Abstract:
Hydrogen holds the promise for alternative clean energy carrier due to its renewable and pollution free
nature. A metal-organic framework (MOF) is designed with graphyne linker. Each graphyne linker is
decorated with two Ca atoms across the linker with average metal binding energy 3.0 eV. The structural,
electronic and hydrogen storage properties of Ca decorated MOF have been explored by using first
principle calculations. On full saturation with hydrogen, each Ca atom of MOF-Ca8 adsorbs a maximum of
six H2 molecules and results in MOF-Ca8-48H2 structure. Further twelve more hydrogen molecules could
be accommodated in the pore space of MOF resulting in the MOF-Ca8-60H2 structure having 7.9
hydrogen wt%. According to the simulations, the H2 molecules can be adsorbed on Ca by Kubas mechanism
with elongation in H H bond distance. The calculated hydrogen interaction energy is found in
the range between 0.25 and 0.30 eV while desorption energy varies between 0.15 and 0.32 eV. The
charge transfer during hydrogen adsorption is investigated by Hirshfeld charge analysis and electrostatic
potential map. The molecular dynamics simulations revealed a high degree of reversibility in hydrogen
adsorption of the system at ambient conditions. The usable capacity of H2 is explored by calculating
occupation number at adsorption and desorption conditions. The energetics and storage capacity meets
the US DOE target which makes the MOF-Ca8 as a potential hydrogen storage material.
