First-Principles Studies for Optimal Model of the Ni/YSZ Triple Phase Boundary in Solid Oxide Cells

To resolve the existing issues of solid oxide cells such as degradation and efficiency improvement, it is essential to understand reaction mechanisms on the surface/interface such as triple phase boundary (TPB) as a highly active site that consists of catalysts, electrolytes, and gas phases. However, the reliable TPB model has not been still uniquely defined to discuss the property. In this study, we have focused on the TPB model comprising Ni catalysts, yttria-stabilized zirconia (YSZ) electrolytes, and gas phases and aimed to theoretically identify a reliable TPB model. In concrete, we identified firstly the stable structure of YSZ surface models by using density functional theory calculations considering different oxygen vacancy positions, yttrium atom arrangements, yttria concentration, and YSZ surfaces. Thereafter, we discussed a reliable Ni/YSZ interface model based on our proposed YSZ model by evaluating different Ni structure types, Ni interfaces in contact with the YSZ surface, and interface positions.