Browsing by Author "Hsieh, Yu-Chi"

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Dealloyed Pt2Os nanoparticles for enhanced oxygen reduction reaction in acidic electrolytes
(2014-05-05)
Lee, Yi-Juei
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Hsieh, Yu-Chi
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Tsai, Ho-Cheng
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Lu, I-Te
;
Wu, Yue-Han
Carbon-supported Pt2Os (Pt2Os/C) nanoparticles in 3.55 nm sizes are synthesized from a wet chemical reflux process. Subsequently, the Pt2Os/C undergoes a dealloying treatment in which multiple cyclic voltammetric scans are imposed to dissolve the Os atoms selectively from the surface of the Pt2Os nanoparticles. X-ray diffraction signals from the dealloyed sample (DA-Pt2Os/C) indicate a fcc phase and composition analysis suggests Pt4Os. Line scans from the scanning transmission electron microscope confirm that the surface of Pt4Os is depleted with the Os atoms. This agrees with our quantum mechanics (Density Funtional theory) calculations, which predict for the Pt3Os composition that the surface skin layer is pure Pt. The DA-Pt2Os/C shows impressive electrocatalytic behaviors (0.29 mA mu g(Pt)(-1) in mass activity and 1.03 mA cm(Pt)(-2) in specific activity) for the oxygen reduction reaction (ORR) in oxygen-saturated 0.1 M aqueous HClO4 solution, as compared to those of commercially available Pt/C and as-synthesized Pt2Os/C. In stability test, the DA-Pt2Os/C demonstrates a better retention of ORR activities and a smaller loss of electrochemical active surface area. We verify experimentally that a four-electron step is responsible for the ORR process occurring on the DA-Pt2Os/C. (C) 2014 Elsevier B.V. All rights reserved.
Displacement Reaction in Pulse Current Deposition of PtRu for Methanol Electro-Oxidation
(2009)
Hsieh, Yu-Chi
;
Wu, Pu-Wei
;
Lu, Yung-Jean
;
Chang, Yun-Min
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材料科學與工程學系
Galvanostatic depositions in rectangular pulses and nitrosol precursors were employed to prepare PtRu nanoparticles on carbon clothes in various sizes and compositions. Variables including current on-time (T(on)), current off-time (T(off)), and current density were explored to identify the optimized catalytic performances for methanol electro-oxidation. Electrochemical characterizations including cyclic voltammetry and hydrogen desorption were carried out. Images from a transmission electron microscope on the PtRu nanoparticles revealed a moderate size distribution. Signals from X-ray patterns indicated a slight shift of diffraction peaks, suggesting that the Ru was alloyed successfully in the Pt lattice. In addition, the amount of alloyed Ru was found to decrease with reduced duty cycles. Composition determinations from inductively coupled plasma mass spectrometry and analysis on the oxidation states from X-ray photoelectron spectroscopy suggested a displacement reaction in which the Ru was alternately deposited and dissolved during T(on) and T(off), while the Pt was deposited continuously. As a result, we observed substantial enrichment of Pt in the PtRu nanoparticles when the duty cycle was shortened.
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.
Effect of anodic dissolution in multi-element nanoparticles on methanol electro-oxidation
(2009-11-03)
Hsieh, Yi-Fan
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Yeh, Kung-Yu
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Wu, Pu-Wei
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Hsieh, Yu-Chi
;
Lin, Pang
Radio frequency sputter deposition was used to deposit multi-element nanoparticles on carbon clothes for methanol electro-oxidation. Results from energy dispersive spectroscope confirmed the composition was Ft(35)Fe(12)Co(12)Ni(20)Cu(12)Ag(9). X-ray diffraction pattern suggested a fcc phase. An electrochemical de-alloying treatment was conducted in an acidic electrolyte with multiple potential sweeps at a scan rate of 20 mV/s for 0-0.3,0-0.5, and 0-0.7 V, respectively. Images from scanning electron microscope after anodic dissolutions demonstrated considerable variations in surface morphologies. Measurements on hydrogen desorption also revealed substantial increase in electrochemical active surface area. Current responses from cyclic voltammetry indicated the sample of 0-0.5 V anodic dissolution with notable enhancement. In mass activities, the same sample exhibited a comparable value to that Of Pt(43)Ru(57) (C) 2009 Elsevier B.V. All rights reserved.
Electrochemical degradation of Nafion ionomer to functionalize carbon support for methanol electro-oxidation
(2011-10-15)
Hsieh, Yu-Chi
;
Chen, Jing-Yu
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Wu, Pu-Wei
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材料科學與工程學系
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Department of Materials Science and Engineering
An effective electrochemical route to produce functional groups on carbon surface is demonstrated. Cyclic voltammetric (CV) sweeps are performed in 0.5 M H(2)SO(4) electrolyte on electrodes containing carbon cloth, Vulcan XC72R, and Nation ionomer. With supply of ambient oxygen, the generation of hydroxyl radicals from the oxygen reduction reaction during CV cycles initiates the decomposition of Nation ionomer that leads to formation of oxygenated functional groups on the carbon surface. Ion chromatography confirms the dissolution of sulfate anions upon CV scans. Raman analysis suggests a minor alteration for the carbon structure. However, X-ray photoelectron spectroscopy indicates a significant increase of oxygenated functional groups in conjunction with notable reduction in the fluorine content. The amount of the oxygenated functional groups is determined by curve fitting of C is spectra with known constituents. These functional groups can also be found by immersing the as-prepared electrode in a solution containing concentrated residues from Nation ionomer decomposition. The functionalized electrode allows a 170% increment of Pt ion adsorption as compared to the reference sample. After electrochemical reductions, the functionalized electrode reveals significant improvements in electrocatalytic abilities for methanol oxidation, which is attributed to the oxygenated functional groups that facilitates the oxidation of CO on Pt. (C) 2011 Elsevier B.V. All rights reserved.
Electrochemical reduction of CO(2) by Cu(2)O-catalyzed carbon clothes
(2009-05-15)
Chang, Tin-Yu
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Liang, Ru-Meng
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Wu, Pu-Wei
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Chen, Jing-Yu
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Hsieh, Yu-Chi
Cu(2)O cubes with average edge lengths of 640 nm were prepared by a chemical reduction approach. The as-synthesized Cu(2)O particles were deposited on carbon clothes for electrochemical characterizations in cyclic voltammetry (CV) and potentiostatic measurements. In 0.5 M NaOH electrolytes saturated with N(2) or CO(2), both the Cu(2)O and carbon clothes were stable at the potential range of 0 to -1.7 V. Comparisons in the Current responses from the CV and potentiostatic measurements suggested the Cu(2)O with notable catalytic abilities for the CO(2) reduction. The mass activity was estimated at 0.94 mA/mg. Chemical analysis from gas chromatography confirmed the methanol to be the predominant product. (C) 2009 Elsevier B.V. All rights reserved.
Electrochemical reduction of CO2 by Cu2O-catalyzed carbon clothes
(2009-05-15)
Chang, Tin-Yu
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Liang, Ru-Meng
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Wu, Pu-Wei
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Chen, Jing-Yu
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Hsieh, Yu-Chi
Cu2O cubes with average edge lengths of 640 nm were prepared by a chemical reduction approach. The as-synthesized Cu2O particles were deposited on carbon clothes for electrochemical characterizations in cyclic voltammetry (CV) and potentiostatic measurements. In 0.5 M NaOH electrolytes saturated with N-2 or CO2, both the Cu2O and carbon clothes were stable at the potential range of 0 to -1.7 V. Comparisons in the Current responses from the CV and potentiostatic measurements suggested the Cu2O with notable catalytic abilities for the CO2 reduction. The mass activity was estimated at 0.94 mA/mg. Chemical analysis from gas chromatography confirmed the methanol to be the predominant product. (C) 2009 Elsevier B.V. All rights reserved.
Electroless Deposition of Ru Films Via an Oxidative-Reductive Mechanism
(2011)
Chen, Jing-Yu
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Hsieh, Yu-Chi
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Wang, Li-Yeh
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Wu, Pu-Wei
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材料科學與工程學系
An electroless Ru plating bath is prepared by mixing Ru precursor (K(2)RuCl(5).xH(2)O), oxidizer (NaClO), stabilizer (NaOH), and reducing agent (NaNO(2)) simultaneously in deionized water at a molar ratio of 1:1:20:10. Instead of conventional direct reduction route, the RuCl(5)(2-) experiences an oxidative-reductive sequence to form metallic Ru on an activated Si substrate. Spectra from ultraviolet-visible and X-ray absorption spectroscopy indicate that the RuCl(5)(2-) is oxidized to form RuO(4) initially, followed by a slight reduction becoming RuO(4)(2-). The RuO(4)(2-) solution is relatively stable and is able to undergo further reduction to render metallic Ru via heterogeneous nucleation and growth. Images from scanning electron microscope demonstrate a solid film of 100 nm with scattered protrusions and cavities after 120 min plating time. Analysis from atomic force microscope determines its surface roughness of 7.8 nm. From X-ray diffraction patterns, the as-deposited film reveals an amorphous structure but turns crystalline after Ar annealing at 400 degrees C for 2 h. Curve-fitting of Ru 3p(3/2) signal from X-ray photoelectron spectroscopy suggests a film composition of 92.49 atom % Ru and 7.51 atom % RuO(2). The electroless Ru plating bath exhibits impressive life time (137 h) and negligible homogeneous precipitation without involving surfactants and unnecessary chemical additives. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3592996] All rights reserved.
Enhancement of bifunctional catalysis by Ir doping of La0.6Ca0.4CoO3 perovskites
(2008-10-15)
Chang, Yun-Min
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Hsieh, Yu-Chi
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Wu, Pu-Wei
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Lai, Chun-Han
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Chang, Tin-Yu
La0.6Ca0.4Co0.8Ir0.2O3 was prepared by solid state reaction synthesis from mixtures of La(NO3)(3)center dot 6H(2)O, Ca (NO3)(2)center dot 4H(2)O, Co(NO3)(3)center dot 6H(2)O, and IrO2 at stoichiometric ratio. Images from scanning electron microscopy on the as-synthesized powders exhibited particles in irregular shape at 100-250 nm in size. X-ray diffraction analysis confirmed the formation of perovskite without the rutile signals from IrO2, suggesting successful incorporation of Ir4+ at the Co cation sites. The carbon nanocapsules (CNCs) were used as an electrocatalyst support. Electrodes for electrochemical measurements were fabricated by depositing mixtures of CNCs, La0.6Ca0.4Co0.8Ir0.2O3 and polymeric binders on commercially available noncatalyzed gas diffusion electrodes. In alkaline electrolyte, the La0.6Ca0.4Co0.8Ir0.2O3/CNCs demonstrated superior performances than those of La0.6Ca0.4Co0.8Ir0.2O3/CNCs and IrO2/CNCs in both charging and discharging current-potential polarization measurements. (c) 2008 Elsevier B.V. All rights reserved.
EQCM Study on Pulse Current Pt Electrodeposition
(2015-12-01)
Lu, I-Te
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Hsieh, Yu-Chi
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Chen, Po-Chun
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Wu, Pu-Wei
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材料科學與工程學系
Electrochemical Quartz Crystal Microbalance (EQCM) was used to investigate the events occurring during current-on (T-on) and current-off (T-off) for pulse current electrodeposition of Pt in both air and Ar atmospheres. The EQCM profiles indicated a transient mass loss when the current was turned on, followed by a linear mass gain associated with the Pt electrodeposition from the H2PtCl6 plating bath. During the T-off, the mass revealed a steady increase until it leveled off after 10 sec. The minute transient mass loss during the initial stage of T-on was attributed to the reduction of the adsorbed PtCl62- whereas the mass gain during the T-off was due to the absorption of PtCl62- onto the freshly-deposited Pt surface. In air atmosphere, the parasitic oxygen reduction reaction consumed part of the reduction current and thus, reduced the Pt plating efficiency by 6%. In addition, smaller mass gains during T-off and T-on were observed for the Pt plating in air atmosphere.
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
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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.
Free-standing Au inverse opals for enhanced glucose sensing
(2016-11-05)
Liao, Chen-Hong
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Hsieh, Yu-Chi
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Huang, Bo-Han
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Pai, Chia-Hao
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Wu, Pu-Wei
We successfully fabricate free-standing gold inverse opals (GIO) with a highly ordered porous structure, adjustable pore size, and large geometric size (2.5 x 2.5 cm(2)). The process involves a vertical electrophoresis to assemble polystyrene (PS) microspheres in a closed-packed form, followed by backfilling of Ni and Au into the interstitial voids among the PS microspheres. Subsequently, the PS microspheres and Ni are removed to render free-standing GIO samples with pore size of 300, 405, and 600 nm, respectively. The free-standing GIO structures reveal a hexagonally-arranged pores with impressive mechanical strength and flexibility. Diffraction patterns from the X-ray diffractometer indicate a strong preferred orientation in the (111) plane. Cyclic voltammetric scans show excessive electrochemical surface area for the GIO samples as compared to that of planar Au in identical footprint. In glucose oxidation, the GIO structures demonstrate apparent current densities that are ten times larger over planar Au. Among the GIO structures, the sample with 300 nm pore size demonstrates the highest specific activity and the largest I-a/I-c value. We believe that the relatively smaller 300 nm pores facilitate the confinement of byproduct intermediates, and thus results in more effective oxidation of glucose. (C) 2016 Elsevier B.V. All rights reserved.
Galvanostatic Pulse Plating of PtRu Nanoparticles for Direct Methanol Fuel Cells
(2008)
Hsieh, Yu-Chi
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Lu, Yung-Jean
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Wu, Pu-Wei
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Chang, Yun-Min
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Chiu, Yu-Fan
A galvanostatic pulse electrodeposition technique of preparing nanoparticulate PtRu electrocatalyst for direct methanol fuel cells has been demonstrated. After extensive cyclic voltammetric analysis, we determined the optimized parameters for the methanol oxidation to be current on-time on 50 ms, current off-time of 400 ms, current density of 50 mA/cM, and total charge of 9.0 C/cm(2) In addition, the catalyst loading was measured at 68 mu g/cm(2) resulting in a mass activity of 213 mA/Pt. mg. The composition for the nanoparticles was confirmed as Pt(65)RU(35). High-magnification images on the specimen indicated fine particles in 4-20 nm with uniform distributions.
High-yield water-based synthesis of truncated silver nanocubes
(2014-02-15)
Chang, Yun-Min
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Lu, I-Te
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Chen, Chih-Yuan
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Hsieh, Yu-Chi
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Wu, Pu-Wei
A high-yield water-based hydrothermal synthesis was developed using silver nitrate, ammonia, glucose, and cetyltrimethylammonium bromide (CTAB) as precursors to synthesize truncated silver nanocubes with uniform sizes and in large quantities. With a fixed CTAB concentration, truncated silver nanocubes with sizes of 49.3 +/- 4.1 nm were produced when the molar ratio of glucose/silver cation was maintained at 0.1. The sample exhibited (100), (110), and (111) planes on the facets, edges, and corners, respectively. In contrast, with a slightly larger glucose/silver cation ratio of 0.35, well-defined nanocubes with sizes of 70.9 +/- 3.8 nm sizes were observed with the (100) plane on six facets. When the ratio was further increased to 1.5, excess reduction of silver cations facilitated the simultaneous formation of nanoparticles with cubic, spherical, and irregular shapes. Consistent results were obtained from transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and UV-visible absorption measurements. (C) 2013 Elsevier B. V. All rights reserved.
Pulse Electrodepositions of PtRu on Large-Area Carbon Nanotubes for Enhancement of Methanol Electro-Oxidation
(2010)
Hsieh, Yi-Fan
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Hsieh, Yu-Chi
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Wu, Pu-Wei
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Liao, Chen-Hong
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Chang, Yun-Min
We employed an electroless deposition technique to prepare Ni seeds uniformly on a carbon cloth, followed by carbon nanotube (CNT) formation at an elevated temperature. Subsequently, a pulse electrodeposition was used to impregnate PtRu nanoparticles on the CNT structure. Similar procedures were performed on carbon supports including Vulcan XC72R, BP2000, and carbon nanocapsules (CNCs) for comparison purposes. Diffraction patterns from an X-ray confirmed a PtRu alloyed phase. An analysis from inductively coupled plasma-mass spectrometry indicated that the PtRu composition was relatively unchanged. Images from scanning and transmission electron microscopes revealed dense CNTs throughout the carbon cloth with nanoparticulate PtRu evenly impregnated. Considerable PtRu aggregations were found on the CNCs and BP2000. We observed a significantly improved coulomb efficiency and an electrochemically active surface area for the CNT-grown carbon cloth. In both apparent current density and mass activity for methanol electro-oxidation, the CNT-grown carbon cloth revealed the largest values. We attribute the performance enhancement to the large-area CNT structure that allowed facile access of electrolytes. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3246002] All rights reserved.
Structural characterizations of Cu3Pt electrocatalyst featuring Pt-rich surface layers synthesized via mechanical alloying and selective dissolution routes
(2013-03-05)
Hsieh, Yi-Fan
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Hsieh, Yu-Chi
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Tseng, Yuan-Chieh
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Wu, Pu-Wei
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Chao, Cheun Guang
We demonstrate a selective electrochemical dissolution route to prepare Cu3Pt catalysts featuring Pt-rich surface layers (Cu3Pt-Pt rich surface) from mechanically alloyed Cu3Pt. These catalysts were investigated by X-ray diffraction and X-ray absorption spectroscopy, and were subjected to electrochemical analyses to evaluate their catalytic properties. With appropriate anodization, Cu3Pt entered an oxygen-evolving regime where the corrosive dissolution of Cu dominated the reaction. Selective dissolution was carried out to prepare Pt-rich layers at the surface, while Cu3Pt was left unreacted at the core. An increase in the anodization duration modified the sample morphology, with the redistribution of Pt atoms to thicken the surface layers. A charge transfer from Pt to Cu accompanied the structural transition from Cu3Pt to Cu3Pt-Pt rich surface upon selective dissolution, rendering the sample to be electronically similar to a metal Pt. However, compared to the metal Pt and conventional Pt-based catalysts, the proposed structure is a more economical catalyst for direct methanol fuel cell, with less need of Pt in raw material but increased electrochemical surface area by exposing enormous Pt at the surface with an increase in the anodization duration. (C) 2012 Elsevier B.V. All rights reserved.
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
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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 La(0.6)Ca(0.4)Co(0.8)Ir(0.2)O(3) perovskite for bi-functional catalysis in an alkaline electrolyte
(2009-04-15)
Chang, Yun-Min
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Wu, Pu-Wei
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Wu, Cheng-Yeou
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Hsieh, Yu-Chi
;
材料科學與工程學系
The amorphous citrate precursor method was employed to prepare perovskite of La(0.6)Ca(0.4)Co(0.8)Ir(0.2)O(3) as a bi-functional electrocatalyst for oxygen reduction and evolution in an alkaline electrolyte. The X-ray diffraction pattern of the as-synthesized powders exhibited a majority phase identical to that of La(0.6)Ca(0.4)CoO(3), indicating successful incorporation of Ir4(+) at the Co cation sites. Scanning Electron Microscope images demonstrated a foam-like microstructure with a surface area of 13.31 m(2) g(-1). For electrochemical characterization, the La(0.6)Ca(0.4)CO(0.8)Ir(0.2)O(3) particles were supported on carbon nanocapsules (CNCs) and deposited on commercially available gas diffusion electrodes with a loading of 2.4 mg cm(-2). In current- potential polarizations, La(0.6)Ca(0.4)Co(0.8)Ir(0.2)O(3)/CNCs revealed more enhanced bifunctional catalytic abilities than La(0.6)Ca(0.4)CoO(3)/CNCs. Similar behaviors were observed in galvanostatic profiles for oxygen reduction and evolution at current densities of 50 and 100mAcm(-2) for 10 min. Moreover, notable changes from zeta potential measurements were recorded for La(0.6)Ca(0.4)Co(0.08)Ir(0.02)O(3) relative to La(0.06)Ca(0.4)CoO(3), In lifetime determinations, where a repeated 3 h sequence of oxygen reduction/resting/oxygen evolution/resting was imposed, La(0.6)Ca(0.4)Co(0.8)Ir(0.2)O(3)/CNCs delivered a stable and sustainable behavior with moderate degradation. (C) 2008 Elsevier B.V. All rights reserved.