Metallic Cobalt@Nitrogen-Doped Carbon Nanocomposites: Carbon-Shell Regulation toward Efficient Bi-Functional Electrocatalysis.

To advance hydrogen economy, noble-metal-free electrocatalysts with good efficiency are urgently demanded. They can be developed from metal-organic frameworks (MOFs) with abundant structure-variety, in which a controlled pyrolysis is desired to rationalize nanostructure and maximize catalytic activity. Herein, the efficient regulation is proposed for the first time on the carbon-shell of MOFs-derived Co@NC nanocomposites via varying temperature and flow-rate during pyrolysis, enabling the good accessibility and the electronic optimization of active Co cores. With moderated temperature and flow-rate, the resulting ultrathin carbon-shell, on the one hand, renders Co cores easily accessible to electrolytes and, on the other hand, promotes the electronic penetration to optimize metallic Co active sites. As expected, the optimal Co@NC affords the benchmarking performance of noble-metal-free electrocatalysts in hydrogen evolution and oxygen reduction reactions, featured by the low overpotentials, the striking kinetic metrics, and the outstanding long-term stability. Elucidating the feasibility to design efficient electrocatalysts via controlled MOFs pyrolysis, this work will open up new opportunities for the development of cost-effective materials in the energy field.