Investigation on electrochemical behavior and degradation mechanism of a reversible solid oxide cell operating at high current densities

Abstract

Reversible solid oxide cell have significant potential for storing energy from intermittent renewable sources. However, the current densities must be increased to improve the energy conversion efficiency and reduce system costs. In this study, a fuel electrode-supported cell with an effective area of 16 cm² was operated for 288 h, switching between solid oxide fuel cell and solid oxide electrolysis cell modes at the current densities of ±1.88 A cm⁻². The electrochemical impedance spectroscopy collected at the open-circuit voltage were analyzed using the distribution of relaxation times and equivalent circuit modeling methods to evaluate the contribution of each electrode process to degradation. The results demonstrated that charge transfer reactions in the fuel and oxygen electrodes were the primary cause of cell performance degradation. According to the post-test analysis, the primary degradation mechanisms are the migration of nickel from the active layer to support layer and the coarsening of nickel in the fuel electrode. Other degradation mechanisms included the segregation of strontium and valence fluctuations of cobalt, which acted synergistically to the oxygen electrode. At elevated current densities, the concurrent migration of nickel in the same direction reduced to a reduction in the triple-phase boundary, which could not be adequately compensated for. This phenomenon significantly impaired the cell performance.