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

Abstract

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 ~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 RuO 2 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.