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

Abstract

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 H₂ desorption. These results highlight Ti²⁺-4N-GQD’s potential for regulating H₂ adsorption and desorption in hydrogen storage applications.