Sc/Ti decorated novel C24N24 cage: Promising hydrogen storage materials

Inspired by the TM−N4 coordination environment and the promising hydrogen adsorption property of the Ti–C4 unit, four novel TM6C24N24 (TM = Sc, Ti) cages with six TM−N4/TM−C4 units are designed simultaneously for the first time in this paper. Their stabilities are studied by using DFT calculations and confirmed by MD simulations. Sc6C24N24(N4) and Ti6C24N24(N4) can absorb 30 hydrogen molecules and keep the original structures intact. The average hydrogen adsorption energy is 0.13–0.26 eV for Sc6C24N24(N4)-6nH2 (n = 1–5), and 0.09–0.23 eV for Ti6C24N24(N4)-6nH2 (n = 1–5). The hydrogen storage capacities are 6.30 wt % and 6.20 wt %, respectively. Besides, the 30H2 can be readily adsorbed on Sc6C24N24(N4) under 160 K and 100% desorbed at 270 K under 0.1 MPa. The desorption temperature could increase if the pressure becomes higher. Sc6C24N24(C4)/Ti6C24N24(C4) complexes are higher in energy than corresponding Sc6C24N24(N4)/Ti6C24N24(N4). They are not suitable as room-temperature hydrogen storage materials due to the structural deformation in the hydrogen storage process.