Abstract
Following COP 30, there has been a notable surge in the demand for more efficient energy storage devices. Supercapacitors are emerging as promising alternatives due to their low cost, long cycle life, high power density, and excellent cycling stability. These attributes make them suitable for both conventional applications and integration into renewable energy systems and smart grids, contributing significantly to the global energy transition. The choice of electrode material directly impacts the electrochemical properties of supercapacitors. Thus, exploring new materials that enhance charge storage capacity while ensuring higher energy efficiency and long-term stability is crucial for the development of high-performance supercapacitors. Nanostructured materials, such as graphene quantum dots (GQDs), have emerged as promising candidates due to their unique properties, including high surface area, exceptional electrical conductivity, structural stability, ease of manufacturing and functionalization, and environmental compatibility. This study investigates the electronic and optical properties resulting from the intercalation of different species of monovalent ions between two graphene quantum dots with hydrogenated edges, using Density Functional Theory (DFT)-based simulations. Simulations were conducted with Gaussian 09 software, employing the CAM-B3LYP functional and a 6-311++G(d,p) basis set. Raman spectroscopy results show shifts in the D and G bands for GQDs intercalated with lithium, sodium, potassium, fluorine, chlorine, and bromine ions. Positive ions generally induce a red shift in the Raman bands, whereas negative ions lead to a blue shift. Disorder ratios derived from Raman spectra suggest increased structural defects with positive ions and a mitigated effect with negative ions. Adsorption energy calculations reveal that lithium ions exhibit the highest interaction with GQDs, while fluorine shows the strongest bonding among anions. Density of States (DOS) analysis indicates significant modifications in the energy levels of the HOMO and LUMO orbitals due to ion intercalation. Positive ions cause a downward shift in both HOMO and LUMO energy levels, while negative ions lead to an upward shift. Analysis of electron density isosurfaces shows uniform distribution for HOMO and LUMO orbitals in pristine GQDs, with variations in density observed near the ions. Positive ions result in lower electronic density near the ion for HOMO and higher density for LUMO, while negative ions show higher density near the ion for HOMO and lower density for LUMO. These findings highlight the role of ionic species in modulating the electronic and structural properties of GQDs, offering insights into their potential applications in advanced energy storage technologies.
