Fig. 1: Schematic illustration of the synthetic process for generating the Co-S-Se spheres.

(1) Multi-shelled Co3O4 spheres were transformed into multi-bishelled CoO/Co9S8 spheres via a mild solution-based sulfurization process. (2) The multi-bishelled Co-S-Se spheres were further prepared by depositing ultrafine Co9Se8 nanoparticles on the CoO/Co9S8 spheres via a selenization process.