Sandwich-type Dimetallocenes And Metal Cluster:The Theoretial Study Of Hydrogen Storage Properties

As a clean energy, because of its environmental protection, large chemical energy, abundance and high efficiency, hydrogen energy is widely considered that it is hopeful to replace fossil energy and ease current environmental pollution. Due to the traditional high compressed hydrogen storage and low temperature liquefaction method have some difficulties on safety, cost and others, using the adsorbed way by storing hydrogen molecules in solid material is deemed that it is potential and hopeful hydrogen storage way at present. The strength of Kubas interaction is intermediate between physisorption and chemisorption, therefore, those adsorbed hydrogen molecules meet the reversible adsorbed-desorbed conditions under ambient pressures and temperatures. However, the previous devised hydrogen storage materials basing Kubas interaction usually involved in the transition metals bond at the same time and reduced the hydrogen storage densities. The sandwich-type dimetallocenes can form a relatively closed space by sandwiching the two transition metals between two Cp rings and avoid metals bond so that the activity of metal can be kept. Therefore, the sandwich-type dimetallocenes achieve the ideal effect of hydrogen storage.Based on the density functional theory, this paper firstly investigated the hydrogen storage properties of sandwich-type dimetallocenes Cp2TM2 ?TM=V or Cr? and we derived the following two conclusions:?1? Cp₂V₂ could adsorb up to seven H₂ molecules and the predicted hydrogen storage density was 5.73wt%. For these adsorbed H₂ molecules, the first molecule was dissociated to two H atoms and formed multicenter hydrogen bonds with two V atoms, high temperatures or catalysts would used at the desorb process. The other six molecules were absorbed on two V atoms by Kubas interaction and met the desorbed conditions under ambient pressures and temperatures.?2? Cp₂Cr₂ could adsorb up to six H₂ molecules and the predicted hydrogen storage density was 4.91wt%. For these adsorbed H₂ molecules, the first two molecules were dissociated to four H atoms and formed multicenter hydrogen bonds with two Cr atoms, high temperatures or catalysts would used at the desorb process. The other four molecules were absorbed on two Cr atoms by Kubas interaction and met the desorbed conditions under ambient pressures and temperatures.In addition, there are three possible positions ?top, bridge, and HCP hollow positions? that can adsorb H₂ molecules on the surface of a metal cluster in general and metal clusters may have some adsorbed hydrogen positions. Therefore, this paper next investigated the hydrogen storage properties of Al₁₅. Based on the density functional theory, we derived the third conclusion:?3? Al₁₅ could adsorb up to five H₂ molecules and the predicted hydrogen storage density was 2.43wt%. For the fifteen Al atoms, except the center one, there were only ten atoms bonded these dissociated H atoms on the top position of Al₁₅; thereinto, one Al atom bonded one H atom correspondingly. These five H₂ molecules met the desorbed conditions under ambient pressures and temperatures.