Theoretical Study on the Encapsulation of Li Atoms inside Boron Nitride Nanotubes: Physical Properties and Catalytic Reactivity for the Oxygen Reduction Reaction

Abstract

Recently, the encapsulation of various species inside boron nitride nanotubes (BNNTs) was identified as an effective method for modifying the physical and chemical properties of boron nitride nanotubes (BNNTs), thus greatly widening their potential applications. In the present work, we have performed comprehensive density functional theory (DFT) calculations to study the effects of the encapsulation of various numbers of Li atoms on the electronic and magnetic properties of a BNNT. The results show that two, three, and four Li atoms can be stably encapsulated inside a BNNT (Eint = −1.198, −2.081, and −2.378 eV, respectively), giving interaction energies that are much larger than that of one Li atom (Eint = −0.052). Because a certain number of electrons are transferred from these encapsulated Li atoms to the BNNT, some impurity levels are induced within the band structures of the BNNT, thus reducing its band gap. Encapsulation of three and four Li atoms renders the BNNT a metallic material, whereas 2Li@BNNT has a semiconducting nature with a small band gap (∼0.70 eV). Furthermore, we explored the catalytic activities of these composites for the oxygen reduction reaction (ORR). The chemisorption of ORR species O2, OOH, and O and the downhill energy landscape of the ORR on the surface of Li-encapsulated BNNTs indicate that Li encapsulation significantly enhances the BNNT chemical reactivity, rendering BNNTs active for the complete four-electron reduction of O2 to 2H2O.