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High-Density Pd Nanorod Arrays on Au Nanocrystals for High-Performance Ethanol Electrooxidation Caihong Fang, Ting Bi, Qian Ding, Zhiqing Cui, Nan Yu, Xiaoxiao Xu, and Baoyou Geng ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b06182 • Publication Date (Web): 09 May 2019 Downloaded from http://pubs.acs.org on May 9, 2019

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ACS Applied Materials & Interfaces

High-Density Pd Nanorod Arrays on Au Nanocrystals for High-Performance Ethanol Electrooxidation Caihong Fang*, Ting Bi, Qian Ding, Zhiqing Cui, Nan Yu, Xiaoxiao Xu, Baoyou Geng*

College of Chemistry and Materials Science, The Key Laboratory of Functional Molecular Solids, Ministry of Education, Anhui Laboratory of Molecular-Based Materials, Center for Nano Science and Technology, Key Laboratory of Electrochemical Clean Energy of Anhui Higher Education Institutes, Anhui Normal University, Wuhu, 241000, China *Corresponding author. E-mail: [email protected]; [email protected].

KEYWORDS: Au/Pd nanocrystals, Pd nanorod array, deposition-dominant growth, electrocatalysts, ethanol oxidation.

ABSTRACT

In the synthesis of Au/Pd bimetallic nanocrystals, a layer-by-layer growth is favorite owing to the low bonding energy between Pd atoms (EPd−Pd) in comparison with EAu−Pd, resulting in homogeneous core/shell nanostructures. Herein, we demonstrate a designed synthetic tactics to unconventional Au/Pd heterostructures through a deposition-dominant growth pathway of the newly reduced Pd atoms, which break the intrinsically favorite layer-by-layer growth. Pd thus

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grows on Au seeds in a heterogeneous nucleation manner. The resulted anisotropic Pd nanorods array on the two basal facets and three side facets of the Au triangular seeds in a high density to form 2D/1D Au/Pd heterostructures. It is noticed that Pd nanorods align in an extremely high order. They grow almost in a row with the base of the rod located overlapped on the Au surface. This versatile approach has been applied to other Au nanocrystal seeds as well, involving hexagonal nanoplates, circular nanodisks, nanorods, and nanobipyramids. Furthermore, the 2D/1D Au/Pd heterostructures exhibit an enhanced electrocatalytic performance toward ethanol oxidation in alkaline condition owing to their unique structure and the exposure of Au. We believe that our synthetic strategy is highly valuable for the construction of multi-metallic nanostructures with desired architectures and thus intriguing properties.

INTRODUCTION Metal nanocrystals (NCs) exhibits fascinating shape- and size-dependent properties in catalysis, photonics, biological science, and spectroscopes1−4, which are systematically tunable by rationally optimizing their preparation routines. Compared to their monometallic counterparts, bimetallic NCs usually show further improved architectural tunabilities in practical applications owing to their synergistic effect, caused by the geometry-dependent electron coupling and the different lattice constants between the monometallic constitution5−7. To this point, the synthetic strategies to the bimetallic nanomaterials in which their shapes are strictly governed are needed. As one of the most important example, the seed-mediated method has been demonstrated as a premier strategy, in which the reduced metal atoms deposit, nuclear, and grow on the presynthesized metal seeds8−12. The delicate control of thermodynamics and kinetics during growth


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procedure allows us to systematically manipulate their structural evolutions and thus accomplish various geometric shapes. Although great successes have been achieved in shape-control synthesis of bimetallic NCs13, a precise control is mechanistically complex and still a representative challenge because the thermodynamics and kinetics are highly sensitive to many parameters, such as the temperature, surfactants, seed structure, and pH value14−16. Among bimetallic NCs, Au−Pd nanostructures are of particular interest due to their distinct catalytic performances in Suzuki reactions17−20, water splitting21, oxidation of alcohols and the formic acids22,23, CO oxidation24,25, and oxidation carbonylation of amines26. Numerous research works have witnessed that the superior performances that Au−Pd NCs exhibited are commonly dependent on their morphological control, which is accomplished through a deliberate design in their synthetic routines27. For Au and Pd with the face-centered cubic crystalline structure, they have a lattice mismatch of ~4.9%, allowing it possible to grow a diverse set of architectural Au−Pd bimetallic nanostructures, especially for the epitaxial core/shell structures based on the seed-mediated method. Through altering the kind and amount of surfactant, temperature, crystalline of Au seeds, pH value, and the foreign metal ions additives, (Au core)/(Pd shell) nanostructures with shapes of octahedra, cubes, octopods, concave octahedra, tetrahexahedrons, hexoctahedrons, and concave cuboids were successfully prepared28−35. It is noticeable that Pd always epitaxially grows on the Au seed NCs to form a traditional core/shell structure with a continuous, homogeneous, and smooth Pd shell. However, for the growth of Pt, another important noble metal, the result is significantly different. It have been extensively investigated that Pt grows on Au surface with a heterogeneous nucleation manner, resulting in a discontinuously porous or dendric Pt shell29,36. The formation of such strikingly structure can be ascribed to the much higher bonding energy of Pt−Pt (306.7 KJ/mol) than that of Au−Pt (60.8


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KJ/mol)37. The energy required for Pt atom diffusion on Au surface is thus higher, resulting in a island growth manner. In contrast, the low EPd−Pd (136 KJ/mol) in comparison to EAu−Pd (142.7 KJ/mol) leads to a layer-by-layer growth mode37, which produces the continuous Pd shell. This means that a well-designed synthetic strategy should be dedicatedly designed to follow the heterogeneous nucleation manner for yielding a discontinuous Pd shell. Very recently, by carefully controlling the deposition rate of Pd on Au nanocages, two types of Au/Pd bimetallic nanostructures with Pd grown on the outer and both outer and inner surfaces were achieved through changing the reduction rate38. Moreover, Xia's group has successfully obtained four distinctive types of Pd NCs by tuning the diffusion rate of Pd atoms on the cubic Pd seeds39,40. These appealing observations inspire us to focus on the control of the diffusion or deposition rate during the seeded growth of bimetallic nanostructures, which will vary the growth mode and become an engaging pathway to constructing more intriguing architectures, with notable example of 2D/1D Au/Pd heterostructures in which Pd nanorods grow on the surface of Au seeds. Such heterogeneous construction can bring new and enhanced properties, or multifunctionality that cannot be found in their parent metal NCs due to the coexistence of the exposed metal component and the synergistic effects between them41. In this work, we demonstrate a novel Au/Pd bimetallic heterostructures by a control of the deposition and diffusion rate of Pd atoms on the surface of Au NCs. The nanorods grow on the two basal facets and three side facets of the Au triangular nanoplates (TANs). It should be mentioned that the Pd nanorods array on the two basal facets in an extremely high order. The key to the successful synthesis relies on a delicate government over the deposition and diffusion rate to break the intrinsically favorite layer-by-layer growth manner. The Pd growth thus follows a heterogeneous nucleation way. This approach is also versatile and applied to other Au nanoplates


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and NCs, including hexagonal nanoplates, circular nanodisks, nanorods, and nanobipyramids. Moreover, the electrocatalytic measurements toward oxidation of ethanol in alkaline demonstrates that the 2D/1D Au/Pd bimetallic electrocatalysts exhibit an enhanced activity and stability due to their unique structure and the exposure of Au. RESULTS AND DISCUSSION In presence of the pre-synthesized seeds, the newly reduced metal atoms will self-nucleate or deposit on the seed surface. The former routine will result in a mixture of the seeds and the isolated metal NCs (Routine I, Figure 1), while the latter leads to the preparation of bimetallic NCs (Routine II, Figure 1). Furthermore, upon deposition, the adsorbed metal atoms have two options: staying at the sites where deposition happed or migrating to other sites through surface diffusion (Figure 1)16,41,42. The exact morphology the nanostructure displaying can be deterministically governed by the relative rate corresponding to atomic deposition (Vdeposition) and the surface diffusion (Vdiffusion). When Vdiffusion >> Vdeposition, most of the adsorbed metal atoms will show a radical diffusion on the seed surface following a Frank-van der Merwe (F-M) manner, promoting the lateral growth. Together with the atom deposition, the adsorbed metal atoms grow layer by layer on the seed surface, resulting in the traditional core/shell architectures. In contrast, when Vdeposition >> Vdiffusion, the newly formed metal atoms will quickly accumulate on the just formed deposition site according to a Volmer-Weber (V-W) mode. The surface diffusion is thus highly suppressed. An island structure and subsequent an unconventional discontinuous nanorod will appear on the surface of the metal seeds, forming a heterogeneous bimetallic nanostructure.


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Figure 1 Schematics showing the designed growth tactics to preparing bimetallic nanostructures. On the basis of the aforementioned theory, we prepared an unconventional 2D/1D Au/Pd homogenous bimetallic NCs using Au TANs as the starting seeds, which were synthesized following a previous method43. The deposition rate was controlled by the adding rate of reductant and the reaction temperature. Typically, the adding rate of reductant (ascorbic acid, AA) was controlled at 0.015 mmol/s and the temperature was 21 °C. Scanning electron microscopy (SEM) images show that Au seeds are triangles with two basal and three side facets (Figure S1). The corresponding 2D/1D Au/Pd NCs show a triangular shape as well, which is inherited from the Au seeds (Figure 2a). Noticeably, Pd nanorods array on the two basal surfaces. Transmission electron microscopy (TEM) imaging demonstrates that Pd nanorods grow vertically on both the basal and side facets (Figure 2b), which is also seen in high-angle annular dark-field scanning TEM (HAADF−STEM) images (Figure S2a,b). Besides, the Pd nanorods arrange in a high order. Further magnified TEM images of a single 2D/1D NC lying flat on the TEM grids indict clearly their high order arrangements as well (Figure 2c,d). The Pd nanorods align almost in a row. It should be pointed out that that Au surface is not fully covered by Pd NCs and exposed partly to the environment. The rod density grown on basal facets is determined to be as high as ~3.6 × 104 µm−2. The diameter was measured to be 4.6 ± 1.2 nm. The Au/Pd NCs standing on the TEM grids reveal that the length of the nanorods grown on the two basal


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facets is equivalent to be 22.3 ± 2.6 nm (Figure 2e). Furthermore, the diameter and length of the nanorod on the side facets was determined to be 3.5 ± 1.2 and 29.0 ± 5.8 nm, respectively. The measured lattice fringes of the Pd nanords grown on the basal and side facets is 0.225 nm, corresponding to Pd (111) plane (Figure 2f,g). Energy-dispersive X-ray (EDX) spectrum indicates the existence Pd and Au elements (Figure S2c). Two prominent peaks in XRD patterns of the 2D/1D Au/Pd nanostructures is ascribed to be the cubic Pd (111) (PDF No.: 88−2335) and cubic Au (111) (PDF No.: 04−0784), respectively (Figure 2h). Furthermore, the EDX elemental mappings of the typical standing and lying 2D/1D nanostructure clearly show that the Au located in the core area and Pd distribute around Au, demonstrating successfully the formation Pd nanorod arrays on both the basal and side facets (Figure 2i).

Figure 2 Representative 2D/1D Au/Pd bimetallic NCs. (a,b) SEM and TEM images of the 2D/1D Au/Pd bimetallic NCs. (c) High-magnification TEM image of a single 2D/1D Au/Pd nanostructure that lies fat on the TEM grids. (d) Schematics of the 2D/1D architecture. (e) High-


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magnification TEM image of a standing 2D/1D Au/Pd nanostructure. (f,g)High resolution TEM (HRTEM) images obtained from the red dashed frame area shown in (d) and (e), respectively. (h) XRD patterns of the typical 2D/1D Au/Pd nanostructures. The standard diffraction peaks for Au (purple lines) and Pd (red lines) are also shown as references. (i) HAADF−STEM image (left) of a representative 2D/1D Au/Pd nanostructure and the corresponding EDX elemental mapping images of Au and Pd. To further verify the growth procedure and formation of the high-order structure, we also investigated the morphological evolution under varying amount of the palladium precursors. The other condition is the same as the typical synthetic procedure. Electron microscopy imaging shows that Pd arrays are undistinguished when the volume of the aqueous H2PdCl4 is lower than 80 µL (0.01M) (Figure S3a−c). Pd arrays become detectable when H2PdCl4 was increased to 100 µL. Clear linear stripes appear on the surface of Au NCs from TEM and HAADF−STEM images (Figure 3a). Such order "lines" are not affected by further increasing the amount of H2PdCl4. Pd nanorods become much obvious if Pd precursor was gradually increased to 1000 µL (Figures 3b−d and S4). The diameter and length of Pd nanorods on the side factes is plotted as a function of the adding H2PdCl4 volume, respectively (Figure 3e). There are three stages for the size variations. (I) The diameter incereses dramatically when the applied H2PdCl4 is quite small (≤ 2 mmol), whereas the length is almost unchanged from 6.6 ± 1.2 to 7.0 ± 1.0 nm. (II) Both the length and diameter boost considerably as further addition of H2PdCl4 (≤ 5 mmol). (III) The length suffers almost a linear increase tendency as the increasing H2PdCl4, while the diameter is saturated. The change in the diameter and length of the nanorods on the basal facets is similar to that of the diameter variation on the side facets (Figure 3f). At a small amount of palladium precursor, the diameter increases quickly (≤ 5 mmol) and then reaches a steady state, while the


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length is almost unchanged at the first stage and then largely prolonged. We believe that the above size variations are caused by the gradually accelerated deposition. At the first stage, the atomic diffusion is dominant, resulting in the size increase in the diameter. As Vdeposition increasing, the atom deposition becomes predominant and suppresses the surface diffusion, leading to the steady diameter and prolonging length. In addition, the Au nanocrystal seed is a critical factor for the formation of 1D Pd nanorod. Without the addition of Au seeds, Pd nanostructures show a particulate shape with a poor size distribution (Figure S5).

Figure 3 (a−d) SEM (top), TEM (middle), and HADDF-STEM (bottom) images of Au/Pd heterostructures grown under the varying H2PdCl4 of 100 µL, 200, 300, and 500 µL, respectively. (e) Variation of the length and diameters of Pd nanorods grown on the side facet of Au seeds as function of the volume of H2PdCl4. (f) Plots of the Pd nanorod diameter and length on the basal facets as a function of the added H2PdCl4 volume. Besides, the growth is achieved in a very short time. Time-dependent shape evolution reveals that the 2D/1D architecture is achievable after the reaction was initiation for just 1 min (Figure


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S6a). After the reaction was carried out for 30 min, the shape has almost no changes (Figure S6b). In addition, the length of the Pd nanorods on the side facets have a negligible change from 35.2 ± 4.8 to 34.8 ± 3.6 nm, which indicates that the growth is finished after the reaction is initiated for just 1 min. Specially, this rapid growth process also ensure the good dispersion owing to the larger hindering force between 2D/1D nanostructures than that of the Au nanoplates. Furthermore, we also examined the versatility by applied this synthetic process to different Au NCs (Figure 4). The anisotropic Pd grown on Au seeds with morphology of both 2D nanoplates (hexagonal nanoplates and circular nanodisks) and the 3D enlonged shapes, (nanorods and nanobipyramids).

Figure 4 TEM images of the Au NC seeds (a−d) and the corresponding Au/Pd heterostructures (e−h). In order to further reveal the role of Vdeposition/Vdiffusion and validate our proposed growth pathway, we also conducted a series of experiments to vary the Vdeposition and Vdiffusion. In general, Vdeposition is highly determined by the supply rate of the newly formed metal atoms, which is directly governed by the reduction rate between the metal precursor and reductant. In an ideal condition without intermediated steps, Vreduction can be expressed as following44: 𝑉reduction = 𝑘[Metal precursor]x[Reductant]y


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where x and y represents the reaction order of the metal precursor and the reductant, respectively. In our synthetic tactics, H2PdCl4 will be reduced immediately to Pd atoms upon dropping the reductant owing to the strong reduction power of AA45,46. Controlling the injection rate of the AA is therefore a simple and convenient method to manipulate Vreduction and thus Vdeposition. In addition, surface diffusion is achieved through the movement of the adsorbed atoms on a surface following a hopping or jumping procedure15. The relative diffusion coefficient (D) that can judge Vdiffusion is expressed as following:44 𝐷 = 𝐷0exp( - 𝐸diffusion/RT) where D0 is the pre-exponential factor, Ediffusion is energy barrier related to diffusion, R is the ideal gas constant, and T is the absolute temperature. Accordingly, Ediffusion and T is the main factor to affect Vdiffusion. Obviously, the temperature is a straightforward method in experiment to tune Vdiffusion. In the first set of experiments, we slowed down the injection rate of AA while the reaction temperature was fixed at 21 °C. In this case, Vdeposition/Vdiffusion is reduced and the diffusion time is prolonged. If our proposed growth mechanism is rational, the diameter of Pd nanocrystals will increase and even change to a continuous traditional core/shell nanostructures. As expect, the Pd nanoparticles scattered on the Au TANs indeed show a stone-like shape when the addition rate of AA is reduced to 0.75 µmol/s for 50 min by a syringe pump (Figure 5a,b). The size of those "stones" is even up to 23 nm, which is quite larger than that of the typical product (4.6 ± 1.2 nm). Moreover, there is a slight aggregation brought by the low growth rate. Furthermore, we supposed that Pd atoms can spread through the Au seeds forming a traditional core/shell nanostructure if the supply rate was further decreased widely. Unfortunately, we cannot obtain the products owing to the serious aggregation caused by the much lower growth rate.


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In the second set of experiments, we performed the metal growth under different reaction temperatures at 0 and 50 °C when the adding rate was kept at 0.015 mmol/s. We should point out that temperature adjustment will lead to an alteration of Vreduction. At a relative low temperature, both Vdeposition and Vdiffusion are small, which will yield a 2D/1D nanostructure as the typical sample. SEM and TEM images for the nanostructures obtained at 0 °C confirm this conclusion (Figure 5c,d ). No byproducts were detected during imaging. However, there are plenty of selfnucleated Pd NCs besides the representative 2D/1D nanostructures when the growth was proceeded at a high temperature of 50 °C (Figures 5e,f and S7). It is believed that the large Vdeposition and Vdiffusion at a high temperature are responsible for the formation of the mixtures. The comparable Vdeposition/Vdiffusion to the typical reaction process results in the successful growth of 2D/1D nanostructures. However, Vreduction increases greatly at an elevated temperature. A part of the newly reduced Pd atoms will self-nuclear immediately instead of colliding on the surface of the Au seeds. In this regard, the Pd NCs produce as byproducts.

Figure 5 (a,b) SEM and TEM image of the NCs obtained at a low supplied rate of AA at 0.75 µmol/s, respectively. (c,d) SEM and TEM images of the heterostructures that were grown at 0 °C. (e,f) SEM and TEM images of the products synthesized at 50 °C.


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Pd-based nanostructures are appealing electrocatalysts toward the oxidation of alcohols in direct fuel cells, especially in the oxidation of ethanol in alkaline electrolyte due to their good activity and faster CO stripping performances47−49. With the assistance of Au, Au/Pd bimetallic NCs even show improved electrocatalytic activity and stability17,50. We therefore employed the typical 2D/1D Au/Pd heterostructures as catalysts to the ethanol electrooxidation in an alkaline and benchmarked against traditional core/shell Au/Pd (CS-Au/Pd), pure Pd nanocubes, and the commercial Pd/C (Detail in Supporting information, Figure S8). For comparison, the mass of Pd in CS-Au/Pd nanostructures is equal to that of the 2D/1D Au/Pd electrocatalysts. Cyclic voltammetry (CV) curves collected under N2-satuated KOH (1 M) at a scan rate of 50 mVs−1 have a peak between −0.3−0.0 V, which is assigned to the reduction of PdO oxidized from Pd during electrocatalytic measurements (Figure S9a)51. Their electrochemical surface area (ECSA) was calculated respectively to be 32.1, 24.9, 28.7, and 36.7 m2g−1 by qualifying their electric charges that are required for PdO reduction. Cyclic voltammetry (CV) curves accessed in the presence of the above electrocatalysts in a mixture of ethanol and KOH depict two characteristic oxidation peaks observed for ethanol oxidation reaction (EOR). The peak in the forward scan at around −0.23 V ascribes to the fresh chemiabsorption and oxidation of ethanol, while the peak in the backward scan at −0.27 V comes primarily from the carbonaceous species generated during the ethanol oxidation. The peak intensity appeared during the forward scan therefore suggests the catalytic activity of the corresponding electrocatalysts. It should be pointed out that the Au TANs used as the seeds in this preparation has a negligible activity toward EOR (Figure S9b). The specific activity calculated by normalized the peak intensity to its ECSA is 0.35 Acm−2 for commercial Pd/C catalysts (Figure 6a). The 2D/1D Au/Pd nanostructures were measured to have the highest specific activity of 1.94 Acm−2, which is 5.6 times that of the commercial Pd/C


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electrocatalysts (0.35 mAcm−2). The CS-Au/Pd and cubic Pd electrocatalysts exhibit a similar specific activity of 1.33 and 1.25 Acm−2. The mass activity based on the Pd mass loading on work electrode made of 2D/1D Au/Pd is 0.62 AmgPd−1, which is 1.9, 1.7, and 2.3 times of the CS-Au/Pd (0.33 AmgPd−1), cubic Pd nanostructures (0.36 AmgPd−1), and commercial Pd/C (0.27 AmgPd−1) (Figure S10a). The specific and mass activities of the above Pd-based electrocatalysts are summarized and shown in Figure 6b. It is clearly that the 2D/1D Au/Pd bimetals display the highest electrocatalytic specific and mass activity. We also further proved the kinetic activity through Tafel slope fitted linearly the applied potential vs log (mass activity) under linear sweep voltammetry (LSV) mode (Figures 6c and S10b). As expect, the low Tafle slope (197.6 mVdec−1) that the 2D/1D Au/Pd electrocatalysts shown compared to CS-Au/Pd (218.1 mVdec−1), Pd cubes (210.0 mVdec−1), and Pd/C (226.4 mVdec−1) demonstrates its high kinetics toward the EOR52,53.

Figure 6 CV curves normalized by their ESCAs (a), specific and mass activities toward EOR (b), and Tafel plots (c) of 2D/1D Au/Pd, CS-Au/Pd, Pd cubes, and commercial Pd/C in a N2-


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saturated mixture of ethanol and ethanol (1.0 M) and KOH (1.0 M), respectively. The annotations in labeled in (a) also applied to (c). In addition to the activity, the durability is another important factor to access the catalytic performance of electrocatalysts. We therefore examined the stability of 2D/1D Au/Pd NCs by both the accelerated CV curves and chronoamperometry (CA) technique. First, the cycling durability of the electrocatalysts was evaluated by running repeatedly the CV tests for 800 cycles between −1.0 and 0.2 V at a fixed the scan rate (50 mVs−1). The plot of the extracted specific activity against cycle number displays that the specific current of commercial Pd/C declines even to 0.17 mgPd−1 after 800 cycles (Figure 7a). For CS-Au/Pd and cubic Pd electrocatalysts, 41.7% and 45.6% is remained. In contrast, the activity diminishes to 0.393 mgPd−1, which exhibits the highest specific activity, when the 2D/1D Au/Pd electrocatalysts were employed instead. Second, the chronoamperometric curves reflect the deactivation in electrocatalytic activity under continuous working condition. The CA measurements were tested at −0.2 V for 3600 s. All the electrocatalysts suffer an unavoidable activity loss at the first stage due to the concentration difference caused by the diffusion of the ethanol on the anode surface and the PdO formation54. The commercial Pd/C catalysts become almost inactive after 1000-s measurement. By a sharp contrast, 2D/1D Au/Pd NCs still show a steady specific activity of 101 mAcm−2 after 3600-s electrocatalysis, which is 1.7 and 5.1 magnitude higher than that of the CS-Au/Pd (60 mAcm−2) and cubic Pd (20 mAcm−2). Moreover, the TEM images of the 1D/2D Au/Pd nanostructures after CA measurement verify their structural stability during electrocatalytic evaluation (Figure S11). CO stripping voltammograms were further performed to gain insight to the stability. For all of the four curves, a peak appears in the first sweep, which is produced by the oxidation of CO that is adsorbed on the electrocatalyst surface. In the second sweep, the CO oxidation peak


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disappears owing to the full oxidation of CO in the first sweep. The most negative potentials suggests ambiguously the weakened CO adsorption on the surface of 2D/1D Au/Pd electrocatalysts and thus the excellent CO-tolerance property they exhibited.

Figure 7 Cycling measurements (a), CA curves (b), and CO stripping curves (c) collected using 2D/1D Au/Pd, CS-Au/Pd, Pd cubes, and commercial Pd/C as the electrocatalysts. The scan rate was fixed at 50 mVs−1. The annotations in (b) also applied to (a) and (c). On the basis of the electrocatalytic evaluation, it is conclusive that 2D/1D Au/Pd nanostructures show an enhanced electrocatalytic performances toward EOR compared to both the pure Pd, commercial Pd/C, and CS-Au/Pd catalysts. We believed that such improvements are attributed to the presence of Au and its unique structure. First, a part of Pd atoms will oxidize to inactive PdO in electrooxidation ethanol, causing the decay in catalytic activity. The existence of Au changes the redox properties of formation/reduction PdO55. This will facilitate the reduction of PdO to Pd, leading to the higher availability of active Pd sites for EOR, which will undoubtedly make the Au/Pd show high activityand stability compared to pure Pd catalysts. Second, lattice stain is also investigated as a primary factor to determine the EOR performances56. The strain effect is highly geometric dependence. For Au/Pd core/shell nanostructure, the lattice stain of Pd shell gradually shrinks when the shell thickness is larger


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than two atomic layers57,58. The CS-Au/Pd nanostructures thus have a negligible strain effect, leading to its similar catalytic performance to that of the Pd cubes. In contrast, the larger lattice stain in 2D/1D Au/Pd is the reason for its higher electrocatalytic activity than that of the CSAu/Pd and Pd/C catalysts. CONCLUSION In conclusion, we demonstrated a robust approach for preparing the unconventional Au/Pd heterostructures through a control of Vdiffusion and Vdeposition. The Pd nanorods array on the basal and side facets of the 2D trianglar nanoplates in a high density. Furthermore, the nanorods on the two basal facets appear in an extremely high order. Such successful control relies on the careful engineering of the Vdiffusion and Vdeposition to achieve a deposition-dominant growth pathway, which can break its intrinsic favorite layer-by-layer growth mode. Moreover, the unique 2D/1D Au/Pd bimetallic nanostructures show improved electrocatalytic performances toward the oxidation of ethanol in alkaline. Our work provides a versatile strategy to constructing welldefined metal heterostructures bimetallic nanostructures with a desired architecture and thus intriguing properties. EXPRIMENTAL SECTION

Synthesis of Au Triangular Nanoplates The Au TANs were prepared using a reported seed-mediated method43. Typically, the seed solution was prepared through the reduction of HAuCl4 (0.01 M, 1 mL) and trisodium citrate (0.01 M, 1 mL) with ice-cold NaBH4 (0.1 M, 1 mL) in deionized water (DI water, 36 mL). The mixture was stirred mildly for 2 minutes and kept undisturbed for 2−6 h at room temperature.


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For synthesizing Au TANs, three solutions were prepared in advance. For both solution A and B, we dropped HAuCl4 (0.01 M, 0.25 mL), KI (0.01 M, 0.05 mL), NaOH (0.1 M, 0.05 mL), and AA (0.1 M, 0.05 mL) into cetyltrimethyammonium bromide (CTAB, 0.05 M, 9 mL) in sequence. The solution C was prepared through the addition of HAuCl4 (0.01 M, 2.5 mL), KI (0.01 M, 0.5 mL), NaOH (0.1 M, 0.5 mL), and AA (0.1 M, 0.5 mL) into CTAB (0.05 M, 90 mL). After that, we titrated the seed solution (1 mL) to the solution A, following by a rapid inversion for 5 s. The resultant solution (1 mL) was added into the solution B, followed by the addition of all above mixtures into the solution C. The mixture was agitated by gentle shaking for 20 s and left undisturbed for 24 h at room temperature. The obtained Au TANs were collected and redispersed into CTAB (40 mL, 0.05 M) for further use. Synthesis of 2D/1D Au/Pd Heterostructures In a typical preparation, the Au TANs (10 mL) was centrifuged and redispersed into DI water (2 mL). The concentration of the residual CTAB was estimated to be 0.5 µM at this stage. After titrating H2PdCl4 (0.01 M, 0.5 mL), AA (0.1 M, 0.3 mL) was introduced into the above solution with a control rate of 0.015 mmol/s at 21 °C. The sample was collected by centrifugation after the reaction was carried out for 5 min. Electrochemical Measurements The glassy electrodes (diameter = 3 mm, Pine Instruments) were first polished with Al2O3 paste which is made of a mixture of Al2O3 microspheres and DI water. The ink suspension involved during the electrocatalytic tests was fabricated by dispersed the electrocatalysts into DI water (1 mL), following by the addition of Nafion (0.5 wt%, 10 µL) under ultrasonication for about 30 min. The working electrode was prepared by dropping the ink solution (6 µL) onto the treated glassy carbon electrode and dried naturally at room temperature.


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A standard three-electrode setup was utilized, in which a Pt foil and a saturated Ag/AgCl electrode was used as the counter and reference electrode, respectively. We purged N2 for ~30 min to remove the dissolved oxygen and achieve N2-satuated solution before each electrocatalytic measurements. The sweep rate was fixed at 50 mVS−1. Moreover, the CO stripping curves were obtained in a N2-satuated aqueous KOH (1 M), following by prebubbling the CO (5% in volume) into the electrolyte for at least 40 min to achieve complete adsorption. All measurements were carried out at room temperature. Characterizations SEM images were obtained in a field emission microscope (Hitachi S4800). TEM imaging was carried out on a microscope (Hitachi HT 7700)operated at 120 kV. HRTEM images were collected on a JEM-2100 microscope operating at 200 kV operating at 200 kV. Elemental mapping and HAADF-STEM imaging were performed on a JEM 2100F microscope. XRD patterns were obtained on Philips X’ Pert system equipped with Cu Kα radiation (λ= 1.5419 Å, scanning rate= 1.0°/min). Our electrochemical performances were evaluated using a CHI760E work station (CH Instruments, China). The inductively coupled plasma atomic emission spectroscopy was acquired by Optima 300DV (PerkinElmer) to determine the mass of the electrocatalysts dropped on the working electrode. FIGURES


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Figure 1 Schematics showing the designed growth tactics to preparing bimetallic nanostructures.

Figure 2 Representative 2D/1D Au/Pd bimetallic NCs. (a,b) SEM and TEM images of the 2D/1D Au/Pd bimetallic NCs. (c) High-magnification TEM image of a single 2D/1D Au/Pd nanostructure that lies fat on the TEM grids. (d) Schematics of the 2D/1D architecture. (e) Highmagnification TEM image of a standing 2D/1D Au/Pd nanostructure. (f,g) High resolution TEM (HRTEM) images obtained from the red dashed frame area shown in (d) and (e), respectively. (h) XRD patterns of the typical 2D/1D Au/Pd nanostructures. The standard diffraction peaks for Au (purple lines) and Pd (red lines) are also shown as references. (i) HAADF−STEM image (left) of a representative 2D/1D Au/Pd nanostructure and the corresponding EDX elemental mapping images of Au and Pd.


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Fgiure 3 (a−d) SEM (top), TEM (middle), and HADDF-STEM (bottom) images of Au/Pd heterostructures grown under the varying H2PdCl4 of 100 µL, 200, 300, and 500 µL, respectively. (e) Variation of the length and diameters of Pd nanorods grown on the side facet of Au seeds as function of the volume of H2PdCl4. (f) Plots of the Pd nanorod diameter and length on the basal facets as a function of the added H2PdCl4 volume.

Fgiure 4 TEM images of the Au NC seeds (a−d) and the corresponding Au/Pd heterostructures (e−h).


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Figure 5 (a,b) SEM and TEM image of the NCs obtained at a low supplied rate of AA at 0.75 µmol/s, respectively. (c,d) SEM and TEM images of the heterostructures that were grown at 0 °C. (e,f) SEM and TEM images of the products synthesized at 50 °C.

Figure 6 CV curves normalized by their ESCAs (a), specific and mass activities toward EOR (b), and Tafel plots (c) of 2D/1D Au/Pd, CS-Au/Pd, Pd cubes, and commercial Pd/C in a N2-satuated mixture of ethanol and ethanol (1.0 M) and KOH (1.0 M), respectively. The annotations in labeled in (a) also applied to (c).


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Figure 7 Cycling measurements (a), CA curves (b), and CO stripping curves collected using 2D/1D Au/Pd, CS-Au/Pd, Pd cubes, and commercial Pd/C as the electrocatalysts. The scan rate was fixed at 50 mVs−1. The annotations in (b) also applied to (a) and (c).

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. TEM image of the Au TANs, HADDF-STEM images of the Au/Pd bimetallic NCs, additional SEM/TEM images of the Au/Pd bimetallic NCs, the CV curves using Au/Pd, CS-Au/Pd, Pd cubes, Pd/C, and Au TANs as the electrocatalysts were presented at supporting information. AUTHOR INFORMATION Corresponding Author *Corresponding author. E-mail: [email protected]; [email protected]. Funding Sources National Natural Science Foundation of China (21871005, 21501005).


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Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the National Natural Science Foundation of China (21871005, 21501005, 21471006). REFERENCES (1) Cheng, H. F.; Yang, N. L.; Lu, Q. P.; Zhang, Z. C.; Zhang, H. Syntheses and Properties of Metal Nanomaterials with Novel Crystal Phases Adv. Mater. 2018, 30, 1707189. (2) Neretina, S.; Hughes, R. A.; Gilroy, K. D.; Hajfathalian, M. Noble Metal Nanostructure Synthesis at the Liquid–Substrate Interface: New Structures, New Insights, and New Possibilities Acc. Chem. Res. 2016, 49, 2243−2250. (3) Jiang, X. Y.; Du, B. J.; Huang, Y. Y.; Zheng, J. Ultrasmall Noble Metal Nanoparticles: Breakthroughs and Biomedical Implications Nano Today 2018, 21, 106−125. (4) Lu, N.; Chen, W.; Fang, G. Y.; Chen, B.; Yang, K. Q.; Yang, Y.; Wang, Z. C.; Huang, S. M.; Li, Y. D. 5‑Fold Twinned Nanowires and Single Twinned Right Bipyramids of Pd: Utilizing Small Organic Molecules to Tune the Etching Degree of O2/Halides Chem. Mater. 2014, 26, 2453−2459. (5) Gilroy, K. D.; Ruditskiy, A.; Peng, H.-C.; Qin, D.; Xia, Y. N. Bimetallic Nanocrystals: Syntheses, Properties, and Applications Chem. Rev. 2016, 116, 10414−10472.


24

Page 25 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6) Sankar, M.; Dimitratos, N.; Miedziak, P. J.; Wells, P. P.; Kiely, C. J.; Hutchings G. J. Designing Bimetallic Catalysts for a Green and Sustainable Future Chem. Soc. Rev. 2012, 41, 8099−8139. (7) Wang, C. S.; Li, J. L.; Lou, Y. K.; Kan, C. X.; Zhu, Y.; Feng, X. Q.; Ni, Y.; Xu, H. Y.; Shi, D. N.; Wei, X. Y. Facile Synthesis and Heteroepitaxial Growth Mechanism of Au@Cu Core– Shell Bimetallic Nanocubes Probed by First-Principles Studies CrystEngComm 2017, 19, 7287−7297. (8) hu, X. Z.; Yip, H. K.; Zhuo, X. L.; Jiang, R. B.; Chen, J. L.; Zhu, X.-M.; Yang, Z.; Wang, J. F. Realization of Red Plasmon Shifts Up to ~900 nm by AgPd-Tipping Elongated Au Nanocrystals J. Am. Chem. Soc. 2017, 139, 13837−13846 (9) Zhu, X. Z.; Jia, H. L.; Zhu, X.-M.; Cheng, S.; Zhuo, X. L.; Qin, F.; Yang, Z.; Wang, J. F. Selective Pd deposition on Au Nanobipyramids and Pd Site-Dependent Plasmonic Photocatalytic Activity Adv. Funct. Mater. 2017, 27, 1700016. (10) Weiner, R. G.; Kunz, M. R.; Skrabalak, S. E. Seeding a New Kind of Garden: Synthesis of Architecturally Defined Multimetallic Nanostructures by Seed-Mediated Co-Reduction Acc. Chem. Res. 2015, 48, 2688−2695. (11) Niu, W. X.; Zhang, L.; Xu, G. B. Seed-Mediated Growth of Noble Metal Nanocrystals: Crystal Growth and Shape Control Nanoscale 2013, 5, 3172−3181. (12) Xia, X. H.; Legna, F.-C.; Tao, J.; Peng, H.-C.; Niu, G. D.; Zhu, Y. M.; Xia, Y. N. Facile Synthesis of Iridium Nanocrystals with Well-Controlled Facets Using Seed-Mediated Growth J. Am. Chem. Soc. 2014, 136, 10878−10881.


25


Page 26 of 32

(13) Liu, X. W.; Wang, D. S.; Li, Y. D. Synthesis and Catalytic Properties of Bimetallic Nanomaterials with Various Architectures Nano Today 2012, 7, 448−466. (14) Wang, W. L.; Zhou, S.; Gilroy, K. D.; Cai, Z. S.; Xia, Y. N. Icosahedral Nanocrystals of Noble Metals: Synthesis and Applications Nano Today 2017, 15, 121−144. (15) Xia, Y. N.; Xia, X. H.; Peng, H.-C. Shape-Controlled Synthesis of Colloidal Metal Nanocrystals: Thermodynamic versus Kinetic Products J. Am. Chem. Soc. 2015, 137, 7947– 7966. (16) Tan, S. F.; Chee, S. W.; Lin, G. H.; Bosman, M.; Lin, M.; Mirsaidov, U.; Nijhuis, C. A. Real-Time Imaging of the Formation of Au–Ag Core–Shell Nanoparticles J. Am. Chem. Soc. 2016, 138, 5190−5193. (17) Su, G.; Jiang, H. Q.; Zhu, H. Y.; Lv, J.-J.; Yang, G. H.; Yan, B.; Zhu, J.-J. Controlled Deposition of Palladium Nanodendrites on the Tips of Gold Nanorods and Their Enhanced Catalytic Activity Nanoscale 2017, 9, 12494−12502. (18) Wang, F.; Li, C. H.; Chen, H. J.; Jiang, R. B.; Sun, L.-D.; Li, Q.; Wang, J. F.; Yu, J. C.; Yan, C.-H. Plasmonic Harvesting of Light Energy for Suzuki Coupling Reactions J. Am. Chem. Soc. 2013, 135, 5588–5601. (19)

Fang, P.- P.; Jutand, A.; Tian, Z.-Q.; Amatore, C. Au–Pd Core–Shell Nanoparticles

Catalyze Suzuki–Miyaura Reactions in Water Through Pd Leaching Angew. Chem. Int. Ed. 2011, 50, 12184−12188. (20) Wang, H. H.; Sun, Z. H.; Yang, Y.; Su, D. S. The Growth and Enhanced Catalytic Performance of Au@Pd Core–Shell Nanodendrites Nanoscale 2013, 5, 139−142.


26

Page 27 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(21) Su, R.; Tiruvalam, R.; Logsdail, A. J.; He, Q.; Downing, C. A.; Jensen, M. T.; Dimitratos, N.; Kesavan, L.; Wells, P. P.; Bechstein, R.; Jensen, H. H.; Wendt, S.; Catlow, C. R. A.; Kiely, C. J.; Hutchings, G. J.; Besenbacher, F. Designed Titania-Supported Au–Pd Nanoparticles for Efficient Photocatalytic Hydrogen Production ACS Nano 2014, 8, 3490−3497. (22) Enache, D. I.; Edwards, J. K.; Landon, P.; Espriu, B. S.; Carley, A. F.; Herzing, A. A.; Watanabe, M.; Kiely, C. J.; Knight, D. W.; Hutching, G. J. Solvent-Free Oxidation of Primary Alcohols to Aldehydes Using Au-Pd/TiO2 Catalysts Science 2006, 311, 362−365. (23) Liu, H.-L.; Nosheen, F.; Wang, X. Noble Metal Alloy Complex Nanostructures: Controllable Synthesis and Their Electrochemical Property Chem. Soc. Rev. 2015, 44, 3056−3078. (24) Xu, J.; White, T.; Li, P.; He, C. H.; Yu, J. G.; Yuan, W. K.; Han, Y.-F. Biphasic Pd−Au Alloy Catalyst for Low-Temperature CO Oxidation J. Am. Chem. Soc. 2010, 132, 10398−10406. (25) Gao, F.; Wang, Y. L.; Goodman, D. W. CO Oxidation over AuPd(100) from Ultrahigh Vacuum to Near-Atmospheric Pressures: the Critical Role of Contiguous Pd Atoms J. Am. Chem. Soc. 2009, 131, 5734–5735. (26)

Duan, H.; Zeng, Y. F.; Yao, X.; Xing, P. Y.; Liu, J.; Zhao, Y. L. Tuning Synergistic

Effect of Au–Pd Bimetallic Nanocatalyst for Aerobic Oxidative Carbonylation of Amines Chem. Mater. 2017, 29, 3671–3677. (27) Zhang, L.; Xie, Z. X.; Gong, J. L. Shape-Controlled Synthesis of Au–Pd Bimetallic Nanocrystals for Catalytic Applications Chem. Soc. Rev. 2016, 45, 3916−3934.


27


Page 28 of 32

(28) Lee, Y. W.; Kim, M.; Kim, Z. H.; Han, S. W. One-step synthesis of Au@Pd core−shell nanooctahedron J. Am. Chem. Soc. 2009, 131, 17036–17037. (29) Fan, F.-R.; Liu, D.-Y.; Wu, Y.-F.; Duan, S.; Xie, Z.-X.; Jiang, Z.-Y.; Tian, Z.-Q. Epitaxial Growth of Heterogeneous Metal Nanocrystals: from Gold Nano-Octahedra to Palladium and Silver Nanocubes J. Am. Chem. Soc. 2008, 130, 6949–6951. (30) Hong, J. W.; Kim, D.; Lee, Y. W.; Kim, M.; Kang, S. W.; Han, W. Atomic‐Distribution‐Dependent Electrocatalytic Activity of Au–Pd Bimetallic Nanocrystals Angew. Chem. Int. Ed. 2011, 50, 8876−8880. (31) Lu, H.-L.; Prasad, K. S.; Wu, H.-L.; Ho, J. A.; Huang, M. H. Au Nanocube-Directed Fabrication of Au−Pd Core−Shell Nanocrystals with Tetrahexahedral, Concave Octahedral, and Octahedral Structures and Their Electrocatalytic Activity J. Am. Chem. Soc. 2010, 132, 14546– 1455. (32) Jing, H.; Wang, H. Controlled Overgrowth of Pd on Au Nanorods Cryst. Eng. Comm. 2014, 16, 9469−9477. (33) Ming, T.; Feng, W.; Tang, Q.; Wang, F.; Sun, L. D.; Wang, J. F.; Yan, C. H. Growth of Tetrahexahedral Gold Nanocrystals with High-Index Facets J. Am. Chem. Soc. 2009, 131, 16350–16351. (34) Chen, H. J.; Shao, L.; Li, Q.; Wang, J. F. Gold Nanorods and Their Plasmonic Properties Chem. Soc. Rev. 2013, 42, 2679−2724.


28

Page 29 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(35) Sun, L. C.; Zhang, Q. F.; Li, G. F.; Villarreal, E.; Fu, X. Q.; Wang, H. Multifaceted Gold– Palladium Bimetallic Nanorods and Their Geometric, Compositional, and Catalytic Tunabilities ACS Nano 2017, 11, 3213–3228. (36) Kim, Y.; Hong, J. W.; Lee, Y. W.; Kim, M.; Kim, D.; Yun, W. S.; Han, S. W. Synthesis of AuPt Heteronanostructures with Enhanced Electrocatalytic Activity toward Oxygen Reduction Angew. Chem. Int. Ed. 2010, 49, 10197–10201. (37) Luo, Y. R. Comprehensive handbook of chemical cond energies: Boca Raton, FL, 2007. (38) Yang, M. X.; Wang, W. X.; Gilroy, K. D.; Xia, Y. N. Controlling the Deposition of Pd on Au Nanocages: Outer Surface Only versus Both Outer and Inner Surfaces Nano Lett. 2017, 17, 5682−5687. (39) Xia, X. H.; Xie, S. F.; Liu, M. C.; Peng, H.-C.; Liu, N.; Wang, J. G.; Kim, M. J. On the Role of Surface Diffusion in Determining the Shape or Morphology of the Noble-Metal Nanocrystals P. Natl. Acad. Sci. USA, 2013, 110, 6669−6673. (40) Yu, Y.; Zhang, Q. B.; Xie, J. P.; Lee, J. Y. Engineering the Architectural Diversity of Heterogeneous Metallic Nanocrystals Nat. Commun. 2013, 4, 1454. (41) Guo, J.; Zhang, Y.; Shi, L.; Zhu, Y. F.; Mideksa, M. F.; Hou, K.; Zhao, W. S.; Wang, D. W.; Zhao, M. T.; Zhang, X. F.; Lv, J. W.; Zhang, J. Q.; Wang, X. L.; Tang, Z. Y. Boosting Hot Electrons in Hetero-Superstructures for Plasmon Enhanced Catalysis J. Am. Chem. Soc. 2017, 139, 17964−17972.


29


Page 30 of 32

(42) Tan, S. F.; Bisht, G.; Anand, U.; Bosman, M.; Yong, X. E.; Mirsaidov, U. In Situ Kinetic and Thermodynamic Growth Control of Au−Pd Core−Shell Nanoparticles J. Am. Chem. Soc. 2018, 140, 11680−11685. (43) Cui, X. M.; Qin, F.; Ruan, Q. F.; Zhuo, X. L.; Wang, J. F. Circular Gold Nanodisks with Synthetically Tunable Diameters and Thicknesses Adv. Funct. Mater. 2018, 28, 1705516. (44) Wang, Y.; Peng, H.-C.; Liu, J.; Huang, C.; Xia, Y. N. Use of Reduction Rate as a Quantitative Knob for Controlling the Twin Structure and Shape of Palladium Nanocrystals Nano. Lett. 2015, 15, 1445−1450. (45) Habas, S. E.; Lee, H.; Radmilovic, V.; Somorjai, G. A.; Yang, P. Shaping Binary Metal Nanocrystals Through Epitaxial Seeded Growth Nat. Mater. 2007, 6, 692–697. (46) Xia, X. H.; Zeng, J.; McDearmon, B.; Zheng, Y. Q.; Li, Q. G.; Xia, Y. N. Silver Nanocrystals with Concave Durfaces and Their Optical and Surface-Enhanced Raman Scattering Properties Angew. Chem. Int. Ed. 2011, 50, 12542−12546. (47) Begum, H.; Ahmed, M. S.; Jeon, S. Highly Efficient Dual Active Palladium Nanonetwork Electrocatalyst for Ethanol Oxidation and Hydrogen Evolution ACS Appl. Mater. Interfaces 2017, 9, 3930−3931. (48) Liu, W.; Herrmann, A.-K.; Bigall, N. C.; Rodriguez, P.; Wen, D.; Oezaslan, M.; Schmidt, T. J.; Gaponik, N. A. Eychmüller Noble Metal Aerogels−Synthesis, Characterization, and Application as Electrocatalysts Acc. Chem. Res. 2015, 48, 154−162. (49) Antolini, E. Palladium in Fuel Cell Catalysis Energy Environ. Sci. 2009, 2, 915−931.


30

Page 31 of 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(50) Wang, J.; Zhang, P.; Xiahou, Y. J.; Wang, D. Y.; Xia, H. B.; Möhwald, H. Synthesis of Au−Pd Alloy Nanowire Networks as Macroscopic, Flexible Electrocatalysts with Excellent Performance ACS Appl. Mater. Interfaces 2018, 10, 602−613. (51) Huang, W. J.; Kang, X. L.; Xu, C.; Zhou, J. H.; Deng, J.; Li, Y. G.; Cheng, S. 2D PdAg Alloy Nanodendrites for Enhanced Ethanol Electroxidation Adv. Mater. 2018, 30, 1706962. (52) Li, S. W.; Yang, H. L.; Zou, H.; Yang, M.; Liu, X. D.; Jin, J.; Ma, J. T. Palladium Nanoparticles Anchored on NCNTs@NGS with a Three-Dimensional Sandwich-Stacked Framework as an Advanced Electrocatalyst for Ethanol Oxidation J. Mater. Chem. A, 2018, 6, 14717–14724. (53) Yang, H. L.; Zhang, X. Y.; Zou, H.; Yu, Z. N.; Li, S. W.; Sun, J. H.; Chen, S. D.; Jin, J.; Ma, J. T. Palladium Nanoparticles Anchored on Three-Dimensional Nitrogen-Doped Carbon Nanotubes as a Robust Electrocatalyst for Ethanol Oxidation ACS Sustainable Chem. Eng. 2018, 6, 7918−7923. (54) Cao, X.; Wang, N.; Han, Y.; Gao, C. Z.; Xu, Y.; Li, M. X.; Shao, Y. H. PtAg Bimetallic Nanowires: Facile Synthesis and Their Use as Excellent Electrocatalysts toward Low-Cost Fuel Cells Nano Energy, 2015, 12, 105−114. (55) Kelly, C. H. W.; Benedetti, T. M.; Alinezhad, A.; Schuhmann, W.; Gooding, J. J.; Tilley, R. D. Understanding the Effect of Au in Au–Pd Bimetallic Nanocrystals on the Electrocatalysis of the Methanol Oxidation Reaction J. Phys. Chem. C 2018, 122, 21718−21723. (56) Celorrio, V.; Quaino, P. M.; Santos, E.; Flórez-Montaño, J.; Humphrey, J. J. L.; GuillénVillafuerte, O.; Plana, D.; Lázaro, M. J.; Pastor, E.; Fermín, D. J. Strain Effects on the Oxidation


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of CO and HCOOH on Au–Pd Core–Shell Nanoparticles ACS Catal. 2017, 7, 1673−1680. (57) Strmcnik, D.; Escudero-Escribano, M.; Kodama, K.; Stamenkovic, V. R.; Cuesta, A.; Marković, N. M. Lattice-Strain Control of the Activity in Dealloyed Core–Shell Fuel Cell Catalysts Nat. Chem. 2010, 2, 454−460. (58) Roudgar, A.; Groß, A. Local Reactivity of Metal Overlayers: Density Functional Theory Calculations of Pd on Au Phys Rev. B: Condens. Mater. Phys. 2003, 67, 033409.

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