Transient characteristics of a solid oxide electrolysis cell under intermittent power-supply conditions

Solid oxide electrolysis cell (SOEC) is a promising electrochemistry device to produce hydrogen from intermittent renewable power sources. To provide a quantitative understanding of the transient characteristics of SOEC, especially under fluctuating power-supply conditions, a numerical 3-D transient simulation is conducted in this study. Through the analysis on the electrical, molar, and thermal responses of SOEC to voltage ramps with different ramp rates and ramp magnitudes, it is found that the discrepancies in transfer rates – electronic/ionic > mass > heat – lead to the electrical undershoots or overshoots after fast voltage changes. A quantitative analysis from linear time-invariant systems shows that the electrical responses of SOEC are governed by two time constants (related to mass transfer and heat transfer) in the functional layer. Based on the acquired time constants, control strategies on dynamic responses of SOEC are discussed. Slowing down the voltage ramp is effective in alleviating the current overshoots induced by mass-transfer lag but ineffective in those induced by heat-transfer lag. In addition, spatial factors, such as the rib and the length of channel, also have significant impacts on the electrical responses, e.g., inducing non-uniform electrical responses in the functional layer. The results of this study are essential for the design and dynamic control of SOEC.