonstrate the important role of AUCA as the capping agent and stabilizer in the formation of the dendritic nanostructures. Fig. 7 describes the formation mechanism of AuPt NDs. Upon the addition of hydrazine hydrate, the precursors of 2 AuCl 4 and PtCl6 are quickly reduced to Au and Pt atoms and fused together to generate AuPt nuclei. Afterwards, AuPt nuclei gradually evolve into AuPt nanodendrites through the epitaxial growth along the (111) directions under the guidance of AUCA and PVP, causing the final formation of well-defined blossom-like nanodendrites. These reveal the crucial role of AUCA as the structure director and capping agent during the nucleation and crystal growth [45].
Electrocatalytic performance of AuPt NDs The ECSA is an important factor in assessing the performance of catalysts [46]. Fig. S2 clearly shows the CV curves of AuPt NDs (curve a), Pt black (curve b), Pt NSs (curve c), Au1Pt3 (curve d) and Au3Pt1 (curve e) catalysts modified electrodes in N2saturated 0.5 M H2SO4 at a scan rate of 50 mV s1, which
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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Fig. 2 e (A) HAADF-STEM image, (BeD) HAADF-STEM-EDS mapping, (E) line scanning profiles, and (F) EDS spectrum of AuPt NDs.
include hydrogen and hydroxyl species (OHad) ad-/de-sorption regions, respectively. The ECSA values are calculated by the hydrogen adsorption peaks. Obviously, the ECSA of AuPt NDs (29.67 m2 g1) is higher than Pt black (17.29 m2 g1), Pt (9.97 m2 g1), Au1Pt3 (9.85 m2 g1) and Au3Pt1 (5.34 m2 g1) under the identical conditions, probably owing to the multiporous structures of AuPt NDs. In order to explore the catalytic activity of AuPt NDs modified electrode, the ORR polarization curves were recorded in O2saturated 0.1 M HClO4 with a rotation rate of 1600 rpm. Fig. 8A shows the linear sweep voltammograms (LSVs) of AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts modified electrodes. The onset potentials of AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 are 0.80, 0.77, 0.72, 0.62 and 0.56 V, whereas their halfwave potentials are 0.72, 0.68, 0.61, 0.55 and 0.45 V, respectively. These results indicate that AuPt NDs show the positive onset potential and half-wave potential. These phenomena demonstrate the enhanced kinetic ability of AuPt NDs for ORR. To further illustrate the intrinsic catalytic activity of AuPt NDs, the associated specific activity and mass activity were
compared with those of Pt black and Pt NSs catalyst (Fig. 8B). It shows that the specific activity of AuPt NDs is 2.65 mA cm2 at 0.70 V, which is larger than Pt black (1.92 mA cm2), Pt NSs (1.76 mA cm2), Au1Pt3 (1.65 mA cm2) and Au3Pt1 (1.03 mA cm2). Similarly, the mass activity of AuPt NDs is 31.55 mA mg1, which is also higher than Pt black (22.41 mA mg1), Pt NSs (17.25 mA mg1), Au1Pt3 (16.89 mA mg1) and Au3Pt1 (9.43 mA mg1). These data demonstrate the better ORR electrocatalytic performances of AuPt NDs than Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts. Besides, the transferred electrons (n) towards ORR on AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts were also estimated by LSVs in O2-saturated 0.1 M HClO4 at different rotational speeds (Fig. 8C and Fig. S3). By calculating from Koutecky-Levich (K-L) equation, the n values are around 3.97, 4.03, 4.09, 4.06 and 3.98 for AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1, respectively (Fig. 8D). These results suggest that the reduction process of O2 to H2O is the four-electron transfer pathway [47], which can provide a faster oxygen reduction rate.
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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Fig. 3 e TEM images of AuPt products prepared with different compositions: (A) Au1Pt3, (C) Au3Pt1, (E and F) Pt NSs. (B) EDS spectrum of Au1Pt3, (D) EDS spectrum of Au3Pt1 nanocrystals.
Fig. 4 e XRD pattern of AuPt NDs. Standard Au (JCPDS-040784) and Pt (JCPDS-04-0802) XRD patterns were provided for comparison.
The ORR catalytic performance of AuPt NDs was further evaluated in alkaline media. Similarly, the LSVs of AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts were recorded with a rotation rate of 1600 rpm in O2-saturated 0.1 M KOH (Fig. S4A).
The onset potential (0.98 V) and half-wave potential (0.87 V) of AuPt NDs are also more positive than those of Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts. And the specific activities of AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 are 2.5, 2.15, 1.93, 1.79 and 1.68 mA cm2, respectively. Also, their corresponding mass activities are 29.49, 25.33, 19.20, 17.65 and 15.25 mA mg1 (Fig. S4B). These data demonstrate the better ORR electrocatalytic performance of AuPt NDs in alkaline media. What' more, the transferred electrons (n) towards ORR on AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts were also estimated by LSVs in O2-saturated 0.1 M KOH at different rotation speeds (Fig. S5). Fig. S4D shows the corresponding K-L plots. It is found that ORR occurred at AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 are also mainly guided by direct four electron reduction mechanism in acid media, as supported by the previous literature [47]. The catalytic activity of AuPt NDs towards HER was firstly evaluated in N2-saturated 0.5 M H2SO4 at the scan rate of 5 mV s1. As shown in Fig. 9A and B, the catalytic current density is 10 mV cm2 at 50 mV for AuPt NDs, accompanied with the smaller onset potential at 27 mV, which are better
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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Fig. 5 e (A) Pt 4f and (B) Au 4f XPS spectra of Au1Pt1, Au1Pt3, Au3Pt1 nanocrystals, and Pt NSs. High-resolution XPS spectra of (C) Au 4f and (D) Pt 4f of AuPt NDs.
Fig. 6 e TEM images of AuPt products obtained in the presence of (A) 5 mM, (B) 10 mM, (C) 20 mM and (D) 50 mM AUCA. Inset shows the corresponding particle-size distribution. than Pt NSs, Au1Pt3 and Au3Pt1 with the catalytic current density of 10 mV cm2 at 93, 230 and 256 mV, whereas their onset potentials are 83, 211, and 231 mV, respectively. Also, these values are comparable to commercial Pt/C (20 wt%)
with the catalytic current density of 10 mV cm2 at 35 mV and the onset potential of 39 mV, respectively, which are similar to the previous work [48,49]. These results demonstrate the comparable catalytic activity of AuPt NDs.
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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Fig. 7 e A schematic illustration of the formation mechanism of AuPt NDs.
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is much better than Pt NSs (48 mV dec1), Au1Pt3 (48 mV dec1) and Au3Pt1 (53 mV dec1), but very close to that of Pt/C (29 mV dec1), which is in good accordance with the previous reports [52,53]. These observations confirm the HER process occurred via the Volmer-Heyrovsky mechanism [54]. The high HER activity of AuPt NDs is not only limited to acid media. The electrochemical performances of AuPt NDs were tested in 0.1 M KOH (Fig. S6), which reveal that AuPt NDs exhibit improved catalytic activity. In the 0.1 M KOH, the onset potential of AuPt NDs is 36 mV, which is more positive than Pt NSs (58 mV), Au1Pt3 (150 mV) and Au3Pt1 (182 mV) when comparable to Pt/C catalyst (12 mV). The corresponding Tafel slope of AuPt NDs is 55 mV dec1. This value is comparable to that of Pt/C (52 mV dec1), but much better than those of Pt NSs (67 mV dec1), Au1Pt3 (70 mV dec1), and Au3Pt1 (123 mV dec1). These results show that AuPt NDs have the similar enhanced catalytic activity trends as in acid media. LSVs were recorded from 0.2 to 0.2 V at 50 mV s1 for 1000 cycles to evaluate the stability of AuPt NDs in 0.1 M KOH and 0.5 M H2SO4. As illustrated in Fig. 9D and S6D, the polarization curves are almost remained unchanged before and after the
Fig. 8 e (A) LSVs of AuPt NDs, commercial Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts in O2-saturated 0.1 M HClO4 at a scan rate of 5 mV s¡1 with the rotating rate of 1600 rpm. (B) Comparison of the corresponding specific and mass activities at 0.70 V. (C) LSVs of AuPt NDs catalysts in O2-saturated 0.1 M KOH at a scan rate of 5 mV s¡1 with different rotating rates: 100, 400, 900, 1600, and 2500 rpm. The current density is calculated by using the geometric area of the RDE. (D) The corresponding K-L plots of different catalyst.
The Tafel slope is regarded as an inherent property of catalysts and a significant standard to evaluate the HER performance [50]. A low Tafel slope causes a greatly enhanced HER rate by increasing the potentials [51]. Fig. 9C shows the Tafel slope of AuPt NDs with the value of 34 mV dec1, which
cycling test, showing the negligible changes of the overpotentials less than 10 mV, indicating the superior stability of AuPt NDs both in acid and alkaline media. The long-term stability of AuPt NDs was also tested by chronoamperometry at 0.3 V in N2-saturated 0.1 M KOH and 0.5 M H2SO4 (the
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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Fig. 9 e (A)e(B) HER polarization curves of AuPt NDs, commercial Pt/C, Pt NSs, Au1Pt3, Au3Pt1 catalysts in 0.5 M H2SO4 at 5 mV s¡1. (B) The corresponding Tafel slopes. (C) The corresponding Tafel slopes. (D) HER activities of AuPt NDs before and after 1000 cycles at a scan speed of 50 mV s¡1. The inset is the chronoamperometric curve of AuPt NDs for 10,000 s at ¡0.30 V in 0.5 M H2SO4.
insets of S6D and Fig. 9D). Clearly, the catalytic current density shows no obvious decrease within 10,000 s, which indicates the improved long-term stability of AuPt NDs after the longterm test.
21162043) and Zhejiang provincial public welfare project (No. 2016C33011).
Appendix A. Supplementary data Conclusions Well-dispersed AuPt NDs were obtained by a facile single-step seedless aqueous method, where AUCA was acted as the capping agent and weak stabilizer. The mass activity and specific activity of AuPt NDs were 31.55 mA mg1 and 2.65 mA cm2 (0.1 M HClO4), 29.49 mA mg1 and 2.5 mA cm2 (0.1 M KOH) for ORR, respectively. The architectures exhibited excellent catalytic activity towards HER with a notably low Tafel slope of 34 mV dec1 (0.5 M H2SO4) and 55 mV dec1 (0.1 M KOH). These results indicated the improved catalytic activities for ORR and HER in comparison to commercial Pt black, Pt/C, Pt NSs, Au1Pt3, and Au3Pt1 catalysts, respectively. The superior performances are ascribed to the synergistic effect of Au with Pt and the unique structure of AuPt NDs. The as-prepared AuPt NDs are promising catalysts in fuel cells and renewable energy.
Acknowledgement This work was financially supported by National Natural Science Foundation of China (Nos. 21475118, 21275130 and
Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ijhydene.2016.07.160.
references
[1] Jahan M, Liu Z, Loh KP. A graphene oxide and coppercentered metal organic framework composite as a trifunctional catalyst for HER, OER, and ORR. Adv Funct Mater 2013;23:5363e72. [2] Zhang L, Su Z, Jiang F, Yang L, Qian J, Zhou Y, et al. Highly graphitized nitrogen-doped porous carbon nanopolyhedra derived from ZIF-8 nanocrystals as efficient electrocatalysts for oxygen reduction reactions. Nanoscale 2014;6:6590e602. [3] Zhong H-X, Wang J, Zhang Y-W, Xu W-L, Xing W, Xu D, et al. ZIF-8 derived graphene-based nitrogen-doped porous carbon sheets as highly efficient and durable oxygen reduction electrocatalysts. Angew Chem Int Ed 2014;53:14235e9. [4] Yang J, Zhou W, Cheng C-H, Lee J-Y, Liu Z. Pt-decorated PdFe nanoparticles as methanol-tolerant oxygen reduction electrocatalyst. ACS Appl Mater Interfaces 2009;2:119e26. [5] Ye G, Gong Y, Lin J, Li B, He Y, Pantelides ST, et al. Defects engineered monolayer MoS2 for improved hydrogen evolution reaction. Nano Lett 2016;16:1097e103.
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[6] Lu J, Zhou W, Wang L, Jia J, Ke Y, Yang L, et al. Core-shell nanocomposites based on gold nanoparticle@ zinc-ironembedded porous carbons derived from metal-organic frameworks as efficient dual catalysts for oxygen reduction and hydrogen evolution reactions. ACS Catal 2016;6:1045e53. [7] Greeley J, Jaramillo TF, Bonde J, Chorkendorff I, Norskov JK. Computational high-throughput screening of electrocatalytic materials for hydrogen evolution. Nat Mater 2006;5:909e13. [8] Zheng J-N, He L-L, Chen F-Y, Wang A-J, Xue M-W, Feng J-J. Simple one-pot synthesis of platinum-palladium nanoflowers with enhanced catalytic activity and methanoltolerance for oxygen reduction in acid media. Electrochim Acta 2014;137:431e8. [9] Fu G, Wu K, Lin J, Tang Y, Chen Y, Zhou Y, et al. One-pot water-based synthesis of Pt-Pd alloy nanoflowers and their superior electrocatalytic activity for the oxygen reduction reaction and remarkable methanol-tolerant ability in acid media. J Phys Chem C 2013;117:9826e34. € tz R, Schnyder B, Schmidt V. [10] Drillet J-F, Ee A, Friedemann J, Ko Oxygen reduction at Pt and Pt70Ni30 in H2SO4/CH3OH solution. Electrochim Acta 2002;47:1983e8. [11] Sku´lason E, Karlberg GS, Rossmeisl J, Bligaard T, Greeley J, Jonsson H, et al. Density functional theory calculations for the hydrogen evolution reaction in an electrochemical double layer on the Pt (111) electrode. Phys Chem Chem Phys 2007;9:3241e50. [12] Grigoriev S, Millet P, Fateev V. Evaluation of carbonsupported Pt and Pd nanoparticles for the hydrogen evolution reaction in PEM water electrolysers. J Power Sources 2008;177:281e5. [13] Domı´nguez-Crespo MA, Ramı´rez-Meneses E, TorresHuerta AM, Garibay-Febles V, Philippot K. Kinetics of hydrogen evolution reaction on stabilized Ni, Pt and Ni-Pt nanoparticles obtained by an organometallic approach. Int J Hydrogen Energy 2012;37:4798e811. [14] Choi K-H, Jang Y, Chung D-Y, Seo P, Jun S-W, Lee J-E, et al. A simple synthesis of urchin-like Pt-Ni bimetallic nanostructures as enhanced electrocatalysts for the oxygen reduction reaction. Chem Commun 2016;52:597e600. [15] Raoof JB, Ojani R, Esfeden SA, Nadimi SR. Fabrication of bimetallic Cu/Pt nanoparticles modified glassy carbon electrode and its catalytic activity toward hydrogen evolution reaction. Int J Hydrogen Energy 2010;35:3937e44. [16] Wei Y-C, Chen T-Y, Liu C-W, Chan T-S, Lee J-F, Lee C-H, et al. The structure modification and activity improvement of PdeCo/C electrocatalysts by the addition of Au for the oxygen reduction reaction. Catal Sci Technol 2012;2:1654e64. [17] Kim Y, Hong JW, Lee YW, Kim M, Kim D, Yun WS, et al. Synthesis of AuPt heteronanostructures with enhanced electrocatalytic activity toward oxygen reduction. Angew Chem Int Ed 2010;49:10197e201. [18] Hu Y, Zhang H, Wu P, Zhang H, Zhou B, Cai C. Bimetallic PtAu nanocatalysts electrochemically deposited on graphene and their electrocatalytic characteristics towards oxygen reduction and methanol oxidation. Phys Chem Chem Phys 2011;13:4083e94. [19] Cao M, Wu D, Cao R. Recent advances in the stabilization of platinum electrocatalysts for fuel-cell reactions. ChemCatChem 2014;6:26e45. [20] Zhang J, Sasaki K, Sutter E, Adzic R. Stabilization of platinum oxygen-reduction electrocatalysts using gold clusters. Science 2007;315:220e2. [21] Liang H-P, Guo Y-G, Zhang H-M, Hu J-S, Wan L-J, Bai C-L. Controllable AuPt bimetallic hollow nanostructures. Chem Commun 2004;13:1496e7. [22] Kawasaki H, Yao T, Suganuma T, Okumura K, Iwaki Y, Yonezawa T, et al. Platinum nanoflowers on scratched
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
9
silicon by galvanic displacement for an effective SALDI substrate. Chem Eur J 2010;16:10832e43. Xiong L, Huang Y-X, Liu X-W, Sheng G-P, Li W-W, Yu H-Q. Three-dimensional bimetallic Pd-Cu nanodendrites with superior electrochemical performance for oxygen reduction reaction. Electrochim Acta 2013;89:24e8. Song P, Mei L-P, Wang A-J, Fang K-M, Feng J-J. One-pot surfactant-free synthesis of porous PtAu alloyed nanoflowers with enhanced electrocatalytic activity for ethanol oxidation and oxygen reduction reactions. Int J Hydrogen Energy 2015;41:1645e53. Eid K, Wang H, Yamauchi Y, Wang L. Facile synthesis of porous dendritic bimetallic PtNi nanocrystals as efficient catalysts for oxygen reduction reaction. Chem Asian J 2016;11:1388e93. Li X-R, Li X-L, Xu M-C, Xu J-J, Chen H-Y. Gold nanodendrities on graphene oxide nanosheets for oxygen reduction reaction. J Mater Chem A 2014;2:1697e703. Kim C, Oh J-G, Kim Y-T, Kim H, Lee H. Platinum dendrites with controlled sizes for oxygen reduction reaction. Electrochem Commun 2010;12:1596e9. Ortiz S, Alcolea Palafox M, Rastogi VK, Tomer R. Solid state simulation of tetramer form of 5-aminoorotic acid: the vibrational spectra and molecular structure study by using MP2 and DFT calculations. Spectrochim Acta Part A 2012;97:948e62. Liu Y, Chen S-S, Wang A-J, Feng J-J, Wu X, Weng X. An ultrasensitive electrochemical sensor for hydrazine based on AuPd nanorod alloy nanochains. Electrochim Acta 2016;195:68e76. Zheng J-N, Li S-S, Ma X, Chen F-Y, Wang A-J, Chen J-R, et al. Popcorn-like PtAu nanoparticles supported on reduced graphene oxide: facile synthesis and catalytic applications. J Mater Chem A 2014;2:8386e95. Zhou W, Li M, Zhang L, Chan SH. Supported PtAu catalysts with different nano-structures for ethanol electrooxidation. Electrochim Acta 2014;123:233e9. Zhao Z-L, Zhang L-Y, Bao S-J, Li C-M. One-pot synthesis of small and uniform Au@ PtCu core-alloy shell nanoparticles as an efficient electrocatalyst for direct methanol fuel cells. Appl Catal B 2015;174:361e6. Li C, Wang H, Yamauchi Y. Electrochemical deposition of mesoporous Pt-Au alloy films in aqueous surfactant solutions: towards a highly sensitive amperometric glucose sensor. Chem Eur J 2013;19:2242e6. Han X, Wang D, Liu D, Huang J, You T. Synthesis and electrocatalytic activity of Au/Pt bimetallic nanodendrites for ethanol oxidation in alkaline medium. J Colloid Interface Sci 2012;367:342e7. Song P, Li S-S, He L-L, Feng J-J, Wu L, Zhong S-X, et al. Facile large-scale synthesis of Au-Pt alloyed nanowire networks as efficient electrocatalysts for methanol oxidation and oxygen reduction reactions. RSC Adv 2015;5:87061e8. Wu L, Zhang S, Wang M, Xu M, Zhu X, Sun D, et al. Surfactant-free synthesis of coral-like platinum nanochains for oxygen reduction reaction. Electrochim Acta 2015;157:101e7. Liu Q, Xu Y-R, Wang A-J, Feng J-J. Simple wet-chemical synthesis of core-shell Au-Pd@ Pd nanocrystals and their improved electrocatalytic activity for ethylene glycol oxidation reaction. Int J Hydrogen Energy 2015;41:2547e53. Liu Q, Xu Y-R, Wang A-J, Feng J-J. A single-step route for large-scale synthesis of core-shell palladium@ platinum dendritic nanocrystals/reduced graphene oxide with enhanced electrocatalytic properties. J Power Sources 2016;302:394e401. Ye W, Kou H, Liu Q, Yan J, Zhou F, Wang C. Electrochemical deposition of AuePt alloy particles with cauliflower-like
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
10
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 0
microstructures for electrocatalytic methanol oxidation. Int J Hydrogen Energy 2012;37:4088e97. Xu C, Wang R, Chen M, Zhang Y, Ding Y. Dealloying to nanoporous Au/Pt alloys and their structure sensitive electrocatalytic properties. Phys Chem Chem Phys 2010;12:239e46. Wang D, Xin HL, Yu Y, Wang H, Rus E, Muller DA, et al. Ptdecorated PdCo@ Pd/C core-shell nanoparticles with enhanced stability and electrocatalytic activity for the oxygen reduction reaction. J Am Chem Soc 2010;132:17664e6. Navarro-Flores E, Chong Z, Omanovic S. Characterization of Ni, NiMo, NiW and NiFe electroactive coatings as electrocatalysts for hydrogen evolution in an acidic medium. J Mol Catal A Chem 2005;226:179e97. Ye W, Yu J, Zhou Y, Gao D, Wang D, Wang C, et al. Green synthesis of PteAu dendrimer-like nanoparticles supported on polydopamine-functionalized graphene and their high performance toward 4-nitrophenol reduction. Appl Catal B 2016;181:371e8. Kostova I, Peica N, Kiefer W. Theoretical and spectroscopic studies of 5-aminoorotic acid and its new lanthanide (III) complexes. J Raman Spectrosc 2007;38:205e16. Ju K-J, Feng J-J, Zhang Q-L, Wei J, Wang A-J. Aminoorotic acid directed synthesis of graphene-supported AuPt nanocrystals with enhanced electrocatalytic properties. Electrochim Acta 2015;41:2547e53. Lan F, Wang D, Lu S, Zhang J, Liang D, Peng S, et al. Ultra-low loading Pt decorated coral-like Pd nanochain networks with enhanced activity and stability towards formic acid electrooxidation. J Mater Chem A 2013;1:1548e52. Sun L, Wang H, Eid K, Alshehri SM, Malgras V, Yamauchi Y, et al. One-step synthesis of dendritic bimetallic PtPd
[48]
[49]
[50]
[51]
[52]
[53]
[54]
nanoparticles on reduced graphene oxide and its electrocatalytic properties. Electrochim Acta 2016;188:845e51. Popczun EJ, McKone JR, Read CG, Biacchi AJ, Wiltrout AM, Lewis NS, et al. Nanostructured nickel phosphide as an electrocatalyst for the hydrogen evolution reaction. J Am Chem Soc 2013;135:9267e70. Xu Y, Wu R, Zhang J, Shi Y, Zhang B. Anion-exchange synthesis of nanoporous FeP nanosheets as electrocatalysts for hydrogen evolution reaction. Chem Commun 2013;49:6656e8. Li Y, Wang H, Xie L, Liang Y, Hong G, Dai H. MoS2 nanoparticles grown on graphene: an advanced catalyst for the hydrogen evolution reaction. J Am Chem Soc 2011;133:7296e9. Kundu MK, Bhowmik T, Barman S. Gold aerogel supported on graphitic carbon nitride: an efficient electrocatalyst for oxygen reduction reaction and hydrogen evolution reaction. J Mater Chem A 2015;3:23120e35. Wang X-D, Xu Y-F, Rao H-S, Xu W-J, Chen H-Y, Zhang W-X, et al. Novel porous molybdenum tungsten phosphide hybrid nanosheets on carbon cloth for efficient hydrogen evolution. Energy Environ Sci 2016;9:1468e75. Son CY, Kwak IH, Lim YR, Park J. FeP and FeP2 nanowires for efficient electrocatalytic hydrogen evolution reaction. Chem Commun 2016;52:2819e22. Fei H, Yang Y, Peng Z, Ruan G, Zhong Q, Li L, et al. Cobalt nanoparticles embedded in nitrogen-doped carbon for the hydrogen evolution reaction. ACS Appl Mater Interfaces 2015;7:8083e7.
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Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction Xuexiang Weng a, Yan Liu a, Ke-Ke Wang a, Jiu-Ju Feng a, Junhua Yuan a, Ai-Jun Wang a,*, Quan-Qing Xu b,** a College of Chemistry and Life Science, College of Geography and Environmental Science, Zhejiang Normal University, Jinhua 321004, China b Faculty of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming 650050, China
article info
abstract
Article history:
Herein, well-dispersed porous AuPt alloy nanodendrites (AuPt NDs) were facilely synthe-
Received 22 May 2016
sized by a single-step seedless approach by using 5-aminouracil-6-carboxylic acid (AUCA)
Received in revised form
as the capping agent and weak stabilizer. The architectures showed large electrochemi-
15 July 2016
cally active surface area (29.67 m2 g1), and enhanced catalytic performances for oxygen
Accepted 18 July 2016
reduction reaction (ORR) and hydrogen evolution reaction (HER) both in acid and alkaline
Available online xxx
media. Specifically, the mass activity and specific activity of the as-made catalyst were 31.55 mA mg1 and 2.65 mA cm2 (0.1 M HClO4), 29.49 mA mg1 and 2.5 mA cm2 (0.1 M
Keywords:
KOH) for ORR, respectively, along with a notably low Tafel slope of 34 mV dec1
Nanodendrites
(0.5 M H2SO4) and 55 mV dec1 (0.1 M KOH) towards HER. This synthetic approach can be
Alloy
explored to fabricate other catalysts with improved catalytic performances in fuel cells and
5-Aminouracil-6-carboxylic acid
renewable energy.
Oxygen reduction reaction
© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
Hydrogen evolution reaction
Introduction As well known, Pt-based nanocatalysts are essential for hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in renewable energy and fuel cells [1e3]. However, the high cost of Pt and the sluggish ORR kinetics on Pt surface [4] have limited their wide applications [5,6], albeit
with the slight small hydrogen absorption energy and minimum overpotential [7]. Alloying Pt with another metal (M ¼ Pd, Ni, Fe, Au, etc.) is practical to solve these problems [8]. Researchers have constructed many Pt-based bimetallic nanocatalysts to improve the catalytic performances [9e12]. Dominguez-Crespo's group synthesized PtNi nanoparticles with enhanced catalytic activity for hydrogen evolution reaction (HER) [13]. Choi et al. synthesized urchin-like PtNi alloy nanocrystals by a
* Corresponding author. ** Corresponding author. E-mail addresses: [email protected] (A.-J. Wang), [email protected] (Q.-Q. Xu). http://dx.doi.org/10.1016/j.ijhydene.2016.07.160 0360-3199/© 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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controlled one-pot method for oxygen reduction reaction (ORR) [14]. Raoof and coworkers fabricated CuPt bimetallic nanoparticles by the galvanic replacement of Cu nanoparticles with Pt for HER [15]. Among Pt-based bimetallic nanocatalysts, AuPt nanocrystals have drawn significant attention because of the unique function of Au [16]. According to the previous literature, the incorporation of Au into Pt catalysts can profoundly enhance the catalytic activity and stability [17,18]. Also, Au can effectively stabilize Pt catalysts, because Au can modify the electronic structure of Pt and reduce the respective d-band center [19,20]. Moreover, the morphologies of nanocatalysts have influence on the catalytic activity [21]. Recently, three-dimensional (3D) dendrite-like nanomaterials are widely investigated because of their large surface areas, providing more active sites available for reactants during ORR [22,23]. Hence, it is important to synthesize porous nanocrystals for the enhanced catalytic behaviors [24]. Wang's group synthesized porous dendritic NiPt nanoparticles for ORR [25]. Li and coworkers constructed Au nanodendrites on graphene oxide nanosheets for ORR [26]. Kim et al. fabricated size-controlled Pt dendrites for ORR [27]. It is interesting and challenging for simple preparation of dendrite-like nanocrystals for ORR and HER under mild conditions. 5-Aminouracil-6-carboxylic acid (AUCA, as described in Fig. S1, Supporting Information, SI) is commonly used to inhibit the metabolic process of the cardioprotective drug dexrazoxane [28]. Herein, with the assistance of AUCA, we facilely synthesized uniform bimetallic AuPt alloy nanodendrites (AuPt NDs) by a single-step seedless aqueous approach. The catalytic properties of AuPt NDs were tested by using ORR and HER as two model systems.
Experimental Preparation of AuPt NDs For the preparation of AuPt NDs, 0.648 mL of H2PtCl6 (38.62 mM), 1.029 mL of HAuCl4 (24.3 mM) and 0.0428 g of AUCA (dissolved by 0.5 mL of 1 M NaOH solution) were put into 5 mL of polyvinylpyrrolidone (PVP) with the concentration of 0.5 wt% under stirring at room temperature. The mixture was diluted to 10 mL. Afterwards, 100 mL of hydrazine hydrate solution (16.5 M) was dropwise put into the system and reacted for 10 min. The resulting solution was centrifuged and the precipitates were obtained by completely washing several times to remove the excess PVP. Finally, the product was dried in vacuum at 60 C for further characterization. For comparison, Au1Pt3 and Au3Pt1 nanocrystals, and Pt nanospheres (NSs) were prepared by changing the ratios of HAuCl4 and H2PtCl6 while the other experiments were kept unchanged.
Electrochemical experiments All the electrochemical measurements were conducted on a conventional three-electrode system [29]. For preparation of AuPt NDs modified electrode, 1 mg of AuPt NDs was firstly put
into 1 mL of water by ultrasonication (1 mg mL1) to form a homogeneous suspension. Next, 6 mL of the suspension and 4 mL of Nafion solution (0.05 wt%) was orderly dropped on the clean glassy carbon electrode (GCE) and then dried in air. For comparison, Au1Pt3, Au3Pt1, Pt NSs, Pt black and Pt/C (20 wt%) catalysts modified electrodes were prepared using the same method. More details of the experimental sections were provided in Supporting Information (SI).
Results and discussion Physical characterization The morphology and size of the as-obtained AuPt NDs were examined by transmission electron microscopy (TEM) images (Fig. 1AeC). As displayed in Fig. 1A and B, the lowmagnification TEM images reveal that the product contains many uniformly well-dispersed dendrites with the mean size of 35.45 nm. Each nanodendrite is consisted of many smaller grains, showing the interconnected porous nanostructures. High-resolution TEM (HRTEM, Fig. 1C) image reveals the welldefined fringes with the d-spacing distances of 0.226 (a), 0.225 (b), and 0.224 nm (c). These values are smaller than that of the face-centered cubic (fcc) Au (0.235 nm), but are very close to that of Pt (0.226 nm) [30], indicating the formation of AuPt alloy [31]. Furthermore, the selected-area electron diffraction (SAED) pattern of one nanodendrite implies their polycrystalline nature (Fig. 1D). The high-angle annular dark-field scanning TEM (HAADFSTEM), energy-dispersive X-ray spectroscopy (EDS) mapping, and EDS line scanning profiles manifest the elemental distribution of AuPt NDs (Fig. 2) [32]. As shown in Fig. 2AeD, Au and Pt are evenly distributed among the whole nanodendrite, which reflects the formation of AuPt alloy [33]. The EDS line scanning profiles (Fig. 2E) show the coexistence of Pt and Au elements, proving their homogeneous distribution of AuPt NDs. According to the EDS analysis, the atomic ratio of Au to Pt is estimated to be 0.79. Additionally, C and Cu elements are also found in the product, which are originated from the copper grid (Fig. 2F). Fig. 3 shows the TEM images of Au1Pt3, Au3Pt1 and Pt nanocrystals synthesized by regulating the molar ratios of HAuCl4 and H2PtCl6. It clearly indicates that the nanocrystals are aggregated together (Fig. 3A and C) and sphere-like Pt nanocrystals are obtained with the relative smooth surface and the size of about 109.2 nm (Fig. 3E and F). These reveal the important role of Au in the process to form the nanodendrites. The asprepared AuPt NDs may have improved electrochemical activity owing to their porous dendrite-like nanocrystals [34]. X-ray diffraction (XRD, Fig. 4) spectra were provided to inspect the crystal structure of AuPt NDs. Apparently, the representative diffraction peaks of AuPt NDs are matched perfectly with those of the fcc structures (2q ¼ 39.15 , 45.51 , 66.75 , and 79.75 , corresponding to the (111), (200), (220), and (311) planes, respectively). Furthermore, the above-mentioned peaks locate between monometallic Au and Pt [35]. It is worthy to note that the intensity ratio of the (111) planes relative to the (200), (220) and (311) planes are about 3.10, 4.57, and 5.54,
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Fig. 1 e (A) Low-, (B) medium-, and (C) high-resolution TEM images of AuPt NDs obtained in the presence of 25 mM AUCA. (D) The corresponding SAED pattern. Inset in (A) shows the particle-size distribution.
respectively, which are much higher than those of bulk Pt and Au [36]. These results strongly demonstrate the preferential crystal growth along the (111) directions in the synthetic process, as supported by the HR-TEM analysis [37]. X-ray photoelectron spectroscopy (XPS) measurements were conducted to analyze the chemical composition and electronic structure of AuPt nanocrystals [38]. As clearly described by Fig. 5A, the peak position of Pt is blue-shifted with the content of Au increased, while Au is red-shifted (Fig. 5B). These phenomena indicate the changes of the electronic structure, the intra- and inter-atomic charges transfer between Au and Pt in AuPt nanocrystals, which are previously reported by the literature [39,40]. The modified electronic structure by alloying Pt with Au has some effects on the electrocatalytic performances of ORR and HER [41,42]. Besides, the atomic ratios of Pt/Au are estimated to be 1.26:1, 2.97:1, and 1:3.05 for Au1Pt1, Au1Pt3 and Au3Pt1, which are in good consistent with the EDS data (Figs. 2F and 3B, D). Fig. 5C and D show the valence states of Pt 4f and Au 4f in AuPt NDs. Obviously, Au0 is the main species, as manifested by the high-resolution Au 4f XPS spectrum, in which Au 4f5/2 and Au 4f7/2 bands are located at 83.95 and 87.62 eV, respectively (Fig. 5C). As described in Fig. 5D, Pt 4f signals are divided into two components, a lower binding energy band (Pt 4f7/2) and a higher one (Pt 4f5/2). The binding energies at 74.22 and 70.89 eV are assigned to Pt 4f5/2 and Pt 4f7/2 of metallic Pt0, and the peaks at 75.02 eV and 71.83 eV come from Pt 4f5/2 and Pt 4f7/2 of Pt2þ. Notably, Pt0 is the primary species in AuPt NDs. These facts manifest the efficient reduction of the precursors 2 (AuCl 4 and PtCl6 ) [43].
Formation mechanism It is well known that AUCA molecules have some positively charged groups, such as amino and imino groups (Fig. S1, SI)
which have strong electrostatic adsorption with negatively 2 charged groups (i.e., AuCl 4 and PtCl6 ) [44]. Fig. 6 shows the effects of the AUCA concentrations on the formation of AuPt NDs. Apparently, the addition of 5 mM AUCA (Fig. 6A) induces the formation of irregular solid nanoparticles with rather large diameter (83.9 nm). And the solid particles become smaller with rough surfaces by increasing the AUCA concentrations up to 10 mM (Fig. 6B). The solid particles become smaller when the AUCA concentration achieves 20 mM (Fig. 6C). And well-dispersed dendrites with an average diameter of 36.5 nm show up by further increasing the concentration of AUCA to 25 mM (Fig. 1A). Alternatively, with the excessive of AUCA (50 mM), the products become relatively small and inhomogeneous (Fig. 6D). These observations strongly demonstrate the important role of AUCA as the capping agent and stabilizer in the formation of the dendritic nanostructures. Fig. 7 describes the formation mechanism of AuPt NDs. Upon the addition of hydrazine hydrate, the precursors of 2 AuCl 4 and PtCl6 are quickly reduced to Au and Pt atoms and fused together to generate AuPt nuclei. Afterwards, AuPt nuclei gradually evolve into AuPt nanodendrites through the epitaxial growth along the (111) directions under the guidance of AUCA and PVP, causing the final formation of well-defined blossom-like nanodendrites. These reveal the crucial role of AUCA as the structure director and capping agent during the nucleation and crystal growth [45].
Electrocatalytic performance of AuPt NDs The ECSA is an important factor in assessing the performance of catalysts [46]. Fig. S2 clearly shows the CV curves of AuPt NDs (curve a), Pt black (curve b), Pt NSs (curve c), Au1Pt3 (curve d) and Au3Pt1 (curve e) catalysts modified electrodes in N2saturated 0.5 M H2SO4 at a scan rate of 50 mV s1, which
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Fig. 2 e (A) HAADF-STEM image, (BeD) HAADF-STEM-EDS mapping, (E) line scanning profiles, and (F) EDS spectrum of AuPt NDs.
include hydrogen and hydroxyl species (OHad) ad-/de-sorption regions, respectively. The ECSA values are calculated by the hydrogen adsorption peaks. Obviously, the ECSA of AuPt NDs (29.67 m2 g1) is higher than Pt black (17.29 m2 g1), Pt (9.97 m2 g1), Au1Pt3 (9.85 m2 g1) and Au3Pt1 (5.34 m2 g1) under the identical conditions, probably owing to the multiporous structures of AuPt NDs. In order to explore the catalytic activity of AuPt NDs modified electrode, the ORR polarization curves were recorded in O2saturated 0.1 M HClO4 with a rotation rate of 1600 rpm. Fig. 8A shows the linear sweep voltammograms (LSVs) of AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts modified electrodes. The onset potentials of AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 are 0.80, 0.77, 0.72, 0.62 and 0.56 V, whereas their halfwave potentials are 0.72, 0.68, 0.61, 0.55 and 0.45 V, respectively. These results indicate that AuPt NDs show the positive onset potential and half-wave potential. These phenomena demonstrate the enhanced kinetic ability of AuPt NDs for ORR. To further illustrate the intrinsic catalytic activity of AuPt NDs, the associated specific activity and mass activity were
compared with those of Pt black and Pt NSs catalyst (Fig. 8B). It shows that the specific activity of AuPt NDs is 2.65 mA cm2 at 0.70 V, which is larger than Pt black (1.92 mA cm2), Pt NSs (1.76 mA cm2), Au1Pt3 (1.65 mA cm2) and Au3Pt1 (1.03 mA cm2). Similarly, the mass activity of AuPt NDs is 31.55 mA mg1, which is also higher than Pt black (22.41 mA mg1), Pt NSs (17.25 mA mg1), Au1Pt3 (16.89 mA mg1) and Au3Pt1 (9.43 mA mg1). These data demonstrate the better ORR electrocatalytic performances of AuPt NDs than Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts. Besides, the transferred electrons (n) towards ORR on AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts were also estimated by LSVs in O2-saturated 0.1 M HClO4 at different rotational speeds (Fig. 8C and Fig. S3). By calculating from Koutecky-Levich (K-L) equation, the n values are around 3.97, 4.03, 4.09, 4.06 and 3.98 for AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1, respectively (Fig. 8D). These results suggest that the reduction process of O2 to H2O is the four-electron transfer pathway [47], which can provide a faster oxygen reduction rate.
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Fig. 3 e TEM images of AuPt products prepared with different compositions: (A) Au1Pt3, (C) Au3Pt1, (E and F) Pt NSs. (B) EDS spectrum of Au1Pt3, (D) EDS spectrum of Au3Pt1 nanocrystals.
Fig. 4 e XRD pattern of AuPt NDs. Standard Au (JCPDS-040784) and Pt (JCPDS-04-0802) XRD patterns were provided for comparison.
The ORR catalytic performance of AuPt NDs was further evaluated in alkaline media. Similarly, the LSVs of AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts were recorded with a rotation rate of 1600 rpm in O2-saturated 0.1 M KOH (Fig. S4A).
The onset potential (0.98 V) and half-wave potential (0.87 V) of AuPt NDs are also more positive than those of Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts. And the specific activities of AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 are 2.5, 2.15, 1.93, 1.79 and 1.68 mA cm2, respectively. Also, their corresponding mass activities are 29.49, 25.33, 19.20, 17.65 and 15.25 mA mg1 (Fig. S4B). These data demonstrate the better ORR electrocatalytic performance of AuPt NDs in alkaline media. What' more, the transferred electrons (n) towards ORR on AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts were also estimated by LSVs in O2-saturated 0.1 M KOH at different rotation speeds (Fig. S5). Fig. S4D shows the corresponding K-L plots. It is found that ORR occurred at AuPt NDs, Pt black, Pt NSs, Au1Pt3 and Au3Pt1 are also mainly guided by direct four electron reduction mechanism in acid media, as supported by the previous literature [47]. The catalytic activity of AuPt NDs towards HER was firstly evaluated in N2-saturated 0.5 M H2SO4 at the scan rate of 5 mV s1. As shown in Fig. 9A and B, the catalytic current density is 10 mV cm2 at 50 mV for AuPt NDs, accompanied with the smaller onset potential at 27 mV, which are better
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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Fig. 5 e (A) Pt 4f and (B) Au 4f XPS spectra of Au1Pt1, Au1Pt3, Au3Pt1 nanocrystals, and Pt NSs. High-resolution XPS spectra of (C) Au 4f and (D) Pt 4f of AuPt NDs.
Fig. 6 e TEM images of AuPt products obtained in the presence of (A) 5 mM, (B) 10 mM, (C) 20 mM and (D) 50 mM AUCA. Inset shows the corresponding particle-size distribution. than Pt NSs, Au1Pt3 and Au3Pt1 with the catalytic current density of 10 mV cm2 at 93, 230 and 256 mV, whereas their onset potentials are 83, 211, and 231 mV, respectively. Also, these values are comparable to commercial Pt/C (20 wt%)
with the catalytic current density of 10 mV cm2 at 35 mV and the onset potential of 39 mV, respectively, which are similar to the previous work [48,49]. These results demonstrate the comparable catalytic activity of AuPt NDs.
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 0
Fig. 7 e A schematic illustration of the formation mechanism of AuPt NDs.
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is much better than Pt NSs (48 mV dec1), Au1Pt3 (48 mV dec1) and Au3Pt1 (53 mV dec1), but very close to that of Pt/C (29 mV dec1), which is in good accordance with the previous reports [52,53]. These observations confirm the HER process occurred via the Volmer-Heyrovsky mechanism [54]. The high HER activity of AuPt NDs is not only limited to acid media. The electrochemical performances of AuPt NDs were tested in 0.1 M KOH (Fig. S6), which reveal that AuPt NDs exhibit improved catalytic activity. In the 0.1 M KOH, the onset potential of AuPt NDs is 36 mV, which is more positive than Pt NSs (58 mV), Au1Pt3 (150 mV) and Au3Pt1 (182 mV) when comparable to Pt/C catalyst (12 mV). The corresponding Tafel slope of AuPt NDs is 55 mV dec1. This value is comparable to that of Pt/C (52 mV dec1), but much better than those of Pt NSs (67 mV dec1), Au1Pt3 (70 mV dec1), and Au3Pt1 (123 mV dec1). These results show that AuPt NDs have the similar enhanced catalytic activity trends as in acid media. LSVs were recorded from 0.2 to 0.2 V at 50 mV s1 for 1000 cycles to evaluate the stability of AuPt NDs in 0.1 M KOH and 0.5 M H2SO4. As illustrated in Fig. 9D and S6D, the polarization curves are almost remained unchanged before and after the
Fig. 8 e (A) LSVs of AuPt NDs, commercial Pt black, Pt NSs, Au1Pt3 and Au3Pt1 catalysts in O2-saturated 0.1 M HClO4 at a scan rate of 5 mV s¡1 with the rotating rate of 1600 rpm. (B) Comparison of the corresponding specific and mass activities at 0.70 V. (C) LSVs of AuPt NDs catalysts in O2-saturated 0.1 M KOH at a scan rate of 5 mV s¡1 with different rotating rates: 100, 400, 900, 1600, and 2500 rpm. The current density is calculated by using the geometric area of the RDE. (D) The corresponding K-L plots of different catalyst.
The Tafel slope is regarded as an inherent property of catalysts and a significant standard to evaluate the HER performance [50]. A low Tafel slope causes a greatly enhanced HER rate by increasing the potentials [51]. Fig. 9C shows the Tafel slope of AuPt NDs with the value of 34 mV dec1, which
cycling test, showing the negligible changes of the overpotentials less than 10 mV, indicating the superior stability of AuPt NDs both in acid and alkaline media. The long-term stability of AuPt NDs was also tested by chronoamperometry at 0.3 V in N2-saturated 0.1 M KOH and 0.5 M H2SO4 (the
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
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Fig. 9 e (A)e(B) HER polarization curves of AuPt NDs, commercial Pt/C, Pt NSs, Au1Pt3, Au3Pt1 catalysts in 0.5 M H2SO4 at 5 mV s¡1. (B) The corresponding Tafel slopes. (C) The corresponding Tafel slopes. (D) HER activities of AuPt NDs before and after 1000 cycles at a scan speed of 50 mV s¡1. The inset is the chronoamperometric curve of AuPt NDs for 10,000 s at ¡0.30 V in 0.5 M H2SO4.
insets of S6D and Fig. 9D). Clearly, the catalytic current density shows no obvious decrease within 10,000 s, which indicates the improved long-term stability of AuPt NDs after the longterm test.
21162043) and Zhejiang provincial public welfare project (No. 2016C33011).
Appendix A. Supplementary data Conclusions Well-dispersed AuPt NDs were obtained by a facile single-step seedless aqueous method, where AUCA was acted as the capping agent and weak stabilizer. The mass activity and specific activity of AuPt NDs were 31.55 mA mg1 and 2.65 mA cm2 (0.1 M HClO4), 29.49 mA mg1 and 2.5 mA cm2 (0.1 M KOH) for ORR, respectively. The architectures exhibited excellent catalytic activity towards HER with a notably low Tafel slope of 34 mV dec1 (0.5 M H2SO4) and 55 mV dec1 (0.1 M KOH). These results indicated the improved catalytic activities for ORR and HER in comparison to commercial Pt black, Pt/C, Pt NSs, Au1Pt3, and Au3Pt1 catalysts, respectively. The superior performances are ascribed to the synergistic effect of Au with Pt and the unique structure of AuPt NDs. The as-prepared AuPt NDs are promising catalysts in fuel cells and renewable energy.
Acknowledgement This work was financially supported by National Natural Science Foundation of China (Nos. 21475118, 21275130 and
Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.ijhydene.2016.07.160.
references
[1] Jahan M, Liu Z, Loh KP. A graphene oxide and coppercentered metal organic framework composite as a trifunctional catalyst for HER, OER, and ORR. Adv Funct Mater 2013;23:5363e72. [2] Zhang L, Su Z, Jiang F, Yang L, Qian J, Zhou Y, et al. Highly graphitized nitrogen-doped porous carbon nanopolyhedra derived from ZIF-8 nanocrystals as efficient electrocatalysts for oxygen reduction reactions. Nanoscale 2014;6:6590e602. [3] Zhong H-X, Wang J, Zhang Y-W, Xu W-L, Xing W, Xu D, et al. ZIF-8 derived graphene-based nitrogen-doped porous carbon sheets as highly efficient and durable oxygen reduction electrocatalysts. Angew Chem Int Ed 2014;53:14235e9. [4] Yang J, Zhou W, Cheng C-H, Lee J-Y, Liu Z. Pt-decorated PdFe nanoparticles as methanol-tolerant oxygen reduction electrocatalyst. ACS Appl Mater Interfaces 2009;2:119e26. [5] Ye G, Gong Y, Lin J, Li B, He Y, Pantelides ST, et al. Defects engineered monolayer MoS2 for improved hydrogen evolution reaction. Nano Lett 2016;16:1097e103.
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 0
[6] Lu J, Zhou W, Wang L, Jia J, Ke Y, Yang L, et al. Core-shell nanocomposites based on gold nanoparticle@ zinc-ironembedded porous carbons derived from metal-organic frameworks as efficient dual catalysts for oxygen reduction and hydrogen evolution reactions. ACS Catal 2016;6:1045e53. [7] Greeley J, Jaramillo TF, Bonde J, Chorkendorff I, Norskov JK. Computational high-throughput screening of electrocatalytic materials for hydrogen evolution. Nat Mater 2006;5:909e13. [8] Zheng J-N, He L-L, Chen F-Y, Wang A-J, Xue M-W, Feng J-J. Simple one-pot synthesis of platinum-palladium nanoflowers with enhanced catalytic activity and methanoltolerance for oxygen reduction in acid media. Electrochim Acta 2014;137:431e8. [9] Fu G, Wu K, Lin J, Tang Y, Chen Y, Zhou Y, et al. One-pot water-based synthesis of Pt-Pd alloy nanoflowers and their superior electrocatalytic activity for the oxygen reduction reaction and remarkable methanol-tolerant ability in acid media. J Phys Chem C 2013;117:9826e34. € tz R, Schnyder B, Schmidt V. [10] Drillet J-F, Ee A, Friedemann J, Ko Oxygen reduction at Pt and Pt70Ni30 in H2SO4/CH3OH solution. Electrochim Acta 2002;47:1983e8. [11] Sku´lason E, Karlberg GS, Rossmeisl J, Bligaard T, Greeley J, Jonsson H, et al. Density functional theory calculations for the hydrogen evolution reaction in an electrochemical double layer on the Pt (111) electrode. Phys Chem Chem Phys 2007;9:3241e50. [12] Grigoriev S, Millet P, Fateev V. Evaluation of carbonsupported Pt and Pd nanoparticles for the hydrogen evolution reaction in PEM water electrolysers. J Power Sources 2008;177:281e5. [13] Domı´nguez-Crespo MA, Ramı´rez-Meneses E, TorresHuerta AM, Garibay-Febles V, Philippot K. Kinetics of hydrogen evolution reaction on stabilized Ni, Pt and Ni-Pt nanoparticles obtained by an organometallic approach. Int J Hydrogen Energy 2012;37:4798e811. [14] Choi K-H, Jang Y, Chung D-Y, Seo P, Jun S-W, Lee J-E, et al. A simple synthesis of urchin-like Pt-Ni bimetallic nanostructures as enhanced electrocatalysts for the oxygen reduction reaction. Chem Commun 2016;52:597e600. [15] Raoof JB, Ojani R, Esfeden SA, Nadimi SR. Fabrication of bimetallic Cu/Pt nanoparticles modified glassy carbon electrode and its catalytic activity toward hydrogen evolution reaction. Int J Hydrogen Energy 2010;35:3937e44. [16] Wei Y-C, Chen T-Y, Liu C-W, Chan T-S, Lee J-F, Lee C-H, et al. The structure modification and activity improvement of PdeCo/C electrocatalysts by the addition of Au for the oxygen reduction reaction. Catal Sci Technol 2012;2:1654e64. [17] Kim Y, Hong JW, Lee YW, Kim M, Kim D, Yun WS, et al. Synthesis of AuPt heteronanostructures with enhanced electrocatalytic activity toward oxygen reduction. Angew Chem Int Ed 2010;49:10197e201. [18] Hu Y, Zhang H, Wu P, Zhang H, Zhou B, Cai C. Bimetallic PtAu nanocatalysts electrochemically deposited on graphene and their electrocatalytic characteristics towards oxygen reduction and methanol oxidation. Phys Chem Chem Phys 2011;13:4083e94. [19] Cao M, Wu D, Cao R. Recent advances in the stabilization of platinum electrocatalysts for fuel-cell reactions. ChemCatChem 2014;6:26e45. [20] Zhang J, Sasaki K, Sutter E, Adzic R. Stabilization of platinum oxygen-reduction electrocatalysts using gold clusters. Science 2007;315:220e2. [21] Liang H-P, Guo Y-G, Zhang H-M, Hu J-S, Wan L-J, Bai C-L. Controllable AuPt bimetallic hollow nanostructures. Chem Commun 2004;13:1496e7. [22] Kawasaki H, Yao T, Suganuma T, Okumura K, Iwaki Y, Yonezawa T, et al. Platinum nanoflowers on scratched
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
[35]
[36]
[37]
[38]
[39]
9
silicon by galvanic displacement for an effective SALDI substrate. Chem Eur J 2010;16:10832e43. Xiong L, Huang Y-X, Liu X-W, Sheng G-P, Li W-W, Yu H-Q. Three-dimensional bimetallic Pd-Cu nanodendrites with superior electrochemical performance for oxygen reduction reaction. Electrochim Acta 2013;89:24e8. Song P, Mei L-P, Wang A-J, Fang K-M, Feng J-J. One-pot surfactant-free synthesis of porous PtAu alloyed nanoflowers with enhanced electrocatalytic activity for ethanol oxidation and oxygen reduction reactions. Int J Hydrogen Energy 2015;41:1645e53. Eid K, Wang H, Yamauchi Y, Wang L. Facile synthesis of porous dendritic bimetallic PtNi nanocrystals as efficient catalysts for oxygen reduction reaction. Chem Asian J 2016;11:1388e93. Li X-R, Li X-L, Xu M-C, Xu J-J, Chen H-Y. Gold nanodendrities on graphene oxide nanosheets for oxygen reduction reaction. J Mater Chem A 2014;2:1697e703. Kim C, Oh J-G, Kim Y-T, Kim H, Lee H. Platinum dendrites with controlled sizes for oxygen reduction reaction. Electrochem Commun 2010;12:1596e9. Ortiz S, Alcolea Palafox M, Rastogi VK, Tomer R. Solid state simulation of tetramer form of 5-aminoorotic acid: the vibrational spectra and molecular structure study by using MP2 and DFT calculations. Spectrochim Acta Part A 2012;97:948e62. Liu Y, Chen S-S, Wang A-J, Feng J-J, Wu X, Weng X. An ultrasensitive electrochemical sensor for hydrazine based on AuPd nanorod alloy nanochains. Electrochim Acta 2016;195:68e76. Zheng J-N, Li S-S, Ma X, Chen F-Y, Wang A-J, Chen J-R, et al. Popcorn-like PtAu nanoparticles supported on reduced graphene oxide: facile synthesis and catalytic applications. J Mater Chem A 2014;2:8386e95. Zhou W, Li M, Zhang L, Chan SH. Supported PtAu catalysts with different nano-structures for ethanol electrooxidation. Electrochim Acta 2014;123:233e9. Zhao Z-L, Zhang L-Y, Bao S-J, Li C-M. One-pot synthesis of small and uniform Au@ PtCu core-alloy shell nanoparticles as an efficient electrocatalyst for direct methanol fuel cells. Appl Catal B 2015;174:361e6. Li C, Wang H, Yamauchi Y. Electrochemical deposition of mesoporous Pt-Au alloy films in aqueous surfactant solutions: towards a highly sensitive amperometric glucose sensor. Chem Eur J 2013;19:2242e6. Han X, Wang D, Liu D, Huang J, You T. Synthesis and electrocatalytic activity of Au/Pt bimetallic nanodendrites for ethanol oxidation in alkaline medium. J Colloid Interface Sci 2012;367:342e7. Song P, Li S-S, He L-L, Feng J-J, Wu L, Zhong S-X, et al. Facile large-scale synthesis of Au-Pt alloyed nanowire networks as efficient electrocatalysts for methanol oxidation and oxygen reduction reactions. RSC Adv 2015;5:87061e8. Wu L, Zhang S, Wang M, Xu M, Zhu X, Sun D, et al. Surfactant-free synthesis of coral-like platinum nanochains for oxygen reduction reaction. Electrochim Acta 2015;157:101e7. Liu Q, Xu Y-R, Wang A-J, Feng J-J. Simple wet-chemical synthesis of core-shell Au-Pd@ Pd nanocrystals and their improved electrocatalytic activity for ethylene glycol oxidation reaction. Int J Hydrogen Energy 2015;41:2547e53. Liu Q, Xu Y-R, Wang A-J, Feng J-J. A single-step route for large-scale synthesis of core-shell palladium@ platinum dendritic nanocrystals/reduced graphene oxide with enhanced electrocatalytic properties. J Power Sources 2016;302:394e401. Ye W, Kou H, Liu Q, Yan J, Zhou F, Wang C. Electrochemical deposition of AuePt alloy particles with cauliflower-like
Please cite this article in press as: Weng X, et al., Single-step aqueous synthesis of AuPt alloy nanodendrites with superior electrocatalytic activity for oxygen reduction and hydrogen evolution reaction, International Journal of Hydrogen Energy (2016), http:// dx.doi.org/10.1016/j.ijhydene.2016.07.160
10
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 6 ) 1 e1 0
microstructures for electrocatalytic methanol oxidation. Int J Hydrogen Energy 2012;37:4088e97. Xu C, Wang R, Chen M, Zhang Y, Ding Y. Dealloying to nanoporous Au/Pt alloys and their structure sensitive electrocatalytic properties. Phys Chem Chem Phys 2010;12:239e46. Wang D, Xin HL, Yu Y, Wang H, Rus E, Muller DA, et al. Ptdecorated PdCo@ Pd/C core-shell nanoparticles with enhanced stability and electrocatalytic activity for the oxygen reduction reaction. J Am Chem Soc 2010;132:17664e6. Navarro-Flores E, Chong Z, Omanovic S. Characterization of Ni, NiMo, NiW and NiFe electroactive coatings as electrocatalysts for hydrogen evolution in an acidic medium. J Mol Catal A Chem 2005;226:179e97. Ye W, Yu J, Zhou Y, Gao D, Wang D, Wang C, et al. Green synthesis of PteAu dendrimer-like nanoparticles supported on polydopamine-functionalized graphene and their high performance toward 4-nitrophenol reduction. Appl Catal B 2016;181:371e8. Kostova I, Peica N, Kiefer W. Theoretical and spectroscopic studies of 5-aminoorotic acid and its new lanthanide (III) complexes. J Raman Spectrosc 2007;38:205e16. Ju K-J, Feng J-J, Zhang Q-L, Wei J, Wang A-J. Aminoorotic acid directed synthesis of graphene-supported AuPt nanocrystals with enhanced electrocatalytic properties. Electrochim Acta 2015;41:2547e53. Lan F, Wang D, Lu S, Zhang J, Liang D, Peng S, et al. Ultra-low loading Pt decorated coral-like Pd nanochain networks with enhanced activity and stability towards formic acid electrooxidation. J Mater Chem A 2013;1:1548e52. Sun L, Wang H, Eid K, Alshehri SM, Malgras V, Yamauchi Y, et al. One-step synthesis of dendritic bimetallic PtPd
[48]
[49]
[50]
[51]
[52]
[53]
[54]
nanoparticles on reduced graphene oxide and its electrocatalytic properties. Electrochim Acta 2016;188:845e51. Popczun EJ, McKone JR, Read CG, Biacchi AJ, Wiltrout AM, Lewis NS, et al. Nanostructured nickel phosphide as an electrocatalyst for the hydrogen evolution reaction. J Am Chem Soc 2013;135:9267e70. Xu Y, Wu R, Zhang J, Shi Y, Zhang B. Anion-exchange synthesis of nanoporous FeP nanosheets as electrocatalysts for hydrogen evolution reaction. Chem Commun 2013;49:6656e8. Li Y, Wang H, Xie L, Liang Y, Hong G, Dai H. MoS2 nanoparticles grown on graphene: an advanced catalyst for the hydrogen evolution reaction. J Am Chem Soc 2011;133:7296e9. Kundu MK, Bhowmik T, Barman S. Gold aerogel supported on graphitic carbon nitride: an efficient electrocatalyst for oxygen reduction reaction and hydrogen evolution reaction. J Mater Chem A 2015;3:23120e35. Wang X-D, Xu Y-F, Rao H-S, Xu W-J, Chen H-Y, Zhang W-X, et al. Novel porous molybdenum tungsten phosphide hybrid nanosheets on carbon cloth for efficient hydrogen evolution. Energy Environ Sci 2016;9:1468e75. Son CY, Kwak IH, Lim YR, Park J. FeP and FeP2 nanowires for efficient electrocatalytic hydrogen evolution reaction. Chem Commun 2016;52:2819e22. Fei H, Yang Y, Peng Z, Ruan G, Zhong Q, Li L, et al. Cobalt nanoparticles embedded in nitrogen-doped carbon for the hydrogen evolution reaction. ACS Appl Mater Interfaces 2015;7:8083e7.
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