Browsing by Author "Chiang, Ya-Chi"

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Tunable nitrogen-doped graphene sheets produced with in situ electrochemical cathodic plasma at room temperature for lithium-ion batteries
(2019-06-01)
Yen, Po-Jen
;
Ilango, P. Robert
;
Chiang, Ya-Chi
;
Wu, Chia-Wei
;
Hsu, Yung-Chi
This paper describes a facile and tunable method, performed at room temperature and amenable to mass-production, for the preparation of nitrogen-doped graphene sheets using in situ electrochemical cathodic plasma exfoliation of a graphite/melamine composite. The plasma generated at the submerged surface of the graphite/melamine composite electrode not only exfoliated the graphite granules into graphene sheets but also induced the doping of nitrogen atoms. The sizes and morphologies of the graphene sheets, comprising four to five layers of graphene, were confirmed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Tuning the concentration of melamine in the graphite/melamine composites led to different levels of nitrogen-doping in the graphene sheets; the stability of the nitrogen-doped graphene sheets was investigated in various harsh environments. Furthermore, the use of the 4.63 at% nitrogen-doped graphene sheets as anode materials resulted in lithium-ion batteries displaying excellent performance, with a capacity of 488 mA h g(-1) at 100 mA g(-1) after 100 cycles that was better than that of the device incorporating pristine graphene sheets (344 mA h g(-1) at 100 mA g(-1) after 100 cycles). This method is a new and tunable approach for producing massive amounts of nitrogen-doped graphene sheets from graphite powder at room temperature. (C) 2019 Elsevier Ltd. All rights reserved.
Using Different Ions to Tune Graphene Stack Structures from Sheet- to Onion-Like During Plasma Exfoliation, with Supercapacitor Applications
(2019-04-23)
Yen, Po-Jen
;
Sahoo, Sumanta Kumar
;
Chiang, Ya-Chi
;
Huang, Shih-Yu
;
Wu, Chia-Wei
In this article, we report a facile and simple approach for tuning graphene nanosheet structures (GNS) with different ions in the electrolytes through cathodic plasma exfoliation process in electrochemical reactions. We obtained sheet- and onion-like GNS when aqueous electrolyte NaOH and H2SO4, respectively, were present during plasma exfoliation in the electrochemical reactions, as evidenced from scanning electron microscopy and transmission electron microscopy images. Moreover, the onion-like GNS exhibited a specific surface area of 464m(2) g(-1) and a supercapacitive performance of 67.1F g(-1), measured at a scan rate of 5mV s(-1) in 1M NaCl; these values were much higher than those (72m(2) g(-1) and 21.6F g(-1), respectively) of the sheet-like GNS. This new approach for efficiently generating tunable stacked graphene structures with different ions, in the cathodic plasma exfoliation process, has promising potentials for use in energy storage devices.