Shin Ae Song

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.

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.

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.

Synthesis of Zirconium-Based Material-Coated LiNi0.8Co0.2O2 Cathode Using a New Coating Method

Zr-compound-coated LiNi0.8Co0.2O2 is prepared in a single step using a new powder coating process, a modified flame spray pyrolysis method using a water-in-oil emulsion precursor solution. Only the Zr precursor is dissolved in the oil phase and the precursors of LiNi0.8Co0.2O2 are dissolved in the water phase. In a flame, precursors in the water phase transform into LiNi0.8Co0.2O2 core particles and the Zr precursor in the oil phase transforms into a coating layer on the LiNi0.8Co0.2O2 surface. After Zr compound coating, both the electrochemical performance and cycle stability are enhanced because the Zr compound coating layer prevents the oxidation of Ni3+ of LiNi0.8Co0.2O2 by acidic electrolyte. Since the Zr compound material is coated to prevent the Li2CO3 formation on the LiNi0.8Co0.2O2 surface, the effectiveness of the Zr compound coating in preventing Li2CO3 formation is investigated. After the as-prepared Zr-compound-coated LiNi0.8Co0.2O2 particles and bare LiNi0.8Co0.2O2 particles were exposed in an air for a month, the changes in morphologies and structures before and after aging were observed by using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It is confirmed that Zr compound coating effectively reduces the amount of Li2CO3 formation.