Engineering Active Sites in Three-Dimensional Hierarchically Porous Graphene-Like Carbon with Co and N-Doped Carbon for High-Performance Zinc-Air Battery

The design of active sites plays an important role in developing highly active oxygen electrocatalysts in Zn-air batteries (ZnABs). Here, we report the formation of cobalt (Co) nanoparticles and thin graphitic N-doped carbon (NC) supported on three-dimensional hierarchically porous graphene-like carbon (Co-NC/3DHPGC) to maximize the accessibility of Co-NC active sites for oxygen reduction/evolution reactions (ORR/OER). The produced Co-NC/3DHPGC exhibits a broad size distribution (5-30 nm) of Co nanoparticles dispersed on the external surface of 3DHPGC and coated with NC to a thickness of similar to 2 nm. We attributed the formation of Co nanoparticles with broad size distribution to the hierarchical porosity of 3DHPGC, which served as a cage to stabilize the Co nanoparticles and increase the metal dispersion; the produced Co nanoparticles catalyze the formation of graphitic NC. Compared with commercial Pt/C and RuO2 catalysts, the resultant Co-NC/3DHPGC exhibits excellent bifunctional ORR/OER electrocatalytic activity and high durability. The high electrocatalytic performance is ascribed to the accessibility of highly active Co-NC sites through mesopores of 3DHPGC. The ZnAB assembled with Co-NC/3DHPGC exhibits high energy density and efficiency. This systematic engineering and rational synthesis strategy may provide new insight into the development of high-performance oxygen electrocatalysts for metal-air batteries and fuel cell technology.