Self-Optimizing Metal-Free Porous Reactors with Dynamic Active Sites Unlock Record Oxygen Reduction Activity

Abstract

Efficient metal-free catalysts are crucial for advancing aluminum-air batteries (AABs), yet their development has been hindered by poor electronic structure optimization and sluggish mass transport. In this work, we developed a hierarchically porous N/S co-doped carbon nanoreactor via an etching-doping pyrolysis strategy, achieving an ultrahigh surface area of 2630 m 2 /g and a wellorganized pore network. The resulting catalyst demonstrated outstanding oxygen reduction reaction (ORR) activity, with half-wave potentials of 0.952 V (vs. RHE; RHE stands for reversible hydrogen electrode) in alkaline and 0.754 V (vs. RHE) in acidic media. When assembled into AABs, it delivered a peak power density of 265 mW/cm 2 and an energy density of 3929 Wh/kg, along with excellent cycling stability. Finite element simulations showed that the hierarchical porosity promoted oxygen diffusion and enhanced reaction kinetics. Furthermore, in-situ characterizations and theoretical calculations revealed that S-C-N configurations dynamically transformed into O pre -S-C-N groups under working conditions, which modulated the electronic structure of adjacent