Browsing by Author "Wang, Cheng-Yu"

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Facilitated hydrogen release kinetics from amine borane functionalization on gate-opening metal-organic framework
(2018-09-25)
Liao, Chi-Wei
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Tseng, Po-Sen
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Chang, Bor Kae
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Wang, Cheng-Yu
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材料科學與工程學系
For the first time, we functionalized the gate-opening metal-organic framework (GO-MOF) of MIL-53(Al) with ammonia borane (AB, NH3BH3) via post-synthesis method. In this report, unusual structural breathing and dehydrogenation behaviors of AB doped MOF (MIL-53-AB) were discovered. Surface coating triggered the GO-MOF breathing phenomenon and opened the structure, and gate was closed after dehydrogenation. The dehydrogenation peak temperature was greatly reduced by 30 degrees C compared to that of pristine AB with suppressed byproduct like ammonia. The MOFs with surface coated AB exhibited remarkably fast hydrogen generation rate and corresponding low apparent activation energy, estimated at < 40 kJ/mol, which is much lower than that of crystalline AB, and even comparable to AB hydrolysis with catalysts. The ammonia borane functionalized MIL-53 has shown greatly improved dehydrogenation from solid phase of AB.
Ga-doped lithium lanthanum zirconium oxide electrolyte for solid-state Li batteries
(2020-09-01)
Mishra, Mrinalini
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Hsu, Che-Wei
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Rath, Purna Chandra
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Patra, Jagabandhu
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Lai, Hong-Zheng
Cubic-phase Li7La3Zr2O12 (LLZO) garnet is a promising solid electrolyte candidate for next-generation Li batteries. As a viable approach, the desired cubic-phase formation of LLZO relies on elemental doping. In this regard, various dopants such as Al and Ga are doped into the LLZO samples, which are synthesized using a solid-state reaction method. The Al-and Ga-doped LLZO can transform to a cubic-phase garnet at 900 degrees C. After 1200 degrees C sintering, a Li2ZrO3 impurity phase is found for the Al-doped LLZO pellet, which still shows many voids and inhomogeneous particles on the surface. The Ga doping seems to be attractive since it can effectively stabilize the cubic phase and desired microstructure within 900-1200 degrees C. Based on the optimized Ga-doped LLZO (LGLZO), various electrolyte architecture designs are developed that include LGLZO pellet electrolytes with and without poly(ethylene oxide) (PEO)-lithium bis(tri-fluoromethylsulfonyl)imide (LiTFSI)-LGLZO coating, and hybrid electrolyte layers of PEO-LiTFSI, PEO-LGLZO, and PEO-LiTFSI-LGLZO composites. Li//LiFePO4 (LFP) cells with various types of electrolytes are assembled, and their charge-discharge properties are investigated. The all-solid-state Li//PEO-LiTFSI-LGLZO//LFP cell exhibits satisfactory charge storage performance, which has revealed potential for practical applications. (c) 2020 Elsevier Ltd. All rights reserved.
Influence of Metal-Organic Framework Porosity on Hydrogen Generation from Nanoconfined Ammonia Borane
(2017-12-14)
Chung, Jing-Yang
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Liao, Chi-Wei
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Chang, Yi-Wei
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Chang, Bor Kae
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Wang, Hao
Hydrogen released from chemical hydride ammonia borane (AB, NH3BH3) can be greatly improved when AB is confined in metal-organic frameworks (MOFs), showing reduced decomposition temperature and suppressed unwanted byproducts. However, it is still debatable whether the mechanism of improved AB dehydrogenation is due to catalysis or nanosize. In this research, selected MOF (IRMOF-1, IRMOF-10, UiO-66, UiO-67, and MIL-53(Al)) were chosen to explore both catalytic effect of the metal clusters and the manipulation of pore size for nanoconfinement by variations in ligand length. When AB particle size was restricted by the controlled micropores of MOFs, we observed that the decomposition temperature was not correlated to the MOF catalytic environment, but inversely proportional to the reciprocal of the particle size. The results correspond well with the derived thermodynamic model for AB decomposition considering surface tension of nanoparticles.
Insight into the Catalytic Effects of Open Metal Sites in Metal - Organic Frameworks on Hydride Dehydrogenation via Nanoconfinement
(2019-10-07)
Wu, Yi-Ju
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Wang, Cheng-Yu
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材料科學與工程學系
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Department of Materials Science and Engineering
Chemical hydride ammonia borane (AB, NH3BH3) draws attentions as a hydrogen storage medium for its high hydrogen capacity (19.6 wt %) and good thermal stability at ambient environments. However, high hydrogen generation temperatures and slow kinetics limit AB practical applications. One way to overcome the obstacles is the nanoconfinement effect: AB incorporated with porous materials has facilitated dehydrogenation process. However, the mechanism is still under debate, and several factors have been proposed, like hydride nanosize or catalytic environments controlled/provided by microporous supports. In this research, metal organic frameworks (MOFs) of Cu-BDC (BDC = benzenedicarboxylate) with/without manipulated active open metal sites by solvent removal/capping are applied for AB thermolysis via nanoconfinement. Both AB@MOFs show the same dehydrogenation peaked temperature regardless of catalytic environments, strengthening the theory that high surface tension from hydride nanosize controlled by MOF microporosity results in reduced dehydrogenation temperature. In addition, compared to solvent-capped MOFs, Cu-BDC with copper open metal sites eliminates byproduct emission and hence increases hydrogen yield from AB and also decreases dehydrogenation activation energy considerably. However, short cycle life due to copper reduction is observed in desolvated Cu-BDC, while lowered dehydrogenation temperature can be kept in solvated MOFs. In general, we clarify possible mechanisms and factors to hydride nanoconfinement and catalysis that improve AB dehydrogenation temperature and kinetics and provide new strategies for future hydride composite materials design.
MgO nanoparticles confined in ZIF-8 as acid-base bifunctional catalysts for enhanced glycerol carbonate production from transesterification of glycerol and dimethyl carbonate
(2020-07-01)
Chang, Cheng-Wei
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Gong, Zi-Jie
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Huang, Nai-Chieh
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Wang, Cheng-Yu
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Yu, Wen-Yueh
MgO-loaded ZIF-8 catalysts (MgO@ZIF-8) with various MgO loadings were prepared and characterized using atomic absorption spectroscopy (AAS), powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FT-IR), N-2 sorption isotherms, field-emission transmission electron microscopy (FE-TEM), and thermogravimetric analysis (TGA). Our results indicate that MgO nanoparticles could deposit onto the ZIF-8 surface with high atom efficiency while maintaining the ZIF-8 structure through a wet-impregnation and calcination process. It is suggested that the surface sites and microporosity of ZIF-8 support provide an adequate environment for the initial deposition of Mg precursor and subsequent growth of MgO nanoparticles through a nanoconfinement effect. MgO@ZIF-8 catalysts were tested for catalytic transesterification of glycerol and dimethyl carbonate to yield glycerol carbonate. It is found that the 50 wt% MgO@ZIF-8 catalyst display an improved catalytic activity than those of MgO and ZIF-8. Furthermore, the MgO@ZIF-8 catalysts showed higher catalytic activities than their physically-mixed counterparts, indicative of a synergistic effect between MgO and ZIF-8, which is explained by a proposed mechanism based on acid-base bifunctional sites on the surface.
Observation and simulation of hydrogen storage via spillover
(2018-09-01)
Wang, Cheng-Yu
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Chang, Cheng-Wei
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Wu, Yi-Ju
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Lueking, Angela D.
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材料科學與工程學系
Hydrogen spillover refers to catalytic dissociation of hydrogen molecules followed by surface diffusion to the catalytic support. This mechanism has been proposed as a means to initiate hydrogen storage at ambient temperature. When catalytic dissociation of hydrogen is used to initiate room temperature hydrogen storage, this initiates weak chemisorption. High variations in experimental uptake, combined with theoretical calculations that are inconsistent with this mechanism, have made this concept controversial. Here, we review hydrogen uptake in porous carbon and metal-organic frameworks (MOFs), with emphasis on spectroscopic evidence of atomic hydrogen bound to the surface and resolution of discrepancies between experimental and theoretical studies. We conclude with a perspective of hydrogen spillover for future material design, hydrogen storage, and fundamental understanding of a process that is crucial for adsorption and catalysis.
Oxygen-selective adsorption in RPM3-Zn metal organic framework
(2017-06-29)
Wang, Cheng-Yu
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Wang, Linxi
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Belnick, Andrew
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Wang, Hao
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Li, Jing
Development of an oxygen selective adsorbent is anticipated to reduce the material and energy requirements for adsorptive separations of air by a factor of four, due to the relative concentrations of N-2 and O-2 in air, thereby decreasing the parasitic energy losses, carbon dioxide emissions, and cost of oxygen purification via pressure-swing adsorption. Here, we report that RPM3-Zn (a. k. a. Zn-2(bpdc)(2)(bpee); bpdc = 4,4'-biphenyldicarboxylate; bpee = 1,2-bipyridylethene) is oxygen selective over nitrogen at temperatures from 77 K to 273 K, although the oxygen capacity of the sorbent decreased markedly at increasing temperatures. Due to an oxygen diffusivity that is similar to 1000-fold greater than nitrogen, the effective oxygen selectivity increases to near infinity at low temperature at equal contact times due to N2 mass transfer limitations for gate-opening. The kinetic limitation for N-2 to open the structure has a sharp temperature dependence, suggesting this effective kinetic selectivity may be "tuned in" for other flexible metalorganic- frameworks. Although the low temperature oxygen selectivity is not practical to displace cryogenic distillation, the results suggest a new mechanism for tailoring materials for kinetic selectivity, namely, capitalizing upon the delayed opening process for a particular gas relative to another. Published by Elsevier Ltd.
Pseudo-Superplastic Characteristics of ZK60 Alloy with Fibrous Microstructure
(2018-01-01)
Wang, Cheng-Yu
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Wang, Jian-Yih
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Saufan, Akhmd
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Fu, Yen-Pei
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材料科學與工程學系
The superplasticity of ZK60 alloy was investigated after thermomechanical treatments (combination of rolling at 473 K and 673 K). ZK60 alloy, with an equiaxial grains microstructure (average grain size 2.6 mu m), showed a maximum elongation of 865.2% with the strain rate 1 x 10(-4) s(-1) under high temperature tensile test at 573 K. Surprisingly, hot-rolled ZK60 samples with fibrous microstructure also displayed pseudo-superplastic behavior with an elongation of 535.2% at the same temperature. Microstructures indicated that the hot-rolled samples with elongated grains exhibited dynamic recovery and recrystallization during high temperature deformation, transforming the fibrous to fine-grained crystals, and thus retaining pseudo-superplastic behavior.