Co/CoO heterojunction rich in oxygen vacancies introduced by O₂ plasma embedded in mesoporous walls of carbon nanoboxes covered with carbon nanotubes for rechargeable zinc-air battery

Herein, Co/CoO heterojunction nanoparticles (NPs) rich in oxygen vacancies embedded in mesoporous walls of nitrogen-doped hollow carbon nanoboxes coupled with nitrogen-doped carbon nanotubes (P-Co/CoOV@NHCNB@NCNT) are well designed through zeolite-imidazole framework (ZIF-67) carbonization, chemical vapor deposition, and O-2 plasma treatment. As a result, the three-dimensional NHCNBs coupled with NCNTs and unique heterojunction with rich oxygen vacancies reduce the charge transport resistance and accelerate the catalytic reaction rate of the P-Co/CoOV@NHCNB@NCNT, and they display exceedingly good electrocatalytic performance for oxygen reduction reaction (ORR, halfwave potential [E-ORR,E- 1/2 = 0.855 V vs. reversible hydrogen electrode]) and oxygen evolution reaction (OER, overpotential (eta(OER, 10) = 377 mV@10 mA cm(-2)), which exceeds that of the commercial Pt/C + RuO2 and most of the formerly reported electrocatalysts. Impressively, both the aqueous and flexible foldable all-solid-state rechargeable zinc-air batteries (ZABs) assembled with the P-Co/CoOV@NHCNB@NCNT catalyst reveal a large maximum power density and outstanding long-term cycling stability. First-principles density functional theory calculations show that the formation of heterojunctions and oxygen vacancies enhances conductivity, reduces reaction energy barriers, and accelerates reaction kinetics rates. This work opens up a new avenue for the facile construction of highly active, structurally stable, and cost-effective bifunctional catalysts for ZABs.