Improving Electrochemical Oxidation/Reduction Kinetics in Single-Component Solid Oxide Cells through Synergistic A-Site Defects and Anion Doping

Solid oxide fuel/electrolysis cells (SOFCs/SOECs) have emerged as promising technologies for reversibly converting chemical and electrical energy. Here, we propose a synergistic approach involving the introduction of A-site defects and anion doping in the perovskite La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) oxide to enhance its electrochemical oxidation/reduction kinetics as an electrode material in single-component SOFCs/SOECs. By creating an A-site deficient and F-doped oxyfluoride, designated as (La0.6Sr0.4)(0.95)Co0.2Fe0.8F0.1O2.9-delta (F-(LS)(0.95)CF), we effectively lower the valence state of both Co and Fe elements, leading to a higher concentration of oxygen vacancies. This synergistic approach yields a remarkable approximately 5-fold increase in the oxygen surface exchange coefficient (k(chem)) and a 50% increase in the bulk diffusion coefficient (D-chem) at 700 degrees C, when compared with LSCF. The resulting F-(LS)(0.95)CF-based single cell demonstrates approximately a 100% higher maximum power density for SOFC operation and a 60% higher current density at 1.3 V for SOEC operation. These improvements are further supported by lower polarization resistances observed in symmetrical cells with F-(LS)(0.95)CF. Furthermore, detailed investigations into the reaction kinetics reveal distinctive behaviors for the hydrogen oxidation reaction when comparing LSCF to F-(LS)(0.95)CF as the electrode material. Specifically, for LSCF, the rate-limiting step is the adsorption and dissociation of H-2, while for F-(LS)(0.95)CF, it primarily involves a charge-transfer reaction. Conversely, for the oxygen reduction reaction, regardless of the electrode material being LSCF or F-(LS)(0.95)CF, the rate-limiting step consistently involves the reduction of oxygen atoms to O-.