Free-standing vertically-aligned nitrogen-doped carbon nanotube arrays/graphene as air-breathing electrodes for rechargeable zinc-air batteries

Developing highly efficient air-breathing electrodes is of significant importance for various energy conversion technologies. In this work, we report the synthesis of free-standing, nitrogen (N)-doped vertically aligned carbon nanotubes (N-VA-CNTs) supported by graphene foam (GF), demonstrating excellent catalytic activity for oxygen electrochemical reactions. The presence and status of N is systematically analyzed; N-doped carbon flake fragments present on the walls of the CNTs are proposed to be responsible for the high electrocatalytic activity. A rechargeable Zn-air battery assembled from this N-VA-CNTs/GF hybrid electrode exhibits much higher power density than those of commercial Pt/C electrocatalysts. Zn-air batteries assembled from N-VA-CNTs/GF with high performance and long-term durability hold great potential in the practical application of free-standing, flexible, rechargeable metal-air batteries.