First-Principles Insights Into Charge Storage Behavior of Nitrogen-Sulphur Co-Doped Graphene

Abstract

The structural, electronic, and charge storage properties of N, S, and N─S co-doped graphene are systematically investigated using first-principles density functional theory (DFT). Electronic structure analysis, including density of states (DOS) and band structure, reveals significant Fermi level modulation and enhanced charge delocalization induced by defect states. Notably, doping drives the system toward metallic behavior, characterized by bands crossing the Fermi level, with the strongest effect observed for S1 and S2 configurations. Among the co-doped configurations, the S1 site exhibits the quantum capacitance (∼109 µF cm⁻²), followed by S2 (∼95 µF cm⁻²) and the ortho configuration (∼82.5 µF cm⁻²), indicating site-dependent electrochemical performance. Formation energy calculations show that N doping (0.167 eV/atom) is energetically more favorable than S doping (0.268 eV/atom), while N─S co-doped systems show moderately higher formation energies, suggesting slightly reduced but still feasible stability. Further, pyridinic N─S co-doped graphene exhibited configuration-dependent electronic and charge-storage properties, where the 1N1S_Pyridinic_GR configuration showed the highest quantum capacitance of ∼120 µF cm⁻² at ∼−0.1 V, while 1N_Pyridinic_1S_GR and 1V1S_N_GR reached ∼102 and ∼48 µF cm⁻², respectively, highlighting its potential for high-performance supercapacitor electrodes.