Interfacial Engineering of CoN/Co 3 O 4 Heterostructured Hollow Nanoparticles Embedded in N-Doped Carbon Nanowires as a Bifunctional Oxygen Electrocatalyst for Rechargeable Liquid and Flexible all-Solid-State Zn-Air Batteries.

The design of economical, efficient, and robust bifunctional oxygen electrocatalysts is greatly imperative for the large-scale commercialization of rechargeable Zn-air battery (ZAB) technology. Herein, the neoteric design of an advanced bifunctional electrocatalyst composed of CoN/Co 3 O 4 heterojunction hollow nanoparticles in situ encapsulated in porous N-doped carbon nanowires (denoted as CoN/Co 3 O 4 HNPs@NCNWs hereafter) is reported. The simultaneous implementation of interfacial engineering, nanoscale hollowing design, and carbon-support hybridization renders the synthesized CoN/Co 3 O 4 HNPs@NCNWs with modified electronic structure, improved electric conductivity, enriched active sites, and shortened electron/reactant transport pathways. Density functional theory computations further demonstrate that the construction of a CoN/Co 3 O 4 heterojunction can optimize the reaction pathways and reduce the overall reaction barriers. Thanks to the composition and architectural superiorities, the CoN/Co 3 O 4 HNPs@NCNWs exhibit distinguished oxygen reduction reaction and oxygen evolution reaction performance with a low reversible overpotential of 0.725 V and outstanding stability in KOH medium. More encouragingly, the homemade rechargeable liquid and flexible all-solid-state ZABs utilizing CoN/Co 3 O 4 HNPs@NCNWs as the air-cathode deliver higher peak power densities, larger specific capacities, and robust cycling stability, exceeding the commercial Pt/C + RuO 2 benchmark counterparts. The concept of heterostructure-induced electronic modification herein may shed light on the rational design of advanced electrocatalysts for sustainable energy applications.