Vibrational and Thermal Properties of Ammonia Borane supported on Polyacrylamide: Composites and Electrospun Fibers

We investigated the phase transition and decomposition properties of Ammonia Borane (NH$_{\mathrm{3}}$BH$_{\mathrm{3}})$ blended with polyacrylamide (M$_{\mathrm{n}}$\textasciitilde 150,000) which is a potential hydrogen storage system. The heat capacity measurements over a temperature range of 180--300 K exhibited an anomaly at around \textasciitilde 223 K, indicating a first-order structural phase transition. The transition enthalphy and entropy showed a decrease by increasing the polymer content in the composites and the phase transition was supressed in the fibers. Those changes could be due to the interaction between polyacrylamide and NH$_{\mathrm{3}}$BH$_{\mathrm{3}}$ after blending. The supression of the phase transition in the fibers could be attributed to the possible changes in bonding and disturbance in dihydrogen bonding network of NH$_{\mathrm{3}}$BH$_{\mathrm{3}}$. Our deyhdrogenation studies between 300-570 K revealed enhanced kinetics. Activation energies were calculated quantitatively and showed a significant decrease after mixing with the polymer, specifically for the electrospun fibers E$_{\mathrm{a}}$ dropped from about 140 kJ/mol to 67 kJ/mol. The improved kinetics was also supported by infrared measurements.