Spectroscopic studies of hydrogen formation from amineborane complexes

The chemical and physical properties of chemical hydrogen storage materials containing boron and nitrogen as potential solid state hydrogen storage materials for on-board applications have been investigated. Ammonia borane (AB) confined within the channels of mesoporous silica (SBA-15 or MCM-41) showed a significant rate enhancement for hydrogen release and a change in the enthalpy of reaction for the release of hydrogen. Spectroscopic studies on the changes in the chemical and physical properties of AB in mesoporous silica were conducted. AB associated with SBA-15 or MCM-41 resulted in an increase in the B-N symmetric stretch line width and the possible appearance of a lower frequency B-N stretch mode, while the B-H and N-H stretching moieties showed little change. The ¹H NMR suggested a change in the environment when AB was deposited on a scaffold, based on the significant narrowing of the resonances. Results from both High Flux Backscattering Spectrometer and Disk Chopper Spectrometer indicated that the deposition of AB on MCM-41 resulted in longer proton residence times and lower energy barriers for proton motion compared to bulk AB. The reduced activation energy for proton motions might partly explain the improved thermolysis and lowering the activation barrier for the loss of the first equivalent of H ₂. Deposition of AB on MCM-41 profoundly impacted the crystallinity and proton motions in AB. This is an abstract of a paper presented in the ACS Fuel Chemistry Meeting Fall 2005 (Washington, DC Fall 2005).