Browsing by Author "Chang, Li-Chung"

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Displacement reaction of Pt on carbon-supported Ru nanoparticles in hexachloroplatinic acids
(2011-03-14)
Hsieh, Yu-Chi
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Chang, Li-Chung
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Wu, Pu-Wei
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Chang, Yun-Min
;
Lee, Jyh-Fu
The displacement reaction of Pt on Ru to form a Ru core and Pt shell (Ru@Pt) bimetallic structure is investigated by immersing the carbon-supported Ru nanoparticles in hexachloroplatinic acids with pH of 1,2.2. and 8, followed by a hydrogen reduction treatment. Results from inductively coupled plasma mass spectrometry suggest that the dissolution of Ru is mostly caused by the reduction of Pt cations. Images from transmission electron microscopy demonstrate a uniform distribution of Ru@Pt in size of 3-5 nm. Spectra from X-ray absorption near edge structure and extended X-ray absorption fine structure confirm that the pH value of hexachloroplatinic acid determines the type of ligands complexing the Pt cations that affects their activity and consequently the severity of displacement reaction and alloying degree of Ru@Pt nanoparticles. As a result, the samples from pH 1 bath reveal a desirable core-shell structure that displays a reduced onset potential in CO stripping and stable catalytic performance for H(2) oxidation while the samples from pH 8 bath indicate the formation of Pt clusters on the Ru surface that leads to poor CO stripping and H(2) oxidation characteristics. (C) 2011 Elsevier B.V. All rights reserved.
Fabrication of Graphene by Electrochemical Exfoliation in Alkaline Electrolytes
(2014-01-01)
Chang, Li-Chung
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Hsieh, Yu-Chi
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Chen, Yong-Min
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Wu, Pu-Wei
;
Lee, Jyh-Fu
Fabrication of graphene was demonstrated by electrochemical exfoliation of graphite in an ammonium hydroxide solution. The processing parameter of applied voltage was optimized to accomplish graphene productivity and desired chemical composition. Images from the atomic force microscopy showed graphene sheets with lateral sizes of several hundred nanometers. Images from the transmission electron microscopy indicated the existence of stacked graphene sheets with thickness of a few graphene layers. Raman spectroscopy confirmed variation of as-synthesized graphene and bulk graphite. X-ray photoemission spectroscopy suggested the formation of graphene oxide at large voltage.
Facile Surface Functionalization of Carbon/Nafion for Enhancement of Methanol Electro-Oxidation
(2010)
Hsieh, Yu-Chi
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Chang, Li-Chung
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Wu, Pu-Wei
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Lee, Jyh-Fu
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Liao, Chen-Hong
We report a facile electrochemical method to produce functional groups on the carbon surface in which multiple cyclic voltammetric (CV) sweeps are imposed in 0.5 M H2SO4 electrolyte on the samples containing carbon cloth, Vulcan XC72R, and Nafion ionomer. With supply of ambient O-2, the generation of radicals from the oxygen reduction and Nafion ionomer degradation enables an accelerated formation of oxygenated functional groups on the carbon surface. Raman analysis reveals structural variation for the carbon electrodes after CV modifications. X-ray photoelectron spectroscopy confirms the alteration of carbon structure in conjunction with notable increase of oxygenated groups and reduction in fluorine amount. The functionalized electrodes allow a 250% increment for PtRu electrodeposition as compared to the reference sample. We carry out electrochemical measurements on methanol electro-oxidation for the PtRu samples. The functionalized electrode demonstrates significant improvement in apparent current density and mass activity as opposed to the reference sample.
Structural characterizations of PtRu nanoparticles by galvanostatic pulse electrodeposition
(2014-01-15)
Hsieh, Yu-Chi
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Chang, Li-Chung
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Tseng, Yuan-Chieh
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Wu, Pu-Wei
;
Lee, Jyh-Fu
We demonstrate that the compositions and structures of PtRu nanoparticles can be altered via adjusting plating variables during galvanostatic pulse electrodeposition. During current-on time (Ton), both Pt and Ru are deposited according to their respective diffusion-limiting current. However, during current-off time (Toff), due to difference in the redox potentials, a displacement reaction is occurring that leads to the reduction of Pt ions from the electrolyte while the Ru atoms in the PtRu nanoparticles experience oxidation reaction and corrosive dissolution simultaneously. Therefore, the duty cycle, defined as Ton/(Ton + Toff), serves as an indicator for the severity of displacement reaction that affects the PtRu makeup. Inductively-coupled mass spectrometry determines the composition as Pt83Ru17, Pt64Ru36, and Pt53Ru47 for duty cycles of 0.077, 0.111, and 0.333, respectively. Images from transmission electron microscope exhibit nanoparticles in sizes of 4-11 nm. Analysis from extended X-ray absorption fine structure (EXAFS) suggests that Pt atoms tend to segregate outward and reside at the alloy's surface upon the displacement reaction. Composition profiles from line scans of energy dispersive X-ray spectroscopy are consistent with atomic structure revealed by EXAFS. (C) 2013 Elsevier B.V. All rights reserved.
Surface modification of commercial PtRu nanoparticles for methanol electro-oxidation
(2013-10-15)
Kuo, Che-Wei
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Lu, I-Te
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Chang, Li-Chung
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Hsieh, Yu-Chi
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Tseng, Yuan-Chieh
The surfaces of commercially available PtRu nanoparticles (PtRu/C) have been successfully modified via a displacement reaction between the Ru atoms on the PtRu/C and the Pt ions in an aqueous hexachloroplatinic acid solution. The concentration of the hexachloroplatinic acid solution was deliberately formulated to allow for the formation of sub-monolayered Pt (Pt(1/16)) and monolayered Pt (Pt(1/8)) on the surface of PtRu/C. Material characterization, including X-ray diffraction patterns and transmission electron microscopy images, showed that the PtRu phases of the samples were identical but that the particle sizes increased slightly after the surface modification. Data from inductively coupled plasma mass spectrometry confirmed the deposition of Pt with negligible loss of Ru. X-ray absorption spectroscopy showed Pt-enriched surfaces, and the surface Pt content decreased in the order Pt(1/8) > Pt(1/16) > PtRu/C. Cyclic voltammetry and chronoamperometry were conducted for methanol electro-oxidation, and our results indicated impressive catalytic ability and carbon monoxide tolerance for Pt(1/16), followed by Pt(1/8) and PtRu/C. The mass activities of Pt(1/16) and Pt(118) increased 223% and 135% over that of PtRu/C. We attributed the observed improvements to the reduced amount of Ru on the PtRu surface, which resulted in an optimized PtRu ratio with enhanced catalytic ability. (C) 2013 Elsevier B.V. All rights reserved.
Synthesis of Pd9Ru@Pt nanoparticles for oxygen reduction reaction in acidic electrolytes
(2015-03-01)
Sun, Yu
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Hsieh, Yu-Chi
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Chang, Li-Chung
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Wu, Pu-Wei
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Lee, Jyh-Fu
Nanoparticles of PdRu, Pd3Ru, and Pd9Ru are synthesized and impregnated on carbon black via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples, PdxRu/C (x = 1/3/9), suggest successful formation of alloy without presence of individual Pd and Ru nanoparticles. Images from transmission electron microscope confirm irregularly-shaped nanoparticles with average size below 3 nm. Analysis from extended X-ray absorption fine structure on both Pd and Ru K-edge absorption profiles indicate the Ru atoms are enriched on the surface of PdxRu/C. Among these samples, the Pd9Ru/C exhibits the strongest electrocatalytic activity for oxygen reduction reaction (ORR) in an oxygen-saturated 0.1 M aqueous HClO4 solution. Subsequently, the Pd9Ru/C undergoes Cu under potential deposition, followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd9Ru surface (Pd9Ru@Pt). The Pd9Ru@Pt reveals better ORR performance than that of Pt, reaching a mass activity of 0.38 mA mu g(pt)(-1), as compared to that of commercially available Pt nanopartides (0.107 mA mu g(pt)(-1)). The mechanisms responsible for the ORR enhancement are attributed to the combined effects of lattice strain and ligand interaction. In addition, this core-shell Pd9Ru@Pt electrocatalyst represents a substantial reduction in the amount of Pt consumption and raw material cost. (C) 2014 Elsevier B.V. All rights reserved.
Using decomposed Nafion ionomers to anchor Pt nanoparticles and improve their durability during methanol electro-oxidation
(2014-01-01)
Hsieh, Yu-Chi
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Chang, Li-Chung
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Chen, Yong-Min
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Wu, Pu-Wei
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Lee, Jyh-Fu
Nafion ionomers were partially decomposed to produce oxygenated functional groups on Vulcan XC72R (XC72R) that enabled increased Pt ion adsorption when the functionalized XC72R was immersed in a 5 mM aqueous H2PtCl6 solution. X-ray absorption spectroscopy spectra indicated that the oxidation state for the Pt ions remained unchanged upon adsorption on the functionalized XC72R whereas a notable reduction in the oxidation state was recorded when the Pt ions were adsorbed onto untreated XC72R. After a hydrogen reduction treatment, the Pt nanoparticles on the functionalized XC72R demonstrated impressive mass activities and durability retention during the methanol electro-oxidation reaction (MOR), compared to those of commercial E-TEK Pt/C samples. After the durability test, transmission electron microscope images showed that the Pt nanoparticles on the functionalized XC72R exhibited significantly reduced agglomeration, and X-ray photoelectron spectra confirmed that the functional groups from the decomposed Nafion ionomers were still present. We attributed the notable durability improvement to the anchoring effect of decomposed Nafion ionomers that prevented the Pt nanoparticles from contacting XC72R directly, thus minimizing the undesirable migration and detachment of Pt nanoparticles during repeated MOR cycles. (C) 2013 Elsevier B.V. All rights reserved.