Anthony K. Burrell

Regeneration of Ammonia Borane Spent Fuel by Direct Reaction with Hydrazine and Liquid Ammonia

A method to regenerate lightweight, hydrogen-rich ammonia borane improves its prospects as a vehicular fuel source. Ammonia borane (H3N-BH3, AB) is a lightweight material containing a high density of hydrogen (H2) that can be readily liberated for use in fuel cell–powered applications. However, in the absence of a straightforward, efficient method for regenerating AB from dehydrogenated polymeric spent fuel, its full potential as a viable H2 storage material will not be realized. We demonstrate that the spent fuel type derived from the removal of greater than two equivalents of H2 per molecule of AB (i.e., polyborazylene, PB) can be converted back to AB nearly quantitatively by 24-hour treatment with hydrazine (N2H4) in liquid ammonia (NH3) at 40°C in a sealed pressure vessel.

The large scale synthesis of pure imidazolium and pyrrolidinium ionic liquids

Ionic liquids are being employed in almost all areas of chemistry and materials, yet there are inherent issues which arise if the utmost care is not taken in the preparation and purification of these materials. They are not easily synthesized and purified using the existing methods. We describe a reliable method for producing large quantities of high quality ionic liquids. Additionally, we show that imidazoliums are not ‘special’ due to their ‘inherently fluorescent’ nature, that spectroscopically clean imidazoliums are attainable, and most classes of ionic liquids do exhibit fluorescent backgrounds when extreme care is not taken during their synthesis and purification.

Potassium(I) amidotrihydroborate: structure and hydrogen release.

Potassium(I) amidotrihydroborate (KNH(2)BH(3)) is a newly developed potential hydrogen storage material representing a completely different structural motif within the alkali metal amidotrihydroborate group. Evolution of 6.5 wt % hydrogen starting at temperatures as low as 80 degrees C is observed and shows a significant change in the hydrogen release profile, as compared to the corresponding lithium and sodium compounds. Here we describe the synthesis, structure, and hydrogen release characteristics of KNH(2)BH(3).

Sapphyrins and heterosapphyrins

Abstract An improved synthesis of 3,8,12,13,17,22-hexaethyl-2,7,18,23-tetramethyl-sapphyrin (1), is reported. Also presented are new synthetic procedures for the formation of 8,12,13,17-tetraethyl-7,18-dimethyl-25,29-dioxasapphyrin (2) and 3,7,18,22-tetraethyl-2,8,17,23-tetramethyl-27-thiasapphyrin (3). In addition the syntheses of two completely new heteroatom substituted sapphyrins; 3,7,18,22-tetraethyl-2,8,17,23-tetramethyl-27-oxasapphyrin (4) and 7,18-diethyl-8,17-dimethyl-25,29-dioxa-27-thiasapphyrin (5), and described in detail. The procedures described provide facile routes to representative members of one of the more widely-studied classes of expanded porphyrin macrocycles.

The coupling between stability and ion pair formation in magnesium electrolytes from first-principles quantum mechanics and classical molecular dynamics

In this work we uncover a novel effect between concentration dependent ion pair formation and anion stability at reducing potentials, e.g., at the metal anode. Through comprehensive calculations using both first-principles as well as well-benchmarked classical molecular dynamics over a matrix of electrolytes, covering solvents and salt anions with a broad range in chemistry, we elucidate systematic correlations between molecular level interactions and composite electrolyte properties, such as electrochemical stability, solvation structure, and dynamics. We find that Mg electrolytes are highly prone to ion pair formation, even at modest concentrations, for a wide range of solvents with different dielectric constants, which have implications for dynamics as well as charge transfer. Specifically, we observe that, at Mg metal potentials, the ion pair undergoes partial reduction at the Mg cation center (Mg(2+) → Mg(+)), which competes with the charge transfer mechanism and can activate the anion to render it susceptible to decomposition. Specifically, TFSI(-) exhibits a significant bond weakening while paired with the transient, partially reduced Mg(+). In contrast, BH4(-) and BF4(-) are shown to be chemically stable in a reduced ion pair configuration. Furthermore, we observe that higher order glymes as well as DMSO improve the solubility of Mg salts, but only the longer glyme chains reduce the dynamics of the ions in solution. This information provides critical design metrics for future electrolytes as it elucidates a close connection between bulk solvation and cathodic stability as well as the dynamics of the salt.

Review of the U.S. Department of Energy’s “Deep Dive” Effort to Understand Voltage Fade in Li- and Mn-Rich Cathodes

The commercial introduction of the lithium-ion (Li-ion) battery nearly 25 years ago marked a technological turning point. Portable electronics, dependent on energy storage devices, have permeated our world and profoundly affected our daily lives in a way that cannot be understated. Now, at a time when societies and governments alike are acutely aware of the need for advanced energy solutions, the Li-ion battery may again change the way we do business. With roughly two-thirds of daily oil consumption in the United States allotted for transportation, the possibility of efficient and affordable electric vehicles suggests a way to substantially alleviate the Countrys dependence on oil and mitigate the rise of greenhouse gases. Although commercialized Li-ion batteries do not currently meet the stringent demands of a would-be, economically competitive, electrified vehicle fleet, significant efforts are being focused on promising new materials for the next generation of Li-ion batteries. The leading class of materials most suitable for the challenge is the Li- and manganese-rich class of oxides. Denoted as LMR-NMC (Li-manganese-rich, nickel, manganese, cobalt), these materials could significantly improve energy densities, cost, and safety, relative to state-of-the-art Ni- and Co-rich Li-ion cells, if successfully developed.1 The success or failure of such a development relies heavily on understanding two defining characteristics of LMR-NMC cathodes. The first is a mechanism whereby the average voltage of cells continuously decreases with each successive charge and discharge cycle. This phenomenon, known as voltage fade, decreases the energy output of cells to unacceptable levels too early in cycling. The second characteristic is a pronounced hysteresis, or voltage difference, between charge and discharge cycles. The hysteresis represents not only an energy inefficiency (i.e., energy in vs energy out) but may also complicate the state of charge/depth of discharge management of larger systems, especially when accompanied by voltage fade. In 2012, the United States Department of Energys Office of Vehicle Technologies, well aware of the inherent potential of LMR-NMC materials for improving the energy density of automotive energy storage systems, tasked a team of scientists across the National Laboratory Complex to investigate the phenomenon of voltage fade. Unique studies using synchrotron X-ray absorption (XAS) and high-resolution diffraction (HR-XRD) were coupled with nuclear magnetic resonance spectroscopy (NMR), neutron diffraction, high-resolution transmission electron microscopy (HR-TEM), first-principles calculations, molecular dynamics simulations, and detailed electrochemical analyses. These studies demonstrated for the first time the atomic-scale, structure-property relationships that exist between nanoscale inhomogeneities and defects, and the macroscale, electrochemical performance of these layered oxides. These inhomogeneities and defects have been directly correlated with voltage fade and hysteresis, and a model describing these mechanisms has been proposed. This Account gives a brief summary of the findings of this recently concluded, approximately three-year investigation. The interested reader is directed to the extensive body of work cited in the given references for a more comprehensive review of the subject.

Controlling the Structure of Supramolecular Porphyrin Arrays

Cis/trans isomerization of the alkene in these pyridine-functionalized porphyrins results in a reorganization of the molecular architecture: the polymeric trans form of 1 transforms into the dimeric cis form when irradiated with UV light. A cis/trans mixture of isomers is obtained when the pure compounds are treated with iodine.

Actinide expanded porphyrin complexes

Abstract In this article the uranyl cation (UO22+) coordination chemistry of several prototypic expanded porphyrins is reviewed. The ability of certain expanded porphyrins, large polypyrrolic ligands, to stabilize complexes containing the uranyl cation is contrasted to that of the porphyrins. These latter systems, well-recognized for their ability to stabilize a range of transition metal complexes, among others, have hitherto been shown to form structurally characterized complexes with only uranium(IV) and thorium(IV) cations among cations of the actinide series. Possible reasons for these differences in cation complexation behavior are discussed.

A Porous Metal−Organic Replica of α-PbO2 for Capture of Nerve Agent Surrogate

A novel metal-organic replica of α-PbO(2) exhibits high capacity for capture of nerve agent surrogate.

Improved Hydrogen Release from Ammonia–Borane with ZIF-8

The promotion for hydrogen release from ammonia-borane (AB) was observed in the presence of ZIF-8. Even at concentrations of ZIF-8 as low as 0.25 mol %, a reduction of the onset temperature for dehydrogenation accompanies an increase in both the rate and amount of hydrogen released from AB.