UC Riverside

Although sustainable thermal energy storage and conversion approaches are becoming increasingly popular, high-power requirements (~107 kWh) in certain energy applications such as spacecraft and jet propulsion, can only be accomplished through direct conversion of chemical to thermal energy through combustion. The current research objective in this field is to alleviate the kinetic and mass transfer limitations impeding rapid energy extraction from solid state fuels possessing high energy density. Part of the dissertation focuses on solving such challenges for boron particles and boron containing complexes, as elemental boron has the highest energy density. This dissertation provides mechanistic insights on selectively altering the thermochemical decomposition pathways of boron containing solid-state borane-ammonia complex with the help of a) ammonium-ion based oxidizing salts and b) polymeric carbonyl groups, to facilitate rapid and complete oxidation of boron in the borane-ammonia complex, which otherwise gets kinetically trapped into boron-nitrogen-hydrogen clusters. The dissertation also provides atomic scale understanding of the manipulation of boron oxide shell by implanting magnesium atoms, as a potential strategy to enhance reactivity of boron particles. Magnesium simultaneously reduces boron oxide creating dangling bonds on boron and induces a net tensile strain on the boron oxide surface, which respectively enhances the adsorption and diffusion rate of oxygen through the boron oxide shell, collectively enhancing the oxidation rate of boron. Significant part of the dissertation also focuses on tuning the reactivity of composites containing aluminum, another high energy density and widely explored solid fuel, by alteration of micro- and meso-structural features, as well as the incorporation of microwave absorbing sensitizers in aluminum-based composites for spatial confinement of the ignition zone when activated using microwave radiation. As a major breakthrough, this dissertation also demonstrates that certain non-flammable condensed phase materials with high energy density such as imidazolinium-ionic liquids can be electrochemically made inflammable and their flame can be dynamically extinguished simply by removing the voltage bias driving the electrochemical reactions. Since most energy dense fuels pose the danger of unintended fire and explosion, this concept paves the path for the development of potentially ‘safe’ fuels, thereby opening multiple avenues for future research.