Showing papers by "Nam Hoon Kim published in 2017"
TL;DR: In this paper, a 3D porous structure based on carbon dot (CD)-supported copper sulphide (CuS)-decorated graphene oxide (GO) hydrogel was designed to improve the specific capacitance, cyclic stability and energy density of CuS as well as GO based supercapacitors.
118 citations
TL;DR: In this article, the sustainable production of H2O2 without organic electron donors by a CdS-reduced graphene oxide (RGO) photocatalyst in sunlight with water and oxygen as resources was demonstrated.
117 citations
TL;DR: In this paper, a novel strategy for synthesis of highly porous nitrogen-sulfur co-doped graphene nanoribbons (NS-GNRs) with enhanced active sites was developed.
116 citations
TL;DR: In this paper, a novel ultra-thin copper nickel sulfide (Cu1−xNixS) nanosheet array supercapacitor electrode was constructed on a 3D Ni backbone through a powerful anion exchange technique and it demonstrated a unique architecture with a substantial degree of porosity.
Abstract: Novel supercapacitor electrodes comprising hierarchical architectures with high specific surface areas, unique porosities, excellent conductivities, and admirable mechanical stabilities are necessary for developing high-performance solid-state supercapacitors. Herein, a novel ultra-thin copper nickel sulfide (Cu1−xNixS) nanosheet array supercapacitor electrode was constructed on a 3D Ni backbone through a powerful anion exchange technique and it demonstrated a unique architecture with a substantial degree of porosity. Accordingly, Cu1−xNixS plays an imperative role in the electrochemical energy storage characteristics of the electrode by accomplishing an ultra-high areal capacitance of 5.88 F cm−2 and a specific capacitance of 2672 F g−1 at a current density of 2 mA cm−2 with an excellent rate capability (71.26% capacitance retention at 20 mA cm−2) and a superior cycling performance (97.33% capacitance retention after 10 000 cycles). To design asymmetric supercapacitors (ASCs), Cu1−xNixS and N, S co-doped graphene nanosheets (NSGNSs) are employed as positive and negative electrodes, respectively. Remarkably, the fabricated ASC exhibits a potential window of ∼1.8 V, which demonstrates an ultra-high energy density of ∼94.05 W h kg−1 at 1.09 kW kg−1 as well as an excellent life cycle (95.86% capacitance retention after 10 000 cycles). Owing to this fact, this investigation offers a simple, scalable, and cost-effective approach for the fabrication of other ternary transition metal sulfides (TMSs), emphasizing great prospects in next-generation energy storage applications.
113 citations
TL;DR: This research first proposes hierarchical Co-Fe3 O4 NS@NG hybrid as an ultrafast charge-discharge anode material for the ASC device, that holds great potential for the development of high-performance energy storage devices.
Abstract: Hierarchical nanostructure, high electrical conductivity, extraordinary specific surface area, and unique porous architecture are essential properties in energy storage and conversion studies. A new type of hierarchical 3D cobalt encapsulated Fe3O4 nanosphere is successfully developed on N-graphene sheet (Co−Fe3O4 NS@NG) hybrid with unique nanostructure by simple, scalable, and efficient solvothermal technique. When applied as an electrode material for supercapacitors, hierarchical Co−Fe3O4 NS@NG hybrid shows an ultrahigh specific capacitance (775 F g−1 at a current density of 1 A g−1) with exceptional rate capability (475 F g−1 at current density of 50 A g−1), and admirable cycling performance (97.1% capacitance retention after 10 000 cycles). Furthermore, the fabricated Co−Fe3O4 NS@NG//CoMnO3@NG asymmetric supercapacitor (ASC) device exhibits a high energy density of 89.1 Wh kg−1 at power density of 0.901 kW kg−1, and outstanding cycling performance (89.3% capacitance retention after 10 000 cycles). Such eminent electrochemical properties of the Co−Fe3O4 NS@NG are due to the high electrical conductivity, ultrahigh surface area, and unique porous architecture. This research first proposes hierarchical Co−Fe3O4 NS@NG hybrid as an ultrafast charge−discharge anode material for the ASC device, that holds great potential for the development of high-performance energy storage devices.
105 citations
TL;DR: A facile and cost-effective anion exchange technique to fabricate a layered, multifaceted, free standing, ultra-thin ternary cobalt molybdenum sulfide nanosheet (Co-Mo-S NS) architecture grown on a 3D porous Ni foam substrate with great potential for future energy storage devices.
Abstract: Layered transition metal sulfides (TMS) are emerging as advanced materials for energy storage and conversion applications. In this work, we report a facile and cost-effective anion exchange technique to fabricate a layered, multifaceted, free standing, ultra-thin ternary cobalt molybdenum sulfide nanosheet (Co–Mo–S NS) architecture grown on a 3D porous Ni foam substrate. The unique Co–Mo layered double hydroxides are first synthesized as precursors and consequently transformed into ultra-thin Co–Mo–S NS. When employed as an electrode for supercapacitors, the Co–Mo–S NS delivered an ultra-high specific capacitance of 2343 F g−1 at a current density of 1 mA cm−2 with tremendous rate capability and extraordinary cycling performance (96.6% capacitance retention after 20 000 cycles). Furthermore, assembled Co–Mo–S/nitrogen doped graphene nanosheets (NGNS) in an asymmetric supercapacitor (ASC) device delivered an excellent energy density of 89.6 Wh kg−1, an amazing power density of 20.07 kW kg−1, and superior cycling performance (86.8% capacitance retention after 50 000 cycles). Such exceptional electrochemical performance of Co–Mo–S NS is ascribed to the good electrical contact with the 3D Ni foam, ultra-high contact area with the electrolyte, and enhanced architectural softening during the charging/discharging process. It is expected that the fabricated, unique, ultra-thin Co–Mo–S NS have great potential for future energy storage devices.
100 citations
TL;DR: 3D N-Co-CNT@NG sensors are also proven to be appropriate for the detection of glucose as well as H2O2 in human serum and outstanding electrochemical performance can be endorsed to the large electroactive surface area, unique porous architecture, highly conductive networks, and synergistic interaction in the novel 3D nanocomposite.
85 citations
TL;DR: In this article, an asymmetric supercapacitor (ASC) was fabricated using sulfonated polyaniline (SPANI) functionalized reduced graphene oxide (G-1) as positive electrode and chemically reduced GO (RGO) as a negative electrode.
83 citations
TL;DR: Results exhibit that the core-shell CuS@CQDs@C HNS nanostructure is one of the potential candidates for supercapacitors and photocatalytic applications.
Abstract: A controlled structural morphology, high specific surface area, large void space, and excellent biocompatibility are typical favorable properties in electrochemical energy storage and photocatalytic studies; however, a complete understanding about this essential topic still remains a great challenge. Herein, we have developed a new type of functionalized carbon hollow-structured nanospheres based on core–shell copper sulfide@carbon quantum dots (CQDs)@carbon hollow nanosphere (CHNS) architecture. This CuS@CQDs@C HNS is accomplished by a simple, scalable, in situ single-step hydrothermal method to produce the material that can be employed as an electrode for electrochemical energy storage and photocatalytic applications. Impressively, the CuS@CQDs@C HNS nanostructure delivers exceptional electrochemical energy storage characteristics with high specific capacitance (618 F g–1 at a current density of 1 A g–1) and an excellent rate capability with an extraordinary capacitance (462 F g–1 at current density of ...
81 citations
TL;DR: A nanohybrid based on porous and hollow interior structured La NiO3 stabilized nitrogen and sulfur codoped graphene (LaNiO3 /N,S-Gr) is successfully synthesized for the first time and opens an interesting class of highly efficient non-Pt catalysts for ORR in alkaline media.
Abstract: A nanohybrid based on porous and hollow interior structured LaNiO3 stabilized nitrogen and sulfur codoped graphene (LaNiO3/N,S-Gr) is successfully synthesized for the first time. Such a nanohybrid as an electrocatalyst shows high catalytic activity for oxygen reduction reaction (ORR) in O2-saturated 0.1 m KOH media. In addition, it demonstrates a comparable catalytic activity, longer working stability, and much better alcohol tolerance compared with commercial Pt/C behavior in same experiment condition. The obtained results are attributed to synergistic effects from the enhanced electrocatalytic active sites on the rich pore channels of porous hollow-structured LaNiO3 spheres and heteroatom doped efficiency on graphene structure. In addition, N,S-Gr can meritoriously stabilize monodispersion of the LaNiO3 spheres, and act as medium bridging for high electrical conductivity, thereby providing large active surface area for O2 adsorption, accelerating reduction reaction, and improving electrochemical stability. Such a hybrid opens an interesting class of highly efficient non-Pt catalysts for ORR in alkaline media.
71 citations
TL;DR: In this article, a cobalt monoxide@manganese oxide core-shell nanostructure on 3D Ni foam (CoO@MnO2/Ni foam) was proposed to produce a material that can be employed as an advanced electrode material for high-energy solid state asymmetric supercapacitors (ASCs).
Abstract: A unique morphology, high specific surface area, extraordinary porosity, and excellent conductive networks are typical favorable properties of pseudocapacitors; however, fully comprehending and interpreting this substantive topic still remains a great challenge. Herein, we present a new strategy for the direct growth of a cobalt monoxide@manganese oxide core–shell nanostructure on 3D Ni foam (CoO@MnO2/Ni foam). This is accomplished by simple, scalable, in situ fabrication methods to produce a material that can be employed as an advanced electrode material for high-energy solid state asymmetric supercapacitors (ASCs). The cost-effective, binder-free 3D CoO@MnO2 core–shell nanostructure delivers excellent electrochemical properties with an ultra-high specific capacitance (1835 F g−1 at a current density of 1 A g−1), tremendous rate capabilities with an extraordinary capacitance of 1198 F g−1 at a current density of 20 A g−1, and outstanding stability (97.7% capacitance retention after 10 000 cycles). ASCs with a maximum potential window of 1.8 V are fabricated by using a 3D CoO@MnO2 core–shell nanohybrid as the positive electrode and N-doped graphene (NG) as the negative electrode in order to validate the outstanding performance for practical energy storage devices. Impressively, the ASCs delivered a high specific capacitance (191 F g−1 at 1 A g−1), excellent energy density (∼85.9 W h kg−1), an ultra-high power density (∼16 769 W kg−1 at 51.7 W h kg−1), and remarkable cycle stability (86.8% capacitance retention after 10 000 cycles). These findings provide a new method to design 3D CoO@MnO2 core–shell nanostructures that are cost-effective and binder-free electrode materials for the development of high-performance energy storage devices.
TL;DR: The obtained results imply that a high quality graphene-encapsulated AuAg alloy (AuAg-GR) nanohybrid is a potential candidate for synthesizing electrochemical sensors in requirement of high sensitivity, long-term stability, and good reproducibility.
TL;DR: In this paper, a facile, cost effective and additive-free successive ionic layer adsorption and reaction (SILAR) technique is demonstrated to develop layer-by-layer assembly of reduced graphene oxide (RGO) and MnO2 (MnO2-RGOSILAR), for designing light-weight and small size supercapacitor electrode.
TL;DR: In this article, a novel hybrid of 2D NiMo-S nanosheet integrated nitrogen doped graphene (NG) is successfully developed via a simple, scalable, and cost-effective hydrothermal process, and its application towards energy conversion devices is explored.
Abstract: A novel hybrid of 2D Ni–Mo–S nanosheet integrated nitrogen doped graphene (NG) is successfully developed via a simple, scalable, and cost-effective hydrothermal process, and its application towards energy conversion devices is explored. The presence of exclusive mesoporous structures combined with an excellent conducting NG network in the Ni–Mo–S/NG hybrid exhibits superior electrocatalytic activities as a counter electrode (CE) for dye-sensitized solar cells (DSSCs) and the oxygen reduction reaction (ORR) in alkaline electrolytes. SEM and TEM studies demonstrate the uniform anchoring of ultra-thin Ni–Mo–S nanosheets on NG networks. The hierarchical Ni–Mo–S/NG hybrid outperformed Ni–Mo–S, NG, and Pt when used as a CE in DSSCs and showed excellent ORR activity. The power conversion efficiency (PCE) of DSSCs with the Ni–Mo–S/NG hybrid as the CE achieved 9.89%, outperforming conventional Pt CEs (8.73%). Furthermore, Ni–Mo–S/NG showed high catalytic activity for the ORR with an onset of 0.98 VRHE and outstanding durability compared to commercial Pt/C. The present study demonstrates the unique role of integrated Ni–Mo–S nanosheets anchored NG towards I3− reduction and the ORR, and demonstrates an efficient strategy for designing highly catalytically active and cost-effective electrocatalysts for DSSC and fuel cell applications.
TL;DR: In this paper, a nanocomposites of pluronic F127 modified reduced graphene oxide (PF127-rGO) with polyethylene glycol plasticize gum arabic (PGA) was prepared by evaporating an aqueous solution mixture of PF127 and PGA.
Abstract: Nanocomposites of pluronic F127 modified reduced graphene oxide (PF127-rGO) with polyethylene glycol plasticize gum arabic (PGA) was prepared by evaporating an aqueous solution mixture of PF127-rGO and PGA. PF127-rGO was synthesized by the in-situ reduction of graphene oxide using hydrazine in presence of pluronic F127 and characterized by the Uv–Vis spectroscopy, transmission electron microscopy (TEM), wide angle x-ray scattering (WAXS), Fourier transforms infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and Raman spectroscopy. The Uv–Vis and Raman spectroscopy results indicate that pluronic F127 functionalization does not hamper the structure of rGO, and TEM image indicates, the pluronic F127 anchored rGO sheets remain exfoliated in diluted aqueous solution of PF127-rGO. WAXS, FTIR and TGA studies confirms the functionalization of rGO with pluronic F127. PF127-rGO 2.5, PF127-rGO 5 and PF127-rGO 7.5 nanocomposites were fabricated, where the numbers represent the weight percentage of PF127-rGO with respect to PGA. The composite films were characterized by field emission scanning electron microscopy (FESEM), FTIR, WAXS and mechanical property study. FESEM and WAXS studies show good dispersion of PF127-rGO sheets in the PGA matrix. The FTIR results indicate a significant interaction between functional groups of PF127-rGO and functional groups of PGA. PF127-rGO 7.5 shows a 124% increase of stress at break and 185% increase of Young's modulus compared to pure PGA.
TL;DR: The excellent electrochemical performance was attributed to synergistic effects of Au, Pt, and GR as well as to the formation of a unique nanoporous structure that provided enhanced electrocatalytic activity, a highly electroactive surface, and fast mass transport.
TL;DR: In this article, NiPd alloy NPs/GNS were synthesized using ammonia-hydrazine method via a surfactant-free hydrothermal process and as-prepared catalysts were characterized using scanning electron microscopy (SEM), TEM, STEM-elemental mapping, XRD, X-ray diffraction, XPS, and Raman spectroscopy.
Abstract: Nickel-palladium alloy nanoparticles over graphene nanosheets (NiPd alloy NPs/GNS) are synthesized using ammonia-hydrazine method via a surfactant-free hydrothermal process. NiPd alloy NPs/GNS represent a new class of electrocatalyst with enhanced activity and stability for formic acid and ethanol oxidation reactions. The as-prepared catalysts are characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), STEM-elemental mapping, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Cyclic voltammetry (CV) and chronoamperometry (CA) studies reveal that bimetallic alloy nanoparticles exhibit higher catalytic activity than monometallic catalysts toward electro-oxidation reactions. The higher activity is mainly attributed to the strong assembly of bimetallic NiPd alloy NPs over graphene sheets. The novel NiPd alloy NPs/GNS catalysts provide a new strategy for superior electro-catalytic performance in next-generation fuel cells.
TL;DR: In this paper, the organo-soluble dodecylamine amine (DDA)-modified reduced graphene oxide was synthesized using two different grafting methods, and the ultraviolet−visible spectra showed that the DMF dispersion of DDA-rGO1 and DDArGO2 followed Beer's law.
TL;DR: In this article, the simultaneous reduction, surface modification, and stitching of graphene oxide (GO) by ethylenediamine (EDA) and triethylenetetramine (TET) was reported to boost the hydrogen gas barrier performance of polyurethane composite-coated nylon films.
Abstract: We report the simultaneous reduction, surface modification, and stitching of graphene oxide (GO) by ethylenediamine (EDA) and triethylenetetramine (TET) to boost the hydrogen gas barrier performance of polyurethane (PU) composite-coated nylon films. TEM and XRD analyses confirmed the formation of stitched EDA-modified GO (EDA-mGO) and TET-modified GO (TET-mGO) while FT-IR spectroscopy, Raman spectroscopy, and thermogravimetric analyses revealed the functionalization and reduction of GO by EDA and TET. EDA-mGO/PU and TET-mGO/PU composites were synthesized using different amounts of EDA-mGO and TET-mGO, respectively, and composites were deposited onto surface modified nylon films by spray coating to prepare hydrogen barrier films. FTIR, XRD, and FESEM analyses showed that both EDA-mGO and TET-mGO were uniformly dispersed into PU matrix. Cross-sectional FESEM showed strong adhesion between the nylon and composites. Coated films exhibited dramatic reduction in hydrogen gas transmission rate (H2GTR) and TET-mGO/PU with 22 wt% TET-mGO exhibited 93% decrease in H2GTR than bare nylon film.
TL;DR: In this article, a novel cotton flower-like hierarchically porous boron nitride (BN) structure was successfully synthesized by pyrolizing a boric acid/melamine mixture at 1100°C in a controlled flow rate ratio of N 2 /H 2.
Abstract: Development of highly efficient adsorbent materials for the wastewater treatment is an excellent, cheap, environmental friendly and sustainable approach. Herein, a novel cotton flower-like hierarchically porous boron nitride (BN) structure was successfully synthesized by pyrolizing a boric acid/melamine mixture at 1100 °C in a controlled flow rate ratio of N 2 /H 2 . The obtained porous BN material with a large specific surface area (SSA) of 1140 m 2 g −1 exhibited high selectivity, fast adsorption rate (∼96% for methylene blue (MB) after 20 min and ∼80% for rhodamine B (RhB) after 10 min) and high adsorption capacities (∼471.2 and 313.4 mg⋅g −1 for MB and RhB, respectively). The excellent selectivity of porous BN material towards dyes adsorption was confirmed from a mixed solution of dye and inorganic salts. In addition, porous BN material remain sustained without losing its adsorption activity even after 10 cycles and exhibited easy regeneration and good reusability which were achieved by a simple heating process. The obtained results indicated that the present porous BN material is a potential candidate for the removal of organic pollutants in water treatment applications.
TL;DR: Vanadium pentoxide (V2O5) nanorod decorated graphene polypyrrole nanocomposites have been synthesized successfully by a facile hydrothermal process for supercapacitor (SC) applications as mentioned in this paper.
Abstract: Vanadium pentoxide (V2O5) nanorod decorated graphene polypyrrole nanocomposites have been synthesized successfully by a facile hydrothermal process for supercapacitor (SC) applications. The morphological study revealed the successful decoration of V2O5 nanorods and polypyrrole (PPy) within the intergallery of graphitic materials due to their high degree of propensity for intercalation which leads to the formation of mesoporous 3D nanostructures. These mesoporous structures can efficiently allow fast diffusion and ion transport at the electrode–electrolyte interface towards high electrochemical utilization and superior performance. Here, decoration of V2O5 within a polymer matrix along with a graphitic material renders different electrical profiles by virtue of their electron hopping within nanocomposites. Galvanostatic charging discharging revealed that VGP was found to be superior with a maximum specific capacitance of 787 F g−1 at a current density of 1 A g−1 using KCl as an electrolyte. These observations were also confirmed by electrochemical measurements through CV and EIS studies. Furthermore, cyclic stability performed for 5000 consecutive cycles also substantiate their high durability and high power delivery uptake. Thus, considering all such key features, V2O5 based nanocomposites can be suitable for SC applications.
TL;DR: A facile approach for the fabrication of chemically modified reduced graphene oxide (RGO) based multilayer films was developed for gas barrier applications in this article, where polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS) were utilized as surface modifiers to yield water-dispersible RGO with opposite charges.
Abstract: A facile approach for the fabrication of chemically-modified reduced graphene oxide (RGO) based multilayer films was developed for gas barrier applications. Polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS) were utilized as surface modifiers to yield water-dispersible RGO with opposite charges. Altering the deposition pH of PEI-RGO layer resulted in different phase morphology and bonding of the multilayer films. PEI-RGO and PSS-RGO were assembled into multilayer films via a layer-by-layer (LbL) assembly method through electrostatic and hydrogen bonding interactions, respectively. The LBL assembly of polymer-decorated RGO based multilayer films were characterized by various characterization techniques. Hydrogen gas transmission rate (H2GTR) of the hydrogen bonding interaction based LbL film with 24 bilayers was 5.8 cc/m2·d·atm; and H2GTR value was 46.2 cc/m2·d·atm for the corresponding LbL film based on electrostatic interactions. Hydrogen bonding interaction based multilayer films exhibited very low H2GTR values compared to electrostatic interaction based multilayer and bare polyethylene terephthalate films.
TL;DR: In this article, an ultra-smooth, highly flexible transparent conducting electrode with a fully embedded structure of the silver coated electrospun polyvinyl alcohol (PVA) nanofiber network is reported.
Abstract: Flexible transparent conducting electrodes (TCEs) in replacement of brittle indium tin oxide (ITO) films are of ultimate importance in the production of flexible and stretchable displays, lighting devices, and solar panels with the ability to resist harsh weather conditions. Herein, the fabrication of an ultra-smooth, highly flexible transparent conducting electrode with a fully embedded structure of the silver coated electrospun polyvinyl alcohol (PVA) nanofiber (PVA@Ag NF) network is reported. These electrodes are fabricated using a scalable electrospinning and thermal evaporation process. The embedded PVA@Ag NF (E-PVA@Ag NF) network TCE structure provides several advantages, including a smooth surface, mechanical stability under high bending stress, and strong adhesion to the substrate with excellent flexibility, without sacrificing the electrical–optical properties. Ultrahigh aspect ratios with fused crossing at the junction points of the PVA@Ag NF network result in a high transmittance (∼90%) at a low sheet resistance (∼2.56 Ω □−1). The E-PVA@Ag NF network TCE structure shows a smooth surface topology (RRMS ∼ 2.0 nm) with excellent bending stability; the sheet resistance of the TCE remains almost constant after 10 000 bending cycles with a 1.0 mm bending radius. Finally, a flexible transparent heater is fabricated and its performance at low operating voltage is reported.
TL;DR: The present work highlights the effective H-π interaction between metallocenes and graphene and their stabilization in the presence of polyaniline (PANI) through π-π interactions, which showed improved charge-transfer properties of graphene after incorporation of Fc and stabilization with PANI.
Abstract: The present work highlights the effective H-π interaction between metallocenes (ferrocene; Fc) and graphene and their stabilization in the presence of polyaniline (PANI) through π-π interactions. The PANI-stabilized Fc@graphene nanocomposite (FcGA) resembled an intertwined network-like morphology with high surface area and porosity, which could make it a potential candidate for energy-storage applications. The relative interactions between the components were assessed through theoretical (DFT) calculations. The specific capacitance calculated from galvanostatic charging/discharging indicated that the PANI-stabilized ternary nanocomposite exhibited a maximum specific capacitance of 960 F g- at an energy density of 85 Wh Kg-1 and a current density of 1 A g- . Furthermore, electrochemical impedance spectroscopy (EIS) analysis confirmed the low internal resistance of the as-prepared nanocomposites, which showed improved charge-transfer properties of graphene after incorporation of Fc and stabilization with PANI. Additionally, all electrodes were found to be stable up to 5000 cycles with a specific capacitance retention of 86 %, thus demonstrating the good reversibility and durability of the electrode material.
TL;DR: In this paper, a lab scale microfluidic reactor with computer-controlled programmable isocratic pumps and online detectors was employed to synthesize CdSe nanocrystal and three reaction parameters, viz. reaction time, the [Cd]/[Se] molar concentration ratio, and the precursor concentrations, were optimized for optical characteristics, the particle diameter, and product yield.
TL;DR: In this article, reduced graphene oxide (rGO)/MnO2 hybrid materials were prepared via a direct redox reaction between MnCl2 and KMnO4 on rGO, and the morphology and microstructure of the as-prepared composite was characterized using field-emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), X-ray diffraction (XRD), and Raman Spectroscopy.