Metal-organic-framework-engaged formation of Co nanoparticle-embedded carbon@Co9S8 double-shelled nanocages for efficient oxygen reduction

Hollow nanostructures with a complex interior and superb structural tenability offer great advantages for constructing advanced catalysts. Herein, we report the designed synthesis of novel Co nanoparticle-embedded carbon@Co9S8 double-shelled nanocages (Co-C@Co9S8 DSNCs) by a metal-organic-framework-engaged strategy. Uniform zeolitic imidazolate framework (ZIF-67)@amorphous CoS yolk-shelled structures are first fabricated and then converted to Co-C@Co9S8 DSNCs by thermal annealing in N-2 flow. The Co-C nanocages inside Co9S8 shells function as the active centers for the oxygen reduction reaction (ORR). The Co9S8 shells prevent the Co-C active centers from aggregation while acting as nanoreactors. As a result, the Co-C@Co9S8 DSNCs exhibit excellent performance for the ORR in terms of low over-potential, high current density, excellent stability and methanol tolerance capability.