Carbon Nanotube-Bridged Graphene 3D Building Blocks for Ultrafast Compact Supercapacitors

Pham, Duy Tho,Lee, Tae Hoon,Luong, Dinh Hoa,Yao, Fei,Ghosh, Arunabha,Le, Viet Thong,Kim, Tae Hyung,Li, Bing,Chang, Jian,Lee, Young Hee American Chemical Society 2015 ACS NANO Vol.9 No.2

<P>The main obstacles to achieving high electrochemical energy density while retaining high power density are the trade-offs of energy <I>versus</I> power and gravimetric <I>versus</I> volumetric density. Optimizing structural parameters is the key to circumvent these trade-offs. We report here the synthesis of carbon nanotube (CNT)-bridged graphene 3D building blocks <I>via</I> the Coulombic interaction between positively charged CNTs grafted by cationic surfactants and negatively charged graphene oxide sheets, followed by KOH activation. The CNTs were intercalated into the nanoporous graphene layers to build pillared 3D structures, which enhance accessible surface area and allow fast ion diffusion. The resulting graphene/CNT films are free-standing and flexible with a high electrical conductivity of 39 400 S m<SUP>–1</SUP> and a reasonable mass density of 1.06 g cm<SUP>–3</SUP>. The supercapacitors fabricated using these films exhibit an outstanding electrochemical performance in an ionic liquid electrolyte with a maximum energy density of 117.2 Wh L<SUP>–1</SUP> or 110.6 Wh kg<SUP>–1</SUP> at a maximum power density of 424 kW L<SUP>–1</SUP> or 400 kW kg<SUP>–1</SUP>, which is based on thickness or mass of total active material.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-2/nn507079x/production/images/medium/nn-2014-07079x_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn507079x'>ACS Electronic Supporting Info</A></P>

Applying the IoT platform and green wave theory to control intelligent traffic lights system for urban areas in Vietnam

( Cao Tho Phan ),( Duy Duong Pham ),( Hoang Vu Tran ),( Trung Viet Tran ),( Phat Nguyen Huu ) 한국인터넷정보학회 2019 KSII Transactions on Internet and Information Syst Vol.13 No.1

This paper proposes an intelligent system performing an application with assistance of an Internet of Things (IoT) platform to control a traffic lights system. In our proposed systems, the traffic lights can be remotely controlled through the Internet. Based on IoT platform, the traffic conditions at different intersections of roads are collected and the traffic lights are controlled in a central manner. For the software part, the algorithm is designed based on the green wave theory to maximize the green bandwidth of arterial roads while addressing a challenging issue: the rapid changes of parameters including cycle time, splits, offset, non-fixed vehicles’ velocities and traffic flow along arterial roads. The issue typically happens at some areas where the transportation system is not well organized like in Vietnam. For the hardware part, PLC S7-1200 are placed at the intersections for two purposes: to control traffic lights and to collect the parameters and transmit to a host machine at the operation center. For the communication part, the TCP/IP protocol can be done using a Profinet port embedded in the PLC. Some graphical user interface captures are also presented to illustrate the operation of our proposed system.

Applying the IoT platform and green wave theory to control intelligent traffic lights system for urban areas in Vietnam

Phan, Cao Tho,Pham, Duy Duong,Tran, Hoang Vu,Tran, Trung Viet,Huu, Phat Nguyen Korean Society for Internet Information 2019 KSII Transactions on Internet and Information Syst Vol.13 No.1

This paper proposes an intelligent system performing an application with assistance of an Internet of Things (IoT) platform to control a traffic lights system. In our proposed systems, the traffic lights can be remotely controlled through the Internet. Based on IoT platform, the traffic conditions at different intersections of roads are collected and the traffic lights are controlled in a central manner. For the software part, the algorithm is designed based on the green wave theory to maximize the green bandwidth of arterial roads while addressing a challenging issue: the rapid changes of parameters including cycle time, splits, offset, non-fixed vehicles' velocities and traffic flow along arterial roads. The issue typically happens at some areas where the transportation system is not well organized like in Vietnam. For the hardware part, PLC S7-1200 are placed at the intersections for two purposes: to control traffic lights and to collect the parameters and transmit to a host machine at the operation center. For the communication part, the TCP/IP protocol can be done using a Profinet port embedded in the PLC. Some graphical user interface captures are also presented to illustrate the operation of our proposed system.

Carbon-Based Materials for Lithium-Ion Batteries, Electrochemical Capacitors, and Their Hybrid Devices.

Yao, Fei,Pham, Duy Tho,Lee, Young Hee Wiley-VCH 2015 ChemSusChem Vol.8 No.14

<P>A rapidly developing market for portable electronic devices and hybrid electrical vehicles requires an urgent supply of mature energy-storage systems. As a result, lithium-ion batteries and electrochemical capacitors have lately attracted broad attention. Nevertheless, it is well known that both devices have their own drawbacks. With the fast development of nanoscience and nanotechnology, various structures and materials have been proposed to overcome the deficiencies of both devices to improve their electrochemical performance further. In this Review, electrochemical storage mechanisms based on carbon materials for both lithium-ion batteries and electrochemical capacitors are introduced. Non-faradic processes (electric double-layer capacitance) and faradic reactions (pseudocapacitance and intercalation) are generally explained. Electrochemical performance based on different types of electrolytes is briefly reviewed. Furthermore, impedance behavior based on Nyquist plots is discussed. We demonstrate the influence of cell conductivity, electrode/electrolyte interface, and ion diffusion on impedance performance. We illustrate that relaxation time, which is closely related to ion diffusion, can be extracted from Nyquist plots and compared between lithium-ion batteries and electrochemical capacitors. Finally, recent progress in the design of anodes for lithium-ion batteries, electrochemical capacitors, and their hybrid devices based on carbonaceous materials are reviewed. Challenges and future perspectives are further discussed.</P>

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Sahoo, Ramkrishna,Pham, Duy Tho,Lee, Tae Hoon,Luu, Thi Hoai Thuong,Seok, Jinbong,Lee, Young Hee American Chemical Society 2018 ACS NANO Vol.12 No.8

<P>Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <I>in situ</I> activated Mn<SUB>3</SUB>O<SUB>4</SUB> and VO<SUB>2</SUB> electrodes. The underlying mechanism indicates a specific potential of ∼1 V <I>vs</I> Ag/AgCl for the oxidation of Mn<SUP>4+</SUP>-to-Mn<SUP>7+</SUP> at the positive electrode and ∼ -0.8 V <I>vs</I> Ag/AgCl for the reduction of V<SUP>3+</SUP>-to-V<SUP>2+</SUP> at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities.</P> [FIG OMISSION]</BR>

Fast-Charging High-Energy Battery-Supercapacitor Hybrid: Anodic Reduced Graphene Oxide-Vanadium(IV) Oxide Sheet-on-Sheet Heterostructure

Sahoo, Ramkrishna,Lee, Tae Hoon,Pham, Duy Tho,Luu, Thi Hoai Thuong,Lee, Young Hee American Chemical Society 2019 ACS NANO Vol.13 No.9

<P>The battery-supercapacitor hybrid (BSH) device has potential applications in energy storage and can be a remedy for low-power batteries and low-energy supercapacitors. Although several studies have investigated electrode materials (particularly for a battery-type anode material) and design for BSHs, the energy density and power density are insufficient (far from the levels required for practical applications). Herein, a hierarchical vanadium(IV) oxide on reduced graphene oxide (rGO@VO<SUB>2</SUB>) heterostructure as an anode and activated carbon on carbon cloth (AC@CC) as a cathode are proposed for fabricating an advanced BSH. The mixed valency of V ions inside the as-prepared VO<SUB>2</SUB> matrix (V<SUP>3+</SUP> and V<SUP>4+</SUP>) facilitates redox reactions at a low potential, giving rise to rGO@VO<SUB>2</SUB> as a typical anode with a working potential of 0.01-3 V (<I>vs</I> Li/Li<SUP>+</SUP>). The sheet-on-sheet heterostructured rGO@VO<SUB>2</SUB> yields a high specific capacity of 1214 mAh g<SUP>-1</SUP> at 0.1 A g<SUP>-1</SUP> after 120 cycles, with a high rate capability and stability. The rGO@VO<SUB>2</SUB>//AC@CC BSH device exhibits a maximum gravimetric energy density of 126.7 Wh kg<SUP>-1</SUP> and a maximum gravimetric power density of ∼10 000 W kg<SUP>-1</SUP> within a working voltage range of 1-4 V. Moreover, it exhibits fast charging times of 5 and 834 s with energy densities of 15.6 and 82 Wh kg <SUP>-1</SUP>, respectively.</P> [FIG OMISSION]</BR>

Leaf Vein-Inspired Nanochanneled Graphene Film for Highly Efficient Micro-Supercapacitors

Chang, Jian,Adhikari, Subash,Lee, Tae Hoon,Li, Bing,Yao, Fei,Pham, Duy Tho,Le, Viet Thong,Lee, Young Hee Wiley Blackwell (John Wiley Sons) 2015 ADVANCED ENERGY MATERIALS Vol.5 No.9

Coaxial Fiber Supercapacitor Using All-Carbon Material Electrodes

Le, Viet Thong,Kim, Heetae,Ghosh, Arunabha,Kim, Jaesu,Chang, Jian,Vu, Quoc An,Pham, Duy Tho,Lee, Ju-Hyuck,Kim, Sang-Woo,Lee, Young Hee American Chemical Society 2013 ACS NANO Vol.7 No.7

<P>We report a coaxial fiber supercapacitor, which consists of carbon microfiber bundles coated with multiwalled carbon nanotubes as a core electrode and carbon nanofiber paper as an outer electrode. The ratio of electrode volumes was determined by a half-cell test of each electrode. The capacitance reached 6.3 mF cm<SUP>–1</SUP> (86.8 mF cm<SUP>–2</SUP>) at a core electrode diameter of 230 μm and the measured energy density was 0.7 μWh cm<SUP>–1</SUP> (9.8 μWh cm<SUP>–2</SUP>) at a power density of 13.7 μW cm<SUP>–1</SUP> (189.4 μW cm<SUP>–2</SUP>), which were much higher than the previous reports. The change in the cyclic voltammetry characteristics was negligible at 180° bending, with excellent cycling performance. The high capacitance, high energy density, and power density of the coaxial fiber supercapacitor are attributed to not only high effective surface area due to its coaxial structure and bundle of the core electrode, but also all-carbon materials electrodes which have high conductivity. Our coaxial fiber supercapacitor can promote the development of textile electronics in near future.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-7/nn4016345/production/images/medium/nn-2013-016345_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn4016345'>ACS Electronic Supporting Info</A></P>