Engineering of Nitrogen Coordinated Single Cobalt Atom Moieties for Oxygen Electroreduction.

The nitrogen coordinated single cobalt atoms embedded in carbon matrix, i.e., Co/N/C material, is cost-efficient and free from iron-ion induced Fenton reagent, which has been thus considered as a promising candidate to replace the well-accepted Pt-based and Fe/N/C materials for oxygen reduction reaction (ORR). Recently, the pyrolysis of metal-organic framework (MOF) precursors has been investigated to achieve well-defined Co/N/C catalysts with high ORR activity. However, the relationships among the composition/structure of MOF precursor, the derived catalysts, and ORR performance have been rarely touched in specialty, while the regulations to achieve single-atom Co/N/C catalysts derived from MOF are confusing. Herein, we engineer several Co-doped MOF (zeolitic imidazolate frameworks, to be specific) precursors with different compositions and structures by tuning synthesis protocols (e.g., ratios, cobalt sources, and reaction time) and investigate the derived catalysts and their ORR properties. The regulations to single-atom Co/N/C are revealed in this work. The superior ORR activity and durability of the optimized Co/N/C catalysts are revealed and attributed to the well-defined Co-N moieties and their stable nanostructures.