Browsing by Author "Lee, Jyh-Fu"

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Anti-site defect effect on the electronic structure of a Bi2Te3 topological insulator
(2018-01-01)
Chuang, Pei-Yu
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Su, Shu-Hsuan
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Chong, Cheong-Wei
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Chen, Yi-Fan
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Chou, Yu-Heng
Tuning the Fermi level (EF) in Bi2Te3 topological-insulator (TI) films is demonstrated on controlling the temperature of growth with molecular-beam epitaxy (MBE). Angle-resolved photoemission spectra (ARPES) reveal that EF of Bi2Te3 thin films shifts systematically with the growth temperature (Tg). The key role that a Bi-on-Te(1) (BiTe1) antisite defect plays in the electronic structure is identified through extended X-ray-absorption fine-structure (EXAFS) spectra at the Bi L-3-edge. Calculations of electronic structure support the results of fitting the EXAFS, indicating that the variation of EF is due to the formation and suppression of BiTe1 that is tunable with the growth temperature. Our findings provide not only insight into the correlation between the defect structure and electronic properties but also a simple route to control the intrinsic topological surface states, which could be useful for applications in TIbased advanced electronic and spintronic devices.
Atomistic nucleation sites of Pt nanoparticles on N-doped carbon nanotubes
(2013)
Sun, Chia-Liang
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Pao, Chih-Wen
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Tsai, Huang-Ming
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Chiou, Jau-Wern
;
Ray, Sekhar C.
The atomistic nucleation sites of Pt nanoparticles (Pt NPs) on N-doped carbon nanotubes (N-CNTs) were investigated using C and N K-edge and Pt L-3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy. Transmission electron microscopy and XANES/EXAFS results revealed that the self-organized Pt NPs on N-CNTs are uniformly distributed because of the relatively high binding energies of the adsorbed Pt atoms at the imperfect sites. During the atomistic nucleation process of Pt NPs on N-CNTs, stable Pt-C and Pt-N bonds are presumably formed, and charge transfer occurs at the surface/interface of the N-CNTs. The findings in this study were consistent with density functional theory calculations performed using cluster models for the undoped, substitutional-N-doped and pyridine-like-N-doped CNTs.
(Ca,Mg,Sr)(9)Y(PO(4))(7):Eu(2+),Mn(2+): Phosphors for white-light near-UV LEDs through crystal field tuning and energy transfer
(2011-01-01)
Huang, Chien-Hao
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Wu, Pin-Jiun
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Lee, Jyh-Fu
;
Chen, Teng-Ming
;
應用化學系
Two series of single-composition (Ca,Mg,Sr)(9)Y(PO(4))(7):Eu(2+) and (Ca(0.5)Sr(0.5))(9)Y(PO(4))(7):Eu(2+),Mn(2+) phosphors were synthesized via high-temperature solid-state reactions. Their emission colors could be tuned from blue to green and eventually to red through tuning the crystal field splitting and energy transfer. On examining the Mn(2+) concentration-dependent photoluminescence properties, we found that co-doping with Mn(2+) would lead to a change in Eu(2+)/Eu(3+) ratio. Moreover, an energy transfer from Eu(2+) to Mn(2+) occurs because of the spectral overlap between the emission band of Eu(2+) and the excitation band of Mn(2+). The resonance-type energy transfer via a dipole-quadrupole interaction mechanism was supported by decay lifetime data and the critical distance of energy transfer was calculated to be 11.09 angstrom A. A trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca(0.5)Sr(0.5))(9)Y (PO(4))(7):0.007Eu(2+),0.02Mn(2+) and blue-emitting (Ca(0.5)Mg(0.5))(9)Y(PO(4))(7):0.007Eu(2+) phosphors into a single package. Such a composite device emitted white light with a correlated color temperature of 6303 K, a color rendering index of 87.4, and color coordinates (0.314, 0.348) close to those of ideal white light. The results suggest that a phosphor blend of (Ca(0.5)Sr(0.5))(9)Y(PO(4))(7):0.007Eu(2+), 0.02Mn(2+) and (Ca(0.5)Mg(0.5))(9)Y(PO(4))(7):0.007Eu(2+) is potentially useful for white n-UV light-emitting diodes (LEDs).
(Ca,Mg,Sr)(9)Y(PO4)(7):Eu2+,Mn2+: Phosphors for white-light near-UV LEDs through crystal field tuning and energy transfer
(2011-01-01)
Huang, Chien-Hao
;
Wu, Pin-Jiun
;
Lee, Jyh-Fu
;
Chen, Teng-Ming
;
應用化學系
Two series of single-composition (Ca,Mg,Sr)(9)Y(PO4)(7):Eu2+ and (Ca0.5Sr0.5)(9)Y(PO4)(7):Eu2+,Mn2+ phosphors were synthesized via high-temperature solid-state reactions. Their emission colors could be tuned from blue to green and eventually to red through tuning the crystal field splitting and energy transfer. On examining the Mn2+ concentration-dependent photoluminescence properties, we found that co-doping with Mn2+ would lead to a change in Eu2+/Eu3+ ratio. Moreover, an energy transfer from Eu2+ to Mn2+ occurs because of the spectral overlap between the emission band of Eu2+ and the excitation band of Mn2+. The resonance-type energy transfer via a dipole-quadrupole interaction mechanism was supported by decay lifetime data and the critical distance of energy transfer was calculated to be 11.09 angstrom A. A trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca0.5Sr0.5)(9)Y (PO4)(7):0.007Eu(2+),0.02Mn(2+) and blue-emitting (Ca0.5Mg0.5)(9)Y(PO4)(7):0.007Eu(2+) phosphors into a single package. Such a composite device emitted white light with a correlated color temperature of 6303 K, a color rendering index of 87.4, and color coordinates (0.314, 0.348) close to those of ideal white light. The results suggest that a phosphor blend of (Ca0.5Sr0.5)(9)Y(PO4)(7):0.007Eu(2+), 0.02Mn(2+) and (Ca0.5Mg0.5)(9)Y(PO4)(7):0.007Eu(2+) is potentially useful for white n-UV light-emitting diodes (LEDs).
Chemical bath deposition of IrO2 films on ITO substrate
(2014-11-01)
Chen, Jing-Yu
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Chen, Yong-Min
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Sun, Yu
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Lee, Jyh-Fu
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Chen, San-Yuan
A chemical bath is shown to deposit an IrO2 film on an ITO substrate. The chemical bath is prepared by mixing an Ir precursor (Na3IrCl6 center dot xH(2)O), an oxidizer (NaClO), a complexing agent (NaNO2), and a complex agent/stabilizer (NaOH) in an aqueous solution at a molar ratio of 1:1.5:10:30. From the UV-vis absorption spectra, complexes such as [Ir(OH)(6)]m(3-), [Ir(NO2)(4)Cl-2](3-), and [Ir(NO2)(3)Cl-3](3-) are identified. These complexes are relatively stable, minimizing the undesirable homogeneous precipitation of IrO2 nanoparticles in favor of the heterogeneous growth of the IrO2 film on the ITO substrate. Diffraction patterns from the as-deposited IrO2 film reveal an amorphous structure. In addition, profiles from X-ray absorption spectroscopy and X-ray photoelectron spectroscopy indicate that the oxidation state of the Ir in the as-deposited IrO2 film is +4. Thermogravimetric analysis confirms the inclusion of 10 wt% hydrated water in the as-deposited IrO2 film. Scanning electron microscope images reveal a continuous solid film with a smooth surface. The amorphous IrO2 film becomes rutile IrO2 phase after a mild heat treatment in air. (c) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Combination of electrophoresis and electro-flocculation for the formation of adhering IrO2 pH sensing films
(2019-07-20)
Wang, Han-Yi
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Hsieh, Yi-Chieh
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Tso, Kuang-Chih
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Chang, Chung-Kai
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Cheng, Yu-Ting
We demonstrate a simple scheme to produce dense and adhering IrO2 thin films on ITO substrates via a bipolar pulsing process combining both electrophoresis and electro-flocculation. Our fabrication steps entail the synthesis of negatively-charged IrO2 nanoparticles in size of 3.5 nm using NaClO as an oxidizer in conjunction with Na3IrCl6, citric acid, and NaOH. Subsequently, multiple bipolar potentiostatic pulses are imposed in which alternating positive and negative potentials engender the electrophoresis of IrO2 nanoparticles, followed by their immediate coalescence facilitated by proton-catalyzed electro-floccu-lation. The resulting IrO2 thin films reveal impressive physical properties in surface uniformity, robust structural integrity, and strong adhesion to the substrate. The as-synthesized IrO2 thin film exhibits an amorphous nature with a pH sensing slope between -73.6 and -71.5 mV/pH, characteristic of super-Nernstian behavior. In contrast, the annealed IrO(2 )sample demonstrates a crystalline rutile phase with a pH sensing slope between -49.5 and -54.7 mV/pH, consistent with typical Nernstian response. Our approach provides a new route for the formation of strong and adhering oxide films from their colloidal constituents. (C) 2019 Elsevier Ltd. All rights reserved.
Conformal deposition of Pt on titania nanotubes to produce a bio-electrode for neuro-stimulating applications
(2018-03-01)
Wu, Yi-Jia
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Chung, Tsai-Wei
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Huang, Jun-Qian
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Wu, Pu-Wei
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Chen, Po-Chun
We develop an alkaline electroless bath for deposition of a conformal Pt layer 40 nm thick on titania nanotubes 800 nm long. The charge storage capacity (CSC) and electrochemically active surface area (ECSA) of this Pt-coated titania nanotube array have been studied to evaluate its potential as a bio-electrode for implantable bioelectronic devices. Images from electron microscopes confirm the formation of a uniform Pt film on both the internal and external surfaces of the nanotubes. The X-ray diffraction pattern indicates a preferred (111) orientation. Analysis from X-ray absorption spectroscopy on the plating bath suggests a reduction sequence of Pt4+ -> Pt2+ -> Pt. The Pt-coated titania nanotube array has large CSC and ECSA values, attributed to the hollow tubular nanostructure with a conformal Pt coating.
Correlation among photoluminescence and the electronic and atomic structures of Sr2SiO4:xEu(3+) phosphors: X-ray absorption and emission studies
(2020-07-29)
Zheng, Shi-Yan
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Chiou, Jau-Wern
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Li, Yueh-Han
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Yang, Cheng-Fu
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Ray, Sekhar Chandra
A series of Eu3+-activated strontium silicate phosphors, Sr2SiO4:xEu(3+) (SSO:xEu(3+), x=1.0, 2.0 and 5.0%), were synthesized by a sol-gel method, and their crystalline structures, photoluminescence (PL) behaviors, electronic/atomic structures and bandgap properties were studied. The correlation among these characteristics was further established. X-ray powder diffraction analysis revealed the formation of mixed orthorhombic alpha'-SSO and monoclinic beta-SSO phases of the SSO:xEu(3+) phosphors. When SSO:xEu(3+) phosphors are excited under ultraviolet (UV) light (lambda=250 nm,similar to 4.96 eV), they emit yellow (similar to 590 nm), orange (similar to 613 nm) and red (similar to 652 and 703 nm) PL bands. These PL emissions typically correspond to 4f-4f electronic transitions that involve the multiple excited D-5(0)-> F-7(J) levels (J=1, 2, 3 and 4) of Eu3+ activators in the host matrix. This mechanism of PL in the SSO:xEu(3+) phosphors is strongly related to the local electronic/atomic structures of the Eu3+-O2- associations and the bandgap of the host lattice, as verified by Sr K-edge and Eu L-3-edge X-ray absorption near-edge structure (XANES)/extended X-ray absorption fine structure, O K-edge XANES and K-alpha X-ray emission spectroscopy. In the synthesis of SSO:xEu(3+) phosphors, interstitial Eu2O3-like structures are observed in the host matrix that act as donors, providing electrons that are nonradiatively transferred from the Eu 5d and/or O 2p-Eu 4f/5d states (mostly the O 2p-Eu 5d states) to the D-5(0) levels, facilitating the recombination of electrons that have transitioned from the D-5(0) level to the F-7(J) level in the bandgap. This mechanism is primarily responsible for the enhancement of PL emissions in the SSO:xEu(3+) phosphors. This PL-related behavior indicates that SSO:xEu(3+) phosphors are good light-conversion phosphor candidates for use in near-UV chips and can be very effective in UV-based light-emitting diodes.
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
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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 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
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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.
Effects of oxygen partial pressure on structural and gasochromic properties of sputtered VOx thin films
(2013-10-01)
Jang, Wei-Luen
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Lu, Yang-Ming
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Lu, Ying-Rui
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Chen, Chi-Liang
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Dong, Chung-Li
VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target in an Ar-O-2 gas mixture and pure O-2. For the films deposited in the gas mixture, the Ar flow rate was controlled at 20 sccm and the oxygen flow rate was controlled at 1, 3, and 5 sccm, respectively. A thin (similar to 5 nm) Pt layer was deposited on the VOx thin films as a hydrogen catalyst. The long-range structural order, short-range atom arrangement, and gasochromic properties of the deposited films were studied. The grazing incidence X-ray diffraction (GIXRD) results indicate that the deposited films are amorphous. Lamellar structures were found at oxygen flow rates of 3 sccm and above. The X-ray absorption spectroscopy (XAS) results show that the short-range atom arrangement of the lamellar VOx thin films is similar to that of crystal V2O5. The GIXRD and XAS results show that the film obtained with the gas mixture and at an oxygen flow rate of 1 sccm did not significantly change after exposure to hydrogen, whereas the other films exhibited decreased interlayer distance, oxidation state, and crystallinity. The color of the films changed from light or deep yellow to gray. The results suggest that the gasochromic properties of the VOx thin films are related to the V2O5-like atom arrangement and the interlayer distance of the lamellar structure. The films deposited with an oxygen flow rate of 3 sccm and above can be applied to H-2 gas sensors. (C) 2013 Elsevier B. V. All rights reserved.
Electrochemical and in situ X-ray spectroscopic studies of MnO2/reduced graphene oxide nanocomposites as a supercapacitor
(2016-07-28)
Chang, Han-Wei
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Lu, Ying-Rui
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Chen, Jeng-Lung
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Chen, Chi-Liang
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Lee, Jyh-Fu
Electrochemical and in situ X-ray absorption spectroscopy (XAS) measurements of various MnO2-coated carbon materials (MnO2/acid-functionalized carbon nanotubes (C-CNT), MnO2/reduced graphene oxide (RGO), and MnO2/RGO-Au electrodes) were conducted to evaluate the supercapacitive performances and electronic structures. MnO2 was deposited on the surface of C-CNT, RGO, and RGO-Au via a spontaneous redox reaction to facilitate the growth of the bulk form of MnO2/C-CNT and the surface forms of MnO2/RGO-based materials. Various forms of MnO2 on the carbon materials exhibited different charge/discharge behaviors. The specific capacitances of the MnO2/RGO and MnO2/RGO-Au electrodes at a current density of 1 A g(-1) were about 433 and 469 F g(-1), respectively; these values are about 1.5 times that of the MnO2/C-CNT (259 F g(-1)) electrode. Specific capacitances of 220 and 281 F g(-1) with retention rates of about 50-60% were obtained from MnO2/RGO and MnO2/RGO-Au, respectively, even at a high current density of 80 A g(-1). Experimental results revealed that the long-term electrochemical stability of the MnO2/RGO-based electrodes (with similar to 90% retention) exceeded that of the MnO2/C-CNT electrode (with similar to 60% retention) after 1000 cycles at a high scan rate of 80 A g(-1). This finding indicates that MnO2/RGO-based electrodes feature excellent cycling stability and rate capacity retention performance. To elucidate the atomic/electronic structures of the MnO2/C-CNT, MnO2/RGO, and MnO2/RGO-Au electrodes during the charge/discharge process, in situ XAS of the Mn K-edge was performed. The MnO2/RGO-based electrodes exhibited the least variations in the pre-peak intensity of the Mn K-edge during the charge/discharge process because a nano-network of MnO2 is homogeneously decorated on the outer surfaces of RGO-based electrodes to facilitate the growth of surface forms of MnO2/RGO and MnO2/RGO-Au. Analytical results further revealed suppression of changes in tunnel size and promotion of insertion/extraction behavior. This work, particularly the combination of cyclic voltammetry with in situ XAS measurements, will be of general value in the fields of nanomaterials and nanotechnology, and in their use in energy storage.
Evolution of the local structure and crystal phase for thin ZnGaO films grown by metal organic chemical vapor deposition
(2019-08-15)
Lin, Xiwen
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Chen, Daihua
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Niu, Wenlong
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Huang, Chiung-Yi
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Horng, Ray Hua
A systematic investigation is reported to comprehend the atomic and crystal structure of several thin ZnGaO films grown by metal organic chemical vapor deposition method using different flow rates of diethylzinc (DEZn) while keeping triethylgallium and oxygen flow rates constant. The x-ray absorption fine structure analysis has indicated that the local structure of Ga absorbing atom is close to that of beta-Ga2O3 at a lower DEZn flow rate of 30 sccm and transforming to ZnGa2O4 structure at higher 60 sccm. There is a certain proportion of Ga ions that occupies the tetrahedral sites. The ratios of tetrahedral and octahedral Ga species (Ga(t)/Ga(o)) are found to be within 5.5-8.8%. The x-ray diffraction patterns showed the crystal structure of ZnGaO films gradually evolving from monoclinic to cubic phase with an increase of DEZn flow rates from 30 sccm to 60 sccm. One film prepared at 40 sccm displays the best crystalline quality and the other grown at 50 sccm exhibits excellent smooth surface having the lowest root mean square value with a roughness of 0.42 nm. The correlation between atomic and crystal structure and the growth is helpful to understand the formation of single-crystalline ZnGa2O4 and its physical mechanism.
Ex-situ soft X-ray absorption spectroscopic investigation of NiCo2O4 annealed in different gases for hydrogen generation by electrolysis of urea
(2019-06-14)
Chang, Han-Wei
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Dong, Chung-Li
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Lu, Ying-Rui
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Huang, Yu-Cheng
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Chen, Chi-Liang
Electrochemical and ex-situ X-ray absorption spectroscopic (XAS) measurements of NiCo2O4 that have been annealed in different gases (Ar and air) were made to evaluate the efficiency of its electrocatalysis of hydrogen generation by the electrolysis of urea. The electrochemical and XAS measurements demonstrated that NCO-Ar contain significant amounts of Co2+ in octahedral coordination was more favorable than NCO-air for urea electrolysis owing to the effective exposure of electrochemical active sites to participate in the Faradic redox reaction. Further insight into the electrocatalytic mechanism of NiCo2O4-based materials during urea electrolysis was obtained using ex-situ soft XAS. The results of ex-situ soft XAS revealed that the variation of the octahedral and tetrahedral coordinations of Co2+ in NCO-Ar and NCO-air importantly contributes to electrocatalytic behavior. NCO-Ar exhibits excellent electrocatalytic activity towards the Co redox couples in a repetitive cycling process owing to the creation of highly efficient active sites (octahedral Co2+). This study presents importantly x-ray spectroscopic determination of the change in electronic structure of catalyst for hydrogen production. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. 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
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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.
Facile Synthesis of Co3O4@CoO@Co Gradient Core@Shell Nanoparticles and Their Applications for Oxygen Evolution and Reduction in Alkaline Electrolytes
(2020-06-01)
Chou, Shih-Cheng
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Tso, Kuang-Chih
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Hsieh, Yi-Chieh
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Sun, Bo-Yao
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Lee, Jyh-Fu
We demonstrate a facile fabrication scheme for Co3O4@CoO@Co (gradient core@shell) nanoparticles on graphene and explore their electrocatalytic potentials for an oxygen evolution reaction (OER) and an oxygen reduction reaction (ORR) in alkaline electrolytes. The synthetic approach begins with the preparation of Co(3)O(4)nanoparticles via a hydrothermal process, which is followed by a controlled hydrogen reduction treatment to render nanoparticles with radial constituents of Co3O4/CoO/Co (inside/outside). X-ray diffraction patterns confirm the formation of crystalline Co(3)O(4)nanoparticles, and their gradual transformation to cubic CoO and fcc Co on the surface. Images from transmission electron microscope reveal a core@shell microstructure. These Co3O4@CoO@Co nanoparticles show impressive activities and durability for OER. For ORR electrocatalysis, the Co3O4@CoO@Co nanoparticles are subjected to a galvanic displacement reaction in which the surface Co atoms undergo oxidative dissolution for the reduction of Pt ions from the electrolyte to form Co3O4@Pt nanoparticles. With commercial Pt/C as a benchmark, we determine the ORR activities in sequence of Pt/C > Co3O4@Pt > Co3O4. Measurements from a rotation disk electrode at various rotation speeds indicate a 4-electron transfer path for Co3O4@Pt. In addition, the specific activity of Co3O4@Pt is more than two times greater than that of Pt/C.
Formation of Cu/MnOx composite film by concurrent electroplating and electrophoresis in an organic solvent
(2018-08-30)
Chiang, Wei-Shen
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Huang, Jun-Qian
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Tso, Kuang-Chih
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Hung, Pei-Sung
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Chen, Po-Chun
A composite Cu/MnOx thin film was fabricated by conducting electroplating of Cu and electrophoresis of MnOx colloids simultaneously in an organic electrolyte. The organic electrolyte was prepared by dissolving copper (II) acetylacetonate and manganese (II) acetylacetonate in ethylene glycol, with addition of 10 vol% acetic acid to improve ionic conductivity. Since both Cu ions and MnOx colloids carry positive charges, the formation of a composite film was achieved by a pulse current mode in which a low current pulse was used for Cu2+ reduction, followed by a high current pulse for the electrophoresis of the MnOx colloids. The Cu/MnOx composite film was dense and its X-ray diffraction pattern revealed a mixture of Cu, Mn2O3, and Mn3O4. Both X-ray photoelectron spectroscopy and X-ray absorption spectroscopy show consistent results confirming the metallic nature of Cu and oxidized state of Mn.
Local geometric and electronic structures of gasochromic VOx films
(2014)
Jang, Wei-Luen
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Lu, Yang-Ming
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Chen, Chi-Liang
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Lu, Ying-Rui
;
Dong, Chung-Li
VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target at room temperature. Local atomic and electronic structures of the films were then modified by thermal annealing. The oxidation state and structural and gasochromic properties of the films were elucidated by X-ray absorption spectroscopy. Analytical results indicate that the as-deposited VOx films were amorphous with mixed V4+ and V5+ valences. The amorphous VOx had a disordered and expanded lamellar structure resembling that of polymer-intercalated V2O5 gels. VOx films were crystallized into orthorhombic V2O5 at 300 degrees C, and the lamellar structure was eliminated at 400 degrees C. Additionally, the gasochromic reaction reduced the vanadium valence via intervalence transitions between V5+ and V3+. Moreover, removing the lamellar structure reduced the gasochromic rate, and the gasochromic reaction transformed the V2O5 crystalline phase irreversibly into an H1.43V2O5 phase. Based on the results of this study, amorphous VOx with a lamellar structure is recommended for use in H-2 gas sensors.
Magnetic and Metal Binding Structural Analysis of Mn,Zn-Metallothionein-Green Fluorescence Fusion Protein
(2012-01-31)
Chen, Ting-Kai
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Lin, Yin-Chih
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Chen, Yu-Chen
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Chen, Yen-Lin
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Tseng, Wei-Lun