Hydrogen adsorption on Ga-doped bilayer graphene: A DFT study

Abstract

Hydrogen, as an environmentally friendly energy source, is pivotal in its storage methods for its development and effective utilization. Graphene boasts advantages such as high specific surface area, excellent electrical properties, and high tunability, making it highly promising for hydrogen storage applications. Compared to monolayer graphene, bilayer graphene exhibits a more easily controllable bandgap, showcasing its potential for hydrogen storage. Additionally, to further enhance the hydrogen adsorption capability of graphene-based substrates, doping methods are commonly employed to adjust their electrical properties. This study proposes a model for hydrogen adsorption on bilayer graphene to investigate its hydrogen storage capacity. Specifically, density functional theory (DFT) computational methods are utilized to study the adsorption of single and multiple hydrogen molecules on monolayer and bilayer graphene, with or without doping with gallium atoms. Furthermore, the underlying reasons for the enhanced hydrogen adsorption in gallium-doped bilayer graphene are systematically analyzed and elucidated. The research findings indicate that pristine graphene exhibits relatively low sensitivity to hydrogen gas, with adsorption energies of only −0.078 and −0.096 eV for monolayer graphene (MG) and bilayer graphene (BG), respectively. However, upon doping gallium atoms into MG and BG, the adsorption energy significantly increases by approximately 30.8 % and 54.1 %. For adsorbing 8 H₂, with average adsorption energies reaching -0.102 eV and −0.163 eV, which is primarily due to the electron in the s orbital of H has been transferred to the d orbital of transition metal Ga. These results indicate that gallium-doped bilayer graphene holds great promise as a hydrogen storage material.