Niobium-decorated 2D biphenylene as a 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) is studied for its hydrogen storage applications in lightweight vehicles. The niobium atom binds strongly to the 2D monolayer with a binding energy of −3.42 eV. The BPh + Nb system adsorbs a total of 5H₂ molecules and provides a gravimetric H₂ uptake of 5.76 wt%, near the DOE requirement of 6.5 wt%. The average hydrogen adsorption energy of the system was found to be −0.61 eV (within the range of 0.2–0.7 eV as suggested by the DOE). The elongation of the H–H bond suggests charge donation and back donation between the d orbital of the metal and the s orbital of hydrogen, representing Kubas-type 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 at higher pressures. The thermal stability of the system was studied by utilizing AIMD simulations, and the system was found to be stable at room temperature. The probability of metal clustering is minimized owing to a high diffusion energy barrier as seen from Cl-NEB calculations. Thus, biphenylene decorated with Nb could be explored as a promising candidate by experimentalists for hydrogen storage in light vehicles.