Engineering the Electronic Structure of Single-Atom Iron Sites with Boosted Oxygen Bifunctional Activity for Zinc-Air Batteries.

Rechargeable zinc-air batteries typically require efficient, durable, and inexpensive bifunctional electrocatalysts to support oxygen reduction/evolution reactions (ORR/OER). However, sluggish kinetics and mass transportation challenges must be addressed if the performance of these catalysts is to be enhanced. Herein, a strategy to fabricate a catalyst comprising atomically dispersed iron atoms supported on a mesoporous nitrogen-doped carbon support (Fe SAs/NC) with accessible metal sites and optimized electronic metal-support interactions is developed. Both the experimental results and theoretical calculations reveal that the engineered electronic structures of the metal active sites can regulate the charge distribution of Fe centers to optimize the adsorption/desorption of oxygenated intermediates. The Fe SAs/NC containing Fe 1 N 4 O 1 sites achieves remarkable ORR activity over the entire pH range, with half-wave potentials of 0.93, 0.83, and 0.75 V (vs reversible hydrogen electrode) in alkaline, acidic, and neutral electrolytes, respectively. In addition, it demonstrates a promising low overpotential of 320 mV at 10 mA cm -2 for OER in alkaline conditions. The zinc-air battery assembled with Fe SAs/NC exhibits superior performance than that of Pt/C+RuO 2 counterpart in terms of peak power density, specific capacity, and cycling stability. These findings demonstrate the importance of the electronic structure engineering of metal sites in directing catalytic activity.