The regulation of coordination structure between cobalt and nitrogen on graphene for efficient bifunctional electrocatalysis in Zn-air batteries

Electrocatalysts with atomically dispersed metal moieties are of importance in enhancing electrocatalysis for a specific reaction including oxygen reduction. However, it is still challenging to modulate the coordination structure of metal atoms with heteroatoms on carbon supports. Herein, an innovative and facile bridging strategy to regulate the coordination structure of cobalt with nitrogen atoms on reduced graphene oxide (rGO) sheets was developed by the interfacial complexation of amino-rich folic acid with cobalt ions on graphene oxide sheets and the subsequent thermal treatment. Typically, the actual coordination interaction between cobalt and nitrogen species was revealed by using X-ray absorption spectroscopy (XAS), exhibiting the Co-N4 coordination structure well-dispersed on reduced graphene oxide. Such unique structure enables the efficient oxygen reduction and evolution reactions via the favorable adsorption and desorption of intermediates. With the enhanced bifunctional electrocatalytic activities, the fabricated Zn-air battery exhibited the excellent performance with large power density of 319.8 mW cm−2 and good long-term stability (over 300 h). This work establishes the synthesis strategy for bridging metal atom with heteroatom on graphene sheets to enhance the bifunctional electrocatalysis toward Zn-air batteries.