Unveiling Lithium Roles in Cobalt-Free Cathodes for Efficient Oxygen Reduction Reaction below 600 °C

Improving the sluggish electrocatalytic oxygen reduction reaction (ORR) over cobalt-free cathodes at 550–800 °C is imperative to circumvent challenges faced by practical operation of intermediate temperature solid oxide fuel cells. In this work, we synthesize novel cobalt-free, lithium (Li)-doped, perovskite oxides Sr_1-xLi_xFe_0.8Nb_0.1Ta_0.1O_3-δ (SLFNTx, x=0–0.1) as cathodes for efficient ORR catalysis. When the Li concentration is less than 0.05, ORR activity is enhanced by over 1.6-fold in comparison to the undoped SFNT below 600 °C in both symmetrical and anode-supported single cells configurations. Our comprehensive investigation over crystal structure, surface, and mixed conductivities revealed that a moderate concentration (<0.05) of Li could bestow the perovskite with a stable cubic perovskite structure that contains an optimal concentration of oxygen vacancies and A-site deficiencies. Such trend originates from the lower electronegativity and smaller size of Li dopant than the strontium host. The lower electronegativity increases oxygen vacancies. The small Li dopant induces thermal-migration of Li species and creates A-site deficiency. These insights highlight an effective strategy to advance the performance of cobalt-free ORR electrocatalyst below 600 °C through in situ thermal surface migration of the A-site cations.