Structural regulation of N-doped carbon nanocages as high-performance bifunctional electrocatalysts for rechargeable Zn-air batteries

The development of highly active, inexpensive, and stable bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts to replace noble metal Pt and RuO2 catalysts remains a considerable challenge for highly demanded reversible fuel cells and metal-air batteries. Herein, a novel nitrogen doped carbon nanocage (N–CNC-900) is fabricated via facile carbonization of bimetal-organic framework (BMOF). The newly obtained N–CNC-900 catalyst is featured by multiple carbon layers with a wide lattice spacing of 0.434 nm and the aperture of approximate 10 nm, ultrahigh specific surface area and abundant N doping amount as well. As results, the optimized N–CNC-900 exhibits a low overpotential of 1.52 V toward OER at a current density of 10 mA/cm2, and also show a large half-wave potential of 0.90 V for ORR, respectively. High activity and stability toward the bifunctional oxygen electrocatalysis are also demonstrated on the N–CNC-900. When explored as air cathode for rechargeable Zn-air battery, a high open-circuit voltage (1.54 V) and long-term stability (after cycling 200 h) can be realized, outperforming the commercial Pt/C + RuO2 association. This outstanding performance can be attributed to improved reaction kinetics of both ORR and OER, which originates from the enlarged lattice spacing in the few-layer conductive carbon nanocage structure and the existing metal-nitrogen-carbon (M-Nx-C). These results forebode the optimized N–CNC-900 presenting a promising application in metal-air batteries, as well the lattice modulation of carbon materials providing a novel approach for designing advanced electrocatalysts.