Publications (70) View all
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Article: Edge-Selectively Functionalized Graphene Nanoplatelets.
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ABSTRACT: Graphene, as a single layer of graphite, is currently the focal point of research into condensed matter owing to its promising properties, such as exceptional mechanical strength, high thermal conductivity, large specific surface area, and ultrahigh electron-transport properties. Therefore, various physical and chemical synthetic procedures to prepare graphene and/or graphene nanoplatelets have been rapidly developed. Specifically, the synthesis of edge-selectively functionalized graphene (EFG) has been recently reported by using simple and scalable approaches, such as "direct" Friedel-Crafts acylation reactions in a mild acidic medium and a mechanochemical ball-milling process. In these approaches, chemical functionalization predominantly take place at the edges of the graphitic layers via the covalent attachment of targeted organic "molecular wedges". In addition, the distortion of the crystalline structures in the basal plane, which is beneficial for preserving the unique properties of the graphitic framework, can be minimized. In addition, the efficient exfoliation of graphene can be achieved, owing to the strong repulsive forces from the covalently linked wedges and strong shear forces during the reaction. Furthermore, EFG shows promising potential in many useful applications, such as highly conductive large-area films, metal-free electrocatalysts for the oxygen-reduction reaction (ORR), and as additives in composite materials with enhanced properties. Herein, we summarize the recent progress and general aspects of EFG, including synthesis, reaction mechanism, properties, and applications.The Chemical Record 04/2013; · 4.38 Impact Factor -
Article: Edge-Exfoliated Graphites for Facile Kinetics of Delithiation.
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ABSTRACT: As high rate charge and discharge characteristics of energy storage devices become more important with the market of electric vehicles intensively growing, the kinetics of lithiation or delithiation of electrode materials for lithium ion batteries are required to be enhanced. Graphites, the most widely used anode materials, have a limited power density at high discharge rates while their alternatives such as silicon and transition metal oxides show even inferior rate capability. This work was motivated from an idea of what if the edge opening of graphite was zipped more open to lithium ions in electrolyte. By edge-selective functionalization, the peripheral d-spacing of graphite (d0) was locally controlled. Larger values of d0 led to higher capacity especially at high discharge rates. Around two-fold enhancement of capacity or energy density was achieved at 50C discharge rate from 110 mAh/g to 190 mAh/g by exfoliating graphite locally in its edge region. Also, the d0 dependency of delithiation kinetics confirmed that the electrochemical step of Li+ influx into or efflux out of interlayer space of graphite is possibly the rate determining step of lithiation or delithiation.ACS Nano 11/2012; · 10.77 Impact Factor -
Article: Large-Scale Production of Edge-Selectively Functionalized Graphene Nanoplatelets via Ball-Milling and Their Use as Metal-Free Electrocatalysts for Oxygen Reduction Reaction.
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ABSTRACT: Edge-selectively functionalized graphene nanoplatelets (EFGnPs) with different functional groups were effi-ciently prepared simply by dry ball-milling graphite in the presence of hydrogen, carbon dioxide, sulfur trioxide, or carbon dioxide/sulfur trioxide mixture. Upon exposure to air moisture, the resultant hydrogen- (HGnP), carboxylic acid- (CGnP), sulfonic acid- (SGnP), and carboxylic acid/sulfonic acid- (CSGnP) functionalized GnPs readily dispersed into various polar solvents, including neutral water. The resultant EFGnPs were then used as electrocatalysts for oxygen reduction reaction (ORR) in an alkaline electrolyte. It was found that the edge polar nature of the newly-prepared EFGnPs without heteroatom doping into their basal plane played an important role in regulating the ORR efficiency with the electrocatalytic activity in the order of SGnP > CSGnP > CGnP > HGnP > pristine graphite. More importantly, the sulfur-containing SGnP and CSGnP were found to have a superior ORR performance to commercially available platinum-based electrocatalyst (Pt/C).Journal of the American Chemical Society 10/2012; · 9.91 Impact Factor -
Article: Strain-induced delamination of edge-grafted graphite.
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ABSTRACT: Edge-selectively grafted graphite (EGG) with poly(ether-ketone) was prepared by the Friedel-Crafts acylation in a mild polyphosphoric acid (PPA)-phosphorous pentoxide (P(2)O(5)) mixture. The homogeneous reaction dope was coagulated in air moisture at different temperatures. The morphology of expanded EGG was changed from balls, balls/rods and rods with respect to coagulation temperatures of 80, 60, 40 and 25 °C, respectively.Chemical Communications 10/2012; 48(90):11109-11. · 6.17 Impact Factor -
Article: Water-dispersible, sulfonated hyperbranched poly(ether-ketone) grafted multiwalled carbon nanotubes as oxygen reduction catalysts.
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ABSTRACT: To endorse sufficient water affinity to multiwalled carbon nanotubes (MWCNTs), dendritic hyperbranched poly(ether-ketone) (HPEK) was first covalently grafted to the surface of a MWCNT via a Friedel-Crafts acylation reaction. The resultant HPEK-grafted MWCNT (HPEK-g-MWCNT) was subsequently sulfonated in chlorosulfonic acid to produce sulfonated HPEK-g-MWCNT (SHPEK-g-MWCNT), which is dispersible well in water showing a zeta potential value of -57.8 mV. The SHPEK-g-MWCNT paper simply formed by filtration of aqueous dispersion has a sheet resistance as low as 63 Ω/sq. Its thin film shows a high electrocatalytic activity for oxygen reduction reaction (ORR). Thus, the newly produced water-dispersible MWCNT is a new class of high performance cathode material for ORR.ACS Nano 06/2012; 6(7):6345-55. · 10.77 Impact Factor
