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Polyhedral Palladium-Silver Alloy Nanocrystals as Highly Active and Stable Electrocatalysts for the Formic Acid Oxidation Reaction.

Fu GT, Liu C, Zhang Q, Chen Y, Tang YW - Sci Rep (2015)

Bottom Line: Polyhedral noble-metal nanocrystals have received much attention and wide applications as electrical and optical devices as well as catalysts.In this work, a straightforward and effective hydrothermal route for the controllable synthesis of the high-quality Pd-Ag alloy polyhedrons with uniform size is presented.As a preliminary electrochemical application, the Pd-Ag alloy polyhedrons are applied in the formic acid oxidation reaction, which shows higher electrocatalytic activity and stability than commercially available Pd black due to the "synergistic effects" between Pd and Ag atoms.

View Article: PubMed Central - PubMed

Affiliation: Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, P. R. China.

ABSTRACT
Polyhedral noble-metal nanocrystals have received much attention and wide applications as electrical and optical devices as well as catalysts. In this work, a straightforward and effective hydrothermal route for the controllable synthesis of the high-quality Pd-Ag alloy polyhedrons with uniform size is presented. The morphology, composition and structure of the Pd-Ag alloy polyhedrons are fully characterized by the various physical techniques, demonstrating the Pd-Ag alloy polyhedrons are highly alloying. The formation/growth mechanisms of the Pd-Ag alloy polyhedrons are explored and discussed based on the experimental observations and discussions. As a preliminary electrochemical application, the Pd-Ag alloy polyhedrons are applied in the formic acid oxidation reaction, which shows higher electrocatalytic activity and stability than commercially available Pd black due to the "synergistic effects" between Pd and Ag atoms.

No MeSH data available.


(A) EDX spectrum, (B) XRD pattern, (C) Pd 3d XPS spectrum, and (D) Ag 3d XPS spectrum of the Pd–Ag alloy polyhedrons. (Note: the vertical black dotted lines in (C) and (D) represent the standard values of Pd3d 5/2 and Ag3d 5/2, respectively).
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f1: (A) EDX spectrum, (B) XRD pattern, (C) Pd 3d XPS spectrum, and (D) Ag 3d XPS spectrum of the Pd–Ag alloy polyhedrons. (Note: the vertical black dotted lines in (C) and (D) represent the standard values of Pd3d 5/2 and Ag3d 5/2, respectively).

Mentions: In a typical synthesis, the Pd–Ag alloy polyhedrons were obtained by reducing K2PdCl4 and AgNO3 precursors with HCHO in polyallylamine hydrochloride (PAH, Scheme S1) aqueous solution at 180 °C for 2 h (see Experimental section for details). The chemical compositions, crystal structures, and chemical states of the products were first analyzed by energy dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) spectra, respectively. EDX analysis shows the products contain both Pd and Ag elements, and the elemental compositions of Pd and Ag are 48.10 and 51.90 at%, in accordance with theoretical stoichiometric proportion (Fig. 1A). The XRD pattern of the Pd–Ag nanocrystals clearly shows the four different diffraction peaks, which can be indexed to (111), (200), (220), and (311) facets of face-centered-cubic (fcc) metal, respectively (Fig. 1B). Meanwhile, no apparent diffraction peaks of pure Pd or Ag are detected, and all diffraction peaks of the Pd–Ag nanocrystals are located between those of Pd (JCPDS-46-1043) and Ag (JCPDS-04-0783), suggesting the formation of the Pd–Ag alloy. The average lattice constant (a) of the Pd–Ag alloy nanocrystals calculated from the four different diffraction peaks is 0.39911 nm, which is bigger than standard value (0.38902 nm)2728 of fcc Pd (JCPDS-46–1043). The lattice expansion originates from the partial replacement of Pd atoms by Ag atoms with a larger atom radius (Pd: 0.128 nm vs. Ag: 0.134 nm). Based on the Vegard’s law29, it can be deduced from the XRD pattern that the ratio of Pd/Ag was approximately 1:1, in accordance with the EDX analysis.


Polyhedral Palladium-Silver Alloy Nanocrystals as Highly Active and Stable Electrocatalysts for the Formic Acid Oxidation Reaction.

Fu GT, Liu C, Zhang Q, Chen Y, Tang YW - Sci Rep (2015)

(A) EDX spectrum, (B) XRD pattern, (C) Pd 3d XPS spectrum, and (D) Ag 3d XPS spectrum of the Pd–Ag alloy polyhedrons. (Note: the vertical black dotted lines in (C) and (D) represent the standard values of Pd3d 5/2 and Ag3d 5/2, respectively).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4556982&req=5

f1: (A) EDX spectrum, (B) XRD pattern, (C) Pd 3d XPS spectrum, and (D) Ag 3d XPS spectrum of the Pd–Ag alloy polyhedrons. (Note: the vertical black dotted lines in (C) and (D) represent the standard values of Pd3d 5/2 and Ag3d 5/2, respectively).
Mentions: In a typical synthesis, the Pd–Ag alloy polyhedrons were obtained by reducing K2PdCl4 and AgNO3 precursors with HCHO in polyallylamine hydrochloride (PAH, Scheme S1) aqueous solution at 180 °C for 2 h (see Experimental section for details). The chemical compositions, crystal structures, and chemical states of the products were first analyzed by energy dispersive X-ray (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) spectra, respectively. EDX analysis shows the products contain both Pd and Ag elements, and the elemental compositions of Pd and Ag are 48.10 and 51.90 at%, in accordance with theoretical stoichiometric proportion (Fig. 1A). The XRD pattern of the Pd–Ag nanocrystals clearly shows the four different diffraction peaks, which can be indexed to (111), (200), (220), and (311) facets of face-centered-cubic (fcc) metal, respectively (Fig. 1B). Meanwhile, no apparent diffraction peaks of pure Pd or Ag are detected, and all diffraction peaks of the Pd–Ag nanocrystals are located between those of Pd (JCPDS-46-1043) and Ag (JCPDS-04-0783), suggesting the formation of the Pd–Ag alloy. The average lattice constant (a) of the Pd–Ag alloy nanocrystals calculated from the four different diffraction peaks is 0.39911 nm, which is bigger than standard value (0.38902 nm)2728 of fcc Pd (JCPDS-46–1043). The lattice expansion originates from the partial replacement of Pd atoms by Ag atoms with a larger atom radius (Pd: 0.128 nm vs. Ag: 0.134 nm). Based on the Vegard’s law29, it can be deduced from the XRD pattern that the ratio of Pd/Ag was approximately 1:1, in accordance with the EDX analysis.

Bottom Line: Polyhedral noble-metal nanocrystals have received much attention and wide applications as electrical and optical devices as well as catalysts.In this work, a straightforward and effective hydrothermal route for the controllable synthesis of the high-quality Pd-Ag alloy polyhedrons with uniform size is presented.As a preliminary electrochemical application, the Pd-Ag alloy polyhedrons are applied in the formic acid oxidation reaction, which shows higher electrocatalytic activity and stability than commercially available Pd black due to the "synergistic effects" between Pd and Ag atoms.

View Article: PubMed Central - PubMed

Affiliation: Jiangsu Key Laboratory of New Power Batteries, Jiangsu Collaborative Innovation Center of Biomedical Functional Materials, School of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, P. R. China.

ABSTRACT
Polyhedral noble-metal nanocrystals have received much attention and wide applications as electrical and optical devices as well as catalysts. In this work, a straightforward and effective hydrothermal route for the controllable synthesis of the high-quality Pd-Ag alloy polyhedrons with uniform size is presented. The morphology, composition and structure of the Pd-Ag alloy polyhedrons are fully characterized by the various physical techniques, demonstrating the Pd-Ag alloy polyhedrons are highly alloying. The formation/growth mechanisms of the Pd-Ag alloy polyhedrons are explored and discussed based on the experimental observations and discussions. As a preliminary electrochemical application, the Pd-Ag alloy polyhedrons are applied in the formic acid oxidation reaction, which shows higher electrocatalytic activity and stability than commercially available Pd black due to the "synergistic effects" between Pd and Ag atoms.

No MeSH data available.