Date/Time Date(s) - 07/04/20082:20 pm - 3:20 pm
Title: Improving hydrogen storage in metal-organic frameworks using exposed metal sites
Speaker: Dr. Yun Liu
Institute: University of Maryland
Location: ITB-AB102
Description:
Due to the dwindling world-wide supply of petroleum along with environmental challenges due to CO2 emissions, it is necessary to develop a sustainable and environmentally friendly energy system for transportation. One intriguing possibility is to use hydrogen as the energy carrier. Indeed, substantial progress has been made over the last few years in developing fuel cells for transportation. However, there is still not a suitable hydrogen storage material. Recently, the synthesis of nano-porous materials with extremely large surface areas, including metal-organic frameworks (MOFs) and amorphous carbons, has led to some progress in understanding the adsorption of hydrogen molecules on material surfaces. However there are still many technological obstacles to their future deployment: 1) The low H2 adsorption enthalpy limits their application to low temperature; and 2) The lack of understanding of surface packing density (SPD) hinders the efficient improvement of H2 uptake. I will present results on the hydrogen adsorption properties of MOFs with an eye to that addressing these two issues. I will show that the hydrogen adsorption enthalpy can be greatly enhanced in many MOFs by exposing coordinatively unsaturated metal centers (CUMCs). In addition, the MOFs with CUMCs generally show larger SPD at 77 K than those without CUMCs. A simple model system is considered to estimate the largest SPD for physisorbed hydrogen molecules on material surface. The physical origin of this dihydrogen binding to CUMCs will be discussed.