Unraveling the formation mechanism of graphitic nitrogen-doping in thermally treated graphene with ammonia.

Xiao-Fei Li,Ke-Yan Lian,Qi Qiu,Yi Luo,Yingchao Wu,Mingsen Deng,Lingling Liu,Jun Jiang

doi:10.1038/srep23495

Abstract

Nitrogen-doped graphene (N-graphene) has attractive properties that has been widely studied over the years. However, its possible formation process still remains unclear. Here, we propose a highly feasible formation mechanism of the graphitic-N doing in thermally treated graphene with ammonia by performing ab initio molecular dynamic simulations at experimental conditions. Results show that among the commonly native point defects in graphene, only the single vacancy 5–9 and divacancy 555–777 have the desirable electronic structures to trap N-containing groups and to mediate the subsequent dehydrogenation processes. The local structure of the defective graphene in combining with the thermodynamic and kinetic effect plays a crucial role in dominating the complex atomic rearrangement to form graphitic-N which heals the corresponding defect perfectly. The importance of the symmetry, the localized force field, the interaction of multiple trapped N-containing groups, as well as the catalytic effect of the temporarily formed bridge-N are emphasized, and the predicted doping configuration agrees well with the experimental observation. Hence, the revealed mechanism will be helpful for realizing the targeted synthesis of N-graphene with reduced defects and desired properties.

Highlights

Nitrogen-doped graphene (N-graphene) has attractive properties that has been widely studied over the years
The substitutional nitrogen-doping (N-doping) has attracted wide interests[2,5,6,7] for its ability to tune and introduce new properties into graphene[8] that considerably broadens the promising applications of graphene including supercapacitors[2,3,9], solar fuel[6,10], lithium-ion batteries[11], molecular sensors[12], electromagnetic devices[13,14,15], and metal-free electrocatalysts for oxygen reduction reactions (ORR)[6,10,16,17,18]
It is reported that graphitic-N plays paramount importance in various promising applications such as ORR17,28,30, molecular sensors[12], water oxidations[10,31], and electromagnetic devices[13,15]

Summary

Introduction

Nitrogen-doped graphene (N-graphene) has attractive properties that has been widely studied over the years. Several crucial factors such as the substrate, temperature, and pressure that seriously influence the N-doping process have been identified both in experiments and theories[6,8,13], the synthesis of high-quality N-graphene with desired structures and properties is still not achieved. These N-species have essentially different effects on the carrier concentration and result in distinct electronic structures of the N-graphene[5,6,8,21,24]. First principles calculations have proved that the occurrence of N-doping at defects of graphene is energetically favorable[27,32,33], but the formation dynamics still need to be established

Methods

Results

Conclusion