Sung Pil Yoon

Methane Steam Reforming in a Pd-Ru Membrane Reactor

Methane steam reforming has been carried out in a Pd-Ru membrane reactor at 500–600 ‡C. The membrane reactor consisted of a Pd-6%Ru tube of 100 mm wall thickness and commercial catalysts packed outside of the membrane. The methane conversion was significantly enhanced in the membrane reactor in which reaction equilibrium was shifted by selective permeation of hydrogen through the membrane. The methane conversion at 500 ‡C was improved as high as 80% in the membrane reactor, while equilibrium conversion in a fixed-bed reactor was 57%. The effect of gas flow rate and temperature on the performance of the membrane reactor was investigated and the results were compared with the simulated result from the model. The model prediction is in good agreement with the experimental result. In order to apply the membrane in practice, however, the thickness of the membrane has to be reduced. Therefore, the effect of membrane thickness on performance of the membrane reactor was estimated using the model.

An Ag-Coated NiO Cathode for MCFCs Operating at Low Temperatures

To increase the lifetime of molten carbonate fuel cell (MCFC) stacks, a reduction of the operating temperature is needed without decreasing the cell performance. In this study, a Ag coating on a conventional NiO cathode material of MCFC was carried out to enhance the cathode performance at the relatively low operating temperature of 600°C. Ag is a material applicable to cathodes for MCFCs because Ag has good catalytic activity for oxygen adsorption and dissociation and high electrical conductivity. The modified cathode was prepared by a vacuum suction method using a nanosized Ag sol suspension, and Ag particles were dispersed homogenously on the surface of a porous Ni plate. After the Ag coating, the cell performance was enhanced significantly from 0.76 to 0.80 V at a 150 mA/cm 2 current density at 600°C. The electrochemical impedance spectra show that the reduction of the charge transfer resistance is the main reason for the improvement of the cell performance after the Ag coating.

Effect of gold subsurface layer on the surface activity and segregation in Pt/Au/Pt3M (where M = 3d transition metals) alloy catalyst from first-principles

The effect of a subsurface hetero layer (thin gold) on the activity and stability of Pt skin surface in Pt3M system (M = 3d transition metals) is investigated using the spin-polarized density functional theory calculation. First, we find that the heterometallic interaction between the Pt skin surface and the gold subsurface in Pt/Au/Pt3M system can significantly modify the electronic structure of the Pt skin surface. In particular, the local density of states projected onto the d states of Pt skin surface near the Fermi level is drastically decreased compared to the Pt/Pt/Pt3M case, leading to the reduction of the oxygen binding strength of the Pt skin surface. This modification is related to the increase of surface charge polarization of outmost Pt skin atoms by the electron transfer from the gold subsurface atoms. Furthermore, a subsurface gold layer is found to cast the energetic barrier to the segregation loss of metal atoms from the bulk (inside) region, which can enhance the durability of Pt3M based catalytic system in oxygen reduction condition at fuel cell devices. This study highlights that a gold subsurface hetero layer can provide an additional mean to tune the surface activity toward oxygen species and in turn the oxygen reduction reaction, where the utilization of geometric strain already reaches its practical limit.

Economic Feasibility Study for Molten Carbonate Fuel Cells Fed with Biogas

Molten carbonate fuel cell (MCFC) power plants are one of most attractive electricity generation systems for the use of biogas to generate high-efficiency ultra-clean power. However, MCFCs are considerably more expensive than comparable conventional electricity generation systems. The commercialization of MCFCs has been delayed more than expected. After being effective in the Kyoto protocol and considerably increasing the fossil price, the attention focused on CO2 regression and renewable energy sources has increased dramatically. In particular, the commercialization and application of MCFC systems fed with biogas have been revived because of the characteristics of CO2 collection and fuel variety of MCFCs. Better economic results of MCFC systems fed with biogas are expected because biogas is a relatively inexpensive fuel compared to liquefied natural gas (LNG). However, the pretreatment cost is added when using anaerobic digester gas (ADG), one of the biogases, as a fuel of MCFC systems because it contains high H2S and other contaminants, which are harmful sources to the MCFC stack in ADG. Thus, an accurate economic analysis and comparison between MCFCs fed with biogas and LNG are very necessary before the installation of an MCFC system fed with biogas in a plant. In this paper, the economic analysis of an MCFC fed with ADG was carried out for various conditions of electricity and fuel price and compared with the case of an MCFC fed with LNG.

Mixed-fuels fuel cell running on methane-air mixture

In order to develop SOFC running on hydrocarbon fuels, we have focused on a new method of improving electrode performance and reducing carbon deposition by coating thin films of samaria-doped ceria (SDC) within the pores of electrode by a sol-gel coating technique. The SDC coating on the pores of anode made it possible to have a good stability for long-term operation due to low carbon deposition and nickel sintering. In this study, we demonstrated a new method of improving electrode performance and reducing carbon deposition by coating thin films of samaria-doped ceria (SDC) and applied the modification technique to two different types of fuel cell structures, anode-supported SOFC and comb-shaped SOFC. From our results, the maximum power density of an anode-supported cell (electrolyte; 8 mol% YSZ and thickness of 30 μm, and cathode; La0.85 Sr0.15 MnO3 ) with the modified anode was about 300 mW/cm2 at 700 °C in the mixture of methane (25%) and air (75%) as the fuel and air as the oxidant. The cell was operated for 500 h without significant degradation of cell performance. For the comb-shaped SOFCs operated in the mixed-fuels fuel cell (MFFC) conditions, the cell performance was 40 mW/cm2 at 700 °C in the CH4 /O2 ratio of 1.Copyright

Preparation of YSZ Coated AISI-Type 316L Stainless Steel by the Sol-Gel Coating Method and Its Corrosion Behavior in Molten Carbonate

The effect of heat-treatment conditions on the corrosion behavior of yttria stabilized zirconia (YSZ) coated AISI-type 316L stainless steels in molten carbonate are investigated. YSZ films on stainless steel were prepared by the sol-gel method. While the sample heat-treated at 800°C for 2 hours in air has an uneven surface microstructure with macrocracks, a YSZ coated sample heat-treated in argon has an even microstructure. The polarization resistance and corrosion rate of YSZ coated sample heat-treated in air were deteriorated from 6.948 Ωcm2 and 364.7 mpy (millimeter per year) to 3.291 Ωcm2 and 769.8 mpy, respectively, by the corrosion for 100 hours due to its poor surface microstructures. At the same experimental condition, meanwhile, those corrosion parameters of YSZ coated sample heat-treated in argon were 15.43 Ωcm2 and 164.2 mpy, respectively, and those were improved to 18.83 Ωcm2 and 134.6 mpy after the corrosion for 100 hours. This is attributed to the YSZ film with well developed surface microstructures. The concentration profiles of elements and X-ray diffractograms indicate that the oxide layer of YSZ coated sample heat-treated in argon had a triple layer structure composed of outer YSZ film, in between Fe2O3 layer, and inner chromium rich layer during corrosion.

Fabrication of an Anode-Supported Sofc with a Sol-Gel Coating Method for a Mixed-Gas Fuel Cell

An anode-supported type solid oxide fuel cell (SOFC) is a promising structure resulting in a very high performance because it consists of a very thin electrolyte. In the preliminary stage, we have succeeded in the fabrication of Samaria-Doped Ceria (SDC) thin film on a porous Ni-Al substrate using a sol-gel coating technique. The thin electrolyte film binds the substrate well and a single cell made with the SDC thin-film electrolyte and porous LSM cathode exhibited a good performance in a mixed-gas condition, even at intermediate temperatures. The single cell, consisting of 20 µm thin SDC electrolytes, the porous Ni-Al anode substrate, and a LSM cathode, exhibited an open circuit voltage of 0.82V and a maximum power density of 0.31 W.cm-2 at 700°C with humidified methane and air mixtures. This cell also generated an open circuit voltage of about 1.1V and a maximum power density of 0.34 W.cm-2 at 600°C with humidified hydrogen as the fuel and air as the oxidant.

Fabrication of electrolyte-impregnated cathode by dry casting method for molten carbonate fuel cells

A dry casting method for fabricating a porous Ni plate, which was used as the cathode for molten carbonate fuel cells, was proposed, and the basic characteristics of the as-prepared cathode were examined and compared with those of a conventional cathode fabricated by using the tape casting method. Through several investigations, we confirmed that the cathode fabricated by using the dry casting method has properties identical to those of the conventional cathode. Electrolyte-impregnated cathodes were also successfully fabricated by using the dry casting method. Several characteristics of the as-prepared electrolyte-impregnated cathodes including their electrical performance were investigated by using tests such as the single cell test. The cell performances of a single cell using a 25-wt% electrolyte-impregnated cathode and not the electrolyte-impregnated cathode were 0.867 V and 0.819 V at a current density of 150 mAcm−2 and 650 °C, respectively. The single cell using a 25-wt% electrolyte-impregnated cathode was also operated stably for 2,000 h. The cell performance was enhanced, and the internal resistance and the charge transfer resistance were reduced after electrolyte impregnation in the cathode. Moreover, the increase in the surface area of the cathode and the further lithiation of the NiO cathode after the electrolyte impregnation in the cathode enhance the area of the three-phase boundary and the electrical conductivity, respectively. However, the cell performance of the single cell using the 35-wt% electrolyte-impregnated cathode was reduced, and the cell could not be operated for a long time because of the rapid increase in the N2 crossover caused by the poor formation of a wet seal.

Development of Reinforced Matrix for Molten Carbonate Fuel Cells by Using Sintering Aids

In order to reinforce a matrix for molten carbonate fuel cell (MCFC), sintering additives having low melting points such as Al [660oC], B2O3 [450oC] and Al(OH)3 powders [320oC] have been included into conventional LiAlO2 green sheets by tape casting method. The mechanical strength was clearly increased by the addition of B2O3 into the LiAlO2 matrix. The enhancement of mechanical strength in the B2O3 -included matrix was mainly attributed to the Li2AlBO4 formation by the reaction between B2O3 and LiAlO2.

Electrical Behaviour and Microstructural Characterization of Magnesia Co-doped Scsz Nanopowders Synthesized by Urea Co-precipitation

Electrical Behaviour and Microstructural Characterization of Magnesia Co-doped ScSZ Nanopowders Synthesized by Urea Co-precipitation Grazia Accardo, Gianfranco Dell’Agli, Domenico Frattini, Luca Spiridigliozzi, Suk Woo Nam , Sung Pil Yoon a Fuel Cell Research Center, KIST-Korea Institute of Science and Technology, Hwarang-ro 14-gil 5, Seongbuk-gu 136-791, Seoul, South Korea b Department of Civil and Mechanical Engineering and INSTM Research Unit, University of Cassino and Southern Lazio, Via G. Di Biasio 43, 03043, Cassino (FR), Italy d16605@kist.re.kr