S.-A. Hong

Effect of the catalytic ink preparation method on the performance of polymer electrolyte membrane fuel cells

The effect of the preparation method of the catalytic inks on the electrode structure and, thus, on the performance of polymer electrolyte membrane fuel cells (PEMFCs) was investigated. Since the catalytic inks, which are a mixture of Pt/C powders, solvent, and ionomers, change into one of the three states: (i) solution; (ii) colloids and (iii) precipitates, according to the interaction between the ionomers and solvents, two different catalytic inks have been prepared for comparison, the solution inks based on iso-propyl alcohol (IPA) and the colloidal inks based on normal butyl acetate. Performance evaluation, electrochemical analyses, and physical property examination revealed that the electrode prepared by a colloidal method showed better results compared to those of the solution method. The former appeared to secure continuity of the ionomer network and higher porosity in the catalytic layer, resulting in higher proton conductivity and less mass transfer resistance.

Modification of polymer electrolyte membranes for DMFCs using Pd films formed by sputtering

Abstract Composite polymer electrolyte membranes were fabricated by depositing Pd films on the surface of Nafion™ membranes by sputtering, and the modified membranes were investigated for their morphologies, methanol permeabilities, protonic conductivities and performances for direct methanol fuel cells (DMFCs). The Pd film acted as a barrier to methanol crossover, but at the same time it also reduced proton conductivity. Though both the methanol permeability and the protonic conductivity through the modified membranes decreased with increasing Pd thickness, the cell performances were almost independent of the Pd thickness. The effects of methanol concentration on the protonic conductivity and the cell performance were also investigated. And, the role of Pd films in DMFCs is discussed in some detail.

Facile synthesis of reduced graphene oxide in supercritical alcohols and its lithium storage capacity

A facile and green method to produce reduced graphene oxide (RGO) nanosheets based on supercritical alcohols is described. The obtained RGO nanosheets exhibited a high carbon-to-oxygen ratio (up to 11.89, determined by X-ray photoelectron spectroscopy), high electronic conductivity (up to 10 600 S m−1), and high lithium storage capacity with good cyclability (652 mA h g−1 at a 50 mA g−1 after 40 cycles) when tested as an anode material.

Crab-Shell Biotemplated SnO2 Composite Anodes for Lithium-Ion Batteries

SnO2 composite materials infiltrated into the hollow carbon channels of a crab-shell biotemplate were hydrothermally synthesized and utilized as anodes for lithium-ion batteries. Varying the reaction temperatures and times of the hydrothermal reaction yielded different SnO2 nanoparticle shapes, characterized by scanning electron microscopy and transmission electron microscopy. The materials prepared at 100 °C (sample S100) were spherical, amorphous in nature, and successfully infiltrated into the hollow carbon channels, while those prepared at 180 °C (sample S180) yielded many rod-like particles on the outer surfaces of the channels. The S100 electrode exhibited better cyclability, corresponding to a capacity of 298 mAh g-1 at 100 cycles, and high rate capability with a capacity retention of 54% at 3 A g-1. The enhanced electrochemical performance of S100 could be attributed to the configuration of the SnO2 particles infiltrating the carbon-coated hollow channels, which accommodated large volume changes during (de)lithiation.