Enhanced quantum capacitance of MX4 (M = Fe, Co, Ni, Cu, and Zn; X = N, P) moieties embedded graphene: a DFT study

In this work, density functional theory calculations are performed to study the impact of embedding transition metal-(N/P)(4) moieties in graphene on its geometric structure, electronic properties, and quantum capacitance. Enhancement of quantum capacitance of transition metal doped nitrogen/phosphorus pyridinic graphenes is observed, which is directly related to the availability of states near the Fermi level. The findings show that electronic properties and hence quantum capacitance of graphene can be tuned by varying transition metal dopants and/or their coordination environment. Modified graphenes can suitably be chosen as positive or negative electrodes of asymmetric supercapacitors depending upon the values of quantum capacitance and stored charges. Furthermore, quantum capacitance can be enhanced by widening the working voltage window. The results can serve as guidelines for the design of graphene-based electrodes in supercapacitor applications.