Lithium-functionalized boron phosphide nanotubes (BPNTs) as an efficient hydrogen storage carrier

Abstract

In this work we have carried out extensive Density Functional Theory (DFT) and ab-initio Molecular Dynamics (AIMD) simulations to study the structural and electronic properties, thermal stability, and the adsorption/desorption processes of hydrogen H₂ molecules on Lithium (Li) functionalized one-dimensional boron phosphide nanotubes (BPNTs), for possible use as materials of H₂-storage media. Our results show that Li atoms can be adsorbed on the hollow sites of (7,7)-BPNT with binding energy ranging from 1.69 eV, for one Li, to 1.65 eV/Li for 14 Li atoms adsorbed on (7,7)-BPNT. These large energies of Li prevent the formation of clusters on the nanotube sidewall. The investigation of the electronic behavior showed that (7.7)-BPNT semiconductor turns metallic upon the Li-adsorption. Furthermore, the average binding energy of H₂-molecules adsorbed on nLi@BPNT(mH₂) systems (with n = 1, 2, 4, 6, 8, 14 and m = 1, 2, 3, 4, with m the number of H₂ for each Li) lies within a range of 0.13–0.20 eV/H₂ which is compatible to the required range for adsorption/desorption of H₂-molecules at room conditions. A H₂-storage gravimetric capacity up to 4.63% was found for 14Li@BPNT(4H₂) system. In addition, AIMD simulation strongly indicates that given adequate monitoring of the temperature, the charge/release process of H₂-molecules can be controlled. Our findings suggest that Li-functionalized (7,7) boron phosphide nanotubes can provide a valuable underlying material for H₂-storage technologies and therefore must certainly be the subject of further experimental exploration.