Boosting oxygen reduction of single atomic iron sites by charge redistribution

Atomically dispersed porphyrin-type iron catalysts have demonstrated great potential to substitute platinum group metals for the oxygen reduction reaction (ORR), yet being subjected to limited active sites and sluggish O2 activation kinetics over the symmetrical planar four-coordinated FeN4 structure. Herein, the charge regulation on FeN4 site is achieved via non-bonding interaction of adjacent nitrogen over high-loading single atomic Fe catalysts to boost their intrinsic ORR activity. The single atomic Fe catalysts exhibit excellent alkaline ORR activity with a half-wave potential of 0.914 V versus reversible hydrogen electrode and tenfold higher kinetic current density than that of Pt/C catalysts. Both experimental and theoretical studies confirm that the secondary nitrogen compensation can anchor greater Fe atoms up to 5.44 wt% with sufficient O2 activation sites and simultaneously break the symmetrical charge distribution of FeN4 site to optimize the adsorption/desorption of oxygen intermediate for accelerating ORR kinetics. Moreover, the single atomic Fe catalysts demonstrate great practical application in liquid and solid zinc-air batteries with long-term cycling stability for 600 and 150 h, respectively, as well as superior flexibility in solid batteries.