Browsing by Author "Yen, Po-Jen"

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A new redox phloroglucinol additive incorporated gel polymer electrolyte for flexible symmetrical solid-state supercapacitors
(2019-06-01)
Phuoc-Anh Le
;
Van-Truong Nguyen
;
Yen, Po-Jen
;
Tseng, Tseung-Yuen
;
Wei, Kung-Hwa
We reported a new and environmentally friendly phloroglucinol additive incorporated polyvinyl alcohol-LiClO4 gel polymer electrolyte for flexible symmetrical solid-state supercapacitors. The incorporation of 10 wt% phloroglucinol into PVA-LiClO4 gel polymer electrolytes results in much higher specific capacitance (114 F g(-1)) than that without phloroglucinol (60 F g(-1)), an increase of 90%, because of the redox reaction of phloroglucinol in the system. We used the PVA-LiClO4 with 10 wt% phloroglucinol as a gel polymer electrolyte in combination with nitrogen-doped graphene nanosheet-based electrodes as the anode and cathode to fabricate a symmetrical solid-state supercapacitor. The fabricated supercapacitor involving the phloroglucinol redox additive has an energy density of 2.3 W h kg(-1) at a power density of 150 W kg(-1), which is higher than the one without a redox additive (1.9 W h kg(-1) at a power density of 150 W kg(-1)). Moreover, the supercapacitor involving the redox additive has good stability; its capacitance remains at up to similar to 94% after 5000 charge/discharge cycles.
An universal electron transport layer involving hydrogen plasma-treated tungsten disulfide nanosheets doped zinc oxide layers for polymer donors with fullerene or small molecule acceptor photovoltaics
(2019-09-01)
Huang, Yi-Jiun
;
Yen, Po-Jen
;
Wang, Hao-Cheng
;
Chen, Hsiu-Cheng
;
Wei, Kung-Hwa
A new universal electron transport layer that involves doping hydrogen-plasma-treated tungsten disulfide (WS2) nanosheets into ZnO for polymer/fullerene or small molecule organic photovoltaics (OPVs) was prepared. A hydrogen plasma treatment was used to alter the structures of WS2 nanosheets such that the W6+ content was converted into W4+; then ZnO:WS2 nanosheets composites were prepared to form electron transport layers (ETLs). The energy band of the ZnO:WS2 films could be tuned from 5.15 to 4.60 eV by varying the concentration of the WS2 nanosheets up to 0.5 wt%. It was found that ZnO:WS2 ETLs exhibited superior charge transport properties than those of the pristine ZnO layer because of the structure changes, as determined from the X-ray scattering characterizations. OPVs incorporating active layers of PTB7-TH/PC71BM and PTB7-TH/IDIC blends exhibited their power conversion efficiencies of 10.3% and 6.7%, respectively, with the incorporation of 0.3 wt% of the WS2 nanosheets, up from 8.9% to 5.4% for the corresponding devices featuring pristine ZnO-relative increases of 16% and 24%, respectively. This study demonstrates the effectiveness of hydrogen plasma treatment for altering the surface structures of two-dimensional transition-metal-dichalcogenide nanosheets, and paves a way for the composite electron transport layers for use in organic photovoltaics.
Carbon Nanotube/Nitrogen-Doped Reduced Graphene Oxide Nanocomposites and Their Application in Supercapacitors
(2017-08-01)
Yang, Chih-Chieh
;
Tsai, Meng-Han
;
Huang, Chun-Wei
;
Yen, Po-Jen
;
Pan, Chien-Chung
Electrodes of carbon-based nanocomposites with high specific surface areas and suitable pore sizes have high potential for improving power and energy densities of supercapacitors. In this study, nitrogen-doped reduced graphene oxide (NrGO) nanosheets were synthesized to increase the specific surface area of reduced graphene oxide (rGO). The specific surface area of NrGO was increased to 633 m(2)g(-1) compared to that of rGO, 450 m(2)g(-1). A series of NrGO/carbon nanotubes (CNTs) nanocomposites were prepared. By using NrGO/CNTs/polyvinylidene difluoride (PVDF)/carbon black/N-methyl-pyrrolidone (NMP) nanocomposites as both of anode and cathode into two electrodes, such symmetric supercapacitor in the 1 M KOH aqueous electrolyte exhibited high specific capacitance (227 F g(-1) at 20 mV s(-1)), fast rate capability (83% capacitance of current density 1 mA cm(-2) at current density 5 mA cm(-2)), low resistance (0.98 Omega), and excellent cycling stability (87% capacitance retention after 10,000 charge/discharge cycles). Moreover, the symmetric supercapacitor in the ionic liquid (BMIMTFSI) electrolyte possessed a wide operating voltage (3 V) and high energy density (89 Wh kg(-1) at 1 mA cm(-2)). The carbon-based hybrid electrode has high potential for use in energy storage and conversion devices.
Cathodic plasma-induced syntheses of graphene nanosheet/MnO2/WO3 architectures and their use in supercapacitors
(2020-05-10)
Huang, Shih-Yu
;
Phuoc-Anh Le
;
Yen, Po-Jen
;
Lu, Yi-Chun
;
Sahoo, Sumanta Kumar
In this study, we synthesized new 0.01-2 mu m graphene nanosheet/MnO2WO3(G/MnO2/WO3) architectures through an electrochemically induced cathodic plasma process in a single batch at a lower temperature (70 degrees C) and for a shorter time (2 h) than those required for the syntheses of similar structures when using a hydrothermal method. We first obtained 0.01-1 mu m leaf-like graphene (G) nanosheets, then 0.1-0.3 mu m long and approximately 10 nm diameter petiole-like MnO2 nanowires on the G nanosheets, and finally 0.20-2.0 mu m petal-like WO3 on MnO2/G - thereby forming the G/MnO2/WO3 architectures - as evidenced using scanning electron microscopy and transmission electron microscopy. We deciphered the step-wise reaction mechanism behind the formation of the G/MnO2/WO3 architectures during the plasma process. The high surface area of 291 m(2) g(-1) in the G/MnO2/WO3 architecture was contributed mainly by the G nanosheets, providing a suitable surface area for diffusion of the charge carriers during the charging and discharging process. As a result, an electrode incorporating the G/MnO2/WO3 architectures exhibited an excellent specific capacitance of 620 F g(-1) - 45 and 200% higher than those of G/MnO2 (421 F g(-1)) and G (189 F g(-1)) electrodes, respectively - at a current density of 0.5 A g(-1). Moreover, the G/MnO2/WO3-incorporated electrode exhibited good electrochemical cycling stability, with 90% capacitance retention over 5000 cycles at 1 A g(-1). Such new G/MnO2/WO3 heterojunction structures, not only provide high-performance electrode applications, but also suggest a potential approach toward fabricating other heterojunction structures having high surface areas for energy storage applications. (C) 2020 Elsevier Ltd. All rights reserved.
Facile production of graphene nanosheets comprising nitrogen-doping through in situ cathodic plasma formation during electrochemical exfoliation
(2017-03-14)
Yen, Po-Jen
;
Ting, Chao-Chi
;
Chiu, Yung-Chi
;
Tseng, Tseung-Yuen
;
Hsu, Yao-Jane
In this paper we report a facile and rapid electrochemical process, involving simultaneous in situ cathodic plasma exfoliation and nitrogen doping, for the production of nitrogen-doped graphene nanosheets. We used a novel electrochemical process to generate the plasma in situ: a graphite rod, serving as a cathode, generated in situ cathodic plasma when it came into slight contact with the electrolyte containing proper nitrogen species that can undergo dissociation with plasma and then form bonds with carbon such as ammonia molecules or nitrate/nitrite anions, resulting in induced exfoliation of the tip of the graphite rod into nitrogen-doped graphene nanosheets. X-ray photoelectron spectroscopy, elemental analysis, and energy-dispersive X-ray spectroscopy revealed that the concentration of nitrogen atoms doped in the graphene nanosheets varied from 0.6 to 0.81 at%. Transmission electron microscopy and scanning electron microscopy revealed that the as-produced nitrogen-doped graphene nanosheets comprised four layers of graphene and had a specific surface area of 164 m(2) g(-1). This process has potential for use in the industrial-scale mass production of nitrogen-doped graphene for various applications.
New Simultaneous Exfoliation and Doping Process for Generating MX2 Nanosheets for Electrocatalytic Hydrogen Evolution Reaction
(2019-04-24)
Van-Truong Nguyen
;
Yang, Tzu-Yi
;
Phuoc Anh Le
;
Yen, Po-Jen
;
Chueh, Yu-Lun
Doping nonmetal atoms into layered transition metal dichalcogenide MX2 structures has emerged as a promising strategy for enhancing their catalytic activities for the hydrogen evolution reaction. In this study, we developed a new and efficient one-step approach that involves simultaneous plasma-induced doping and exfoliating of MX2 bulk into nanosheets-such as MoSe2, WSe2, MoS2, and WS2 nano sheets-within a short time and at a low temperature (ca. 80 degrees C). Specifically, by utilizing active plasma that is generated with an asymmetric electrical field during the electrochemical reaction at the surface of the submerged cathode tip, we are able to achieve doping of nitrogen atoms, from the electrolytes, into the semiconducting 2H-MX2 structures during their exfoliation process from the bulk states, forming N-doped MX2. We selected N-doped MoS2 nanosheets for demonstrating their catalytic hydrogen evolution potential. We modulated the electronic and transport properties of the MoS2 structure with the synergy of nitrogen doping and exfoliating for enhancing their catalytic activity. We found that the nitrogen concentration of 5.2 atom % at N-doped MoS2 nanosheets have an excellent catalytic hydrogen evolution reaction, where a low overpotential of 164 mV at a current density of 10 mA cm(-2) and a small Tafel slope of 71 dec mV(-1)-much lower than those of exfoliated MoS2 nanosheets (207 mV, 82 dec mV(-1)) and bulk MoS2 (602 mV, 198 dec mV(-1))-as well as an extraordinary long-term stability of >25 h in 0.5 M H2SO4 can be achieved.
Plasma-assisted electrochemical exfoliation of graphite for rapid production of graphene sheets
(2014)
Van Thanh, Dang
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Li, Lain-Jong
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Chu, Chih-Wei
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Yen, Po-Jen
;
Wei, Kung-Hwa
We describe a new and highly efficient plasma-assisted electrochemical exfoliation method, involving a plasma-generated graphite cathode and a graphite anode, for the production of graphene sheets from electrodes in a basic electrolyte solution in a short reaction time.
Probing the electrochemical properties of an electrophoretically deposited Co3O4/rGO/CNTs nanocomposite for supercapacitor applications
(2016-01-01)
Kumar, Nagesh
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Huang, Chun-Wei
;
Yen, Po-Jen
;
Wu, Wen-Wei
;
Wei, Kung-Hwa
This study reports the electrochemical performance of pseudosupercapacitor electrodes composed of cubic phase Co3O4 nanoparticles, reduced graphene oxide (rGO) and functionalized MWCNTs based nanocomposites. The Co3O4/rGO/CNTs nanocomposites have been synthesized using a hydrothermal method and the EPD technique has been used to make binder free electrodes of the nanocomposite materials for supercapacitor applications. The effects of graphene oxide (GO) concentration and the ratio of GO/CNTs on the electrochemical performance of the nanocomposite material have been investigated. From the experimental results, the Co3O4/rGO/CNTs nanocomposite synthesized with 2 mg mL (1) GO concentration and 10 : 1 GO/CNT ratio exhibits a good specific capacitance of 850 F g (1) at a 5 mV s(-1) scan rate and 790 F g(-1) at 1 A g(-1), excellent rate capability and good cyclability in 1 M KOH. Furthermore, we have successfully designed an aqueous electrolyte-based asymmetric pseudocapacitor using Co3O4/rGO/CNTs nanocomposite as an anode and N-doped graphene nanocomposite as a cathode. The operating voltage of our optimized asymmetric pseudocapacitor is 1.4 V and it exhibits the maximum energy density and power density of 19.6 W h kg(-1) and 7250 W kg(-1), respectively. These results suggest that our EPD grown nanocomposite binder free electrode and our designed asymmetric pseudocapacitor have a good potential for practical applications.
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.