Osmotic pressure-induced pocket-like spheres with Fe single-atom sites for the oxygen reduction reaction

Hollow structures have been developed as an important type of material in energy and catalysis fields. The fabrication of hollow structures usually employs hard templates, which certainly complicates the synthesis process. Herein, we adopt a facile, self-template method to prepare nitrogen/metal-rich hollow spheres. Meanwhile, the osmotic pressure caused by core decomposition leads to the formation of pockets. During the synthesis, the pocket sizes can be controlled by adjusting Fe content. The carbonized pocket-like spheres decorated with single Fe atoms (Fe/NC(PS)) exhibit fantastic oxygen reduction reaction performance due to the promoted utilization of active sites. This well-designed catalyst presents remarkable half-wave potential (0.92 V, vs. RHE) and high electrochemistry stability, which outperforms that of the commercial Pt/C under alkaline conditions. Besides, when applied to Zn-air batteries, the as-prepared Fe/NC(PS) catalyst provides high power density, super discharging capacity, and durable cycling performance. We adopted a self-template method to prepare nitrogen/metal-rich hollow pocket-like spheres as an efficient ORR catalyst. The unique-structured catalyst promoted utilization of active sites and exhibits remarkable ORR performances.