Correlation between microstructure and catalytic and mechanical properties during redox cycling for Ni-BCY and Ni-BCZY composites

In this work, we investigated changes in catalytic activity and cumulative redox strain (CRS) of Ni-BaCe_0.8Y_0.2O₃ (Ni-BCY) and Ni-BaCe_0.6Zr_0.2Y_0.2O₃ (Ni-BCZY) after reduction and oxidation (redox) cycles at 800 °C. The chemical interaction between a NiO particle and a BCY particle (or a BCZY particle) was analyzed by hydrogen temperature-programmed reduction (H₂-TPR) technique. The reduction peak temperature of NiO-BCY and NiO-BCZY decreased with redox cycles. After 3 redox cycles, the reduction peak temperature of NiO-BCY became lower than the peak of NiO-BCZY. The results indicate NiO particles had a stronger bonding with BCZY particles than with BCY particles after redox cycles. The dimensional change of the composites under redox cycles was examined by thermomechanical analysis. After three redox cycles, CRS of NiO-BCY was higher than that of NiO-BCZY. This result indicates doping Zr to BCY stabilized structure. SEM images of NiO-BCY and NiO-BCZY show that Ni particles aggregated after redox cycles, leading to structure destruction and volume expansion of the composites. Moreover, NiO-BCY samples have larger and more cracks than NiO-BCZY samples after redox cycles.