Niobium Decorated 2D Biphenylene as High Capacity Hydrogen Storage Material: Combined DFT and AIMD Simulations

Abstract

Hydrogen has cemented its place as an alternative clean energy source, especially in the transportation sector. Here, a recently synthesized 2D carbon allotrope, Biphenylene (BPh) decorated with Niobium (Nb) has been studied for its hydrogen storage applications in light weight vehicles. Niobium atom binds strongly to the 2D monolayer with a binding energy of -3.42 eV. The BPh+ Nb system adsorbs a total of 5 H2 molecules with a gravimetric H2 uptake of 5.76 wt.%, higher than the DOE requirement of 5.5 wt.% with target year 2025. The average hydrogen adsorption energy of the system was found to be -0.61 eV (within the range of -0.2 to -0.7eV as suggested by DOE). The elongation of the H-H bond suggests the charge donation and back donation between d orbital of the metal and s orbital of hydrogen, representing Kubas type of interactions. A vapor pressure of 1 bar can be achieved at nearly 380 K, suggesting a strong interaction of hydrogen with the BPh+Nb system at room temperature and an enhanced hydrogen storage capacity with increase of pressures. The thermal stability of the system was studied by utilizing the Ab-initio Molecular Dynamics simulations and the system was found to be stable at room temperature whereas all positive phonon frequencies ensure dynamic stability.The probability of metal clustering seems to be negligible owing to a high diffusion energy barrier as seen from sophisticated Cl-NEB calculations. Thus, the biphenylene decorated with Nb could be explored as a promising candidate by experimentalists for hydrogen storage in light vehicles.