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

Abstract

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.