Optimal Modeling of Ni/YSZ Triple Phase Boundary in Solid Oxide Cells Using First-Principles Calculations

Abstract

Power generation with renewable energy using solid oxide cells (SOCs) has been widely researched. To solve the existing problems of SOCs, such as degradation and efficiency improvement, it is essential to understand reaction mechanisms on the surface/interface such as triple phase boundary (TPB) composed of catalysts, electrolytes, and gas phases. However, a reliable TPB model has not been uniquely defined to discuss the property. This study 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 by using density functional theory calculations. The stable structure of YSZ surface models was first identified considering various oxygen vacancy positions, yttrium atom arrangements, yttria concentration, and YSZ surfaces. Thereafter, a reliable Ni/YSZ interface model was discussed by evaluating various Ni structure types, Ni interfaces in contact with the YSZ surface, and interface positions. As a result, we have proposed a more reliable YSZ surface structure than previous reports and reasonable Ni/YSZ interface models considering the computational cost to discuss the properties of TPB. These findings will contribute to the improved design of SOCs as high-performance energy conversion systems for sustainable energy storage.