First-principles calculation of quantum capacitance of metals doped graphenes and nitrogen/metals co-doped graphenes: designing strategies for supercapacitor electrodes

In this paper, we investigated the quantum capacitance and the integrated charge of graphene-based materials based on first-principles density functional theory calculations. Transition metals doped in a graphene plane will not move out of the graphene plane and will finally form an accurate symmetrical structure. Meanwhile, for transition metals doped out of plane, regardless of the positions that the metals were placed, they will conform to the same stable M–MV complexes eventually. Meanwhile, the introduction of N atoms makes the Al atom hybridization state tend to be consistent. Al3–NNN (the Al-embedded, nitrogen doped monovacancy graphene-based complexes, and the number of N atoms represents the number of N atoms surrounding the Al) and Al4–NNNN (Al-embedded, nitrogen doped divacancy graphene-based complexes) have the same Al atom hybridization, but it is different in the Al doped monovacancy graphene complexes (Al–MV) and the Al doped divacancy graphene complexes (Al–DV). In addition, we also found that both the Sc doped monovacancy graphene and the Al4–N (Al-embedded, nitrogen doped divacancy graphene-based complexes) can be used as candidates for the negative electrode materials of asymmetric supercapacitors. The results can provide valuable insights into the design and preparation of electrodes for high-performance supercapacitors.