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

Abstract

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 Li_N-GaN and Co_N-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 V_N-GaN nanosheets yielded the gravimetric densities up to 8.158% (2Co-V_N-GaN) that well above the gravimetric DOE achieve. The 2Li_N-GaN and 2Co_N-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.

Keywords: DFT calculations; Desorption enthalpy; Hydrogen storage; Metal decoration GaN nanosheets; QATIM.