Restricted diffusion preparation of fully-exposed Fe single-atom catalyst on carbon nanospheres for efficient oxygen reduction reaction

Single-atom catalysts (SAC) stabilized by nitrogen in carbon support are promising candidates for oxygen reduction reaction (ORR). However, conventional preparation methods usually lead to encapsulation of metallic centers in matrix and thus the utilization efficiency (UE) is underexploited. Herein, we report a novel strategy to prepare an Fe-SAC with all Fe atoms anchored on the surface of carbon nanospheres, which exhibited an extraordinary UE of 80% for ORR. This efficiency was achieved by coating polydopamine spheres with silica, followed by the pyrolysis of their blend with FeCl3. During thermal treatment, Fe migrates across the silica shell by atomic exchange with silicon, which inhibits the aggregation of Fe and allows Fe atoms to anchor on the surface. As such, it showed excellent ORR activity at a low Fe content. Zn-air batteries assembled using this catalyst showed a peak power density of 113 mW cm−2 and specific capacity of 710 mAh gZn−1.