Dual Single‐Atomic Ni‐N4 and Fe‐N4 Sites Constructing Janus Hollow Graphene for Selective Oxygen Electrocatalysis

Abstract Nitrogen‐coordinated metal single atoms in carbon have aroused extensive interest recently and have been growing as an active research frontier in a wide range of key renewable energy reactions and devices. Herein, a step‐by‐step self‐assembly strategy is developed to allocate nickel (Ni) and iron (Fe) single atoms respectively on the inner and outer walls of graphene hollow nanospheres (GHSs), realizing separate‐sided different single‐atom functionalization of hollow graphene. The Ni or Fe single atom is demonstrated to be coordinated with four N atoms via the formation of a Ni‐N 4 or Fe‐N 4 planar configuration. The developed Ni‐N 4 /GHSs/Fe‐N 4 Janus material exhibits excellent bifunctional electrocatalytic performance, in which the outer Fe‐N 4 clusters dominantly contribute to high activity toward the oxygen reduction reaction (ORR), while the inner Ni‐N 4 clusters are responsible for excellent activity toward the oxygen evolution reaction (OER). Density functional theory calculations demonstrate the structures and reactivities of Fe‐N 4 and Ni‐N 4 for the ORR and OER. The Ni‐N 4 /GHSs/Fe‐N 4 endows a rechargeable Zn–air battery with excellent energy efficiency and cycling stability as an air‐cathode, outperforming that of the benchmark Pt/C+RuO 2 air‐cathode. The current work paves a new avenue for precise control of single‐atom sites on carbon surface for the high‐performance and selective electrocatalysts.