Browsing by Author "Pu, Nen-Wen"

Now showing 1 - 3 of 3

A Holey Graphene Additive for Boosting Performance of Electric Double-Layer Supercapacitors
(2020-04-01)
Huang, Jun-Bin
;
Patra, Jagabandhu
;
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
;
Lin, Chun-Shuan
;
Pu, Nen-Wen
;
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.
Hydrous ruthenium oxide-tantalum pentoxide thin film electrodes prepared by thermal decomposition for electrochemical capacitors
(2020-07-01)
Xie, Jian-De
;
Hsu, Kai-Hsiang
;
Patra, Jagabandhu
;
Su, Ching-Yuan
;
Lee, Sheng-Wei
In this work, we have fabricated high-performance thin-film electrodes for electrochemical capacitors (ECs) via thermal decomposition syntheses of RuO2-Ta2O5 coating layers on Ti substrates. The influences of decomposition temperature as well as the Ru/Ta molar ratio on material and electrochemical properties of the EC electrodes are systematically investigated. The thermal decomposition of 300 degrees C preserves a large fraction of hydrous RuO2 center dot xH(2)O within the hybrid oxide and consequently improves the electrode capacitance. The amorphous Ta2O5 incorporation can manipulate the RuO2 crystallinity and thus its specific capacitance. An optimal Ru/Ta molar ratio of 7:3 is determined for the RuO2-Ta2O5 electrode, which can deliver an energy density of 4.8 Wh kg(-1) at a power density of 8720 W kg(-1) (or 8.3 Wh L-1 at 15,000 W L-1). In addition, an excellent durability of 97.6% capacitance retention after 3000 charge-discharge cycles is found for this electrode. The proposed RuO2-Ta2O5 thin-film electrode has paved the way for next-generation ECs with superior capacitances, energy/power densities, and cyclability.