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

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.