Functional Nanofiber Composites of Ammonia Borane for Hydrogen Storage

Temperature dependence of thermal and vibrational properties of Ammonia Borane (NH$_{\mathrm{3}}$BH$_{\mathrm{3}})$ - polymer (e.g. polyacrylamide, polyethylene oxide) composites (in bulk and electrospun nanofiber forms) was measured to understand the structural phase transition behavior and dehydrogenation response. Heat capacity measurements revealed the first-order solid-solid phase transition at 223 K. The transition was suppressed in nanofiber composites which can be attributed to the disruption of the dihydrogen bonding network due to the fiber formation via electrospinning technique. The thermal quantities decreased with the increase in polymer content for the bulk composites. The interaction between the polymer (O of C$=$O or C-O bond) and NH$_{\mathrm{3}}$BH$_{\mathrm{3}}$ (B of B-N bond) could be the cause of the changes. Variable tempearture infrared studies between 400-4000 cm$^{\mathrm{-1}}$ will be discussed to bring insight to this phenomena. Kinetic properties were also investigated to understand the dehydrogenation process between 300-570 K. Activation energies were found to be the smallest for the nanofiber composites reveal the improved kinetics for these new functional materials. The suppression of the unwanted impurities were also supported by the measurements.