COMPUTATIONAL STUDY OF GRAPHITE AS HYDROGEN STORAGE MATERIAL USING DENSITY FUNCTIONAL THEORY METHODS

• Main Author: Gunawan, Rahmat
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/35010
• Institution: Institut Teknologi Bandung

Interaction studies of graphite component as hydrogen storage materials have been investigated theoretically with density functional theory method or DFT. In this calculation, the material will be compared with the graphite modified namely graphite intercalated compounds or GICs, especially by alkali metal intercalates (Li, Na and K). The properties of the electronic structure, energetics and the charge contribution of atomic orbital in the hydrogen- graphite system, GICs, and hydrogen-GICs are studied through the calculation approach of gradient-corrected PBE (Perdew-Burke-Ernzerhof ) for the acqui- sition of exchange-correlation energy. This calculation is further strengthened by the use of plane wave basis set, and calculation of electron-nucleus interac- tions using Vanderbilt ultrasoft pseudopotential. Computational study yielded four main relaxation of molecular geometry, the determination of the electronic energy band structure, density of energy state, and the contribution of atomic orbital of system through analysis of the charge density differences. Calculation and determination of the geometry relaxation of the potential energy surface calculated by the search of hydrogen molecules on the surface of graphite, give 3.2 ?A on top as the best position with minimum energy of -0.019 eV. The analysis of electron energy bands, density of states, and electron charge density, indicates that there is an increase in charge contri- bution of atomic orbital from the graphite surface to molecular hydrogen, by forming a hybridized orbital of ?-? and ??-?? in the valence and conduction energy region. The investigations for the interaction of alkali metals on the surface of graphite give the prefered site at the hollow position for each of the alkali metals at the distance of 1.7 ?A, 2.3 ?A, and 2.6 ?A from the plane with the interaction energy of -1.37 eV, -0, 66 eV, -0.96 eV, for the Li, Na and K metals, respectively. The interaction and contribution of atomic orbital form hybridization orbital of 2s ? ?; 2p ? ? and 3s ? ?; 3p ? ? in the valence energy region and hybridization orbital of 2s ? ??; 2p ? ?? and 3s ? ??; 3p ? ?? in the conduction energy region for Li and Na metals, respectively. K metals do not involve p orbital, so that they only generate hybridization orbital of 4s ? ? and 4s ? ?? on the valence and conduction energy region. Calculation and determination of the geometry relaxation of the potential energy surface for the interaction of H2 molecules on the surface GICs interca- lates with alkali metal (Li, Na, and K) produces umbrella-like pattern, where each molecule of H2 will be approached and surrounded by the alkali metals. The best construction of all three metal intercalates is Li, as the system H2/Li/graphite produce the expected behavioral pattern of H2 molecules to be utilized as hydrogen storage. The analysis of electron energy bands, density of states, and electron charge density, indicates an increase in charge contri- bution of atomic orbital from the graphite surface to molecular hydrogen, by forming a hybridized orbital of ?-2s ? ?; ?-2p ? ? and ?-3s ? ?; ?-3p ? ? in the valence energy region and ??-2s ? ??; ??-2p ? ?? and ??-3s ? ??; ??- 3p ? ?? in the conduction energy region for Li and Na metal intercalates, respectively. K metal intercalates still do not involve p orbitals, so that only generate hybridization orbital of ?-4s ? ? and ??-4s ? ?? on the valence and conducting energy. Computational chemistry calculations indicate that Li gave the model presence of atomic hydrogen capacity batter than Na and K. These results show quali- tatively, the increase in hydrogen storage capacity of GICs, where for every one of alkali atoms can adsorp six molecules of hydrogen.