Redox stability and electrochemical study of nickel doped chromites as anodes for H2/CH4-fueled solid oxide fuel cells

The influence of nickel and strontium incorporation in LaCrO3 on the crystalline structure, redox behavior and electrochemical performance by impedance spectroscopy using symmetrical cells has been studied. Namely, the La1-xSrxCr1-yNiyO3-delta (x = 0, 0.15: y = 0.05, 0.1, 0.2) system was investigated. Structural and redox evolution has been monitored by X-ray diffraction in oxidized and reduced samples. Reduced samples kept the initial perovskite structure although metallic nickel nanoparticles were detected on the perovskite grain surface by TEM analysis. The re-oxidized surface did not present nickel particles, suggesting the nickel re-incorporation into perovskite lattice coupled with cation diffusion. The perovskites were tested as SOFC anodes and the polarization resistance depended on the nickel stoichiometry and the reduction temperature. La0.85Sr0.15Cr0.9Ni0.1O3-delta reduced at 800 degrees C showed the lowest polarization resistance, both in hydrogen and methane. In fact this composition showed a 20% methane conversion at 900 degrees C for the methane steam reforming in a fixed bed reactor. Tolerance to redox cycling was proved electrochemically by in situ treatments of La0.85Sr0.15Cr0.9Ni0.1O3-delta electrode. Materials were further analyzed by TPR and XPS (in oxidized and reduced state) in order to identify the possible species involved in the electrocatalytic processes. (C) 2011 Elsevier B.V. All rights reserved.