Development of nano-metal – graphene structured materials for hydrogen storage

Ngqalakwezi, Athule
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Operative solutions in the storage of hydrogen remain the main challenge in achieving an economy that is solely based on hydrogen. Energy storage, consumption and production are the fundamental challenges that hinder this development. To date no material has met the Department of energy requirements for energy storage and due to this; a lot of research has been undertaken for the development of hydrogen storage materials for on-board applications. In material based storage of hydrogen, poor kinetics and poor thermodynamics of developed materials have hindered their progress towards practical applications. As such, a need for material that will store hydrogen and have favorable kinetics and thermodynamics is a priority. In this work, graphene based nanocomposites were synthesized for hydrogen storage applications. The primary aim of the work was to synthesize a nanocomposite that will desorb hydrogen at low temperature. The precursor graphene was synthesized using both the improved Tours method and the modified hummer’s method. The graphene was reduced using various reducing methods and the effect of the reduction method on the hydrogen storage capacity of the material was evaluated. The metal/graphene nanocomposites were evaluated for hydrogen storage capacity at various pressures. The nanocomposites were then tested. An economic evaluation of the graphene nanocomposite was conducted to determine the feasibility of the material. The characterization done in this work, XRD, FTIR and RAMAN confirmed that the graphite was successfully oxidized and the graphite oxide was successfully reduced to graphene. Elemental analysis (XRF, TEM-EDS) confirmed that the calcium and nickel were successfully incorporated into the graphene matrix. The metal/graphene was charged with hydrogen at various pressures 5, 10 and 15 bars and a proportional relationship between increasing pressure and adsorbed hydrogen was established. The hydrogen charged metal/graphene nanocomposite was then tested using TGA and TPD to test the hydrogen storage capacity and desorption temperatures thereof. The Ca/graphene desorbed hydrogen around 150°C, a temperature significantly lower than the one reported in literature. The Ca/graphene adsorbed 3.99 wt% of hydrogen while the Ni/graphene adsorbed about 2.78 wt% hydrogen. The reducing agent does affect the hydrogen storage capacity of the metal/graphene. It was found that NH3 reduced Ca/graphene took up more hydrogen due to the N-doping effect of the NH3 which enhances the uptake of hydrogen. The economic evaluation was also done successfully
A dissertation submitted to School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, 2021