Subnanometer iron clusters confined in a porous carbon matrix for highly efficient zinc–air batteries†
At the molecular level, metal coordinates are crucial for stabilizing an appropriate electronic configuration for high-efficiency oxygen reduction reaction (ORR) electrocatalysts. In this work, an excellent platform to realize the decoration of Fe coordinates at the subnanometer scale into nitrogen-doped carbon networks (designated as Fe–Fe@NC) is provided. X-ray absorption spectroscopy confirmed the precise configuration of Fe coordinates with Fe–Fe and Fe–N coordinations at the molecular level. As a cathode catalyst, the newly developed Fe–Fe@NC exhibited superior ORR performance and a higher peak power density of 175 mW cm−2 in Zn–air batteries. Unlike most reported pristine Fe-based catalysts, Fe–Fe@NC also showed good oxygen evolution reaction (OER) activity, with a low operating potential (1.67 V vs. RHE) at a current density of 10 mA cm−2. Calculations based on density functional theory revealed that the Fe–Fe coordination in Fe subclusters favored the 4e− transfer pathway and, thus, achieved highly active catalytic performance. This work reveals that iron clusters at the subnanometer scale provide an optimized electronic structure for enhanced ORR activity.