Ultrafine\nCo-based Nanoparticle@Mesoporous Carbon Nanospheres toward High-Performance\nSupercapacitors

A general synthetic\nmethodology is reported to grow ultrafine cobalt-based nanoparticles\n(NPs, 2–7 nm) within high-surface-area mesoporous carbon (MC)\nframeworks. Our design strategy is based on colloidal amphiphile (CAM)\ntemplated oxidative self-polymerization of dopamine. The CAM templates\nconsisting of a hydrophobic silica-like core and a hydrophilic PEO\nshell can coassemble with dopamine and template its self-polymerization\nto form polydopamine (PDA) nanospheres. Given that PDA has rich binding\nsites such as catechol and amine to coordinate metal ions (e.g., Co<sup>2+</sup>), PDA nanospheres containing Co<sup>2+</sup> ions can be\nconverted into hierarchical porous carbon frameworks containing ultrafine\nmetallic Co NPs (Co@MC) using high-temperature pyrolysis. The CAM\ntemplates offer strong “nanoconfinements” to prevent\nthe overgrowth of Co NPs within carbon frameworks. The yielded ultrafine\nCo NPs have an average size of <7 nm even at a very high loading\nof 65 wt %. Co@MC can be further converted into various oxides and\nsulfides, e.g., CoO, Co<sub>3</sub>O<sub>4</sub>, CoS<sub>2</sub> and\ntransition-metal doped bimetallic Co<sub><i>x</i></sub>M<sub>1–<i>x</i></sub>S<sub>2</sub>, without significantly\nchanging the size of NPs. As a proof-of-concept application, the porous\nCo-based NPs@MC hybrids were used as electrode materials for supercapacitors,\nwhich exhibit excellent supercapacitive performance with outstanding\nlong-term cycling stability, due to the features such as ultrafine\nsize, controllable chemical compositions, hierarchical porous structures,\nand full coverage of conductive carbons.