Min Sik Nam

Controlled electrochemical growth of Co(OH)2 flakes on 3D multilayered graphene foam for high performance supercapacitors

The present research describes successful enchase of Co(OH)2 microflakes by the potentiodynamic mode of electro-deposition (PED) on porous, light weight, conducting 3D multilayered graphene foam (MGF) and their synergistic effect on improving the supercapacitive performance. Structural and morphological analyses reveal uniform growth of Co(OH)2 microflakes with an average flake width of ∼30 nm on the MGF surface. Moreover, electrochemical capacitive measurements of the Co(OH)2/MGF electrode exhibit a high specific capacitance of ∼1030 F g−1 with ∼37 W h kg−1 energy and ∼18 kW kg−1 power density at 9.09 A g−1 current density. The superior pseudoelectrochemical properties of cobalt hydroxide are synergistically decorated with high surface area offered by a conducting, porous 3D graphene framework, which stimulates the effective utilization of redox characteristics and mutually improves electrochemical capacitive performance with charge transport and storage. This work evokes scalable electrochemical synthesis with the enhanced supercapacitive performance of the Co(OH)2/MGF electrode in energy storage devices.

A binder free synthesis of 1D PANI and 2D MoS2 nanostructured hybrid composite electrodes by the electrophoretic deposition (EPD) method for supercapacitor application

A facile, binder-free approach is applied, along with the electrophoretic deposition (EPD) method, to fabricate large-scale, hybrid 2D MoS2 nanosheets and 1D polyaniline (PANI) nanowires based electrodes on a conducting substrate for supercapacitor electrode material. The entire substrate surface is uniformly decorated by electrophoretically assembled MoS2 2D nanosheets and 1D nanowires of PANI, revealed by structural and morphological analysis. The electrochemical capacitive measurements of the MoS2/PANI hybrid electrode exhibit a specific capacitance of ∼485 F g−1 at a low charging–discharging current density (1 mA cm−2). The MoS2:PANI composition ratio was varied as 1:1, 1:2 and 1:3 to achieve high supercapacitive performance. The maximum supercapacitive performance (∼812 F g−1) was obtained for a 1:2 ratio of MoS2 and PANI, with high energy density (112 W h kg−1) and power density (0.6 kW kg−1). Synergistic interactions between conductive 1D PANI and 2D MoS2 nanosheets with high surface area lead to a high supercapacitive performance. A binder approach to the direct synthesis of hybrid electrode by the EPD method eradicates the drawbacks offered by conventional electrodes prepared by the general slurry coating technique with resistive binders.

PolyHIPE Derived Freestanding 3D Carbon Foam for Cobalt Hydroxide Nanorods Based High Performance Supercapacitor

The current paper describes enhanced electrochemical capacitive performance of chemically grown Cobalt hydroxide (Co(OH)2) nanorods (NRs) decorated porous three dimensional graphitic carbon foam (Co(OH)2/3D GCF) as a supercapacitor electrode. Freestanding 3D porous GCF is prepared by carbonizing, high internal phase emulsion (HIPE) polymerized styrene and divinylbenzene. The PolyHIPE was sulfonated and carbonized at temperature up to 850 °C to obtain graphitic 3D carbon foam with high surface area (389 m2 g−1) having open voids (14 μm) interconnected by windows (4 μm) in monolithic form. Moreover, entangled Co(OH)2 NRs are anchored on 3D GCF electrodes by using a facile chemical bath deposition (CBD) method. The wide porous structure with high specific surface area (520 m2 g−1) access offered by the interconnected 3D GCF along with Co(OH)2 NRs morphology, displays ultrahigh specific capacitance, specific energy and power. The Co(OH)2/3D GCF electrode exhibits maximum specific capacitance about ~1235 F g−1 at ~1 A g−1 charge-discharge current density, in 1 M aqueous KOH solution. These results endorse potential applicability of Co(OH)2/3D GCF electrode in supercapacitors and signifies that, the porous GCF is a proficient 3D freestanding framework for loading pseudocapacitive nanostructured materials.

Surface plasmon enhancement of photoluminescence in photo-chemically synthesized graphene quantum dot and Au nanosphere

Graphene quantum dots (GQDs) are promising candidates for potential applications such as novel optoelectronic devices and bio-imaging. However, insufficient light absorption to exhibit their intriguing characteristics. The strong confinement of light caused by the Au nanoparticles as an antenna can considerably boost the light absorption. With the assistance of ultraviolet irradiation, we prepared bluish-green luminescent nanospheres by the hybridization of GQD and Au nanoparticles (GQD/Au). These nanospheres showed a photoluminescence quantum yield of up to 26.9%. The GQD/Au nanospheres were synthesized using a solution of GQDs and HAuCl4 by a photochemical method with the reduction of GQDs and the formation of metallic Au. The GQDs and Au nanoparticles self-assembled and aggregated into nanospheres via aurophilicity and hydrogen bonding interactions. The average size of the GQD/Au nanospheres was found to be in the range of 150–170 nm, which is much larger than that of the pristine GQDs (4–7 nm). The GQD/Au nanospheres exhibited an absorption band at 541 nm, which indicates the presence of Au in the nanospheres. The typical absorbance features of GQDs were observed near 236 and 303 nm. The photoluminescence characteristics were investigated using the excitation and emission spectra. The GQD/Au nanospheres exhibited two emission peaks at 468 and 529 nm in the visible range. The green fluorescent peak located at 529 nm was newly generated by the hybridization. The GQD/Au nanospheres showed an emission efficiency which was two times more than that of the intrinsic GQDs. The reason for this increase was the surface plasmon resonance from the Au particles, which improved the fluorescence property of the resulting nanospheres. These nanospheres can be perceived as outstanding candidates for applications such as displays, optoelectronic devices, and imaging of the biological samples with high emission intensity.

Fabrication of ultra-high energy and power asymmetric supercapacitors based on hybrid 2D MoS2/graphene oxide composite electrodes: a binder-free approach

Two-dimensional (2D) atomically thick materials, graphene oxide (GO) and layered molybdenum disulfide (MoS2) nanosheets have been potentially investigated as novel energy storage materials due to their unique physicochemical properties. The present manuscript describes a facile binder-free approach to fabricate large-scale hybrid 2D MoS2/GO nanosheet-based electrodes using the electrophoretic deposition (EPD) method on a conducting substrate (nickel foam) for supercapacitor device applications. Structural and morphological analysis reveals uniform decoration of the electrophoretically assembled 2D MoS2/GO nanosheets over the entire substrate surface. The electrochemical supercapacitive measurements of the MoS2/GO hybrid electrode show a high specific capacitance of ∼613 F g−1 at a low scan rate. Moreover, the MoS2/GO//GO electrode-based asymmetric supercapacitor device reveals ultra-high energy (23 W h kg−1) and power (17 kW kg−1) density. The superior electrochemical properties of the 2D MoS2 synergist with high surface area offered by conducting GO and mutually MoS2/GO improves the electrochemical capacitive performance with charge transport and storage. The direct hybrid electrode fabrication by the EPD method (a binder approach) eliminates the drawbacks offered by resistive binders in conventional electrodes. The present experimental findings can evoke scalable binder-free synthesis of MoS2/GO hybrid electrodes with enhanced supercapacitive performance in energy storage devices.

Tension assisted metal transfer of graphene for Schottky diodes onto wafer scale substrates.

We developed an effective graphene transfer method for graphene/silicon Schottky diodes on a wafer as large as 6 inches. Graphene grown on a large scale substrate was passivated and sealed with a gold layer, protecting graphene from any possible contaminant and keeping good electrical contact. The Au/graphene was transferred by the tension-assisted transfer process without polymer residues. The gold film itself was used directly as the electrodes of a Schottky diode. We demonstrated wafer-scale integration of graphene/silicon Schottky diode using the proposed transfer process. The transmission electron microscopy analysis and relatively low ideality factor of the diodes indicated fewer defects on the interface than those obtained using the conventional poly(methyl methacrylate)-assisted transfer method. We further demonstrated gas sensors as an application of graphene Schottky diodes.

Hydrothermally Synthesis Nanostructure ZnO Thin Film for Photocatalysis Application

ZnO has nanostructured material because of unique properties suitable for various applications. Amongst all chemical and physics methods of synthesis of ZnO nanostructure, the hydrothermal method is attractive for its simplicity and environment friendly condition. Nanostructure ZnO thin films have been successfully synthesized on fluorine doped tin oxide (FTO) substrate using hydrothermal method. A possible growth mechanism of the various nanostructures ZnO is discussed in schematics. The prepared materials were characterized by standard analytical techniques, i.e., X-ray diffraction (XRD) and Field-emission scanning electron microscopy (SEM). The XRD study showed that the obtained ZnO nanostructure thin films are in crystalline nature with hexagonal wurtzite phase. The SEM image shows substrate surface covered with nanostructure ZnO nanrod. The UV-vis absorption spectrum of the synthesized nanostructure ZnO shows a strong excitonic absorption band at 365 nm which indicate formation nanostructure ZnO thin film. Photoluminescence spectra illustrated two emission peaks, with the first one at 424 nm due to the band edge emission of ZnO and the second broad peak centered around 500 nm possibly due to oxygen vacancies in nanostructure ZnO. The Raman measurements peaks observed at , , and indicated that nanostrusture ZnO thin film is high crystalline quality. We trust that nanostructure ZnO material can be effectively will be used as a highly active and stable phtocatalysis application.