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George Z. Chen - One of the best experts on this subject based on the ideXlab platform.

  • Capacitive and non-capacitive faradaic Charge Storage
    Electrochimica Acta, 2016
    Co-Authors: Li Guan, Linpo Yu, George Z. Chen
    Abstract:

    This article aims to offer a critical overview of selected literature on capacitive and non-capacitive faradaic Charge Storage. It is particularly relevant to the concept of pseudocapacitance that is generally described as a result of fast surface faradaic processes. In general, faradaic processes represent electron transfer reactions at the interface between an electrode and its contacting solid or liquid electrolyte phase that is able to accept or donate electrons. Obviously, not all faradaic processes can be associated with pseudocapacitance. The question is how to differentiate pseudocapacitance related faradaic Charge Storage from the others. Therefore, attempts have been made to apply the band model for semiconductors to account qualitatively for the origin of pseudocapacitance. Capacitive and non-capacitive faradaic processes are then proposed to define and differentiate different Charge Storage mechanisms in supercapacitor and battery. On the other hand, the unequal electrode capacitance approach and the use of Ca2+ in aqueous electrolytes are discussed in relation with enhanced energy capacity of supercapacitors. In addition, the principle of supercapattery as a hybrid device is explained with recent literature examples.

  • organoaqueous calcium chloride electrolytes for capacitive Charge Storage in carbon nanotubes at sub zero temperatures
    Chemical Communications, 2015
    Co-Authors: Li Guan, George Z. Chen, Yun Gao, Zhanbin Qin, Xiaomian Wang
    Abstract:

    Solutions of calcium chloride in mixed water and formamide are excellent electrolytes for capacitive Charge Storage in partially oxidised carbon nanotubes at unprecedented sub-zero-temperatures (e.g. 67% capacitance retention at −60 °C).

  • theoretical specific capacitance based on Charge Storage mechanisms of conducting polymers comment on vertically oriented arrays of polyaniline nanorods and their super electrochemical properties
    Chemical Communications, 2011
    Co-Authors: Chuang Peng, George Z. Chen
    Abstract:

    A recently claimed ultra high specific capacitance of 3407 F g−1 for aligned polyaniline nanorods by the titled communication is shown to be contradictory to both the mechanism of Charge Storage in conducting polymers, and the experimental findings in other nanofibrils of polyaniline, and may thus stimulate debate.

Ho Seok Park - One of the best experts on this subject based on the ideXlab platform.

  • elucidating surface redox Charge Storage of phosphorus incorporated graphenes with hierarchical architectures
    Nano Energy, 2015
    Co-Authors: Hae Jin Kim, Jinyong Hong, Young Mee Jung, Kideok D Kwon, Jing Kong, Ho Seok Park
    Abstract:

    Abstract The incorporation of heteroatoms into carbon nanomaterials is extremely crucial for tuning their electronic and surface properties, but phosphorus (P) incorporation into hierarchical structure remains challenging and its Charge Storage mechanism is obscure. Herein, we investigate surface redox Charge Storage of hierarchically structured, P-incorporated graphene architectures (hpGAs). As probed by in-situ and ex-situ spectroscopic techniques and density functional theory, the P=O site of C–P=O bonding with the most favorable proton binding energy is identified and associated with highly reversible and fast pseudocapacitive behavior. As a consequence of synergistic effects arising from compositional and structural features, the hpGAs show dramatic improvements in capacitance, rate capability, and cyclic stability. This work broadens our knowledge about the unique surface Charge Storage phenomenon originating from the controlled heteroatom chemistry using combined spectroscopic and computational methods.

  • unveiling surface redox Charge Storage of interacting two dimensional heteronanosheets in hierarchical architectures
    Nano Letters, 2015
    Co-Authors: Qasim Mahmood, Seongmin Bak, Xiaoqing Yang, Min Gyu Kim, Sol Yun, Hyeon Suk Shin, Woosik Kim, Paul V Braun, Ho Seok Park
    Abstract:

    Two-dimensional (2D) heteronanosheets are currently the focus of intense study due to the unique properties that emerge from the interplay between two low-dimensional nanomaterials with different properties. However, the properties and new phenomena based on the two 2D heteronanosheets interacting in a 3D hierarchical architecture have yet to be explored. Here, we unveil the surface redox Charge Storage mechanism of surface-exposed WS2 nanosheets assembled in a 3D hierarchical heterostructure using in situ synchrotron X-ray absorption and Raman spectroscopic methods. The surface dominating redox Charge Storage of WS2 is manifested in a highly reversible and ultrafast capacitive fashion due to the interaction of heteronanosheets and the 3D connectivity of the hierarchical structure. In contrast, compositionally identical 2D WS2 structures fail to provide a fast and high capacitance with different modes of lattice vibration. The distinctive surface capacitive behavior of 3D hierarchically structured heteron...

Bruce Dunn - One of the best experts on this subject based on the ideXlab platform.

  • oxygen vacancies enhance pseudocapacitive Charge Storage properties of moo3 x
    Nature Materials, 2017
    Co-Authors: Hyungseok Kim, John B Cook, Bruce Dunn, Sarah H Tolbert, Hao Lin, Vidvuds Ozolins
    Abstract:

    The short charging times and high power capabilities associated with capacitive energy Storage make this approach an attractive alternative to batteries. One limitation of electrochemical capacitors is their low energy density and for this reason, there is widespread interest in pseudocapacitive materials that use Faradaic reactions to store Charge. One candidate pseudocapacitive material is orthorhombic MoO3 (α-MoO3), a layered compound with a high theoretical capacity for lithium (279 mA h g-1 or 1,005 C g-1). Here, we report on the properties of reduced α-MoO3-x(R-MoO3-x) and compare it with fully oxidized α-MoO3 (F-MoO3). The introduction of oxygen vacancies leads to a larger interlayer spacing that promotes faster Charge Storage kinetics and enables the α-MoO3 structure to be retained during the insertion and removal of Li ions. The higher specific capacity of the R-MoO3-x is attributed to the reversible formation of a significant amount of Mo4+ following lithiation. This study underscores the potential importance of incorporating oxygen vacancies into transition metal oxides as a strategy for increasing the Charge Storage kinetics of redox-active materials.

  • pseudocapacitive Charge Storage in thick composite mos 2 nanocrystal based electrodes
    Advanced Energy Materials, 2017
    Co-Authors: John B Cook, Hyungseok Kim, Terri C Lin, Chunhan Lai, Bruce Dunn, Sarah H Tolbert
    Abstract:

    A synthesis methodology is demonstrated to produce MoS2 nanoparticles with an expanded atomic lamellar structure that are ideal for Faradaic-based capacitive Charge Storage. While much of the work on MoS2 focuses on the high capacity conversion reaction, that process is prone to poor reversibility. The pseudocapacitive intercalation-based Charge Storage reaction of MoS2 is investigated, which is extremely fast and highly reversible. A major challenge in the field of pseudocapacitive-based energy Storage is the development of thick electrodes from nanostructured materials that can sustain the fast inherent kinetics of the active nanocrystalline material. Here a composite electrode comprised of a poly(acrylic acid) binder, carbon fibers, and carbon black additives is utilized. These electrodes deliver a specific capacity of 90 mAh g−1 in less than 20 s and can be cycled 3000 times while retaining over 80% of the original capacity. Quantitative kinetic analysis indicates that over 80% of the Charge Storage in these MoS2 nanocrystals is pseudocapacitive. Asymmetric full cell devices utilizing a MoS2 nanocrystal-based electrode and an activated carbon electrode achieve a maximum power density of 5.3 kW kg−1 (with 6 Wh kg−1 energy density) and a maximum energy density of 37 Wh kg−1 (with 74 W kg−1power density).

Sarah H Tolbert - One of the best experts on this subject based on the ideXlab platform.

  • oxygen vacancies enhance pseudocapacitive Charge Storage properties of moo3 x
    Nature Materials, 2017
    Co-Authors: Hyungseok Kim, John B Cook, Bruce Dunn, Sarah H Tolbert, Hao Lin, Vidvuds Ozolins
    Abstract:

    The short charging times and high power capabilities associated with capacitive energy Storage make this approach an attractive alternative to batteries. One limitation of electrochemical capacitors is their low energy density and for this reason, there is widespread interest in pseudocapacitive materials that use Faradaic reactions to store Charge. One candidate pseudocapacitive material is orthorhombic MoO3 (α-MoO3), a layered compound with a high theoretical capacity for lithium (279 mA h g-1 or 1,005 C g-1). Here, we report on the properties of reduced α-MoO3-x(R-MoO3-x) and compare it with fully oxidized α-MoO3 (F-MoO3). The introduction of oxygen vacancies leads to a larger interlayer spacing that promotes faster Charge Storage kinetics and enables the α-MoO3 structure to be retained during the insertion and removal of Li ions. The higher specific capacity of the R-MoO3-x is attributed to the reversible formation of a significant amount of Mo4+ following lithiation. This study underscores the potential importance of incorporating oxygen vacancies into transition metal oxides as a strategy for increasing the Charge Storage kinetics of redox-active materials.

  • pseudocapacitive Charge Storage in thick composite mos 2 nanocrystal based electrodes
    Advanced Energy Materials, 2017
    Co-Authors: John B Cook, Hyungseok Kim, Terri C Lin, Chunhan Lai, Bruce Dunn, Sarah H Tolbert
    Abstract:

    A synthesis methodology is demonstrated to produce MoS2 nanoparticles with an expanded atomic lamellar structure that are ideal for Faradaic-based capacitive Charge Storage. While much of the work on MoS2 focuses on the high capacity conversion reaction, that process is prone to poor reversibility. The pseudocapacitive intercalation-based Charge Storage reaction of MoS2 is investigated, which is extremely fast and highly reversible. A major challenge in the field of pseudocapacitive-based energy Storage is the development of thick electrodes from nanostructured materials that can sustain the fast inherent kinetics of the active nanocrystalline material. Here a composite electrode comprised of a poly(acrylic acid) binder, carbon fibers, and carbon black additives is utilized. These electrodes deliver a specific capacity of 90 mAh g−1 in less than 20 s and can be cycled 3000 times while retaining over 80% of the original capacity. Quantitative kinetic analysis indicates that over 80% of the Charge Storage in these MoS2 nanocrystals is pseudocapacitive. Asymmetric full cell devices utilizing a MoS2 nanocrystal-based electrode and an activated carbon electrode achieve a maximum power density of 5.3 kW kg−1 (with 6 Wh kg−1 energy density) and a maximum energy density of 37 Wh kg−1 (with 74 W kg−1power density).

Rajan Jose - One of the best experts on this subject based on the ideXlab platform.

  • Physical reduction of graphene oxide for supercapacitive Charge Storage
    'Elsevier BV', 2020
    Co-Authors: Yar Asfand, Dennis, John Ojur, Mohamed Saheed, Mohamed Shuaib, Norani, Muti Mohamed, Irshad, Muhammad Imran, Mumtaz Asad, Rajan Jose
    Abstract:

    The oxygen-containing functional groups in graphene oxide (GO) impose considerable limitations in their applications requiring chemical inertness and electrical conductivity such as supercapacitive Charge Storage. Chemical reduction of GO has been frequently employed; however, processing of large volume of hazardous solvents impose severe environmental concerns. This article demonstrates the optical reduction of freeze dried GO into reduced GO (rGO) by a computer controlled laser engraver as a plug and operate device. The conversion of GO into rGO as a function of laser powers has been monitored by X-ray diffraction, X-ray photon electron spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, Thermogravimetric analysis, and field emission scanning microscopy. The rGO thus produced has been evaluated for their Charge Storage capability in aqueous electrolytes. The best performing laboratory prototype demonstrated one of the best energy density of rGO electrodes in an aqueous electrolyte. The promising properties of the supercapacitors thereby developed as well as cost effectiveness and potential for large scale production engaging laser engraving process, the present work offers numerous potentials for deploying efficient and low cost supercapacitive devices

  • Void Space Control in Porous Carbon for High-Density Supercapacitive Charge Storage
    'American Chemical Society (ACS)', 2020
    Co-Authors: Vijayan, Bincy Lathakumari, Izan Izwan Misnon, Reddy M. Venkatashamy, Adams Stefan, Nurul Khairiyyah, Mohd Zain, Yang Chun-chen, Anilkumar, Gopinathan M., Rajan Jose
    Abstract:

    High density Charge (energy) Storage under supercapacitive mode requires an electrode which would deliver larger space for Charge accumulation and offer larger electrochemical potential difference at an electrode–electrolyte interface. Porous carbon has been a preferred electrode for commercial supercapacitors; however, the Charge storability is much lower to the state-of-the-art Charge Storage devices such as lithium ion batteries. We show that one of the primary limiting factors is the voids in porous carbon, which do not contribute to the capacitance as their sizes are much larger than the size of the solvated/unsolvated ions in the electrolyte. We activate these voids by filling them with a flower-shaped 3D hierarchical pseudocapacitive material (MnCo2O4) by assuming that flower-shaped fillers would provide additional easily accessible surface for Charge adsorption. Less than 10wt.% MnCo2O4 in these voids through a simple wet impregnation results in five-fold increase in Charge storability of porous carbon from palm kernel shells. Laboratory prototypes of electrochemical double layer capacitors are fabricated using the void-filled-carbon electrodes, which show five-fold higher specific energy than that of pure carbon and are cycled over 5000 times with >95% capacitance retention. The present strategy of activating the voids by hierarchical 3D nanostructures could be applied to build high performance energy Storage devices

  • continuous nanobelts of nickel oxide cobalt oxide hybrid with improved capacitive Charge Storage properties
    Materials & Design, 2017
    Co-Authors: Midhun Harilal, Syam G Krishnan, Bincy Lathakumary Vijayan, Venkatashamy M Reddy, Stefan Adams, Andrew R Barron, Mashitah M Yusoff, Rajan Jose
    Abstract:

    This paper reports the synthesis of continuous nanobelts, whose thickness is less than half of its pore diameter, of a material hybrid composing of nanograins of nickel oxide and cobalt oxide by electrospinning technique and their capacitive Charge Storage properties. While the constituent binary metal oxides (NiO and Co3O4) formed solid cylindrical nanofibers the hybrid and a stoichiometric compound in the Ni-Co-O system, i.e., spinel-type NiCo2O4, formed as thin nanobelts due to the magnetic interaction between nickel and cobalt ions. The nanobelts showed six-fold larger surface area, wider pores, and impressive Charge Storage capabilities compared to the cylindrical fibres. The hybrid nanobelts showed high specific capacitance (CS ~ 1250 F g− 1 at 10 A g− 1 in 6 M KOH) with high capacity retention, which is appreciably larger than found for the stoichiometric compound (~ 970 F g− 1 at 10 A g− 1). It is shown that the hybrid nanobelts have lower internal resistance (1.3 Ω), higher diffusion coefficient (4.6 × 10− 13 cm2 s− 1) and smaller relaxation time (0.03 s) than the benchmark materials studied here.

  • Effect of processing parameters on the Charge Storage properties of MgCo2O4 electrodes
    'Elsevier BV', 2017
    Co-Authors: Krishnan, Syam G., Harilal Midhun, Izan Izwan Misnon, Reddy M. Venkatashamy, Adams Stefan, Rajan Jose
    Abstract:

    Three morphologies of magnesium cobaltite (MgCo2O4), viz. cuboidal microcrystals, nanoflowers, and nanospheres, were synthesized using hydrothermal and molten salt methods and evaluated their electrochemical energy Storage properties. Among them cuboidal microcrystal and nanoflowers were obtained by a facile hydrothermal route – the former with ethylene glycol and the latter with hexadecyltrimethylammonium bromide as surfactants. The cuboidal microcrystals showed layered flake microstructure with an appreciable space between the layers (~ 100 nm), which would facilitate ion movement between the flakes. The electrochemical studies of the materials revealed the superiority of MgCo2O4 cuboidal microcrystals as a Charge Storage medium over the nanoflowers and nanospheres, the reasons for this is deeply investigated and reported herewith. The specific Charge stored in the MgCo2O4 cuboidal microcrystal electrode was ~ 345 C g−1 at a specific current of 1 A g−1 which was superior to nanoflowers (~ 178 C g−1) and nanospheres (~ 139 C g−1) at the similar current density in 3 M LiOH electrolyte. The MgCo2O4 cuboidal microcrystals also demonstrated superior Charge retention (~ 110%) after 3000 cycles over the other electrodes demonstrating its practical utility as a Charge Storage material