Active-Site Imprinted M-N-C Electrocatalysts: Tailor-Made Synthesis and Tuned Activity

Due to the abundance and inexpensiveness of their constituent elements and their atomic dispersion, metal- and nitrogen- co-doped carbons (M-N-Cs) are currently the best alternative among noble-metal-free catalysts set to replace critical raw materials in several fundamentally important electrochemical reactions such as oxygen reduction reaction (ORR) and CO₂reduction reaction (CO2RR).<br/>Due to the metastability of the active M-N₄ sites at the temperature of their pyrolytic formation, the final transition metal loading is currently limited and significant amounts of inorganic by-products are formed. Although synthesis protocols have been successfully optimized, multiple processing steps are required, making the preparation time-consuming.<br/>In previous work, it has been showed that via an active-site imprinting strategy followed by a transmetalation reaction, Mg-N-C and Zn-N-C containing Mg-N₄ and Zn-N₄ sites respectively, can be transformed into ORR active Fe-N-C electrocatalysts, avoiding the formation of elemental iron, or iron carbide side phases. This synthetic method allows for high yields, controlled morphology and high metal loadings.<br/>In this contribution, it will be presented how Zn−N₄sites in tailor-made Zn−N−C materials are utilized as an active-site imprint for the preparation of the corresponding M−N−C catalysts with a high loading of atomically dispersed metal. The current state of this class of materials is discussed in terms of synthetic methods, activity and stability.