Browsing by Author "Liu, Yih-Ming"

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A Holey Graphene Additive for Boosting Performance of Electric Double-Layer Supercapacitors
(2020-04-01)
Huang, Jun-Bin
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Patra, Jagabandhu
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Lin, Ming-Hsien
;
Ger, Ming-Der
;
Liu, Yih-Ming
We demonstrate a facile and effective method, which is low-cost and easy to scale up, to fabricate holey graphene nanosheets (HGNSs) via ultrafast heating during synthesis. Various heating temperatures are used to modify the material properties of HGNSs. First, we use HGNSs as the electrode active materials for electric double-layer capacitors (EDLCs). A synthesis temperature of 900 degrees C seems to be optimal, i.e., the conductivity and adhesion of HGNSs reach a compromise. The gravimetric capacitance of this HGNS sample (namely HGNS-900) is 56 Fg(-1). However, the volumetric capacitance is low, which hinders its practical application. Secondly, we incorporate activated carbon (AC) into HGNS-900 to make a composite EDLC material. The effect of the AC:HGNS-900 ratio on the capacitance, high-rate performance, and cycling stability are systematically investigated. With a proper amount of HGNS-900, both the electrode gravimetric and volumetric capacitances at high rate charging/discharging are clearly higher than those of plain AC electrodes. The AC/HGNS-900 composite is a promising electrode material for nonaqueous EDLC applications.
Comparison of field emission performances and durability of three nanocarbon materials
(2020-07-01)
Youh, Meng-Jey
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Lin, Chun-Shuan
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Pu, Nen-Wen
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Liu, Yih-Ming
;
Youh, Ru-Yi
The performances and operation lifetime of field emission (FE) cathodes made by spray-coating three different nanocarbon materials-carbon nanotubes (CNTs), graphene (GE), and carbon nanocoils (CNCs)-were compared. Though CNTs had the benefits of the lowest turn-on field, CNCs exhibited the most stable cycle-to-cycle repeatability and a significantly longer life than CNTs and GE under a continuous high-current-density operation. The microscopic morphology and Raman spectra of these nanocarbon emitters before and after the 50-h life tests were examined in order to understand the damage mechanism and the cause of their distinct performance decay behaviors. The results indicated that CNCs, whose diameters are significantly larger than those of CNTs and the thickness of GE, can withstand the thermal effects of high current density with the least degree of damage in the morphology and microstructure. According to our performance and life tests, CNTs are most suitable for low-voltage small-current FE applications because of their highest field enhancement factor and lowest turn-on field, while CNCs are a more favorable candidate for high-voltage long-term applications such as FE x-ray tubes.
Effect of Pretreatment Process on the Adhesion and Corrosion Resistance of Nickel-Boron Coatings Deposited on 8620H Alloy Steel
(2020-01-01)
Cheng, An-Yu
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Sheu, Hung-Hua
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Liu, Yih-Ming
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Hou, Kung-Hsu
;
Hsieh, Pei-Yi
In this work, Ni-B coatings were electrodeposited on the 8620H steel substrates, the substrates were carried out with different pretreatment including without pretreatment, after sandblasting by glass sand and after sandblasting by emery powders. The results of scratch test indicated that the best adhesion strength of Ni-B coatings occurred at the 8620H steel substrates carried out with sandblasting by emery powders, the Ni-B coatings still did not be damaged when the load increase to 50 N. The values of Ni-B coatings deposited on different pretreatment condition such as without pretreatment, after sandblasting by glass sand and after sandblasting by emery powders are approximately at 9.46x 10(-6), 8.62x 10(-6) and 2.31 x 10(-6) A/dm(2), respectively. All the samples carried out with a wear process at a load of 20 N, the icorr values of Ni-B coatings deposited on different conditions 1.96x 10(-5), 1.54x 10(-5) and 6.72x 10(-6) A/dm(2), respectively. The results show that the Ni-B coatings deposited on the 8620H steel substrates carried out with sandblasting by emery powders has the best adhesion strength and corrosion resistance due to the Ni-B coatings did not be damaged during wear process.