Understanding Degradation Onset in High Temperature Electrolysis Cells with Transmission X-Ray Microscopy

Abstract

High temperature electrolysis (HTE) cells struggle to reach lifetimes in the thousands of hours for hydrogen production from steam. While oxygen-conducting solid oxide electrolysis cells (o-SOECs) are a more mature technology than proton-conducting (p-SOECs) counterparts, both types of cell suffer from multiple decomposition modes including: delamination of layers, atomic migration, secondary phase formation, and reaction at the triple-phase boundaries at the electrodes. While the macroscopic results of these decomposition modes have been reported, the mechanisms driving onset and evolution of these decomposition modes is not well understood. In this work, we report on the results of a collaborative effort between four national laboratories to investigate the onset of decomposition in aged HTE cells using transmission X-ray microscopy (TXM) at SSRL at SLAC of o-SOEC and p-SOEC cells. Using TXM we volumetrically image, in 3D, the density of aged cells with 30 nm x 30 nm x 30 nm voxel (3D pixel) resolution. Using this technique, we investigate the nucleation of interfacial voids and the near-environment around those voids; revealing insight into the mechanism driving void formation. SSRL’s TXM also enables the use of X-ray absorption near edge structure (XANES) measurements at each voxel, which yields stoichiometric and oxidation state maps of key elements. This XANES data, combined with TXM, allows identification of how elemental migration, and oxidation state changes, drive the formation of voids. Similarly, the evolution of the triple-phase boundaries at the electrodes is investigated using a combination of TXM and XANES. Together, this work demonstrates a powerful technique for investigating the onset and evolution of decomposition in a range of HTE cells.