Densely Populated Isolated Single CoN Site for Efficient Oxygen Electrocatalysis

Abstract

Atomically dispersed transition metals confined with nitrogen on a carbon support has demonstrated great electrocatalytic performance, but an extremely low concentration of metal atoms (usually below 1.5%) is necessary to avoid aggregation through sintering which limits mass activity. Here, a salt‐template method to fabricate densely populated, monodispersed cobalt atoms on a nitrogen‐doped graphene‐like carbon support is reported, and achieving a dramatically higher site fraction of Co atoms (≈15.3%) in the catalyst and demonstrating excellent electrocatalytic activity for both the oxygen reduction reaction and oxygen evolution reaction. The atomic dispersion and high site fraction of Co provide a large electrochemically active surface area of ≈105.6 m 2 g−1, leading to very high mass activity for ORR (≈12.164 A mg Co−1 at 0.8 V vs reversible hydrogen electrode), almost 10.5 times higher than that of the state‐of‐the‐art benchmark Pt/C catalyst (1.156 A mg Pt−1 under similar conditions). It also demonstrates an outstanding mass activity for OER (0.278 A mg Co−1). The Zn‐air battery based on this bifunctional catalyst exhibits high energy density of 945 Wh kg Zn−1 as well as remarkable stability. In addition, both density functional theory based simulations and experimental measurements suggest that the CoN 4 sites on the carbon matrix are the most active sites for the bifunctional oxygen electrocatalytic activity.