Monodisperse cobalt sulfides embedded within nitrogen-doped carbon nanoflakes: an efficient and stable electrocatalyst for the oxygen reduction reaction

Unique hollow hybrid structures composed of well-dispersed catalyst nanoparticles embedded in a carbon matrix offer great advantages for constructing advanced supported catalysts. Herein, we report the designed synthesis of Co9S8 and nitrogen doped hollow carbon sphere (Co9S8/NHCS) composites by carbonization of metanilic anions within the confinement of two-dimensional galleries of hollow spherical cobalt-aluminum layered double hydroxides. The Co9S8/NHCS composites are composed of numerous porous carbon nanoflakes, and monodisperse Co9S8 nanoparticles are embedded within the carbon nanoflakes. Electrochemical measurements show that the Co9S8/NHCS catalysts prepared at 900 degrees C exhibit superior oxygen reduction reaction (ORR) activity, resulting in the highest ORR performance to date among all transition metal sulfide-based ORR catalysts in both alkaline and acidic electrolytes. This interlayer confined reaction approach may provide an efficient platform for the synthesis of other functional materials for alternative applications.