(Invited) Early-Onset Degradation of (La,Sr)(Co,Fe)O3 in Solid Oxide Electrolysis Cells
Authors: Slomski Heather S , Kaufman Jonas , Dzara Michael , Strange Nicholas A. , Hartvigsen Jeremy , Kane Nicholas , Casteel Micah , Wood Brandon C. , Ginley David , Kweon Kyoung E. , Gorman Brian , Shulda Sarah 
Published: December 2024

The increasing need for global hydrogen ideally depends on low-cost 1$/kg green hydrogen. The DOE’s Energy Earthshot initiative aims to reduce the cost of green hydrogen to achieve this goal in a decade. There are a number of pathways of which solid oxide electrolysis cells (SOECs) are one of the most attractive1. SOECs have high demonstrated efficiency for hydrogen production without precious metal catalysts but at present with limited lifetimes2–4. SOEC’s have a layered structure consisting of an LSCF-GDC composite cathode (La0.6Sr0.4Co0.2Fe0.8O3-δ / gadolinium doped ceria), a GDC barrier layer, YSZ (yttrium stabilized zirconia) electrolyte, and Ni-YSZ anode support layer. This structure exhibits various degradation mechanisms initiating at both the air and fuel electrode at high operating temperatures predominately at the interfaces5,6.

Understanding the mechanisms behind cell degradation and their potential effects on cell performance is critical to reach hydrogen Earthshot goals. There has been significant focus on the coarsening of Ni in the fuel electrode and advancement made in reducing its negative effects on cell performance over time 7. Another significant mechanism is due to the degradation of LSCF at temperatures above 550 °C 8. As LSCF degrades, Sr migrates from the structure and becomes mobile throughout the cell. This poses problems as it reaches the electrolyte and forms SrZrO3 which causes both ohmic losses and potential mechanical failure9. This study focuses on the initiation of this mechanism and its progression in the break in period of the cell. Extensive characterization of early-onset degradation is achieved through SEM (Scanning Electron Microscopy), STEM EDS (Scanning Transmission Electron Microscopy), XANES (X-ray Absorption Near Edge Structure) and Synchrotron XRD (X-ray Diffraction). These techniques are then paired with first principles calculations of the 6428-LSCF phase stability in modeling the stoichiometric changes to rhombohedral LSCF in the cell. Together this allows us to achieve spatial mapping, phase progression over time, and predict stoichiometry changes in early onset degradation. These methods identify several unique phases that result from the degradation of LSCF some of which are known to impact cell lifetimes. Identifying the pathways of early onset degradation allows for mitigation strategies to be developed for cell sintering and fabrication.

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