Theoretical Understanding of Effects of Operating Modes on the Performance Durability of Solid Oxide Cells: A Comparison between Potentiostatic and Galvanostatic Operations

Abstract

In solid oxide cells (SOCs), the choice between galvanostatic (constant current) and potentiostatic (constant voltage) modes does not significantly affect the performance of SOCs as long as the cell components remain unchanged and intact. However, the degradation of cell components, which leads to changes in electrochemical and physical properties of the cell, elevates the importance of the selected operating mode. This paper aims to investigate the effects of galvanostatic and potentiostatic operating modes on the evolving properties of SOCs and their subsequent influence on performance durability. Employing non-equilibrium thermodynamic analysis, a crucial approach for understanding the degradation phenomena within an active electrochemical system, this study aims to provide in-depth insights into how these operating modes affect the longevity and efficacy of SOCs. Key findings include: In cases where oxygen electrode (OE) degradation is accelerated by higher partial pressure of oxygen ( pO2 ), operating under constant voltage electrolysis can mitigate the high pO2 at the OE|electrolyte (OE|EL) interface. Conversely, if OE degradation occurs more rapidly under a lower pO2, constant current electrolysis is more effective in suppressing degradation by achieving a high pO2 at the OE|EL interface. For degradation of the fuel electrode (FE) due to higher pO2, constant current electrolysis is beneficial for more stable performance, which helps maintain low pO2 at the FE|EL interface. When FE degradation is accelerated by lower pO2, constant voltage electrolysis can avert low pO2 at the FE|EL interface. In practical scenarios, more complex degradation mechanisms come into play, especially when pO2 significantly deviates from initial conditions. Degradation in one electrode can influence pO2 in the other electrode, a phenomenon more pronounced in potentiostatic than in galvanostatic electrolysis.