Exploring yttrium doped C24 fullerene as a high-capacity reversible hydrogen storage material: DFT investigations

Abstract

By employing the state-of-the-art density functional theory, we report the hydrogen storage capability of yttrium decorated C24 fullerene. Single Y atom attached on C24 fullerene can reversibly adsorb a maximum number of 6 H2 molecules with average adsorption energy − 0.37 eV and average desorption temperature 477 K, suitable for fuel cell applications. The gravimetric weight content of hydrogen is 8.84%, which exceeds the target value of 6.5 wt% H by the department of energy (DoE) of the United States. Y atom is strongly bonded to C24 fullerene with a binding energy of − 3.4 eV due to a charge transfer from Y-4d and Y-5 s orbitals to the C-2p orbitals of C24 fullerene. The interaction of H2 molecules with Y atom is due to the Kubas type interaction involving a charge donation from the metal d orbital to H 1 s orbital, and back donation causing slight elongation of H-H bond length. The stability of the system at the highest desorption temperature is confirmed by ab-initio molecular dynamics simulations, and the metal-metal clustering formation has been investigated by computing the diffusion energy barrier for the movement of Y atoms. We have corrected all the calculated energies for the van der Waals (vdW) interactions by applying the dispersion energy corrections, in addition to the contribution of the GGA exchange-correlation functional. The C24 +Y system is stable at room temperature, and at the highest desorption temperature, the presence of a sufficient diffusion energy barrier prevents metal-metal clustering. Furthermore, binding energies of H2 are within the target value by DoE (−0.2 to 0.7 eV/H2), while H2 uptake (8.84% H) is higher than DoE’s criteria. Therefore, we propose that Y decorated C24 fullerene can be tailored as a practically viable potential hydrogen storage candidate.