Enhanced hydrogen storage performance of Li and Co functionalized h-GaN nanosheets: DFT study

Based on the density functional theory (DFT) computations, we investigated the hydrogen storage performances of alkali metal (Li) and transition metal (Co) decorated the defective GaN nanosheets. Fundamental aspects including the interaction properties, bonding characteristics, adsorption ability, frontier orbital, HOMO-LUMO energy gaps, natural bond orbital (NBO) analysis, projected densities of states (PDOS) and statistical thermodynamic stability have been demonstrated to analyze the interaction properties of H2 molecules. As a theoretical strategy, non-covalent interactions (NCI) and the atoms in molecules (QTAIM) descriptors were performed to depict weak interactions. The LiN-GaN and CoN-GaN systems and the H2 uptake capacity revealed to be 7.78% and 5.55%, respectively. Our results demonstrated that H2 molecules are introduced sequentially on the Li and Co that functionalized both sides of VN-GaN nanosheets yielded the gravimetric densities up to 8.158% (2Co-VN-GaN) that well above the gravimetric DOE achieve. The 2LiN-GaN and 2CoN-GaN are energetically more effective for the H2 adsorption, stable and preferred than pristine GaN nanosheet. Additionally, two binding mechanisms including polarization of the hydrogen molecules and σ orbitals hybridization of H2 molecules have been investigated to explain the interaction of H2 molecules. The hydrogen desorption enthalpy and desorption temperatures of hydrogen molecules, indicating the H2 molecules are easy to desorb from Li and Co decorated defective GaN nanosheets. These results suggest the possibility of an excellent and promising nanostructural material to improve the performance of hydrogen storage for in fuel cells application at ambient temperature.