Mo-doped La_0·6Sr_0·4FeO_3-δ as an efficient fuel electrode for direct electrolysis of CO₂ in solid oxide electrolysis cells

Conversion of CO₂ into CO in solid oxide electrolysis cells (SOECs) at high temperatures is an attractive route for CO₂ utilization and intermittent renewable resource storage. In this study, La_0·6Sr_0·4Fe_1-xMo_xO_3-δ-Gd_0.1Ce_0·9O_2-δ (LSFM_x-GDC; x = 0, 0.05, 0.10, 0.15) composites are evaluated as fuel electrodes of SOECs for the direct electrolysis of CO₂. XRD results show that the lattice parameters slightly increase with increasing Mo doping content, x, and that the solid-solution concentration of Mo in LSFM_x is limited to x ≤ 0.1. LSFM_x shows good chemical compatibility with GDC and excellent stability without decomposition under a CO₂ or reducing atmosphere. The optimal electrode composition with x = 0.05 exhibits minimal polarization resistance at 600–800 °C. A current density of 1.06 A cm⁻² at 1.5 V and 800 °C is achieved by the LSFM_0.05-GDC fuel electrode in an electrolyte-supported single cell; this current density represents an increase of approximately 50% compared with that obtained using a non-Mo-doped electrode. The mechanism of the effect of Mo doping is also investigated, and the results of X-ray photoelectron spectroscopy, temperature-programmed desorption of CO2, and analysis of the distribution of relaxation time reveal that introduction of Mo promotes the formation of oxygen vacancies, which enhance CO₂ adsorption and improve the diffusion and exchange of oxygen species. Such improvement ultimately accelerates surface reaction kinetics.