Sm_(0.5)Sr_(0.5)Co_(0.4)M_(0.6)O_3(M=Co,Mn,Fe)作为IT-SOFCs阴极的结构与性能

Structure and Properties of Sm_(0.5)Sr_(0.5)Co_(0.4)M_(0.6)O_3(M=Co,Mn,Fe) as IT-SOFCs Cathodes

通过X射线衍射(XRD)、热重、热膨胀、电导率以及交流阻抗等测试方法,研究了Sm0.5Sr0.5Co0.4M0.6O3(M=Co,Mn,Fe;分别简写为SSCC,SSCM,SSCF)作为中低温固体氧化物燃料电池(IT-SOFCs)阴极的结构与性能.研究表明,固相法合成的Sm0.5Sr0.5Co0.4M0.6O3均为正交钙钛矿型结构,材料的结构参数和性能都与M元素半径及M—O的键能有关.晶胞参数随着Co、Mn、Fe的顺序增大.材料的氧空位浓度、热膨胀系数、电导率、电极催化活性随着Co、Fe、Mn的顺序降低.同时由于SSCM较低的氧空位浓度,使得电极反应受到氧在电极内的扩散过程控制,具有较差的电极催化性能,而SSCC和SSCF较高的氧空位浓度,电极反应同时受到电极表面氧还原反应和氧离子在电极中的扩散过程混合控制.由于SSCF具有较高的氧扩散系数,使得700℃以上SSCF电极表面氧还原电阻(ASR)也低于SSCC的,因而出现了SSCF的总电极催化活性高于SSCC的现象.

The structure and performance of Sm0.5Sr0.5Co0.4M0.6O3（M=Co, Mn, Fe; denoted SSCC, SSCM and SSCF, respectively） as intermediate temperature-solid oxide fuel cells （IT-SOFCs） cathodes were investigated by X-ray diffraction （XRD）, thermogravimetry （TG）, thermal expansion, electrical conductivity and electrochemical impedance spectroscopy （EIS）. The Sm0.5Sr0.5Co0.4M0.6O3 system has an orthorhombic structure. The crystal parameter increases in the following order： Co, Mn, Fe, while the oxygen content, thermal expansion and electrical conductivity decrease in the same order. The electrocatalytic activity of SSCM cathodes is limited by the oxide ion diffusion process because of low oxide ion vacancy, while the electrocatalytic activity of SSCC or SSCF is controlled by an oxygen exchange process on the cathode surface and an oxide ion diffusion process in the cathode because of the high oxide ion vacancy. The area specific resistance （ASR） of SSCF is lower than that of the SSCC above 700 ℃ because of the high oxide diffusion coefficient of SSCF, so the total electrocatalytic activity of SSCF is higher than that of SSCC.