Understanding electronic configurarions and coordination environment for enhanced ORR process and improved Zn-air battery performance

Electronic configurations and coordination environment of catalysts play the crucial roles for oxygen reduction reaction (ORR). However, most of current efforts have been focused on the geometry design and recognition of active sites, resulting in the rare studies on the intrinsic activity of reaction sites and the synergistic effects between metal centers and external environment. Herein, a dual performance optimization of iron phthalocyanine (FePc) molecules is realized via introducing reduced graphene oxide (rGO) as the carrier. Coupling of rGO and Fe-N4 moiety can further boost Fe 3d electron spin state transition and C 2p charge delocalization. The higher spin state of Fe ions and more Fe-N4 local charge accelerate the electron transfer between Fe sites and adsorbed reactants/intermediates, rendering in an enhanced ORR performance. Under alkaline conditions, the ORR activity (Tafel slope of 39.1 mV dec−1 and an onset potential of 0.98 V vs. RHE) and durability of optimal catalyst exceed commercial Pt/C and many reported Fe-N-C electrocatalysts. Both liquid and solid state Zn-air batteries driven by this catalyst also exhibit satisfactory practical application potential. This work provides a novel insight into the Fe 3d orbitals electronic structure and internal charge whereabouts of catalyst in oxygen electroreduction reactions.