Accelerated Reactive Force Field Molecular Dynamics Simulation on the Diffusion Process in Ni/YSZ Anode of SOFCs with Collective Variable-Driven Hyperdynamics

Due to advantages such as high efficiency, low emissions, and fuel flexibility, solid oxide fuel cells (SOFCs) have garnered significant attention as promising power sources for automotive applications. Nickel/yttria-stabilized zirconia (Ni/YSZ) is one of the most widely used anode materials in SOFCs, as it can catalyze both chemical and electrochemical reactions of carbon-containing fuels. However, the direct use of carbon-containing fuels can lead to carbon deposition on the Ni/YSZ anode, negatively impacting the performance and reliability of automotive SOFC systems. The diffusion of carbon atoms within nickel plays a crucial role in the carbon deposition process and requires further investigation. The oxygen atoms that spillover from YSZ also participate in main reactions such as carbon deposition and electrochemical reactions in Ni. Molecular dynamics (MD) is one of the main methods for studying atomic diffusion in crystalline structures. In this study, reactive force field molecular dynamics (ReaxFF-MD) models of Ni and Ni/YSZ crystal structures are established. The operating temperature of automotive SOFCs is typically 500-700°C, which results in a low frequency of diffusion events in the ReaxFF-MD model, leading to high computational costs. Therefore, an acceleration technique known as collective variable-driven hyperdynamics (CVHD) is employed to extend the time scale of the simulations. The diffusion coefficient of carbon atoms in nickel at low temperatures is calculated. Additionally, the spillover process of oxygen atoms in YSZ is considered, and the diffusion coefficients of oxygen atoms in both Ni and YSZ are calculated. The Arrhenius equation parameters for carbon and oxygen diffusion in nickel are determined, laying the foundation for further studies on the mechanisms of carbon deposition and oxidation on Ni/YSZ anode materials.