FIRST-PRINCIPLES STUDIES CONCERNING OPTIMIZATION OF HYDROGEN STORAGE IN NANOPOROUS REDUCED GRAPHITE OXIDE

CARLA BELÉN ROBLEDO; MARIANA ISABEL ROJAS; OSVALDO CÁMARA; EZEQUIEL PEDRO MARCOS LEIVA

Córdoba

Workshop; Quantum Espresso Spring School; 2015

Facultad de Ciencias Químicas, Univ. Nac. de Córdoba

Hydrogen is an energy carrier that can be used asfuel for vehicle use of both combustion engines and fuel cells. The challengefor its implementation is to improve the storage tanks in order to obtain lowvolume, safe and efficient hydrogen storage. One promising possibility is tostore hydrogen by ad/absorbing it in porous carbonaceous materials, becausethey are lightweight, present a high surface area and have low commercial cost.The hydrogen adsorption energy should be around 0.2 to 06 eV/ molecule to beable to achieve a reversible storage mechanism. It should also allow manyloading/unloading cycles of. Unfortunately, in pristine graphite the bindingenergy of H2 molecules is too low. Graphite oxide (GO) is apromisory candidate for hydrogen storage since it posseses hydroxyls and epoxygroups in the structure, which produce increase of the interplanar distancebetween graphene planes due to repulsion between the functional groups, forminga porous structure. The hydrogen molecules could interact with the oxygenfunctional groups and also be stored in the pores.In this work by means of theoretical calculationsusing density functional theory (DFT) as implemented in the Quantum-Espressocode, we studied the structures of GO and reduced graphite oxide (GOH), withoxidation in the range of 12.5% to 50%. GOH is obtained by hydrogenating the epoxy groups. The effect of oxidationon the pore size and its effect on the absorption energy of the hydrogenmolecules was evaluated. It was observed that the pore size increases withoxidation. For the highest degree of oxidation,the pore is 0.58 nm wide. Theoptimum level of oxidation for storing hydrogen is 37.5%  with an adsorption energy of -0.2 eV /molecule.It can be concluded that for optimum hydrogenstorage in porous carbonaceous materials, oxidation must be controlled toachieve a homogeneous oxidation material of 37.5% of oxygenated functionalgroups and / or use intercalation compounds to optimize the pore size.