메탄 SOFC 시스템의 촉매연소반응용 Cu-Mn 산화물 촉매 개발 및 응용에 관한 연구

Abstract

Solid Oxide Fuel Cells (SOFCs) are promising energy conversion device which has high energy efficiency and environmentally friendly, especially distributed generation for buildings. There are many kinds of studies on the SOFC systems, but in this study, we focused on two issues: (1) purification and energy recycling of SOFC stack flue gas and (2) decreasing temperature deviation in large active area SOFCs. For issue (1), we designed integrated thermal unit (ITU) which is integrated device of reformer, heat exchanger, combustor. Especially for combustor, an efficient oxidation catalyst was developed to increase the combustion efficiency of unreacted CO, H2, and CH4 in flue gas of SOFC stack. Amorphous Cu-Mn oxide catalyst (CuMnLa/Alumina) showed high catalytic activity, but significant degradation occurred due to phase transition to spinel structure at high temperatures (T > 650 °C). La0.8Sr0.2Mn0.67Cu0.33O3 perovskite (LSMC(p)) supported CuO or Mn2O3 exhibited improved thermal stability than CuMnLa/Alumina catalyst. Especially in case of 50Mn/LSMC(p), after the catalyst was exposed to 800 °C for 24 h, T50 of CO, H2 and CH4 was achieved at 170, 230 and 600 °C, respectively. This result is much lower than that of CuMnLa/Alumina, which was exposed to the same condition. The high combustion efficiency is due to retention of the Cu2+-Mn3+ redox couple, and supply of lattice oxygen from LSMC(p), especially at high temperature. Developed 50Mn/LSMC(p) was introduced to simply designed reforming-oxidation coupled (ROC) reactor and compared with CuMnLa/Alumina, in terms of CH4 conversion in methane steam reforming reaction. When the temperature of SOFC stack flue gas was 650 °C, the increase in CH4 conversion with using 50Mn/LSMC(p) (44.9 %) was two times higher than using CuMnLa/Alumina (20.3 %). For issue (2), the main reason for temperature deviation in SOFC is the endothermic reaction of direct reforming process. An idea with combustion of methane at cathode to compensate this endotherm was proposed. The LSMC(p) which was developed in issue (1) and used as support material was applied to SOFC cathode for methane combustion. In this study, the applicability of LSMC(p) as SOFC cathode was investigated and compared with LSM(p) which is well-known conventional cathode material for SOFCs. The performance of LSMC(p) cathode cell at 800 °C was 299 mW/cm2 which is 10 % higher than that of LSM(p) cathode cell, due to its higher electrical and oxygen ion conductivity at this operating temperature.