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 Sr₂FeMoO_6−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 (-Ce_0.8Gd_0.2O_1.9)/GDC/8YSZ/GDC/La_0.58Sr_0.4Co_0.2Fe_0.8O₃ (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 0.016 mV h⁻¹ for 500 h measurement. The SFM electrode exhibited a high degradation of around 0.765 mV h⁻¹ and a striking structural instability through the evolution of a dense layer at the SFM/GDC interface after 300 h.