Hole defects and nitrogen doping in graphene: implication for supercapacitor applications.

One great challenge for supercapacitor is to achieve high energy capacity and fast charge/discharge rates simultaneously. Porous graphene with large surface area is a promising candidate for electrode materials of supercapacitor. Using first-principles calculations and non-equilibrium Green's function technique, we have explored the formation energies, mechanical properties, diffusion behaviors and electrical conductance of graphene sheets with various hole defects and/or nitrogen doping. Interestingly, graphene sheets with pyridinic-like holes (especially hexagonal holes) can be more easily doped with nitrogen and still retain the excellent mechanical properties of pristine graphene that is beneficial for the long cycle life. Porous graphene electrode with moderate hole diameter of 4.2-10 Å facilitates efficient access of electrolyte and exhibit excellent rate capability. In addition, doping with nitrogen as electron donors or proton attractors leads to charge accumulation and generates higher pseudocapacitance. Transmission coefficients of N-doped graphene sheets with pyridinic-like holes are only moderately reduced with regard to that of pristine graphene and are insensitive to the detailed geometry parameters. Overall, N-doped graphene with pyridinic-like holes exhibits exciting potentials for high performance energy storage in supercapacitor devices.