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

Abstract

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 La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (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 (La 0.6 Sr 0.4 ) 0.95 Co 0.2 Fe 0.8 F 0.1 O 2.9-δ (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 °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 – .

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