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