Influence of external electric field regulating hydrogen adsorption on graphene quantum dots, graphene quantum dots with defects, and metal-ion-doped graphene quantum dots

Hydrogen storage is crucial for efficient hydrogen energy utilization, but current materials often require extreme conditions, such as low temperatures (<20.15 K) or high pressures (350-700 atm), and an ideal adsorption energy between -0.2 and -0.6 eV. This study employs density functional theory (DFT) to explore hydrogen adsorption on graphene quantum dots (GQDs), including pristine GQDs, nitrogen-substituted divacancy defect GQDs (4N-GQDs), and metal-ion-doped 4N-GQDs (M-4N-GQDs, M = Ti2+, Fe2+, Cu2+, Zn2+). Pristine and 4N-GQDs show comparable adsorption energies (-0.02 eV), while M-4N-GQDs exhibit stronger adsorption, ranging from -0.221 to -0.025 eV. Ti2+-4N-GQD achieves an optimal adsorption energy of -0.221 eV, making it highly suitable for hydrogen storage. The metal center's charge transfer upon hydrogen adsorption influences binding strength. An external electric field (EEF) further reduces adsorption energy, promoting H-2 desorption. These results highlight Ti2+-4N-GQD's potential for regulating H-2 adsorption and desorption in hydrogen storage applications.