Processing of composites based on NiO, samarium-doped ceria and carbonates (NiO-SDCC) as anode support for solid oxide fuel cells

NiO-SDCC composites consisting of NiO mixed with Sm-doped ceria (SDC) and carbonates (Li2CO3 and Na2CO3) were sintered at different temperatures and reduced at 550 degrees C. The influence of reduction on structure of the NiO-SDCC anode support for solid oxide fuel cells (SOFCs) was investigated. Raman spectra of the NiO-SDCC samples sintered at 500, 600 and 700 degrees C showed that after reducing at 550 degrees C NiO was reduced to Ni. In addition, SDC and carbonates (Li2CO3 and Na2CO3) did not undergo chemical transformation after reduction and were still detected in the samples. However, no Raman modes of carbonates were identified in the NiO-SDCC pellet sintered at 1000 degrees C and reduced at 550 degrees C. It is suspected that carbonates were decomposed at high sintering temperature and eliminated due to the reaction between the CO32- and hydrogen ions during reduction in humidified gases at 550 degrees C. The carbonate decomposition increased porosity in the Ni-SDCC pellets and consequently caused formation of brittle and fragile structure unappropriated for SOFC application. Because of that composite NiO-SDC samples without carbonates were also analysed to determine the factors affecting the crack formation. In addition, it was shown that the different reduction temperatures also influenced the microstructure and porosity of the pellets. Thus, it was observed that Ni-SDC pellet reduced at 800 degrees C has higher electrical conductivity of well-connected microstructures and sufficient porosity than the pellet reduced at 550 degrees C.