Enhancement of hydrogen binding affinity with low ionization energy Li2F coating on C60 to improve hydrogen storage capacity

• Metals or clusters with low ionization energy are found to have a large hydrogen binding affinity.
• Superalkali Li2F has much lower ionization energy than pure Li.
• Superalkali Li2F is used to coat onto C60 for room-temperature hydrogen storage materials.
• The C60/Li2F system shows better hydrogen storage ability than C60/Li system.
• The mechanism for the enhanced hydrogen binding energy is found to be the improved charge transfer between Li2F and H2.

The capacity of hydrogen storage for solid sorbents depends strongly on the binding affinity between hydrogen molecules and solid sorbents. By coating C60 with a low ionization energy material (Li2F), we obtained an enhanced binding energy and an improved electron transfer between H2 and hosts. With the first-principles calculations and charge analysis, we found that the orbital interactions play a dominant role in this system and eventually 68H2 molecules can be stably stored by a C60(Li2F)12 cluster with a binding energy of 0.12 eV/H2. The resulting gravimetric and volumetric density of H2 stored on C60(Li2F)12 are 10.86 wt% and the 59 g/L through calculations. Our investigation indicates that metals or metal clusters with lower ionization energies would be beneficial to enhance interactions between hydrogen and hosts, and thus, the hydrogen storage capacities for solid sorbents can be greatly improved.