High‐Loading Single Atoms via Hierarchically Porous Nanospheres for Oxygen Reduction Reaction with Superior Activity and Durability

Abstract Rational design and facile synthesis of single‐atom catalysts featuring high‐density active sites and favorable mass transport are crucial for electrocatalysis. Herein, a facile route is reported to craft a battery of high‐loading (up to 9.36 wt.%) and readily accessible single transition‐metal atoms anchored on hierarchically porous hollow carbon nanospheres (denoted TM‐SAC‐HC; TM═Fe, Co, Ni, and Cu) as robust electrocatalysts for oxygen reduction reaction (ORR). Intriguingly, the TM‐SAC‐HC possesses a hollow interior with well‐structured porosities on the carbon shell. Such hierarchically porous hollow carbon nanospheres adequately expose the dense metal‐atom active sites, boosting the mass transport. Remarkably, Fe‐SAC‐HC in an alkaline electrolyte manifests a superior ORR activity (E_1/2 = 0.92 V) and an excellent durability (ΔE_1/2 = −15 mV after 30 000 potential cycles and 90% current retention after 48 h continuous operation), outperforming most state‐of‐the‐art TM‐based catalysts and commercial Pt/C. Zinc–air batteries assembles using Fe‐SAC‐HC as the air electrode deliver a peak power density of 186.6 mW cm⁻² and a special capacity of 805.7 mAh g⁻¹. Moreover, theoretical calculations reveal that Fe─N₄ moieties situated within micropores significantly lower energy barriers, leading to superior ORR activity. This work provides a foundation for the rational design of high‐efficiency catalysts for energy conversion and storage.