Space-confined pyrolysis strategy to self-catalyze the growth of carbon nanotube-wrapped Co₃O₄ electrocatalyst for lithium-O₂ batteries

Lithium-oxygen batteries (LOBs) are emerging as one of the most powerful candidates for the next-generation green energy-storage devices due to their high theoretical energy density. However, the high polarization and poor cycling stability have hampered their practical applications that heavily depend on the dual-functional cathodes with abundant highly active sites to promote the mass/electron transfer for efficient oxygen reduction and evolution. Herein, a space-confined pyrolysis strategy is proposed by coating a Co-based metal-organic framework composite precursor (ZIF-8 @ZIF-67) with an inorganic SiO₂ layer, which efficiently inhibits the precursor loss and nanostructure collapse during the high-temperature carbonization and yields a high-performance carbon nanotube-wrapped Co₃O₄ electrocatalyst. Thereinto, the Co within the precursor can act as the self-catalyst for the growth of abundant carbon nanotubes, which not only generates more catalytic sites but also improves the electronic conductivity. Systematic investigations reveal that the resultant Co₃O₄ wrapped with carbon nanotubes (Co₃O₄/CNTs) possesses significantly improved bifunctional oxygen reduction and evolution activity when compared with the Co₃O₄ counterpart derived from the traditional direct pyrolysis, which is benefited from the large content of active sites and strong mass/electron transfer capabilities to allow the exceptional rate performance and cycling stability of LOBs. The space-confined pyrolysis strategy described herein may help to exploit the highly efficient electrocatalysts.