Evaluation of Ca3(Co,M)2O6 (M=Co, Fe, Mn, Ni) as new cathode materials for solid-oxide fuel cells

Abstract

Series compounds Ca3(Co0.9M0.1)2O6 (M=Co, Fe, Mn, Ni) with hexagonal crystal structure were prepared by sol–gel route as the cathode materials for solid oxide fuel cells (SOFCs). Effects of the varied atomic compositions on the structure, electrical conductivity, thermal expansion and electrochemical performance were systematically evaluated. Experimental results showed that the lattice parameters of Ca3(Co0.9Fe0.1)2O6 and Ca3(Co0.9Mn0.1)2O6 were both expanded to certain degree. Electron-doping and hole-doping effects were expected in Ca3(Co0.9Mn0.1)2O6 and Ca3(Co0.9Ni0.1)2O6 respectively according to the chemical states of constituent elements and thermal-activated behavior of electrical conductivity. Thermal expansion coefficients (TEC) of Ca3(Co0.9M0.1)2O6 were measured to be distributed around 16×10−6K−1, and compositional elements of Fe, Mn, and Ni were especially beneficial for alleviation of the thermal expansion problem of cathode materials. By using Ca3(Co0.9M0.1)2O6 as the cathodes operated at 800°C, the interfacial area-specific resistance varied in the order of M=Co<M=Fe<M=Ni<M=Mn, and the over-potential increased in the order of M=Fe≈M=Co<M=Mn<M=Ni. Among all of these compounds, Ca3(Co0.9Fe0.1)2O6 showed the best electrochemical performance and the power density as high as ca. 500mWcm−2 at 800°C achieved in the single cell with La0.8Sr0.2Ga0.83Mg0.17O2.815 as electrolyte and Ni–Ce0.8Sm0.2O1.9 as anode. Ca3(Co0.9M0.1)2O6 (M=Co, Fe, Mn, Ni) can be used as the cost-effective cathode materials for SOFCs.