Degradation Behavior of Galvanostatic and Galvanodynamic Cells for Hydrogen Production from High Temperature Electrolysis of Water

Abstract

High temperature electrolysis of water using solid oxide electrochemical cells (SOEC) is a promising technology for hydrogen production with high energy efficiency and may promote decarbonization when coupled with renewable energy sources and excess heat from nuclear reactors. One of the challenges facing the commercial deployment of this technology is improving the cost competitiveness of hydrogen produced by electrolysis, which, among other factors, critically depends on the long-term durability of the SOEC system under relevant duty cycles. To extend the lifetime and optimize hydrogen production costs over projected lifetimes, fundamental knowledge of degradation mechanisms and rates as a function of operating conditions is a critical gap to close. Degradation mechanisms of solid oxide electrolysis cells are often coupled with each other and may vary based on cell overpotential and current, making them difficult to isolate and investigate effectively. Pulse Width Modulation (PWM) can be used to create a low-time scale variation under operating conditions that can identify non-linear degradation mechanisms between current and voltage. The short-term perturbations caused by PWM can help relieve stressors compared to cells running under constant (e.g., galvanostatic) conditions, even if the average current that the cell experiences over time is the same. In this work, water electrolysis cells were operated under dynamic conditions and compared with galvanostatic cells with respect to overall cell lifetime and degradation behavior. Specifically, the increases in overpotential and impedance are analyzed and compared between these two different operating modes to provide insights into the differences between average and instantaneous current.