Abstract
Hydrogen gas produced from water has the potential to be a promising alternative clean energy carrier to power fuel cells for electric vehicles. Besides transportation, the electricity generated from hydrogen based fuel cells can be used to operate household electrical appliances and other fuel cell-based device. Moreover, compared to existing hydrogen production techniques such as steam methane reforming, coal gasification etc. which produce greenhouse gases as byproducts, hydrogen produced from water is an environment-friendly technique. This clean hydrogen produced from water can also be used in the production of ammonia, in chemical industries and refineries, and electronic industry. However, efficient and sustained production of hydrogen gas under mild hydrothermal conditions without generating impurities such as carbon monoxide (which poisons fuel cells), has been a challenge for the scientific community. Moreover, storing hydrogen in a vehicle risks inflammation. Therefore, there is an unmet need for an efficient hydrogen production technology in which there is no need for hydrogen storage (hydrogen is flammable) and it is produced from environment-friendly sources such as water as per requirement. In this dissertation, we report the production of hydrogen gas from water under mild hydrothermal conditions using (a) nanostructured cobalt, carbon dioxide (CO2), and aqueous sodium hydroxide (NaOH), and (b) nanostructured cobalt and aqueous sodium carbonate (Na2CO3). The synthesized nanostructured cobalt was characterized by scanning electron microscopy (SEM) to determine its size distribution and to observe the sharp nanostructure features on the surface of cobalt particles. Nitrogen-Brunauer–Emmett–Teller (N2-BET) technique was used to determine the specific surface area of the synthesized cobalt particles. High purity hydrogen production (~99% by volume) was achieved by carrying out reactions in a batch reactor and varying parameters such as temperature, amount of nanostructured cobalt, volume of solution, CO2 pressure, and NaOH concentration. Moreover, experiments were performed to investigate the mechanism of hydrogen production. X-ray diffraction (XRD) was performed on the solid byproduct collected from the reactor at the end of the reaction to investigate the characteristics of the byproducts. In addition, the solution collected from the reactor at the end of the reaction was analyzed by atomic absorption spectroscopy to investigate the presence of cobalt ions in the solution. The results and conclusions of characterization of solid and solution byproducts, and a thorough study of the previously reported literature were used to propose a mechanism for the hydrogen production reaction. After optimization of the reaction parameters for the hydrogen production reaction in the batch reactor to obtain ~99% pure hydrogen, the second set of experiments focused on obtaining high purity hydrogen using column instead of the batch reactor in order to design and develop a continuous hydrogen generator. To perform the hydrogen production reaction in a column and develop continuous hydrogen generator, we wanted to simplify the hydrogen production process. While performing hydrogen production reactions in the batch reactor, we observed that when the reaction was performed in which CO2+NaOH was replaced with Na2CO3 as the reactant (the other reactants being cobalt and water), hydrogen production was achieved. Therefore, parameters such as temperature, amount of nanostructured cobalt, volume of solution, and Na2CO3 concentration were optimized to obtain high purity (~97% by volume) hydrogen production in the column reactor. Subsequently, a continuous hydrogen generator set-up was designed, and reactions were performed for 5-7 days and the purity of hydrogen production was measured everyday by gas chromatography using H2 Peak Performer instrument.