Browsing by Author "Liao, Chen-Hong"

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A combined electrochemical route to fabricate large-area and free-standing inverse opaline film
(2016-07)
Liao, Chen-Hong
;
Hung, Pei-Sung
;
Wu, Cheng-Yeou
;
Chen, Hsin-Yi
;
Wu, Pu-Wei
A combined electrochemical route involving electrophoresis and electrodeposition is developed to fabricate a large-area unsupported nickel inverse opaline film with thickness less than 10 pm. A vertical electrophoresis allows for the packing of 495 nm polystyrene microspheres on an ITO-coated glass to form a colloidal crystal with significantly reduced defects. Subsequently, a nickel electrodeposition is employed to fill the interstitial voids among the close-packed polystyrene microspheres, followed by the removal of the colloidal template in a two-stage process, leaving a robust nickel skeleton with hexagonally arranged pores and interconnected pore channels. This nickel skeleton is then detached from the ITO-coated glass via a liquid nitrogen treatment, rendering a free-standing nickel inverse opaline film in 2 x 2 cm(2). Porometer measurements indicate a narrow pore size distribution consistent with images from scanning electron microscope. We determine that the intensity ratio of (111)/(100) diffraction peak is an indicator for the strength of the Ni inverse opals, and thus affects its structural integrity upon detachment from the ITO-coated glass. (C) 2016 Elsevier B.V. All rights reserved.
Combination of microspheres and sol-gel electrophoresis for the formation of large-area ordered macroporous SiO2
(2017-12-01)
Liao, Chen-Hong
;
Hung, Pei-Sung
;
Cheng, Yu
;
Wu, Pu-Wei
;
材料科學與工程學系
A simple and effective fabrication scheme involving sequential electrophoretic depositions of polystyrene (PS) microspheres (500 nm and 1 mu m in diameter) and SiO2 sols (similar to 5 nm in diameter) to produce large-area ordered macroporous SiO2 inverse opals (2 x 2 cm(2)) on ITO substrates is demonstrated. The zeta potentials for PS microsphere suspension and SiO2 sols are measured to determine an optimized processing window in which both samples carry negative surface charges and sol-gel transformation can be properly implemented. Our approach entails the electrophoresis of PS microspheres to render a colloidal crystal with negligible defects. Afterward, SiO2 sols are infiltrated to the interstitial voids among the closely-packed PS microspheres via another electrophoresis process, followed by an oxidation treatment to remove the PS colloidal template and complete the densification of SiO2 gels. The resulting SiO2 inverse opals reveal impressive surface uniformity and structural integrity. Fourier transform infrared spectroscopy confirms the complete removal of PS microspheres, leaving an intact SiO2 skeleton, whereas X-ray diffraction pattern indicates its amorphous nature.
Facile Electrochemical Fabrication of Large-Area ZnO Inverse Opals with Reduced Defects
(2011)
Huang, Yi-Jui
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Liao, Chen-Hong
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Huang, Bo-Han
;
Chen, Wan-Ying
;
Wu, Pu-Wei
We demonstrate a facile fabrication scheme to construct large-area ZnO inverse opals on an indium-tin-oxide substrate with significantly reduced defects and improved stoichiometry. The fabrication steps involve the preparation of colloidal template via vertical electrophoresis of polystyrene (PS) microspheres in 720 nm radius, followed by galvanostatic electrodeposition of ZnO in the interstitial voids among the PS microspheres. Subsequently, the sample undergoes a heat-treatment in air at 500 degrees C for different time to remove the colloidal template, leaving an integral ZnO skeleton with thickness adjusted by the electrodeposition time. Since the colloidal template is deliberately designed with desirable thickness and considerable uniformity, the electroplating of ZnO can be achieved in a reduced ethanol/water ratio that allows faster growth rate and improved ZnO structure. Scanning electron microscope images demonstrate negligible microstructural defects for the ZnO inverse opals. X-ray diffraction reveals a wurtzite hexagonal lattice with (002) preferred orientation. In addition, both X-ray photoelectron spectroscopy and photoluminescence spectra suggest improved crystallinity and stoichiometry with increasing heat-treatment time. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3552604] All rights reserved.
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
;
Lee, Jyh-Fu
;
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
;
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.
High throughput fabrication of large-area colloidal crystals via a two-stage electrophoretic deposition method
(2019-09-10)
Hung, Pei-Sung
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Liao, Chen-Hong
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Chou, Yu-Szu
;
Wang, Guang-Ren
;
Wang, Chuan-Jyun
An effective and high-throughput method is demonstrated to produce a colloidal crystal with impressive crystallinity. The fabrication procedure involves a two-stage electrophoresis process in which a vertical electrophoretic deposition of polystyrene microspheres (495 nm) is conducted on an ITO substrate to form a colloidal crystal in size of 4 x 4 cm(2), followed by a horizontal electrophoresis to improve the packing crystallinity. Relevant parameters associated with the horizontal electrophoresis step including voltage polarity, bipolar voltage offset, and operation frequency are investigated. Their effects over the crystallinity of the colloidal crystals are verified quantitatively and qualitatively by structural observation via scanning electron microscope and optical reflectance spectra. We determine that the imposition of an alternately-changing bias of 80/0/-120/0 V at 10 Hz (25 ms in each bias) enables the production of colloidal crystals with the largest grain size (106 mm) and the smallest grain boundary (170 nm), as compared to samples prepared from a single vertical electrophoresis step. We attribute the improved crystallinity of the colloidal crystal to the bipolar bias that engenders localized movements of the microspheres, rendering them to pack more closely with reduced defects. (C) 2019 Elsevier Ltd. All rights reserved.
Mechanical properties of three-dimensional ordered macroporous Ni foam
(2018-03-15)
Liao, Chen-Hong
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Hung, Pei-Sung
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Cheng, Yu
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Chang, Shou-Yi
;
Wua, Pu-Wei
We employ a sequential electrophoresis and electrodeposition approach to fabricate a large-area ordered macroporous Ni foam in 5 x 5 cm(2) via a template route. Images from scanning electron microscope exhibit hierarchical structures with hexagonally-arranged pores and interconnected pore channels. For as-prepared and annealed ordered macroporous Ni foams, the loading-depth profiles from nano indentation show typical elastic and plastic deformation. Upon annealing, moderate growth in grain size is observed, resulting in lower hardness and Young's modulus. In contrast, for disordered macroporous Ni foam and solid Ni film, nano indentation results reveal larger hardness and undetermined Young's modulus. The ordered macroporous foam reveals hardness that is 22% of that of solid Ni film, a value close to its theoretic packing density of 24%. (C) 2017 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
;
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 characterization of colloidal crystals and inverse opals using transmission X-ray microscopy
(2014-07-15)
Huang, Bo-Han
;
Wang, Chun-Chieh
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Liao, Chen-Hong
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Wu, Pu-Wei
;
Song, Yen-Fang
A nondestructive tomographic technique was used to determine the crystallographic information of colloidal crystals comprising of polystyrene (PS) microspheres, as well as their silver inverse opals. The properties of the colloidal crystals, such as defects, grain size, grain boundaries, stacking sequence, and grain orientation, were determined using the full field transmission X-ray microscopy (TXM) with a spatial resolution of 50 nm. The PS microspheres (500-750 nm) which underwent a vertical electrophoresis process to form a face-centered cubic (fcc) close-packed structure with an ABCABC packing sequence. In addition, the colloidal crystal exhibited multiple grains, and an orientation variation of 6.1 degrees in the stacking direction between two neighboring grains. (C) 2014 Elsevier Inc. All rights reserved.