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Carbonaceous Anodes Derived from Sugarcane Bagasse for Sodium-Ion Batteries
(2019-05-21)
Rath, Purna Chandra
;
Patra, Jagabandhu
;
Huang, Hao-Tzu
;
Bresser, Dominic
;
Wu, Tzi-Yi
To realize the sustainability of Na-ion batteries (NIBs) for large-scale energy storage applications, a resource-abundant and cost-effective anode material is required. In this study, sugarcane bagasse (SB), one of the most abundant types of biowaste, is chosen as the carbon precursor to produce a hard carbon (HC) anode for NIBs. SB has a great balance of cellulose, hemicellulose, and lignin, which prevents full graphitization of the pyrolyzed carbon but ensures a sufficiently ordered carbon structure for Na+ transport. Compared with HC derived from waste apples, which are pectin-rich and have less cellulose than SB, SB-derived HC (SB-HC) has fewer defects and a lower oxygen content. SB-HC thus has a higher first-cycle sodiation/desodiation coulombic efficiency and better cycling stability. In addition, SB-HC has a unique flake-like morphology, which can shorten the Na+ diffusion length, and higher electronic conductivity (owing to more sp(2)-hybridized carbon), resulting in superior high-rate charge-discharge performance to apple-derived HC. The effects of pyrolysis temperature on the material characteristics and electrochemical properties, evaluated by using chronopotentiometry, cyclic voltammetry, and electrochemical impedance spectroscopy, are systematically investigated for both kinds of HC.
Porous Polyimide and Carbon Nanotubes: Solvent Vapor-Induced Transformation in the Nanochannels of Anodic Aluminum Oxide Templates
(2019-04-01)
He, Hung-Chieh
;
Tu, Yi-Hsuan
;
Li, Jia-Wei
;
Lin, Yu-Liang
;
Chen, Jiun-Tai
Polyimides (PIs) have attracted wide attention because of their exceptional thermal stability and applications in areas such as printed circuit boards and multichip modules. It remains a great challenge, however, to control the morphologies and properties of PI-based nanomaterials, especially porous PI-based nanotubes. In this work, a versatile method to fabricate porous PI nanotubes via the template method is developed, with a solvent vapor-induced transformation process. First, polyamic acid (PAA) solutions are used as precursors and infiltrated into the nanochannels of anodic aluminum oxide templates, forming PAA nanotubes. After the samples are annealed in tetrahydrofuran or dimethylformamide vapors, depression of the PAA tubes occurs, causing the formation of pores. The porous PAA nanotubes can be further converted to porous PI and carbon nanotubes by imidization and carbonization processes, respectively. The pore sizes of the porous nanomaterials can be controlled by changing the type of the annealing solvent and the solvent annealing time.
Supercapacitive Properties of Micropore- and Mesopore-Rich Activated Carbon in Ionic-Liquid Electrolytes with Various Constituent Ions
(2019-01-24)
Quoc Dat Nguyen
;
Patra, Jagabandhu
;
Hsieh, Chien-Te
;
Li, Jianlin
;
Dong, Quan-Feng
Ionic-liquid (IL) electrolytes, characterized by large potential windows, intrinsic ionic conductivity, low environmental hazard, and high safety, are used for micropore- and mesopore-rich activated-carbon (AC(micro) and AC(meso)) supercapacitors. IL electrolytes consisting of various cations [1-ethyl-3-methylimidazolium (EMI+), N-propyl-N-methylpyrrolidinium (PMP+), and N-butyl-N-methylpyrrolidinium (BMP+)] and various anions [bis(trifluoromethylsulfonyl)imide (TFSI-), BF4-, and bis(fluorosulfonyl)imide (FSI-)] are investigated. The electrolyte conductivity, viscosity, and ion transport properties at the AC(micro) and AC(meso) electrodes are studied. In addition, the capacitance, rate capability, and cycling stability of the two types of AC electrodes are systematically examined and post-mortem material analyses are conducted. The effects of IL composition on the charge-discharge capacitances of the AC(micro) electrodes are more pronounced than those for the AC(meso) electrodes. The FSI-based IL electrolytes, for which electrochemical properties are cation dependent, are found to be promising. Incorporating EMI+ with FSI- results in a low electrolyte viscosity and a fast ion transport, giving rise to optimized electrode capacitance and rate capability. Replacing EMI+ with PMP+ increases the cell voltage (to 3.5 V) and maximum energy density (to 42 Wh kg(-1)) of the AC(micro) cell at the cost of cycling stability.
Effects of NH3 Flow Rate During AlGaN Barrier Layer Growth on the Material Properties of AlGaN/GaN HEMT Heterostructure
(2017-10-01)
Lumbantoruan, Franky J.
;
Wong, Yuen-Yee
;
Huang, Wei-Ching
;
Yu, Hung-Wei
;
Chang, Edward-Yi
NH3 flow rate during AlGaN barrier layer growth not only affects the growth efficiency and surface morphology as a result of parasitic reactions but also influences the concentration of carbon impurity in the AlGaN barrier. Carbon, which decomposes from metal precursors, plays a role in electron compensation for AlGaN/GaN HEMT. No 2-dimensional electron gas (2-DEG) was detected in the AlGaN/GaN structure if grown with 0.5 slm of NH3 due to the presence of higher carbon impurity (2.6 x 10(19) cm(-2)). When the NH3 flow rate increased to 6.0 slm, the carbon impurity reduced to 2.10 x 10(18) atom cm(-3) and the 2 DEG electron density recovered to 9.57 x 10(12) cm(-2).
Deposition of Carbon Nanowall Flowers on Two-Dimensional Sheet for Electrochemical Capacitor Application
(2009)
Hung, Tsung-Chi
;
Chen, Chia-Fu
;
Whang, Wha-Tzong
;
材料科學與工程學系
;
Department of Materials Science and Engineering
We have used bias-assisted microwave plasma chemical vapor deposition to synthesize (i) two-dimensional carbon nanowalls [(2D CNWs), monolayer] and (ii) three-dimensional carbon nanowalls [(3D CNWs), double-layer] on carbon cloth in a CH(4)/CO(2) system. The specific surface area of the 3D CNW electrode (1580 m(2)/g) was considerably larger than that of the 2D CNW electrode (364 m(2)/g). This higher surface area and more porous structure of the 3D CNW electrode resulted in its capacitance reaching as high as ca. 198 F/g at a scan rate of 10 mV/s. Electrochemical measurements suggested that this 3D electrode is a promising material for application in electrical storage devices.
A Promising Approach to the Synthesis of 3D Nanoporous Graphitic Carbon as a Unique Electrocatalyst Support for Methanol Oxidation
(2010)
Tiwari, Jitendra N.
;
Tiwari, Rajanish N.
;
Chang, Yun-Min
;
Lin, Kun-Lin
;
材料科學與工程學系
A 3D nanoporous graphitic carbon (g-C) material is synthesized by using an adamantane (C(10)H(16)) flame, and utilized to support a Pt(50)-Ru(50) alloy catalyst. The physico-chemical properties of the Pt(50)-Ru(50)/3D nanoporous g-C electrode are examined by a range of spectroscopy techniques as well as Brunauer-Emmett-Teller surface area analysis. Cyclic voltammetry measurements are used for electrochemical characterization of the Pt(50)-Ru(50)/3D nanoporous g-C electrode. The electrochemical investigations show that the supported Pt(50)-Ru(50) has excellent activity and stability towards methanol electro-oxidation. Good CO tolerance is also shown, and considered to be due to the presence of Ru nanoparticles. It is proposed that Ru is able to promote the oxidation of strongly adsorbed CO on Pt by supplying an oxygen source: RU(OH)(ad). Moreover, the presence of 3D nanopores in the g-C support may also contribute to the observed higher current density by virtue of the easy transport of methanol and the oxidation products through these nanopores.

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