Surface reconstruction of SrCoO_2.52 nanofibers as bifunctional oxygen electrocatalyst for rechargeable Zn-air batteries

Rechargeable metal-air battery is an emerging renewable energy technology with advantages of high efficiency, zero pollution and environmental friendliness. The development of efficient and cost-effective oxygen electrocatalyst plays a key role in tackling the performance restrain of air electrode for rechargeable metal-air batteries, especially for Zn-air batteries. Herein, we reported surface reconstruction on a complex metal oxide, SrCoO_2.52 (SCO) utilizing selective ion corrosion to boost its activity for O₂ electrocatalysis and Zn-air batteries. Based on the difference in bond strength between Sr–O and Co–O, a selective etching of Sr cation on the surface of SCO nanofibers has been realized using a gentle wet chemical method. The selective Sr etching altered both the crystal and electronic structure of the catalyst surface, reconstructing the surface to form a cobalt-rich layer over the SCO matrix. The obtained core-shell structure significantly enhanced the activity of the SCO catalyst for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The bifunctional SCO catalyst was applied as air electrode for rechargeable Zn-air batteries, delivering a power density of 191 mW cm^-2 and a stability of 500 charging-discharging cycles outperforming that of the IrO₂‖Pt/C composite (180 mW cm^-2 and 100 cycles). The performance enhancement was proposed to be due to the surface reconstruction increasing the exposure and approachability of the active Co sites and improving the redox ability of the Co cations. This work not only presents an efficient method of reconstructing SCO with highly active surface for oxygen electrocatalysis and Zn-air batteries, but also may arouse interest to design advanced complex metal oxides with surface-regulating potential for various electrocatalytic applications.