N/S Co-Doped Graphdiyne as an Electrode Material for Supercapacitor Applications: A Computational Study

Abstract

The need for efficient and sustainable energy storage systems has increased due to the world's growing energy consumption and the depletion of fossil fuel supplies. Supercapacitors have attracted a lot of interest because of their remarkable power density, quick charge and discharge rates, and extended cycle life, which make them ideal for uses like grid stabilization and electric vehicles. Supercapacitor electrodes are often made of carbon-based materials, particularly two-dimensional (2D) frameworks, because of their large surface area, adjustable electrical characteristics, and strong chemical stability. In this study, a comprehensive first principle study was used to examine the potential of graphdiyne (GDY), a 2D carbon allotrope made up of sp- and sp²-hybridized carbon atoms, as an electrode material for supercapacitors. This study investigated nitrogen (N) and sulphur (S) doping and co-doping at different locations. Stability of doped structures was determined based on formation energies and cohesive energies. Pristine GDY exhibited a large band gap (3.52 eV) and low density of states (DOS) near the Fermi level, it shows that GDY has limited intrinsic conductivity. Doping with N and S significantly reduced the band gap. The chemical hardness was also reduced, accompanied by an increase in electrophilicity, it indicates improved reactivity and charge storage capability. Electron Localization Function (ELF) analyses revealed balanced regions of localized and delocalized electron density, with intense localization at heteroatom sites in co-doped structures, it indicates efficient charge trapping and transport. Charge Density Difference (CDD) maps further confirmed substantial charge x redistribution around dopant atoms, indicating enhanced active sites for ion adsorption. Density close to the Fermi level was revealed by Density of States (DOS) analysis, and this is directly correlated with better quantum capacitance. DOS plots showed a marked increase in states near the Fermi level for co-doped systems, directly correlating with enhanced quantum capacitance and electrochemical performance. These findings highlight the potential of heteroatom- doped GDY structures, particularly co-doped configurations, as high-performance supercapacitor electrode ma terials, paving the way for next-generation sustainable energy storage technologies.