Solid oxide electrolysis cells (SOECs) as a highly efficient energy conversion technology exhibit an immense potential in converting CO₂ into valuable chemicals during the electrolysis process, thereby providing an effective pathway to achieve carbon neutrality goals. However, the inadequate catalytic performance of conventional Ni-YSZ fuel electrode is a pivotal constraint hindering the advancement of SOEC technology. Lanthanum-strontium titanate (LST) perovskite oxides have a superior mixed ionic-electronic conductivity (MEIC) under cathodic polarization, making them a promising alternative fuel electrode for the SOECs. However, the performance of LST in CO₂ reduction reactions (CO₂RR) remains inadequate. In this work, Cu nanoparticles-decorated (La₄Sr₄)_0.9Ti_8-xCu_xO₂₆ (LSTCux, with x=0.4, 0.8, 1.2, and 1.6) layered perovskite oxides as a novel fuel electrode were synthesized by a conventional solid-phase reaction method.

For the synthesis of (La₄Sr₄)_0.9Ti_8-xCu_xO₂₆ (LSTCux, x=0.4, 0.8, 1.2, 1.6), La₂O₃, SrCO₃, TiO₂, and CuO as raw materials were weighed, ground for 2 h, and calcinated at 1400 ℃ for 10 h. Subsequently, the samples were reduced in H₂ atmosphere at 800 ℃ for 10 h, yielding the reduced samples of LSTCu-rx. A solid electrolyte-supported structure was adopted with commercial SSZ electrolyte disks. To prevent reactions, the GDC slurry was spin-coated on the both sides of the SSZ disks and sintered at 1400 ℃ for 3 h to obtain a dense GDC functional layer. LSTCu-rx and LSCF powders were mixed with organic binders to prepare electrode slurries, which were then coated on the both sides of the electrolyte disk and sintered at 900 ℃ for 3 h, resulting in LSTCu-rx|GDC|SSZ|GDC|LSCF structured SOEC button cell. Silver paste and silver wires were applied on the both sides of the cell as current collectors.

The phase compositions of LSTCux and LSTCu-rx were characterized by X-ray diffraction (XRD). The morphology was determined by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS). The elemental valence states were determined by X-ray photoelectron spectroscopy (XPS). The electrochemical performance was analyzed by Solartron equipment. CO₂ electrolysis tests were performed on the SOEC button cells via the measurement of j-V curves and electrochemical impedance spectroscopy (EIS).

The results indicate that the electrode exhibits superior electrochemical activity and stability in CO₂ Reduction Reactions (CO₂RR). The results of electrochemical performance tests reveal that at 850 ℃ and 2.0 V, the SOECs utilizing LSTCu-r0.4, LSTCu-r0.8, LSTCu-r1.2, and LSTCu-r1.6 as electrodes have current densities of 1.07, 2.01, 1.65, and 1.52 A/cm², respectively. Among them, LSTCu-r0.8 has the maximum current density with polarization resistance (R_p) and Ohmic resistance (R_Ω) of 0.12 and 0.05 Ω·cm², respectively. These results indicate that LSTCu-r0.8 possesses superior electrocatalytic activity and efficient electron transport.

The LSTCu-rx series of fuel electrodes exhibited superior electrochemical performance and catalytic activity, particularly in the field of CO₂ electrolysis. Among them, LSTCu-r0.8 could be used as a promising material for CO₂ electrolysis fuel electrodes due to its efficient CO₂ adsorption and conversion capabilities, excellent electron transport properties, and stable electrochemical performance. In the future, the further optimization of the preparation process and exploration of a wider range of reaction conditions could be conducted to achieve a more efficient and stable CO₂ electrolysis process.