Ultrafine Co-based Nanoparticle@Mesoporous Carbon Nanospheres toward High-Performance Supercapacitors

A general synthetic methodology is reported to grow ultrafine cobalt-based nanoparticles (NPs, 2-7 nm) within high-surface-area mesoporous carbon (MC) frameworks. Our design strategy is based on colloidal amphiphile (CAM) templated oxidative self-polymerization of dopamine. The CAM templates consisting of a hydrophobic silica-like core and a hydrophilic PEO shell can coassemble with dopamine and template its self-polymerization to form polydopamine (PDA) nanospheres. Given that PDA has rich binding sites such as catechol and amine to coordinate metal ions (e.g., Co²⁺), PDA nanospheres containing Co²⁺ ions can be converted into hierarchical porous carbon frameworks containing ultrafine metallic Co NPs (Co@MC) using high-temperature pyrolysis. The CAM templates offer strong "nanoconfinements" to prevent the overgrowth of Co NPs within carbon frameworks. The yielded ultrafine Co NPs have an average size of <7 nm even at a very high loading of 65 wt %. Co@MC can be further converted into various oxides and sulfides, e.g., CoO, Co₃O₄, CoS₂ and transition-metal doped bimetallic Co_xM_1-xS₂, without significantly changing the size of NPs. As a proof-of-concept application, the porous Co-based NPs@MC hybrids were used as electrode materials for supercapacitors, which exhibit excellent supercapacitive performance with outstanding long-term cycling stability, due to the features such as ultrafine size, controllable chemical compositions, hierarchical porous structures, and full coverage of conductive carbons.