Enhancing the CO₂ Adsorption of the Cobalt-Free Layered Perovskite Cathode for Solid-Oxide Electrolysis Cells Gains Excellent Stability under High Voltages via Oxygen-Defect Adjustment

Solid-oxide electrolysis cells are a clean energy conversion device with the ability to directly electrolyze the conversion of CO 2 to CO efficiently. However, their practical applications are limited due to insufficient CO 2 adsorption performance of the cathode materials. To overcome this issue, the A-site cation deficiency strategy has been applied in a layered perovskite PrBaFe 1.6 Ni 0.4 O 6-δ (PBFN) cathode for direct CO 2 electrolysis. The introduction of 5% deficiency at the Pr/Ba site leads to a significant increase in the concentration of oxygen vacancies (nonstoichiometric number δ of oxygen vacancies increased from 0.093 to 0.132), which greatly accelerates the CO 2 adsorption performance as well as the O 2– transport capacity toward the CO 2 reduction reaction (CO 2 RR). CO 2 temperature-programmed desorption indicates that A-site cation-deficient (PrBa) 0.95 Fe 1.6 Ni 0.4 O 6-δ (PB95FN) shows a larger desorption peak area and a higher desorption temperature. PB95FN also exhibits a greater presence of carbonate in Fourier transform infrared (FT-IR) spectroscopy. The electrical conductivity relaxation test shows that the introduction of the 5% A-site deficiency effectively improves the surface oxygen exchange and diffusion kinetics of PB95FN. The current density of the electrolysis cell with the (PrBa) 0.95 Fe 1.6 Ni 0.4 O 6-δ (PB95FN) cathode reaches 0.876 A·cm –2 under 1.5 V at 800 °C, which is 41% higher than that of PB100FN. Moreover, the PB95FN cathode demonstrates excellent long-term stability over 100 h and better short-term stability than PB100FN under high voltages, which can be ascribed to the enhanced CO 2 adsorption performance. The PB95FN cathode maintains a porous structure and tightly binds to the electrolyte after stability testing. This study highlights the potential of regulating oxygen defects in layered perovskite PrBaFe 1.6 Ni 0.4 O 6-δ cathode materials via incorporation of cation deficiency toward high-temperature CO 2 electrolysis.