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Cycles of reversible hydrogenation reactions are important for at least two different energy-related applications: reversible chemical hydrogen storage and thermally regenerative fuel cells. Hydrogen fuel is a green alternative to conventional hydrocarbon fuels for transportation applications. This is because the combustion product of hydrogen is simply water, which is non-toxic and ubiquitous. Hydrogen is also an attractive fuel because of its high energy content; however, because it is a gas it has poor volumetric energy density. In Chapter 2, ionic liquids consisting of both cations and anions that can undergo reversible dehydrogenative aromatization were used to chemically store hydrogen. Cations investigated included pyridinium ions, which were easily hydrogenated but could not be regenerated through the dehydrogenation of piperidinium ions; and carbazole containing ammonium (whose synthesis failed) and imidazolium (which failed to hydrogenate) cations. The anions studied were heterocyclic carboxylates and sulfonates, these ions were observed to undergo both hydrogenation and dehydrogenation to various degrees when reacted in solution. However, as components of ionic liquids, they fail to react at a significant rate. The viscosity of the fluids was suspected to be hindering the diffusion of either hydrogen or the ions to or from the catalyst surface. In addition to using hydrogen as the primary source of energy in a vehicle, reversible hydrogenation can form the basis of a thermally regenerative fuel cell: a device that converts low grade vehicle waste heat, from a conventional engine, into electricity for the vehicles auxiliary power units. In Chapter 3, secondary benzylic alcohols, in particular 1-phenyl-1-propanol, were determined to be able to undergo dehydrogenation to the corresponding ketone rapidly and with extremely high selectivity over a palladium on silica catalyst. The dehydrogenation gave an initial rate of hydrogen evolution of 4.6 l of hydrogen per gram of palladium per minute and the enthalpy and entropy of the dehydrogenation is +56 kJ mol-1 and +117 J mol-1 K-1. This adsorbed energy can then be released as electricity in a fuel cell and be used to power auxiliary units in a vehicle without decreasing fuel economy. / Thesis (Ph.D, Chemistry) -- Queen's University, 2011-08-29 16:19:06.012

<p>Metal hydrides hydrogen storage materials have the ability to reversibly absorb and release large amounts of hydrogen at low temperature and pressure. In this study, metal hydride materialsemployed as negative electrodes in Ni-MH batteries are investigated. Attention is on AB5 alloys due to their intermediate thermodynamic properties. However, AB5 alloys a have&nbsp / tendency of forming oxide film on their surface which inhibits hydrogen dissociation and penetration into interstitial sites leading to reduced capacity. To redeem this, the materials were micro-encapsulated by electroless deposition with immersion in Pd and Pt baths. PGMs were found to increase activation, electrochemical activity and H2 sorption kinetics of the MH alloys. Between the two catalysts the one which displayed better performance was chosen. The materials were characterized by X-ray difractommetry, and the alloys presented hexagonal CaCu5 &ndash / type&nbsp / structure of symmetry P6/mmm. No extra phases were found, all the modified electrodes displayed the same behavior as the parent material. No shift or change in peaks which corresponded to Pd or Pt were observed. Scanning Electron Microscopy showed surface morphology of the materials modified with Pd and Pt particles, the effect of using different reducing agents (i.e., N2H4 and NaH2PO2), and alloys functionalized with &gamma / -aminosopropyltrietheosilane solution prior to Pd deposition. From all the surface modified alloys, Pt and Pd particles were observed on the&nbsp / surface of the AB5 alloys. Surface modification without pre-functionalization had non-uniform coatings, but the prefunctionalized exhibited more uniform coatings. Energy dispersive X-ray Spectroscopy and Atomic Absorption Spectroscopy determined loading of the Pt and Pd on the surface of all the alloys, and the results were as follows: EDS ( Pt 13.41 and Pd 31.08wt%), AAS (Pt 0.11 and Pd 0.78wt%). Checking effect of using different reducing agents N2H4 and NaH2PO2 for electroless Pd plating the results were as follows: EDS (AB5_N2H4_Pd- 7.57 and AB5_NaH2PO2_Pd- 31.08wt%), AAS (AB5_N2H4_Pd- 11.27 and AB5_NaH2PO2_Pd- 0.78wt%). For the AB5 alloys pre-functionalized with &gamma / -APTES, the results were: EDS (10.24wt%) and AAS (0.34wt%). Electrochemical characterization was carried out by charge/discharge cycling controlled via potential to test the AB5 alloy. Overpotential for unmodified, Pt and Pd modified&nbsp / electrodes were -1.1V, -1.24V, and -1.60V, respectively. Both modified electrodes showed discharge overpotentials at lower values implying higher specific power for the battery in comparison with the unmodified electrodes. However, Pd electrode exhibited higher specific power than Pt. To check the effect of the reducing agent the results were as follows: AB5_ N2H4_Pd (0.4V) and AB5_NaH2PO2_Pd (-0.2V), sodium hypophosphite based alloy showing lower overpotential values, implying it had higher specific power than hydrazine based bath. Alloy prefunctionalized with &gamma / -APTES, the overpotential was (0.28V), which was higher than -0.2V of the alloy without pre-functionalization, which means pre-functionalization with &gamma / -APTES did not improve the performance of the alloy electrode. Polarization resistance of the electrodes was investigated with Electrochemical Impedance Spectroscopy. The unmodified alloy showed high resistance of&nbsp / 21.6884 while, both Pt and Pd modified electrodes exhibited decrease 14.7397 and 12.1061 respectively, showing increase in charge transfer for the modified electrodes. Investigating the effect of the reducing agent, the alloys exhibited the following results: (N2H4 97.8619 and NaH2PO2 12.1061) based bath. Alloy pre-functionalized with &gamma / -APTES displayed the&nbsp / resistance of 9.3128. Cyclic Voltammetry was also used to study the electrochemical activity of the alloy electrodes. The voltammograms obtained displayed the anodic current peak at -0.64V&nbsp / o -0.65V for the Pt and Pd modified electrodes, respectively. Furthermore, the electrode which was not coated with Pt or Pd the current peak occurred at -0.59V. The Pd and Pt coated&nbsp / alloy electrodes represented lower discharge overpotentials, which are important to improve the battery performance. Similar results were also observed with alloy electrodes Pd modified&nbsp / using N2H4 (-0.64V) and NaH2PO2 (-0.65V). For the electrode modified with and without &gamma / -APTES the over potentials were the same (-0.65V). PGM deposition has shown to significantly&nbsp / improve activation and hydrogen sorption performance and increased the electro-catalytic activity of these alloy electrodes. Modified electrodes gave better performance than the unmodified&nbsp / electrodes. As a result, Pd was chosen as the better catalyst for the modification of AB5 alloy. Based on the results, it was concluded that Pd electroless plated using NaH2PO2 reducing agent&nbsp / had better performance than electroless plating using N2H4 as the reducing agent. Alloy electrode pre-functionalized with &gamma / -APTES gave inconsistent results, and this phenomenon needs to&nbsp / be further investigated. In conclusion, the alloy modified with Pd employing NaH2PO2 based electroless plating bath exhibited consistent results, and was found to be suitable candidate for&nbsp / use in Ni-MH batteries.</p>

The theoretical and experimental work in this thesis is primarily aimed at i) the quantification of the strengths of a number of hydrogen bonded systems, and ii) exploring the relationships that exist between the various physico-chemical properties determined in this study, which are related to the hydrogen bonding phenomenon. To this end a three part study of some hydrogen bonded systems has been undertaken. The study involves using a number of theoretical and experimental procedures, including a theoretical ab initio molecular orbital study, infrared spectroscopic determinations and a thermodynamic investigation involving measuring enthalpies and volumes of mixing and applying a theoretical model of interacting liquid mixtures. Conclusions based on ab initio molecular orbital theory, thermodynamic and infrared spectroscopic results conducted in this work include: i) the proton donating ability of the three hydrogen donor moieties studied in this work decreases in the order O-H > N-H ~ S-H, ii) the proton accepting competence of the three electron donor atoms considered in this work decreases in the order N > 0 > S in all cases except in the liquid phase systems involving dipropylamine and propane-1-thiol as proton donors, where the proton accepting ability of the atoms is in the opposite order i.e. S > 0 > N, and iii) a direct correlation exists between the shift in the A-H stretching wavenumber and the hydrogen bond interaction energy. . Although a number of factors influence the stability of the hydrogen bond, it was also tentatively concluded that in liquid phase systems involving weakly self-associated hydrogen bond donor molecules, the available surface area of the proton accepting atom becomes the dominant strength determining factor, otherwise factors such as basicity and electronegativity dominate. / Thesis (Ph.D.)-University of Natal, Durban, 1995

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Arguably the greatest confrontation for humanity and the Arguably the greatest confrontation for humanity and the natural world is addressing the shortfalls of our current energy sources and the threat that intensive consumption has on the environment. By harvesting the immense energy of the sun and converting it into clean fuels such as H2, these issues may be resolved. Inefficiencies of current technology have made the realization of an energy changeover extremely challenging. A viable solution would be an integrated system of the absorbing and conversion components embedded in a membrane. The membrane must house the electrode assembly, block product crossover, and manage ionic and electronic charges generated while remaining passive to the photoelectrochemical process. The first approach to developing such a membrane involves the formation of a composite of the electrically conducting polymer PEDOT and the inorganic acid PMA. It was found that the material possessed excellent electrical conductivity as a function of pH and oxidation state, and stability against overoxidation, while the ionic conductivity remained insufficient. This was combatted with the addition of the proton conductor Nafion®, which was combined in the desired ratio to optimize the material conductivities. Membranes capable of maintaining steady-state pH gradients, with the motivation to operate the oxygen- and hydrogen-generating sides in their optimal pH, were also investigated. It is herein confirmed that these membranes are able to maintain a pH gradient of 14 units indefinitely while adding no additional thermodynamic perturbance to the system. Membranes were constructed by combining ion exchange layers with interchangeable materials in an interfacial layer to develop a photoelectrochemically-adapted membrane. A transparent conducting oxide, conducting polymer, and graphene materials were selected, with the former two exhibiting inadequate activity. However, it was found that graphene oxide demonstrates activity that is comparable or better than commercially available membranes. Its presence also stabilized the membrane. The shortfall of graphene oxide is that it is an insulator. Chemical reduction was used to introduce electrical conductivity by removing the functional groups, which was controlled by the exposure conditions. It is shown that a reduced graphene oxide membrane can meet the figures of merit outlined for these integrated energy systems.