Ji-Hyuk Choi

3 D Network-Structured Crumpled Graphene/Carbon Nanotube/Polyaniline Composites for Supercapacitors

Crumpled graphene (CGR) is considered a promising supercapacitor material to achieve high power and energy density because it could overcome the disadvantages of 2u2009D GR sheets such as aggregation during the electrode fabrication process, reduction of the available surface area, and limitation of the electron and ion transport. Even though CGR shows good results, carbon materials are limited in terms of their capacitance performance. Here, we report highly enhanced supercapacitor materials by fabricating a 3u2009D composite containing CGR, carbon nanotubes (CNTs), and polyaniline (PANI). The CNTs increased the basal spacing and bridged the defects for electron transfer between the GR sheets in CGR. PANI can enhance the rate of conduction of electrons and offer high pseudocapacitance originating from its redox reactions. The synergistic effect of the CNTs and PANI may also result in a higher electrochemical capacitance and better stability than each individual component as electrode materials for supercapacitors in a two-electrode system. More importantly, the performance of the supercapacitors can be further enhanced by employing 2u2009D GR as the binder for the composite electrodes, resulting in specific capacitance of 456u2005Fu2009g-1 , rate capability of 89u2009%, and cyclic stability of 97u2009% after 1000u2005cycles.

Synthesis of 3D Silver-Graphene-Titanium Dioxide Composite via Aerosol Spray Pyrolysis for Sensitive Glucose Biosensor

A sensitive glucose biosensor was developed based on the adsorption of glucose oxidase by a three-dimensional silver-graphene-titanium dioxide (3D Ag-GR-TiO2) composite electrode. Aerosol spray pyrolysis was employed to synthesize the 3D Ag-GR-TiO2 composite using a colloidal mixture of a silver acetate precursor (C2H3AgO2), graphene oxide, and TiO2 nanoparticles. The effects of the operating temperature, gas flowrate, and TiO2 concentration on the particle properties were investigated. The particle morphology of all 3D Ag-GR-TiO2 composites was spherical in shape. The average sizes of composites could be controlled from 0.45 to 0.64 μm with the variation of process variables. Ag nanoparticles less than 10 nm in diameter were deposited on the surfaces of the TiO2 nanoparticles and GR after a reduction process. The characteristics of the glucose biosensor fabricated with the as-prepared 3D Ag-GR-TiO2 composite were assessed through cyclic voltammetry measurements. The biosensor exhibited a high current flow as well as clear redox peaks, resulting in a superior ability of the catalyst in terms of the electrochemical reactions. The highest sensitivity of glucose biosensor was obtained by 3D Ag-GR-TiO2 composite, which was 12.2 μA/mM·cm2, among 3D Ag-GR-TiO2, 3D Ag-GR, and 3D GR-TiO2 composites. Copyright 2015 American Association for Aerosol Research

One-Step Synthesis of Pt/Graphene Composites from Pt Acid Dissolved Ethanol via Microwave Plasma Spray Pyrolysis.

Pt nanoparticles-laden graphene (Pt/GR) composites were synthesized in the gas phase from a mixture of ethanol and Pt precursor by microwave plasma spray pyrolysis. The morphology of Pt/GR composites has the shape of wrinkled sheets of paper, while Pt nanoparticles (Pt NPs) that are less than 2.6u2009nm in the mean diameter are uniformly well deposited on the surface of GR sheets stacked in only three layers. The Pt/GR composite prepared with 20 wt% of Pt had the highest specific surface area and electrochemical surface area of up to 402u2009m2 g−1 and 77u2009m2 g−1 (Pt), respectively. In addition, the composite showed superior electrocatalytic activity compared with commercial Pt-carbon black. The excellent electrocatalytic activity was attributed to the high specific surface area and electrochemical surface area of the Pt/GR composite directly produced by microwave plasma spray pyrolysis. Thus, it is clearly expected that the Pt/GR composite is a promising material for DMFC catalysts.