Electrochemical Performance and Durability of High-Temperature Solid Oxide Electrolysis Cells with SFM and SFM-GDC Fuel Electrodes for Hydrogen and Syngas Production

Abstract

The present study focuses on highly catalytic double-perovskite Sr2FeMoO6-δ (SFM) fuel electrode materials for Solid Oxide Electrolysis Cells (SOECs). The redox stability was characterized using XRD and in-situ TEM analyses to visualize phase conversion above 800 °C after reduction in Ar-3-4% H2. Phase formation of mixed Ruddlesden-Popper, (double‑) perovskite phases, and Fe nanoparticle exsolution was observed and related to the in operando enhanced catalytic performance. Electrolyte-supported single cells with SFM (-Ce0.8Gd0.2O1.9)/GDC/8YSZ/GDC/La0.58Sr0.4Co0.2Fe0.8O3 (LSCF) were prepared and electrochemically evaluated in the range of 750 °C to 900 °C using DC- and AC-techniques. The high electrochemical performance of -1.26 A∙cm-2 and -1.27 A∙cm-2 under steam and co-electrolysis conditions respectively, exceeded state-of-the-art Ni-YSZ by ~38% and was comparable to Ni-GDC fuel electrodes in electrolyte-supported button cells. A long-term durability test was conducted for 500 h at -0.3 A∙cm-2 and 900 °C under steam electrolysis conditions with a fuel gas composition of 50% H2O + 50% H2. The SFM-GDC fuel electrode showed outstanding stability of 15.6 mV∙kh-1 for 500 h measurement. The SFM shows high degradation of around 765 mV∙kh‑1 and a striking structural instability through the evolution of a dense layer at the SFM/GDC interface after 300 h.