Ultrathin Cobalt Oxide Layers as Electrocatalysts for High-Performance Flexible Zn-Air Batteries

Synergistic improvements in the electrical conductivity and catalytic activity for the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) are of paramount importance for rechargeable metal-air batteries. In this study, one-nanometer-scale ultrathin cobalt oxide (CoO_x ) layers are fabricated on a conducting substrate (i.e., a metallic Co/N-doped graphene substrate) to achieve superior bifunctional activity in both the ORR and OER and ultrahigh output power for flexible Zn-air batteries. Specifically, at the atomic scale, the ultrathin CoO_x layers effectively accelerate electron conduction and provide abundant active sites. X-ray absorption spectroscopy reveals that the metallic Co/N-doped graphene substrate contributes to electron transfer toward the ultrathin CoO_x layer, which is beneficial for the electrocatalytic process. The as-obtained electrocatalyst exhibits ultrahigh electrochemical activity with a positive half-wave potential of 0.896 V for ORR and a low overpotential of 370 mV at 10 mA cm^-2 for OER. The flexible Zn-air battery built with this catalyst exhibits an ultrahigh specific power of 300 W g_cat ^-1 , which is essential for portable devices. This work provides a new design pathway for electrocatalysts for high-performance rechargeable metal-air battery systems.