Phase stability, redox-behavior and carbon-tolerance of Sr_1−x(Ti_0.3Fe_0.7−yNi_y)O_3−δ with exsolved nanoparticles

Ni-exsolution from perovskites has gained significant attention in the area of electrode materials for fuel and electrolysis cells due to their potential for high catalytic activity, tolerance to degradation, improved redox-cycling stability, and regeneration of the nanoparticles. We investigated the exsolution behavior and phase stability of bulk Sr_1−x(Ti_0.3Fe_0.7−yNi_y)O_3−δ ceramics at various temperatures and atmospheres. To assess its tolerance to carbon deposition, Sr_1−x(Ti_0.3Fe_0.7−yNi_y)O_3−δ was compared with commonly used Ni-YSZ materials in the presence of tar-containing biogas. Nanoparticle exsolution was observed in the entire investigated temperature range of 710-900 °C. Above a reduction temperature of 740 °C, Sr_1−x(Ti_0.3Fe_0.7−yNi_y)O_3−δ partially transforms to a Ruddlesden-Popper phase, while reverting back to the perovskite phase during reoxidation. This phase transition resulted in material expansion and the formation of cracks. Moreover, exposure of reduced Sr_1−x(Ti_0.3Fe_0.7−yNi_y)O_3−δ to ambient air or H₂O led to the formation of secondary phases and fragmentation of sintered pellets. Remarkably, when compared to Ni-YSZ, these materials exhibited no degradation in terms of carbon deposition or Ni dusting after exposure to tar-containing biogas.