Synthesis and characterization of (La_0.75Sr_0.25)Cr_0.5Mn_0.5O_3-δ, a redox-stable, efficient perovskite anode for SOFCs

Perovskite-related materials, (La_0.75Sr_0.25)_1–xCr_0.5Mn_0.5O_3–( 0 ≤ x ≤ 0.1) (LSCM), have been synthesised and examined as potential anode materials for solid oxide fuel cells (SOFCs). La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ exhibits a rhombohedral structure. It appears to be chemically compatible with yttria-stabilized zirconia (YSZ) to at least 1300°C. At 900°C, its electrical conductivity is about 38 S/cm in air and 1.5 S/cm in 5% H₂ (p_O210^–21 atm). Good performance was achieved using LSCM as anode with a polarization resistance 0.9 and 0.47 Ω cm² in wet 5% H₂/Ar and wetH₂, respectively. The anode polarization was further reduced to 0.6 and 0.25 Ω cm² in wet 5% H₂/Ar and wetH₂ when a thin layer of Ce_0.8Gd_0.2O_2–(CGO) layer was coated between YSZ and LSCM anode. Stable performance was sustained for at least for 4 h operating in wet methane. By improving the electrode microstructure, the electrode polarization resistance approaches 0.2 Ω cm² at 900°C in 97% H₂/3% H₂O for LSCM containing a small amount of YSZ to improve adherence but without CGO. Very good performance is achieved for methane without using excess steam. Using ambient humidification (i.e., 3% H₂O), the same performance is achieved with methane at 950°C as for hydrogen at 850°C. The anode is stable in both fuel and air conditions and shows stable electrode performance in methane. Thus, both redox stability and operation in low-steam hydrocarbons have been demonstrated, overcoming two of the major limitations of the current generation of nickel zirconia cermet SOFC anodes. LSCM and other complex perovskites are promising anode materials for SOFCs. (C) 2004 The Electrochemical Society.