High coverage of hydrogen on a (10,0) single-walled boron nitride nanotube

The binding energy of hydrogen atoms to a (10,0) single-walled boron nitride nanotube (SWBNNT) is calculated at 25%, 50%, 75%, and 100% coverage using the density functional theory. The average binding energy is highest at 50% coverage when the H atoms are adsorbed on the adjacent B and N atoms along the tube axis and the value is $-53.93\mathrm{kcal}∕\mathrm{mol}$, which is similar to half of the $\mathrm{H}\mathrm{H}$ binding energy. Also, the band gap $(-4.29\mathrm{eV})$ of the pristine (10,0) SWBNNT is decreased up to $-2.01\mathrm{eV}$ for the H-adsorbed BNNT with 50% coverage.

Figure 1

(Color online) Hydrogen decorations considered in this study to investigate the binding energies of H on the exterior wall of (10,0) SWBNNT as a function of H coverage. In DFT calculations, only four layers of the BNNT (half of the present tube structures along the tube axis) were considered due to computational limitation. Here, the pink, blue, and white atoms mean boron, nitrogen, and hydrogen, respectively. In the case of 25% H coverage, the 25cov̱1 indicates all boron pattern, the 25cov̱2 all nitrogen pattern, the 25cov̱3 the line pattern, and the 25cov̱4 the zigzag pattern. In 50% coverage, the 50cov̱1 means the pairs of rings pattern, the 50cov̱2 all boron pattern, the 50cov̱3 the line pattern, the 50cov̱4 the spiral pattern, and the 50cov̱5 the pairs of lines pattern. Also, the 75cov̱1 is the pattern of 75% H coverage having the 20 $\mathrm{B}\mathrm{H}$ and 10 $\mathrm{N}\mathrm{H}$ in unit cell of the BNNT and the 75cov̱2 is the pattern having 10 $\mathrm{B}\mathrm{H}$ and 20 $\mathrm{N}\mathrm{H}$.

Figure 2

TDOS for (a) pristine (10,0) SWBNNT and (b) (10,0) SWBNNT with 50% H coverage, called 50cov̱5 in Fig. 1. The dotted lines in each figure refer to the Fermi energy level. The arrow in (b) indicates one band in the band gap, caused by hydrogen chemisorption.