A general model of electrochemical impedance spectroscopy and its application to hydrogen storage materials

As the global need for energy increases, scientists and engineers have found a possible solution by using hydrogen to power our world. Although hydrogen can be combusted as a fuel, it is considered an energy carrier for use in fuel cells wherein it is consumed (oxidized) without the production of greenhouse gases.;The U.S. Department of Energy (DOE) formed a Center of Excellence for Chemical Hydrogen Storage, and this work stems from that project. The DOE has identified boron hydrides as being the main compounds of interest as hydrogen storage materials. The various boron hydrides are then oxidized to release their hydrogen, thereby forming a "spent fuel" in the form of a lower boron hydride or even a boron oxide. The ultimate goal of this project is to take the oxidized boron hydrides as the spent fuel and hydrogenate them back to their original form so they can be used again as a fuel. Thus this research is essentially a boron hydride recycling project.;One class of boron hydrides, called polyhedral boranes, became of interest to the DOE due to their ability to contain a sufficient amount of hydrogen and their physical and chemical safety attributes. Unfortunately, the research performed here has shown that polyhedral boranes do not react in such a way as to allow enough hydrogen to be released, nor do they appear to undergo hydrogenation from the spent fuel form back to the original hydride.;After the polyhedral boranes were investigated, the project goals remained the same but the hydrogen storage material was switched by the DOE to ammonia borane. Ammonia borane was found to undergo an irreversible hydrogen release process, so a direct hydrogenation was not able to occur. To achieve the hydrogenation of the spent ammonia borane fuel, an indirect hydrogenation reaction is possible by using compounds called organotin hydrides. In this process, the organotin hydrides will hydrogenate the spent ammonia borane fuel at the cost of their own oxidation, which forms organotin halides. To enable a closed-loop cycle, my task was then to be able to hydrogenate the organotin halides back to their hydride form.;In addition to this experimental work, a parallel project was carried out to develop a new model of electrochemical impedance spectroscopy (EIS). The EIS technique is capable of probing complex chemical and electrochemical reactions, and this model was written into a computer code that allowed the input of experimental EIS data and the extraction of kinetic parameters based on a best-fit analysis of theoretical reaction schemes.