Encapsulation of Co/Co3O4 hetero-nanoparticles within the inner tips of N-doped carbon nanotubes: Engineering Mott-Schottky nanoreactors for efficient bifunctional oxygen electrocalysis toward flexible zinc-air batteries

The development of economical, efficient and durable bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of paramount importance for the substantial advancement of flexible and rechargeable metal-air batteries. The delicate manipulation of metal/semiconductor heterointerfaces represents a powerful leverage to boost the electrocatalytic performance due to the Mott-Schottky effect. Herein, we demonstrate a typical Mott-Schottky electrocatalyst by ingeniously encasing Co/Co3O4 hetero-nanoparticles within the inner tips of N-doped carbon nanotubes (abbreviated as Co/Co3O4@N-CNTs hereafter) through a facile and scalable hydrogel-bridged pyrolysis strategy. Experimental and theoretical findings collectively manifest that the spontaneous charge redistribution at the Co/Co3O4 heterointerfaces is essential to promote the charge transfer capability, lower down the reaction barriers for oxygen electrocatalysis, and ultimately boost the intrinsic activities. Accordingly, the well-designed Co/Co3O4@N-CNTs exhibit admirable ORR and OER activities and long-term robustness in KOH medium, exceeding the commercial Pt/C and RuO2 benchmarks, respectively. Furthermore, the Co/Co3O4@N-CNTs-assembled flexible all-solid-state zinc-air battery displays a high power density, remarkable rate capability, excellent rechargeablity and outstanding mechanical flexibility even under severe deformations, predicting the great potentials in diverse next-generation wearable electronic devices. The rationale of the construction of Mott-Schottky heterojunctions may provide an innovative and instructive avenue to design diversified energy nanomaterials.