MSE Grads Talk: Emily Ghosh

Speaker: Emily Ghosh, Boston University

Title:: Quantification of 4 Phase Microstructural Changes in Solid Oxide Electrolysis Cell Fuel Electrodes

Abstract: Solid Oxide Electrolysis Cells (SOECs) are considered a promising solution to the increased grid-scale energy demand as they can offer long term energy storage to supplement the use of renewable resources with known intermittencies and over production issues while providing a clean option for hydrogen fuel generation. However, long time operation at the high temperatures required for sufficient electrochemical activity leave SOECs prone to various modes of degradation, significantly decreasing the overall cell lifetime. One such issue is the phase instability of Ni in the porous Ni-YSZ fuel electrodes. Ni is crucial to fuel electrode performance due to its catalytic activity and role as the electrical conduit between electrochemical reaction sites. Its instability can cause loss of electrical connectivity in the electrode, reaction site deactivation and degraded cell performance. Accurate characterization of its morphological evolution can thus help us better understand how to mitigate this degradation and extend SOEC lifetimes. In this work, a novel scanning electron microscopy (SEM) imaging technique is presented to characterize percolated (connected) Ni, unpercolated (disconnected) Ni, YSZ, and pore phases of a Ni-YSZ fuel electrode in a single image to provide holistic view of the Ni-YSZ 4-phase microstructure. This allows for characterization of the effects of operation exposures on the morphological and location dependent Ni phase changes. Microstructural changes in the Ni-YSZ active and support layers were characterized after long term electrolysis (SOEC) operation with respect to untested microstructure. Both regions were characterized for degradation after chemical and electrochemical exposure by examining electrochemically active and inactive regions of the tested cell. 4-Phase analysis revealed significant changes from both exposures and significant changes in the support layer in comparison to the active layer. Observations on total Ni migration within the electrode are also presented.