P-Block Metal Atoms Induced the Spin State Transition of Fe-N-C Catalyst for Efficient Oxygen Reduction

Abstract

A deep understanding of the role of spin configurations of Fe-N-C catalyst in the adsorption and desorption of oxygen intermediates during ORRs is critical for the development of new catalysts for ORR. Herein, we successfully implanted p-block metal single sites (SnN4, SbN4) into the Fe-N-C system to vary the spin states of Fe species and investigated the ORR performance of active metal centers with varying effective magnetic moments. Combined with zero-field cooling (ZFC) temperature-dependent magnetic susceptibility measurements and DFT calculations, we successfully established correlations between the spin state and ORR activity. Magnetic analysis reveals that the p-block metal catalytic sites can effectively induce a low-to-high (or medium) spin state transition of Fe centers. Consequently, the 3d orbital electrons in Fe,M-N-C catalysts penetrate the antibonding π-orbital of oxygen more easily, thus optimizing the adsorption/desorption of key oxygen intermediates on Fe-N-C catalysts.  As a result, the optimized Fe,M-N-C catalyst exhibits a half-wave potential of 0.97 V in a 0.1 M KOH electrolyte, as well as higher durability than conventional Pt/C catalysts. Moreover, the Fe,M-N-C catalysts show encouraging performance in a rechargeable Zn–air battery with high power density and long-term cyclability, indicating the real applicability of these Fe,M-N-C catalysts.

Keywords: oxygen reduction reaction, p-block metal single sites, the spin-related interaction, Fe electron delocalization.