Electroactive nanoparticle directed assembly of functionalized graphene nanosheets into hierarchical structures with hybrid compositions for flexible supercapacitors.

Choi, Bong Gill,Huh, Yun Suk,Hong, Won Hi,Erickson, David,Park, Ho Seok RSC Pub 2013 Nanoscale Vol.5 No.9

<P>Hierarchical structures of hybrid materials with the controlled compositions have been shown to offer a breakthrough for energy storage and conversion. Here, we report the integrative assembly of chemically modified graphene (CMG) building blocks into hierarchical complex structures with the hybrid composition for high performance flexible pseudocapacitors. The formation mechanism of hierarchical CMG/Nafion/RuO2 (CMGNR) microspheres, which is triggered by the cooperative interplay during the in situ synthesis of RuO2 nanoparticles (NPs), was extensively investigated. In particular, the hierarchical CMGNR microspheres consisting of the aggregates of CMG/Nafion (CMGN) nanosheets and RuO2 NPs provided large surface area and facile ion accessibility to storage sites, while the interconnected nanosheets offered continuous electron pathways and mechanical integrity. The synergistic effect of CMGNR hybrids on the supercapacitor (SC) performance was derived from the hybrid composition of pseudocapacitive RuO2 NPs with the conductive CMGNs as well as from structural features. Consequently, the CMGNR-SCs showed a specific capacitance as high as 160 F g(-1), three-fold higher than that of conventional graphene SCs, and a capacitance retention of >95% of the maximum value even after severe bending and 1000 charge-discharge tests due to the structural and compositional features.</P>

Microwave-assisted synthesis of highly water-soluble graphene towards electrical DNA sensor

Choi, Bong Gill,Park, HoSeok,Yang, Min Ho,Jung, Young Mee,Lee, Sang Yup,Hong, Won Hi,Park, Tae Jung The Royal Society of Chemistry 2010 Nanoscale Vol.2 No.12

3D Macroporous Graphene Frameworks for Supercapacitors with High Energy and Power Densities

Choi, Bong Gill,Yang, MinHo,Hong, Won Hi,Choi, Jang Wook,Huh, Yun Suk American Chemical Society 2012 ACS NANO Vol.6 No.5

<P>In order to develop energy storage devices with high power and energy densities, electrodes should hold well-defined pathways for efficient ionic and electronic transport. Herein, we demonstrate high-performance supercapacitors by building a three-dimensional (3D) macroporous structure that consists of chemically modified graphene (CMG). These 3D macroporous electrodes, namely, embossed-CMG (e-CMG) films, were fabricated by using polystyrene colloidal particles as a sacrificial template. Furthermore, for further capacitance boost, a thin layer of MnO<SUB>2</SUB> was additionally deposited onto e-CMG. The porous graphene structure with a large surface area facilitates fast ionic transport within the electrode while preserving decent electronic conductivity and thus endows MnO<SUB>2</SUB>/e-CMG composite electrodes with excellent electrochemical properties such as a specific capacitance of 389 F/g at 1 A/g and 97.7% capacitance retention upon a current increase to 35 A/g. Moreover, when the MnO<SUB>2</SUB>/e-CMG composite electrode was asymmetrically assembled with an e-CMG electrode, the assembled full cell shows remarkable cell performance: energy density of 44 Wh/kg, power density of 25 kW/kg, and excellent cycle life.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-5/nn3003345/production/images/medium/nn-2012-003345_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn3003345'>ACS Electronic Supporting Info</A></P>

Preparation of the MnO₂/Macroporous Carbon for PET Glycolysis

Choi, Bong Gill,Yang, MinHo The Korean Powder Metallurgy Institute 2018 한국분말재료학회지 (KPMI) Vol.25 No.3

Plastic pollution is threatening human health and ecosystems, resulting in one of the biggest challenges that humanity has ever faced. Therefore, this study focuses on the preparation of macroporous carbon from biowaste (MC)-supported manganese oxide ($MnO_2$) as an efficient, reusable, and robust catalyst for the recycling of poly(ethylene terephthalate) (PET) waste. As-prepared $MnO_2/MC$ composites have a hierarchical pore network and a large surface area ($376.16m^2/g$) with a narrow size distribution. $MnO_2/MC$ shows a maximum yield (98%) of bis(2-hydroxyethyl)terephthalate (BHET) after glycolysis reaction for 120 min. Furthermore, $MnO_2/MC$ can be reused at least nine times with a negligible decrease in BHET yield. Based on this remarkable catalytic performance, we expect that $MnO_2$-based heterogeneous catalysts have the potential to be introduced into the PET recycling industry.

Programmable Peptide-Directed One Dimensional Array of Gold Nanoparticles on Single-Walled Carbon Nanotubes for Biosensor

Bong Gill CHOI,Min Ho YANG,Tae Jung PARK,Sang Yup LEE 한국생물공학회 2011 한국생물공학회 학술대회 Vol.2011 No.4

Programmable peptide-directed two dimensional arrays of various nanoparticles on graphene sheets

Choi, Bong Gill,Yang, Min Ho,Park, Tae Jung,Huh, Yun Suk,Lee, Sang Yup,Hong, Won Hi,Park, HoSeok Royal Society of Chemistry 2011 Nanoscale Vol.3 No.8

<P>In this research, we report an innovative, chemical strategy for the <I>in situ</I> synthesis and direct two-dimensional (2D) arraying of various nanoparticles (NPs) on graphenes using both programmed-peptides as directing agents and graphenes as pre-formed 2D templates. The peptides were designed for manipulating the enthalpic (coupled interactions) constraint of the global system. Along with the functionalization of graphene for the stable dispersion, peptides directed the growth and array of NPs in a controllable manner. In particular, the sequences of peptides were encoded by the combination of glutamic acid (E), glycine (G), and phenylalanine (F) amino acids as follows: (E-G-F)<SUB>3</SUB>-G, with E for the interaction with NPs and F and G for the interaction with graphenes. For the entropic (restricted geometry) constraint, graphene was used as a 2D scaffold to tune the size, density, and position of NPs, while maintaining the intrinsic properties for electrochemical applications. The excellent quality of the resultant hybrids was demonstrated by their high electrocatalytic activity in the electrooxidation of methanol. This synergistic combination of peptides and graphenes allowed for a uniform 2D array and spontaneous organization of various NPs (<I>i.e.</I>, Pt, Au, Pd, and Ru), which would greatly expand the utility and versatility of this approach for the synthesis and array of the advanced nanomaterials.</P> <P>Graphic Abstract</P><P>Direct synthesis and uniform two-dimensional arraying of discrete nanoparticles were readily accomplished using programmable peptides as directing agents and graphenes as pre-formed 2D templates. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1nr10276a'> </P>

Facilitated Ion Transport in All-Solid-State Flexible Supercapacitors

Choi, Bong Gill,Hong, Jinkee,Hong, Won Hi,Hammond, Paula T.,Park, HoSeok American Chemical Society 2011 ACS NANO Vol.5 No.9

<P>The realization of highly flexible and all-solid-state energy-storage devices strongly depends on both the electrical properties and mechanical integrity of the constitutive materials and the controlled assembly of electrode and solid electrolyte. Herein we report the preparation of all-solid-state flexible supercapacitors (SCs) through the easy assembly of functionalized reduced graphene oxide (f-RGO) thin films (as electrode) and solvent-cast Nafion electrolyte membranes (as electrolyte and separator). In particular, the f-RGO-based SCs (f-RGO-SCs) showed a 2-fold higher specific capacitance (118.5 F/g at 1 A/g) and rate capability (90% retention at 30 A/g) compared to those of all-solid-state graphene SCs (62.3 F/g at 1A/g and 48% retention at 30 A/g). As proven by the 4-fold faster relaxation of the f-RGO-SCs than that of the RGO-SCs and more capacitive behavior of the former at the low-frequency region, these results were attributed to the facilitated ionic transport at the electrical double layer by means of the interfacial engineering of RGO by Nafion. Moreover, the superiority of all-solid-state flexible f-RGO-SCs was demonstrated by the good performance durability under the 1000 cycles of charging and discharging due to the mechanical integrity as a consequence of the interconnected networking structures. Therefore, this research provides new insight into the rational design and fabrication of all-solid-state flexible energy-storage devices as well as the fundamental understanding of ion and charge transport at the interface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-9/nn202020w/production/images/medium/nn-2011-02020w_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn202020w'>ACS Electronic Supporting Info</A></P>

Innovative Polymer Nanocomposite Electrolytes: Nanoscale Manipulation of Ion Channels by Functionalized Graphenes

Choi, Bong Gill,Hong, Jinkee,Park, Young Chul,Jung, Doo Hwan,Hong, Won Hi,Hammond, Paula T.,Park, HoSeok American Chemical Society 2011 ACS NANO Vol.5 No.6

<P>The chemistry and structure of ion channels within the polymer electrolytes are of prime importance for studying the transport properties of electrolytes as well as for developing high-performance electrochemical devices. Despite intensive efforts on the synthesis of polymer electrolytes, few studies have demonstrated enhanced target ion conduction while suppressing unfavorable ion or mass transport because the undesirable transport occurs through an identical pathway. Herein, we report an innovative, chemical strategy for the synthesis of polymer electrolytes whose ion-conducting channels are physically and chemically modulated by the ionic (not electronic) conductive, functionalized graphenes and for a fundamental understanding of ion and mass transport occurring in nanoscale ionic clusters. The functionalized graphenes controlled the state of water by means of nanoscale manipulation of the physical geometry and chemical functionality of ionic channels. Furthermore, the confinement of bound water within the reorganized nanochannels of composite membranes was confirmed by the enhanced proton conductivity at high temperature and the low activation energy for ionic conduction through a Grotthus-type mechanism. The selectively facilitated transport behavior of composite membranes such as high proton conductivity and low methanol crossover was attributed to the confined bound water, resulting in high-performance fuel cells.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2011/ancac3.2011.5.issue-6/nn2013113/production/images/medium/nn-2011-013113_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn2013113'>ACS Electronic Supporting Info</A></P>

Charge transfer interactions between conjugated block copolymers and reduced graphene oxides

Choi, Bong Gill,Hong, Won Hi,Jung, Young Mee,Park, HoSeok Royal Society of Chemistry 2011 Chemical communications Vol.47 No.37

<P>The charge transfer interactions between reduced graphene oxides and conjugated block copolymers were confirmed by various spectroscopic methods, giving rise to manipulation of the electrical properties of the former.</P> <P>Graphic Abstract</P><P>The charge transfer interactions between graphenes and conjugated block copolymers, analyzed by spectroscopic methods, lead to manipulation of the electrical properties. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c1cc13465e'> </P>

Enhanced Pseudocapacitance of Ionic Liquid/Cobalt Hydroxide Nanohybrids

Choi, Bong Gill,Yang, MinHo,Jung, Sung Chul,Lee, Kyoung G.,Kim, Jin-Gyu,Park, HoSeok,Park, Tae Jung,Lee, Sang Bok,Han, Young-Kyu,Huh, Yun Suk American Chemical Society 2013 ACS NANO Vol.7 No.3

<P>Development of nanostructured materials with enhanced redox reaction capabilities is important for achieving high energy and power densities in energy storage systems. Here, we demonstrate that the nanohybridization of ionic liquids (ILs, 1-butyl-3-methylimidazolium tetrafluoroborate) and cobalt hydroxide (Co(OH)<SUB>2</SUB>) through ionothermal synthesis leads to a rapid and reversible redox reaction. The as-synthesized IL-Co(OH)<SUB>2</SUB> has a favorable, tailored morphology with a large surface area of 400.4 m<SUP>2</SUP>/g and a mesopore size of 4.8 nm. In particular, the IL-Co(OH)<SUB>2</SUB>-based electrode exhibits improvement in electrochemical characteristics compared with bare Co(OH)<SUB>2</SUB>, showing a high specific capacitance of 859 F/g at 1 A/g, high-rate capability (∼95% retention at 30 A/g), and excellent cycling performance (∼96% retention over 1000 cycles). AC impedance analysis demonstrates that the introduction of ILs on Co(OH)<SUB>2</SUB> facilitates ion transport and charge transfer: IL-Co(OH)<SUB>2</SUB> shows a higher ion diffusion coefficient (1.06 × 10<SUP>–11</SUP> cm<SUP>2</SUP>/s) and lower charge transfer resistance (1.53 Ω) than those of bare Co(OH)<SUB>2</SUB> (2.55 × 10<SUP>–12</SUP> cm<SUP>2</SUP>/s and 2.59 Ω). Our density functional theory (DFT) calculations reveal that the IL molecules, consisting of anion and cation groups, enable easier hydrogen desorption/adsorption process, that is, a more favorable redox reaction on the Co(OH)<SUB>2</SUB> surface.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2013/ancac3.2013.7.issue-3/nn305750s/production/images/medium/nn-2012-05750s_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn305750s'>ACS Electronic Supporting Info</A></P>