Degradation behavior of galvanostatic and galvanodynamic cells for hydrogen production from high temperature electrolysis of water

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. Apart from the technoeconomic considerations, commercial deployment of this technology critically depends on the long-term performance and durability of SOEC cells/stacks, especially under dynamic operations to withstand the intermittency of renewable energy. Herein, SOEC operation was conducted under galvanodynamic conditions and compared with galvanostatic cells to examine the effect on degradation behavior at an average current density of -0.75 A cm- 2 at 750 degrees C. While dynamic operation shows no significant impact on the overall degradation rates compared to constant current operation, minor performance improvement was observed at potentials above 1.5 V when switched to galvanodynamic mode. The relatively lower overpotential during dynamic operation could not be explained by the negligible changes in the electrochemical impedance or cell temperature. Multiphysics modeling reveals that the oxygen partial pressure (PO2) in the electrolyte oscillates with the alternating current density under dynamic operations. The minor improvement in cell performance under dynamic mode might be associated with the relatively lower PO2 buildup as compared with that under galvanostatic operation. In addition, dynamic operation at high frequencies could effectively lower the extreme PO2 in the electrolyte, thus relieving stresses in the cells and alleviating cell degradation.