Heung-Yong Ha

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.

A Study on the Effect of Water Freezing on the Characteristics of Polymer Electrolyte Membrane Fuel Cells

The author assumes that pure liquid metal is composed of molecular oscillators whose energy states are classified into two subgroups, i.e., A and B states, each being accesible to either one of the two sorts of lattice sites. The partition function involves constants characteristic of substance, which are obtainable from the Debye characteristic temperature assigned to its solid state. Calculation has been made for the various thermodynamic properties such as the vapor pressure, the entropy, and the heat capacity of liquid metals of GroupⅠelements over the temperature range from the melting points to the boiling points. The theoretical values thus obtained are in good accordances with those observed, within experimental error, although a slight derivation is observed in the atomic heat capacity.

Effects of the Variables in the Fabrication of Anode on the Performance of DMFC

Single cell performance has been investigated and characterized with variables in the fabrication of DMFC anode. The performance was checked as a function of ionomer content which affects ion conductivity in the catalyst layer, and catalyst slurry solvent which determines structure of agglomerates consisting of an ionomer and a catalyst. Anode with total ionomer to catalyst ratio of 0.6 showed the best performance and the lowest polarization resistance. Also, electrochemically effective surface area increased with ionomer content. As solubility of the ionomer decreases with decreasing solvent polarity, the size of agglomerates consisting of a catalyst and an ionomer became larger in the less polar solvent. The anode using DPK

Simulation of Direct Methanol Fuel Cells Employing Computational Fluid Dynamics(CFD)

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Characteristics of composite bipolar plates for polymer electrolyte membrane fuel cells

A numerical analysis of electrochemical reaction and dynamics of the fluid flow in the channels of a DMFC separator was carried out by using a commercial Computational Fluid Dynamics(CFD) code fluent(ver.6.0). From the simulation work, many valuable informations were obtained in terms of distributions of velocity, pressure, temperature, concentration and current density over the flow field. And it was possible to optimize the flow field structure by using the simulation results. The simulation work using the Cm code was found very helpful in analysing the phenomena occurring in the fuel cell and optimizing the structures of electrodes and flow field.