|dc.description.abstract||A brief overview of the dissertation given in this abstract is divided into five
points showing its topicality, objective, goals, scientific novelty, and practical significance.
The topicality is reflected in a need for the replacement of the fossil fuels driven
economy with economy oriented towards renewable sources of energy, in which hydrogen
is used as an energy carrier. This need is dictated by three reasons: (i)
ecological problems mostly induced by the carbon dioxide emission; (ii) limitedness
of the reserves of hydrocarbons; (iii) political issues related to the localization of
hydrocarbons in few places around the globe. In any implementation of hydrogen
economy, which is a possible cure for the mentioned issues, the production and storage
of hydrogen are the most challenging tasks to solve. The dissertation is focused
on the problem of hydrogen storage. For today, none of the known materials meets
all the requirements imposed on practical on-board hydrogen storage media.
The main idea proposed and explored in this dissertation is the "hierarchical
storage of hydrogen". We envisage materials that would offer various means of
reversible hydrogen binding. Each level of hydrogen storage would have different
characteristics that become advantageous in different circumstances. A material
with hierarchical hydrogen storage could be superior in comparison with conventional
materials, in which hydrogen is bound at one level only. In particular, we
explore materials in which a fraction of hydrogen is physically bound and the remaining
part is chemically bound. The physical binding provides hydrogen that
is kinetically easily accessible, whereas the chemical binding assures a high overall
hydrogen density. We suggest that hydrogen clathrates of a high hydrogen content
material, like ammonia borane, could serve as models of hierarchical hydrogen
An objective of the dissertation is thus to validate the possibility of storage of
molecular hydrogen in clathrates of ammonia borane using methods of theoretical
chemistry and materials science.
The goals of the dissertation can be formulated as follows: (i) to identify possible
structures of clathrates of ammonia borane; (ii) to estimate hydrogen capacity
of the clathrates; (iii) to estimate pressure-temperature regimes required for the
stabilization of these clathrates.
The scientific novelty of the dissertation includes: (i) formulation of the "hierarchical
hydrogen storage" concept; (ii) formulation of construction principles for
clathrates of ammonia borane and identification of their possible structures; (iii)
estimation of hydrogen capacity of the clathrates; (iv) development of a model of
clathrates phase equilibria, which is based on the energy of intermolecular host-guest
interactions and the entropy of guest molecules enclosed in clathrate cages; (v) an
estimation of the pressure-temperature stability zone for these clathrates.
The practical significance of the dissertation is in justification of further experimental
works on clathrates of ammonia borane, for which the required stabilization
pressure and temperature conditions are determined.
The work proposed and thoroughly explored hierarchical method of hydrogen
storage and resulted in identification of stable cages and periodic structures of possible
clathrates of ammonia borane. The most stable extended system of these
clathrates was found to be more stable than molecular crystal of ammonia borane
at low temperatures. Hydrogen capacity of this hypothetical clathrate structure was
estimated to be 21 wt%. To predict the pressure-temperature stability zone of the
material a model of clathrate phase equilibria has been formulated and tested on
known hydrates. The model showed that clathrates of ammonia borane could be
stabilized at ambient pressure when temperature is lowered to 77 K.||en_US