A Phosphorus Acid‐Assisted Route to High‐Loading Single‐Atom Iron Catalysts for Advanced Batteries

Abstract The development of efficient oxygen reduction reaction (ORR) catalysts is critical for advancing rechargeable metal‐air batteries. While single‐atom iron catalysts (Fe‐SACs) are promising platinum alternatives, a major synthesis challenge lies in achieving high metal loading without sacrificing atomic dispersion. Here, a high‐loading (7.0 wt.%) iron single‐atom catalyst (P─Fe─N/C) synthesized via a phosphoric acid‐assisted approach is presented. This innovative method involves the carbonization of a nitrogen‐doped carbon precursor derived from ZIF‐8, pre‐loaded with Fe 3 ⁺ and phosphoric acid. This strategy facilitates the simultaneous achievement of dense atomic Fe dispersion and phosphorus incorporation within the carbon matrix. The incorporated phosphorus elevates the spin state of the Fe centers, disrupting the symmetry of the electronic density of states at high‐density Fe sites, a critical factor for enhanced O 2 activation. Consequently, P─Fe─N/C exhibits exceptional oxygen reduction reaction (ORR) activity, achieving a half‐wave potential of 0.905 V (vs RHE) in alkaline media, as corroborated by modeling and kinetic studies. Notably, this catalyst enables high‐performance liquid and solid‐state zinc‐air batteries, delivering high power densities and exceptional operational stability. This work not only showcases an advanced catalyst but also proposes a generalizable methodology for the development of high‐loading single‐atom catalysts.