Decoration of graphene sheets by metal oxide particle: synthesis, characterization, and application in hydrogen storage
Goharibajestani, Zahra (2017) Decoration of graphene sheets by metal oxide particle: synthesis, characterization, and application in hydrogen storage. [Thesis]
This is the thesis for a doctorate of Sabanci University and relates to the synthesis of graphene based nanocomposites as media to store hydrogen gas. The aim of this work is to develop such materials with improved hydrogen storage capacity at ambient temperature and pressures that can also provide the adaptability to onboard systems and public safety. In the first part of this work, graphene sheets were decorated by 2.8 wt% transition metal oxide (TiO2, NiO, Fe3O4, CuO) for hydrogen uptake. Among these nanocomposites, sample decorated with Fe3O4 showed the maximum hydrogen uptake of 0.4 wt% at room temperature while TiO2 showed the highest improvement in the isosteric heat of adsorption (12kJ/mol at a surface coverage of 50%) when normalized by maximum uptake at 298k due to the strong interaction between hydrogen molecules and substrate. Moreover, a series of graphene-based nanocomposites with different TiO2 contents (10, 12 and 15 wt%) have been prepared via a facile chemical method. The highest hydrogen uptake of 0.39 wt% was obtained for the sample with 12 wt% TiO2 nanoparticle that is 125% higher than the iv hydrogen adsorption of the parent graphene material. In the next part of this work, homogeneously distributed TiO2 nanoparticles with (001) reactive facets were grown over nitrogen-doped reduced graphene oxide sheets by a solvothermal method. Hydrogen storage capacity of the system was significantly improved to 0.91 wt% that is the highest hydrogen storage ever reported for graphene-based nanocomposites at room temperature and low pressures. Importantly, this nanocomposite exhibits ~91% capacity retention through 5 cycles with more than 88% release of the stored hydrogen at ambient conditions. In the last part of the thesis, we reported the development of a heterogeneous catalyst consisting of Al2O3 nanoparticle and low amounts of Pd that markedly enhances the hydrogen uptake of RGO. It was shown that incorporation of 1 wt% heterogeneous catalyst (<0.3 wt% Pd) significantly increased the hydrogen storage capacity of RGO from 0.17 wt% to 0.31 wt%. This indicated a rise of hydrogen uptake by a factor of 1.8 in RGO nanocomposite.
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