A Method for Time-Resolved Characterization of Polarization-Induced Solid Oxide Cell Microstructure Evolution

Abstract

Solid oxide cell long-term durability experiments are resource-intensive and have limited ability to capture the interdependence of microstructural evolution and electrochemical performance. Studies of microstructural degradation mechanisms are usually limited to before and after life-test images. Here we describe a life testing method that simultaneously operates multiple symmetric cells under different conditions, simultaneously providing information on electrolysis and fuel cell operation, while sampling the microstructure during operation. The method utilizes laser-cutting to exactly define different cell areas, allowing testing under different current densities with a single current source, and facilitating removal of segments of the cells during life tests, allowing for microstructural evaluation at intermediate times. The method is demonstrated in Ni-YSZ / YSZ / Ni-YSZ fuel-electrode-supported cells at low H2O/H2 ratios. Characterization using SEM-based imaging techniques shows pronounced microstructural damage that increases rapidly with increasing current density and time, mirroring observed electrochemical degradation. The present results agree with prior reports for SOC operation under such conditions but reveal new features of the degradation process via the unique capability of time-resolved imaging.

Microstructural Changes in Ni-YSZ Electrodes Operated in Fuel Cell and Electrolysis Modes: Effect of Gas Diffusion Limitations

“…ESSCs were produced by tape casting, lamination, and co-sintering as described elsewhere 9 . ESSCs were then reduced and laser-scribed 9 , producing samples with 4 discrete removable sections (see insets in Figure 1) that can be analyzed during the life test. Samples were cut into 1.0, 0.75, and 0.5 cm 2 squares to create different current densities with a single current source.…”

“…This would also explain why the condition is more severe at electrolyzer stack inlet than outlets; at the latter steam content has been greatly diminished. Here we use a method developed by Cox that uses laser-scribed Ni-YSZ electrodesupported symmetric cells (ESSC) to study polarization-induced microstructural evolution by periodic sampling the microstructure over time while maintaining an accurately controlled cell area 9 . The ESSCs enable rapid screening by parallel or in-series operation in the same environmental chamber, simultaneous anodic (fuel cell) and cathodic (electrolyzer) polarization of Ni-YSZ, and the elimination of seals, but the simultaneous operation of the two electrodes requires that both electrodes stably operate in a given gas condition, making high steam operation difficult without oxidation of Ni in the anode.…”