Protruding N-doped carbon nanotubes on elongated hexagonal Co-N-C nanoplates as bifunctional oxygen electrocatalysts for Zn-air batteries

Development of bifunctional oxygen electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reactions (OER) is urgently needed for advanced energy storage and conversion devices including rechargeable Zn-air batteries. Herein, we put forward the design and synthesis of nitrogen-doped carbon nanotubes binding Co-N-C elongated hexagonal nanoplates (denoted as Co-N-C@NCNTs) through a metastable bimetallic ZnCo-ZIF-L topochemical phase conversion and subsequent pyrolysis strategy. The highly open and conductive architectures with an elongated shape of a carbon nanoplate substrate can not only effectively prevent the agglomeration of catalytically active sites comprised of both Co nanoparticles and atomic Co-N_x species, but also accelerate the electron and ion transport during the catalytic process to improve the mass transfer efficiency, resulting in enhanced electrocatalytic performance in both electrocatalytic activity and stability. As expected, the Co-N-C@NCNTs showed excellent bifunctional ORR/OER performance with an overpotential gap of 0.748 V and satisfactory stability. Using Co-N-C@NCNTs as air-cathode catalysts for rechargeable Zn-air batteries, the assembled cells exhibit a remarkable peak power density of 237.8 mW cm⁻² and long-term cycling stability of up to 130 h.