Master of Science
Hydrogen has been regarded as a promising candidate to replace the conventional fossil fuel, and thus attracted enormous research efforts. However, hydrogen storage remains to be a big challenge to its practical applications. Consequently, the investigation of suitable hydrogen storage materials has become a highly active research field. Here we reported the first high pressure studies of three promising hydrogen storage materials, N(CH3)3BH3, NH(CH3)2BH3 and NaNH2BH3 by Raman and IR spectroscopy.
First, N(CH3)3BH3 was studied at room temperature and pressures up to 30 GPa. Under ambient conditions, N(CH3)3BH3 forms rhombohedral crystals. During compression, two phases transitions were observed, which was evidenced by the rich profile changes in Raman and IR spectra as well as by examining the pressure dependence of Raman and IR modes. Raman and IR spectra collectively revealed consistent structural information of N(CH3)3BH3. The pressure-induced phase transitions were reversible, indicated by the recovered Raman and IR modes upon decompression.
Similarly, the other two hydrogen storage materials, NH(CH3)2BH3 and NaNH2BH3 were investigated under high pressures up to 20 and 14 GPa, respectively. NH(CH3)2BH3 was found to experience two phase transitions from the parent monoclinic structure. An interesting red shift and subsequent blue shift cycle of N-H stretching mode was also observed. The decompression experiment suggested that the pressure-induced phase transitions were reversible. The changes of Raman and IR spectra under pressure together with factor group analysis provided us a chance to examine the possible high-pressure structure. On the other hand, NaNH2BH3, which crystalizes into orthorhombic structure at ambient pressure,underwent two phase transitions during the compression process. The pressure-induced phase transitions turned out to be reversible upon decompression. Moreover, the bonding behaviors of NaNH2BH3 were found to be different from NH3BH3, which has implications for improved hydrogen storage performance.
Yu, Zhihao, "In Situ High-Pressure Studies of Ammonia Borane Derivatives by Vibrational Spectroscopy" (2013). Electronic Thesis and Dissertation Repository. 1403.