Elucidating the Role of B-Site Cations toward CO₂ Reduction in Perovskite-Based Solid Oxide Electrolysis Cells

Solid oxide electrolysis cells (SOECs) are promising for the selective electrochemical conversion of CO₂, or mixed streams of CO₂ and H₂O, into high energy products such as CO and H₂. However, these systems are limited by the poor redox stability of the state-of-the-art Ni-based cathode electrocatalysts. Due to their favorable redox properties, mixed ionic-electronic conducting (MIEC) oxides have been considered as promising alternatives. However, improvement of the electrochemical performance of MIEC-based SOEC electrocatalysts is needed and requires an understanding of the factors that govern their activity. Herein, we investigate the effect of B-site 3d metal cations (Cr, Fe, Co, Ni) of LaBO₃ perovskites on their CO₂ electrochemical reduction activity in SOECs. We find that their electrochemical performance is highly dependent on the nature of the B-site cation and trends as LaFeO₃ > LaCoO₃ > LaNiO₃ > LaCrO₃. Among these perovskites, LaNiO₃ is the least stable and decomposes under electrochemical conditions. In situ characterization and ab initio theoretical calculations suggest that both the nature of the B-site cation and the presence of oxygen surface vacancies impact the energetics of CO₂ adsorption and reduction. These studies provide fundamental insights critical toward devising ways to improve the performance of MIEC-based SOEC cathodes for CO₂ electroreduction.