Computational and Experimental study of Hydrogen Generation and Storage on Graphene and Cellulose doped with Nb, Mg, and Ti

Abstract

Finding a smooth transition from fossil fuel to cleaner and sustainable energy sources is a must to guarantee energy security in the future. Hydrogen is a promising energy carrier that could be an alternative to fossil fuels. Therefore, in this thesis, we firstly carried out a theoretical and experimental study to investigate the hydrogen generation through the hydrolysis of graphene oxide and cellulose functionalized with magnesium, titanium, and niobium. Secondly, a theoretical investigation was carried out on the hydrogen storage for graphene doped with niobium and cellulose doped with magnesium, titanium, and niobium. A Homemade apparatus was designed and built-in order to measure the hydrogen production of graphene and cellulose doped with magnesium, titanium, and niobium. Various characterization techniques such as thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to provide a complementary description of the thermal stability, crystallinity, elemental composition, and surface morphology that offer support for the composite materials' successful preparation. Theoretical and experimental study of hydrogen production via hydrolysis of graphene oxide (GO) functionalized with metals such magnesium, titanium, and niobium revealed that the hydrogen generation efficiencies of the composite materials take on the following order: niobium doped graphene oxide (GONb) > titanium doped graphene oxide (GOTi) > magnesium doped graphene oxide (GOMg). These results agree with the catalytic activities of TiO2 and NbO2 and the inhibitory effects of MgO. Furthermore, the results of the experimental and theoretical investigation of the hydrolysis of microcrystalline cellulose (MCC) and microcrystalline cellulose coated with magnesium, titanium, and niobium revealed that the solvent plays an integral part in the hydrogen yield. The results of this study showed that the addition of NaCl inhibits the hydrogen yield of microcrystalline cellulose compared with the pure water. Also, we demonstrated that urea and NaOH have the same effect as NaCl on the hydrogen output from MCC. In addition, the ball milling enhances the hydrogen yield of MCC in water and MCC reacting with magnesium, titanium, and niobium in water. The hydrogen storage on graphene doped with niobium revealed free Nb atoms could bind six H2 molecules in the binding energy interval [0.228 eV – 0.630 eV] in the quasi-molecular form, and the maximum temperature to desorb all the absorbed H2 would be 466 K. Moreover, our results demonstrate that the complex graphene doped with niobium (GR@Nb) can absorb six H2 in the energy window of 0.398 eV to 0.680 eV in the quasi-molecular form. Furthermore, our results predict that the desorption of the nH2-Nb complex can be suppressed when 7.25 % of N atoms are doped on graphene, and the storage capacity of 2NGR@2Nb is 8 wt%. Finally, the hydrogen storage in pure cellulose and cellulose doped with magnesium, titanium, and niobium were studied. The results showed that the interaction of hydrogen with pure cellulose occurs in the gas phase. In addition, our results predict that cellulose doped with niobium is the most favorable medium where 6H2 molecules are stored with adsorption energy in the range [0.198 – 0.765 eV] and the maximum temperature needed to release all the hydrogen is TD= 978 K.