Highly doped and exposed Cu(I)-N active sites within graphene towards efficient oxygen reduction for zinc-air batteries

A coordinatively unsaturated copper-nitrogen architecture in copper metalloenzymes is essential for its capability to catalyze the oxygen reduction reaction (ORR). However, the stabilization of analogous active sites in realistic catalysts remains a key challenge. Herein, we report a facile route to synthesize highly doped and exposed copper(I)-nitrogen (Cu(I)-N) active sites within graphene (Cu-N(C)C) by pyrolysis of coordinatively saturated copper phthalocyanine, which is inert for the ORR, together with dicyandiamide. Cu(I)-N is identified as the active site for catalyzing the ORR by combining physicochemical and electro-chemical studies, as well as density function theory calculations. The graphene matrix could stabilize the high density of Cu(I)-N active sites with a copper loading higher than 8.5 wt%, while acting as the electron-conducting path. The ORR activity increases with the specific surface area of the Cu-N(C)C catalysts due to more exposed Cu(I)-N active sites. The optimum Cu-N(C)C catalyst demonstrates a high ORR activity and stability, as well as an excellent performance and stability in zinc-air batteries with ultralow catalyst loading.