Optimized nitrogen-doped carbon with a hierarchically porous structure as a highly efficient cathode for Na-O-2 batteries

Development of an efficient air cathode for metal-air batteries composed of an element that is abundant on earth is a scientific and technical challenge. Here, nitrogen (N)-doped carbon cathodes were prepared using two conventional doping methods, namely ammonia activation (ammoxidation) and introduction of an N-containing precursor. Interestingly, the introduction of N-containing precursors to prepare the N-doped carbon material not only gave a different pore distribution with increased surface area but also maintained considerable N content, unlike the use of the ammoxidation method - thus greatly enhancing the catalytic activity (low overpotential) and improving the discharge capacity (6905 mA h g(-1)) and cycle life (from 8 to 66 cycles) in sodium-oxygen batteries compared with the pure carbon material. This study also stresses the importance of adopting the optimized synthesis method to prepare the N-doped carbon cathode.