Well-dispersed Co-Co3O4 hybrid nanoparticles on N-doped carbon nanosheets as a bifunctional electrocatalyst for oxygen evolution and reduction reactions

Bifunctional catalysts are vital for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in metal-air batteries. In this work, Co-Co3O4/N-doped carbon nanosheets (NCNs) were developed as highly efficient bifunctional oxygen catalysts via the pyrolysis of a hybrid ZIF-67/CNs precursor. It is found that the introduced CNs play important roles. On one hand, the introduced CNs can tune the surface contents of Co, N and/or O species that are closely correlated with OER and ORR activity. On the other hand, they also facilitate to achieve high specific surface areas for the catalysts. In addition, the introduced CNs helps the formed Co-Co3O4 hybrid nanoparticles with uniform and small sizes to be well distributed on the NCNs substrates. Despite such important roles, it should be noted that a moderate content of the introduced CNs is required to achieve optimal oxygen catalytic activity. As a result, the optimized ZIF-67/CNs(1)-600 exhibits a low value of rho (similar to 350 mV) for OER and a high value of E-1/2 (similar to 0.85 V) for ORR. Its overall bifunctional activity (AE) is as low as similar to 0.73 V, which is comparable to the recent reported Co-based catalysts. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.