Fundamental problems of hydrogen and renewable energy and fuel all technologies

Theoretical search for optimized structures of nanocarbon systems characterized by a high adsorption capacity for molecular hydrogen

The structure of the complexes of the transition state of chemisorption of hydrogen molecules on PAM С54Н18 (a) and its nitrogen- (С52N2Н18) (b) and boron derivative (С52В2Н18) (c)

Area of applications

The results obtained in the course of the project will be used to determine the composition and structure of adsorption centers for carbonaceous materials of various nature, in particular doped graphene, which have a high adsorption capacity relative to molecular and atomic hydrogen, and the formation energy of adsorption complexes (AK). The estimation of adsorption capacity of carbon nanostructures will be based on the data obtained on the equilibrium spatial structure of their constituents and types of physical and chemical interactions of both molecular and supramolecular nature.

Brief description

For the implementation of theoretical studies, computer simulation has been applied, which, being an alternative to experimental research methods, is based on techniques and approaches of quantum mechanics and quantum chemistry. The corresponding mathematical technique and numerical methods of calculation are increasingly used to describe the properties of chemical compounds, solids and adsorption complexes on its surface, which allows us to evaluate the results of any experimental variant at the atomic-molecular level. At the same time, previous researches concerning the study of the possibilities of using carbon materials as a storage medium of hydrogen allowed, together with the analysis of the results of research, let is possible to evaluate the probability of the existence of effective hydrogen accumulators.

Expected properties

Theoretical calculations by modern methods of quantum chemistry provide valid information regarding the structure and energy parameters of adsorption complexes of hydrogen without the involvement of long-term and expensive experimental studies. Comparing their results with the experimental data allows us to adjust the calculation method and to plan rationally the direction of the experiment.

Advantages

Based on the results of quantum chemical and molecular-dynamic calculations of the spatial structure and properties of adsorption complexes of atomic and molecular hydrogen with carbon systems of various nature (single-and multi-wall nanotubes, clusters of graphene-like structure), for the practical realization of methods of designing active centers of adsorbents on a carbonaceous basis with a high adsorption capacity relative to atomic and molecular hydrogen.

Project development

An analysis of the results of quantum chemical calculations testified the exothermicity of dissociative adsorption of molecular hydrogen in nitrogen-containing and boron-containing graphene-like materials. At the same time, for the models of pure carbon graphene-like layer, the estimated data indicate a low probability of chemical adsorption of molecular hydrogen on it under normal conditions. Dissociative chemisorption of hydrogen molecules, regardless of the nature of the heteroatom in the polyaromatic molecule, is thermodynamically more probable on the periphery of the model clusters than that in their center. The calculated activation energy and the chemisorption energy of the hydrogen molecule, regardless of the size of the polyaromatic molecule, are the lowest for its boron analogue. The energy of the chemisorption of the hydrogen molecule depends on the size of the model and the position of the atoms of boron and nitrogen, has negative meanings, indicating that the process is unconscious. For all considered cases, the energy parameters of chemisorption indicate the ineffectiveness of the use of pure carbon material for the chemical adsorption of molecular hydrogen in comparison with nitrogen and boron-containing ones. However, the use of a hydrogen adsorbent as a boron-containing carbonaceous material is not appropriate, in connection with its significantly negative values of the chemisorption energy, and hence the irreversibility of the hydrogen adsorption-desorption process.

Contact information

Executing : O.O. Chuiko Institute of Surface Chemistry, National Academy of Sciences of Ukraine.

Project 11 «Theoretical search for optimized structures of nanocarbon systems characterized by a high adsorption capacity for molecular hydrogen».

Project leader:

Academician of NAS of Ukraine,
Doctor of Chemical Sciences,
Professor

Kartel Mykola T.