Rak-Hyun Song

Carbon-free cobalt oxide cathodes with tunable nanoarchitectures for rechargeable lithium–oxygen batteries

Carbon-free cobalt oxide cathodes for lithium-oxygen batteries are fabricated via an electrodeposition-conversion process. The Co3O4-only cathodes show a remarkably reduced voltage gap (by ca. 550 mV compared to the carbon-only cathode) as well as excellent long-term cyclability.

Effects of flow rate and starvation of reactant gases on the performance of phosphoric acid fuel cells

Abstract Effects of reactant gas flow rates and starvation on the performance of phosphoric acid fuel cells were studied using single cells. As the reactant gas flow rates of single cell increased, the performance of the cell increased, and then remained constant. The optimum flow rates of hydrogen, oxygen and air under cell operating condition of 150 mA/cm2 at 190°C were found to be 5 cc/min·cm2, 5 cc/min·cm2, and 15 cc/min·cm2 at 1 atm and room temperature, respectively. The open circuit voltage of the single cell decreased with increasing oxygen flow rate at constant hydrogen flow rate, which is attributed to the increased gas cross-over rate. When the reactant gases were again supplied to the cell after gas starvation, the cell voltage losses were found to be about 5 mV in the case of hydrogen starvation and about 1 mV for oxygen starvation, and the voltage loss was independent of gas starvation time. These results were discussed from the electrochemical viewpoint of the cell.

Influence of CO concentration and reactant gas pressure on cell performance in PAFC

Abstract The effects of CO concentration and reactant gas pressure on cell performance in phosphoric acid fuel cell have been studied by measuring current–voltage characteristics and by using ac impedance technique. The single cells were tested as a function of CO concentration of 0– 0.986 vol % in fuel gas and of reactant gas pressure of 0– 4 atm in the range of temperature of 160–220°C. The presence of CO has significant effect on the electrode interfacial resistance above 0.721 vol % CO due to CO adsorption. These results were discussed as related to electrode reaction kinetics. In the pressurized cell, both internal resistance and electrode impedance of the cell decreased with increasing gas pressure, which are considered to increase the cell performance.

Characterization and performance analysis of silicon carbide electrolyte matrix of phosphoric acid fuel cell prepared by ball- milling method.

Abstract The effect of ball milling in making a silicon carbide slurry for the electrolyte matrix of a phosphoric acid fuel cell (PAFC) was studied by measuring the zeta potential and the particle-size distribution, and by analyzing cell performance. The ball-milled slurry gives a better particle distribution than the conventional mechanical-stirring method, and the particle distribution of the slurry depends on balling time and pH, which is confirmed by zeta potential. A single cell with a ball-milled electrolyte matrix also displays high performance. It is concluded that the ball-milling method is preferable to the mechanical-stirring procedure for preparing silicon carbide slurries.

La 0.8 Ca 0.2 CrO 3 Interconnect Materials for Solid Oxide Fuel Cells: Combustion Synthesis and Reduced-Temperature Sintering

Sub-micrometer powders for ceramic interconnects of solid oxide fuel cells were synthesized by the aqueous combustion process. The materials were prepared from the precursor solutions with different glycine (fuel)-to-nitrate (oxidant) ratios (). Single-phase powders with a perovskite structure were obtained after combustion when was equal to or larger than 0.480. Especially, the stoichiometric precursor with

Characteristics of (Ca,Sr)-doped LaCrO 3 Coating Layer for Ceramic Interconnect of Solid Oxide Fuel Cell

Using Pechini method, we synthesized the (LCC41) and (LSCC) powders for slurry dip coating, and (LCC27) powder for air plasma spray coating. The sintering property of the powders and their coating properties were investigated. The average particle sizes of the LCC41, LSCC, LCC27 were 0.6, 0.9, , respectively. The relative density of LCC41 bulk was to be found about 98%. The LSCC coating on anode support prevented Ca migration of the coated LCC41 on the anode some or less, which was confirmed from EDS result. The air plasma spray-coated LCC27 with the dip-coated LCC41 were more dense and showed better electrical conductivity than those of the air plasma spray-coated LCC27 and the dip-coated LSCC and LSCC41. The LCC41 and LCC27 showed good electrical conductivities, but the LSCC had a poor electrical conductivity probably due to low sinterability.

Development of Two-layer Electrode for Direct Methanol Fuel Cell

The performance of the Direct Methanol Fuel Cell (DMFC) using multi-layer electrode, which prepared by various anode catalysts and Nafion membranes, was studied for reducing the amount of the metal catalyst loaded in the MEA system. The amount of the catalyst used in this experiment was in cathode and in anode, respectively. The best performance was to be of MEA3 at and 2 bar in this experiment. However, the overall performance of the DMFC was maintained almost the same compared to the general commercial catalyst systems.

Electrosprayed Polymer-Hybridized Multidoped ZnO Mesoscopic Nanocrystals Yield Highly Efficient and Stable Perovskite Solar Cells

Solid-state perovskite solar cells have been expeditiously developed since the past few years. However, there are a number of open questions and issues related to the perovskite devices, such as their long-term ambient stability and hysteresis in current density–voltage curves. We developed highly efficient and hysteresis-less perovskite devices by changing the frequently used TiO2 mesoscopic layer with polymer-hybridized multidoped ZnO nanocrystals in a common n–i–p structure for the first time. The gradual adjustment of ZnO conduction band position using single- and multidopant atoms will likely enhance the power conversion efficiency (PCE) from 8.26 to 13.54%, with PCEmax = 15.09%. The highest PCEavg of 13.54% was demonstrated by 2 atom % boron and 6 atom % fluorine co-doped (B, F:ZnO) nanolayers (using optimized film thickness of 160 nm) owing to their highest conductivity, carrier concentration, optical transmittance, and band-gap energy compared to other doped films. We also successfully apply a fine polyethylenimine thin layer on the doped ZnO nanolayers, causing the reduction in work function and overall demonstrating the enhancement in PCE from ∼10.86% up to 16.20%. A polymer-mixed electron-transporting layer demonstrates the remarkable PCEmax of 20.74% by decreasing the trap sites in the oxide layer that probably reduces the chances of carrier interfacial recombination originated from traps and thus improves the device performance. Particularly, we produce these electron-rich multidoped ZnO nanolayers via electrospray technique, which is highly suitable for the future development of perovskite solar cells.

Development of Tubular Solid Oxide Fuel Cells with Advanced Anode Current Collection

In this study, tubular SOFC unit cell with advanced anode current collector was fabricated to improve the cell performance. First, we prepared two types of single cells having the same manufacture processes such as the same electrolyte, electrode coating condition and sintering processes. And then to compare the developed single cell performance with conventional cells, we changed the anode current collecting methods. From the impedance analysis and I-V curve analysis, the cell performance of advanced cell is much higher than that of conventional cell.

Fabrication and Electrochemical Characterization of LSM/GDC based Cathode Supported Direct Carbon Fuel Cells

In this study, successive coating and co-sintering techniques have been used to fabricate LSM/GDC based cathode supported direct carbon fuel cells. The porous LSM/GDC cathode substrate, dense, thin and crack free GDC and ScSZ layers as bi-layer electrolyte, and a porous Ni/ScSZ anode layer was obtained by co-firing at . The porous structure of LSM/GDC cathode substrate, after sintering at , was obtained due to the presence of GDC phase, which inhibits sintering of LSM because of its higher sintering temperature. The electrochemical characterization of assembled cell was carried out with air as an oxidant and carbon particles in molten carbonate as fuel. The measured open circuit voltages (OCVs) were obtained to be more than 0.99 V, independent of testing temperature. The peak power densities were 116, 195 and at 750, 800 and , respectively.