First-principles study of stability, electronic structure and quantum capacitance of B-, N- and O-doped graphynes as supercapacitor electrodes

The structures, stability, electronic properties, and quantum capacitance (C q) of alpha-, beta-, and gamma-graphyne monatomic layer doped with B, N, and O atoms, respectively, were studied using density functional theory. Two different doping sites (i.e. D1 and D2) were considered. Upon replacement of C atoms in the three graphynes with B and N atoms, the structure of graphynes was minimally distorted. This change was mainly manifested as a negligible adjustment of bond length around the doped atoms and lattice constant. However, with O atom doping, the structural distortion of graphynes was obvious in the majority of cases. The doping of these atoms significantly improved the electronic state of the original graphyne near the Fermi level, thereby improving graphyne C q. Pristine graphynes with large pores and specific surface area exhibited better C q performance than that of pure graphene. C q of graphynes doped with B, N, and O showed significant advantage over that of doped graphene, especially that of alpha-, beta-, and gamma-graphyne with B doping at D1 and alpha-graphyne with O doping at D1. Interestingly, beta-graphyne with O doping at D2 showed a considerably symmetrical C q. Thus, element-doped graphynes have great potential as electrode materials for supercapacitors.