Ni migration of Ni-YSZ electrode in solid oxide electrolysis cell : an integrated model study

Abstract

During the long-term operation of solid oxide electrolysis cell (SOEC), the coarsening and depletion of the Ni phase of the electrode are found to decrease the cell performance and limit cell durability. In this study, a comprehensive numerical study is conducted to quantitatively evaluate the degradation process in the fuel electrode of SOEC. The phase-field model is adopted to track the Ni phase migration process and generate the electrode structures with Ni depletion. An electrode model based on the lattice Boltzmann method is then used to evaluate the electrochemical performance of the fuel electrode. It is found that the maximum width of the Ni depletion region can reach 3–4 μm. The Ni depletion will aggravate the coarsening of the Ni phase. The corresponding electrochemical evaluation also shows that the randomly distributed ionic particles in the porous fuel electrode lengthens the ion transport path and increases the electrode ohmic overpotential. The Ni depletion also increases the activation overpotential loss due to the reduction of the active reaction sites. The severe Ni depletion can increase the total overpotential by up to 52.8% compared to the initial state. Besides, increasing the wettability of the Ni phase can effectively suppress the reduction of active reaction sites due to Ni coarsening.