Browsing by Author "Hsieh, Yi-Chieh"

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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
;
Chang, Chung-Kai
;
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 RuO2 on Cu via a Galvanic Cementation Reaction
(2019-06-28)
Lin, Chun
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Chou, Shih-Cheng
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Tso, Kuang-Chih
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Hsieh, Yi-Chieh
;
Chan, Ting-Shan
We develop a seedless wet chemical process to deposit uniform RuO2 on a Cu substrate. Our approach entails the synthesis of volatile RuO4 colloids in a pH 9 aqueous solution from the oxidation of RuCl52- by ClO-, followed by a galvanic cementation reaction in which the Cu undergoes a mild oxidation in conjunction with the reduction of RuO4 to produce a dense and conformal RuO2 thin film on the Cu surface. The nature for the chemical reactions and constituents involved are investigated by UV-Vis, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. Both as-deposited and annealed RuO2 films are characterized by scanning electron microscope and X-ray diffractometer. The as-deposited RuO2 film, with a thickness of 199 nm, reveals an amorphous structure and after an Ar annealing, becomes crystalline in rutile phase. In between the RuO2 and Cu, there are presence of CuO from the displacement cementation reaction, and Cu2O from the parasitic Cu corrosion as expected from the Pourbaix diagram. These Cu oxides, with a thickness of 330 nm, provide sufficient adhesive bonding between RuO2 and Cu. (c) The Author(s) 2019. Published by ECS.
Core-Shell Pd9Ru@Pt on Functionalized Graphene for Methanol Electrooxidation
(2018-01-01)
Kuo, Chih-Chia
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Chou, Shih-Cheng
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Chang, Yu-Chen
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Hsieh, Yi-Chieh
;
Wu, Pu-Wei
A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps (CV) are performed in a 0.5 M H2SO4 aqueous solution on electrodes consisting of carbon cloth, graphene, and Nafion ionomer. Upon exposure to ambient oxygen, the formation of hydroxyl radicals from the oxygen reduction reaction during the CV cycles initiates the decomposition of the Nafion ionomer, which produces oxygenated functional groups on the graphene surface. Using contact angle measurements and X-ray photoelectron spectroscopy, various amounts of Nafion ionomer are explored to determine the optimum conditions for graphene functionalization. Afterwards, Pd9Ru nanoparticles with an average size of 3-4 nm are synthesized and impregnated on functionalized graphene (FGN). To prepare core-shell electrocatalysts, Pd9Ru/FGN is subjected to Cu underpotential deposition followed by a galvanic displacement reaction to deposit a Pt monolayer on the Pd9Ru surface (Pd9Ru@Pt). The assynthesized sample (Pd9Ru@Pt/FGN) exhibits enhanced performance in methanol electrooxidation, which includes abetter activity and lower susceptibility to poisoning by intermediates. The electrochemically active surface area (ECSA) of Pd9Ru@Pt/FGN shows a value that is 1.5-fold larger than that of Pd9Ru@Pt on untreated graphene (Pd9Ru@Pt/GN). In the durability tests, Pd9Ru@Pt/FGN and Pd9Ru@Pt/GN demonstrate losses in the ECSA of 14.9% and 30.3%, respectively. (C) 2018 The Electrochemical Society.
Development of IrO2 bio-ink for ink-jet printing application
(2019-09-01)
Hsieh, Yi-Chieh
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Wang, Han-Yi
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Tso, Kuang-Chih
;
Chang, Chung-Kai
;
Chen, Chi-Shih
We develop a chemical formulation to synthesize stable IrO2 colloidal solution as a bio-ink for ink-jet printing purpose. This wet chemical process entails Na3IrCl6 and NaClO as the Ir precursor and oxidizer, respectively. In addition, citric acid and sodium hydroxide are employed as the complex agent and pH adjuster. The pH value of the IrO2 colloidal solution could be readily adjusted over a broad range without incurring undesirable precipitation. Their respective zeta potential decreases from positive to negative with increasing pH values. The IrO2 colloidal solution demonstrates impressive chemical stability over extended storage at 5 and 65 degrees C. Images from transmission electron microscope indicate the average size for the IrO2 nanoparticles to be 3.5 nm. The X-ray diffraction pattern from the heat-treated IrO2 sample shows a polycrystalline rutile phase. The IrO2 colloidal solution undergoes repeated filtering and washing to retrieve the IrO2 nanoparticles. After an annealing at 450 degrees C for 2 h in air, the crystalline IrO2 nanoparticles are resuspended in a 0.5 wt% aqueous medium as the bio-ink for ink-jet printing on an ITO substrate. Our method enables the synthesis of stable IrO2 nanoparticles in a neutral solution at 25 degrees C, which provides a facile and effective approach over conventional ones that require alkaline environment at elevated temperature.
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
;
Sun, Bo-Yao
;
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.