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An Efficient Way To Suppress the Competition between Adsorption of H2 and Desorption of nH2–Nb Complex from Graphene Sheet: A Promising Approach to H2 Storage
journal contribution
posted on 2018-12-07, 18:49 authored by Omar Faye, Jerzy A. SzpunarWe performed first-principles
calculations to investigate the electronic
structure and hydrogen storage capacity of bare niobium (Nb) and niobium-decorated
graphene (GR@Nb). The results predict that bare Nb can bind 6 H2 molecules in the quasi-molecular form to reach saturation
with the binding energy of hydrogen in the range 0.2–0.7 eV.
In addition, the maximum temperature of desorption was 466 K. We demonstrated
that the most favorable site for Nb atoms is the hollow site of graphene
with a binding energy of 1.783 eV. Moreover, we analyzed the stability
of Nb dopant on the graphene surface by means of reaction barriers
calculations and an ab initio molecular dynamics simulation. Our calculations
reveal that an energy barrier of 0.435 eV is required for a Nb atom
to move from one hollow site to the adjacent hollow site, which is
far greater than the energy of thermal vibration of Nb at 300 K. We
show that Nb-decorated graphene doped with nitrogen atoms at 7.25%
can absorb 12 H2 molecules in the quasi-molecular form
with an average binding energy of 0.410 eV at an average desorption
temperature of 520 K. Our results predict that desorption of nH2–Nb complex from a graphene sheet can
be suppressed by increasing the concentration of nitrogen atoms to
7.25%. Finally, the storage capacity of 2NGR@2Nb is about 8 wt %.
These results clearly demonstrate that Nb-decorated graphene with
a 7.25% concentration of nitrogen atoms is a promising candidate for
H2 storage for mobile applications.