Effects of Metal Ions and Ligand Functionalization on Hydrogen Storage in Metal-Organic Frameworks by Spillover

Hydrogen storage by spillover is a promising technique to enhance the hydrogen uptakes in metal-organic frameworks (MOFs) at room temperatures. However, to date, little is known on the structure-property relationships of MOFs for spillover storage. In this work, the effects of chemical composition of MOFs on hydrogen storage by spillover were studied systematically. Two series of MOFs with similar surface areas and formula units but different metal ions (M) or organic linkers (L), M(OH)BDC (BDC = terephthalate) or Zn4OL3, were prepared and employed as the receptors for spiltover hydrogen atoms. It was found that the M(OH)BDC series with various metal ions exhibited very close hydrogen capacities at room temperature. However, the functionalization of the BDC ligand in IRMOF-1 with various groups affected the storage capacity by spillover significantly. The decorations of functional groups with strong electrophilicity (i.e., electron withdrawing ability) on the BDC linkers remarkably enhanced the hydrogen uptakes by spillover. The experimental results were in good agreement with the density functional theory (DFT) calculations, which showed that the hydrogenations of the ligands with electron-withdrawing groups were thermodynamically more favored than those with electron-donating ones on the MOF structures. The new findings could provide a potential way to fabricate new metal-organic frameworks with high hydrogen storage capacities by spillover at room temperature..