Enhanced quantum capacitance in 3d-transition metal porphyrin functionalized graphene

Highlights: • Porphyrin functionalized (4NDV) graphene exhibit large quantum capacitance (C_Q). • 3d-TM atoms incorporated at the centre of 4NDV strongly bind with N-atoms. • Sc -4NDV graphene can be a prominent cathode candidate for asymmetric supercapacitor. • 4NDV and Fe-4NDV graphene may serve as anode in asymmetric supercapacitor. Application of the functionalized graphene as electrode for supercapacitor has received a lot of attention recently. In the present work, we investigate applicability of transition metal atom decorated defective graphene for enhanced quantum capacitance compared to pristine graphene. The calculated results based on density functional theory find that Mn, Fe, Co, and Ni prefer in-plane configurations, and Sc, Ti, V, and Cr prefer an out-of-plane configuration of the functionalized graphene. A significant increase in quantum capacitance for the porphyrin functionalized graphene is predicted with the peak value is 149μF/cm². Decoration of transition metal atoms results into lowering of quantum capacitance except for Sc and Fe for which we predict the capacitance to be 177μF/cm² and 220μF/cm², respectively. The results clearly show that degree of localization of 3d states near the Fermi level essentially controls the value of the quantum capacitance in metal decorated functionalized graphene.