Because of the growing concerns over the depletion of fossil fuel supplies, environmental pollution and global warming caused by a steep increase in carbon dioxide and other greenhouse gases in the atmosphere, much attention has been given to the development of renewable energy sources that are the only long-term solution to the energy requirements of the world&rsquo / s population, on the way towards a sustainable energy future. Hydrogen has been considered as a clean and environmentally benign new energy carrier for heating, transportation, mechanical power and electricity generation. However, the lack of effective, safe, and low-cost hydrogen storage materials for mobile, portable, and stationary applications is one of the major hurdles to be overcome for the implementation of hydrogen economy. Among various solid state hydrogen storage materials, chemical hydrogen storage materials such as sodium borohydride (NaBH4) and ammonia borane (H3NBH3) have received much attention as promising candidates for fuel cell applications under ambient conditions due to their high gravimetric and volumetric hydrogen storage capacities. Both sodium borohydride and ammonia borane generate hydrogen upon hydrolysis in the presence of suitable metal catalysts. Transition metal nanoclusters can be used as active catalysts to catalyze the hydrolysis reactions of sodium borohydride and ammonia borane for hydrogen generation since they exhibit unique properties that differ from their bulk counterparts. Although the catalytic activity of metal nanoclusters increases with decreasing particle size, they are unstable with respect to agglomeration into the bulk metal leading to a significant decrease in activity in their catalytic applications. Therefore, the exploitation of microporous and mesoporous materials with ordered porous structures as hosts to encapsulate metal nanoclusters has attracted great interest since the pore size restriction of these host materials could limit the growth of nanoclusters leading to an increase in the percentage of the catalytically active surface atoms. In this dissertation, we report the preparation, characterization and the investigation of the catalytic activities of zeolite confined cobalt(0) nanoclusters in the hydrolysis of sodium borohydride and ammonia borane. The zeolite confined cobalt(0) nanoclusters were prepared by the reduction of cobalt(II)-exchanged zeolite-Y by sodium borohydride in aqueous solution at room temperature with no alteration in the framework lattice or loss in the crystallinity. The characterization of zeolite confined cobalt(0) nanoclusters were done by using inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-visible spectroscopy (DR-UV-Vis), infrared spectroscopy (IR), Raman spectroscopy, and N2 adsorption-desorption technique. The catalytic activity of zeolite confined cobalt(0) nanoclusters and the kinetics of hydrogen generation from the hydrolysis of sodium borohydride and ammonia borane were studied depending on catalyst concentration, substrate concentration and temperature. The rate laws and the activation parameters (Arrhenius activation energy, Ea / activation enthalpy, &Delta / H# / and activation entropy, &Delta / S#) for both catalytic hydrolysis reactions were calculated from the obtained kinetic data.

The property transition metal nanoclusters are more active catalysts than their bulk counterparts because of increasing proportion of surface atoms with decreasing paricle size. The development of efficient and economical catalysts to further improve the kinetic properties under moderate conditions is therefore important for the practical application of nanoclusters as catalyst in the hydrogen generation from hydrolysis of ammonia borane this. In this regard, the development of active iron catalysts is a desired goal because it is the most ubiquitous of the transition metals, the fourth most plentiful element in the Earth&rsquo / s crust. In this dissertation, we report the preparation, characterization and investigation of the catalytic activity of the water soluble polymer stabilized iron(0) nanoclusters. They were prepared from the reduction of iron(III) chloride by a mixture of sodium borohydride (NaBH4, SB) and ammonia borane (H3NBH3, AB) mixture in the presence of polyethylene glycol (PEG) as stabilizer and ethylene glycol as solvent at 80 &deg / C under nitrogen atmosphere. PEG stabilized iron(0) nanoclusters were isolated from the reaction solution by centrifugation and characterized by SEM, EDX, TEM, HRTEM, XRD, UV-Vis, ICP-OES and FT-IR techniques. PEG stabilized iron(0) nanoclusters have almost uniform size distribution with an average particle size of 6.3 &plusmn / 1.5 nm. They were redispersible in water and yet highly active catalyst in hydrogen generation from the hydrolysis of AB. They provide a turnover frequency of TOF = 6.5 min-1 for the hydrolysis of AB at 25.0 &plusmn / 0.5 &deg / C. The TOF value is the best ever reported among the Fe catalyst and comparable to other non-noble metal catalyst systems for the catalytic hydrolysis of AB. Kinetics of hydrogen generation from the hydrolysis of AB in the presence of PEG stabilized iron(0) nanoclusters were also studied by varying the catalyst concentration, substrate concentration, and temperature. This is the first kinetic study on the hydrolysis of AB in the presence of an iron catalyst. Moreover, PEG stabilized iron(0) nanoclusters can be separated magnetically from the catalytic reaction solution by using a magnet and show catalytic activity even after tenth run.

This dissertation presents the preparation and characterization of rhodium(0) nanoparticles supported on hydroxyapatite, and investigation of their catalytic activity in hydrogen generation from the hydrolysis of hydrazine-borane and ammonia-borane. Rh+3 ions were impregnated on hydroxyapatite by ion-exchange / then rhodium(0) nanoparticles supported on hydroxyapatite were formed in-situ during the hydrolysis of hydrazine-borane at room temperature. The rhodium(0) nanoparticles supported on hydroxyapatite were isolated as black powders by centrifugation and characterized by ICP-OES, SEM, TEM, EDX, XRD, XPS, and N2 adsorption-desorption spectroscopy. Rhodium(0) nanoparticles supported on hydroxyapatite have a mean particle size of 2.7&plusmn / 0.7 nm. The catalytic activity of rhodium(0) nanoparticles supported on hydroxyapatite was tested separately in the hydrolysis of hydrazine-borane and ammonia-borane. The hydrolysis of hydrazine-borane was started by adding the precatalysts, Rh+3-exchanged hydroxyapatite into the aqueous solution of hydrazine-borane / whereas, the hydrolysis of ammonia-borane was initiated by adding the catalyst rhodium(0) nanoparticles supported on hydroxyapatite which have been isolated from the first run of hydrolysis of hydrazine-borane. Rhodium(0) nanoparticles supported on hydroxyapatite provide a turnover frequency value of 6700 h-1 in the hydrolysis of hydrazine-borane at room temperature. The reuse experiments reveal that these supported nanoparticles are isolable, bottlable, and redispersible in solution. Furthermore, they retain 62 % of their initial activity at the fifth run in the hydrolysis of hydrazine-borane with release of 3 equivalents hydrogen. Activity of rhodium(0) nanoparticles supported on hydroxyapatite is maintained after the redispersion of the sample and 3 equivalents hydrogen generation from the hydrolysis of ammonia-borane confirms the activity of preformed catalyst. Rhodium(0) nanoparticles supported on hydroxyapatite provide a turnover frequency value of 3990 h-1 in the hydrolysis of ammonia-borane at room temperature.

Ordered mesoporous silicas have been shown to have a variety of useful applications ranging from adsorbents for containments to supports for catalysts. While these materials have received a good deal of attention in the literature there is still much opportunity for new technologies. We present research describing a novel approach to incorporate functionality onto the pore surfaces of these materials as well as a highly active catalyst for the Suzuki-Miyaura reaction. Our approach to selectively graft functionality on to the pore walls of the mesoporous silicas SBA-15 and MCM-41 involves treating the materials loaded with a structure directing agent (SDA), with hexamethyldisilazane that passivates the external surface through silylation. Once the SDA is removed the mesopores can be functionalized selectively using standard methods. A test designed to look at the passivation layer is also described. The catalyst developed is designated Pd-SBA-15-SH(g) and it is active for the Suzuki-Miyaura reaction. The activity, recyclability and leaching of Pd-SBA-15-SH(g) was found to be superior to related materials. A mechanistic analysis suggests the catalyst is a reservoir for soluble Pd metal. A key challenge that is holding back wide scale application of ammonia borane (NH3BH3) as a hydrogen storage material for mobile applications is the dearth of regeneration strategies. Presented are our forays into the development of an organic hydride based regeneration strategy. The first phase of the project focused on the reaction between Hantzsch esters and B(C6F5)3. N-substituted Hantzsch esters were found to transfer hydride to boron in >90 % yield. Mechanistic analysis of the reaction suggests either a SET mechanism or a highly asynchronous transition state. A novel hydride transfer equilibrium promoted by B(C6F5)3 was observed and it operated at temperatures below -10 ºC. N,N-ditertbutyl-dihydroimidazole is also an effective hydride donor to B(C6F5)3 as well as other Lewis acids that are more relevant mimics to those invoked in regeneration schemes. When the redistribution of B(SPh)3 is carried out with N,N-ditertbutyl-dihydroimidazole in the presence of NEt3 and CH2Cl2 at 50 ºC, BH2(NEt)3(SPh) is formed. CH2Cl2 functions as a thiol scavenger under the reaction conditions. 1-Octene trapping experiments provided indirect evidence for the formation of diborane, a critical component in the regeneration of NH3BH3. / Thesis (Ph.D, Chemistry) -- Queen's University, 2011-09-09 14:51:54.697

Recently, ammonia borane has increasingly attracted researchers’ attention because of its merging applications, such as organic synthesis, boron nitride compounds synthesis, and hydrogen storage. This dissertation presents the results from several studies related to ammonia borane. The pressure-induced tetragonal to orthorhombic phase transition in ammonia borane was studied in a diamond anvil cell using in situ Raman spectroscopy. We found a positive Clapeyron-slope for this phase transformation in the experiment, which implies that the phase transition from tetragonal to orthorhombic is exothermic. The result of this study indicates that the rehydrogenation of the high pressure orthorhombic phase is expected to be easier than that of the ambient pressure tetragonal phase due to its lower enthalpy. The high pressure behavior of ammonia borane after thermal decomposition was studied by in situ Raman spectroscopy at high pressures up to 10 GPa. The sample of ammonia borane was first decomposed at ~140 degree Celcius and ~0.7 GPa and then compessed step wise in an isolated sample chamber of a diamond anvil cell for Raman spectroscopy measurement. We did not observe the characteristic shift of Raman mode under high pressure due to dihydrogen bonding, indicating that the dihydrogen bonding disappears in the decomposed ammonia borane. Although no chemical rehydrogenation was detected in this study, the decomposed ammonia borane could store extra hydrogen by physical absorption. The effect of nanoconfinement on ammonia borane at high pressures and different temperatures was studied. Ammonia borane was mixed with a type of mesoporous silica, SBA-15, and restricted within a small space of nanometer scale. The nano-scale ammonia borane was decomposed at ~125 degree Celcius in a diamond anvil cell and rehydrogenated after applying high pressures up to ~13 GPa at room temperature. The successful rehydrogenation of decomposed nano-scale ammonia borane gives guidance to further investigations on hydrogen storage. In addition, the high pressure behavior of lithium amidoborane, one derivative of ammonia borane, was studied at different temperatures. Lithium amidoborane (LAB) was decomposed and recompressed in a diamond anvil cell. After applying high pressures on the decomposed lithium amidoborane, its recovery peaks were discovered by Raman spectroscopy. This result suggests that the decomposition of LAB is reversible at high pressures.

Historically, hypergolic propellants have utilized fuels based on hydrazine and its<br>derivatives due to their good performance and short ignition delays with the commonly used<br>hypergolic oxidizers. However, these fuels are highly toxic and require special handling<br><div>precautions for their use.</div><div><br></div><div>In recent years, amine-boranes have begun receiving attention as potential alternatives to<br>these more conventional fuels. The simplest of these materials, ammonia borane (AB, NH3BH3)<br>has been shown to be highly hypergolic with white fuming nitric acid (WFNA), with ignition<br>delays as short as 0.6 milliseconds being observed under certain conditions. Additionally,<br>thermochemical equilibrium calculations predict net gains in specific impulse when AB based<br>fuels are used in place of the more conventional hydrazine-based fuels. As such, AB may serve as<br>a relatively less hazardous alternative to the more standard hypergolic fuels.</div><div><br></div><div>Presented in this work are the results of five major research efforts that were undertaken<br>with the objective of developing high performance fuels based on ammonia borane as well as<br>characterizing their combustion behavior. The first of these efforts was intended to better<br>characterize the ignition delay of ammonia borane with WFNA as well as investigate various fuel<br>binders for use with ammonia borane. Through these efforts, it was determined that Sylgard-184<br>silicone elastomer produced properly curing fuel samples. Additionally, a particle size dependency<br>was observed for the neat material, with the finer particles resulting in ignition delays as short as<br>0.6 milliseconds, some of the shortest ever reported for a hypergolic solid fuel with WFNA.</div><div><br></div><div>The objective of the second area of research was intended to adapt and demonstrate a<br>temperature measurement technique known as phosphor thermography for use with burning solid<br>propellants. Using this technique, the surface temperature of burning nitrocellulose (a homogeneous solid propellant) was successfully measured through a propellant flame. During the<br>steady burning period, average surface temperatures of 534 K were measured across the propellant<br>surface. These measured values were in good agreement with surface temperature measurements<br>obtained elsewhere with embedded thermocouples (T = 523 K). While not strictly related to<br>ammonia borane, this work demonstrated the applicability of this technique for use in studying<br>energetic materials, setting the groundwork for future efforts to adapt this technique further to<br>studying the hypergolic ignition of ammonia borane.</div><div><br></div><div>The third research area undertaken was to develop a novel high-speed multi-spectral<br>imaging diagnostic for use in studying the ignition dynamics and flame structure of ammonia<br>borane. Using this technique, the spectral emissions from BO, BO2, HBO2, and the B-H stretch<br>mode of ammonia borane (and its decomposition products) were selectively imaged and new<br>insights offered into the combustion behavior and hypergolic ignition dynamics of ammonia<br>borane. After the fuel and oxidizer came into contact, a gas evolution stage was observed to<br>precede ignition. During this gas evolution stage, emissions from HBO2 were observed, suggesting<br>that the formation of HBO2 at the AB-nitric acid interface may help drive the initial reactant<br>decomposition and thermal runaway that eventually results in ignition. After the nitric acid was<br>consumed/dispersed, the AB samples began burning with the ambient air, forming a quasi-steady<br>state diffusion controlled flame. Emission intensity profiles measured as a function of height above<br>the pellet revealed the BO/BO2-based emissions to be strongest in the flame zone (corresponding<br>to the highest gas temperatures). Within the inner fuel-rich region of the flame, the HBO2 emission<br>intensity peaked closer to the fuel surface after which it unexpectedly began to decrease across the<br>flame zone. This is seemingly in contradiction to the current understanding that HBO2 is a stable product species and may suggest that for this system it is consumed to form BO2 and other boron oxides.</div><div><br></div><div>The fourth area of research undertaken during this broader research effort investigated the<br>use of ammonia borane and other amine borane additives on the ignition delay and predicted<br>performance of novel hypergolic fuels based on tetramethylethylenediamine (TMEDA). Despite<br>these materials being in some cases only sparingly soluble in TMEDA, solutions of ammonia<br>borane, ethylenediamine bisborane, or tetramethylethylenediamine bisborane in TMEDA resulted<br>in reductions of the mean ignition delays of 43-51%. These ignition delay reductions coupled with<br>the significantly reduced toxicity of these fuels compared to the conventional hydrazine-based<br>hypergolic fuels make them promising, safer alternatives to the more standard hypergolic fuels.<br>Attempts were made to improve these ignition delays further by gelling the TMEDA, allowing for<br>amine borane loadings beyond their respective solubility limits. Moving to these higher loadings<br>had mixed results however, with the ignition delays of the AB/EDBB-based fuels increasing<br>significantly with higher AB/EDBB loadings. The ignition delays of the TMEDABB-based fuels<br>on the other hand decreased with increasing TMEDABB loadings, though the shortest were still<br>comparable to those found with the saturated fuel solutions.</div><div><br></div><div>The final research area that was undertaken was focused on scaling up and developing fuel<br>formulations based on ammonia borane for use in a small-scale hypergolic hybrid rocket motor.<br>Characterization of the regression rate behavior of these fuels under motor conditions suggested<br>the fuel mass flow rate was driven primarily by the thermal decomposition of the ammonia borane.<br>This mechanism is fundamentally different from that which governs the regression rate of most<br>conventional solid fuels used in hybrid rockets as well as that of ethylenediamine bisborane, a<br>similar material in the amine borane family of fuels. Understanding this governing mechanism further may allow for its exploitation to enable high, nearly constant fuel mass flow rates<br>independent of oxidizer mass fluxes. If successful, this would enable further optimization of the<br>design for rocket systems utilizing these fuels, resulting in levels of performance that rival that of<br>the more conventional hydrazine-based fuels.<br></div>

<div> <p>This research addresses the issues of electrical energy storage that warfighters in the U.S. military face. A device is presented that combines an on-demand hydrogen reactor with a state of the art proton exchange membrane fuel cell. This thesis focuses on the design criteria and analysis of the chemical hydride reactor. On demand hydrogen release can occur by controlling the hydrolysis reaction of Ammonia Borane (AB). Maleic acid is used to promote rapid release of hydrogen and trap the ammonia released from AB. Reactor designs are categorized as either delivering liquid or solid ammonia borane into an acid filled reactor. In an effort to design as simple of a system as possible, the delivery mechanisms presented do not use electronically powered devices. The primary safety criterion is that the hydrogen does not overly pressurize and meets the consumption rate of the fuel cell. Two liquid delivery architectures are proposed and tested using the assumption that a pressure differential between two chambers will deliver ammonia borane solution into a reactor. Methods of controlling the exposure of solid ammonia borane to a promoter is also presented. Pressed AB pellets were experimentally analyzed in order to characterize the interaction of solid AB in acidic solution. Designs are ranked against each other using system parameters that are applicable to man portable device. Liquid delivery architectures provided a safe and robust method of hydrolysis control. A bag reactor system that met the hydrogen requirements of a fuel cell was developed and tested. When used to compliment a fuel cell and military grade batteries, such a reactor will save weight and volume for extended missions requiring electronic equipment.<b></b></p> </div> <b><br></b>

<p>This dissertation describes the design and characterization of a lightweight hydrogen reactor coupled to a proton exchange membrane fuel cell for portable power delivery. The system is intended to recharge portable batteries in the absence of an established electrical power supply. The presented work can be divided into two endeavors; the first being an investigation of various hydrogen generation pathways and the second being the design, fabrication, and testing of a system to house hydrogen generation and deliver electrical power.</p> <p>Two hydrogen storage materials are considered for this work: ammonia borane and sodium borohydride. Organic acids are investigated for their ability to accelerate the hydrolysis of either material and generate hydrogen on-demand. In the case of ammonia borane, organic acids are investigated for a secondary role beyond reaction acceleration, serving also to purify the gas stream by capturing the ammonia that is produced during hydrolysis. Organic acids are found to accelerate the hydrolysis of ammonia borane and sodium borohydride with relative indifference towards the purity of water being used. This is advantageous as it allows the user to collect water at the point of use rather than transport highly pure water for use as a reactant. Collecting water at the point of use increases system energy density as only ammonia borane or sodium borohydride and an organic acid are transported with the system hardware.</p> <p>A custom hydrogen reactor is developed to facilitate hydrolysis of ammonia borane or sodium borohydride. The reactor is paired with a fuel cell to generate electrical power. The rate of hydrogen being generated by the system is modulated to match the fuel cell’s consumption rate and maintain a relatively constant pressure inside the reactor. This allows the system to satisfy a wide range of hydrogen consumption rates without risking over pressurization. The system is shown to produce up to 0.5 sLpm of hydrogen without exceeding 30 psia of hydrogen pressure or a temperature rise greater than 35°C.</p><p>The envisioned use for this system is portable battery charging for expeditionary forces within the United States military. This application informed several design choices and is considered when evaluating technological maturation. It is also used to compare the designed system to existing energy storage technologies.</p>

This thesis reports the investigation of molecular materials for hydrogen storage applications with a particular emphasis on alkali-metal amidoboranes. I have developed new routes for the synthesis of $alpha$-LiNH$_{2}$BH$_{3}$ and NaNH$_{2}$BH$_{3}$, and have studied their hydrogen storage properties by thermogravimetric analysis, variable temperature X-ray and neutron diffraction and inelastic neutron scattering. I report the synthesis and full structural characterization of two new materials, KNH$_{2}$BH$_{3}$ and $beta$-LiNH$_{2}$BH$_{3}$, and have performed initial studies on a tetragonal phase of a variant of LiNH$_{2}$BH$_{3}$ with a preliminary structure solution. I have also performed variable temperature neutron diffraction on ammonium borodeuteride, ND$_{4}$BD$_{4}$, and report the full structural characterisation of the three phases identified as a result of these measurements. Furthermore, variable temperature inelastic neutron scatting (INS) measurements were performed on ammonia borane, NH$_{3}$BH$_{3}$, and the results are discussed in terms of crystallographic phase changes.

Drei Wasserstoffgenerator-Systeme (WGS) auf Basis chemischer Hydride wurden in dieser Arbeit als Labormuster ausgelegt, gefertigt und in ihren Betriebseigenschaften analysiert. Es wurden ein 20 W-WGS und zwei 100 W-WGS untersucht. Als chemische Hydride wurden Amminboran und Natriumborhydrid ausgewählt. Aufgrund ihrer vergleichsweise einfachen Lagerfähigkeit, ihren moderaten Freisetzungsbedingungen und ihrer volumetrisch wie gravimetrisch hohen Wasserstoffdichten erschienen sie in besonderer Weise geeignet für Wasserstoffgeneratoren im Kleinleistungsbereich. Zwar zeigen diese chemischen Hydride zurzeit hinsichtlich ihrer Kosten, ihrer Energieeffizienz bei der Herstellung und ihrer Umweltverträglichkeit keine Vorteile gegenüber verdichtetem Wasserstoff, jedoch besitzen sie mit ihrer hohen, auf das Hydrid bezogenen Energiedichte ein positives Alleinstellungsmerkmal. Bei der Entwicklung der WGS standen daher neben der Betriebszuverlässigkeit und Regelbarkeit die Optimierung der systembezogenen Energiedichte WGS im Fokus.