Construction of hollow urchin-like carbon frameworks with Co, P, N doping and encapsulated Co/Co2P heterojunction as bifunctional electrocatalysts for rechargeable Zn-air batteries

Abstract

Controllable preparation of advanced electrocatalysts with well-designed architecture and desirable active sites, is full of challenges for rechargeable Zn-air batteries (ZABs). Herein, a hollow urchin-like bifunctional oxygen electrocatalyst (HCoPNC@Co/Co2P-PNCNTs) is developed by assembling P,N-doped carbon nanotubes with confined Co/Co2P heterojunction on heteroatom-doped carbon hollow spheres viain-situ polymerization/deposition, pyrolysis and topical phosphorization strategy. According to the analysis of experiments and theory calculates, the Co/Co2P@NC core-shell structure at the top of each CNT is verified to facilitate the electrons transfer and the conversion between the adsorbed intermediates, guaranteeing gloriously intrinsic catalytic activity. Meanwhile, the urchin-like hierarchical frameworks build a desirable conductive and mass transport network, ensuring the efficient exposure of the electrocatalytic active sites and excellent structural stability. Therefore, the “framework-active sites” feature endows HCoPNC@Co/Co2P-PNCNTs with superior catalytic activities towards both oxygen reduction reaction (ORR, half-wave potential of0.83 V) and oxygen evolution reaction (OER, overpotential of 350 mV @ 10 mA cm-2) in alkaline electrolyte. Expectedly, the as-assembled ZABs based on HCoPNC@Co/Co2P-PNCNTs deliver a large peak power density of 250 mW cm-2 and a robust charge-discharge cycling stability with negligible voltage decay for 110 h at 2 mA cm-2, illustrating its great practical application in advanced metal-air batteries.