Papers by Author: Nam Hoon Kim

Abstract: A facile approach for the reduction of graphene oxide (GO) using of Tin (Sn) powder and dilute hydrochloric acid at room temperature (RT) and at 50 °C upto 0.5-3 h has been reported. The as-prepared high quality crystalline graphene has been characterized using various analytical techniques. The rate of reduction scales with the reaction time for both RT and 50 °C as evidenced from electrical conductivity data. The graphene samples reduced at RT shows high electrical conductivity value due to the presence of un-reacted Sn-particles. resulting the enhancement in the However, the graphene prepared at 50 °C shows low electrical conductivity in comparison to the room temperature reduced graphene. XPS elemental analysis is in good agreement with this observation.

Abstract: Preparation of functionalized graphene by electrochemical exfoliation of graphite rod using sodium dodecyl benzene sulfonate (SDBS) is reported. SDBS solution has been used as the electrolyte as well as functional groups. SDBD is an anionic surfactant which helps to provide uniform dispersion in water and prevents the π-π π-π stacking as well. XRD result indicates the formation of graphene whereas; the functionalization of graphene was confirmed through the FT-IR spectrum, which shows presence of peaks corresponding to SO₃^-. UV-vis spectroscopy demonstrates the dispersibility of SDBS-functionalized graphene, and peaks of SDBS and graphene appeared at 225 nm and 260nm, respectively. Raman spectroscopy show I_D/I_GIDIG ratio is < 1. It means that defects of SDBS-functionalized graphene are reduced.

Abstract: The development of sulfonated poly (ether ether ketone)-based (SPEEK) membranes by the incorporation of layered double hydroxide (LDH) as inorganic nanofiller has been achieved and its potential application in proton exchange membrane fuel cells (PEMFCs) has been investigated. The physical properties and proton conductivity of SPEEK matrix incorporated layered double hydroxide (LDH) were analyzed and found that the incorporation of LDH to SPEEK improves the thermal stability, water uptake and proton conductivity compared to the virgin SPEEK. The proton conductivity of the SPEEK/LDH composite membrane containing 3 wt% LDH has been found to be 229.9 mS/cm where as the virgin SPEEK shows the proton conductivity value 147.6 ms/cm at 80 °C and 100 %RH.

Abstract: Graphene/CeO₂ nanocomposite has been successfully prepared by directly growing CeO₂ nanoparticles on graphene sheets via in-situ reduction of graphene oxide containing the metal precursor. The presence of cetyltrimethyl ammonium bromide (CTAB) results the formation of CeO₂ nanoparticles with a narrow size distribution. The structural, morphological, particles size and optical properties of the synthesized products were investigated through X-ray diffraction (XRD), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FT-IR) and UVvis absorbance spectroscopy, respectively. The XRD pattern shows that graphene/CeO₂ nanocomposite is highly crystalline in nature. Growth of CeO₂ nanoparticles with size in range of 5-18 nm on the graphene sheet were observed by TEM measurement. Optical energy band gap was calculated to be ~3.30 eV corresponding to direct transition. The catalytic activity of the synthesized nanocomposite was investigated taking hydrazine hydrate as a model system. Significant enhancement in the peak current with respect to CeO₂ was observed on graphene/CeO₂ nanocomposite-based electrode demonstrating the higher catalytic activity of graphene/CeO₂ nanocomposite-based electrode.

Abstract: Nafion-clay nanocomposite membrane has been prepared by dispersing unmodified and acid activated Laponite XLS in Nafion 20% dispersion. The resulting membranes possess better proton conductivity and mechanical strength as compared to the virgin membrane. Acid activation of the nanoclay leads to the in-situ generation of H₃PO₄ by the hydrolysis of the peptizer present on the surface of the nanoclay. The in-situ generated H₃PO₄ helps in improving all the technical properties of the nanocomposite including the water uptake and proton conductivity of the nanocomposite, containing acid activated clay compared to the nanocomposite, containing unmodified clay. The maximum proton conductivity of 270.2 mS/cm is achieved at 110 °C for the nanocomposite membrane containing 3% acid-activated Laponite compared to 136.2 mS/cm for the virgin Nafion. Keywords: Nafion, clay, nanocomposite, peptizer, polymer electrolyte membrane fuel cell (FEMFC), proton conductivity, membrane

Abstract: SDBS modified graphene was prepared by electrochemical method using Sodium dodecylbenzenesulfonate (SDBS) as electrolyte and graphite rod as electrode. The anode graphite rod was corroded and deposited at the bottom of the electrolyte solution. The obtained graphene was characterized by Atomic force microscopy (AFM), Raman and Fourier transform infrared spectra (FT-IR). AFM images indicated that most of the layers had the thickness of less than 2 nm, suggesting the fromation of single layer of graphene. The resulting graphene showed very good dispersion stability both in water and in organic solvents (ethanol, acetone).

Abstract: The extruded poly ether ether ketone (PEEK) and glass fibre were used to obtain the co-woven hybrid fibre fabrics and converted into composites using compression moulding technique. The effect of shear stress and shear rate on the shear viscosity of PEEK was investigated to optimise the process conditions for converting hybrid fabrics into composites. The mechanical properties such as flexural strength and inter laminar shear strength (ILSS) as a function of number of layers of fabric have been evaluated. Low velocity (2.1 m/s) repeated drop weight impact tests were carried out on the fabricated composites at 5 and 10 J incident energy. Dielectric properties as a function of temperature and frequency have been carried out. Flammability behaviour of composites has been carried out using cone calorimeter. The data generated shows that glass-PEEK based composites are excellent potential materials for advanced structural composites.

Abstract: Acid doped polybenzimidazole membrane has been prepared for proton exchange membrane fuel cell. The present work aims at improving the proton conductivity without losing mechanical properties at high doping level by modifying poly (2,5-benzimidazole) (ABPBI). The nitration of ABPBI has been carried out with acid mixture of HNO3 and H2SO4 at 30oC. This nitro compound has been reduced successfully by stannous chloride/dimethylacetamide in presence of hydrochloric acid. Fourier transform infrared (FT-IR) spectra confirm the presence of primary amine groups in the ABPBI structure. The primary amine functionalized ABPBI has been cross-linked by hexamethylene diisocyanate and casted onto glass Petridis using dimethyl sulfoxide as solvent. Membrane doped with phosphoric acid shows comparatively higher proton conductivity, but lower tensile strength.

Abstract: The bipolar plates were fabricated using compression molding of graphite (GR), carbon black (CB), multi-wall carbon nanotubes (MWNTs), carbon fibers (CF) and powder type epoxy resin. The electrical conductivity and flexural properties of the composites was increased with increasing the content of fibrous conducting fillers e.g., MWNTs and CF. However, when particulate fillers such as CB and GR were used, the electrical conductivity was increased, but the flexural properties deteriorated with increasing filler content up to certain content. A comparison was also made between the current-voltage (I-V) performances of fabricated composite bipolar plates and commercial graphite bipolar plate. The I-V characteristic in single cell test exhibited more uniform power density at both higher and lower current density and single cell performance increased with increasing the electrical conductivity.

Abstract: The present work deals with the functionalization of graphene sheet and preparation of functionalized graphene/linier low density polyethylene (LLDPE) nanocomposites by solution-mix techniques. Dodecyl amine (DA) has been used for the surface modification of graphene oxide (GO) and hydrazine as reducing agent. Fourier transform infrared (FTIR) spectra exhibits the appearance of new peaks in the functionalized graphene (DA-G), which suggests the functionalization of graphene by DA. X-ray diffraction (XRD) analysis infers the formation of fully exfoliated DA-G/LLDPE nanocomposites. The tensile strength (TS) and elongation at break (EB) of the composites are higher in comparison to neat LLDPE. The nanocomposites with only 0.5 wt.% of DA-G content results in TS and EB to be 17% and 10% higher compared to neat LLDPE. TGA shows that the thermal stability of the DA-G/LLDPE nanocomposites is higher compared to pure matrix polymer.