Enhancing the CO₂ Adsorption of the Cobalt-Free Layered Perovskite Cathode for Solid-Oxide Electrolysis Cells Gains...

Solid-oxide electrolysis cells are a clean energy conversion device with the ability to directly electrolyze the conversion of CO₂ to CO efficiently. However, their practical applications are limited due to insufficient CO₂ adsorption performance of the cathode materials. To overcome this issue, the A-site cation deficiency strategy has been applied in a layered perovskite PrBaFe_1.6Ni_0.4O_6-δ (PBFN) cathode for direct CO₂ 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 CO₂ adsorption performance as well as the O^2- transport capacity toward the CO₂ reduction reaction (CO₂RR). CO₂ temperature-programmed desorption indicates that A-site cation-deficient (PrBa)_0.95Fe_1.6Ni_0.4O_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)_0.95Fe_1.6Ni_0.4O_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 CO₂ 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_1.6Ni_0.4O_6-δ cathode materials via incorporation of cation deficiency toward high-temperature CO₂ electrolysis.