High catalytic activity of Fe-based perovskite fuel electrode for direct CO₂ electroreduction in SOECs

A solid oxide electrolysis cell (SOEC) can effectively convert greenhouse gas CO₂ to fuel gas CO by using renewable electricity and industrial waste heat for sustainable development. However, this state-of-the-art Ni-based ceramic fuel electrode suffers from the degradation of coking deposition and Ni aggregation in CO₂ atmosphere. Herein, we report Nb substitution for ferrite-based perovskite oxides La_0.6Sr_0.4Fe_1−xNb_xO_3-δ (x = 0, 0.05, 0.1, 0.15, LSFNbx) as potential fuel electrodes for the direct electrolysis of CO₂ in SOEC. Doping Nb into Fe site greatly enhances the redox stability of LSF and restrains the surface Sr segregation under oxidizing/reducing condition. Among the samples, LSFNb_0.1-GDC (La_0.6Sr_0.4Fe_0.9Nb_0.1O_3-δ-Gd_0.1Ce_0.9O_2-δ) presents the lowest polarization resistance under different applied voltages at 800 °C. Distribution of relaxation times analysis shows that Nb doping could significantly improve the catalytic activity in CO₂ reduction reaction and accelerate surface adsorption/dissociation. Meanwhile, the electrolyte-supported single cell with LSFNb_0.1-GDC fuel electrode achieves a current density of 0.85 A cm⁻² at 1.5 V and 800 °C, which is 25% higher than that of LSF. Moreover, the LSFNb_0.1-GDC single cell presents good stability at a constant voltage of 1.2 V for 40 h, demonstrating excellent coking resistance for pure CO₂ electrolysis. This work suggests that Nb doping is a promising strategy to enhance the redox stability and catalytic activity of ferrite-based perovskite fuel electrode for SOEC.