Cobalt oxide-coated N- and B-doped graphene hollow spheres as bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions

Abstract

A simple and scalable method has been developed for the synthesis of Co₃O₄-coated N- and B-doped graphene hollow spheres (Co₃O₄/NBGHSs). These Co₃O₄/NBGHSs are highly active for both oxygen reduction and evolution reactions and can exhibit higher electrocatalytic activities and better durability than commercial Pt/C and RuO₂/C, respectively, demonstrating them to be efficient bi-functional electrocatalysts. In-depth analysis shows that the coupling between Co₃O₄ and NBGHSs, strong interaction with adsorbed O₂, high electric conductivity, and the specific hollow structure play important roles in imparting the higher electrocatalytic activities to the Co₃O₄/NBGHSs. When tested as cathode catalysts for Zn–air batteries, the Co₃O₄/NBGHSs exhibit better performance and higher stability than the Pt/C catalyst and other catalysts reported previously. This strongly suggests that the Co₃O₄/NBGHSs could be used as efficient electrocatalysts for metal–air batteries with great potential to replace precious metal/carbon based materials.