Solution-Phase Synthesis of Co-N-C Catalysts Using Alkali Metals-Induced N-C Templates with Metal Vacancy-Nx sites

Nitrogen-coordinated metal sites (MNx) in metal- and nitrogen-co-doped carbon (M-N-C) catalysts are known for their versatile and promising electrocatalytic activity. However, the synthesis of MNx moieties with desired configuration and catalytic property is still quite challenging using the conventional high-temperature treatment approach. In this study, we demonstrate the solution-phase synthesis of Co-N-C catalysts via the formation of CoNx moieties at metal vacancy-Nx (MVNx) sites on nitrogen-doped carbon (N-C) templated by alkali metals, including sodium and potassium. The formation of CoNx sites is confirmed via a combined approach of various physical characterization techniques, elemental analysis, and electrochemical analysis. For each series of Co-N-C catalysts templated by the same alkali metal (e.g., Na or K), there is a correlation between the CoNx content and the electrocatalytic activity for the oxygen reduction reaction (ORR). Moreover, the correlation of CoNx content with ORR activity also depends on the type of sacrificial alkali metals, suggesting the role of sacrificial metals in creating MVNx sites with a diverse coordination environment. These findings may further guide the future development of M-N-C electrocatalysts with abundant and versatile MNx moieties through this solution-phase coordination approach.