Changes in Microstructure of Ni-Co Dispersed Samaria-Doped Ceria Hydrogen Electrodes for the Improved Durability via Reversible Cycling Operation of Solid Oxide Cells

We have quantitatively analyzed changes in the microstructure of double-layer hydrogen electrodes for solid oxide cells (SOCs), which consist of porous samaria-doped ceria (SDC) with highly dispersed Ni-Co nanoparticles as the catalyst layer (CL) and a thin current collecting layer of Ni-YSZ cermet, whose durability we recently found to undergo a remarkable improvement via reversible cycling operation between steam electrolysis and fuel cell-modes. It was demonstrated by focused ion beam-scanning electron microscopy (FIB-SEM) that the Ni content in the CL was nearly fully maintained by the cycling operation, compared with a significant decrease in Ni after the electrolysis single-mode operation. The lower parts of many Ni-Co particles were observed to be anchored tightly on the SDC support after the cycling operation, probably due to a strong interaction between Ni-Co and SDC. Such a stabilization of the microstructure is proposed to contribute to the improved durability.