초음파 분무 열분해법을 이용한 나노 다공성 La_(0.6)Sr_(0.4)CoO_(3-δ) 입자 제조 및 코팅을 통한 산소분리 투과막 특성 분석

Abstract

기체분리막이란 기체 혼합물 중 특정 기체성분만을 분리해낼 수 있는 막으로 낮은 에너지소비, 장치의 간소화, 가공의 용이성, 낮은 투자 및 운용비용 등 여러 가지 장점으로 인하여 다른 방법들에 비해 혼합기체의 분리가 간단하다. 특히 산소이온전도에 의한 투과에 의해 분리가 이루어지는 산소투과분리막에 많은 관심이 집중되고 있는데, Teraoka 등에 의해 높은 이온전도도를 갖는 물질로 보고된 LaCoO3 조성을 기본으로 한 페롭스카이트 (perovskite)계 산화물 (ABO3)을 사용하며, 여러 양이온을 치환한 이온전도체에 대하여 많은 연구가 이루어지고 있다. LaSrGaFeO3의 경우 고체산화물 연료전지의 대표적인 전극 물질 중 하나이며, 현재까지 알려진 바에 따르면 가장 높은 이온전도도를 보이는 재료로 알려져 있다. 하지만 장시간 작동될 때 극심한 환원 분위기에 의해 상변태와 미세구조 변형이 일어나고, 이로 인해 낮은 안정성을 나타내며 반응성이 저하되는 단점을 가지고 있다. 이러한 단점을 보완하기 위해 나노 La0.6Sr0.4CoO3-δ박막을 코팅하여 표면 개질을 시도하였고, 다공성 박막을 제조하여 삼상계면의 확대로 인한 반응성과 안정성 향상을 도모하였다.; Teraoka et al. were the first to reported perovskite-oxides(ABO3) such as La0.6Sr0.4CoO3-δ(LSC) with high ionic conductivity. The properties of these oxides can be easily modified by the substitution of the A-site cation by another metal elements with lower valance. In the La1-xSrxCoO3 system, for instance, the substitution of Sr2+ for La3+ causes oxygen holes in the lattice, keeping the balance of electric neutrality. Such the vacancies produced in the lattice are well known to play an important role in diffusion of oxygen anions in the lattice matrix. At present, the perovskite-oxide has been studied the cathode material of Solid Oxygen Fuel Cell(SOFC). The SOFC cathode is required not only high electronic conductivity but also high ionic conductivity. In addition, to increase active sites, it should contain enough nano porosity to maintain the three phase boundary(TPB) among oxygen, electrode and electrolyte. In that sense, LSC powder is a very attractive material because it consists of a good electronic and ionic conductor. The LSC powder can also keep enough porosity as synthesized by ultrasonic spray pyrolysis method. Another application of perovskite-oxide is oxide separation membrane which could separate oxygen gas component among gas mixture. In addition, it has been studied these membranes because of various advantages such as low energy consumption, simple equipment, easy process and low cost. If this material of membrane maintained porosity, it could occur efficient reaction in inter surface of membrane and gas mixture. In this paper, it is investigated powder preparation from mixture of precursor and addition of polymer for the nano pore of LSC powder by ultrasonic spray pyrolysis method. And we reported here an improvement of ionic conductivity by coating nano porous LSC or Pt-doped LSC powder on LSGF membrane It was succeeded to preparation of nano porous LSC by ultrasonic spray pyrolysis method. According to addition of water-soluble polymer, it was possible to control of pore. On the oxygen permeation experiment, oxygen flux increased by coated nano porous or Pt-doped LSC powder on LSGF. It is able to conclude that cathode of SOFC and oxygen separation membrane with porosity of LSC could occurred active sites by increasing of surface area and they could consider efficient reaction. And Highly dispersed nm-sized Pt particles effectively enhanced the performance of the cathode, which is a promising cathode for medium temperature SOFCs.