Woong Moo Lee

Platinum nanoparticles prepared by a plasma-chemical reduction method

Platinum nanoparticles were prepared by reducing H2PtCl6 dissolved in water with the help of hydrogen plasma generated right above the aqueous solution, thus the small surface area of the solution contacting the plasma becomes the active reaction zone. This simple method to fabricate the nanoparticles did not necessitate use of reducing agents and polymer protective materials. The average particle size was around 2 nm with the solution temperature set at 10 °C.

An analytical theory of corona discharge plasmas

In this paper we describe an analytical investigation of corona discharge systems. Electrical charge and the energy transfer mechanism are investigated based on the circuit analysis. Efficient delivery of electrical energy from the external circuit to the reactor chamber is a major issue in design studies. The optimum condition obtained in this paper ensures 100% energy transfer. Second-order coupled differential equations are numerically solved. All the analytical results agree remarkably well with numerical data. The reactor capacitor plays a pivotal role in circuit performance. The voltage profile is dominated by the reactor capacitor. Corona discharge properties in the reactor chamber are also investigated, assuming that a specified voltage profile V(t) is fed through the inner conductor. The analytical description is based on the electron moment equation. Defining the plasma breakdown parameter u=V/Rcp, plasma is generated for a high-voltage pulse satisfying u>uc, where uc is the critical breakdown p...

Ozone production by nanoporous dielectric barrier glow discharge in atmospheric pressure air

This study is aimed at demonstrating plasma-chemical ozone production based on low temperature atmospheric pressure glow discharge through nanoporous dielectric barriers. The 20kHz ac driven discharge is formed in air or oxygen gas flowing in the axial direction of the cylindrical plasma reactor containing four parallel aluminum rods covered with nanoporous alumina films. The discharge utilizing nanoporous dielectric barrier is more uniform and more energy efficient in ozone generation than the discharge through smooth-surface dielectric barriers.

Room-temperature slot microplasma in atmospheric pressure air between cylindrical electrodes with a nanoporous alumina dielectric

Slot microplasma in low temperature, atmospheric pressure air is developed for applications in surface, gas, or biomedical treatments. Dielectric barrier discharge between two parallel aluminum (Al) rods covered with nanoporous alumina films, ∼60μm thick and mean pore diameters of ∼40nm, is driven by 20kHz ac power. The glow microplasma is stable and spatially uniform, using 2–10W, in the gap of 100–500μm between the rods of 3mm diameter and 5cm long. This type of slot discharge operational in ambient temperature atmospheric pressure air can provide large-scale nonthermal plasma for any applications requiring continuous low temperature treatments.

Electrochemical acceleration of hydrogen transfer through a methanol impermeable metallic barrier

Placing a hydrogen conducting, methanol impermeable metallic barrier like palladium (Pd) is a well-known method for preventing methanol crossover through solid polymer electrolyte for direct methanol fuel cells (DMFCs). It was demonstrated in our study that the hydrogen transfer rate through the barrier was greatly enhanced when a negative bias potential in reference to the cell anode was applied on the barrier, a thin Pd foil of 25 μm thick. The power consumed for such bias application was less than 2% of the operational power of the cell. The current density/voltage curves of the DMFC showed that the proper bias application on the hydrogen saturated Pd barrier increased the cell power by more than five times from the value obtained without the bias modification. But the real advantage of the biased barrier was that it actually reduced the resistance of the polymer electrolyte (Nafion) when it was placed in the electrolyte with the cell current density maintained lower than 40 mA cm -2 (equivalent to maintain the cell voltage higher than 0.4 V in our experimental conditions). Eventual falloff of the power delivered by the cell with the barrier in higher current region should be attributed to mismatch of the charge transfer rate at the Pd/Nafion interfaces with the increased overall current density.

Carbon-Supported Platinum Nanoparticles Synthesized by Plasma-Chemical Reduction Method for Fuel Cell Applications

Carbon supported platinum nanoparticles were synthesized by reducing H 2 PtCl 6 precursor dissolved in water containing carbon powders by a plasma-chemical method. The fast reduction of the precursor was achieved with the help of active hydrogen species generated in the plasma zone contacting the surface of the aqueous solution. The size of the Pt particles supported on the carbon was in the range of 3 to 5 nm with the solution temperature set at 5°C. The performance of the proton exchange membrane fuel cell employing as-prepared Pt/C as the electrocatalyst was comparable to that using commercial Pt/C catalyst.

Hydrogen Isotope Separation by Plasma-Chemical Method

Deuterium transfer (exchange) reaction as shown in HDO+H2=H2O+HD was studied as a case similar to the tritium transfer reaction as shown in DTO+D2=D2O+DT, the first step in tritium isotope separation of the tritiated heavy water DTO. The transfer reaction was plasma-chemically catalyzed by allowing a gas mixture such as H2O/D2, D2O/H2, H2O/HDO/H2 or H2O/D2O/HDO/H2 to flow through an atmospheric pressure discharge zone formed in a reaction chamber, the inner temperature of which was maintained just above 100°C. The plasma-chemical reactions diagnosed by infrared and emission spectroscopy revealed that the mixture underwent instantaneous deuterium transfer reactions as it passed the zone. The effectiveness of the method was demonstrated by high deuterium transfer rate, high separation factor of the transfer and a possibility of miniaturizing the separation facility.

Methanol sensor operative in wide range of fuel concentration and temperature with fast response

An electrochemical methanol sensor for monitoring the fuel concentration in direct methanol fuel cells was constructed using a thin composite membrane as the electrolyte. The 6 μm thick composite membranes were prepared by impregnating porous polyethylene-terephthalate film with Nafion ionomer. The resulting sensor is capable of monitoring the fuel in any concentration up to pure methanol. This can be accomplished by placing a palladium film at the interface between the anode and the membrane. The sensor is also operative even at ambient temperature and responds quickly to concentration changes, i.e., in less than 2 s.

Density profiles of corona discharge plasmas

Abstract Corona discharge properties in the reactor chamber are investigated, assuming that a specified voltage profile V ( t ) is fed through the inner conductor. The analytical description is based on the electron moment equation. Defining the plasma breakdown parameter u = V R c p , plasma is generated for a high voltage pulse satisfying u > u c , where u c is the critical breakdown parameter defined by the geometrical configuration. Here, u is in units of a million volts per m per atm, and R c is the outer conductor radius. It is found that the plasma density profile generated inside the reactor chamber depends very sensitively on the system parameters. A small change of a physical parameter can easily lead to a density change of one order of magnitude.