Gyoung Hwa Jeong

Synthesis of noble metal/graphene nanocomposites without surfactants by one-step reduction of metal salt and graphene oxide.

We carried out hydrazine-free, surfactant-free synthesis of noble metal/graphene nanocomposites. The reduction of the noble metals and GO was carried out simultaneously in hot water using ascorbic acid as a reductant. In the noble metal/graphene nanocomposites of Pd, Pt, Au, and Ag nanoparticles, the GO and metal salts were reduced completely by this synthetic method. In addition, the Pd/graphene nanocomposites showed good catalytic activity in the Suzuki coupling reaction and could be reused many times without loss of catalytic activity.

Metal Oxide/Graphene Composites for Supercapacitive Electrode Materials.

Graphene composites with metal or metal oxide nanoparticles have been extensively investigated owing to their potential applications in the fields of fuel cells, batteries, sensing, solar cells, and catalysis. Among them, much research has focused on supercapacitor applications and have come close to realization. Composites include monometal oxides of cobalt, nickel, manganese, and iron, as well as their binary and ternary oxides. In addition, their morphological control and hybrid systems of carbon nanotubes have also been investigated. This review presents the current trends in research on metal oxide/graphene composites for supercapacitors. Furthermore, methods are suggested to improve the properties of electrochemical capacitor electrodes.

Diameter-Controlled and Surface-Modified Sb 2 Se 3 Nanowires and Their Photodetector Performance

Due to its direct and narrow band gap, high chemical stability, and high Seebeck coefficient (1800 μVK−1), antimony selenide (Sb2Se3) has many potential applications, such as in photovoltaic devices, thermoelectric devices, and solar cells. However, research on the Sb2Se3 materials has been limited by its low electrical conductivity in bulk state. To overcome this challenge, we suggest two kinds of nano-structured materials, namely, the diameter-controlled Sb2Se3 nanowires and Ag2Se-decorated Sb2Se3 nanowires. The photocurrent response of diameter-controlled Sb2Se3, which depends on electrical conductivity of the material, increases non-linearly with the diameter of the nanowire. The photosensitivity factor (K = Ilight/Idark) of the intrinsic Sb2Se3 nanowire with diameter of 80–100 nm is highly improved (K = 75). Additionally, the measurement was conducted using a single nanowire under low source-drain voltage. The dark- and photocurrent of the Ag2Se-decorated Sb2Se3 nanowire further increased, as compared to that of the intrinsic Sb2Se3 nanowire, to approximately 50 and 7 times, respectively.

One-pot synthesis of thin Co(OH)2 nanosheets on graphene and their high activity as a capacitor electrode

We synthesized Co(OH)2/graphene composites from graphite without a graphene oxide (GO) step. The Co(OH)2/graphene composite exhibited a specific capacitance of 960 F g−1 at a current density of 10 A g−1. In addition, after 5000 cycles of charge/discharge operation, the Co(OH)2/graphene composite maintained its initial specific capacitance value of 93.4% at a current density of 30 A g−1.

One-pot synthesis of Au@Pd/graphene nanostructures: electrocatalytic ethanol oxidation for direct alcohol fuel cells (DAFCs)

Surfactant-free bimetallic Au@Pd core-shell NPs on graphene sheets were fabricated from Au, Pd ions and graphene oxide by one-step reduction using ascorbic acid as an eco-friendly reducing agent. Au@Pd NPs with about 7 nm size are evenly distributed on the surface of graphene. The core/shell structures were confirmed with X-ray diffraction (XRD) and High-angle annual dark field scanning transmission microscopy (HAADF-STEM) mapping analysis. Prepared Au@Pd/graphene nanocomposites show an excellent electrocatalytic activity toward ethanol oxidation: If value that was the best for our catalysts is 11.6 A mg−1, which is about 5 times as high as that of the previous catalyst. The data resulted from extremely optimized bimetallic structure of a small Au core and a thin Pd shell. Pd atoms are constantly encouraged by adjacent Au atoms.

ZrO2-SiO2 nanosheets with ultrasmall WO3 nanoparticles and their enhanced pseudocapacitance and stability.

We report on the first synthesis of porous ZrO2-SiO2 sheets with well-defined ultrasmall WO3 nanoparticles for energy storage performance. In our system, for improving the surface deterioration of electrode, we use the ZrO2-SiO2 sheets using graphene oxide as a template to access electrode substrate. The synthesized electrode with about 20 nm thickness and about 10 nm pores, has a maximum value of 313 F/g at current density of 1 A/g and a minimum value of 160 F/g at current density of 30 A/g in the specific capacitance. In addition, over 90% of its initial specific capacitance is retained when they are cycled up to 2500 cycles.

Mesoporous hollow carbons on graphene and their electrochemical properties

We report the formation of mesoporous hollow carbons with diameters of about 30–40 nm on a graphene (MHCG) surface formed using graphite, the surfactant Pluronic F-127, and porous silica on the graphene as a template to produce a sheet. The specific surface area of the sample produced is 1793.45 m2 g−1, which is hundreds of times larger than that of graphite (31.38 m2 g−1). When applied to supercapacitor electrodes, the MHCG electrode exhibits outstanding maintenance of energy density above 30 W h kg−1 even under 1 kW kg−1 power density, which is attributed to extremely fast electron supply through graphene layers and facile penetration of electrolyte through highly-developed mesopores.

Surfactants-free noble metal/graphene nanocomposites synthesis and their catalytic application

We synthesized surfactant-free, hydrazine-free noble metal/graphene nanocomposites. The ascorbic acid was used for co-reducing agent for graphene oxide and noble metals in hot water solvent. In our synthetic method the GO (GO means graphene oxide) and metal salts (Pd, Pt, Ag and Au nanoparticles) were successfully reduced. As a result, the noble metal/graphene nanocomposites of Pd, Pt, Ag and Au nanoparticles were prepared. Furthermore, the Pd/graphene nanocomposites were applied in Suzuki coupling reaction as a catalyst and showed good catalytic activity.

The direct formation of noble metal (Pd, Pt, Au, and Ag) and graphene nanocomposites from graphite

We describe the first time on the direct and facile method for noble metal/graphene nanocomposites from graphite without reductants. In our system, the irradiant white-light instead of the chemical reductant exerts the influence on the synthesis of noble metal nanoparticles on graphene. Noble metal salts adsorbed on the surfaces of graphene flakes which were functionalized with ionic surfactants were reduced by irradiation with white light. In particular, noble metal nanoparticles were more evenly distributed on the surface of graphene which was functionalized with SDS than with CTAB.