Oxygen Evolution on Perovskite-Type Cobaltite Anodes: An Assessment of Materials Science-Related Aspects

Abstract

Ceramic anodes, made of perovskite-type rare-earth and strontium cobaltites substituted in both sublattices, exhibit a high electrocatalytic activity towards oxygen evolution in alkaline media. This work analyzes the relationships between cation composition, defect structure, electronic conductivity and electrochemical performance for a wide group of perovskite-like cobaltites, including Ln1-yAyCoO3-δ (Ln= Pr, Nd, Sm; A= Sr, Ca; y= 0-0.4), La1-x-ySrxBiyCoO3-δ (x= 0-0.6, y= 0-0.1), La0.7-xSr0.3CoO3-δ (x= 0-0.10), Sr1-xBaxCoO3-δ (x= 0.1-0.2) and SrCo1-yMyO3-δ (M=Fe, Ni, Ti, Cu; y= 0.1-0.6). The materials were prepared by the standard ceramic technique and characterized employing XRD, TGA, iodometric titration, and total conductivity measurements. A relatively high electrochemical performance in alkaline solutions was observed for (La,Sr)CoO3-based compositions with a moderate A-site deficiency. For SrCoO3-based materials, an increase in the oxygen evolution rate was found when co-substituting cobalt with several transition metal cations, such as Fe3+/4+ and Cu2+/3+. The results show that, in general, the key composition-related factors influencing electrochemical activity in alkaline media include the oxygen vacancy concentration, the average positive charge density in the crystal lattice, and possible blocking of active sites on the electrode surface.